Heavy Ions at the LHC: First Results

Transcription

1 Heavy Ions at the LHC: First Results Thomas Schaefer North Carolina State University

2 Heavy ion collision: Geometry R Au /γ y R Au x b z rapidity : y = 1 2 log ( E + pz E p z ) transverse momentum : p 2 T = p 2 x + p 2 y

3 Bjorken expansion Experimental observation: At high energy ( y ) rapidity distributions of produced particles (in both pp and AA) are flat dn dy const Physics depends on proper time τ = t 2 z 2, not on y All comoving (v = z/t) observers are equivalent Analogous to Hubble expansion

4 Bjorken expansion τ =const t η =const hadrons QGP pre equilibrium projectile target z

5 Bjorken expansion: Hydrodynamics Boost invariant expansion u µ = γ(1,0,0, v z ) = (t/τ, 0,0, z/τ) solves Euler equation (no longitudinal acceleration) µ (su µ ) = 0 Solution for ideal Bj hydrodynamics s(τ) = s 0τ 0 τ d dτ [τs(τ)] = 0 T = const τ 1/3 Exact boost invariance, no transverse expansion, no dissipation,...

6 Numerical estimates Total entropy in rapidity interval [y, y + y] S = sπr 2 z = sπr 2 τ y = (s 0 τ 0 )πr 2 y R Use S/N 3.6 s 0 τ 0 = 1 πr 2 S y z = τ y s 0 = 3.6 ( dn πr 2 τ 0 dy ) Bj estimate Depends on initial time τ 0. Assume QGP equation of state s 0 = 2π2 45 N dt 3 0 Fixes initial temperature (and energy density)

7 BNL and RHIC

8 Multiplicities 400 Au+Au 19.6 GeV 600 Au+Au 130 GeV dn ch /dη dn ch /dη η η % 6-15% Au+Au 200 GeV 25-35% 35-45% dn ch /dη % 45-55% η Phobos White Paper (2005)

9 Bjorken expansion

10 LHC: Pb+Pb s NN = 2.76 TeV

11 Predictions: Limiting fragmentation

12 Result vs Predictions: mini-jets, color glass,...

13 Alice results: Scaling with energy

14 What does it mean? Factor 2.2 in multiplicity: factor 2.85 in energy density, factor 1.3 in temperature (at fixed τ 0 ) AA pp: extra multiplicity per participant pair. Simple saturation works better than improved saturation.

15 Chemical equilibrium at freezeout Ratio 1 s NN =130 GeV T (MeV) crossover quark gluon plasma end point π - π + Data Model T=165.5, µ b =38 MeV - K K + p p Λ Λ Ξ Ξ Ω Ω K + π + - K π - p π - Λ π - Ξ π - Ω π - φ K - * K K NA49 SIS, AGS RHIC hadrons µ B (MeV) Andronic et al. (2006)

16 Collective behavior: Radial flow Radial expansion leads to blue-shifted spectra in Au+Au Au+Au p+p 1/(2π) d 2 N / (m T dm T dy) [c 4 /GeV 2 ] STAR preliminary Au+Au central s NN = 200 GeV K - π - 1/(2π) d 2 N / (m T dm T dy) [c 4 /GeV 2 ] K - STAR preliminary p+p min. bias s NN = 200 GeV π - p 10-2 p m T - m 0 [GeV/c 2 ] m T - m 0 [GeV/c 2 ] v T 0.6c! m T = p 2 T + m2

17 Collective behavior: Elliptic flow Hydrodynamic expansion converts coordinate space anisotropy to momentum space anisotropy Anisotropy Parameter v Hydro model π K p Λ PHENIX Data π + +π K +K p+p STAR Data 0 K S Λ+Λ b Transverse Momentum p T source: U. Heinz (2005) dn p 0 d 3 p = v 0 (p ) (1 + 2v 2 (p ) cos(2φ) +...) pz =0 (GeV/c)

