jaroslav bielčík czech technical university prague high-p t physics at lhc, march 2008, tokaj open...
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Jaroslav BielčíkCzech Technical
University
Prague
High-pT physics at LHC , March 2008, Tokaj
Open heavy flavor at RHIC
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)
Heavy quarks as a probe• p+p data: baseline of heavy ion measurements test of pQCD calculations
• Due to their large mass heavy quarks are primarily produced by gluon fusion in early stage of collision production rates calculable by pQCDM. 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
parton
hot and dense medium
light
M.Djordjevic PRL 94 (2004)
ENERGY LOSS
dead-cone effect:
Dokshitzer and Kharzeev, PLB 519, 199 (2001)
Open heavy flavor
%07.080.3..
,, 00
RB
KDKD Direct: reconstruction of all decay products
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 muonsc + + anything (B.R.: 9.5%)
5
Charm measurements at RHIC
STAR measurements:
Signal/Spectra
D0 K c + X (y=0, low pT) c,b e + X
Flow & energy loss
RAA from NPE
PHENIX measurements:
Signal/Spectra
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
7
STAR Preliminary
Direct D-meson reconstruction at STAR
D0
Phys. Rev. Lett. 94 (2005)
• 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
7.4~/ NS
8
PHENIX Preliminary
Year5 pp 200 GeV
Direct D-meson reconstruction at PHENIX
• p+p 200 GeV/c: D0K+ - 0 decay channel0 identified via 0 decay Only visible signal in 5<pT<15 GeV/c No visible signal below 5 GeV/c and above 15 GeV/c
peak is not at right [email protected]
9
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 [email protected]
10
Leptons from HF decay at PHENIX
PHENIX Preliminary
PHENIX PRL, 98, 172301 (2007)
• 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
p+p 200GeV/c
11
• High-tower EMC trigger => high pT electrons
• FONLL scaled by ~5, describes shape of p+p spectra well suggesting bottom contribution
STAR high pT NP electrons
STAR
Phys. Rev. Lett. 98 (2007) 192301 STAR Phys. Rev. Lett. 98 (2007) 192301 PHENIX Phys. Rev. Lett. 97 (2006) 252002
12
Heavy quarks in p+p from e+e- at PHENIX
c dominant
b dominant
After subtraction of Cocktail -Fit to a*charm+ b*bottom (with PYTHIA shape)
Extracted cross sections in good agreement with single e result.arXiv:0802.0050
Charm cross-section
PRL 94 (2005)
Both STAR and PHENIX are self-consistent
observation of binary scaling
STAR results ~ 2 times larger than PHENIX
Consistent with NLO calculation
however error bands are huge
Total cross-section with large theoretical uncertainty.
15
Elliptic flow v2 – NPE from HF decays
• 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
PHENIX Run4
PRL, 98, 172301 (2007)
d+Au: no suppression expected slight enhancement
expected (Cronin effect) Peripheral Au+Au:
no suppression expected Semi-Central Au+Au: very little suppression expected
RAA from d+Au to central Au+Au
STAR hadrons pT> 6 GeV/c
Central Au+Au: little suppression expected ?!
tpp
tAA
colltAA dpdN
dpdN
NpR
/
/1)(
Nuclear modification factor
STAR Phys. Rev. Lett. 98 (2007) 192301 PHENIX Phys.Rev.Lett.98 (2007) 172301
Non-photonic electrons suppressionsimilar to hadrons
pT (NPE) < pT (D NPE)
PRL 98, 172301 (2007)
e± from heavy flavor
Nuclear Modification Factor RAA
very similar to light hadron RAAcareful:
– 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)highest pT
– RAA(e±) ~ RAA(0) ~ RAA()
crucial to understand:
what is the bottom contribution? ideal:
RAA of identified charm and bottom hadrons
Radiative energy loss
• Radiative energy loss alone in medium with reasonable parameters does not describe the data
Djordjevic, Phys. Lett. B632 81 (2006)
Armesto, Phys. Lett. B637 362 (2006)
• What are the other sources of energy loss ?
