1 / 25

Medium information from harmonic flow & jet quenching in relativistic HI collisions

Medium information from harmonic flow & jet quenching in relativistic HI collisions. Subrata Pal Tata Institute of Fundamental Research, Mumbai, India. Outline A brief history of jet quenching in HI collision AMPT model updated with jets & new PDF

lyndon
Télécharger la présentation

Medium information from harmonic flow & jet quenching in relativistic HI collisions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Medium information from harmonic flow & jet quenching in relativistic HI collisions Subrata Pal Tata Institute of Fundamental Research, Mumbai, India • Outline • A brief history of jet quenching in HI collision • AMPT model updated with jets & new PDF • AMPT predictions versus RHIC & LHC data: • Particle yield, Anisotropic flow, Jet quenching • Conclusions

  2. Jet quenching schematic view of jet production Leading hadron + pT hadrons N N -pT hadrons Balancing hadron PHENIX: PRL 88 (2002) 022301. STAR: PRL 91 (2003) 172302. • High pT > 2 GeV back-to-back partons (jets) produced from initial hard NN collision • Fragmentation of the jets produce a cluster of high pT hadrons (also called jets!) • p+p or d+A: no QGP formed, both the back-to-back jets survive • Central A+A: If QGP formed, one or both jets in the dense partonic medium suffer energy loss– jet quenching RAA(pT) =1: Particle yield in A+A collision is simply superposition of independent p+p collisions. RAA(pT) 1 at high pT : Deviation from this simple superposition concept (viz final-state effects). High pT hadron yield in central Au+Au suppressed compared to p+p collision in-medium jet energy loss

  3. Jet formalism Inclusive hadron distribution – calculable in pQCD p+p colln: zc = ph/pq Parton distribution fns Perturbative cross section Fragmentation fn Jet quenching: pQCD energy loss ΔEof partons by gluon bremsstrahlung ΔE A+A colln: zc=ph/(pq-ΔE) Gyulassy, Levai, Vitev NPB 594 (2001) 371 Jet quenching also sensitive to: Initial spatial parton distribution; Nuclear shadowing of PDF; Collective flow sQGP + large soft particle production  nonperturbative physics systematic model study reqd.

  4. ΔE AMultiPhase Transport model (AMPT) Inclusive hadron distribution – calculable in pQCD Energy loss Lin, Ko, Li, Zhang, SP, PRC72 (2005) 064901 • Initial particle distribution obtained from updated HIJING 2.0 model • Strings from HIJING converted to valence (anti)quarks – String Melting • Partons scatter in ZPC model with elastic scattering cross section: • Phase-space coalescence of freeze-out partons produce the hadrons • Hadrons evolve with (in)-elastic scatterings via ART transport model σ≈ 9s2/μ2

  5. Hard jets & its energy loss in AMPT Momentum distributionof hard partons from LO pQCD in p+p collision GRV94 Gaussian NLO SP, Pratt, PLB 574 (2003) 14 Total energy loss by a jet of energy E via gluon radiation SP, PRC 80 (2009) 041901(R) Parton density Number of gluons emittedfrom ΔE is related to entropy increase ΔS T = ε(r,τ)/3ρ(r,τ) From parton cascade σ ≈ 9s2/2μ2 Radiated gluons scatter in medium with Parton hadron duality: Ng → Nπ

  6. AMPT with updated HIJING 2.0 Deng,Wang, Xu, PLB 701 (2011) 133 • GRV parametrization of parton distribution function • c.m. energy dependence in 2-component HIJING 2.0 p0 = 2 GeV/c PDF in nucleus: Impact parameter dependent shadowing sq = 0.1 (fixed) from deep-inelastic-scattering data off nuclear targets. sgfitted to centrality dependence of measured dNch/dy in A+A collision.

