Incoherent multiple scattering in pA and Vector boson-tagged jet - PowerPoint PPT Presentation

Incoherent multiple scattering in pA and Vector boson-tagged jet production in AA Hongxi Xing NU/ANL In collaboration with Z-B. Kang and I. Vitev Santa Fe Jet and Heavy Flavor 2017

Outline q Multiple scattering expansion in p+A collisions Nuclear modifications: small-x suppression and large-x enhancement Probe QCD dynamics of coherent and incoherent multiple scattering q Vector boson-tagged jet production in A+A collisions Excellent channel to constrain quark energy loss effect q Summary 2

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§ Multiple scattering expansion Y = ln 1 forward x ����������� ������� ����������������������� ���������������� ������� Parton density increases �������������� backward ln Q 2 I. Vitev, J. Qiu, PLB, 2006 § Coherent multiple scattering (small-x) ✓ m ◆ 1 1 Probing length: � 2 R Q ⇠ x b P b p In forward rapidity region, x b is small, the probe interacts with the whole nucleus coherently. 4

Incoherent multiple scattering in p+A collisions § Backward rapidity region – incoherent multiple scattering Single scattering Double scattering ✓ m ◆ 1 1 Probing length: < 2 R Q ∼ x b P b p In backward rapidity region, x b is large. The probe interacts with the nucleus incoherently, we need to calculate multiple scattering contributions order by order, the leading contribution comes from double scattering. § multiple scattering expansion d σ pA → hX = d σ ( S ) pA → hX + d σ ( D ) pA → hX + · · · Z dz Z dx 0 Z dx d σ ( S ) = α 2 s X x f b/A ( x ) H U s, ˆ s + ˆ x 0 f a/p ( x 0 ) z 2 D c ! h ( z ) ab ! cd (ˆ t, ˆ u ) δ (ˆ t + ˆ u ) E h d 3 P h S a,b,c 5

§ Double scattering Feynman diagrams ( as an example) qq 0 → qq 0 Initial state double scattering x ′ P ′ x ′ P ′ x ′ P ′ p c p c p c k g k ′ k g k ′ k ′ k g g g g p d p d p d ( x 1 + x 3 ) P x 1 P ( x 1 + x 3 ) P x 1 P ( x 1 + x 3 ) P x 1 P ( L ) ( R ) ( M ) Final state double scattering x ′ P ′ x ′ P ′ x ′ P ′ p c p c p c p d p d p d k ′ k ′ k ′ k g k g k g ( x 1 + x 3 ) P ( x 1 + x 3 ) P ( x 1 + x 3 ) P x 1 P x 1 P x 1 P g g g ( M ) ( L ) ( R ) § Double scattering cross section (twist-4 contribution) Z dz Z dx 0 d σ ( D ) ∂ 2 ✓ − 1 ◆  1 � Z x 0 f a/p ( x 0 ) z 2 D c ! h ( z ) dx 1 dx 2 dx 3 T ( x 1 , x 2 , x 3 ) H ( x 1 , x 2 , x 3 , k ? ) E h 2 g ρσ ∝ d 3 P h ∂ k ρ 2 ? ∂ k σ ? k ⊥ 6

§ Final contribution (incoherent multiple scattering) Kang, Vitev, HX , PRD 2013 ✓ 8 π 2 α s ◆ α 2 Z dz Z dx 0 Z dx d σ ( D ) s X s + ˆ = z 2 D c ! h ( z ) x 0 f a/p ( x 0 ) x δ (ˆ t + ˆ u ) E h d 3 P h N 2 c − 1 S a,b,c 2 3 4 x 2 ∂ 2 T ( i ) ∂ T ( i ) b/A ( x ) b/A ( x ) + T ( i ) X 5 c i H i s, ˆ b/A ( x ) ab ! cd (ˆ t, ˆ u ) − x × ∂ x 2 ∂ x i = I,F Only central-cut contributes. c I = − 1 t − 1 ˆ ˆ s c F = − 1 t − 1 ˆ ˆ u  C F H U a=quark ab → cd double scattering  H I ab → cd = (a: incoming) C A H U a=gluon hard factor  ab → cd C F H U  c=quark ab → cd  H F ab → cd = (c: outgoing) C A H U c=gluon  ab → cd 7

