Transcript Document 7239081

Open heavy flavor at RHIC
Jaroslav Bielčík
Czech Technical
University
Prague
High-pT physics at LHC , March 2008, Tokaj
Outline
•
•
Motivation for heavy flavor physics
Spectra:
– Charm mesons: D0
– Non-photonic electrons
– Heavy flavor e+e- pairs
•
•
Flow/Energy loss
Summary
QM 2008: Y.Zhang (overview), A. Shabetai (STAR), D. Hornback(PHENIX)
R. Averbeck (PHENIX), Y. Morino (PHENIX)
[email protected]
2
Heavy quarks as a probe
• p+p data:
 baseline of heavy ion measurements
 test of pQCD calculations
parton
• Due to their large mass heavy quarks
hot and dense medium
ENERGY LOSS
are primarily produced by gluon fusion in
early stage of collision
 production rates calculable by pQCD
light
M. Gyulassy and Z. Lin, PRC 51, 2177 (1995)
• heavy ion data:
• Studying flow of heavy quarks
 understanding of thermalization
• Studying energy loss of heavy quarks
 independent way to extract properties
of the medium
M.Djordjevic PRL 94 (2004)
dead-cone effect:
[email protected]
3
Dokshitzer and Kharzeev, PLB 519, 199 (2001)
Open heavy flavor
Direct: reconstruction of all decay products
D 0  K   , D 0  K   ,
B.R.  3.80  0.07%
Indirect: charm and beauty via electrons
c  e+ + anything (B.R.: 9.6%)
b  e+ + anything (B.R.: 10.9%)
issue of photonic background
charm (and beauty) via muons
c  + + anything (B.R.: 9.5%)
[email protected]
4
Charm measurements at RHIC
STAR measurements:
PHENIX measurements:
 Signal/Spectra
 Signal/Spectra
D0  K
c   + X (y=0, low pT)
c,b  e + X
 Flow & energy loss
D0  K-+0
c   + X (<y>=1.65, pT>1 GeV/c)
c,b  e + X
e+e-
 Flow & energy loss
Elliptic flow from NPE
RAA from NPE
RAA from NPE
[email protected]
5
SPECTRA
[email protected]
6
Direct D-meson
reconstruction at STAR
D0
S / N ~ 4.7
Phys. Rev. Lett. 94 (2005)
STAR Preliminary
• K invariant mass distribution in d+Au, Au+Au minbias, Cu+Cu
minbias at 200 GeV collisions
• No displaced vertex used => only pT<3.3 GeV/c
[email protected]
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Direct D-meson reconstruction at
PHENIX
• p+p 200 GeV/c:
 D0K+ - 0 decay channel
0 identified via 0  gg decay
 Only visible signal in 5<pT<15 GeV/c
 No visible signal below 5 GeV/c and above 15 GeV/c
PHENIX Preliminary
Year5 pp 200 GeV
peak is not at right position
[email protected]
8
Leptons from HF decay at STAR
STAR Preliminary
• STAR charm cross section: combined fit of muons, D0 and low pT electrons
 90% of total kinematic range covered
• New Cu+Cu D0 spectrum agree with Au+Au after number of binary scaled
• Low pT muon constrains charm cross-section
[email protected]
9
Leptons from HF decay at PHENIX
PHENIX PRL, 98, 172301 (2007)
p+p 200GeV/c
PHENIX Preliminary
• Electron spectrum is harder than muon spectrum, within errors they are consistent
at intermediate pT
• Systematically higher than FONLL calculation (up to factor ~ 4)
• Integral e yield follows binary scaling, high pT strong suppression at central AuAu
collisions
[email protected]
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STAR high pT NP electrons
• High-tower EMC trigger
=> high pT electrons
• FONLL
scaled by ~5,
describes shape of p+p spectra well
suggesting bottom contribution
STAR
Phys. Rev. Lett. 98 (2007) 192301
[email protected]
STAR Phys. Rev. Lett. 98 (2007) 192301
PHENIX Phys. Rev. Lett. 97 (2006) 252002
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Heavy quarks in p+p from e+e- at
PHENIX
After subtraction of Cocktail -
Fit to a*charm+ b*bottom
(with PYTHIA shape)
Extracted cross sections
in good agreement with
single e result.
c dominant
arXiv:0802.0050
b dominant
[email protected]
12
Charm cross-section
PRL 94 (2005)
Total cross-section with large
theoretical uncertainty.
Both STAR and PHENIX are self-consistent
 observation of binary scaling
STAR results ~ 2 times larger than PHENIX
Consistent with NLO calculation
[email protected]
 however error bands are huge
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ENERGY LOSS/FLOW
[email protected]
14
Elliptic flow v2 – NPE from HF decays
PHENIX Run4
PRL, 98, 172301 (2007)
• Non-zero elliptic flow for electron from heavy flavor decays
→ indicates non-zero D v2, partonic level collective motion.
• Strongly interact with the dense medium at early stage of HI collisions
• Light flavor thermalization
[email protected]
15
RAA from d+Au to central Au+Au
STAR Phys. Rev. Lett. 98 (2007) 192301
PHENIX Phys.Rev.Lett.98 (2007) 172301
Nuclear modification factor
STAR hadrons pT> 6 GeV/c
1 dN AA / dpt
RAA ( pt ) 

