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

q Multiple scattering expansion in p+A collisions

Excellent channel to constrain quark energy loss effect

Outline

q Summary q Vector boson-tagged jet production in A+A collisions

2

Probe QCD dynamics of coherent and incoherent multiple scattering Nuclear modifications: small-x suppression and large-x enhancement

3

• lnQ2

Y = ln 1 x 4

Parton density increases

§ Multiple scattering expansion § Coherent multiple scattering (small-x)

• I. Vitev, J. Qiu, PLB, 2006

1 Q ⇠ 1 xbPb 2R ✓m p ◆ In forward rapidity region, xb is small, the probe interacts with the whole nucleus coherently. Probing length:

backward forward

5

Single scattering Double scattering

Eh dσ(S) d3Ph = α2

s

S X

a,b,c

Z dz z2 Dc!h(z) Z dx0 x0 fa/p(x0) Z dx x fb/A(x)HU

ab!cd(ˆ

s, ˆ t, ˆ u)δ(ˆ s + ˆ t + ˆ u)

§ multiple scattering expansion

Incoherent multiple scattering in p+A collisions

§ Backward rapidity region – incoherent multiple scattering

dσpA→hX = dσ(S)

pA→hX + dσ(D) pA→hX + · · ·

1 Q ∼ 1 xbPb < 2R ✓m p ◆

In backward rapidity region, xb is large. The probe interacts with the nucleus incoherently, we need to calculate multiple scattering contributions order by

• rder, the leading contribution comes from double scattering.

Probing length:

6

§ Double scattering Feynman diagrams

qq0 → qq0

Initial state double scattering

x1P (x1 + x3)P x′P ′

pc pd k′

g

kg

(M) x1P (x1 + x3)P x′P ′

pc pd k′

g

kg

(L) x1P (x1 + x3)P x′P ′

pc pd k′

g

kg

(R)

Final state double scattering ( as an example)

Eh dσ(D) d3Ph ∝ Z dz z2 Dc!h(z) Z dx0 x0 fa/p(x0) Z dx1dx2dx3T(x1, x2, x3) ✓ −1 2gρσ ◆ 1 2 ∂2 ∂kρ

?∂kσ ?

H(x1, x2, x3, k?)

• k⊥

§ Double scattering cross section (twist-4 contribution)

x1P (x1 + x3)P x′P ′

pc pd k′

g

kg

(M)

kg

x1P

k′

g

(x1 + x3)P x′P ′

pc pd

(L) x1P (x1 + x3)P x′P ′

pc pd kg k′

g

(R)

7

§ Final contribution (incoherent multiple scattering) double scattering hard factor

(a: incoming) (c: outgoing)

Only central-cut contributes. Kang, Vitev, HX, PRD 2013

Eh dσ(D) d3Ph = ✓ 8π2αs N 2

c − 1

◆ α2

s

S X

a,b,c

Z dz z2 Dc!h(z) Z dx0 x0 fa/p(x0) Z dx x δ(ˆ s + ˆ t + ˆ u) × X

i=I,F

2 4x2 ∂2T (i)

b/A(x)

∂x2 − x ∂T (i)

b/A(x)

∂x + T (i)

b/A(x)

3 5 ciHi

ab!cd(ˆ

s, ˆ t, ˆ u) cI = − 1 ˆ t − 1 ˆ s cF = − 1 ˆ t − 1 ˆ u HI

ab→cd =

   CF HU

ab→cd

a=quark CAHU

ab→cd

a=gluon HF

ab→cd =

   CF HU

ab→cd

c=quark CAHU

ab→cd

c=gluon

8

0.5 1 1.5 2 2.5 3 −2.5 −2 −1.5 −1 −0.5

p+Au min. bias, √s = 200 GeV, 2 < pT < 5 GeV

RpA y

h±, ξ2 = 0.12 h±, ξ2 = 0.09 π0, ξ2 = 0.12 π0, ξ2 = 0.09

4π2αs Nc T (I)

q,g/A(x) = 4π2αs

Nc T (F )

q,g/A(x) = ξ2 ⇣

A1/3 − 1 ⌘ fq,g/A(x) ξ2 = 0.09 − 0.12 GeV 2

§ Nuclear modification factor – light hadron

Incoherent multiple scattering leads to significant enhancement effect in intermediate p_T region.

0.6 0.8 1 1.2 1.4 1.6 1.8 2 3 4 5 6 7 8 9 10 11

π0 in p+Au min. bias, √s = 200 GeV, |y| < 0.35

RpA pT (GeV)

PHENIX prel. High-twist ξ2 = 0.12 High-twist ξ2 = 0.09

preliminary preliminary Only one parameter, fixed by DIS data Kang, Vitev, HX, in preparation

9

Heavy meson production in p+A

§ Incoherence multiple scattering in heavy meson production

dσpA→HX = dσ(S)

pA→HX + dσ(D) pA→HX + · · ·

Single scattering Double scattering

HQ HQ

0.5 1 1.5 2 2.5 1 2 3 4 5 6 7 8 9 10

Theory PHENIX -2.0 < y < -1.4 Heavy-flavor muons in d+Au min. bias, √s=200 GeV

pT (GeV) RdAu 0.5 1 1.5 2 2.5 2 4 6 8 10 12 14 16 18 20

Theory ALICE -4.0 < y < -2.96 (preliminary) Heavy-flavor muons in p+Pb min. bias, √s=5020 GeV

pT (GeV) RpPb

Kang, Vitev, HX, PLB 2015

Probe of parton energy loss mechanism

Jet tomography

§ Knowledges of initial states - pp baseline § Jet-medium interaction § Medium evolution

