Heavy Flavor Physics in HIC with STAR Heavy Flavor Tracker Yifei Zhang (for the STAR HFT Group) Hirschegg 2010, Austria Outline:  Physics motivation  Charmed hadron  D&B  e  Summary Lawrence Berkeley National Lab

Partonic energy loss at RHIC STAR: Nucl. Phys. A757, 102(2005). Light quark hadrons strongly suppressed in central Au+Au collisions. Jet quenching: The away-side correlation in back-to-back ‘jets’. How about heavy quarks? Explore pQCD in hot dense medium R AA (c,b) measurements are needed! Light quark hadrons strongly suppressed in central Au+Au collisions. Jet quenching: The away-side correlation in back-to-back ‘jets’. How about heavy quarks? Explore pQCD in hot dense medium R AA (c,b) measurements are needed! May 11, 2015 Yifei Zhang LBNL 2 May 11,

Yifei Zhang LBNL 3 May 11, Heavy quark energy loss The R AA of single electron from heavy flavor decay is suppressed as strong as that of light flavor hadrons at high p T (> 6 GeV/c). 1. Directly measure D-meson R AA 2. Separately measure R AA of D  e & B  e Heavy quark energy loss mechanism, interactions with hot dense medium. The R AA of single electron from heavy flavor decay is suppressed as strong as that of light flavor hadrons at high p T (> 6 GeV/c). 1. Directly measure D-meson R AA 2. Separately measure R AA of D  e & B  e Heavy quark energy loss mechanism, interactions with hot dense medium. STAR PRL 98 (2007) E-loss: b < c < q

Partonic collectivity at RHIC STAR: QM2009 STAR: preliminary May 11, 2015 Yifei Zhang LBNL 4 May 11, Low p T (≤ 2 GeV/c): hydrodynamic mass ordering High p T (> 2 GeV/c): number of quarks ordering s-quark hadron: smaller interaction strength in hadronic medium light- and s-quark hadrons: similar v 2 pattern Collectivity developed at partonic stage! In order to test early thermalization: v 2 (p T ) of c- and b-hadrons data are needed!

May 11, 2015 Yifei Zhang LBNL 5 Charmed baryon  c   c yield (rare 10%, small c  ~ 60  m, 3-body decay).  measure  c / D 0 ratio enhancement, di-quark? Lee, et. al, PRL 100 (2008)

May 11, 2015 Yifei Zhang LBNL 6 Bottom from electron channel Important for understanding the bottom contribution in current NPE measurements. Large systematic errors for both theory (FONLL) and data (STAR e-h correlation). Need improve the measurement accuracy. Measure this ratio directly from spectra. Important for understanding the bottom contribution in current NPE measurements. Large systematic errors for both theory (FONLL) and data (STAR e-h correlation). Need improve the measurement accuracy. Measure this ratio directly from spectra.  No B meson spectra measured.  Separately measure B  e spectrum will indirectly measure B meson spectrum from its decay kinematics.  B  e = NPE  D  e STAR HFT has the capability to measure D 0 decay vertex topologically via hadronic decay channel. Measured D 0 spectrum constrains D  e.

May 11, 2015 Yifei Zhang LBNL 7 STAR Detector TOF+TPC+ HFT Large acceptance Mid-rapidity |  | < 1 Full barrel coverage 0 <  < 2  PXL

May 11, 2015 Yifei Zhang LBNL 8 Inner Tracking Detectors TPC Volume Outer Field Cage Inner Field Cage SSD IST PXL FGT HFT

May 11, 2015 Yifei Zhang LBNL 9 Inner Tracking Detectors  SSD existing single layer detector, double side trips.  IST 500  m x 1cm strips along beam direction, it guides tracks from the SSD through PIXEL detector. It is composed of 24 liquid cooled ladders equipped with 6 silicon strip-pad sensors..  PIXEL double layers, 18.4x18.4  m pixel pitch, 2 cm x 20 cm each ladder. Deliver ultimate pointing resolution, hit density for 1st layer ~ 60 cm. -2  SSD existing single layer detector, double side trips.  IST 500  m x 1cm strips along beam direction, it guides tracks from the SSD through PIXEL detector. It is composed of 24 liquid cooled ladders equipped with 6 silicon strip-pad sensors..  PIXEL double layers, 18.4x18.4  m pixel pitch, 2 cm x 20 cm each ladder. Deliver ultimate pointing resolution, hit density for 1st layer ~ 60 cm. -2 Detector Radius (cm) Hit Resolution R/  - Z (  m -  m) Radiation length SSD2330 / 8571% X 0 IST14170 / %X 0 PIXEL 88.6 / 8.6~0.32 %X / 8.6~0.32% X 0