N coll dN pp / dpt
Non-photonic electrons suppression
similar to hadrons
pT (NPE) < pT (D  NPE)
d+Au: no suppression expected
Peripheral
slight
Au+Au:
enhancement
Semi-Central
Au+Au:
Central
Au+Au:
no
expected
suppression
(Cronin
expected
effect) ?!
very
little
suppression
expected
little
suppression
expected
[email protected]
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Nuclear Modification Factor RAA
l very similar to light hadron RAA
l
PRL 98, 172301 (2007)
l
e± from heavy flavor
careful:
– decay kinematics!
– pT(e±) < pT(D)
intermediate pT
– indication for quark mass
hierarchy as expected for radiative
energy loss
(Dokshitzer and Kharzeev, PLB 519(2001)199)
l
highest pT
– RAA(e±) ~ RAA(0) ~ RAA(h)
l crucial to understand:
what is the bottom contribution?
l ideal:
RAA of identified charm and bottom hadrons
Radiative energy loss
STAR Phys. Rev. Lett. 98 (2007) 192301
PHENIX Phys.Rev.Lett.98 (2007) 172301
• parameters of medium in
models extracted from hadron data
• Radiative energy loss alone
in medium with reasonable
parameters does not describe
the data
• What are the other sources
of energy loss ?
Djordjevic, Phys. Lett. B632 81 (2006)
Armesto, Phys. Lett. B637 362 (2006)
[email protected]
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Role of collisional energy loss
STAR Phys. Rev. Lett. 98 (2007) 192301
PHENIX Phys.Rev.Lett.98 (2007) 172301
• Collisional/elastic energy loss may
be important for heavy quarks
• Still not good agreement at high-pT
Wicks, nucl-th/0512076
van Hess, Phys. Rev. C73 034913 (2006)
[email protected]
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Charm alone?
STAR Phys. Rev. Lett. 98 (2007) 192301
PHENIX Phys.Rev.Lett.98 (2007) 172301
• Since the suppression of
b quark electrons is smaller
– charm alone agrees better
• What is b contribution?
[email protected]
20
(be)/(ce+be)
Bottom contribution to NPE
• Difficult to interpret suppression without the knowledge of
charm/bottom
•
Data shows non-zero B contribution
• Good agreement among different analyses.
• Data consistent with FONLL.
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Conclusions
• Heavy flavor is an important tool to understand HI physics at RHIC
• RHIC results are interesting and challenging
charm cross section
• Binary scaling in charm production
• Differences between STAR and PHENIX
produced in initial phase
will be addressed
• NLO is consistent with data
large uncertainties
non-photonic electrons
• strong high-pT suppression in Au+Au
large energy loss of c+b
• heavy quark energy loss not understood
• b relative contribution consistent with FONLL
important b contribution
• none zero charm flow is observed at RHIC energy
does b also flow?
[email protected]
22
Estimating h/s
l transport models
l
Rapp & van Hees (PRC 71, 034907 (2005))
– diffusion coefficient required for simultaneous fit of
RAA and v2
– DHQx2T ~ 4-6
l
Moore & Teaney (PRC 71, 064904 (2005))
– difficulties to describe RAA and v2 simultaneously
– calculate perturbatively (and argue that plausible
also non-perturbatively)
– DHQ/ (h/(e+P)) ~ 6 (for Nf = 3)
PRL 98, 172301 (2007)
l at B = 0
l e + P = Ts
l then
l h/s = (1.3-2.0)/4
Comparison with other
estimates
R. Lacey et al.: PRL 98:092301, 2007
H.-J. Drescher et al.: arXiv:0704.3553
h / s  (1.1  0.2  1.2) / 4
S. Gavin and M. Abdel-Aziz:
PRL 97:162302, 2006
pTfluctuations STAR
v2 PHENIX
& STAR
l
v2 PHOBOS
h / s  (1.4  2.4) / 4
estimates of h/s based on
flow and fluctuation data
l
l
l
indicate small value as well
close to conjectured limit
significantly below h/s of helium (4h/s
~ 9)
conjectured quantum limit
h / s  (1.0  3.8) / 4
Charm ~ y
[email protected]
25
Uncertainty of c/b relative contribution
• FONLL:
Large uncertainty on c/b crossing
3 to 9 GeV/c
Beauty predicted to be
significant above 4-5 GeV/c
[email protected]
26
Muon measurement
TPC+TOF
• Low-pT (pT < 0.25 GeV/c)
muons can be measured
with TPC + ToF
0.17 < pT < 0.21 GeV/c
0-12% Au+Au


