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Quarkonia and h eavy flavor: where do we stand ? What next?

Quarkonia and h eavy flavor: where do we stand ? What next?. E. Scomparin (INFN-Torino). Sensitive to the temperature of QGP. Quarkonia. Probe the opacity of QGP. Open heavy quarks. Heavy quark energy loss…. Fundamental test of our understanding

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Quarkonia and h eavy flavor: where do we stand ? What next?

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  1. Quarkonia and heavy flavor:where do we stand ? What next? E. Scomparin (INFN-Torino) Sensitive to the temperature of QGP Quarkonia Probe the opacity of QGP Open heavy quarks

  2. Heavy quark energy loss… • Fundamental test of our understanding • of the energy loss mechanism, since • E depends on • Properties of the medium • Path length • …but should also critically depend on the properties of the parton • Casimir factor (CRg =3 , CRq =4/3) • Quark mass (dead cone effect) Equark< Egluon Eb< Ec < Elight q which should imply RAAB> RAA D> RAA  with S. Wicks, M. Gyulassy, JPG35 (2008) 054001

  3. y z x … and elliptic flow • Due to their large mass, c and b quarks should take longer time (= more re-scatterings) to be influenced by the collective expansion of the medium  v2(b) < v2(c) • Uniqueness of heavy quarks: cannot be destroyed and/or created in the medium  Transported through the full system evolution • Low/intermediatepT: collective motion, thermalization • HighpT: path-length dependence of heavy-quark energy loss J. Uphoff et al., PLB 717 (2012), 430 Reaction plane Pb Pb LHC: unprecedented abundance of heavy quarks Opportunity for a deeper understanding of the underlying physics

  4. Pb-Pb and p-Pb: results on D-mesons B. Abelev et al. (ALICE), arXiv:1405.3452 • D0, D+and D*+RAAagree • within uncertainties • Comparison with corresponding • results for p-Pb collisions • Strong suppression of prompt D mesons in central collisions •  up to a factor of 5 for • pT≈10 GeV/c Effect observed in central Pb-Pb due to strong final state effects induced by hot partonic matter

  5. Charm(ed) and strange: DS RAA • First measurement of Ds+in AA collisions • Expectation: enhancement of the • strange/non-strange D meson yield at • intermediate pTif charm hadronizes via • recombinationin the medium • Strong Ds+ suppression (similar as • D0, D+ and D*+) for 8<pT<12 GeV/c • More statistics needed to conclude • about the low-pT region

  6. Pb-Pb and pPb: results on B,D muons Forward rapidity: 2.5<y<4 B. Abelev et al. (ALICE), PRL109 (2012) 112301 • Larger suppression (factor 3-4) in the • 10% most central collisions with • respect to 40-80% centrality class • Suppression in the 10% most • central Pb-Pb collisions due to • ahot matter effect • No separation of B/D decays

  7. Pb-Pb and pPb: results on B,D electrons Central rapidity: |y|<0.6 • Results available up to pT=18 GeV/cfor central events (EMCAL) • Clear suppression for central collisions in the studied pT range • Stronger suppression for central collisions (hint) • RpPbcompatible with unity within uncertainties  Pb-Pb suppression due • to final state effects • Noseparation D vs B

  8. First Be measurement in Pb-Pb • Analysis based on the study of the • electron impact parameter distribution • Indicates RAA<1 for pT>3 GeV/c • RpPb (be) compatible with unity: • b-quark affected by the interaction • with the hot medium

  9. Comparison D vs /h • Test the mass ordering of energy loss • E(q,g)>E(c) ?  Not evident, but…. • Different quark spectrum • Ds enhancement may bring down D • Fragmentation effect M.Djordjevic, PRL112, 042302 (2014)

  10. Charm vs beauty • Comparing direct D results • with non-prompt J/ • Similar kinematic range • (pT~10 GeV/c) • In agreement with • expectations • RAA(B)>RAA(D) • Comparison withmodels •  mass-related effect R. Aaij et al.(LHCb), JHEP 02(2014) 072 • p-Pb results on b •  small or no effect at backward • and forward y • What about mid-y ?

