DOE HEP Continuation Proposal from Duke University High Energy Physics to Department of Energy Office of Science Project Title: Research in High Energy Physics at Duke University Project Director: A. T. Goshaw Principal Investigators: • Task A (Hadron Collider Research): A. Goshaw, A. Kotwal, M. Kruse, S. Oh • Task N (Neutrino Research): K. Scholberg, C. Walter • Task K (Accelerator Physics): Y. Wu Period of time report covers: June 2006 to November 2009 DOE award number: DE-FG05-91ER40665 Address: Physics Department Box 90305 Duke University Durham, NC 27708-0305 1
Transcript
DOE HEP Continuation Proposal
from
Duke University High Energy Physics
to
Department of Energy Office of Science
Project Title: Research in High Energy Physics at Duke University
Project Director: A. T. Goshaw
Principal Investigators:
• Task A (Hadron Collider Research): A. Goshaw, A. Kotwal, M. Kruse, S. Oh• Task N (Neutrino Research): K. Scholberg, C. Walter• Task K (Accelerator Physics): Y. Wu
Period of time report covers: June 2006 to November 2009
This Continuation Proposal describes research in experimental elementary particle physicscarried out by the Duke University High Energy Physics (HEP) group during 2007 and 2008,and plans for the last year of this current three-year grant (2009). The Duke HEP groupconsists of seven faculty members, two senior scientists, and typically six post docs and fivegraduate students. There are two main thrusts of the research program. Measurements atthe energy frontier are used to test aspects of elementary particle theory described by theStandard Model (SM) and to search for new forces and particles beyond those containedwithin the SM. The neutrino sector is explored using data obtained from a large neutrinodetector located in Japan. The measurements provide information about neutrino massesand the manner in which neutrinos change species in particle beams.
The high energy research uses proton and antiproton colliding beams. The experimentsare done at the Fermilab Tevatron (proton-antiproton collisions at a center of mass energyof 1.96 TeV) and at the CERN Large Hadron Collider (proton-proton collisions at 14 TeV).The neutrino program uses data obtained from the Super-Kamiokande detector. This water-filled Cherenkov counter is used to detect and measure the properties of neutrinos producedin cosmic ray showers, and from neutrino beams produced from accelerators in Japan.
The material in this report is structured as specified in the OHEP guidelines for Con-tinuation Proposals. As requested, this includes a description of our recent research activitieswith plans for the next year, budgets for the current and upcoming budget periods, and asummary of personnel with their research commitments.
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2 Overview of Duke High Energy Physics Program
This report describes the research activities of the Duke HEP group during the first twoyears of our current three-year DOE/OS grant, and plans for the next year.
2.1 Introduction
Our research is focused on measurements using hadron colliders and high energy neutrinobeams. The active experiments are:
• CDF at the Tevatron
• ATLAS at the LHC
• Neutrino physics at Super-K and T2K
The CDF and ATLAS experiments form the basis of our research at the energy frontier.We measure properties of electroweak bosons and top quarks, and search for Higgs bosons andother phenomena beyond the Standard Model. A technical coherence is achieved through ourcontributions to charged particle tracking at CDF (the Central Outer Tracker) and ATLAS(the Transition Radiation Tracker). The research programs at CDF and ATLAS are carriedout by five Duke faculty members (Professors Goshaw, Kotwal, Kruse, Oh and Phillips), twosenior scientists, four post docs, and four graduate students. These research activities aregrouped into Task A of this DOE grant
The neutrino research program uses the Super-Kamiokande detector to measure prop-erties of atmospheric and accelerator-produced neutrinos. The studies using neutrino beamfrom K2K will continue with the T2K experiment (an off-axis neutrino beam from Tokaito Super-Kamiokande). This research is carried out by by two faculty members (ProfessorsScholberg and Walter), two post docs and two graduate students. The neutrino researchprogram is described under Task N.
2.2 Summary of research activities
Detailed descriptions of our research programs are included in the following sections. Weinclude here a summary of physics goals and contributions Duke has made to each of theexperiments.
• Research at CDF
Research at the Fermilab Tevatron using the CDF detector has been a central partof the Duke HEP program for over 15 years. During the past year we have madesignificant contributions to the following research topics:
– measurements of top quark properties
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– electroweak physics (W mass, di-boson production)
– searches for the Higgs boson
– searches for new phenomena (CHAMPS and new gauge bosons)
Although diverse research topics, there is a coherence through the use of high PT
leptons and W/Z bosons as the basic physics objects. The measurements requireprecision tracking information, which is one of the strengths of the Duke HEP group.Duke physicists have served as physics co-conveners of the top, electroweak and QCDphysics groups. Professor Kruse is currently Co-convener of the newly-formed CDFHiggs Discovery Group.
The Duke HEP group has made significant contributions to the operation of the CDFexperiment:
– Offline Project Co-leader
– Grid computing development
– Central Outer Tracker maintenance
– Silicon Detector maintenance
We plan to continue our involvement with the CDF experiment for next year, but witha reduction of effort as our ATLAS activities ramp up.
• Research at ATLAS
The future of our hadron collider physics program will be at the CERN LHC usingthe ATLAS detector. As discussed in our three-year grant proposal, Duke has mademajor contributions to the design, construction and installation of the barrel transitionradiation tracker (TRT). Our current service work is based upon experience from theCDF experiment with tracking detector alignment, tracking reconstruction, and offlinedata processing. Our contributions over the past year include:
– TRT installation and commissioning
– TRT cosmic ray studies
– Development of offline TRT performance diagnostics
– Tracking detector alignment
– Chair of the US ATLAS Institutional Board
Our physics research program is building upon the analysis techniques that we havedeveloped using CDF data. Early measurements of basic electroweak processes willprovide a solid basis for participation in the rich spectrum of discoveries expected atthe LHC.
