Overview of heavy ion CMS results

Transcription

1 Overview of heavy ion CMS results Gian Michele Innocenti on behalf of the CMS Collaboration Massachusetts Institute of echnology Rencontres de Moriond QCD and High Energy Interactions March 19th - 26th,

2 Understanding hot QCD medium with CMS We aim at creating a hot and dense deconfined medium by means of ultrarelativistic heavy ion collisions Did we create a strongly interacting medium? Have we observed quarkonia dissociation in the medium? peripheral collision central collision How partons interact with the medium? Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 2

3 Did we create a medium? ime Anisotropic azimuthal distribution: dn/d(ϕ-ψ 2 ) dn/d(ϕ-ψ 2 ) ~ 1+2v 2 cos[2(ϕ-ψ 2 )] Pressure-driven expansion Demonstration by an ultracold atom gas system Data ϕ-ψ 2 [rad] y ϕ x v 2 : elliptic flow initial azimuthal asymmetry of the fireball In presence of a strongly interacting medium: azimuthal particle anisotropy smaller particle density here v2>0 higher particle density here Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 3

4 Indications of a medium in PbPb v2>0 that increases in peripheral events. Precise measurement of other harmonics vn constraint on the initial energy fluctuations vn measurements well described by hydrodynamic models with very low shared viscosity (η/s~0.2) We created an almost perfect fluid! Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 4

5 he ridge PbPb ppb pp Back-to-back jet contribution single jet contribution Same structure observed in high multiplicity PbPb, ppb and pp collisions! collective effect two particles with very different η are connected Do we observe flow phenomena in ppb and even in pp? Alternative explanation that does not involve QGP? JHEP 09 (2010) 091, PLB 718 (2013) 795, CMS PAS FSQ Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 5

6 Long range correlation in pp at 13 ev Associated yield / (GeV/c) CMS Preliminary pp pp s = 13 ev, N s = 7 ev, N Glasma+BFKL, N Glasma+BFKL, N CMS PAS FSQ offline trk offline trk offline trk offline Yield trk Yield 100, 13 ev 100, 7 ev (a) 1.0 < p Glasma+BFKL, 13 ev Glasma+BFKL, 7 YeV < 2.0 GeV/c 2.0 < η < 4.0 (b) Associated yield p (GeV/c) N offline trk No double ridge in low multiplicity pp Almost linear increase with multiplicity Predictions from gluon saturation model= long-range correlation arising from initial collimated gluon emissions, NO from collective phenomenal CMS PAS FSQ Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 6

7 Probing the medium with high p particles High p quarks and gluons interact with the medium and lose energy High p hadrons and jets get quenched by the medium Di-jet event in PbPb collisions: leading jet p = 205 GeV subleading jet p = 70 GeV Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 7

8 Quantifying the jet quenching p,1 ~ p,2 Aj~0 p,1 >>p,2 Aj~1 large fraction of events with large Aj with respect to MC without jet quenching ce DJE 100% p p γ Jet φ γ > 60 GeV/c η < 1.44 Jγ Photon / Z -1-1 s NN =2.76eV, PbPb 150 µb, pp 5.3 pb > 30 GeV/c η > 7 π 8 Jet < 1.6 dn Jγ x Jγ dx Jγ 30% - 50% N 1 γ Jet dn Jγ x Jγ dx Jγ 10% - 30% N 1 γ XJγ= p Jet /p γ x Jγ ~10% of the jet energy is lost. Where does the energy go? 0% - 10% PRC 84 (2011) , CMS-HIN Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 8

9 How transverse energy is distributed in the jet cone No modification in ppb (Observed modification in PbPb is not from initial state effect) Enhancement of low p particles inside the jet cone Depletion of intermediate p particles PRC 90 (2014) , CMS-HIN Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 9

10 Where the energy goes? φ 2 What is the angular distribution of these particles with respect to the dijet system?? Projection on the dijet axis Charged particle azimuthal angle Dijet axis φ dijet φ 1 Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 10