§ Nuclear modification factor – light hadron Kang, Vitev, HX , in preparation 1 . 8 3 h ± , ξ 2 = 0 . 12 R pA R pA PHENIX prel. preliminary High-twist ξ 2 = 0 . 12 preliminary h ± , ξ 2 = 0 . 09 High-twist ξ 2 = 0 . 09 π 0 , ξ 2 = 0 . 12 1 . 6 2 . 5 π 0 , ξ 2 = 0 . 09 1 . 4 2 1 . 2 1 . 5 1 1 0 . 8 π 0 in p+Au min. bias, √ s = 200 GeV, | y | < 0 . 35 p+Au min. bias, √ s = 200 GeV, 2 < p T < 5 GeV 0 . 6 0 . 5 2 3 4 5 6 7 8 9 10 11 − 2 . 5 − 2 − 1 . 5 − 1 − 0 . 5 0 p T (GeV) y 4 π 2 α s q,g/A ( x ) = 4 π 2 α s q,g/A ( x ) = ξ 2 ⇣ ⌘ T ( I ) T ( F ) A 1 / 3 − 1 f q,g/A ( x ) N c N c Only one parameter, fixed by DIS data ξ 2 = 0 . 09 − 0 . 12 GeV 2 Incoherent multiple scattering leads to significant enhancement effect in intermediate p_T region. 8

Heavy meson production in p+A § Incoherence multiple scattering in heavy meson production d σ pA → HX = d σ ( S ) pA → HX + d σ ( D ) pA → HX + · · · Single scattering Double scattering H Q H Q Kang, Vitev, HX , PLB 2015 2.5 2.5 R dAu R pPb PHENIX -2.0 < y < -1.4 ALICE -4.0 < y < -2.96 (preliminary) 2 Theory 2 Theory 1.5 1.5 1 1 0.5 0.5 Heavy-flavor muons in d+Au min. bias, √ s=200 GeV Heavy-flavor muons in p+Pb min. bias, √ s=5020 GeV 0 0 0 1 2 3 4 5 6 7 8 9 10 0 2 4 6 8 10 12 14 16 18 20 p T (GeV) p T (GeV) 9

Probe of parton energy loss mechanism Jet tomography Knowledges of initial states - pp baseline § Jet-medium interaction § Medium evolution § 10

Ideal channel for hard probes – V+Jet Z § Electroweak bosons are not affected by the hot dense medium § Provide good constraints on the energy and flavor origins of the away-side parton shower § Uncertainties from background contributions are significantly reduced 11

p+p baseline § NLO fixed order calculation § Sudakov resummation Photon+jet: Dai, Vitev, Zhang, PRL 2012 See Guangyou’s talk Z+jet: Neufeld, Vitev, PRL 2012 § Parton shower Monte Carlo simulation Pythia 8: Leading order pQCD + leading logarithmic parton shower 10 2 10 1 CMS CMS PYTHIA-8 p+p PYTHIA-8 p+p 10 0 10 1 γ +jet, √ s = 8 TeV Z+jet, √ s = 7 TeV R = 0 . 5 , p J R = 0 . 5 , | y J | < 2 . 4 T > 30 GeV T [pb / GeV] T [pb / GeV] 10 − 1 | y J | < 2 . 4 , | y γ | < 1 . 4 71 < m ℓℓ < 111 GeV | p ℓ T | > 20 GeV , | y ℓ | < 2 . 4 10 0 10 − 2 d σ / dp J d σ / dp γ 10 − 1 10 − 3 10 − 2 10 − 4 10 − 5 10 − 3 0 100 200 300 400 500 600 700 0 50 100 150 200 250 300 350 400 450 p J T p γ T Reasonable good description of the LHC p+p data 12

