Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions

Transcription

1 CMS PHENIX STAR sphenix Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions Jan Fiete Grosse-Oetringhaus, CERN XIII. Strong and Electroweak Matter June 2018 LHCb ALICE ATLAS

2 Short recapitulation: Basic Concepts Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 2

3 A Heavy-Ion Collision dn ch /dh up to 2000 particles particle detection Time t = 4 cm/c kinetic freeze-out t = 10 fm/c chemical freeze-out hadronization hydrodynamic evolution pre-equilibrium collision t = ~1 fm/c t = 0 fm/c Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 3

4 Centrality & Glauber Activity depends strongly on impact parameter b Few to 1600 nucleon-nucleon collisions Central b ~ 0 e.g. 0-5% Peripheral b ~ R e.g % Multiplicity vs. b Accessible experimentally N ch and SE T grows with decreasing b Soft (low p T ) ~ participants (N part ) Hard (high p T ) ~ collisions (N coll ) from Glauber calculations / MC Plot: A. Toia Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 4

5 Flow Overlap region of colliding nuclei is not isotropic Spatial anisotropy (almond shape) different pressure gradient momentum-space anisotropy (particle level) Classical picture: Overlap of nuclei elliptic flow (v 2 ) Today s picture Initial state density fluctuations higher-order anisotropies y x Fourier coefficients v n of single-particle distribution wrt n th order participant plane dn d A 1 2 v n cos n( n n ) e 4 e 3 Traditional wisdom: needs significant reinteractions between medium constituents / small Knudsen number Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 5

6 Particle Production and Hadronization Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 6

7 7 orders of magnitude Particle Yields in Pb-Pb 5 TeV 12 different particles p K K 0 K * f p L X W d 3 L H 3 He Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 7

8 Experimental Effort: Particle Identification Displaced vertices K 0 S p p (ct = 2.7 cm) L p p (ct = 7.9 cm) Direct particle identification p K p d 3 He 3 H Invariant mass p f K K K * K p p p L X Cascade X L + p p p p W L + K p p K Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 8

9 Particle Yields in Pb-Pb 5 TeV Fit with statistical (thermal) model Relativistic ideal quantum gas of hadrons 3 parameters: V, T, m B At LHC, m B ~ 1 MeV, fixed by antip/p ratio T = 153 MeV (3 MeV lower than at 2.76 TeV due to proton yield) p K K 0 K * f p L X W d 3 L H 3 He Particle yields well described by equilibrium thermal models over 7 orders of magnitude Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 9

10 System Comparison Strangeness enhancement Deuteron enhancement pp p-pb Pb-Pb K* Suppression p? Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 10

11 Particle Yields in Pb-Pb 5 TeV Nuclei! p K K 0 K * f p L X W d 3 L H 3 He Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 11

12 Nuclei: Production Mechanism Heavy and fragile objects in agreement with thermal model at chemical freeze out S 3 vs. s NN Open puzzle: No re-scattering of anti-nuclei in hadronic phase despite large dissociation cross-section Naïve coalescence after kinetic freeze-out does not describe the data S 3 = 1 Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 12

13 Parton-Medium Interactions Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 13

14 R AA R AA vs. p T Particles HI collision more than superposition of nucleonnucleon collisions with incoherent fragmentation? R AA dnaa / dpt N dn / dp coll pp T R AA = 1 no modification R AA!= 1 medium effects Charged particles up 400 GeV/c Jets up to 1 TeV p T dependence Hadrons: consistent with constant DE Jets: suggest increase of ΔE vs E More insight: D. QM R AA vs. p T Jets Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 14

15 g-jet Correlations Photon: fixes initial parton energy dn/dx Jg vs. x Jg p T,g g p T,jet Significant difference central Pb-Pb vs. pp ATLAS-CONF x Jg = p T,jet / p T,g Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 15

16 Jet Substructure Techniques applied in pp collisions extended to Pb-Pb collisions Resolve inner structure of a jet Challenge: large background contribution from underlying event Example: z g of two leading sub jets dn/dz g vs. z g PRL 120 (2018) z g min( p p p T1 T1, pt 2) T 2 asymmetric splittings increase symmetric splittings decrease Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 16