  11. Direct B in p-Pb (mid-y) B+ J/ψ K+ B0 J/ψ K* BS J/ψ φ pT>10 GeV/c • Use FONLL for pp reference cross section • RpAFONLLis compatible with unity for all three B-mesons

  12. RpPb& RAA for jets and b jets CMS preliminary pPb pPb Central PbPb Central PbPb S. Chatrchyan et al. (CMS), arXiv:1312.4198 • Discriminating variable  Flight distance of the secondary vertex • b-jet fraction  template fits to secondary vertex inv. mass distributions • b-jetR AAismuch smaller than R pPb strong in-medium effects • No jet modification in p-Pb collisions • No flavour dependence of the effect

  13. D-meson and HFE/HFM v2 • Firstmeasurements of charm anisotropy in heavy-ion collisions B. Abelev et al. (ALICE), arXiv:1405.2001 • Similar amount of v2for D-mesons and charged pions • Similar v2values for HF decay muons and HF decay electrons (different y) • All channels show positive v2(>3  effect) Information on the initial azimuthal anisotropy transferred to charm quarks

  14. Open charm: model comparisons • Simultaneous measurement/description of v2 and RAA •  Understanding heavy quark transport coefficient of the medium B. Abelev et al. (ALICE), arXiv:1405.2001 • Wealth of theory calculations • Main features correctly reproduced • Simultaneous comparison with v2 and RAA gives strong constraint • to the models  still challenging!

  15. Open charm/beauty: short summary • Abundant heavy flavour production at the LHC • Allows for precision measurements • Can separate charm and beauty (vertex detectors!) • Indication for RAAbeauty>RAAcharm • RAAbeauty>RAAlight at low pT, effect vanishing at very high pT • RAAcharm vs. RAAlightcomparison more delicate • Indication (3s) for non-zero charm elliptic flow at low pT • Hadrochemistry of D meson species:firstintriguing result on Ds

  16. Quarkonia: from color screening… Screening of strong interactionsin a QGP T. Matsui and H. Satz, PLB178 (1986) 416 • Screening stronger at high T • D maximum sizeof a bound • state, decreases when T increases • Different states, differentsizes Resonance melting QGP thermometer A. Adare et al. (PHENIX), arXiv:1404.2246

  17. …to regeneration (for charmonium!) At sufficiently high energy, the cc pair multiplicity becomes large • Statistical approach: • Charmoniumfully melted in QGP • Charmoniumproduced, together • with all other hadrons, at chemical freeze-out, • according to statistical weights P. Braun-Munzinger and J. Stachel, PLB490 (2000) 196 • Kinetic recombination: • Continuousdissociation/regenerationover • QGP lifetime Contrary to the color screening scenario this mechanism can lead to a charmoniumenhancement if supported by data, charmoniumlooses status as “thermometer” of QGP ...and gains status as a powerful observable for the phase boundary

  18. Low pTJ/: ALICE B. Abelev et al., ALICE arXiv:1311.0214. • Compare J/ suppression, RHIC (sNN=0.2 TeV) vs LHC (sNN=2.76 TeV) • Results dominated by low-pT J/ • Strongercentrality dependence at lower energy • Systematically larger RAA values for central events in ALICE RHIC energy  suppression effects dominate Possible interpretation: LHC energy  suppression + regeneration How can this picture be validated?

  19. RAA vs pT Global syst: 8% ALICE 10% PHENIX B. Abelev et al., ALICE arXiv:1311.0214. • Charm-quark transverse momentum spectrum peaked at low-pT • Recombination processes expect to mainly enhance low-pTJ/ •  Expect smaller suppression for low-pTJ/  observed! • Opposite trend with respect to lower energy experiments • Fair agreement with transport and statistical models (not shown)

  20. Non-zero v2 for J/ at the LHC E.Abbas et al. (ALICE), PRL111(2013) 162301 • The contribution ofJ/ from (re)combination should lead • to asignificant elliptic flow • signal at LHC energy • Asignificant v2 signal is observed by BOTH ALICE and CMS • The signal remains visible even in the region where the • contribution of(re)generation should be negligible • Due to path length dependence of energy loss ? • In contrast to these observations STAR measures v2=0

  21. CNM effects are not negligible! • Suppression at backward + central rapidity • No suppression (enhancement?) at forward rapidity • Fair agreement with models (shadowing + energy loss) • (Rough) extrapolation of CNM effects to Pb-Pb evidence for hot matter effects! R. Aaij et al.(LHCb), JHEP 02(2014) 072 B. Abelev et al. (ALICE), JHEP 02(2014) 073

  22. Weakly bound charmonia: (2S) ALICE: evidence for strong suppression effects in pT-integrated p-Pb collisions (compared to J/), increasing with the event activity CMS: from enhancement to strong suppression moving from intermediate (pT >3 GeV/c) to large (pT>6.5 GeV/c) transverse momentum How can these observation be reconciled ?