18 Elliptic flow II: Multiplicity scaling v 2 /ε 0.25 HYDRO limits E lab /A=11.8 GeV, E877 E lab /A=40 GeV, NA E lab /A=158 GeV, NA49 s NN =130 GeV, STAR s NN =200 GeV, STAR Prelim (1/S) dn ch /dy source: U. Heinz (2005)

19 Viscous Corrections Longitudinal expansion: Bj expansion solves Navier-Stokes equation ( 4 entropy equation 1 ds s dτ = η + ζ ) τ stτ Viscous corrections small if 4 3 η s + ζ s (Tτ) early Tτ τ 2/3 η/s const η/s < τ 0 T 0 late Tτ const η T/σ τ 2 /σ < 1 Hydro valid for τ [τ 0, τ fr ]

20 Viscous corrections to T ij (radial expansion) T zz = P 4 3 η τ T xx = T yy = P increases radial flow (central collision) decreases elliptic flow (peripheral collision) Modification of distribution function δf = 3 8 Correction to spectrum grows with p 2 Γ s T 2 f 0(1 + f 0 )p α p β α u β η τ δ(dn) dn 0 = Γ s 4τ f ( p T ) 2

21 Elliptic flow III: Viscous effects v 2 (percent) ideal η/s=0.03 η/s=0.08 η/s=0.16 STAR p T [GeV] Romatschke (2007), Teaney (2003)

22 Elliptic flow IV: Systematic trends Deviation from ideal hydro increases for more peripheral events increases with p source: R. Snellings (STAR)

23 Elliptic flow V: Predictions for LHC e p /e x ( v 2 /e x ) η/s = 10-4 η/s = 0.08 η/s = 0.16 RHIC Glauber RHIC CGC LHC Glauber LHC CGC PHOBOS/CGC PHOBOS/Glauber (1/S overlap )(dn ch /dy)[fm -2 ] Romatschke, Luzum (2009) Busza (QM 2009)

24 Elliptic flow VI: Recombination quark number scaling of elliptic flow Anisotropy Parameter v Hydro model π K p Λ PHENIX Data STAR Data π + +π h +h + - K +K K 0 S p+ p Λ+ Λ Transverse Momentum p T (GeV/c) v 2 /n Polynomial Fit π + +π - 0 K S p+ p Λ+Λ STAR Preliminary + - K +K Ξ+Ξ (qq) (mes) p mes = 2pqu Data/Fit (qqq) (bar) p bar = 3pqu p T /n (GeV/c)

25 Alice flow

26 Flow excitation function

27 What does it mean? Hydro rules! RHIC data not an accident. Differential v 2 exactly equal to RHIC (!?) Integrated v 2 somewhat high: mean p T increase? acceptance?

28 Jet quenching R AA = n AA N coll n pp source: Akiba [Phenix] (2006)

29 Jet quenching II Disappearance of away-side jet φ) dn/d( φ) dn/d( 1/N 1/NTRIGGER Trigger d+au FTPC-Au 0-20% p+p min. bias Au+Au Central φ (radians) source: Star White Paper (2005)

30 Jet quenching III: The Mach cone azimuthal multiplicity dn/dφ (high energy trigger particle at φ = 0) wake of a fast quark in N = 4 plasma Chesler and Yaffe (2007) source: Phenix (PRL, 2006), W. Zajc (2007)

31 Jet quenching: Theory 10.0 energy loss governed by RHIC data ˆq = ρ q 2 dq 2 dσ dq 2 q (GeV 2 /fm) pion gas QGP (GeV/fm 3 ) 0.1 cold nuclear matter larger than pqcd predicts? relation to η? (ˆq 1/η?) also: large energy loss of heavy quarks source: R. Baier (2004)

32 ATLAS mono-jet Event display of a highly asymmetric dijet event, with one jet with E T > 100 GeV and no evident recoiling jet, and with high energy calorimeter cell deposits distributed over a wide azimuthal region. Only tracks with p T > 2.6 GeV.

33 What does it mean? Jets can be identified in AA environment. E T > 100 GeV jet is stopped! Proof of principle, detailed analysis needed.