17 Charm v 2 vs. p T Are there sufficient interactions between medium and heavy quarks? Charm v 2 > 0 Charm quarks flow with the medium How are charmed hadrons formed at freeze out? L c /D ratio larger than in pp D s /D 0 ratio larger than in pp L c and D s give large contribution to total cross-section L c /D 0 vs. p T D s /D 0 vs. p T Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 17

18 Sequential suppression for Y family Y(3S) limit for now Y Suppression Clear hierarchy, no clear turn-on Smooth evolution of T with centrality R AA vs. N part R AA vs. N part R AA vs. N part CMS-HIN arxiv: Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 18

19 Parity Violation in the Strong Interaction Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 19

20 Chiral Magnetic Effect Spectator charge causes large magnetic field (~10 18 Gauss) Aligns spins Domains with non-zero topological charge (local) chirality flip Leads to charge separation Experimental correlator Y Same sign = signal Opposite sign = control Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 20

21 Earlier Results Signal observed increasing with increasing centrality Magnitude similar at 0.2 TeV (STAR) and 2.76 TeV (ALICE) Magnitude similar in Pb-Pb and p-pb Issue: Large backgrounds due to local charge conservation (resonance decays, momentum conservation, parton fragmentation) g 112 vs. centrality g 112 /v 2 vs. N ch PRL110 (2013), PRL118 (2017), Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 21

22 Event Shape Engineering Large event-by-event variation of v n nucl-ex/ Final-state v 2 correlated with initial-state eccentricities e 2 (hydro with small h/s) At fixed centrality, split events by event-by-event v 2 (q vector) [Schukraft, Timmins, Voloshin (PLB719 (2013) 394)] v 2 vs. p T elliptic Large q 2 large v 2 Small q 2 small v 2 round PRC 93, (2016) CME backgrounds proportional to v 2 Possibility to constrain background Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus central peripheral 22

23 Latest Results f CME vs. centrality Event shape engineering, modelling of magnetic field + initial state models allows limit on CME f CME = maximal signal contribution in correlator Limit set on signal 7% at 95 C.L. Isobar run planned at RHIC this year Test Z 2 magnetic field dependence f CME vs. N ch ALICE, PLB 777, 151 CMS, PRC 97 (2018) Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 23

24 Small Systems p-pb d-au pp Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 24

25 Paradigm Shift dn d A 1 2 v n cos n( n n ) Traditional wisdom: needs significant reinteractions between medium constituents / small Knudsen number Significantly challenged in recent years! Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 25

26 Two-Particle Correlation h Away-side jet + flow (D ~ p, elongated in Dh) f Beam axis Near-side jet + resonances,... (D ~ 0, Dh ~ 0) Near-side flow ridge (D ~ 0, elongated in Dh) Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 26

27 Pb-Pb vs. pp Pb-Pb pp Near-side ridge (flow) only in Pb-Pb at least everyone thought so for a long time Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 27

28 CMS, PLB718 (2013) 795 CMS, JHEP09(2010)091 Near-Side Ridge here: h = h lab 0.005% of MB observed in very high-multiplicity pp collisions 0.005% events with highest multiplicity pp N offline,trk > 110 observed in high multiplicity p-pb collisions ~40% events with highest multiplicity Surprisingly large magnitude p-pb 3.1% of MB Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 28

29 The Double Ridge here: h = h lab Subtraction procedure to isolate ridge contribution from jet correlations No ridge seen in % and similar to pp 0-20% % = Discovery! two ridges! ALICE, PLB719 (2013) 29 Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 29

30 Where are we today? Large number of observations of effects in p-pb collisions which were traditionally associated with Pb-Pb only Even in pp collisions, some of these effects observed Absence of these effects in archived e+e- data (LEP) In the following, overview of selected highlights Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 30

