Jet quenching in pa and AA

Transcription

1 Jet quenching in pa and AA Jefferson Lab Electron Ion Collider User Group Meeting Catholic University of America, Washington D.C, USA July 30 - August 2, 2018

2 Collectivity in AA and pa CMS Collaboration, Phys. Rev. Lett. 115, Collective behavior observed in small systems!2

3 R AA R AA = dn AA /d 2 p T dy hn coll idn pp /dp 2 T dy Suppression of high-pt hadron spectrum AA relative to pp Clear probe of jet quenching ALICE Collaboration, Phys. Lett. B 720 (2013) 52!3

4 R pa Minimum bias ppb Central PbPb ALICE Collaboration, arxiv: Sign of QGP?!4

5 The R AA -high p T -v 2 puzzle!5

6 R AA CMS Collaboration, JHEP (2017) Austin Baty, QM2018!6

7 High-p T V 2 LHC RHIC Central Semiperipheral J. Xu et al. JHEP 1408 (2014) 063!7

8 Formalism C. Andrés et al. Eur. Phys. J. C 76, 475 (2016) Single-inclusive cross section: d AA!h+X dp T dy = Z dx1 x 1 dx 2 x 2 dz z X i,j,k x 1 f i/a (x 1,Q 2 )x 2 f j/a (x 2,Q 2 ) dˆij!k dˆt D k!h (z,µ 2 F ) CTEQ6.6 + EPS09 Fragmentation functions: Z 1 D (med) 1 z k!h (z,µ2 F ) = d P E ( ) 1 D(vac) k!h 1,µ2 F 0 DSS ENERGY LOSS: ASW Quenching Weights (QWs) Probability distribution of a fractional energy loss, parton in the medium!8 = E/E, of the hard

9 Quenching Weights Based on two assumptions: Fragmentation functions are NOT medium-modified Total coherence case: Jets lose energy as a single parton FFs vacuum-like Casalderrey-Solana, Mehtar-Tani, Salgado, Tywoniuk, PLB (2013) KT, HP 2016 Gluon emissions are independent Good approximation for soft radiation J. P. Blaizot, F. Dominguez, E. Iancu and Y. Mehtar-Tani, JHEP (2013)!9

10 Quenching Weights II Computed in the Multiple Soft Scattering approximation (r)n( ) ' 1 2 ˆq( )r2 Perturbative tails neglected Dynamic medium (Scaling relations): ω eff c (x 0, y 0, τ prod, ϕ) = dξ ξ q(ξ) Reff (x 0, y 0, τ prod, ϕ) = 3 2 dξ ξ2 q(ξ) Relation between q and the hydrodynamic properties of the medium q(ξ) = K 2ϵ 3/4 (ξ) Fitting parameter EKRT hydro!10

11 EKRT hydrodynamics EKRT event by event hydrodynamics Initial conditions: minijets + saturation model τ 0 = fm η/s = 0.2 T ch = 175 MeV Phys. Rev. C 93, (2016) T dec = 100 MeV Before thermalization: q(ξ) = q(τ 0 ) for ξ < τ 0 q(ξ) = 0 for ξ < τ 0!11

12 R AA at 200 GeV q(ξ) = q(τ 0 ) for ξ < τ 0 χ 2 to obtain the best value of K. Δχ 2 = 1.!12

13 R AA at 2.76 TeV q(ξ) = q(τ 0 ) for ξ < τ 0 χ 2 to obtain the best value of K. Δχ 2 = 1.!13

14 The scalar product Fourier expansion where: R AA (p T, ϕ) R AA (p T ) = v n hard n=1 (p T ) cos [ nϕ nψn hard (p T )] v hard n (p T ) = 1 2π 2π 0 dϕ cos [ nϕ nψ hard n (p T )] R AA (p T, ϕ) R AA (p T) n = 1 n arctan 2π dϕ sin 0 (nϕ) R AA (p T, ϕ) dϕ cos (nϕ) R AA (p T, ϕ) ψ hard 2π 0 A description of high-p T anisotropic flow needs both hard and soft sectors Scalar product: vsoft n vn exp (p T ) = v hard n (p T ) cos [ n ( ψn soft 2 ( vsoft n ) ψ hard n (p T ))] Average over all the events Matthew Luzum and Jean-Yves Ollitrault, Phys. Rev. C87 (2013) J. Noronha-Hostler et al., Phys. Rev. Lett. 116, (2016)!14

15 High-p T V 2 v n (p T ) = vsoft n vn hard (p T ) cos(n[ ψn soft (v soft n ) 2 ψ hard n ]) Hydro: v-usphydro PbPb 2.76 TeV τ 0 = 0.6 fm McGlauber η/s = 0.08 T F = 130 MeV MCKLN η/s = 0.11 T F = 120 MeV de Energy loss dl L J. Noronha-Hostler et al. Phys. Rev. Lett. 116, (2016) NO energy loss before thermalization!15

16 High-p T V 2 η/s = 0.2 τ 0 = fm Preliminary!!16

17 Dependence on τ 0!17

18 R AA η/s = 0.2 T dec = 175 MeV Preliminary! *Only central values plotted 18

19 High-p T V 2 η/s = 0.2 T dec = 175 MeV Preliminary!!19

20 Limitations Perturbative tails neglected Only included in CUJET and AMY ASW QWs supported by coherence: if coherence is broken they could fail Scaling relations only proven for q 1/τ α Collisional energy loss neglected!20

21 Open questions Is the scalar product the complete solution to the R AA -v 2 puzzle? When does the energy loss start? Energy loss before thermalization? Do the initial conditions of the hydro play a key role? And the freeze-out? And the viscosity? Could high-p T harmonics be used to constrain the detailed mechanism of energy loss?!21

22 Jet quenching in pa?!22

23 High-p T v 2 in ppb ppb 5.02 TeV 0-5% MARTINI + MUSIC C. Park et al. Nucl. Part. Phys. Proc. 289(2017)!23

24 Backup slides!24

25 Quenching Weights P(ΔE) = 1 n=0 n! [ dω i i=1 n di (med) (ω i ) dω ] δ ( ΔE n i=1 ω i ) exp 0 dω di(med) dω! di(med) d! = sc R (2 ) 2! 2 2Re Z 1 0 dy l Z 1 y l Z dȳ l du Z! 0 dk? e ik? u e u=r(ȳ l 2 Z ) Dr exp 4i y=0 Z ȳ l y l d 1 2! 2 1R ȳ l d n( ṙ 2 n( ) 3 5!25

26 arxiv:hep-ph/ , R. Baier.!26

27 EKRT Hydro Phys. Rev. C 93, (2016)!27