11 Missing p versus Δ φ 2 What is the angular distribution of these particles with respect to the dijet system?? Projection on the dijet axis Charged particle azimuthal angle Dijet axis φ dijet φ 1 Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 11

12 Missing p versus Δ φ 2 What is the angular distribution of these particles with respect to the dijet system?? Projection on the dijet axis Charged particle azimuthal angle Dijet axis φ dijet φ 1 Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 12

13 Subleading jet direction Missing p versus Δ in PbPb High p imbalance at small Δ Balanced by more low p particles in subleading jet direction Extends up to large Δ JHEP 01 (2016) 006 Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 13

14 Does the energy loss depend on parton flavour? ΔEg > ΔEu,d,s > ΔEc > ΔEb R light particle AA < R D AA < R B AA? Hints of different suppression for D and non-prompt J/ψ at low p! Same suppression observed for inclusive jets and b-tagged jets CMS-HIN , PRL 113 (2014) Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 14

15 Heavy-Flavour production in ppb mb GeV/c dσ dp 1 pa CMS Preliminary nb (5.02 ev) ppb data, -2 < η < 2 lab PYHIA Z2 (5.02 ev) Data/PYHIA c jet p [GeV/c] B + production in ppb compatible with predictions from FONLL scaled by A=208 tagged c and b-jet production compatible with predictions from PYHIA scaled by A=208 HF ppb production not significantly modified by cold nuclear matter effects (e.g. PDF modification in nuclei) PRL 116 (2016) , CMS-HIN ,PLB 754 (2016) 59 Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 15

16 Have we observed quarkonia dissociation? in presence of a coloured medium, the qqbar potential is screened Quarkonia melt in the QGP! Less bounded states melts at lower temperature diss (1S) > diss (2S) > We should observe a hierarchy in the dissociation of different quarkonia states depending on their binding energies Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 16

17 Upsilon suppression in PbPb -1 pp 5.4 pb s = 2.76 ev -1 PbPb 166 µb s NN = 2.76 ev 2 ) ) Events / ( 0.1 GeV/c p p CMS Preliminary y < 2.4 µ 1 µ 2 > 3.5 GeV/c > 4.0 GeV/c pp 2 Events / ( 0.1 GeV/c Cent % y < 2.4 p p CMS Preliminary µ 1 µ 2 > 3.5 GeV/c > 4.0 GeV/c PbPb m µ + µ (GeV/c 2 ) m µ + µ (GeV/c 2 ) Υ(1S) Υ(2S) Υ(3S) Υ(2S) slightly suppressed Υ(3S) not visible! We observe what we call sequential suppression of Υ states in PbPb collisions! CMS-HIN Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 17

18 Conclusions Did we create a strongly interacting medium? evidences that we created in PbPb collisions a medium that behaves like a perfect fluid pp and ppb? did we create QGP there? How partons interact with the medium? high p partons lose energy in the deconfined medium as observed by studying jet suppression the energy lost by the quenched partons goes to soft particles far from the initial parton direction Did we observe quarkonia dissociation in the medium? evidence of sequential suppression of bottomonia states (GeV/c ) Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 18 ) 2 Events / ( 0.1 GeV/c PbPb 166 µb m µ + - µ Cent % y < 2.4 p p 2 µ 1 > 3.5 GeV/c µ 2 = 2.76 ev s NN CMS Preliminary > 4.0 GeV/c

19 BACKUP Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 19

20 CMS detector EM and hadronic calorimeters Photons, Jet Forward Calorimeter: MB triggers, centrality Inner tracker: charged particles Muon detectors Muon HCAL ECAL η < 2.4 η < 5.2 η < 3.0 racker η < 2.5 Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 20

21 Charged particle RAA In absence of in-medium effect RAA=1 In presence of in-medium energy loss: p spectra in Pb-Pb shifted at low p RAA<1 Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 21

