Heavy Flavor measurements with the ALICE EMCAL detector
Mark HeinzYale University
EMCAL Meeting, Nantes, July 16, 2008
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Outline
Heavy flavor physics with EMCAL The Essentials
Simulation Status at CD-2 What needs to be done for PPR 2008. B-tagging algorithms
The Optionals (“exciting future measurements”)
Outlook & Summary
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Testing pQCD Current theoretical estimates for bottom and charm
production at LHC still have large uncertainties. Charm x-section measurements disagree at RHIC for STAR
and PHENIX by a significant amount.
Theory Uncertainties: NLO pQCD, pp, s = 14 TeV
CERN/LHCC 2005-014,hep-ph/0601164
Large uncertainty in cross-sections
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Medium effects on Heavy quarks
Parton energy loss in the medium Magnitude of Dead-cone effect and
quark mass dependence within a limited kinematical range
Quark vs gluon energy loss in the medium (Color Factors) B-jets constitute a very pure sample
of quark jets.
Distinction between AdS/CFT and pQCD?
WHDG, nucl-th/0512076
The Essentials
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Annual Heavy Flavor electrons vs backgrounds More detailed rate-plot for 1 year of Pb+Pb running in
EMCAL acceptance.
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Electron/Hadron ratio We will need to identify high-pt (>10 GeV/c) electrons. How large are the
hadron backgrounds? Track-EMCAL cluster matching
Max. track-matching efficiency for electrons in Hijing events with tuned EMCAL cuts is ~90% up to 30 GeV/c
~400
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EMCAL PID (electron vs hadron) Using matched cluster track-pairs we determine the
momentum/Energy (p/E) ratio of tracks
Resolution of p/E peak for two differentenergies
ElectronsPions
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Background Electron Sources Full Simulation of photons in ALIROOT v4-06 include newer
GEANT model of TOF-Geometry (additional material)
<10% convert before TRD/TOF
Integrated over area of EMCAL
Start of EMCAL: 454cm
PYTHIA+GEANT Simulation of mono-energetic photons
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Statistical reach of B-jets By triggering on high-pt electrons tightly correlated with the b-jet (Cone
dR<0.2) we are biasing our sample to high pt B-jets. For 70 GeV/c B-jets we obtain about a factor 5 more statistics using a
electron trigger A sample of several hundred B-jets with momenta up to 80 Gev/c will be
acquired during 1 month Pb-Pb running
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B-tag: A method - Displaced Vertex Method
The method pursued here has previously been used by CDF to identify secondary vertices from semi-leptonic decays.
Breakdown of method: Find a high-pt electron trigger particle in
EMCAL Pair with all charged hadrons within a cone
of radius dR. Reconstruct “approximate” (average
between B-D decay) secondary vertex and apply more cuts to reduce backgrounds from other leptonic decays.
Plot Lxy distribution and obtain B-contribution from positive/negative imbalance
D0
B-
e-
K/e
Pe+K
r
PrimVtx
SecVtx
Lxy= r .pe+k / |pe+k|
Lxy
CDF Phys.Rev.D66 (2002))
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Charm backgrounds (dominant source) Due to the shorter life-time secondary vertices will naturally
have a narrower Lxy distribution. To further reduce displaced vertices from charm by cutting on
the electron-hadron M_inv. Me+h < M + Me + Mh = MD ~ 1.9 GeV
Beauty (after cut) Charm (after cut)
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Signal vs. Backgrounds
Electron pT-cut > 10 GeV/c Min. 6 ITS-hits on both electron/hadron track Inv mass of (elec-kaon) mass > 1.7 GeV Pair DCA < 200 m B-Tag = |Lxy| > 600 m
Backgrounds
Cuts used for analysis
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Efficiencies & Rejection
All sources
B-jets
Dalitz
ConversionsCharm
B-jets
B-jets B-jets
More stats needed, higher pT
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W backgrounds
pT pT
EMCAL Acceptance EMCAL Acceptance
B-jet electrons W electrons
So far only a qualitative look
~10x higher stats
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DVM Comparison: B-jet vs WB-jets W
Standard cuts
Standard cuts +Minv> 1.7 GeV(charm rejection)
Standard cuts +Minv> 1.7 GeV + Max ITS-hits
Blue = Signal = right - left
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Displaced Vertex simulation results
After applying DVM cuts the signal efficiency is ~30-40%, whereas the backgrounds are factor ~100 suppressed.