• Neutrino research
Duke’s neutrino physics program uses the Super-Kamiokande detector for studies ofatmospheric and accelerator-produced neutrinos, and is making preparations for theT2K off-axis beam experiment. On Super-K in the past year we have been active in:
– Ultra-high energy astrophysical neutrino searches
– Proton identification algorithms for oscillation analysis
– B − L-violating proton decay searches
Our Super-K service work is extensive and primarily in support of our physics interests.The current activities focus on
– Fully-contained and partially-contained event reduction
– Outer detector PMT calibration and data quality control
– Outer detector simulation tuning
– Outer-detector-based reconstruction and event selection software
– Ring-counting reconstruction software
– New Root-based software development
– Offline group leadership
– Outer detector electronics upgrade
These activities are ongoing as we work on the first Super-K III analyses, and preparefor the electronics upgrade in 2008. We will bring our extensive experience on K2Kto T2K, for which we have taken a leadership role in the planned 2KM intermediatedetector. The 2KM detector is to be located where the neutrino beam spectrum willbe similar to that at Super-K and will be a valuable component of T2K for the θ13
measurement.
2.3 Summary of personnel
We summarize in Table 1 the Duke HEP research personnel and the expected distributionof their research efforts averaged over the next year.
2.4 Summary of budgets
Details of the task budgets and budget justification are included in the following sections ofthis report. We include in Table 2 a high-level summary comparing our approved budgetsfor 2007 and 2008 to the proposed budgets for 2009.
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Table 1: Duke University HEP Personnel as of June 2008 and research effort projected in2009Person Position Fraction of research effort
CDF and ATLAS Neutrino
A. Goshaw James B. Duke Professor 10% and 90%A. Kotwal Associate Professor 70% and 30%M. Kruse Associate Professor 60% and 40%S. Oh Professor 30% and 70%T. Phillips Associate Research Professor 80% and 20%K. Scholberg Associate Professor 100%C. Walter Assistant Professor 100%
D. Benjamin Senior Research Scientist 30% and 70%C. Wang Senior Research Scientist 30% and 70%
A. Bocci Post Doc 0% and 100%M. Fechner Post Doc 100%B. Jayatilaka Post Doc 100% and 0%Jared Yamaoka Post Doc 0% and 100%New post doc Post Doc 0% and 100%New post doc Post Doc 100%
J. Deng Graduate Student (graduated) 100% and 0%D. Hidas Graduate Student 100% and 0%R. Wendell (graduated) Graduate Student 100%R. Shekhar Graduate Student 100% and 0%Y. Zeng Graduate Student 100% and 0%
M. Damian Staff Assistant 33% and 33% 33%W. Ebenstein Technical Support 10% and 10% 10%J. Fowler Engineer 0% and 100%
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Table 2: Budget Summary for current budgets for 2007 and 2008, and projected budget for2009Task 2007) 2008 (current) 2009 (requested)
A (CDF and ATLAS) $865K $863K $yyyKCDF (Fermilab) $51K $46K $46KN (Neutrinos) $132K $187K $yyyKK (Accelerators) $55K $0 $0Supplements (Task A) $15K $112K $0Supplements (Task N) $25K $0 $0
3 Project Description: Task A -Hadron Collider Physics
(CDF and ATLAS)
The research activities of the scientists supported by Duke HEP Task A are carried out atthe CDF and ATLAS experiments. In this section we summarize research accomplishmentsmade over the past two years, and plans for a transition from research at the CDF experimentto physics at the LHC with the ATLAS detector.
3.1 Introduction
This has been a very exciting and productive time for us, with many physics measurementsusing CDF data coming to completion, and preparations for the start up of LHC data takinglater this year.
We continue to be deeply involved with the CDF experiment. Mark Kruse serves as Co-convener of the CDF Higgs Discovery Group with responsibility for uniting the collaborationsdirect searches for a light Higgs boson. Mark, Doug Benjamin, Dean Hidas and ValentinNecula continue to improve sensitivity for Higgs bosons in the W ∗W decay mode, with theexpectation of first exclusion limits around 160 GeV/c2 this summer. Ashutosh Kotwal andRavi Shekar has been using advanced statistical techniques to improve the sensitivity for alow mass Higgs boson in the ZH channel. These direct searches are complimented by indirectevidence for a light Higgs from recent W and top mass measurements at CDF, which predicta low SM Higgs boson favorable for discovery at the Tevatron. Ashutosh Kotwal lead thegroup that made a new W mass measurement at 80413±48 MeV/c2, the world’s best from asingle experiment using only 200 pb−1 of data. This measurement is now continuing using 2fb−1 of data with a goal of a W mass uncertainty 25 MeV/c2. Bo Jayatilaka has been heavilyinvolved with improving the top mass measurement using dilepton events. We also continuea variety of new physics searches. Tom Phillips has improved particle timing measurementsat CDF, and used these to search for heavy, massive charged particles (CHAMPs). JainrongDeng, Chris Lester, Al Goshaw and Tom Phillips continue Duke’s searches for anomalousgauge couplings using Zγ and Wγ events. ByeongRok Ko, Ahutosh Kotwal, Seog Oh andChiho Wang are searching for new gauge bosons in the Z ′ → e+e− and Z ′ → µ+µ− channels.
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These CDF physics analyses are described in more detail below, along with our continuingstrong support of CDF operations.
Our activities within the ATLAS collaboration have increased greatly over the pastyear. The installation and commissioning of the TRT barrel tracker, lead by Jack Fowler,Seog Oh and Chiho Wang, now has this detector ready for data taking. Andrea Bocci hastaken on responsibility for the TRT alignment and in the summer of 2008 will become theleader of the ATLAS inner tracker software group. Andrea, Mark Kruse and Richard Wall(now at Yale) have carried out studies of the TRT performance using cosmic ray data. DougBenjamin is responsible for developing online diagnostic tests for the performance of theTRT.
We have also become very active in the preparations for physics analyses using ATLASdata. Andrea Bocci, Ashutosh Kotwal and Al Goshaw have contributed to studies of dibosonproduction, resulting in two ATLAS physics notes. Kotwal and Goshaw are also servingas reviewers of articles to be published by the Collaboration, describing the potential forearly Standard Model physics measurements. We have established an ATLAS physics groupdedicated to new physics searches using measurements of Wγ and Zγ production. Finally,Goshaw was elected Chair of the US ATLAS Institutional Board in January 2008, and isworking to strengthen the physics analysis opportunities for US physicists.