  7. dNch/dy in HIC at RHIC & LHC (0-5)% Centrality Parameters in AMPT In string fragmentation function, Default HIJING: a=0.9, b=0.5 GeV-2. s=0.33, =3.226 fm-1   = 1.5 mb HIJING: dNch/dη||η|0.5 = 705 (RHIC) = 1775 (LHC) • Parton scatterings lead to 15% decrease in dNch/dy at RHIC & LHC!! • Hadron scattering insensitive to dN/dη. AMPT hadron yield ratios at LHC SP, Bleicher, PLB 709 (2012) 82

  8. Centrality dependence of dNch/dη Au+Au collisions at RHIC: Measured charged hadron multiplicity density per participant pair constrains gluon shadowing parameter sg= 0.10 - 0.17 Pb+Pb collisions at LHC: Stronger centrality dependence in ALICE data due to large minijet production (at small x) gives a stringent constraint on sg≈0.17 [5] HIJING2 (w/o FSI) fits with sg=0.20 - 0.23 Deng,Wang, Xu, PLB 701 (2011) 133 ALICE Collab, PRL 106 (2011) 032301

  9. z y x 2 3 4 Anisotropic flow vn in HI collision vn are Fourier coeff in φ distribution of particles relative to the Reaction Plane Elliptic flow v2: initial spatial ellipticity converted to final momentum anisotropy by interaction among particles Ollitrault, PRD 46 (1992) 229 RPcannot be measured directly. Estimated by 2 Origin of triangular flow v3: fluctuations in the position of participant nucleons 2, 4 particle azimuthal correlations: Alver & Roland, PRC 81 (2010) 054905 Event Plane angle: nonflow part Odd harmonics = 0 Borghini et al, PRC 64 (2001) 054901 Odd harmonics ≠ 0

  10. Anisotropic flow @ RHIC SP, Bhalerao, in prep. Ma, Wang, PRL 106 (2011) 162301 AMPT b=0 • v2 > v3 > v4 in AMPT (b0) describes RHIC data • Initial spatial asymmetry and matter flow in AMPT consistent with RHIC

  11. Anisotropic flow @ LHC 0-5% centrality 30-40% centrality ALICE, PRL 107 (2011) 032301 • <vn> slightly larger at LHC due to large <pT> • Magnitude, pattern of vn(pT) at RHIC & LHC similar! At LHC larger densitybut faster expansion • Av.v2,v3,v4 described by AMPT over large centrality RHIC

  12. Charged particle spectra @ RHIC & LHC STAR Collab, PRL 91 (2003) 0172302 ALICE Collab, PLB 696 (2011) 30 p+p, Au+Au @ RHIC AMPT spectra agrees with STAR data up to high pTfor both peripheral & central collisions p+p @ LHC AMPT spectra is less steep at high pT compared to the ALICE data obtained from interpolation between s = 0.9 and 7 TeV • Pb+Pb @ LHC • Peripheral collision: AMPT spectra agrees with ALICE data. • 0-5% central collision: Enhanced energy loss in AMPT even withelasticparton-parton scattering. SP, Bleicher, PLB 709 (2012) 82

  13. 4 <pTtrig<6 GeV/c Trig + x Momentum conservation away -x Jet quenching and lost jet remnants Dijet asymmetry ratio Au+Au @ 200 GeV at b=0 fm Zhang et al, PRL 98 (2006) Overall momentum imbalance: projection of all track pT on pT,trig Trigger SP, Pratt, PLB 574 (2003) 14 0-30% Pb+Pb @ 2.76 TeV dN/dpx= Trigger Away side Trigger side  Trigger jet is surface biased Unbalanced jet Balanced jet Away side:energy lost by high pT partons is converted to soft particles with |px| < 600 GeV/c Low pT, momentum balanced in an event Out-of-cone low pT particles balance the event In-cone large mom. imbalance at high pT

  14. pT(trig)  pT(assoc) Dihadron azimuthal angle correlation SP, PRC 80 (2009) 041901(R) Data: PHENIX, PRC 78 (2008) 014901 = 3-4 GeV/c Background v2 subtracted p+p in pQCD agrees with data Default:away-side hadrons peak → small rescatterings and dNg/dy String melting Low pT:away-side jet traverse into dense medium, scatter & thermalize → broad distribution around Δφ = π High pT:Jets produced near surface → “conical flow” peaks at Δφ = π ± 1 Data p+p: peaks at near side & away-side (Δφ≈π) Au+Au: away side peak shifts to Δφ≈π± 1.2 SM with σ = 10 mb explains Au+Au data

