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Charm and Electrons in. Thomas Ullrich, STAR/BNL International Workshop on Electromagnetic Probes of Hot and Dense Matter ECT, Trento June 8, 2005. Outline. STAR’s Heavy Flavor Program Detector capabilities Experimental techniques Open Charm (and Beauty) Production - PowerPoint PPT Presentation
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Charm and Electrons in
Thomas Ullrich, STAR/BNL
International Workshop onElectromagnetic Probes of
Hot and Dense MatterECT, Trento June 8, 2005
2
Outline STAR’s Heavy Flavor Program
Detector capabilities Experimental techniques
Open Charm (and Beauty) Production Non-photonic electrons
p+p: the referenced+Au: cold nuclear matter effectsAu+Au: ( QM’05)
D mesonsd+Au: charm cross-sectionAu+Au: ( QM’05)
Thermalization of heavy quarks ? Au+Au: v2 of non-photonic electrons
Quarkonia: J/ and Summary and Outlook
3
Detecting D-Mesons via Hadronic Decays
Hadronic Channels: D0 K (B.R.: 3.8%) D K p (B.R.: 9.1%) D*± D0π (B.R.: 68% 3.8% (D0 K ) = 2.6%) D0 K (B.R.: 6.2% 100% () = 6.2%) c p K (B.R.: 5%)
4
Detecting D-Mesons via Hadronic Decays
Hadrons in STAR:TPC: tracking, PIDSVT: vertex’ing, PIDZDC/CTB: centrality/trigger
TPC: High tracking efficiency for tracking
hadrons (~90%) p/p ~ 1% at 1 GeV/c large acceptance ||<1 PID (dE/dx) limits:
p up to 1 GeV/c K, up to 0.7 GeV/c
SVT: current vertex’ing performance not
sufficient to resolve typical charm secondary vertices (c ~ 120(D0) - 315(D) m) background
Current analyses are based on TPC alone
5
General Techniques for D Reconstruction1. Identify charged daughter tracks through
energy loss in TPC
2. Alternatively at high pT use h and assign referring mass (depends on analysis)
3. Produce invariant mass spectrum in same event
4. Obtain background spectrum via mixed event
5. Subtract background and get D spectrum
6. Often residual background to be eliminated by fit in region around the resonance
Exception D*: search for peak aroundm(D*)-m(D0) =0.1467 GeV/c2
D0
D0D*
6
Detecting Charm/Beauty via Semileptonic D/B Decays
Semileptonic Channels: c e+ + anything (B.R.: 9.6%)
D0 e+ + anything (B.R.: 6.87%) D e + anything (B.R.: 17.2%)
b e+ + anything (B.R.: 10.9%) B e + anything (B.R.: 10.2%)
single “non-photonic” electron continuum
“Photonic” Single Electron Background: conversions (0 ) 0, ’ Dalitz decays , , … decays (small) Ke3 decays (small)
7
Detecting Charm/Beauty via Semileptonic D/B Decays
Electrons in STAR:TPC: tracking, PIDBEMC (tower, SMD): PID
EEMC (tower, SMD): PIDToF patch: PID
8
Electron ID in STAR – EMC
1. TPC for p and dE/dx● e/h ~ 500 (pT dependent)
2. Tower E p/E● e/h ~ 100 (pT dependent)
3. Shower Max Detector (SMD) shape to reject hadrons
● e/h ~ 20
4. e/h discrimination power ~ 105
Works for pT > 1.5 GeV/c
electrons
hadrons
9
Electron ID in STAR – ToF Patch
Electron identification: TOF |1/ß-1| < 0.03 TPC dE/dx electrons
electrons
MRPC – ToF (prototype):/30
10
Inclusive Single Electrons p+p/d+Au
Inclusive non-photonic spectra : How to assess photonic background?
