First one-two years Physics at LHC
Workshop on LHC Physics
TIFR, September4-8,2006
Monoranjan GuchaitTIFR
CMS,ATLAS notes, talks from ICHEP06,
Many papers, review articles, presentations,
Home pages….
Compilation…
The LHC Experiment
Proton Proton Collsion
Center of Mass energy :14 TeV
Luminosity 1034cm-2s-1
New energy domain( ~8 times)
New luminosity domain(~100 times)
The LHC Experiment
• Physics Goals:
- Testing Standard Model at 14 TeV
Complete with Higgs discovery
- New Discovery? SUSY, Quantum Gravity…
- Anything else?
LHC Schedule
Machine and Experiments closed : 31 st August, 2007
First collisions at cm: 900 GeV with L ~ 1029cm-2s-1, November 2007. - Static run, mainly to debug machine and detectors - Commissioning run at Injection energy until end 2007, then shutdown.
First Collision at cm =14 TeV : Spring 2008 2808 X 2808 bunches, 25 ns bunch crossing,
Expected to achieve few fb-1 by the end of 2008
Interesting Physics….
Experimental Challenges• The total p-p cross section ~100 mb
• At design luminosity about 109 inelastic events/second
• Trigger should reduce this event no more than about 100 events/s for storage and analysis within an interval 25ns, needs a very efficient design of the readout and trigger systems.
Needs a good synchronization among different channels.. …………..many more
Computation.. And Computation 15petabyte(PB) per year, professing them and
making the information available to thousands of Physicists all round the world.
For Comparison: ALEPH: Total data 3.5 TB D0 1992-’96 stored 30 TB( “Farm” came up) LHC 15PB/year ( 1PB = 103TB) Model: Tiered structures, 100,000 processors multi-PB disk, tape
capacity(co-processors estimation 2004)
Pre-Collision Phase
First detector understanding before commisioning with real collision
Detector Alignment and Calibration
Both ATLAS and CMS has developed simulation studies in order to better understand how to use data.
On going Study.. In CMS this month there will be a Workshop to decide
the strategy for 2007 run.
CMS Detector
Initial Detectors • CMS will start without muon RPC in the region 1.6 < < 2.1• Fourth layer of the end cap muon chambers will be absent during
the pilot run• NO EE and pixel detector, but will be installed during the shut down
after the 2007 run----thinking the psossibility to install all these for new two months delay.
• ATLAS will start with two pixel layers (instead three) and without Transition Radiation Tracker in the region 2 <eta<2.4.
What about Trigger and DAQ: Initial L1 rate 50kHz(instead of 100) and 35 kHz(instead of 75) in ATLAS.
Performances Good muon identification and momentum Resolution over a wide range of momenta in the region || < 2.5 ( about 1%
at 100 GeV/C2).
Good charged particle momentum resolution (~ 1% at 100 GeV/c2) and rec. eff. in the inner tracker. Eff. b/tau tagging and triggering on taus
Good electromagnetic energy resolution,good diphoton,dielectron resolution(<1 %) wide geometric coverage(eta <2.5), measurement of the direction of photons and/or correct localization of the promary interaction vetext, pi0 rejection.
Good missing ET and dijet mass resolution with fine lateral segmentaion ( X φ < 0.1 X 0.1) in HCAL.
First Data• 1 fb-1(100 pb-1)= 6 months(few days) at L=1032cm-2sec-1
with 50% data taking efficiency a few 1/fb per experiment at the
end of 2008
W,Z events will be used for calibrationTop events also will be used to for JES,..
Calculations and tools
• For many of the interesting physics processes, higher order calculation exist, still there is a wish list..
Event Generators: PYTHIA, HERWIG,ISAJET
Physics process; ALPGEN,MC@NLO,MCFM,NLOJET++, Madgraph,Comphep….
Outline
SM at 14 TeV
- UE events studies
- Jet Studies
- W/Z studies
- Early Top Physics
New Physics
- Zprime
- Higgs
- SUSY..
Cross sections
Min Bias and UE events
• MB events: Events collected with a trigger that is not very restrictive are referred as MB events.
• UE is everything else accompanying the hard scattering component, consists of “beam-beam remnants” and from particles arising from soft or semi-soft multiple interactions(MPI). UE receives contribution from
ISR and FSR
Hard Scattering
PT(hard)
Outgoing Parton
Outgoing Parton
Initial-State Radiation
Final-State Radiation
Hard Scattering
PT(hard)
Outgoing Parton
Outgoing Parton
Initial-State Radiation
Final-State Radiation
Proton AntiProton
Underlying Event Underlying Event
Proton AntiProton
Underlying Event Underlying Event
“Hard Scattering” Component
“Underlying Event”
TheTH
The UE is an unavoidable background to most collider observables, requires good understanding
MB and UE modeling
The Multiple parton interaction model extending pQCD to the soft regime, describe the physics of MB and UE
• MPI models are implemented in the general purpose simulation program lik
General purpose simulation programs PYTHIA, JIMMY, SHERPA, HERWIG are modeled for MB and UE.