Electrons from all sources (before DVM method)
Electrons from all sources (after DVM method)
What needs to be done ?(short-term until PPR)
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PPR 2008
Physics Performance Report (PPR) will be prepared for EMCAL for end of 2008. Effort lead by Rene Bellwied 6 different topical working groups formed
All current studies need to be upgraded with more statistics and current version of AliRoot
Electron-Hadron-ID needs to be checked with results from 2007 Testbeam to ensure stability
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Preliminary work matrix (PPR)Task Tools Manpower Statistics
Revisit rates
(higher stats)
PYTHIA + Material ---kinematics info
0.5 person 100k x 15 jet pT bins
Re-check e-ID (track-matching, p/E)
PYTHIA/HIJING + Full simulation
0.5 person Single e, 0 10k x ~10 pT ranges
100k x 15 jet pT bins + 10k HIJING bkg
Electron and E-Jet trigger
(rates/bkg)
PYTHIA/HIJING + AliEMCALTrigger, HLT
Trigger Group?
100k x 15 jet pT bins + 10k HIJING bkg
Electron spectra/RAA
(eB/D corresp., compare to TPC and TPC+TRD)
PYTHIA + Full simulation
1 person 100k x 15 jet pT bins
100k x ~5 pThard bins each of MSEL4 and MSEL5
D/B Spectra/RAA (e+D, J/Psi+K, mis-ID)
PYTHIA + Full simulation
1-2 people 100k x 15 jet pT bins
100k x ~5 pThard bins each of MSEL4 and MSEL5
B-jets (DVM,W,JETAN reco, FF, other tag methods)
PYTHIA/HIJING + Full simulation
2-3 people 100k x ~5 pThard bins each of MSEL4 and MSEL5
50-100k W-boson decays
10k HIJING bkg
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Non-photonic Electron R-AA Most importantly compare to measurements in Alice with
TPC and TPC+TRD to identify a kinematic regime where EMCAL is unique. How will the EMCAL triggering help enhance our yields ?
Determine photonic conversion probabilities and develop conversion vertex rejection methods ?
non phot. el.
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B-tagging
Start of with jet-finding algorithm A brief overview of some different algorithms for b-
tagging (see studies by CDF,D0,CMS…) Secondary, displaced vertex type algorithm (Karlsruhe) Soft lepton tag (INFN) Track-impact parameter based (INFN PISA)
In the end several tags can always be combined in a linear discriminant (LDA) method.
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CMS Secondary Vertex Tracker (Weiser et al.)
CMS Note 2006/14
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B-Tagging: Track Impact Parameter Based
More details in CMS-Note (Rizzi et al, INFN Pisa) 2006/19
Tagging Variables
First studies were started in Alice by Bonvini, Antinori et al (PWG3, Sep 2007)
“Exciting new measurements”
My personal selection of QM 08 high-lights High-Pt J/ Electron-Charm correlations
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Electron-Charm correlations
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(K) invariant mass distribution
w/o electron triggerw/o electron triggerw/ non-photonic electron triggerw/ non-photonic electron trigger
Clear D0 signal w/o background subtraction
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Electron – Charm correlations (2)
A. Mischke (HP 2008)
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J/ at high-pT
Zebo Tang (STAR) QM08
Investigate heavy quarkonium production mechanism and hadronization
• In p+p collision
• Gluon fusion
• Charm fragmentation
• Feed down
• In heavy ion collision
• Gluon energy loss
• Heavy quark energy loss
• Hot-wind dissociation in QGP
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High-pT J/ Dissociation or not?
• Double the pT range to 10GeV/c
• Consistent with no suppression at high pT: RAA(pT>5 GeV/c) = 0.9±0.2•Low pT:
RAA(pT<4 GeV/c) = ~0.5
•Indicates RAA increase from low pT to high pT
• Most models expect a decrease RAA at high pT: AdS/CFT: H. Liu, K. Rajagopal and U.A. Wiedemann, PRL 98, 182301(2007) and hep-ph/0607062
Two Component Approach: X. Zhao and R. Rapp, hep-ph/07122407 private communicationZebo Tang (STAR), QM08
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J/Psi – hadron correlations
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J/Psi – hadron correlations
Zebo Tang (STAR), QM08
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Summary
Baseline studies were performed for US CD-2 document in Dec 2007 Need to be updated and improved
EMCAL Physics Performance Report (PPR) is next deadline Structure & meetings are in place
We need to continue to watch new results from RHIC More studies of other observables need to be started now
with a goal of having simulations beyond the PPR
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Backup
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Z-Boson decay into electrons
Dielectron decays: Main source of background
are jets from misidentified pions.
An isolation cut is mandatory. A track i is rejected if it is found a track j with pt > 2 GeV/c || 0.1 && || 0.1 rad
Zaida . , HP2008R. Bailhache et al: Proc. QM08,
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D0 measurement of weak boson
PRL 1995
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Z/W predictions from Tevatron toLHC Probe PDF’s