PHENIX 1: cocktail method
PHENIX 2: converter method
STAR: measurement of main background sources
ToF + TPC: 0.3 GeV/c < pT < 3 GeV/c
TPC only: 2 < pT < 3.5 GeV/c
EMC + TPC:pT > 1.5 GeV/c
11
Photonic Single Electron Background Subtraction in pp and dAu
Method:1. Select an primary electron/positron
(tag it)2. Loop over opposite sign tracks
anywhere in TPC3. Reject tagged track when m <
mcut ~ 0.1 – 0.15 MeV/c2
4. Cross-check with like-sign
Rejection Efficiency: • Simulation/Embedding
• background flat in pT
• weight with measured 0 spectra (PHENIX)
conversion and 0 Dalitz decay reconstruction efficiency ~60%
• Relative contributions of remaining sources: PYTHIA/HIJING + detector simulations
Invariant Mass Square
Rejected
Signal
Opening Angle
conversion and 0 Dalitz decay reconstruction efficiency :~60% at pT>1.0 GeV/c
12
Photonic Single Electron Background Subtraction
pT dependent hadron contamination (5-30%) subtracted
Excess overbackground
13
Non-Photonic Single Electron Spectra in p+p and d+Au
14
Nuclear Effects RdAu ?
Nuclear Modification Factor: inelpp
dAubindAu
TppdAu
TdAudAu NT
ddpdT
ddpNdR
/ where;/
/2
2
Within errors compatible with RdAu = 1 …
… but also with RdAu(h)
NOTE: RdAu for a given pT comes from heavy mesons from a wide pT range p(D) > p(e) (~ 1.5-3) makes interpretation difficult
hadrons
15
D0 Mesons in d+Au
Mass and Width consistent with PDG values considering detector effects:• mass=1.867±0.006 GeV/c2;• mass(PDG)=1.8645±0.005 GeV/c2
• mass(MC)=1.865 GeV/c2
• width=13.7±6.8 MeV• width(MC)=14.5 MeV
cp
dy
dN
T
y
Aud
D
/GeV 08.032.1
008.0004.0028.00
0
16
Obtaining the Charm Cross-Section cc
From D0 mesons alone: ND0/Ncc ~ 0.540.05
Fit function from exponential fit to mT spectra
Combined fit: Assume D0 spectrum follows a power law function Generate electron spectrum using particle composition from PDG Decay via routines from PYTHIA Assume: dN/dpT(D0, D*, D, …) have same shape only normalization
In both cases for d+Au p+p: pp
inel = 42 mb
Nbin = 7.5 0.4 (Glauber) |y|<0.5 to 4: f = 4.70.7 (PYTHIA) RdAu = 1.3 0.3 0.3
17
Charm Cross-Section cc
pp Charm Cross-Section
From D0 alone:
cc = 1.3 0.2 0.4 mb
From combined fit:
cc = 1.4 0.2 0.4 mb
18
Discrepancy between STAR and PHENIX ?
STAR from d+Au: cc = 1.4 0.2 0.4 mb (PRL94,062301)PHENIX from p+p (preliminary): cc = 0.709 0.085 + (+0.332,0.281) mbPHENIX from min. bias Au+Au: cc = 0.622 0.057 0.160 mb (PRL94,082301)
Reality check: 1.4 0.447 mb and 0.71 0.343 mb are not so bad given thecurrently available statistics (soon be more!)
pp p
SPS, FNAL (fixed target) and ISR (collider) experiments
19
Discrepancy between STAR and PHENIX ?
90%
15%
Combined fit of STAR D0 and PHENIX electrons:No discrepancy: cc=1.1 0.1 0.3 mb
STAR: PRL 94, 062301 (2005)PHENIX p+p (QM04): S. Kelly et al. JPG30(2004) S1189
20
Statistical model (e.g. A. Andronic et. al. PLB 571,36(2003)) : Largecc yield in heavy ion collisions J/ production through recombination possible J/ enhancement
Consequences of High Cross-Section: J/ Recombination
In stat models: cc typically from pQCD calculations (~390 b)
STAR cc much larger enhancement (~3-4) for J/ production in central Au+Au collisions
PHENIX’s upper limit would invalidate the expectation from large cc ?!