31 Higher-Order Cumulants Is the observed structure a multi-particle effect? v 2 vs. N ch pp p-pb Pb-Pb Yes! At least 8 particles involved in Pb-Pb and p-pb. Even in pp collisions, at least 6 particles involved Magnitude of v 2 similar in pp, p-pb and Pb-Pb Differences in details, e.g. v 2 {2} ~ v 2 {4} in pp, but v 2 {2} > v 2 {4} in larger systems PLB 765 (2017) 193 Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 31

32 Identified Particles How does the observed effect behave for different particles? v 2 vs. p T v 2 vs. p T p-pb protons kaons pions PLB 726 (2013) 164 p-pb arxiv: Mass ordering at low p T ( radial flow and expansion) Crossing at intermediate p T as observed in Pb-Pb collisions Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 32

33 Charm & Beauty Can similar effects be observed for heavy quark? v 2 vs. p T v 2 vs. p T p-pb p-pb D J/y Signal observed for D, J/y, leptons from HF decays Heavy quarks participate in the collective effects observed Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 33

34 Initial or final state effect? What is the relation to the shape of the initial state? RHIC geometry scan Prediction by hydrodynamic models p-au v n vs. p T v 2 d-au 3 He-Au v 3 arxiv: Triangular initial state large v 3 Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 34

35 e + e - (archived ALEPH data) Can we observe the same structures in e + e - collisions? Y(Df) vs. Df Yen-Jie Lee, Quark Matter 2018 No ridge found in ee collisions! Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 35

36 Strangeness Production K 0 /p L/p Strange baryon production increases with increasing multiplicity X/p K 0, L, X, W Pb-Pb Smooth across system (pp, p-pb, Pb-Pb) Multiplicity only relevant variable here? pp p-pb W/p Need more overlap for final answer Traditional MC codes fail to reproduce trend Tjorben Sjostrand (QM 18): need new framework for baryon production Nature Phys.13(2017)535 Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 36

37 Energy loss? R pa vs. p T R pa vs. p T R pa vs. p T hadrons PRL110 (2013) D mesons J/y from B No significant signal observed in R pa for hadrons, D and B Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 37

38 Solved Puzzle: Peripheral R AA R AA vs. p T R AA ~ 0.8 in peripheral Pb-Pb collisions N part ~ 5-10, like in p-pb and there the R pa ~ 1 Shown to be caused by biases Event selection Nucleon-nucleon impact parameter: in peripheral Pb-Pb collisions, the average NN impact parameter is larger than in pp Above 80% reproduced by simple superposition model HG-PYTHIA (Loizides, Morsch, Phys.Lett. B773 (2017) ) R AA vs. centrality arxiv: No need to involve energy loss in peripheral collisions Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 38

39 What Next? Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 39

40 The quest for the QGP has turned into a precision exercise The questions remain puzzling What is the underlying dynamics? Open Questions Model describing long wavelength (ideal fluid) and short wave-length ("quenching") behavior What are the (relevant) degrees of freedom / microscopic structure? How to derive behavior from QCD? QGP onset in light of the discoveries in small systems Christian Bierlich, Workshop on physics at HL-LHC, Collective effects in small and dilute systems? Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 40

41 W/p ratio Historic smoking gun observables R AA, Flow, Strangeness Different turn-on expected as underlying dynamics driven by different variable Smooth increase to first order Connect small and large systems Fine structure to second order Potential to learn about underlying dynamics their driving variables QGP Onset vw / ep vw CMS, PLB 724 (2013) 213 ALICE, arxiv: R AA 2, central 2 2 / R ep 2 AA central bias corr. (at 7 GeV/c) Relative Effect W/p pp p-pb Pb-Pb v 2 /e 2 R AA at 7 GeV/c ALICE, Nature Phys.13(2017)535 Disclaimer: numerous caveats in this comparison Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus dn ch /dh 41

42 The Next 10 Years LHC run 2 RHIC run Upgrades LHC LS2 LHC: collimators + injectors ALICE: Tracking, DAQ (rate x100) ATLAS: Fast tracker trigger (rate x2) CMS: pixel detector (rate x2) LHCb: VELO, tracker, DAQ (rate x10) LHC Run (numbers for Pb-Pb) L = cm -2 s -1 ~ 50 khz rate SPS, FAIR, NICA not shown here sphenix const. STAR upgrades RHIC run sphenix events read out Sampled 50 nb -1 STAR 10 9 events read out 10 nb -1 (ALICE, CMS, ATLAS) Upgrades LHC LS3 ATLAS: Tracker (acc x2) Timing CMS: Tracker (acc x2) Encap Calorimeter LHCb: TOF? Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 42