Tunned with data from UA5 and Tevatron
Hard scattering events are having different topological structures in the -φ regions.
Regions sensitive to UE components of the interaction.
UE event studies :Jet Production
Charged Jet #1Direction
“Toward”
“Transverse” “Transverse”
“Away”
Charged Particle Correlations PT > 0.5 GeV/c || < 1
• Look at charged particle correlations in the azimuthal angle relative to the leading charged particle jet.
• Define || < 60o as “Toward”, 60o < || < 120o as “Transverse”, and || > 120o as “Away”.
• All 3 regions have the same size in - space, x = 2x120o = 4/3.
UE at CDF
Extrapolation to LHC
Example: top physics
Different UE models shift top mass by about ~ 5 GeVNeeds very good tunning!
Inclusive Jets
• The measurement of jet production cross section at LHC will provide a stringent test of pQCD at a regime which was not probed before so far.
• The first data will be used to provide systematics connected
to measurements.
QCD is a background to almost all New physics scenarios.
A high pT tails to inclusive jets are sensitive to new physics A bad estimations of errors may lead to fake as a new physics
Computed using NLOJET,CTEQ6.1
Different Sub processes
Jets at Tevatron
Uncertainties:JES ~10% for low pT and ~60% at High pT
Energy resolution below 10%, UE: -22% to 4%Hadronisation:13% to 4%
LHC:Statistical Errors
• Statistics is not a problem..
e.g for pT ~ 1 TeV, about 1%
for large pseudorapidty region
it is ~10% for L = 1fb-1
Assuming one month luminosity
@1032cm-2sec-1 and 40% trigger
efficiency
Theoretical Errors
Main Sources µR and µF
Parton distribution Function(PDF)
~10% for pT ~ 1 TeV
For PDF, mainly g(x), at low x,e.g. ~15% for pT =1 teV
Experimental Errors
• Main Source
- Jet Energy Scale(JES)
- Luminosity Measurements
- resolution, triggering efficiency
UE subtraction….
Detector effects:Jet Reconstruction
- R and ET threshold
- Calo Jet to Particle level jet,
jet Calibration 1% uncert. In JES→10% on σ(Jet)5% uncert. In JES→30% on σ(Jet)
Gamma+jet CalibrationDifferent available processes for calibration (/Z+jet, Wjj (from top decay))
Example:make use of the PT balance in +jets
Event selection: selection of events with isolated photons, no high-PT secondary jet, photon and jet well separated in the transverse plane (Et
isol < 5 GeV, ETjet2 < 20 GeV,
φγ,jet > 172°)
Trigger efficiencies included in the analysis,stat error smal (well below 1%) after 10 fb-1
The main systematics is due to non leading radiation effects, QCD backgrounds, gluon-light jet difference, etc.
W/Z at LHC
• LHC is a W and Z factory • For L=1/fb
σ(W→lν)~ 15 nb, ~107 events
σ(Z→ll) ~1.5nb, ~106 events
Theory cross section 2-4% accuracy
Mass, width, W/Z+jets
PDF constraining.
Detector Performances
ECAL calibration using Z→ee
Alignment using Z→µµ
Lepton identification
Luminosity measurements
W/Z at Tevatron
Very good agreement with theoryLuminosity error dominates ~5-6%
W/Z at LHC
σ(W→µν+X)=14700±7(stat)±485(syst)Systematic ~3.3% (dominated by theory)
σ(Z→µµ+X)=1160±2(stat)±27(syst.)heory)Systematic 2.3%( dominated by theory)
Theoretical prediction ~4%Luminosity measurement~6-7%
expected
Luminosity measurement
• Theory accuracy about 2-3%Strategy:I. Count the number of events within
some sets of cutsII. Compare against a theoretical
simulation subject to same cuts OR Take a MC and evaluate the
acceptance (A) of the cuts, to get the cross section
σ = 1/A N/Lum
Accuracy of the calculation dependence of accuracy of calculation A.
6-7% accuracy expected..
Parton Distribution Function
Proton StructureNeed to understand for testing SM and BSM
PDFs are determined by global analyses of dataFrom DIS,DY and jet production
Two major groups regularly update whenever new data available:MRS,CTEQ
ALL the above groups provide a way to estimate the error on the central PDF
LHAPDF : calculates the PDF uncertainties for any observables
Parton Distribution Function(PDF)
Proton Structure
Need to understandFor testing SM and BSM
very low x
X1,2=(M/14TeV)exp(±y)y:rapidity
Q=M, mass of the final state
Parton Distribution:HERA
HERA PDF: fair agreement
PDF: W/Z process
The experimental uncertainty small to
Distinguish the PDF sets.
