Latest results on Quarkonium production in nuclear matter at the LHC

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1 Latest results on Quarkonium production in nuclear matter at the LHC Nicolas Filipovic ELTE Particle Physics Seminar April 27th, 2016

2 Outline A Quarkonium in the QGP Charmonium results in Run 1 Bottomonium results in Run 1 Outlook 2

3 Napi ajánlat A time-dependent picture of a central heavy ion collision τ=0 τ~10 fm/c The Observable: the Nuclear modification factor 3

4 Some context Quark gluon Plasma A hot, dense, deconfined and collective state of matter QCD EoS at T > Tc drives the evolution LHC, RHIC, FAIR, to characterise the QGP Quarkonium states in the QGP Matsui & Satz, 1986 Break up above a dissociation temperature Experimental outcome : RAA < 1 Many states = many Td = measure of the TQGP The QGP thermometer 4 A. Mócsy, Eur.Phys.J.C61(2008)

5 More context PRD (2008) What theorists do: Find in medium properties of a quarkonium potential Screening of the free energy Broadening of the spectral function with T Relate the spectral functions to a nuclear modification factor R AA plugging in a dynamic model Estimate fraction of suppression due to non QGP effects Then, go to conference and make claims Our analysis suggests that J/ψ is melted by 1.46 TC We find that J/ψ is stable up to T=1.62 TC Nonaka et al Ding et al 2010

6 More context What experimentalists do: Muons! Υ µµ pp PbPb Measure quarkonium states in dilepton decays Compare with a 'no QGP' baseline Estimate the nuclear modification factor RAA No modifications if PbPb = Ncoll x pp RAA = 1 CMS-HIN Krouppa et al., Phys. Rev. C 92, (2015) 6 Then, go to conference and pay a drink to the theorist with the most credible claim

7 Quarkonia Heavy quark antiquark bound system Produced via gluon fusion Heavy quarks b or c Easily detectable in dilepton decay Resonant states of various binding energy, mass 7

8 Family portrait Bottomonia Charmonia 8

9 Charmonia J/ψ ψ(2s) pp data, the 'reference' Phys. Rev. Lett. 113 (2014)

10 J/ψ suppression at the LHC CMS-HIN PT(ψ) > 6.5 GeV/c Nuclear modification factor RAA for prompt J/ψ Suppression pattern already seen at SPS and RHIC Prompt J/ψ : probe for deconfinement Not covered here: Non prompt J/ψ, coming from B meson decay probe b quark energy loss 10

11 J/ψ suppression at the LHC Main observation from LHC Run 1: J/ψ break up could lead to suppression and recombination ALICE ALICE J/ψ data in forward muon arm is flatter vs centrality ALICE central arm data could be increasing with centrality... High pt J/ψ melted in the plasma and regenerated at low pt?? CMS N.b.: n(cc) ~ 50 in a central PbPb collision at LHC 11

12 J/ψ regeneration at the LHC If charmonia break up in the plasma and recombine in flight at LHC, is it also true at RHIC? Look at the kinematics! CERN-PH-EP ALICE (LHC) data in 2.76 TeV vs ALICE Phenix (RHIC) data in 200 GeV PHENIX At LHC, can test statistical regeneration and transport models in the plasma 12

13 J/ψ regeneration at the LHC? Further testing the data: If recombination: can expect it in the 'bulk' of the QGP (y~0) Let's not forget gluon shadowing, energy loss, absorption... CERN-PH-EP y ~ 0 data compatible with shadowing forward rapidity: additional nuclear absorption is possible... ALICE PHENIX But, how do we really assess this? 13

14 p Pb collisions At LHC, ppb collisions at s = 5.02 TeV QGP Pb p EPb = 1.58 A TeV Ep = 4 TeV J/ψ is sensitive to gluon PDF in the nucleus Gluon shadowing depletion of J/ψ yields at forward rapidities Coherent energy loss Saturation effects co mover interaction... 14

