Heavy Flavor Physics in HIC with STAR Heavy Flavor Tracker Yifei Zhang (for the STAR HFT Group) Hirschegg 2010, Austria Outline: Physics motivation

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 RHICSTAR: 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 RAA(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 RAA(c,b) measurements are needed!

April 18, 2023 Yifei Zhang LBNL 2April 18, 2023 2


Heavy quark energy loss

The RAA of single electron from heavy flavor decay is suppressed as strong as that of light flavor hadrons at high pT (> 6 GeV/c).

1.Directly measure D-meson RAA

2.Separately measure RAA of De & Be Heavy quark energy loss mechanism, interactions with hot dense medium.

The RAA of single electron from heavy flavor decay is suppressed as strong as that of light flavor hadrons at high pT (> 6 GeV/c).

1.Directly measure D-meson RAA

2.Separately measure RAA of De & Be Heavy quark energy loss mechanism, interactions with hot dense medium.

STAR PRL 98 (2007) 192301

E-loss: b < c < q

Partonic collectivity at RHIC

STAR: QM2009

STAR: preliminary


Low pT (≤ 2 GeV/c): hydrodynamic mass orderingHigh pT (> 2 GeV/c): number of quarks ordering s-quark hadron: smaller interaction strength in hadronic medium light- and s-quark hadrons: similar v2 pattern

Collectivity developed at partonic stage!

In order to test early thermalization: v2(pT) of c- and b-hadrons data are needed!

April 18, 2023 Yifei Zhang LBNL 5

Charmed baryon c

c yield (rare 10%, small c ~ 60m, 3-body decay).

measure c/ D0 ratio enhancement, di-quark?

Lee, et. al, PRL 100 (2008) 222301


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 Be spectrum will indirectly measure B meson spectrum from its decay kinematics.

Be = NPE De

STAR HFT has the capability to measure D0 decay vertex topologically via hadronic decay channel. Measured D0 spectrum constrains De.


STAR Detector

TOF+TPC+HFT

Large acceptance

Mid-rapidity

|| < 1

Full barrel coverage

0 < < 2

PXL


Inner Tracking Detectors

TPC Volume

Outer Field Cage

Inner Field Cage SSDISTPXL

FGT

HFT


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

DetectorRadius

(cm)

Hit Resolution

R/ - Z (m - m)Radiation

length

SSD 23 30 / 857 1% X0

IST 14 170 / 1700 1.32 %X0

PIXEL8 8.6 / 8.6 ~0.32 %X0

2.5 8.6 / 8.6 ~0.32% X0


Simulation Performance

pointing resolution in r- to primary vertex for single particles (of K, +, p.) including all hits in HFT.< 20 m at high pT.

pointing resolution in r- to primary vertex for single particles (of K, +, p.) including all hits in HFT.< 20 m at high pT.

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.


Hadronic channels

STAR HFT has the capability to reconstruct the displaced vertex of

D0K (B.R.=3.8%) and

c Kp (B.R.=5.0%, c c=59.9 m)

D0

C


D0 reconstruction

- Central Au+Au collisions: top 10% events. - The thin detector allows measurements down to pT ~ 0.5 GeV/c.

After topological cut


Error estimate of D0 Rcp

Assuming D0 Rcp distribution as charged hadron: directly measure charm quark energy loss.

500M Au+Au m.b. events at 200 GeV.

- Charm RAA energy loss mechanism!

Assuming D0 Rcp distribution as charged hadron: directly measure charm quark energy loss.


- Charm RAA energy loss mechanism!

RCP=a*N10%/N(60-80)%


Error estimate of D0 v2

Assuming D0 v2 distribution from quark coalescence.


Charm-quark flow Thermalization of light-quarks!

Charm-quark does not flow Drag coefficients


c reconstruction

Good D0 pT distribution measurement as reference.

The unique charmed baryon.

c / D0 ratio => enhancement?

Good D0 pT distribution measurement as reference.

The unique charmed baryon.

c / D0 ratio => enhancement?


B capability -- electron channels

particle c (m) Mass (GeV)

qc,b →x (F.R.)

x →e (B.R.)

D0 123 1.865 0.54 0.0671

D± 312 1.869 0.21 0.172

B0 459 5.279 0.40 0.104

B 491 5.279 0.40 0.109

1) Be = NPE De

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 RatioF.R. = Fragmentation Ratio

Pixel layers

dca


Dca distributions and spectra

Electrons: nFitPts > 15, -1 < eta < 1, 2 PXL hits required, in several pT bins.

The photon converted electron outside of pixel detector (~ 70%) can be removeddue 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 pT bins.

The photon converted electron outside of pixel detector (~ 70%) can be removeddue 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.


(Be)/NPE ratio

(Be)/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.

(Be)/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.


Electron RCP

Nuclear modification factor RCP 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).

Nuclear modification factor RCP 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).


Measure v2 from dca

B e v2 and D e v2 can be measured from different dca cuts. For example:

Case Cut (cm) e(D) eff. (%) e(B) eff. (%) r = e(B)/NPE

I < 0.005 45.5 22.3 0.325

II > 0.02 15.3 39.6 0.718

r v2(B) + (1-r) v2(D) = v2(NPE)

v2(B) is B e v2

v2(D) is D e v2

v2(NPE) is the total non-photonic electron v2 after dca selection.


Error estimate for electron v2

Assuming D meson v2 from quark coalescence (curves).

Decay form factor[1] was used to generate D e v2 distributions.

r v2(B) + (1-r) v2(D) = v2(NPE)v2(D) is D e v2

v2(B) is B e v2 , 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 D0-mesom v2(pT)

Symbols: D decay e v2(pT)

Vertical bars: errors for b decay e v2(pT) from 200 GeV 500M minimum bias Au + Au events

Cuts: DCA on decay electrons


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 D0 e pT 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 D0 e pT shape uncertainties (open box).

Nu Xu 23/25

Physics of the Heavy Flavor Tracker

at STAR

1) The STAR HFT measurements (p+p and Au+Au) (1) Heavy-quark cross sections: D0,±,*, DS, C , B…

(2) Both spectra (RAA, RCP) and v2 in a wide pT region.

(3) Charm hadron correlation functions

(4) Full spectrum of the heavy quark hadron decay electrons

2) Physics (1) Measure heavy-quark hadron v2, 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 Xu 24/25

Projected Run Plan1) First run with HFT: 200 GeV Au+Au

v2 and RCP with 500M M.B. collisions

2) Second run with HFT: 200 GeV p+p

RAA

3) Third run with HFT: 200 GeV Au+Au

Centrality dependence of v2 and RAA

Charm background and first attempt for

electron pair measurements

C baryon with sufficient statistics

Documents

Heavy Flavor Physics in HIC with STAR Heavy Flavor Tracker Yifei Zhang (for the STAR HFT Group) Hirschegg 2010, Austria Outline: Physics motivation