The presentation of these Task A activities is structured as follows:
• CDF physics analyses
• CDF detector and offline support
• Plans for CDF research in 2009
• ATLAS detector support
• Preparation for ATLAS physics
• Plans for ATLAS research in 2009
3.2 CDF physics analyses
In this section we briefly review the status of physics analyses using CDF data. The resultingpublications and reports are listed at the end of the section.
3.2.1 Vector boson pair production
Run II CDF data provides an excellent opportunity for studies of one of the most basicpredictions of the Standard Model, namely the non-Abelian nature of the gauge-boson cou-plings. Specific predictions of the SU(2)L x U(1)Y electroweak theory can be analytically
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tested using a combination of the production of Wγ, Zγ, WW , WZ and ZZ events. Chan-nels with leptonic decays of the W and Z have low backgrounds, and are good for precisiontests of the Standard Model including searches for anomalous couplings. Research at Dukehas resulted in four publications on this topic over the past few years, with two analyses inprogress We summarize here are progress on analyses over the past year on measurementsof Wγ and Zγ production.
We measure W/Zγ production using electron and muon decays of W/Z bosons. Thereaction pp̄ → lνγ has contributions from W bosons produced with initial and final stateradiation, and from the direct WWγ coupling. The pp̄ → l+l−γ channel includes Z/γ∗
production with initial state quark and final state lepton radiation. Over the past year wehave worked on increasing the acceptance of the electrons and muons, and gained a factorof about two in statistics (Jianrong Deng and Tom Phillips). We have currently analyzed 2fb−1 (1 fb−1) of data in the muon (electron) channel and our goal is to add 2 fb−1 of datawhere the Z boson has decayed into two neutrinos and publish the result. The precisionof these measurements is now limited by the determination of the photon ID efficiencyand backgrounds. Over the past year we have developed a new method for measuring thephoton ID (Jianrong Deng), and have improved significantly the determination of photonbackgrounds (Chris Lester and Al Goshaw). Results were presented at the DPF meetings(Deng and Lester), the Lake Louise Winter Institute (Phillips), and the APS April meeting(Phillips). Figure 1 shows a comparison of the measured photon ET spectra to StandardModel predictions. We are using these these data to put limits on new physics that willgenerally appear as an excess in high ET photons.
Our plan for the next year is to complete our studies of W/Zγ production and publishonce we have added the Z → νν data. The electron channel was the Ph.D. thesis of JianrongDeng (now at UC Irvine). Once this is published we will decide whether to further pursuethese measurements with CDF or ATLAS data (see the ATLAS discussion below). Onerelated project we are pursuing is a search for the rare decay mode W → πγ, which uses thetools we have developed for photon measurements This was the subject of an undergraduatethesis for Chris Lester, and should be completed this summer.
3.2.2 Search for Charged Massive Stable Particles
Most searches for new massive particles predicted by extensions to the Standard Modelassume that the particles decay immediately, so the mass limits from these searches donot apply if the particles live long enough to exit the detector. Particles could have longlifetimes because of weak coupling constants, limited phase space for their decay, or becauseof a new conserved (or nearly conserved) quantity. We are searching for charged massivestable particles, or CHAMPs, some examples of which might be long-lived SUSY stops orstaus, fourth-generation quarks with weak couplings, or Kaluza-Klein modes of StandardModel particles if there are compact universal extra dimensions.
Tom Phillips and Rick Snider (Fermilab) have carried out a model-independent searchfor CHAMPs at CDF by looking for slow, high-momentum particles using timing information
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Z+JetγSM Z
AGC(h4 = 0.0047)
-1CDF Run II Preliminary, 2.0 fb
Figure 1: Photon ET distribution for Zγ events where the Z decays to electrons or muons.The blue curve shows the Standard Model predictions, and the dashed red curve shows thepredictions including an anomalous ZZγ coupling.
from the time-of-flight (TOF) system and the Central Outer Tracker (COT). Tom Phillipsdeveloped the timing measurement in the COT that makes this analysis possible.
CHAMPs are expected to be highly penetrating, so they are expected to trigger themuon system. A single candidate with mass above 100 GeV/c2 was found in 1 fb−1 of datawith an expected background of 1.5 ± 0.2 events (see Figure 2. Applying this result to areference model of a supersymmetric stable stop squark we were able to increase the lowerlimit on the mass from the LEP bound of 100 GeV/c2 to 250 GeV/c2. The PRL is in theCDF godparenting process.
The 1 fb−1 analysis is on the verge of being sensitive to weakly produced CHAMPsabove the LEP limit of 100 GeV/c2, but the low-mass background will need to be reducedin addition to adding additional luminosity. Tom Phillips has already developed some tech-niques that should reduce the low-mass background, but cleaning up this background appearsto require the next generation of CDF tracking software. This software has been written,but plans for processing new and existing data are on hold because of lack of resources. Ex-tending the CHAMPs analysis to include additional luminosity may depend upon whetheror not the CDF offline group decides to reprocess existing data with the next generationsoftware.
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)2 (GeV/cTOF
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Stop2140 GeV/c Stop2220 GeV/c
Figure 2: The background prediction (red) and observed mass distribution (green) forCHAMP candidates. The mass is calculated from the time-of-flight velocity and the trackmomentum. Also shown are the expected signals for 140 GeV/c2 and 220 GeV/c2 stop.
3.2.3 Search for a Z ′ boson in the dimuon channel
The Standard Model is usually viewed as an effective theory, expected to be modified athigher energies. Larger symmetry groups, eg. those motivated above, may undergo sponta-neous symmetry breaking such that a broken U(1) gauge symmetry may appear. Associatedwith it would appear a new, neutral heavy boson, called the Z ′ boson. Like the SM Zboson, the decay Z ′ → ll̄ provides an excellent experimental signature, due to the excellentefficiency and momentum resolution of the leptons.
