1. Open charm production in pp and Pb-Pb collisions in ALICE at the LHC
Kai Schweda (for the ALICE Collaboration)
Physikalisches Institut
University of Heidelberg / GSI Darmstadt
Hadrons in the Nuclear Medium, ECT*, Trento
17 May 2012

2. Open charm production in pp and Pb-Pb collisions in ALICE at the LHC
Kai Schweda (for the ALICE Collaboration)
Physikalisches Institut
University of Heidelberg / GSI Darmstadt
Hadrons in the Nuclear Medium, ECT*, Trento
17 May 2012

3. Hadrons in the Nuclear Medium, ECT*, Trento
Outline
Introduction
LHC and ALICE
Heavy-quark production in pp
Heavy-quark production in Pb-Pb
Summary
17 May 2012
Hadrons in the Nuclear Medium, ECT*, Trento

4. 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.
17 May 2012
Hadrons in the Nuclear Medium, ECT*, Trento

5. Where does all the charm go ?
J/(charmonium) 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
17 May 2012
Hadrons in the Nuclear Medium, ECT*, Trento

6. The Large Hadron Collider at CERN
Alice
collision system sNN (GeV) p+p 7000
p+p 2760
Pb + Pb 2760

7. Resolution: 600M pixels (750 Mbytes)
Size: 16 x 16 x 25 meters
Resolution: 600M pixels (750 Mbytes)
Readout: 17.5 terabytes/s, ~4 Gbytes/s to tape
TRD
ITS
TPC
Central barrel (ITS, TPC, TRD, TOF) || < 0.9
Muon spectrometer: -4.0 < y < -2.5 6

8. 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

9. Particle Identification – dE/dx
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
17 May 2012
Hadrons in the Nuclear Medium, ECT*, Trento

10. Heavy-quark detection
Open-charm reco. in ALICE
D0  K
D+  K
D*  D0
Under study:
Ds  KK
D0  K
c  pK
c  
c  K0S
plot: courtesy of D. Tlusty.
e.g., D0  K- +  , c = 123 m
displaced decay vertex is signature of heavy-quark decay
17 May 2012
Hadrons in the Nuclear Medium, ECT*, Trento

11. Open-charm spectra from pp @ 7 TeV
ALICE, JHEP 1201 (2012) 128; arXiv: [hep-ex].
covers spectrum from 1 up to 24 GeV/c
17 May 2012
Hadrons in the Nuclear Medium, ECT*, Trento

12. Hadrons in the Nuclear Medium, ECT*, Trento
Charm hadronization
ALICE, arXiv: [hep-ex].
Charm hadronization
Pv = fraction of D-mesons in vector state (V) to all mesons (V+S)
World average: Pv = 0.60 ± 0.01
Stat. model, T=164 ± 10 MeV: Pv = 0.58 ± 0.13, agrees with data
HQET predicts Pv = 3/(3+1) = 0.75
17 May 2012
Hadrons in the Nuclear Medium, ECT*, Trento

13. Charm hadronization, cont’ed
Pv independent on collision energy and system
Charm quark does not remember how it was created
In hindsight, justifies factorization Ansatz
Charm hadronization described by stat. model
N.B. Lund fragm. + Clebsch-Gordan coupling: Pv = 0.63
HQEFT (m=∞), mass differences negligible, NOT justified for charm but exp. checked for B mesons (Δm/m = 40 MeV/5000 GeV)
17 May 2012
Hadrons in the Nuclear Medium, ECT*, Trento

14. Hadrons in the Nuclear Medium, ECT*, Trento
Time scales
production of a pair of charm quarks at time scale tc = 1/2mc = 0.08 fm
hadronization at time scale thad = 1fm
This means the creation of charm quarks and their hadronization is decoupled
factorization Ansatz to describe charmed hadron production
17 May 2012
Hadrons in the Nuclear Medium, ECT*, Trento

15. Open-charm cross section
ALICE, arXiv: [hep-ex].
LHC: First collider measurements at TeV scale
ATLAS & LHCb agree with ALICE
upper band of theory describes experimental data
17 May 2012
Hadrons in the Nuclear Medium, ECT*, Trento

16. Nuclear Modification Factor - RAA
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 !
17 May 2012
Hadrons in the Nuclear Medium, ECT*, Trento

17. Charm nuclear modification factor
ALICE, arXiv: [nucl-ex].
In Pb-Pb collisions: Charmed hadrons are suppressed by factor ~5 when compared to simple binary scaling from pp
17 May 2012
Hadrons in the Nuclear Medium, ECT*, Trento

18. Comparison to other hadrons
ALICE, arXiv: [nucl-ex].
Mass ordering in RAA? J/ψ B (upper) D (middle) π (lower)
17 May 2012
Hadrons in the Nuclear Medium, ECT*, Trento

19. Hadrons in the Nuclear Medium, ECT*, Trento
Shadowing, …
ALICE, arXiv: [nucl-ex].
Initial state: gluon distribution in p different from Pb, e.g. shadowing, gluon saturation, … ?
Observed suppression not an initial state effect
need p-Pb data to check !
17 May 2012
Hadrons in the Nuclear Medium, ECT*, Trento

20. Hadrons in the Nuclear Medium, ECT*, Trento
Model calculations
D mesons charged hadrons
17 May 2012
Hadrons in the Nuclear Medium, ECT*, Trento

21. Heavy  quark Correlations
Charm and anti-charm quarks created in pairs and thus correlated
Look for modifications in Pb+Pb collisions
Study transport properties / thermalization
PYTHIA: p + 14 TeV
Heavy-quark production correlated due to QCD processes such as pair creation (backward), gluon splitting (forward), etc.
Expetced for pp
Modified in PbPb --> probe early thermalization
X. Zhu, M. Bleicher, S.L. Huang, K.S., H. Stöcker, N. Xu, and P. Zhuang, PLB 647 (2007) 366.
G. Tsildeakis, H. Appelshäuser, K.S., J. Stachel, NPA 858 (2011) 86; arXiv: [nucl-ex].
17 May 2012
Hadrons in the Nuclear Medium, ECT*, Trento

22. Heavy  quark Correlations*
CMS trigger: inspected 200 x 109 p+p collisions
BBbar, establish correlations exist in p+p !
Look out for modifications in Pb+Pb
Heavy-quark production correlated due to QCD processes such as pair creation (backward), gluon splitting (forward), etc.
Expetced for pp
Modified in PbPb --> probe early thermalization
*CMS collaboration:JHEP 1102 (2011) 136; arXiv: v2 [hep-ex].
17 May 2012
Hadrons in the Nuclear Medium, ECT*, Trento

23. Hadrons in the Nuclear Medium, ECT*, Trento
Summary & Outlook
ALICE has measured charmed hadron production pp and Pb-Pb collisions at LHC
charm hadronization described by statistical model
Suppression of D meson production in Pb-Pb when compared to binary NN-collision scaling from pp
Not an initial state effect
Nov-2011: high-luminosity Pb-Pb data run (15x)
end 2012: p-Pb control measurement
2013/14: machine consolidation
Then pp and Pb-Pb collisions at design energy !
17 May 2012
Hadrons in the Nuclear Medium, ECT*, Trento