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

Heavy flavor measurements with high-pT electrons

in the ALICE EMCalMark Heinz (for the ALICE Collaboration)

Yale University

26th Winter Workshop on Nuclear DynamicsOcho Rios, Jamaica, Jan 2-9 2010

Winter Workshop 2010, Jamaica 2M.Heinz (Yale)

Physics Motivation (p+p)• Beauty physics in p+p (examples):

– Transverse momentum spectrum, X-section, (normalization for “Quarkonia” studies)

– Jet-Shapes – Fragmentation function

X-section vs NLO

CDF (PRD78,2008)

Y(r

/R)

Jet-Shape


Physics Motivation (Heavy Ion)• Investigate energy loss of quarks vs. gluons• Investigate differences between the predictions of pQCD

vs ADS/CFT

Horowitz, Gyulassy (arXiv:0804.4330)

RHIC (200 GeV)

S.Wicks et al (Nucl.Phys.A784 (2007)

RAA(charm)/RAA(beauty)

pQCD

ADS/CFT


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 Run 2010 configuration(Pb+Pb low luminosity)


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.


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 Simulation


Hadron Rejection Power (HRP)• 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)

• 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.

From published NIM paperarXiv: 0912.2005

Simulation


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 W-electrons. This can be further reduced by secondary vertex strategies.

PYTHIA

Winter Workshop 2010, Jamaica 9

Corrected Spectra

• Efficiency corrected rates of non-photonic electron candidates

• Systematical errors indicate the variation of EMCAL PID criteria

M.Heinz (Yale)

PYTHIA Simulation


B-Tagging: Displaced Vertex Method

• The method previously used by CDF to identify secondary vertices from semi-leptonic 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 B-contribution from positive/negative imbalance

D0

B-

e-

Kp/e

Pe+K

r

PrimVtx

SecVtx

Lxy= r .pe+k / |pe+k|

Lxy

CDF Phys.Rev.D66 (2002))

M.Heinz, arXiv: 0712.2422


Method Cuts• Tracks

– Track Impact Parameter < 0.5 cm (electron)– Silicon Hits: ITS>=4– PT > 1.0 GeV/c (associated hadrons)

• Secondary Vertex– 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


Sign-Dca Lxy

• The method relies on the fact that the B-meson creates a displaced vertex with ct~500mm.


Electron tag efficiency• Tagging algorithm can be tuned by requiring a

given number of heavy flavor vertices which pass our cuts


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)

PYTHIA jets (pThard 12-150 GeV/c) PYTHIA jets (pT

hard 12-150 GeV/c)

Signal Efficiency Fake rejection


Expected tagged Jet yield

M.Heinz (Yale)


Conclusions & OutlookConclusions• 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 …

Backup


CMS Electron Tag performance

c uds g

-

M.Heinz (Yale)

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

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