Δy = 1
Δy = 2
Δy = 3
Δy = 4
21
NLO/FONLL
Recent calculations in NLO (e.g. R. Vogt et al. hep-ph/0502203) Calculations depend on:
quark mass mc
factorization scale F (typically F = mc or 2 mc)
renormalization scale R (typically R = F) parton density functions (PDF)
Hard to obtain large with R = F (which is used in PDF fits)
Fixed-Order plus Next-to-Leading-Log (FONLL) designed to cure large logs for pT >> mc where mass is not relevant
K factor (NLO NNLO) ?
b
bb
FONLLbb
NLOcc
FONLLcc
99.067.0
381134
400146
87.1
244 ;256
from hep-ph/0502203
22
NLO/FONLL
For pT spectra mT2
for calculations 2 m2
pT integrated < direct calculated FONLL higher over most pT than NLO Choice of FF plays big role Uncertainty bands:
reflect uncertainties in and mc
23
Charm Total Cross Section
Can we confirm or rule out Cosmic Ray experiments? (Pamir, Muon, Tian Shan) under similar conditions?NPB (Proc. Suppl.) 122 (2003) 353Nuovo Ciment. 24C (2001) 557
X. Dong USTC
NLO calculations under-predict current cc at RHIC More precise data is needed high statistics D mesons in pp
PHENIX,STAR:stat. error only
24
Comparison: Non-Photonic Electrons with NLO
FONLL calculations:
Charm:
scaled by STAR/FONLL
Bottom:
Can be estimated from fit of sum to data (numbers soon)
Errors used: data + FONLL uncertainty bands
Plenty of room for bottom !!!
25
High-pT D0-Meson Spectra in d+Au
How is it done ? Assumptions: same shape of D0,
D*, D spectra D0 K defines low pT points
D0 K defines one high-pT point
Combined allow power law fit Allows to move D* and D
spectra into place Cross-check with known ratios
Problem: D*/D0 and D/ D0 not well known (pT, s dependent ?)
Note: spectrum depends onone point: D0 K
26
High-pT D-Meson Spectra in d+Au
Headache: Spectra very hard (too hard) NLO: fragmentation function function (Peterson FF needs c = b) ? Yield at 10 GeV/c only factor 3 below CDF (LO/NLO ~ 10) ?
Intensive systematic studies of D0 K of many people over many month …
27
High-pT D-Meson Spectra in d+Au
Until we found the problem … subtle effect after correction no significant signal D0 K “combined” low to high-pT D0 spectra is gone
Upper limits from D0 K (90% CL)
Note: D* itself is still valid!!! Now a “standalone” spectra. Doesn’t affect possibility of studying RAA in Au+Au
28
Strong Elliptic Flow at RHIC
Strong elliptic flow at RHIC (consistent with hydro limit ?) Scaling with Number of Constituent Quarks (NCQ)
partonic degrees of freedom !? (v2/n) vs. (pT/n) shows no mass and flavor dependence Strong argument for partonic phase with thermalized light quarks
What’s about charm? Naïve kinematical argument: need Mq/T ~ 7 times more collisions to thermalize v2 of charm closely related to RAA
29
Charm Elliptic Flow from the Langevin Model
Diffusion coefficient in QGP: D = T/M momentum drag coefficient) Langevin model for evolution of heavy quark spectrum in hot matter Numerical solution from hydrodynamic simulations pQCD gives D(2T) 6(0.5/s)2
AMPT:(C.M. Ko)
← =10 mb
← =3 mb
30
Charm Elliptic Flow through Resonance Effects
Van Hees & Rapp, PRC 71, 034907 (2005) Assumption: survival of resonances in the QGP Introducing resonant heavy-light quark scattering heavy particle in heat bath of light particles (QGP) + fireball evolution
time-evolved c pT spectra in local rest frame
“Nearly” thermal: T ~ 290 MeV
Including scalar, pseudoscalar, vector, and axial vector D-like-mesons gives:
σcq→cq(s1/2=mD)≈6 mb
Cross-section is isotropic the transport cross section is 6 mb, about 4 times larger than from pQCD t-channel diagrams
31
How to Measure Charm v2
Best: D mesons need large statistics, high background not yet
Alternative: Measure v2 of electrons from semileptonic charm decays
Emission angles are well preserved above p = 2 GeV/c 2-3 GeV Electrons correspond to ≈3-5 GeV D-Mesons
32
Analysis: v2 of Non-Photonic Electrons
Same procedures as for single electrons (incl. background subtraction) But much harder cuts (plenty of statistics) Special emphasis on anti-deuteron removal γ-conversions, π0-Dalitz electrons removed via invariant mass
