Recent Results and Surprises from Ultrarelativistic Heavy-Ion - PowerPoint PPT Presentation

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

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

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

Centrality & Glauber • Activity depends strongly on impact parameter b – Few to 1600 nucleon-nucleon collisions Multiplicity vs. b Central Peripheral b ~ 0 b ~ R e.g. “0 - 5%” e.g. “60 - 90%” • Accessible experimentally – N ch and S E T grows with decreasing b • Soft (low p T ) ~ participants (N part ) from Glauber • Hard (high p T ) ~ collisions (N coll ) calculations / MC Plot: A. Toia Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 4

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 y – Initial state density fluctuations  higher-order anisotropies x • Fourier coefficients v n of single-particle distribution wrt n th order participant plane   e 3 dN       A 1 2 v cos n ( )  e 4 n n n d 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

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

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

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

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) Particle yields well described by equilibrium thermal models over 7 orders of magnitude p f p L X W K K 0 K * d 3 L H 3 He Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 9

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

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

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

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

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

g -Jet Correlations p T, g g • Photon: fixes initial parton energy dN/dx J g vs. x J g p T,jet Significant difference central Pb-Pb vs. pp ATLAS-CONF-2018-009 x J g = p T,jet / p T, g Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 15

dN/dz g vs. z g Jet Substructure PRL 120 (2018) 142302 • 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 min( p , p )  T 1 T 2 z  g p p T 1 T 2 asymmetric splittings symmetric splittings  increase  decrease Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 16

v 2 vs. p T Charm • 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 0 vs. p T D s /D 0 vs. p T 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 Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 17

Y Suppression • Sequential suppression for Y family – Y(3S) limit for now • 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-16-023 arXiv:1805.04387 Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 18

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

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

g 112 vs. centrality Earlier Results PRL110 (2013), 012301 • 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 g 112 /v 2 vs. N ch PRL118 (2017), 122301 • Issue: Large backgrounds due to local charge conservation (resonance decays, momentum conservation, parton fragmentation) Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 21

Event Shape Engineering nucl-ex/0701025 • Large event-by-event variation of v n • 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 round Small q 2  small v 2 PRC 93, 034916 (2016) peripheral central • CME backgrounds proportional to v 2 – Possibility to constrain background Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 22

f CME vs. centrality Latest Results ALICE, PLB 777, 151 • 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 CMS, PRC 97 (2018) 044912 Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 23

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

Paradigm Shift   dN       A 1 2 v cos n ( )  n n n d 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

Two-Particle Correlation Away-side jet + flow ( D ~ p , elongated in Dh ) h 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