15 J/ψ in ppb collisions at the LHC CMS-HIN big (temporary) caveat: in Run 1, no pp reference at 5 TeV can't compute RpA ppb snn = 5 TeV Cross section for prompt J/ψ production in ppb Some asymmetry is seen... let's compare left and right. 15

16 J/ψ in ppb collisions at the LHC CMS-HIN RFB is the forward backward ratio Reads as: whatever causes the depletion at y>0 is stronger/weaker than what causes the y<0 distribution LHC ppb snn = 5 TeV 16

17 So far so good? Not the end of the story... One cold nuclear effect or many? Initial state effect (shadowing) or final (absorption)? Tentative way out: Compare excited state ψ(2s) with J/ψ Initial state effects should be the same Lesser bound ψ(2s) smaller survival w co moving hadrons... 17

18 ψ(2s) in ppb ALICE has given a try in Run 1 CERN-PH-EP TeV ppb / 7 TeV pp, ~ RpPb forward rapidity region backward rapidity region J/ψ supppression finds good agreement with shadowing & E loss Unfortunately, not enough to describe ψ(2s) suppression Counterintuitive: time spent in nucleus < time to form a ψ(2s) 18

19 Charmonium recap. J/ψ : Strongly suppressed at high p T, much less at low pt Clear signs of recombining from outgoing c quarks Cold nuclear matter effects compared (w/o reference data at 5 TeV...) Conclusion: several mechanisms in both hot and cold regimes Ψ(2S): Controversial Run 1 results were not shown... Frantically waiting for PbPb results from Run 2 In the meantime, ψ(2s) 'unexpectedly' suppressed in ppb Wrong assumptions or 'QGP drop' or anything else? How to reconcile/meet with the quarkonium melting picture? Suggestion: go heavy (next part) 19

20 Bottomonia Υ(1S) Υ(2S) Blue: PbPb CMS data Red: pp data (scaled) CMS-HIN Υ(3S)

21 Upsilons at the LHC Heavier, clearer probes CMS-HIN No regeneration ( ~ 5 b quarks per central PbPb collision) Ordered suppression Peripheral Y(2S): suppressed of a factor 4... why? Central Y(1S), RAA ~ 0.3 why? 21

22 Some hand waving Q: What is the fraction of Y(1S) coming CMS-HIN from excited state feed down? A: look at pt dependent feed down fractions from various experiments (compiled by H. Wöhri) At high pt, feed down ~ 50% At low pt, feed down ~ 30% Pure melting of excited states in central PbPb Y(1S) suppression would be ~ 70 % at low pt? 22

23 Kinematics of Y suppression: pt Y(1S,2S) suppression in PbPb measured up to pt < 20 GeV/c CMS-HIN Flat pattern overall, RAA Y(1S) ~ 0.43 Contrary to recombination in J/ψ. Theory comparison to a potential model with Td Y(1S) ~ 450 MeV + hydrodynamics (momentum anisotropies) + recent feed down fractions (LHC) What is the amount of shadowing, nuclear absorption, energy loss? look at ppb data, see further 23

24 Kinematics of Y suppression: y Y(1S,2S) suppression in PbPb measured vs. rapidity (CMS and ALICE) CMS-HIN Flat pattern maintained + Hint of more ALICE Theory comparison struggling with forward rapidity data... What is the amount of shadowing, nuclear absorption, energy loss? look at ppb data, see next. 24

25 Upsilons in cold nuclear matter From previous experience: JHEP 1404 (2014) 103 Y(1S) yield is always larger than excited states RAA ~ N(PbPb)/N(pp) for any given quarkonia Construct the 'double ratio' of Y(nS) over Y(1S) informs on additional suppression suffered by excited states R AA (ns) (N Y (ns ) / N Y (1 S) )AA = = R AA (1 S) ( N Y (ns ) / N Y (1 S) )pp PbPb In PbPb: clear additional suppression, In pp: ~20% extra modification on excited states ppb 25