Kotwal and collaborators have designed and performed an analysis in the dimuonchannel, to search 2.3 fb−1 of CDF Run II data for evidence of the production and decayprocess Z ′ → µµ̄. Kotwal performed a precise alignment and calibration of the CDF driftchamber using cosmic rays, for this dataset, in order to achieve the best momentum resolutionpossible. This work results in the narrowest possible dimuon mass peak, giving the bestsearch sensitivity. Through our work on the W boson mass measurement, we have developeda deep understanding of muon tracking, which is the key aspect of this search. The cosmicray tagger developed by Kotwal has achieved very good performance, making the cosmicray background negligible. The improvements we developed in the drift chamber trackreconstruction and fitting have allowed us to suppress “ghost” muons from π, K decays inflight to a very low level. We have also developed the statistical methods to search the datafor all possible mass values of a heavy Z ′ resonance, and to quantify the significance of a
Figure 3: The distribution of m−1µµ (TeV−1) for the data (points), the individual backgrounds
(colored histograms) and the summed background (red histogram). We use the inversedimuon mass because the tracking resolution is approximately constant in this variable.
The search has been designed as a “blind” analysis, i.e. the entire procedure is de-veloped without access to the collider data. Figure 3 shows the comparison of the dataevents with the backgrounds. We find no significant excess above backgrounds, and excludeZ ′ → µµ̄ resonances with SM-like couplings below 1 TeV.
3.2.4 Global study of High-PT dilepton events (MCK)
3.2.5 Precision Physics - the CDF W Mass Analysis
The mass of the W boson is one of the most precise and important measurements at theTevatron. It is influenced by the existence of new particles via quantum mechanical cor-rections, making it a sensitive observable to probe the Higgs boson mass and to probe newphysics. In the Minimal Supersymmetric extension of the Standard Model (MSSM), forexample, additional corrections can increase the predicted W mass by up to 250 MeV.
Kotwal led the first W mass measurement from CDF Run 2 data, which was based on200 pb−1. An important success of our analysis is the determination of a consistent detectorenergy and momentum calibration using the experimental data, with a precision of 0.03%.The lack of a consistent energy/momentum scale for electrons was an unresolved issue in theCDF Run 1 analysis - the issues have been successfully resolved in Run 2 during the courseof our analysis. Our result, MW = 80413 ± 34(stat) ± 34(syst) = 80413 ± 48 MeV, is the
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most precise single measurement of the W boson mass. Inclusion of our result in the globalelectroweak fit reduces the predicted mass of the SM Higgs boson by 6 GeV and decreasesits range to mH = 76+33
−24 GeV. This result has been published in Phys. Rev. Lett. 99,151801 (2007) and has been accepted for publication in Phys. Rev. D.
3.2.6 Top Mass Measurement with Dileptons
The top quark mass mt is another key parameter of the Standard Model. The mass valueis needed to calculate various radiative corrections in the SM, in order to compare values ofprecision observables to predictions and hence test the theory.
In the dilepton decay channel, top quark pair production is followed by the quarksdecaying into W bosons and b quarks, and both W bosons decay into leptons (electrons ormuons): tt̄ → Wb + Wb̄ → lν̄b + l̄′ν ′b̄. Due to the presence of two neutrinos in the finalstate, the mass fit is under-constrained on an event by event basis. In spite of this challenge,it is possible to perform an event-by-event analysis by assigning a mt-dependent probabilityto each event, and obtaining a best-fit mt value from the ensemble of event probabilities.
Jayatilaka, Shekhar, and Kotwal have extracted the top quark mass from dileptonevents using such a per-event technique. More information is extracted from each event, inthe form of a posterior probability curve P(mt), as compared to the use of a single number tocharacterize the event. We use a multivariate method to extract all the kinematic informationin the event in order to construct P(mt). This method uses the full vector of kinematics ~xfrom the event, ie. the momentum 3-vectors of the two leptons and the two b-quark jets, andinformation on the remaining transverse energy flow in the event, as input to the SM matrixelement M(~x; mt) for top quark pair production. We then use Bayes Theorem to obtainthe posterior probability P(mt), from the SM prediction of the probability for producing anevent with kinematics ~x.
This technique has the benefits that the full event information is combined with thecomplete SM prediction of top quark production and decay, in order to constrain the mea-sured top quark mass. We have published in Physical Review D 75:031105(R) (2007)the world’s best published measurement of the top quark mass in the dilepton channel:
mt = 164.5 ± 3.9(stat) ± 3.9(syst.) GeV,
using 1 fb−1 of CDF Run II data.
Following this publication, we have augmented this multivariate “matrix-elements”technique with a novel method of optimizing the event selection. The matrix-elements tech-nique extracts the most information about the measured parameter for a given sample ofcandidate events. However the event selection criteria are not defined by the method. Ideally,one wants to select the sample (containing an admixture of signal and background eventswith a kinematics-dependent signal efficiency and background contamination), that maxi-mizes the sensitivity to the measured parameter. We solve this difficult heuristic problemby using neural networks in a novel application for high energy physics. In a method mod-elled on biological evolution, we create a set of randomly-generated neural networks, whose
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inputs are the event kinematics. Each network’s output is used to provide a binary cut toselect/reject a candidate event. The optimum network is defined as the one whose selectedcandidate sample would provide the smallest statistical uncertainty on the mt measurement.This optimum network is created as follows: all networks in the initial set are tested onsimulated samples of signal and background events (pseudo-experiments). A subset of net-works that predict the smallest mt uncertainty is “bred”, ie. copied and randomly modifiedto create a new full set of networks. In this way the “fittest” networks are used to derivethe next generation of networks, and this “breeding of the fittest” process is iterated untilthe generations asymptote to an optimal performance. The final event selection on the datasample is performed using the “best” network from all generations, which is typically fromthe final generation.