22 How to quantify the energy loss? Nuclear modification factor number of binary nucleon-nucleon collisions in a PbPb collision In absence of in-medium effect RAA=1 In presence of in-medium energy loss: p spectra in Pb-Pb shifted at low p RAA<1 Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 22

23 Flow in PbPb collisions = geometry + fluctuations Collective behaviour in heavy-ion collisions as crucial probes to test: hydrodynamics and transport coefficient in the bulk Initial state conditions degree of freedom and particle production mechanisms Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 23

24 We did create a medium in PbPb! dn/d(φ-ψ2) 1+2v2 cos[2(φ-ψ2)] 2.76 ev smaller particle density here v2>0 higher particle density here As expected due to initial geometry asymmetry! non zero elliptic flow (v2>0) suggests we created a strongly interacting medium that also exibiths properties of a almost perfect fluid! Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 24

25 v2 in peripheral PbPb collisions v2>0 in peripheral collisions is the first important evidence that the fireball exhibits a collective behaviour: different pressure gradient due to the geometric anisotropy of the fireball well predicted by hydrodynamics! IN PLANE Is this really collectivity? v2{2} can be affected by non-flow phenomena v2{4}=v2{6}= v2{8} telling that similar results are extracted by considering 2, 4, 8 particles. OU OF PLANE Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 25

26 Understanding the ridge in ppb collisions Many evidences suggests hydro behaviour in ppb collisions: vn present similar behaviour vs p as observed in PbPb collisions E.g. v2{2} > v2{4} v2{6} v2{8} stronger radial flow (v1) that in PbPb as a consequence of the more explosive system created in ppb collisions Clear mass ordering in the v2 as function of p as expected in the HP of collective motions Are there alternative explanations to hydro? Other explanations describes this collective phenomena as a consequence of pure initial state interactions: Color Glass Condensate (CGC) pqcd-based models Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 26

27 esting hydrodynamics models In ultra-central PbPb collisions not sensitive to the geometry anisotropy we can test the transport coefficients of the fireball Hydro-models can reproduce the various harmonics vn assuming values of the shared viscosity close to KKS bound he medium shows collective behaviours well described by hydrodynamics calculation and presents the properties of an almost perfect fluid Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 27

28 ridge in pp collisions 3 10 CMS Preliminary 0.04 pp s = 7 ev ppb s NN = 5.02 ev c 2 {4} < p < 3 GeV/c similar ridge observed in high multiplicity pp collisions at 7 and 13 ev CGC models fails at describing the ridge yield at high multiplicity A full understanding of the pp flow-like phenomena is still far c 2 {4} 0 2 v 2 {4} = 3% v 2 {4} = 4% offline N trk in high multiplicity pp collisions, hints of non zero v2 from 4-particle correlations limited by low statistics Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 28

29 Missing p versus Δ in pp Subleading jet direction Asymmetry inside the jet cone Integrated curve from 0 to Δ JHEP 01 (2016) 006 Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 29

30 p-dependence of the di-jet imbalance Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 30

31 di-jet angular correlation Correlation peak is the same in data and Pythia across all values of p Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 31

32 Momentum balance of dijets events In MC, large components of tracks with p 4-8 GeV/c Overall momentum balance of the events is always recovered <p >=0 Dijet momentum imbalance is not related to undetected activity In both MC and Data, the large negative contribution (leading jet) with p>8 GeV balanced by tracks with p GeV/c In data the missing p is compensated mostly by low p particles < 4 GeV Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 32

33 Jet shapes radial distribution of transverse momentum of tracks inside the jet cone r track axial distance from the jet axis Deviations from unity indicate modification of jet structure in the nuclear medium No sizeable modification of the jet shape with respect to pp in peripheral PbPb excess of transverse momentum fraction emitted at large radii moderate broadening of jets! Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 33

34 Photon-jet correlations R Jγ CMS Preliminary s NN =2.76eV, PbPb 150 µb, pp 5.3 pb PbPb Data pp Data Smeared pp reference PYHIA + HYDJE φ 7 π N part xjγ=p,jet/p,γ Jγ > <x Jγ > CMS Preliminary s NN =2.76eV, PbPb 150 µb, pp 5.3 pb PbPb Data pp Data Smeared pp reference PYHIA + HYDJE φ 7 π N part RJγ=fraction of diet events with a jet partner Jγ > Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 34