- this helps to constrain charm
cross-section
• Separate different muon
contributions using MC
simulations:
m2=(p/b/g)2
minv2 (GeV2/c4)
Inclusive 
 from charm
 from  / K (simu.)
Signal+bg. fit to data
- K and  decay
- charm decay
- DCA (distance of closest
approach) distribution is very
different
(STAR), Hard Probes 2006
[email protected]
27
Conversion from dN/dy to Cross-Section

NN
cc
 dN
Cu Cu
D0
/ dy 
pp
inel
Cu Cu
bin
/N
 f /R
dN D0 / dy  0.132  / - 0.025 (stat.)
pp
 inel
 42 mb
p+p inelastic cross section
number of binary collisions
Cu Cu
N binary
 51.52  1.04 - 2.87
f  4.7  0.7
ratio from e e collider data R  N
/ N cc  0.54  0.05
D0
conversion to full rapidity
+ -
   0.94  0.18( stat.) mb
sys. error from dN dy to  conversion  0.17  0.18 mb
NN
cc
*Systematic error measurement for dN/dy in progress.
[email protected]
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Electron ID in STAR – EMC
1. TPC: dE/dx for p > 1.5 GeV/c
•
Only primary tracks
(reduces effective radiation
length)
• Electrons can be discriminated
well from hadrons up to 8 GeV/c
• Allows to determine the remaining
hadron contamination after EMC
2. EMC:
a) Tower E ⇒ p/E~1 for eb) Shower Max Detector
• Hadrons/Electron shower
develop different shape
85-90% purity of electrons
(pT dependent)
[email protected]
K
p
d

electrons
all
p>1.5 GeV/c2
p/E
SMD
hadrons
electrons
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Photonic electrons background
 Background: Mainly from g conv and 0,h Dalitz
 Rejection strategy:
For every electron candidate
 Combinations with all TPC
electron candidates
 Me+e-<0.14 GeV/c2 flagged photonic
 Correct for primary electrons
misidentified as background
 Correct for background rejection efficiency
~50-60% for central Au+Au
Inclusive/Photonic:
Excess over photonic electrons observed
for all system and centralities
=> non-photonic signal
[email protected]
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CC: comparison with other
measurements
[email protected]
31
[email protected]
32
Combined Fit
D0, e ,  combined fit
Power-law function with parameters
dN/dy, <pT> and n to describe the D0
spectrum
Generate D0e decay kinematics
according to the above parameters
Vary (dN/dy, <pT>, n) to get the min.
2 by comparing power-law to D0
data and the decayed e shape to e
and  data
Spectra difference between e and  ~5%
(included into sys. error)
Advantage: D0 and  constrain low pT
e constrains higher pT