Our analysis of 2 fb−1 of CDF Run II data, using the above amalgamation of matrix-element and evolutionary neural network techniques, is complete and is being reviewed forpublication in Physical Review Letters . The use of the evolutionary neural networktechnique for event selection resulted in a 20% improvement in the statistical uncertainty,over the use of likelihood fitting using matrix elements alone. This latest preliminary resultis
mt = 171.2 ± 2.7(stat) ± 2.8(syst) GeV,
again the world’s best measurement of the top quark mass in the dilepton channel.
3.2.7 Searches for the Higgs boson
The discovery of a Higgs Boson would have profound consequences for our understandingof Electroweak Symmetry Breaking and the generation of the masses of the W± and Zvector bosons and of the fermions. With the LHC looming, the discovery of a Higgs bosonis generating more and more interest. With the Tevatron now working extremely well, thereis also a chance that CDF and DØ will see evidence for a Higgs boson before the LHC.This realization initiated a large effort by both collaborations to take advantage of thisopportunity. Duke has been playing central roles in this effort as summarised below.
At the beginning of 2007 CDF initiated a new “Higgs Discovery Group” in a push tooptimise our chances of seeing a Higgs. This group is being co-convened by Kruse (withMatt Herndon from the University of Wisconsin). There is a huge amount of activity in thisgroup, with many analyses looking for Higgs in a lot of different ways, and developing newtechniques to optimally exploit the data. This has required a considerable effort to manageand direct. Our large array of latest results can be found at:http://www-cdf.fnal.gov/physics/new/hdg/hdg.html .
Highlights this year will include the exclusion of Higgs bosons around 160 GeV, representingthe first time a hadron collider has excluding any mass range of Higgs bosons, and expectedcross-section limits of less than 3 times the Standard Model value for Higgs masses around120 GeV, the preferred region for a SM Higgs.
Kruse is also involved in the combination of Higgs results between the CDF and DØcollaborations. Details can be found at the combination webpage (together with others
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involved):http://tevnphwg.fnal.gov/ .
Collaboration between both experiments will be an important effort toward the Tevatron’sability to exclude or discovery a Higgs boson. The latest results are shown in Figure ??and demonstrate the enormous strides made over the last year and more in narrowing inon the Higgs boson. At a mass of 160 GeV, the combined expected limit is 1.6 timesthe SM prediction with an observed limit of 1.1 times the SM cross-section (which alreadyrepresents a 90% C.L. exclusion at 160 GeV), while at 115 GeV, the expected (observed)limit is 3.8 × σSM (3.3 × σSM )
3.2.8 SM Higgs H → WW search
One of our graduate students (Dean Hidas, supervised by Kruse) is conducting a search forH → WW ∗ (W ∗ indicates that one of the W bosons can be off-shell depending on the Higgsmass considered) using the “dilepton” decay mode, when both W boson decay leptonically.This is an extension to the first H → WW ∗ analysis at CDF Run 2 conducted by Kruse(in supervising U. of Wisconsin student Sunny Chuang). This analysis is a very involvedand high-profile effort and is being conducted as part of a larger analysis group (involvingin total 20 people). Hidas is the lead graduate student on this effort and is shoulderingmost of the responsibility in getting our results ready for the summer 2008 conferences.The analysis involves a combination of advanced techniques; a Neural Network (NN), and aMatrix-Element technique (first done by the UCSD group as an independent analysis). Thiscombination of techniques improves the sensitivity from either one technique by about 10%.The 95% CL limits on σ(gg → H) × BR(H → WW ∗) are displayed in Figure 4 for 2.4 fb−1
of data, are at present about 2 times away from the SM prediction.
3.2.9 SM Higgs Search in the ZH Associated Production Mode
The electroweak measurements, via SM fits, prefer a low value of the SM Higgs mass, makingthe search for a low-mass Higgs boson a very interesting topic. In this mass range (mH < 130GeV), the principle modes of sensitivity for the Tevatron are the associated production modesof Higgs boson along with a W or Z boson, where the Higgs is radiated off the latter. TheHiggs then decays predominantly into a pair of b quarks.
One of the final states of the process Z +H → ll̄bb̄ leads to a very similar final state asthe top mass analysis discussed above, i.e. two charged leptons and two b quarks. Exploitingthis similarity, Shekhar, Jayatilaka and Kotwal are pursuing a search for the SM Higgs bosonin this mode. This is Shekhar’s thesis topic. To obtain as high a sensitivity as possible, we areusing the per-event likelihood technique, where the likelihood is constructed from SM matrixelements for the signal and background processes. We choose the measurement parameter tobe the fractional ZH content of the data, for a given value of the Higgs boson mass. As withthe top mass measurement, we exploit the full kinematic information in the data events,including all momentum and angular correlations such as those due to the Higgs being ascalar particle. Additional gains in sensitivity are achieved by using the evolutionary neural
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Figure 4: Cross-section limits (at 95% CL on σ(gg → H) × BR(H → WW ∗)) as a ratio ofthe SM value. mass. Shown are the expected and observed limits, as a fucntion of Higgsmass, from the two analyses mentioned in the text for 2.4 fb−1 of CDF data.
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network method of event selection.
A new idea we have incorporated is to use the evolutionary neural network to generatea multivariate function that tunes the leading-order matrix element probabilities, such thatthey provide a more accurate description of the higher-order SM processes. This idea leadsto additional gains in sensitivity, because the likelihood fitter will use improved probabilitydensity functions for the signal and background processes.
This analysis is nearing completion and will be submitted for publication later thisyear.
3.2.10 Doubly Charged Higgs
Extensions of the SM predict larger Higgs sectors. For instance, the introduction of a Higgstriplet containing neutral, singly, and doubly-charged members is required in the Left-RightSymmetric Model, which is well-motivated by the recent discovery of neutrino oscillations.The Supersymmetric Left-Right Model further implies a relatively light doubly-charged Higgsboson (H±±), motivating its search at the Tevatron. Furthermore, the experimental signa-ture is clean with high efficiency and low background, making the search for the (H±±) anideal hunting ground for new physics.