May 11, 2015 Yifei Zhang LBNL 10 Simulation Performance pointing resolution in r-  to primary vertex for single particles (of K,  +, p.) including all hits in HFT. < 20  m at high p T. pointing resolution in r-  to primary vertex for single particles (of K,  +, p.) including all hits in HFT. < 20  m at high p T. Tracking efficiency of single  + for 3 pileup hits densities. 1xRICHII pile up effect was included in the simulation. Tracking efficiency of single  + for 3 pileup hits densities. 1xRICHII pile up effect was included in the simulation.

May 11, 2015 Yifei Zhang LBNL 11 Hadronic channels STAR HFT has the capability to reconstruct the displaced vertex of D 0  K  (B.R.=3.8%) and  c   Kp (B.R.=5.0%,  c c  =59.9  m) D0D0 CC

May 11, 2015 Yifei Zhang LBNL 12 D 0 reconstruction - Central Au+Au collisions: top 10% events. - The thin detector allows measurements down to p T ~ 0.5 GeV/c. After topological cut

May 11, 2015 Yifei Zhang LBNL 13 Error estimate of D 0 R cp Assuming D 0 R cp distribution as charged hadron: directly measure charm quark energy loss. 500M Au+Au m.b. events at 200 GeV. - Charm R AA  energy loss mechanism! Assuming D 0 R cp distribution as charged hadron: directly measure charm quark energy loss. 500M Au+Au m.b. events at 200 GeV. - Charm R AA  energy loss mechanism! R CP =a*N 10% /N (60-80)%

May 11, 2015 Yifei Zhang LBNL 14 Error estimate of D 0 v 2 Assuming D 0 v 2 distribution from quark coalescence. 500M Au+Au m.b. events at 200 GeV. Charm-quark flow  Thermalization of light-quarks! Charm-quark does not flow  Drag coefficients

May 11, 2015 Yifei Zhang LBNL 15  c reconstruction Good D 0 p T distribution measurement as reference. The unique charmed baryon.  c / D 0 ratio => enhancement? Good D 0 p T distribution measurement as reference. The unique charmed baryon.  c / D 0 ratio => enhancement?

May 11, 2015 Yifei Zhang LBNL 16 B capability -- electron channels particle c  (  m) Mass (GeV) q c,b →x (F.R.) x →e (B.R.) D0D D±D± B0B BB ) B  e = NPE  D  e 2) The distance of closest approach to primary vertex (dca): Due to larger c , B  e has broader distribution than D  e Dca of D +  e is more close to that of B  e. need more constraint. B.R. = Branching Ratio F.R. = Fragmentation Ratio Pixel layers dca

May 11, 2015 Yifei Zhang LBNL 17 Dca distributions and spectra Electrons: nFitPts > 15, -1 < eta < 1, 2 PXL hits required, in several p T bins. The photon converted electron outside of pixel detector (~ 70%) can be removed due to their random large DCA distributions. The main background are conversion from beam pipe and electron from  0,  Dalitz decays. Normalized by the F.R. and B.R., and total electron yield was normalized to STAR measured NPE spectrum. Electrons: nFitPts > 15, -1 < eta < 1, 2 PXL hits required, in several p T bins. The photon converted electron outside of pixel detector (~ 70%) can be removed due to their random large DCA distributions. The main background are conversion from beam pipe and electron from  0,  Dalitz decays. Normalized by the F.R. and B.R., and total electron yield was normalized to STAR measured NPE spectrum.