35 Sequential suppression R AA CMS Preliminary PbPb = 2.76 ev s NN 0-100% Inclusive ψ(2s) (6.5 < p < 30 GeV/c, y < 1.6) ϒ(3S) ( y < 2.4), 95% upper limit ϒ(2S) ( y < 2.4) prompt J/ψ (6.5 < p < 30 GeV/c, y < 2.4) ϒ(1S) ( y < 2.4) 0.4 Υ(1S) J/ψ 0.2 ψ(2s) Υ(3S) Υ(2S) Binding energy [GeV] Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 35

36 J/ψ-ψ(2S) suppression: a proof of recombination? =RAA(ψ(2S))/RAA(J/ψ) R AA 1.4 PbPb Preliminary s NN = 2.76 ev CMS: prompt J/ ψ ALICE: inclusive J/ ψ y < < y < < p < 30 GeV/c pp ] / [ N ψ(2s) /N J/ψ ] [ N ψ(2s) /N J/ψ PbPb 3 CMS PbPb & pp = 2.76 ev < p 6.5 < p s NN < 30 GeV/c, 1.6 < y < % CL < 30 GeV/c, y < N part N part Low p J/ψ measurements from ALICE compared to CMS results suggest a possible contribution of charm recombination in the medium ψ(2s) more suppressed than J/ψ in central PbPb collisions. Is recombination more relevant for excited J/ψ states? (sequential recombination) Simple kinematic effect? radial flow? Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 36

37 Also puzzles in pp Other phenomena, other that color screening, could lead to a suppression sequence that depends on the binding energy! ϒ(1S)/ ϒ(1S) pp ppb s = 2.76 ev s NN = 5.02 ev PbPb s NN = 2.76 ev y < 2.4 CM ϒ(2S)/ ϒ(2S) pp s = 2.76 ev ppb s NN = 5.02 ev ϒ(3S)/ ϒ(3S) pp s = 2.76 ev ppb s NN = 5.02 ev 4 3 ϒ(1S) ϒ(1S) 4 3 ϒ(2S) ϒ(2S) 4 3 ϒ(3S) ϒ(3S) η <2.4 N tracks / N η <2.4 tracks total CMS y < 1.93 CM η <2.4 N tracks / N η <2.4 tracks total CMS y < 1.93 CM Evolution (w.r.t. minbias) of the individual x-sections with the increase of track multiplicity around the state even in pp collisions: 2 1 η <2.4 N tracks / N η <2.4 tracks total CMS y < 1.93 CM Additional final-state effects affecting more the excited states than the ground state? Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 37

38 what happens to charmonia? R AA 1.4 PbPb Preliminary s NN = 2.76 ev CMS: prompt J/ ψ ALICE: inclusive J/ ψ y < < y < < p < 30 GeV/c J/ψ RAA at lower p (<6.5 GeV) J/ψ RAA at higher p (>6.5 GeV) Much more J/ψ seems to survive at low p N part What does it mean? At low p there could be an antagonistic mechanism to dissociation or melting J/ψ created by combining c-cbar quarks that are aboundant in the deconfined QCD medium Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 38

39 Long range correlation in pp at 13 ev Associated yield / (GeV/c) CMS Preliminary PbPb s = 2.76 ev ppb s = 5.02 ev pp s = 13 ev pp s = 7 ev 2.0 < η < < p < 2.0 GeV/c We can extract the double ridge associated yield projecting the correlation plot along ΔΦ offline Very similar behaviour in pp, ppb and PbPb collisions but with different magnitude N trk Almost no dependence on the collision energy What kind of phenomenal are we observing? CMS PAS FSQ Gian Michele Innocenti, MI, Moriond QCD 2016, Overview of CMS heavy ion results 39