Transcript Monte Calor Study of Hard and Soft Interactions报告人：张一飞

Heavy Flavor Physics in HIC with STAR
Heavy Flavor Tracker
Yifei Zhang (for the STAR HFT Group)
Lawrence Berkeley National Lab
Outline:
 Physics motivation
 Charmed hadron
 D&B  e
 Summary
Hirschegg 2010, Austria
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
RAA(c,b) measurements are needed!
July 17, 2015
Yifei Zhang LBNL
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Heavy quark energy loss
STAR PRL 98
(2007) 192301
E-loss: b < c < q
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.
2.
Directly measure D-meson RAA
Separately measure RAA of De & Be
Heavy quark energy loss mechanism, interactions with hot dense medium.
July 17, 2015
Yifei Zhang LBNL
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Partonic collectivity at RHIC
STAR: preliminary
STAR: QM2009
Low pT (≤ 2 GeV/c): hydrodynamic mass ordering
High 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!
Yifei Zhang
LBNL
July 17, 2015
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Charmed baryon c
Lee, et. al, PRL 100 (2008) 222301
 c yield (rare 10%, small c ~ 60m, 3-body decay).
 measure c/ D0 ratio enhancement, di-quark?
July 17, 2015
Yifei Zhang LBNL
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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.
July 17, 2015
 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 D0
decay vertex topologically via hadronic decay
channel.
Measured
D0 spectrum constrains De.
Yifei Zhang
LBNL
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STAR Detector
TOF+TPC+
HFT
Large
acceptance
Mid-rapidity
|| < 1
Full barrel
coverage
0 <  < 2p
PXL
July 17, 2015
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Inner Tracking Detectors
HFT
SSD
IST
PXL
Inner Field Cage
Outer Field Cage
TPC
Volume
July 17, 2015
Yifei Zhang LBNL
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Inner Tracking Detectors
Detector
Radius Hit Resolution
(cm) R/ - Z (m - m)
Radiation
length
SSD
23
30 / 857
1% X0
IST
14
170 / 1700
1.32 %X0
8
8.6 / 8.6
~0.32 %X0
2.5
8.6 / 8.6
~0.32% X0
PIXEL
 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
July 17, 2015
Yifei Zhang LBNL
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Simulation Performance
pointing resolution in r- to primary
vertex for single particles (of K, p+, p.)
including all hits in HFT.
< 20 m at high pT.
July 17, 2015
Tracking efficiency of single p+
for 3 pileup hits densities.
1xRICHII pile up effect was
included in the simulation.
Yifei Zhang LBNL
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Hadronic channels
D0
C
STAR HFT has the capability to
reconstruct the displaced vertex of
D0Kp (B.R.=3.8%) and
c pKp (B.R.=5.0%, c c=59.9 m)
July 17, 2015
Yifei Zhang LBNL
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D0 reconstruction
After topological cut
- Central Au+Au collisions: top 10% events.
- The thin detector allows measurements down to pT ~ 0.5 GeV/c.
July 17, 2015
Yifei Zhang LBNL
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Error estimate of D0 Rcp
RCP=a*N10%/N(60-80)%
Assuming D0 Rcp distribution as charged hadron: directly measure charm
quark energy loss.
500M Au+Au m.b. events at 200 GeV.
- Charm RAA
July 17, 2015
energy loss mechanism!
Yifei Zhang LBNL
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Error estimate of D0 v2
Charm-quark flow
Thermalization
of light-quarks!
Charm-quark does
not flow
Drag coefficients
Assuming D0 v2 distribution from quark coalescence.
500M Au+Au m.b. events at 200 GeV.
July 17, 2015
Yifei Zhang LBNL
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c reconstruction
Good D0 pT distribution
measurement as reference.
The unique charmed baryon.
c / D0 ratio => enhancement?
July 17, 2015
Yifei Zhang LBNL
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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
Pixel layers
B.R. =
Branching Ratio
F.R. =
Fragmentation Ratio
1) 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
July 17, 2015
Dca of D+  e is more close to that
of B  e. need more constraint.
Yifei Zhang LBNL
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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 removed
due to their random large DCA distributions. The main background are conversion from
beam pipe and electron from p0, Dalitz decays.
Normalized by the F.R. and B.R., and total electron yield was normalized to STAR
measured NPE spectrum.
July 17, 2015
Yifei Zhang LBNL
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(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.
July 17, 2015
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Electron RCP
Curves:
H. van Hees et al.
Eur. Phys. J. C61, 799(2009).
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).
July 17, 2015
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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.
July 17, 2015
Yifei Zhang LBNL
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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.
Blue: c-quark flows // Red: c-quark does not
Dashed-curves: Assumed D0-mesom v2(pT)
Symbols: D decay e v2(pT)
[1] H.D. Liu et. al, PLB 639, 441 (2006)
Vertical bars: errors for b decay e v2(pT) from
200 GeV 500M minimum bias Au + Au events
Cuts: DCA on decay electrons
July 17, 2015
Yifei Zhang LBNL
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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).
July 17, 2015
Yifei Zhang LBNL
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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
23/25
Projected Run Plan
1) 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
Nu Xu
24/25