May 11, 2015 Yifei Zhang LBNL 18 (B  e)/NPE ratio  (B  e)/NPE ratio can be directly measured from spectra with HFT, no model dependence, reduce systematic errors.  Expected errors are estimated for 50 M Au+Au central events (open circles) and 500 μb -1 sampled luminosity with a “high tower” trigger (filled circles). Open stars represent preliminary results from 200 GeV p+p collisions via e-h correlation.  (B  e)/NPE ratio can be directly measured from spectra with HFT, no model dependence, reduce systematic errors.  Expected errors are estimated for 50 M Au+Au central events (open circles) and 500 μb -1 sampled luminosity with a “high tower” trigger (filled circles). Open stars represent preliminary results from 200 GeV p+p collisions via e-h correlation.

May 11, 2015 Yifei Zhang LBNL 19 Electron R CP Nuclear modification factor R CP of electrons from D meson and B meson decays. Expected errors are estimated for 500 M Au+Au minimum-bias events (open symbols) and 500 μb -1 sampled luminosity with a “high tower” trigger (filled symbols). Curves: H. van Hees et al. Eur. Phys. J. C61, 799(2009).

May 11, 2015 Yifei Zhang LBNL 20 Measure v 2 from dca B  e v 2 and D  e v 2 can be measured from different dca cuts. For example: CaseCut (cm)e(D) eff. (%)e(B) eff. (%)r = e(B)/NPE I< II> r  v 2 (B) + (1-r)  v 2 (D) = v 2 (NPE) v 2 (B) is B  e v 2 v 2 (D) is D  e v 2 v 2 (NPE) is the total non-photonic electron v 2 after dca selection.

May 11, 2015 Yifei Zhang LBNL 21 Error estimate for electron v 2 Assuming D meson v 2 from quark coalescence (curves). Decay form factor [1] was used to generate D  e v 2 distributions. r  v 2 (B) + (1-r)  v 2 (D) = v 2 (NPE) v 2 (D) is D  e v 2 v 2 (B) is B  e v 2, which can be extracted from this equation. [1] H.D. Liu et. al, PLB 639, 441 (2006) Blue: c-quark flows // Red: c-quark does not Dashed-curves: Assumed D 0 -mesom v 2 (p T ) Symbols: D decay e v 2 (p T ) Vertical bars: errors for b decay e v 2 (p T ) from 200 GeV 500M minimum bias Au + Au events Cuts: DCA on decay electrons

May 11, 2015 Yifei Zhang LBNL 22 Charm and bottom cross section NLO pQCD predictions of charm and bottom total cross sections per nuclear nuclear collisions. Statistics estimated for charm cross section in p+p, Au+Au mb, Au+Au central at 200 and 500 GeV. Statistics estimated for bottom cross section in Au+Au mb and central at 200 GeV. Systematic errors are estimated from D 0  e p T shape uncertainties (open box). NLO pQCD predictions of charm and bottom total cross sections per nuclear nuclear collisions. Statistics estimated for charm cross section in p+p, Au+Au mb, Au+Au central at 200 and 500 GeV. Statistics estimated for bottom cross section in Au+Au mb and central at 200 GeV. Systematic errors are estimated from D 0  e p T shape uncertainties (open box).

Nu Xu23/25 Physics of the Heavy Flavor Tracker at STAR 1) The STAR HFT measurements (p+p and Au+Au) (1) Heavy-quark cross sections: D 0,±,*, D S,  C, B… (2) Both spectra (R AA, R CP ) and v 2 in a wide p T region. (3) Charm hadron correlation functions (4) Full spectrum of the heavy quark hadron decay electrons 2) Physics (1) Measure heavy-quark hadron v 2, heavy-quark collectivity, to study the medium properties e.g. light-quark thermalization (2) Measure heavy-quark energy loss to study pQCD in hot/dense medium. e.g. energy loss mechanism (3) Measure charm/bottom cross section to test pQCD in hot/dense medium. (4) Analyze hadro-chemistry including heavy flavors

Nu Xu24/25 Projected Run Plan 1) First run with HFT: 200 GeV Au+Au  v 2 and R CP with 500M M.B. collisions 2) Second run with HFT: 200 GeV p+p  R AA 3) Third run with HFT: 200 GeV Au+Au  Centrality dependence of v 2 and R AA  Charm background and first attempt for electron pair measurements   C baryon with sufficient statistics