For light H±± bosons with small couplings to leptons, the boson may have a sufficientlylong life-time to be detected as a doubly-charged particle. For the search in the long-livedmode, Kotwal exploited the quadrupled ionization of the H±± in this search, which was theMasters thesis topic of his graduate student Joshua Tuttle. We used an a-priori “blind-to-data” strategy to define two separate sets of ionization cuts. The loose cuts, to be usedexclusively for setting a mass limit, seek to maximize efficiency. The tight cuts, to be usedonly to quote observation of H±± signal, further suppress the mis-identification backgrounds.The tight cuts were optimized for single-event sensitivity by using ionization informationfrom the calorimeters and the drift chamber. Loose cuts use drift chamber ionization only.Upon unblinding the signal data sample, we found no H±± candidates in either category. Weset a lower mass limit of 134 GeV/c2 for the quasi-stable H±± boson, which is much morestringent than the previous best limit of 97.3 GeV/c2 from the DELPHI collaboration. Thepaper describing this result has been published in Physical Review Letters 95:071801(2005).
3.2.11 Searches for Exotic and Excited Leptons
The fermion multiplicity in the standard model motivates a description in terms of underlyingsubstructure, in which all quarks and leptons consist of fewer, more elementary particlesbound by a new strong interaction. In this compositeness (CI) model, quark-antiquarkannihilations may result in the production of excited lepton states, such as the excitedelectron, e∗ and the excited muon µ∗. The SM gauge group may be embedded in larger gaugegroups such as SO(10) or E(6), motivated by grand unified theories or string theory. Theseembeddings also predict additional, exotic fermions such as the e∗ and the µ∗, which can be
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produced via their gauge interactions (GM model). Kotwal has published two analyses usingthe CDF Run II data, searching for the e∗ and the µ∗, respectively, both in the ll∗ → llγmode.
In the gauge-mediated model, we excluded Me∗ < 430 GeV for f/Λ ≈ 0.01 GeV−1
at the 95% confidence level (C.L.), extending the exclusion region well beyond other limits.Here f represents a coupling strength and Λ represents the energy scale of new physics. Wehave also presented the first e∗ limits in the CI model as a function of Me∗ and Λ, excluding100 < Me∗ < 906 GeV for Me∗ = Λ. These search results for excited and exotic electronsare the first at a hadron collider. The results have been published in Physical ReviewLetters 94:101802 (2005).
We performed a similar search for excited and exotic muon production, using a signif-icantly larger dataset. The search was significantly more sensitive than LEP for high massvalues, and HERA has no sensitivity for µ∗ production, making this search quite unique.This was the first hadron-collider search in the context of the GM model, and extended pre-vious mass limits in both the GM and CI models. In the GM model, we exclude Mµ∗ < 400GeV/c2 for 10−3 GeV−1 < f/Λ < 10−1 GeV−1 at the 95% C.L., well beyond previous lim-its. We have also presented the first µ∗ limits in the CI model as a function of Mµ∗ andΛ, excluding Mµ∗ < 853 GeV/c2 for Λ = Mµ∗ . Kotwal supervised the senior honors thesisof Edward Daverman, an undergraduate at Duke, on this topic. These results have beenpublished in Physical Review Letters 97:191802 (2006).
3.3 CDF Service
Members of the CDF group have been involved in key operational roles at CDF.
3.3.1 CDF Grid Computing
Since March 2007, Doug Benjamin has been the CDF physicist responsible for the CDFCAF’s located at FNAL. These computer farms include the production farm, user analysisfarms (both grid-based and tranditional condor pool) and the CDF Open Science Gridgateway (NAMCAF). His responsibilities have included coordinating work of the computerprofessionals and physicists responsible for providing operational support for these farms.Benjamin also provides operations support for the users. This support includes respondingto user queries and debugging the system problems as they arise. During this time Benjaminrole evolved from supporting the CDF computing at FNAL to the CDF Grid Coordinator.
As CDF Grid Coordinator, Benjamin was responsible for the CDF grid computingin North America, Asia and Europe. He has had to coordinate activities with all of thepersonel supporting the CDF grid computing on the Open Science Grid (OSG) and EGEEgrids (Europe and Asia). Additionally, Benjamin was one of the primary contacts betweenOSG and CDF. He participated in the validation and testing of the new releases of the OSGsoftware as the CDF representative. He also was the primary support for CDF computingon the OSG. Benjamin’s term as CDF grid coordinator ended in July 2008.
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Benjamin has responsible for adapting the CDF Grid Middleware to use the samesoftware as CMS for running CDF jobs on the grid (glideinWMS). This software will allowCDF to better utilize the computing resources across the OSG and will reduce the CDFlabor used to keep the CDF computing operational.
3.3.2 Calibration Coordinator (BJ)
3.3.3 other service
All the group members participated in data-taking shifts on the CDF experiment. Kotwalserved as the co-coordinator for the CDF conference presentations for all the Winter 2008conferences.
3.4 Preparation for research using ATLAS data
3.4.1 Diboson physics at ATLAS
The Duke HEP group has initiated an ATLAS working group that is preparing for Wγ andZγ measurements . In particular, we (Bocci and Goshaw) have been modifying the W/Zγevent generators being used at CDF for use in the LHC 14 TeV pp collisions. This involvedsome modifications of the matrix element code provided by Uli Baur to produce Les Houchesformat files that can be introduced into PYTHIA for showering and hadronization. Theseleading-order matrix element predictions will be scaled by next-to-leading-order k-factorcorrections.
Our goal is to make first measurements of Standard Model Wγ and Zγ production usingearly LHC data. The 10 TeV pp run expected in the fall of 2008 will be useful in takinga first look at W and Z inclusive production using the electron and muon decay channels.However the Wγ and Zγ measurements will require ≈ 100 pb−1 of data, that will not beavailable until 14 TeV pp data taking in early 2009. The most challenging part of theseanalyses is the clean identification of photons, and the evaluation of the rate at which jets inW/Z+jet events fake photons. We have considerable experience photon measurements fromour CDF analyses, and are learning how to apply this to the measurements of photons usingthe ATLAS liquid argon calorimeters.