  23.  suppression: CMS results S. Chatrchyan et al.(CMS), PRL 109 (2012) 222301 • More weakly bound states ((2S), (3S)) show strong suppression • in Pb-Pb, compared to (1S) • Expected signature for QGP-related suppression • Regeneration effects expected to be negligible for bottomonia

  24. First accurate determination of  suppression • Suppression increases with • centrality • First determination of (2S) • RAA:already suppressed in • peripheral collisions • (1S) (see also ALICE) • compatible with suppression • of bottomonium states decaying • to (1S)  Probably yes, also taking into account the normalization uncertainty S. Chatrchyan et al.(CMS), PRL 109 (2012) 222301 B. Abelev et al. (ALICE), arXiv:1405.4493 Is (1S) dissoc. threshold still beyond LHC reach ?  Run-II

  25. (1S) vs y and pT from CMS+ALICE • Start to investigate the kinematic dependence of the suppression • Suppression concentrated at low pT • (opposite than for J/, no recombination here!) • Suppression extends to large rapidity (puzzling y-dependence?)

  26. Do not forget CNM… • In the  sector, the influence of CNM effects is small S. Chatrchyan et al.(CMS), JHEP 04(2014) 103 • Hints for suppression of (1S) at forward rapidity? • (Small) relative suppression of (2S) and (3S) wrt(1S) at mid-rapidity • Qualitative agreement with models within uncertainties • CNM cannot account for all of the effect observed in Pb-Pb

  27. Evolution of relative yields: pp, p-Pb, Pb-Pb S. Chatrchyan et al.(CMS), JHEP 04(2014) 103 • Strong correlation of charmonia/bottomonia/open charm relative yields • as a function of quantities related to the hadronic activity in the event • Observation related to the role of MPI in pp also in the hard sector ?

  28. Charmonia/bottomonia: short summary • Twomain mechanisms at play • Suppression in a deconfined medium • Re-generation(for charmonium only!) at high s • can qualitativelyexplainthe main features of the results • In the charmonium sector • RAAweak centrality dependence at all y, largerthan at RHIC • Less suppression atlow pTwith respect to high pT • CNM effects non-negligible but cannot explain Pb-Pb observations • In the bottomonium sector • Clear ordering of the suppression of the three  states with • their binding energy  as expected from sequential melting • (1S) suppression consistent with excited state suppression • (50% feed-down)

  29. Conclusions • Complete set of results from run-I is now available • Confirm the role of heavy quarks/quarkoniaas privileged • probesfor the study of Quark-Gluon Plasma • Open charm/beauty mesons are strongly affected by the medium • Energy loss pattern, including mass-related effects, • in agreement with calculations • Significant v2 confirms the presence of collective effects (low pT) • as well as path-length dependence of energy loss (high pT) • Charmonia/bottomonia are suppressed in the QGP according to • their binding energy • Charmonium results show clear effects of re-generation during • the QGP-phase and/or at phase boundary • Many (most) of the heavy-quark/quarkonia related observables • would benefit from more data to sharpen the conclusions • Run-II at sNN~5.1 TeV, 2015-2017 • Experiment upgrades, 2018 onwards

  30. Backup

  31. LHC, 3 factories for heavy quark in Pb-Pb CMS ALICE ATLAS

  32. ATLAS open heavy flavours • ATLAS measures muons from HF in |h|<1.05, 4<pT<14 GeV/c • No pp at 2.76 TeVreference available, use RCP rather than RAA HF yield through fit of templates for discriminant variable C • RCP subject to statistical fluctuations  use RPCtoo! • ~flat vspTup to 14 GeV/c, different from inclusive RCP! If ~no suppression for 60-80%  central ~ forward suppression

  33. Data vs models: HFE Simultaneous description of heavy-flavor electrons RAAand v2 Challenge for theoretical models 33

  34. Intermezzo: multiplicity dependenceof D and J/ yields • Should help to explore • the role of multi-parton • interactions in pp • collisions • The ~linear increase of • the yields with charged • multiplicities and the • similar behaviour for D • and J/ are remarkable….. …but need to be explained!

