1. Open charm production with ALICE at the LHC
Kai Schweda (for the ALICE Collaboration)
Physikalisches Institut
University of Heidelberg / GSI Darmstadt
Thanks to Directors of this school !
Erice, 34th Course
17 Sep 2012

2. Outline Introduction Heavy-quark production in pp
Heavy-quark production in Pb-Pb
Summary
17 Sep 2012
Erice, 34th Course

3. Time Scales QGP life time 10 fm/c ≈ 310-23 s
thermalization time 0.2 fm/c ≈ 710-25 s
formation time (e.g. charm quark): 1/2mc = 0.08 fm/c ≈ 310-25 s
collision time 2R/g = fm/c ≈ 210-26 s
Plot: courtesy of R. Stock.
17 Sep 2012
Erice, 34th Course

4. Heavy - flavor: a unique probe
mc,b » QCD : new scale
mc,b ≈ const., mu,d,s ≠ const.
initial conditions: test pQCD 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 Sep 2012
Erice, 34th Course

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 Sep 2012
Erice, 34th Course

6. Heavy-quark detection
Open-charm reco. in ALICE
D0  K
D+  K
D*  D0 Ds  KK
Under study:
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 Sep 2012
Erice, 34th Course

7. Open-charm spectra from pp @ 7 TeV
ALICE, JHEP 1201 (2012) 128; arXiv: [hep-ex]; D* analysis: Y. Wang, PhD thesis, Univ. Heidelberg, in preparation;
F. Schaefer, bachelor thesis, Univ. Heidelberg (2012).
covers spectrum from 1 up to 24 GeV/c
17 Sep 2012
Erice, 34th Course

8. Open-charm cross section
ALICE, arXiv: [hep-ex];
J. Wilkinson, bachelor thesis, Univ. Heidelberg (2011);
S. Stiefelmaier, bachelor thesis, Univ. Heidelberg (2012).
LHC: First collider measurements at TeV scale
ATLAS & LHCb agree with ALICE
experimental data sits in the upper theory band
17 Sep 2012
Erice, 34th Course

9. Charm hadronization
Pv: fraction of D-mesons in vector state (V) to all mesons (V+S), Pv = V / (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
ALICE, arXiv: [hep-ex];
J. Wilkinson, bachelor thesis, Univ. Heidelberg (2011);
S. Stiefelmaier, bachelor thesis, Univ. Heidelberg (2012).
17 Sep 2012
Erice, 34th Course

10. 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 Sep 2012
Erice, 34th Course

11. Charm: Nuclear Modification
In Pb-Pb collisions: Suppresion by factor ~5 when compared to simple binary scaling from pp
Covers 1 – 36 GeV/c
pp reference measured only up to 24 GeV/c + extrapolation
17 Sep 2012
Erice, 34th Course

12. Comparison to other hadrons
Mass ordering in RAA? J/ψ  B (upper) D (middle) π (lower)
g,W,Z-bosons: RAA ≈ 1 (!) checks normalization, does not probe the medium
ALICE, arXiv: [nucl-ex],
CMS Z-boson: Phys. Rev. Lett. 106 (2011)
17 Sep 2012
Erice, 34th Course

13. Model calculations Rising RAA solely due to spectrum in pp
Still have to learn from theory about medium properties, i.e. qhat, ehat
Not an initial state effect
Erice, 34th Course
17 Sep 2012

14. Anisotropy Parameter v2
coordinate-space-anisotropy  momentum-space-anisotropy y py x px
Initial/final conditions, EoS, degrees of freedom

15. 2nd Fourier Coefficient – v2
D-meson v2 analysis:
R. Grajcarek, PhD thesis, Univ. Heidelberg, in preparation.
Substantial v2 of charm, comparable to charged hadrons
17 Sep 2012
Erice, 34th Course

16. v2 - Model calculations
Models needs to simultaneously describe v2 and R AA
Stringent constraint, gets tougher with more precision/data
17 Sep 2012
Erice, 34th Course

17. Next steps Extract power spectrum of vn, like WMAP*
Compare pp high multiplicity vs Pb+Pb
Mach cone vs medium response for heavy-quarks (well defined probes)
h/s
*WMAP data: The NASA/WMAP Science team;
QGP plot: B. Schenke, S. Jeon, and C. Gale, arXiV:
17 Sep 2012
Erice, 34th Course

18. 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 Sep 2012
Erice, 34th Course

19. 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 Sep 2012
Erice, 34th Course

20. Upgrading the Inner Detector
upgrade Concept recently approved by the ALICE Collaboration
targeted for LHC shutdown
Conceptual Design Report CERN-LHCC
17 Sep 2012
Erice, 34th Course

21. LHC: Tentative Schedule
2010/11: long run with pp collisions at 7 TeV
1 month of Pb+Pb collisions each year
2012: long run with pp at 8 TeV
2012/13: p+Pb control measurement
2013/14: Machine consolidation and training
2014: pp and Pb+Pb at full energy
2017/18: long shutdown, luminosity + detector upgrades
2019: pp and Pb+Pb at high luminosity
17 Sep 2012
Erice, 34th Course