3.4.2 Di-lepton physics at ATLAS
*** Mark and Ashutosh’s contributions ***
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3.4.3 Reviews of ATLAS physics publications
The ATLAS Collaboration is carrying out extensive Computing Simulation Studies thatexercise the data reconstruction software that is expected to be used for first physics analyses.The goal is to carry out the complete analysis chain of many physics channels using pseudo-data from event generators passed through the ATLAS detector simulation. The results ofthese studies will establish base line expectations for early LHC measurements. A summaryof these analyses will be presented in a collection of ATLAS Notes (so-called CSC notes),that are being subjected to a full internal review, thus also exercising the complete ATLASpublication process.
The Duke HEP group has been heavily involved with this ATLAS CSC exercise. We(Bocci, Goshaw and Kotwal) worked with the ATLAS Diboson group to prepare the physicsnote that describes the expectation of early measurements of the WW, WZ, ZZ, Wγ andZγ channels. This includes estimates of the expected sensitivity to new physics via tri-linearanomalous gauge couplings. We also served as reviewers of other analyses: the W massmeasurement (Kotwal) and studies of W/Z bosons plus jets (Goshaw). Goshaw also is areferee for the Standard Model Chapter that will be published by the ATLAS Collaboration.
3.4.4 General support of US ATLAS
The US ATLAS Institutional Board consists of members from each of the 43 US ATLASinstitutions, and thus provides a forum for discussion of the preparation of the US for partic-ipation in LHC physics. In January of 2008 Goshaw was elected Chair of this InstitutionalBoard . In this role he works with the Leaders of the US ATLAS Research Program, HowardGordan, Mike Tuts and Jim Shank, on issues that bridge the gap between the Research Pro-gram (M and O, Computing, and Upgrades) and the ATLAS physics groups supported atindividual ATLAS institutions. In particular he has worked to establish an ATLAS ”Tier3 Task Force” that would study the manner in which University groups local computingfacilities will interface with the Research Program’s Tier1/Tier2 computing infrastructure.This has been a hole in the US LHC physics analysis chain, and needs to be addressed bythe collaboration. Goshaw was also part of the organizing committee for the US ATLASWorkshop of the Americas held at SImon Fraser University, June 16-19, 2008.
3.5 ATLAS Support (SO)
3.6 Physics plans of Task A at CDF and ATLAS
3.6.1 W boson mass
** Ashutosh ***
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3.6.2 Higgs Boson searches
** Mark**
3.6.3 CHAMPS searches
** Tom**
3.6.4 Diboson physics
The next year (through 2009) will see a transition of our studies of electroweak physics fromthe Tevatron (CDF) to the LHC (ATLAS). Our immediate goal is the publication of themeasurements of Zγ production using ≈ 2.0 fb−1 of CDF data. This will include Z decaychannels into e+e−, µ+µ− and νν . The combination of these channels should provide thebest limits to date on certain anomalous neutral gauge coupling parameters (hZ
3 ,hZ4 ,hγ
3 , hγ4).
This research is being carried out by Deng, Goshaw, Lester, and Phillips. Jianrong Deng’sreceived her Ph.D based upon this research and is now a post doc at UC Irvine.
With the start of LHC operation expected soon, it makes sense to move our studiesof the production of dibosons from CDF to ATLAS. Based upon the current schedule weshould observe the first Wγ and Zγ events in mid-2009. Our preparations for measurementsinclude a study of the matrix element generators used to predict pp → W/Zγ + X. We willtransfer those used at the Tevatron where production of W/Zγ is dominated by qq̄ collisions.Interesting new production channels open up at LHC energies, including vector-boson-fusionwhere for example Z + W+ → W+γ would be sensitive to Standard Model quartic couplings.We will collaborate on these measurements with other ATLAS groups using the subgroupmeetings we have organized.. The W/Zγ studies will provide a natural path to other dibosonproduction (W+W−, W−Z and ZZ), and will provide experience for Higgs boson searchesthat rely upon vector boson fusion.
3.6.5 W rare decays
We are a search for the rare decay mode W → γπ. This was part of the senior thesisproject of a Duke student Chris Lester, now a graduate student at U. of Penn. We (Bocci,Goshaw and Phillips) will continue working with Lester on this measurement, with the goalof completing it by the end of the summer 2008. We expect this will improve the sensitivityfor this rare decay by a factor of ≈ 100.
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3.7 Task A Budget Discussion (all)
3.8 Recent CDF Publications
The analyses and service work discussed above have resulted in several publications, or arein the process of being published. They are as follows:
• T. Aaltonen et al. [CDF Collaboration], “First Run II Measurement of the W BosonMass”, Phys. Rev. D 77, 112001 (2008). [Hays, Jayatilaka & Kotwal]
• T. Aaltonen et al. [CDF Collaboration], “First measurement of the W boson massin run II of the Tevatron”, Phys. Rev. Lett. 99, 151801 (2007). [Hays, Jayatilaka &Kotwal]
• A. Baranovski et al., “CDF II production farm project”, Nucl. Instrum. Meth. A572, 399 (2007). [Jayatilaka & Kotwal]
• J. Antos et al., “Data processing model for the CDF experiment”, IEEE Trans. Nucl.Sci. 53, 2897 (2006). [Jayatilaka & Kotwal]
• A. V. Kotwal and J. Stark, “Measurement of the W boson mass at the Tevatron”, tobe published in Ann. Rev. Nucl. Part. Sci. 58 (2008).
• A. Abulencia et al. [CDF Collaboration], “Precision measurement of the top-quarkmass from dilepton events at CDF II”, Phys. Rev. D 75, 031105(R) (2007). [Jayatilaka& Kotwal]
• D. Acosta et al. [CDF Collaboration], “Search for excited and exotic muons in the µγdecay channel in pp̄ collisions at
√s = 1.96 TeV”, Phys. Rev. Lett. 97, 191802 (2006).
[Gerberich, Hays & Kotwal]
• D. Acosta et al [CDF Collaboration], “Search for W and Z bosons in pp̄ → 2 jets + γat
• D. Acosta et al. [CDF Collaboration], “Search for long-lived doubly-charged Higgsbosons in pp̄ collisions at
√s = 1.96 TeV”, Phys. Rev. Lett. 95, 071801 (2005).