43 Detector Upgrades Significant detector upgrades at LHC for ALICE, ATLAS, CMS, LHCb and for STAR at RHIC New detector sphenix replaces PHENIX at RHIC Accelerators + detectors willl be factories for D, B, J/y, Y, thermal dileptons, nuclei and jets 10 nb -1 Pb-Pb (LHC) 35 nb -1 Au-Au* (RHIC) 200 pb -1 pp* (LHC) MB events MB events 10 6 pp events N ch > 12 <N ch > (250 particles in h < 1.5) * not yet approved Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 43

44 Charm Hadronization How does charm recombine from the QGP? Baryon/meson ratios D s /D, L c /D, L b /B Very challenging: e.g. L c ct ~ 60 mm Influence of recombination and radial flow L c /D vs. p T ALICE CERN-LHCC R AA y(2s)/j/y vs. N part Influence of melting and regeneration Compare states with different binding energy Validation of recombination and coalescence models current stat. unc ~ 70% ALICE Upgrade Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 44

45 Heavy Quarks Do heavy quarks thermalize? Light vs. heavy-quark flow Constrain temperature dependence of diffusion coefficient R AA vs. N part D v 2 vs. p T Beauty transport coefficients compared to lattice QCD Bottomonia flow in reach Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 45

46 Energy Loss Precise medium tomography Di-jet imbalance, g-jet, Z 0 -jet Path-length dependence with event-shape engineering bjet v 2 vs. p T dn/x Jg vs. x Jg Quark-mass dependence Flavour identified fragmentation fct Path-length dependence through v 2 Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 46

47 Thermal Radiation & Nuclei Access space-time evolution of medium Temperature ( 10-25% uncertainty) Radiation from all stages of the expansion Change of r spectral function connected to chiral symmetry restoration dn/dm ee vs. M ee S vs. L int 4 L H 4 L He r 0-10% ALICE Projection Thermal radiation CERN-LHCC Precision era for (anti-)(hyper-)nuclei production Production mechanism: (advanced) coalescence vs. thermal model Input to astrophysical background, e.g. for AMS Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 47

48 Collectivity in Small Systems Can reach extremely rare (10-11 ) pp events 200 pb -1 Sampling events Significant overlap between pp and PbPb In multiplicity up to ~65% centrality If pp behaves HI, we shall see standard HI physics Including jet quenching if effects driven by final state If not, we can see the differences In addition: MB sample for low-multiplicity limit What is smallest droplet of matter showing collective behavior? Origin of collectivity in few particle system? (color reconnection, gluon interference, escape, ) P(N ch ) vs. N ch Today 65% central Pb-Pb p-pb pp <N ch > >25k events Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 48

49 Pb-Pb 100 km circumference Future Collider Projects ( ) s NN = 39 TeV (Pb-Pb) 63 TeV (p-pb) 100 TeV (pp) LHC Geneva FCC dn ch /dh 3600 V fm 3 e (t = 1 fm/c) GeV/fm 3 Future Circular CERN nb -1 per month (12-40x LHC) Conceptual Design Report by fall 2018 Further reading: Physics case FCC week SPPC in China Combined with e + e - machine Funding for R&D available Further reading: Physics case Pre CDR Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus one of several site candidates (close to Hong Kong) Manqi Ruan, Hard Probes

50 Summary Precision measurements from RHIC and LHC experiments Transition from simple fine tuning to comprehensive modelling Agreement/discrepancy of details may contain key to understanding Paradigm shift followed by discoveries small systems Ample evidence for collective phenomena No significant parton energy loss Hints that collective phenomena exist in few particle systems Data sample will be increased by factor 100 in next ten years Thank you for your attention Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 50