PDF errors are sensitive to e rapidity
Distributions
ATLAS studies shows it is possible to distinguish different PDF if Exp. Uncertainty ~3-5% CTEQ61
MRST02 ZEUS02
CTEQ61 MRST02 ZEUS02
e- rapidity e+ rapidity
GeneratedGenerated
y
d(W
e
)/dy
y
d(W
e
)/dy
Reconstructed Reconstructed
W±→e±ν rapidity distributions
eWud
eWdu
Constraining PDF : ATLAS
ZEUS-PDF BEFORE including W data
e+ CTEQ6.1 pseudo-data
ZEUS-PDF AFTER including W data
W rapidity events, CTEQ6.1, ATLFAST, 4% syst err(by hand),100/pbUncertainties is reduced, error low x gluon by 50% are reduced
Top Physics
Early top Physics
• Top cross section ~840pb(1±5%(scale)+3%(pdf))• gg fusion : 90%• qq annhilation:10% For low L=1033cm-2sec-1, every 4 second one
“lepton+jet” event, and one second one top pair.
~ 0.1 m top events for L=1fb-1
Top mass and cross section
Top production is one of main SM background for most of the new physics signal. Top events can be used for estimating JES, b-tagging,
One lepton modeDilepton modeHadronic mode
J/psi mode
Top Physics: Dilepton mode
• Two OS lepton with pt>20GeV, at least two b-tagged jets with pt>30GeV,Etmiss>30GeV
• Upper cuts on the number of high pt jets.
• Backgrounds: Z+jets,
Top Physics: Single lepton mode
• Single muon trigger, at least one muon with pt > 20 GeV,
• Four non-overlapping jets with Et>30,
• Two of them b –jets• And the other two non b-tagged
jets• Etmiss>40GeV• Upper cuts on the multiplicity of
jets
tt → bWbW →bbqqµν
mt(semi-leptonic,1fb-1)=±0.7(stat.)±1.9(syst.)GeV/C2
Top Physics: Hadronic Final states
• Four Partonic jets, two b-jets, huge QCD backgrounds challenging
• Selection inclusive jet trigger, b-jet trigger,
• Events shape variables like centrality,aplanarity
• Used to supres the QCD backgrounds.
mt(semi-leptonic,1fb-1)=±0.6(stat.)±4.2(syst.)GeV/C2
tt → bWbW →bbqqqq
Top Physics: J/psi meson
• J/psi arises mainly from B quark fragmentation
• Reconstruction of J/psi gives significant information about b flight direction.
• Top reconstruction is done taking lepton from W decays and leptons from J/psi
• Rate is too low, Br ~ 10-5
• => 4500 events for 10/fb• Systematic uncert.
contributes:
mt=1.47 GeV/c2
Single top production
• Direct measurement of vtb2
• V-A structures,polarised top, Spin of top,good candidate
• Background for new physics• Coupling structures tWb, can
indicate some new physics
• Results: t-channel• Bg W+jets, • Signal events survived 7000 for
L=30/fb, S/B=3• Result s-channel:• Signal events 2050, S/B=0.15
tw channel:Bg top pairSignal events 4700 events,S/B~1/7
Top Physics: summaryCMS
• A combined top mass accuracy ~ 1GeV/C2
for 10-20/fb data will be feasible
Z’
Zprime:Very Easy to Discover• Additional Z’ boson predicted by
Superstring inspired, GUT, Dynamical Symmetry breaking
model, little Higgs.. Current limit >0.6-0.7 TeV Tevatron reach ~ 1 TeV pp →Z’ →µ+ µ-,
Main Dominant SM: DY
Z prime(contd.)
Large enough to find up tp ~1 TeV, for 0.1 /fb, signal as a mass peak, DY is very easily managable
New Discovery: SUSY
SUSY at TeV Scale, m~ 1 TeVLarge cross section
~10 events/day
Decision for ILC!!
SUSY Discovery
Understanding Etmiss is one of the Experimental Challenge!
Higgs?
Please See talk by A.NikitenkoLooks like difficult case for 1/fb
Is Tevatron a competitor?
Outlook• With first data 1-10/fb
• Detector Understanding..
• Measure charge particle multiplicity ( within few hours of data taking)
Measure QCD jet cross section ~ 30%
W/Z cross section.. Top signal with 100/pb and top
cross section and mass PDF constraining UE events ……..
Z’ prime studiesNew Discovery
Higgs!
International meetings in 2009Exciting news!