  15. Flow contribution to dihadron correlation PHENIX, PRC 78 (2008) 014901 Ma & Wang, PRL 106 (2011) 162301 AMPT : On subtraction of harmonic flows vn (n=2-6), away side peaks suppressed  v3 contributes most to double peak PHENIX data: Au+Au: away side peaks at Δφ≈π±1.2  only v2 contribution subtracted

  16. Jet quenching data in HI Collision Medium effects at high pT quantified by nuclear modification factor: SPS energy: rising/flat RAA≈ 1 with pT little/no jet energy loss RAA(LHC) < RAA(RHIC) at pT < 6 GeV/c: Enhanced energy loss as the medium is denser at LHC than at RHIC Rise of RAA at pT > 7 GeV/c due to slow fall with increasing pT of primary jet spectra (pQCD physics)

  17. Jet quenching at RHIC & LHC Au+Au @ 200 GeV • RAAin AMPT describes RHIC data  Model parton energy loss consistent with that of the evolving medium (RAA)ch > (RAA)0 Larger (anti)baryon yield than 0from parton coalescence Pb+Pb @ 2076 GeV • Stronger suppression in AMPT for 0-5% centrality due to significant jet energy loss in a dense matter: •   c: [ c(LHC)≈ 2c(RHIC) ] • Recombination of hard partons in AMPT not enough to enhance RAA. • Medium at LHC less opaque?? • Smaller RAA in AMPT leaves no room for model study of energy loss by gluon radiation?? ALICE: PLB 696 (2011) 30

  18. Is large E-loss in models generic at LHC? Horowitz, Gyulassy, NPA 872(2011) 265 Further experimental results and theoretical investigations required • Control d+Pbexpt required to get sg. • Decrease in saturation parameter sg enhance RAA but destroys dNch/dy fit. • Understanding the medium opacity. • Coupling of geometry to flow. • Approximations in E-loss equation. Suggestions:

  19. Modification of jet-medium coupling s pQCD screening mass (T dependent) Parton elastic scattering cross section Estimate initial Ti at RHIC & LHC: Fixed values used in AMPT at RHIC & LHC: Scaling reln (~10% viscous entropy production) s = 0.33, =3.22 fm-1   = 1.5 mb Gyulassy, Matsui, PRD 29 (1984) 419 SP, Pratt, PLB 578 (2004) 310 QGP with massless gas of light q, q-bar (0-5)% exptdNch/dyy≈0≈687 (RHIC), 1601(LHC) i = 1fm/c ≈ 320 MeV  ≈ 1.4 mb(RHIC) ≈436 MeV ≈0.76 mb(LHC) Ti s= 0.33 Quenching at LHC suggest thermal suppression of QCD coupling s by ~30% Alternative: =3.22 fm-1 isconstant at RHIC & LHC To get  = 0.76 mb at LHC requires s = 0.24

  20. Summary • dNch/dy at RHIC and LHC quite sensitive to parton scattering • dNch/dy versus Centrality data at LHC strongly constrains sg = 0.17 • AMPT fluctuations and matter flow agree with measured v2 > v3 > v4 • AMPT jet quenching consistent with RHICdata at all centralities • Quenching data at LHC suggests thermal decrease in s by ~30% • Lost jet energy & its medium excitations re-appear as soft particles

  21. RESERVE SLIDES

  22. AMPT comparison with p+p collision data Measured charged hadron spectra well described in AMPT model up to high pT pT in AMPT underpredict data  Hadron production by recombination is not efficient in p+p collision

  23. Elliptic flow (v2) in AMPT model Charged hadrons Lin, Ko, PRC 65 (2002) 034904 Lin, Ko, Li, Zhang, SP, PRC72 (2005) 064901 • String melting enhances parton density • v2well explained with string melting & parton recombination • v2 sensitive to parton elastic σqq→qq (= 6 mb best fit) → dense partonic medium required to explain v2

  24. Origin of v2, v3 in AMPT Alver & Roland, PRC 81 (2010) 054905 <v2>  2: Final elliptic flow proportional to initial eccentricity <v3>  3: Final triangular flow proportional to initial triangularity

  25. h spectra in pp and RAA @ LHC • charged particle spectra • in pp at √s = 0.9, 2.76, 7 TeV H. Appelshäuser, Talk at Quark Matter 2011

More Related