0. Heavy-flavor production in pp and Pb-Pb collisions at LHC with ALICE
Kai Schweda (for the ALICE Collaboration)
Physikalisches Institut
University of Heidelberg
Hadron 2011, Munich
16 Jun 2011

1. Outline Introduction LHC and ALICE Heavy-quark production in pp
Heavy-quark production in Pb-Pb: D-mesons, e and 
Summary
16 Jun 2011
Hadron 2011, Munich

2. Heavy - flavor: a unique probe
mc,b » QCD : new scale
mc,b ≈ const., mu,d,s ≠ const.
initial conditions: test pQCD, R, F probe gluon distribution
early partonic stage: diffusion (), drag () flow, jets, correlations probe thermalization
hadronization: chiral symmetry restoration confinement statistical coalescence J/ enhancement / suppression Q2
time
X. Zhu, M. Bleicher, S.L. Huang, K.S., H. Stöcker, N. Xu, and P. Zhuang, PLB 647 (2007) 366.
16 Jun 2011
Hadron 2011, Munich

3. Where does all the charm go ?
J/(charmonium)
c.f. talk by F. Kramer,
17:30, Quarkonia 5. c
D*+ Ds D0 D±
Total charm cross section: open-charmed hadrons, e.g. D0, D+, D*+, c, … and c,b  e() + X
Quarkonia, e.g. J/ carries 1% of total charm
16 Jun 2011
Hadron 2011, Munich

4. Heavy-quark detection
plot: courtesy of A. Mischke.
Open-charm reco. in ALICE
D0  K
D+  K
D*  D0
Under study:
Ds  KK
D0  K
c  pK
c  
c  K0S
e.g., D0  K- +  , c = 123 m
displaced decay vertex is signature of heavy-quark decay
16 Jun 2011
Hadron 2011, Munich

5. Large Hadron Collider LHC at CERN Alice
collision system sNN (TeV) #Events analyzed (M)
p+p
p+p
Pb + Pb

6. Central barrel (ITS, TPC, TRD, TOF) || < 0.9
Size: 16 x 26 meters
Weight: 10,000 tons
Detectors: 18
TRD
ITS
TPC
Central barrel (ITS, TPC, TRD, TOF) || < 0.9
Muon spectrometer: -4.0 < y < -2.5 6

7. First Pb+Pb collisions in ALICE !
ALICE is designed for
Highest multiplicities dN/d up to 6000
Excellent tracking & particle identification down to lowest momentum ~ 100 MeV/c

8. Particle Identification
dE/dx: 5% resolution
Time-of flight, resolution: 120 ps (Pb-Pb) 160 ps (p-p)
TPC dE/dx: separate p from K up to 1.1 GeV
Time of flight: separate K from up to ~ 1.5 GeV
16 Jun 2011
Hadron 2011, Munich

9. Silicon Pixel Alignment
6 silicon layers
2 most inner: pixel layers (at r = 3.9 and 7 cm)
Alignment from cosmics and collisions current resolution: 14 m (design 11 m)
No deterioration from pp to Pb-Pb multiplicities
16 Jun 2011
Hadron 2011, Munich 9

10. Open-charm spectra from pp @ 7 TeV
FONLL: M. Cacciari et al., priv. commun.; GM-VFNS:: B. Kniehl, priv. commun.
1/4 of total statistics, from 2 up to 12 GeV/c; extend to <2 GeV/c and >20 GeV/c with present data on tape
16 Jun 2011
Hadron 2011, Munich

11. Open-charm cross section
LHC: First collider measurements at TeV scale
ATLAS & LHCb agree with ALICE
upper band of theory describes experimental data
16 Jun 2011
Hadron 2011, Munich

12. Heavy-flavor electrons from pp
Electron background: cocktail based on measured  spectra + mt scaling
+ pQCD prompt phot.
Hadron contamination < 10%
Extract electrons from semi-leptonics decays c,b  e + X
FONLL predictions agree with data
16 Jun 2011
Hadron 2011, Munich

