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

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

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

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

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

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

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

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

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

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

Open-charm spectra from pp @ 7 TeV ALICE, JHEP 1201 (2012) 128; arXiv:1111.1553 [hep-ex]. covers spectrum from 1 up to 24 GeV/c 17 May 2012 Hadrons in the Nuclear Medium, ECT*, Trento

Hadrons in the Nuclear Medium, ECT*, Trento Charm hadronization ALICE, arXiv:1205.4007 [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

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

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

Open-charm cross section ALICE, arXiv:1205.4007 [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

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

Charm nuclear modification factor ALICE, arXiv:1203.2160 [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

Comparison to other hadrons ALICE, arXiv:1203.2160 [nucl-ex]. Mass ordering in RAA? J/ψ B (upper) D (middle) π (lower) 17 May 2012 Hadrons in the Nuclear Medium, ECT*, Trento

Hadrons in the Nuclear Medium, ECT*, Trento Shadowing, … ALICE, arXiv:1203.2160 [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

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

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 + 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: 0908.0427 [nucl-ex]. 17 May 2012 Hadrons in the Nuclear Medium, ECT*, Trento

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:1192.3194v2 [hep-ex]. 17 May 2012 Hadrons in the Nuclear Medium, ECT*, Trento

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