26 Upsilons in cold nuclear matter ATLAS, ALICE, LHCb data in ppb + pp data driven 5 TeV Y nuclear modification factor ppb with pp in ppb: compatible (contrary to J/ψ) * CMS sees some excited state suppression in ppb where does it come from? 26

27 Multiplicity dependent effects JHEP 1404 (2014) 103 CMS Y in ppb: look at excited/ground state ratios Falling vs. multiplicity in the tracker ( η < 1.93) Flat vs. forward energy from the rest of the collision event (4< η <5.2) 27

28 Multiplicity dependent effects Excited/ground state ratios JHEP 1404 (2014) 103 Falling vs. multiplicity in the tracker ( η < 1.93) Steeper dependence in pp than in ppb...why? Is the multiplicity affecting differently Y ppb production? Are Y produced differently with multiplicity? 28

29 Self normalised cross section ratios JHEP 1404 (2014) 103 X axis: multiples of the average event multiplicity Y axis: units of the averaged Y(nS) cross section Example: in the bin where the multiplicity is 3 times the average, the Y(1S) cross section is 7 times its average value. 29 Y(1S) > Y(2S) > Y(3S)

30 Y suppression summary Y in PbPb Suppressed, ordered, flat kinematics Could be one effect pt independent Could be suppression + feed down, both pt dependent (let's look at higher pt asap) Y in ppb: 1S: ~unmodified (with the precision at hand) 2S, 3S: altered w.r.t. 1S multiplicity effect? Y in pp: Strong dependence with associated multiplicity Each state, differently (with the precision at hand) Look for sources of enhancements (multi parton process, partons radiating an Y...) also in open heavy flavour (B,D) 30

31 Look to the future Run 2 : PbPb and pp both at 5 TeV...coming soon. 5 TeV: already on tape from Run 1, ppb(2017) : likely 8 TeV (as pp 2012 data) Plenty of ratios to play with...sigh More sensitivity to high pt, excited states, Must have : working extrapolation for ppb PbPb All 4 LHC experiments will contribute... fun! 31

32 Thank you The End 32

33 Comparing J/Psi and Upsi RAA vs. pt 33 RAA vs. y

34 The CMS detector 34

35 HI collisions in a nutshell LHC PbPb collisions What we measure: + Temperature of the QGP + modified particle production need a clear baseline need to understand nuclear effects > nuclear absorption, 1 > PDF modification in nucleus Look at pa collisions, AB collisions Karsch, 2015

36 Heavy ion collisions At LHC, Pb ions (A=208) collide at sqrt(snn) = 2.76 TeV 36

37 Heavy ion collisions At t < 0.1 fm/c Hard particle production 37

38 Heavy ion collisions Z, W, 'hard' partons: if colour blind: unaffected if coloured: affected... 38

39 QGP at colliders Medium expands and cools down At t <10 fm/c Soft particle production, collectivity 39 Quarks and gluons Thermal photons

40 Probes of the QGP At t > 10 fm/c: final state particles propagate to the detector Soft probes Light and strange hadrons Thermal photons Hard probes High pt jets of quarks or gluons Heavy flavor hadrons (B, D) Quarkonia Different informations on the QGP evolution 40

41 Quarkonia 41

42 Particle reconstruction in CMS 42

43 Measuring Psi(2S) Double ratios in PbPb CMS Double ratios in ppb ALICE and PHENIX dau + Most systematic uncertainties cancel in the ratio 2S statistics are sparse (and misleading) 43

44 Measuring Psi(2S) Double ratios in ppb ALICE vs pt + Most systematic uncertainties cancel in the ratio 2S statistics are sparse (and misleading) 44

45 Extrapolation to PbPb Hypotheses: Quarkonium produced in 2 >1 process Shadowing dominates the CNM effects CNM factorize in +/ y Can formulate RpA * RaP = RAA with proper x coverage in PbPb 45 R. Arnaldi, QM2015