• parameters of medium in models extracted from hadron data
STAR Phys. Rev. Lett. 98 (2007) 192301 PHENIX Phys.Rev.Lett.98 (2007) 172301
Role of collisional energy loss
Wicks, nucl-th/0512076van Hess, Phys. Rev. C73 034913 (2006)
• Collisional/elastic energy loss may be important for heavy quarks
• Still not good agreement at high-pT
STAR Phys. Rev. Lett. 98 (2007) 192301 PHENIX Phys.Rev.Lett.98 (2007) 172301
Charm alone?
• Since the suppression of b quark electrons is smaller – charm alone agrees better
• What is b contribution?
STAR Phys. Rev. Lett. 98 (2007) 192301 PHENIX Phys.Rev.Lett.98 (2007) 172301
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Bottom contribution to NPE
• Good agreement among different analyses. • Data consistent with FONLL.
(b
e)/(
ce+
b
e)
• Difficult to interpret suppression without the knowledge of charm/bottom
• Data shows non-zero B contribution
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 produced in initial phase• Differences between STAR and PHENIX will be addressed • NLO is consistent with data
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?
large uncertainties
PRL 98, 172301 (2007)
at B = 0 + P = Ts
then /s = (1.3-2.0)/4
transport modelsRapp & van Hees (PRC 71, 034907 (2005))
– diffusion coefficient required for simultaneous fit of RAA and v2
– DHQx2T ~ 4-6
Estimating /s
Moore & Teaney (PRC 71, 064904 (2005))
– difficulties to describe RAA and v2 simultaneously– calculate perturbatively (and argue that plausible
also non-perturbatively)
– DHQ/ (/(+P)) ~ 6 (for Nf = 3)
4/)8.30.1(/ s
S. Gavin and M. Abdel-Aziz: PRL 97:162302, 2006
pTfluctuations STAR
Comparison with other estimates 4/)2.12.01.1(/ s
R. Lacey et al.: PRL 98:092301, 2007
v2 PHENIX & STAR
4/)4.24.1(/ s
H.-J. Drescher et al.: arXiv:0704.3553
v2 PHOBOS
conjectured quantum limit
estimates of /s based on flow and fluctuation data
indicate small value as well close to conjectured limit significantly below /s of helium (s
~ 9)
Uncertainty of c/b relative contributionUncertainty 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
• Low-pT (pT < 0.25 GeV/c) muons can be measured with TPC + ToF
- this helps to constrain charm cross-section
• Separate different muon contributions using MC simulations:
- K and decay
- charm decay
- DCA (distance of closest approach) distribution is very different
minv2 (GeV2/c4)
0.17 < pT < 0.21 GeV/c
0-12% Au+Au
Muon measurementT
PC
+T
OF
Inclusive from charm from / K (simu.)Signal+bg. fit to data
(STAR), Hard Probes 2006
m2=(p//)2
Conversion from dN/dy to Cross-Section
mbstat
NNR
f
N
mb
dydN
NNcc
ccD
CuCubinary
ppinel
D
.)(18.094.0
05.054.0/
7.07.4
2.87-1.0451.52
42
(stat.) 0.025 -/ 0.132/
0
0
RfNdydN CuCubin
ppinel
CuCu
D
NNcc ///0
p+p inelastic cross section
conversion to full rapidity
ratio from e+e- collider data
number of binary collisions
mb 18.017.0 conversion dy todN fromerror sys. *Systematic error measurement for dN/dy in progress.
hadrons electrons
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 e-
b) Shower Max Detector • Hadrons/Electron
shower develop different shape
85-90% purity of electrons
(pT dependent)
electrons
K p d
all
p>1.5 GeV/c2
p/ESMD
Electron ID in STAR – EMC
Photonic electrons background Background: Mainly from conv and 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
Power-law function with parameters dN/dy, <pT> and n to describe the D0 spectrum
D0, e , combined fit
Generate D0e 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
Advantage: D0 and constrain low pT
e constrains higher pT
Spectra difference between e and ~5% (included into sys. error)
Combined Fit