Remaining 37% photonic electron background subtracted with v2max=17%
Reaction plane resolution res ~ 0.7 Consistency check: PYTHIA + MEVSIM (v2 generator) + analysis chain OK
v2 = cos(2[Φ-Ψ]) / Ψres
Phenix : Min. BiasStar: 0-80%STAR: stat. errors only
Phenix:nucl-ex/0404014 (QM2004)nucl-ex/0502009 (submitted to PRC)Star:J. Phys. G 190776 (Hot Quarks 2004)J. Phys. G 194867 (SQM 2004)
v2 of Non-Photonic Electrons
Indication of strong non-photonic electron v2
consistent with v2(c) = v2(light quark) smoothly extending from PHENIX results Teany/Moor D (2T) = 1.5 (s = 1?) expect substantial suppression RAA
Greco/Ko Coalescence model (shown above) appears to work well
34
Quarkonia in STAR
STAR: Large acceptance ||<1 High tracking efficiency (90%) J/ acceptance efficiency (pT
e > 1.2 GeV/c) ~ 10%
: Acceptance efficiency (pTe > 3.5 GeV/c) ~ 14%
Without Trigger (min. bias running): Min bias (100 Hz): 18 J/ and 0.02 per hour running
Signal-to-Background Ratios S/B > 1: 1 for S/B = 1:25 – 1:100 for J/
Seff = S/(2(B/S)+1) significance close to that of J/
STAR needs quarkonia triggers
35
Quarkonia Trigger in STAR
J/ e+ e: L0-trigger: 2 EMC tower with E > 1.2 GeV (~60° apart) L2-trigger (software): veto , better E, 2.5 < Minv < 3.5 GeV/c2
Efficiency currently too low in Au+Au (pp only) need full ToF
e+ e: L0-trigger: 1 EMC tower with E > 3.5 GeV L2-trigger (software): Minv > 7 GeV/c2
High Efficiency (80%) – works in Au+Au
Tests in Au+Au show it works small background counts = expectations Need full EMC for that
2004 ½ barrel EMC 2005 ½ - ¾ barrel EMC
triggerthreshold No N+++N--
subtracted
36
Summary and Outlook
Heavy Flavor Production in RHI is the next big topic that needs to be addressed STAR has solid baseline measurements in pp and d+Au
D0 in d+Au from pT = 0 - 3 GeV/c
D* in d+Au mesons from pT = 1.5 – 6 GeV/c Non-photonic single electrons in p+p and d+Au from 1.5 – 10 GeV/c
Measurements indicate a large cc in pp at RHIC d/dy|y=0 = 0.300.04(stat)0.09(sys) mb NLO pQCD calculations under predict this value (~ a factor of 3-5) Large cc appear to rule out expectation of J/ψ enhancement from some
charm coalescence and statistical models
Preliminary results on v2 of non-photonic electrons indicate substantial elliptic flow of charm in Au+Au collisions at RHIC consistent with v
2c = v
2light-q theory calculations
consistent (smoothly extending) with PHENIX results try to extend to higher pT range (possibly b dominated)
First Results on J/ and soon
37
Argonne National Laboratory Institute of High Energy Physics - Beijing University of Bern University of Birmingham Brookhaven National Laboratory California Institute of Technology University of California, Berkeley University of California - Davis University of California - Los Angeles Carnegie Mellon University Creighton University Nuclear Physics Inst., Academy of Sciences Laboratory of High Energy Physics - Dubna Particle Physics Laboratory - Dubna University of Frankfurt Institute of Physics. Bhubaneswar Indian Institute of Technology. Mumbai Indiana University Cyclotron Facility Institut de Recherches Subatomiques de
Strasbourg University of Jammu Kent State University Institute of Modern Physics. Lanzhou Lawrence Berkeley National Laboratory Massachusetts Institute of Technology Max-Planck-Institut fuer PhysicsMichigan State University Moscow Engineering Physics Institute
City College of New York NIKHEF Ohio State University
Panjab University Pennsylvania State University
Institute of High Energy Physics - Protvino Purdue UniversityPusan University
University of Rajasthan Rice University
Instituto de Fisica da Universidade de Sao Paulo
University of Science and Technology of China - USTC
Shanghai Institue of Applied Physics - SINAP SUBATECH
Texas A&M University University of Texas - Austin
Tsinghua University Valparaiso University
Variable Energy Cyclotron Centre. Kolkata Warsaw University of Technology
University of Washington Wayne State University
Institute of Particle Physics Yale University
University of Zagreb
545 Collaborators from 51 Institutionsin 12 countries
STAR Collaboration