Flavor origins of the recoil jets 1 . 2 1 . 2 q + ¯ q + ¯ γ + jet , √ s = 5 . 02 TeV p + p , √ s = 5 . 02 TeV q q q (¯ q )+g q (¯ q )+g | y J | < 1 . 6 , p Z p γ T > 60 GeV T > 60 GeV 1 1 0 . 8 0 . 8 Fractions Fractions 0 . 6 0 . 6 0 . 4 0 . 4 0 . 2 0 . 2 0 0 50 100 150 200 250 300 350 400 450 500 50 100 150 200 250 300 350 400 450 500 p J p J T T § leading logarithmic approximation § Isolated photon: minimize contributions from jet fragmentation § Both photon+jet, Z+jet productions are dominated by q+g channel -> the produced jet originates from light quark, good probe of quark energy loss effect 13

Jet energy loss in nuclear medium Final-state quark-gluon plasma effects include medium-induced parton splitting and the dissipation of the energy of the parton shower through collisional interactions in the strongly-interacting matter. Neufeld, Vitev, PRC 2012 Parton shower energy dissipation in the QGP § Neufeld, Vitev, HX , PRD 2014 14

Medium induced radiative energy loss § SCET G (Idilbi, Majumder, Ovanesyan, Vitev …) • Medium induced gluon radiation • Ovanesyan, Vitev, 2012 Z ∞ dN g q,g ( ω , r ) 1 Z ✓ 1 d σ el ( ∆ z ) ◆� d 2 q − δ 2 ( q ) C R α s d ∆ z ∝ d ω dr λ g ( ∆ z ) σ el ( ∆ z ) d 2 q 0  ( k − q ) 2 ⇢ �� 2 k · q 1 − cos ∆ z × k 2 ( k − q ) 2 2 ω 15

V+jet production in heavy ion collisions Suppression of jets (soft gluon approximation) § Z 1 d ✏ P q,g ( ✏ ) J ( q,g ) ( ✏ ) d � LO+PS � p V T , J ( q,g ) ( ✏ ) p J � d � AA 1 X q,g T = dp V T dp J dp V T dp J h N bin i 0 T T q,g Superposition of proto-jets of initially higher transverse momentum • p J P T = J q,g ( ✏ ) p J T T = 1 − f q,g · ✏ Fraction of the energy redistributed • outside the jet R R R E ω d 2 N g 0 dr ω coll d ω q,g f q,g ( R, ω coll ) = 1 − d ω dr R R max R E 0 d ω ω d 2 N g dr q,g 0 d ω dr probability to lose energy due to multiple gluon emission (Poisson approx.) • 10 P( ε ) Pb+Pb d ✏ P ( ✏ ) ✏ = h ∆ E i Z Z d ✏ P ( ✏ ) = 1 E 1 Kang and Vitev, PRD 84,014034 (2011) g -1 10 q c E J =25 GeV b -2 -1 10 10 1 ε 16

Transverse momentum asymmetry (Z+jet) Z p J max p J d σ (x JV , p V T (x JV , p J x JV = p J T )) d σ T min dp J T T = T x 2 d x JV dp V T dp J p V p J JV T T T 1 . 8 Part of the parton shower energy is CMS p+p CMS Pb+Pb 0 − 30% 1 . 6 Z+jet redistributed outside of the jet cone √ s = 5 . 02 TeV PYTHIA-8 p+p Rad. and Coll. E-loss g=2.0 radius, the jets p T are pushed to 1 . 4 Rad. and Coll. E-loss g=2.2 lower values, with boson p T 1 . 2 unchanged. This redistribution 1 d σ JZ dx JZ results in the downshift of x JV 0 . 8 σ Z 1 distribution. 0 . 6 0 . 4 Pythia pp baseline is narrower than 0 . 2 CMS measured x JZ, mainly due to the 0 smearing in CMS measurements. 0 0 . 5 1 1 . 5 2 x JZ 17