[Tuttle, Hays & Kotwal]
• D. Acosta et al. [CDF Collaboration], “Search for excited and exotic electrons in theeγ decay channel in pp̄ collisions at
√s = 1.96 TeV”, Phys. Rev. Lett. 94, 101802
(2005). [Gerberich & Kotwal]
• M. Bogdan et al, “A 96-Channel FPGA-Based Time-to-Digital Converter,” Nucl. In-strum. Meth. A554, 444–457 (2005). [Phillips, with U. Chicago]
• C. Hays, Y. Huang, A. V. Kotwal, H. K. Gerberich, S. Menzemer, K. Rinnert, C. Lecci,M. Herndon, and F. D. Snider, “Inside-Out Tracking at CDF”, Nucl. Instrum. Meth.A538, 249 (2005).
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• Search for ZZ and ZW Production in ppbar Collisions at√
• Measurement of the W+W− Production Cross Section in pp̄ Collisions at√
s = 1.96TeV Using Dilepton Events,hep-ex/0501050, Phys. Rev. Lett. 94, 211801 (2005). [Cabrera, Goshaw, Kruse]
• D. Acosta et al. [CDF Collaboration], “Search for doubly-charged Higgs bosons de-caying to dileptons in pp̄ collisions at
√s = 1.96 TeV”, Phys. Rev. Lett. 93, 221802
(2004). [Hays & Kotwal]
• V. M. Abazov et al. [CDF Collaboration and DØ Collaboration and Tevatron Elec-troweak Working Group], “Combination of CDF and DØ Results on W boson massand width”, Phys. Rev. D 70, 092008 (2004). [Kotwal]
• Measurement of the tt̄ Production Cross Section in pp̄ Collisions at√
s = 1.96 TeVUsing Dilepton Events,hep-ex/0404036, Phys. Rev. Lett. 93, 142001 (2004). [Coca, Kruse]
• T. Affolder et al., “CDF Central Outer Tracker,” Nucl. Instrum. Meth. 526249–299(2004). [Brozovic, Khazins, Kirby, Kotwal, Phillips, Robertson and Tamburello]
• Search for Higgs bosons decaying to W boson pairs in the dilepton channel from pp̄collisions at 1.96 TeV”,to be submitted to PRL. [Coca, Kruse, with S. Chuang(Wisconsin)]
• A global analysis of the high-PT dilepton signature from pp̄ collisions at 1.96 TeV,to be submitted to PRL. [Carron, Coca, Kruse]
• A. Abulencia et al., “Direct search for dirac magnetic monopoles in pp̄ collisions at√s = 1.96 TeV,” submitted to Phys. Rev. Lett. [Phillips, with MIT and Fermilab]
3.9 Recent conference talks
• H. Gerberich, ”Searches for BSM (non-SUSY physics) at the Tevatron”, Hadron Col-lider Physics Symposium, July 2005.
• A. Goshaw - “Review of di-boson production at the Tevatron”, invited talk at HadronCollider Physics July 2005, Les Diabrelets, Switzerland.
• C. Hays, “W Mass Systematics”, TeV4LHC Workshop, Batavia, IL, October, 2005.
• C. Hays, “W Mass and Properties”, XIII International Workshop on Deep InelasticScattering, Madison, WI, April 2005.
• C. Hays, “W Boson Mass Measurement at the Tevatron”, XL Rencontres de Moriond,La Thiule, Italy, March 2005.
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• B. Jayatilaka, “Top Quark Mass Measurement with a Matrix Element Method in theDilepton Channel at CDF”, APS Meeting, Jacksonville, April 2007.
• B. Jayatilaka, “First Measurement of the W Boson Mass with CDF in Run II”, APSMeeting, Jacksonville, April 2007.
• B. Jayatilaka, “Top Quark Mass Measurement with a Matrix Element Method in theDilepton Channel at CDF”, Division of Particles and Fields Meeting, Honolulu, Novem-ber 2006.
• A. Kotwal, “Standard Model Measurements and Higgs Searches at the Tevatron”,Invited Plenary talk at the SLAC Summer Institute, Stanford, July 2007.
• A. Kotwal, “The First Run 2 Measurement of the W Boson Mass by CDF”, InvitedPlenary talk, LoopFest VI Conference, “Radiative Corrections for the LHC and ILC”,Fermilab, April 2007.
• A. Kotwal, “Science Results from Computing Grids”, Invited Plenary talk, Open Sci-ence Grid All-Hands Meeting, San Diego Supercomputer Center, March 2007.
• A. Kotwal, “The First Run 2 Measurement of the W Boson Mass by CDF”, InvitedPlenary talk, ATLAS Overview Collaboration Meeting, February 2007.
• A. Kotwal, “The First Run 2 Measurement of the W Boson Mass by CDF”, InvitedPlenary talk, Aspen Winter Conference, January 2007.
• A. Kotwal, “The First Run 2 Measurement of the W Boson Mass by CDF”, JointTheoretical-Experimental Physics Seminar, Fermilab, January 2007.
• A. Kotwal, “Searching for Doubly-Charged Higgs Bosons”, Colloquim at NorthernIllinois University, September 2006.
• A. Kotwal, “The W Mass Measurement at the Tevatron and Lessons for ATLAS”,Invited talk at the ATLAS Collaboration Meeting, February 2005.
• M. Kruse, “The Race for the Higgs Boson”, Invited Plenary talk, 2007 PhenomenologySymposium: Prelude to the LHC, Madison, WI, May 2007.
• M. Kruse, “Properties of the Top Quark”, Invited Plenary talk, Aspen Winter Confer-ence, January 2007.
• M. Kruse, “Particle Physics at the Energy Frontier”, Colloquium at University of NorthCarolina, Wilmington, April 2006.
• M. Kruse, April 13, 2006, “Particle Physics at the Energy Frontier”, Colloquium atSyracuse University.
• M. Kruse, May 2005, “Diboson Physics at CDF”, Frontiers in Comtempory Physics,