  35. Different centrality dependence high vs low pT •  might be due to D “pushed” from high pT

  36. Hints from theory • Theory is on the data ! Fair agreement, but…. • … one model has no CNM, no regeneration • …the other one has both CNM and regeneration • (which would be responsible for all (2S) in central events) Still too early to claim a satisfactory understanding ?

  37. p-Pb results: collective effects ? • Study ofthecorrelationfunctionbetweentriggerparticles(electrons fromheavy‐flavourhadrondecay) • and associatedparticles(chargedhadrons) Difference of highest multiplicity event class (0-20% multiplicity) and lowest multiplicity event class (60-100%) (removes jet-like corr.) • Double ridge structure observed also • for HF e-h correlation as in h-h • correlations • For h-h correlations it has been • described in terms of hydro or CGC

  38. CMS results: prompt J/ at high pT CMS PAS HIN-2012-014 • Strikingdifferencewith respect to ALICE • No saturation of the suppression vs centrality • Factor 5 suppression for central events • NosignificantpTdependence from 6.5 GeV/c onwards • (Re)generation processes expected to be negligible

  39. The beginning of the story… …28 years after the prediction of J/ suppression by Matsui and Satz … 18 years after the prediction of radiativeenergy loss by the BDMPS group

  40. … and the story goes on …28 years after O beams were first accelerated in the SPS …14 years after Au beams were first accelerated at RHIC … and barely 3.5 years (!!!) after Pb beams first circulated inside the LHC

  41. Experimental techinques: charm • Semi-leptonic decays • High-pT single leptons • (pioneered at RHIC) Non-negligible background issues • Direct reconstruction • of the decay products • (D-mesons) Needs Vertexing resolution Particle ID Topological cuts

  42. Experimental techniques: beauty Non-prompt J/ • Fraction of non-prompt J/yfrom • simultaneous fit to m+m- invariant mass • spectrum and pseudo-proper decay length • distributions(pioneered by CDF) • Expected shapes from sidebands (background) • +MC templates (signals) b-jet measurements • Jets are taggedby cutting on • discriminating variables based • on the flight distance of the • secondary vertex •  enrich the sample with b-jets • b-quark contribution extracted using template • fits to secondary vertex inv. mass distributions

  43. Selected charm pp results • Excellent testing ground for QCD • calculations • Good agreement between data and • models at BOTH s=7 and 2.76 TeV • Confirmed by single-lepton studies • D-hadron correlations • Promising tool to investigate • production mechanisms • Gluon splitting  no away-side • LO (also NLO)  Back-to-back

  44. p-Pb results: CNM • RpPb for HFE (mid-rapidity) • compatible with 1 • HFM (forward rapidity) to be • shown at QM2014 • Absence of significant CNM effects • Similarity to PHENIX not really • expected (different shadowing) • Direct measurements confirm RpPb~1 • (with smaller uncertainties!) • Compatible D-meson production ratios • between pp and p-Pb for all the • measured states (D0,D+,Ds+,D*+)

  45. Comparisons LHC vs RHIC Same model can reproduce results at the two energies • Qualitative • agreement • also for HFE

  46. Comparison direct vs indirect ? backup Megliomuone + elettrone • Comparison e,  resultsvs direct D • not straightforward (decay • kinematics) • High pT:pTe ≈0.5·pTD • Larger suppression for D than for e? • B component may have larger RAA 46

  47. b-jet tagging • Clear suppression of b-jets • RAA vs pTshows suppression • up to very large pT • Trend vs centrality well visible • Central b-jet suppression consistent • with that in inclusive jets At large pT the effects related to quark mass become negligible

  48. High pTJ/: comparison CMS vs STAR • Opposite behaviour • when compared to • low-pTresults • Suppression is stronger • at LHC energy • (by a factor ~3 compared • to RHIC for central events) • Negligible (re)generation effects expected here • Is the suppression for central events (RAA~0.2) compatible with • afull suppression of all charmonia(excluding corona) ?

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