Heavy flavor measurements with high-p electrons in the ALICE EMCal

Heavy flavor measurements with
high-pT electrons
in the ALICE EMCal
Mark Heinz (for the ALICE Collaboration)
Yale University
26th Winter Workshop on Nuclear Dynamics
Ocho Rios, Jamaica, Jan 2-9 2010
Physics Motivation (p+p)
• Beauty physics in p+p (examples):
– Transverse momentum spectrum, X-section,
(normalization for “Quarkonia” studies)
– Jet-Shapes
– Fragmentation function
Jet-Shape
Y(r/R)
X-section vs NLO
CDF (PRD78,2008)
M.Heinz (Yale)
Winter Workshop 2010, Jamaica
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Physics Motivation (Heavy Ion)
• Investigate energy loss of quarks vs. gluons
• Investigate differences between the predictions of pQCD
vs ADS/CFT
RHIC (200 GeV)
RAA(charm)/RAA(beauty)
pQCD
ADS/CFT
Horowitz, Gyulassy (arXiv:0804.4330)
S.Wicks et al (Nucl.Phys.A784 (2007)
M.Heinz (Yale)
Winter Workshop 2010, Jamaica
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Electron Identification in Alice
 Barrel (TPC/TRD/TOF)
 Superior electron/hadron
discrimination up to p~10 GeV/c
 EMCal
 Very good electron/hadron
discrimination for p > 10 GeV/c.
PID parameters tuned.
 4 Super-modules installed in
ALICE
 5th SM at calibration stage at
Yale University
 Energy calibration of detector
with p0 currently underway
 Part of routine data-taking
 Sufficient coverage for day 1
physics
M.Heinz (Yale)
Run 2010 configuration
(Pb+Pb low luminosity)
Winter Workshop 2010, Jamaica
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Electron Rates (PYTHIA)
• PYTHIA Rates are scaled to 1 month of Pb+Pb running (0.5mb-1s-1, 106
sec, A2)
• Significant beauty-electron yield out to pT~50 GeV/c
• Dominant background are W-electrons above 20 GeV/c
• Hadron/Electron ratio is 500-800. Sets scale for PID performance.
M.Heinz (Yale)
Winter Workshop 2010, Jamaica
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EMCAL PID: E/p
• For electron identification we use the ratio of Ecluster/ptrack.
• Track-Cluster matching efficiency ~65%
• The electron peak can be cleanly separated from pions. Material
interaction in front of the EMCAL does deteriorate the performance.
Simulation
M.Heinz (Yale)
Winter Workshop 2010, Jamaica
Simulation
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Hadron Rejection Power (HRP)
From published NIM paper
arXiv: 0912.2005
• Results from CERN test-beam for
energies 40-80 GeV. These compare
well to ideal simulation (ie. no
additional detector material in front of
EMCAL)
Simulation
• Results from simulation for a set of
optimized cuts for electron
identification and full ALICE detector
simulation. For ~65% electron
efficiency we obtain a HRP between
400-1000.
M.Heinz (Yale)
Winter Workshop 2010, Jamaica
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Electron Spectra
• Reconstructed conversion electron vertices are found by the V0-finder
and tagged using an invariant mass cut (Minv<100 MeV). These are
then subtracted from the inclusive electrons.
• After EMCAL PID non-photonic electron candidates dominate
misidentified hadrons by at least factor 10.
• Dominant background to b-electrons above 20 GeV/c from Welectrons. This can be further reduced by secondary vertex strategies.
PYTHIA
M.Heinz (Yale)
Winter Workshop 2010, Jamaica
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Corrected Spectra
• Efficiency corrected
rates of non-photonic
electron candidates
• Systematical errors
indicate the variation of
EMCAL PID criteria
M.Heinz (Yale)
Winter Workshop 2010, Jamaica
PYTHIA Simulation
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B-Tagging:
Displaced Vertex Method
p/e
K
• The method previously used by CDF to
identify secondary vertices from semileptonic decays. Further development
and implementation in ALICE.
• 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
using an identified electron and all
associated hadrons
– apply more cuts to reduce backgrounds
from other leptonic decays.
– Plot Lxy distribution and obtain Bcontribution from positive/negative
imbalance
Pe+K
eD0
SecVtx
r
BPrimVtx
Lxy= r .pe+k / |pe+k|
CDF Phys.Rev.D66 (2002))
M.Heinz, arXiv: 0712.2422
M.Heinz (Yale)
Winter Workshop 2010, Jamaica
Lxy 10
Method Cuts
• Tracks
– Track Impact Parameter < 0.5 cm (electron)
– Silicon Hits: ITS>=4
– PT > 1.0 GeV/c (associated hadrons)
• Secondary Vertex
–
–
–
–
–
M.Heinz (Yale)
pairDCA < 0.02 cm
R= √Dh2+Df2 (electron-hadron) < 1.0 rad
Vertex length < 1.0 cm
SignDCA Lxy > 0.1
Invariant Mass (e+k) > 1.5
Winter Workshop 2010, Jamaica
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Sign-Dca Lxy
• The method relies on the fact that the B-meson creates a
displaced vertex with ct~500mm.
M.Heinz (Yale)
Winter Workshop 2010, Jamaica
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Electron tag efficiency
• Tagging algorithm can be tuned by requiring a
given number of heavy flavor vertices which
pass our cuts
M.Heinz (Yale)
Winter Workshop 2010, Jamaica
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B-Jet Tagging performance in p+p
• FASTJET Jet-Finding Algorithm: kT, R= 0.4 (anti-kT comparable)
• Standard definitions:
– Efficiency = tagged B-jets/MC-B-jets
– Fake Rejection = Non B-Jet efficiency
• Algorithm currently tuned for maximum fake rejection. Studies
ongoing to map out full cut-space
• Results comparable to CMS Soft Lepton Tag (Note 2005/058)
Signal Efficiency
Fake rejection
PYTHIA jets (pThard 12-150 GeV/c)
M.Heinz (Yale)
PYTHIA jets (pThard 12-150 GeV/c)
Winter Workshop 2010, Jamaica
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Expected tagged Jet yield
M.Heinz (Yale)
Winter Workshop 2010, Jamaica
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Conclusions & Outlook
Conclusions
•
EMCAL PID (using E/p method) works well and we expect a hadron
rejection power of 400-1000 (65% efficiency) for 10 GeV/c< pT <80 GeV/c.
Hadron/Electron ratios from MC in this range are ~500.
•
Reconstructed electrons after subtraction of the photonic component and
EMCAL PID dominate the background of mis-identified hadrons by at
least a factor 10.
•
Preliminary studies of B-jet tagging algorithms in simulated p+p events
have been performed. First results for efficiency and fake rejection using
the displaced vertex method have been calculated and are comparable to
similar methods used in other experiments.
•
Tagged Jet-yields should be sufficient for measurements of B-jets to
pT~50-60 GeV/c.
Outlook
•
More optimization of B-tagging algorithms
•
First look at real data …
M.Heinz (Yale)
Winter Workshop 2010, Jamaica
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Backup
CMS Electron Tag performance
 c
 uds
 g
-
M.Heinz (Yale)
Winter Workshop 2010, Jamaica
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