13. Disentangele beauty from charm
b-quark has longer lifetime than c-quark
Larger displacement from collision vertex
Disentangle electrons from semi-leptonics decays c,b  e + X
FONLL predictions agree with data
16 Jun 2011
Hadron 2011, Munich

14. Muons from heavy-flavor in pp
Measured d/dp from 2-10 GeV/c, d/d in -4.0 <  < 2.5
FONLL predictions describe data well
FONLL indicates dominance of beauty at pt > 6 GeV/c
16 Jun 2011
Hadron 2011, Munich

15. Fast parton probing the medium
J.D. Bjorken, PRD 27 (1983) 140;
Graphics: courtesy of T. Ullrich.
Leading
Hadron
quark-gluon plasma
quarks and gluons propagate in QCD medium
interactions with the medium modify parton momentum
characteristic of medium properties
mass ordering predicted: E() > E(D) > E(B)
Dokshitzer and Kharzeev, PLB 519 (2001) 199.
16 Jun 2011
Hadron 2011, Munich

16. Nuclear Modification Factor
K. Aamodt et al. (ALICE coll.), Phys. Lett. B 696 (2011) 30.
define RAA, expect unity in the absence of nuclear effects (for hard processes)
<TAA> accounts for the number of binary nucleon-nucleon collisions
at RHIC, suppression of factor ~5
at LHC, suppression of factor ~6
strong medium effects !
16 Jun 2011
Hadron 2011, Munich

17. Invariant mass spectra in Pb-Pb at highest-multiplicities
16 Jun 2011
Hadron 2011, Munich

18. pp reference at 2.76 TeV
most pp data taken at 7 TeV, Pb-Pb at 2.76 TeV
Scaled pp data to 2.76 TeV using FONLL 2.76/7 factor, propagated full theoretical uncertainty
Relative scaling uncertainty: 25% GeV/c) to 10% 10 GeV/c)
Checked against short pp 2.76 TeV run (3 days)
16 Jun 2011
Hadron 2011, Munich

19. QCD-medium modification
In Pb-Pb collisions: Charmed hadrons are suppressed by factor ~5 when compared to simple scaling from pp
16 Jun 2011
Hadron 2011, Munich

20. Comparison to light-quark hadrons
Charm suppression as strong (or a bit less ?) than 
High-luminosity Pb-Pb run 2011 will give decisive answer
16 Jun 2011
Hadron 2011, Munich

21. QCD-medium modification
Initial state: gluon distribution in p different from Pb, e.g. shadowing, gluon saturation, … ?
Observed suppression not an initial state effect; need p-Pb !
16 Jun 2011
Hadron 2011, Munich

22. QCD-medium modification
Electron background: cocktail based on measured  spectra + mt scaling
+ pQCD prompt phot.
Hadron contamination < 10%
Extract electrons from semi-leptonics decays c,b  e + X
16 Jun 2011
Hadron 2011, Munich

23. QCD-medium modification
Electrons from semi-leptonic decays of heavy-quarks suppressed by factor ~
Also  at larger rapidity suppressed by a factor of 3 (FONLL: dominated by b-decays)
16 Jun 2011
Hadron 2011, Munich

24. Model calculations most predictions are for design energy (5.5 TeV)
Radiative E, similar suppr. for D and 
Rad. + coll. E, fair description
Light-cone wave function approach, somewhat high for D, ok for 
Need high-luminosity Pb-Pb data, end of 2011 !
16 Jun 2011
Hadron 2011, Munich

25. Summary & Outlook
and 7 TeV, heavy-quark production addressed by means of D-mesons, e, 
2.76, heavy quarks are suppressed up to a factor of 5
Not an initial state effect
Nov-2011: high-luminosity Pb-Pb data run
end 2012: (probably) p-Pb control measurement or early  Characterize QGP by precise heavy-quark production measurements
16 Jun 2011
Hadron 2011, Munich

26. Charm production and decay
16 Jun 2011
Hadron 2011, Munich