10

11

Ideal channel for hard probes – V+Jet

§ 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 Z

12

10−3 10−2 10−1 100 101 102 50 100 150 200 250 300 350 400 450

γ+jet, √s = 8 TeV R = 0.5, pJ

T > 30 GeV

|yJ| < 2.4, |yγ| < 1.4

dσ/dpγ

T [pb/GeV]

pγ

T CMS PYTHIA-8 p+p

10−5 10−4 10−3 10−2 10−1 100 101 100 200 300 400 500 600 700

Z+jet, √s = 7 TeV R = 0.5, |yJ| < 2.4 71 < mℓℓ < 111 GeV |pℓ

T| > 20 GeV, |yℓ| < 2.4

dσ/dpJ

T [pb/GeV]

pJ

T CMS PYTHIA-8 p+p

§ Parton shower Monte Carlo simulation

Pythia 8: Leading order pQCD + leading logarithmic parton shower Reasonable good description of the LHC p+p data

§ NLO fixed order calculation

Photon+jet: Dai, Vitev, Zhang, PRL 2012 Z+jet: Neufeld, Vitev, PRL 2012

p+p baseline

§ Sudakov resummation

See Guangyou’s talk

13

0.2 0.4 0.6 0.8 1 1.2 50 100 150 200 250 300 350 400 450 500 γ + jet, √s = 5.02 TeV pγ

T > 60 GeV

Fractions pJ

T q + ¯ q q(¯ q)+g

0.2 0.4 0.6 0.8 1 1.2 50 100 150 200 250 300 350 400 450 500 p + p, √s = 5.02 TeV |yJ| < 1.6, pZ

T > 60 GeV

Fractions pJ

T q + ¯ q q(¯ q)+g

Flavor origins of the recoil jets

§ 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

Jet energy loss in nuclear medium

14

§ Parton shower energy dissipation in the QGP

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 Neufeld, Vitev, HX, PRD 2014

15

§ Medium induced radiative energy loss

• SCETG (Idilbi, Majumder, Ovanesyan, Vitev …)
• Medium induced gluon radiation

Ovanesyan, Vitev, 2012 dN g

q,g(ω, r)

dωdr ∝ CRαs Z ∞ d∆z 1 λg(∆z) Z d2q ✓ 1 σel(∆z) dσel(∆z) d2q − δ2(q) ◆ × 2k · q k2(k − q)2 ⇢ 1 − cos (k − q)2 2ω ∆z

V+jet production in heavy ion collisions

§ Suppression of jets (soft gluon approximation)

• probability to lose energy due to multiple gluon emission (Poisson approx.)

10

• 1

1 10 10

• 2

10

• 1

1 q c b g EJ=25 GeV Pb+Pb ε P(ε)

Kang and Vitev, PRD 84,014034 (2011) Z d✏P(✏) = 1

16

Z d✏P(✏)✏ = h∆Ei E

• Fraction of the energy redistributed
• utside the jet
• Superposition of proto-jets of initially higher transverse momentum

1 hNbini dAA dpV

T dpJ T

= X

q,g

Z 1 d✏Pq,g(✏)J(q,g)(✏)dLO+PS

q,g

• pV

T , J(q,g)(✏)pJ T

• dpV

T dpJ T

fq,g(R, ωcoll) = 1 − R R

0 dr

R E

ωcoll dω ωd2N g

q,g

dωdr

R Rmax dr R E

0 dω ωd2N g

q,g

dωdr

PT = Jq,g(✏)pJ

T =

pJ

T

1 − fq,g · ✏

17

Transverse momentum asymmetry (Z+jet)

Part of the parton shower energy is redistributed outside of the jet cone radius, the jets pT are pushed to lower values, with boson pT

• unchanged. This redistribution

results in the downshift of xJV distribution. Pythia pp baseline is narrower than CMS measured xJZ, mainly due to the smearing in CMS measurements.

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 0.5 1 1.5 2

Z+jet √s = 5.02 TeV 1 σZ dσJZ dxJZ

xJZ

CMS p+p CMS Pb+Pb 0 − 30% PYTHIA-8 p+p

• Rad. and Coll. E-loss g=2.0
• Rad. and Coll. E-loss g=2.2

dσ dxJV = Z pJ

T max

pJ

T min dpJ

T

pJ

T

x2

JV

dσ(xJV, pV

T(xJV, pJ T))

dpV

T dpJ T

xJV = pJ

T

pV

T

18

Transverse momentum asymmetry (photon+jet)

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 0.5 1 1.5 2

γ + jet √s = 5.02 TeV 0 − 10% 1 σγ dσJγ dxJγ

xJγ

CMS p+p prel. CMS Pb+Pb prel. 0 − 10% PYTHIA-8 p+p

• Rad. and Coll. E-loss g=2.0
• Rad. and Coll. E-loss g=2.2

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 0.5 1 1.5 2

γ + jet √s = 5.02 TeV 30 − 50% 1 σγ dσJγ dxJγ

xJγ

CMS p+p prel. CMS Pb+Pb prel. 30 − 50% PYTHIA-8 p+p

• Rad. and Coll. E-loss g=2.0
• Rad. and Coll. E-loss g=2.2

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 0.5 1 1.5 2

γ + jet √s = 5.02 TeV 30 − 50% 1 σγ dσJγ dxJγ

xJγ

ATLAS p+p prel. ATLAS Pb+Pb prel. 30 − 50% PYTHIA-8 p+p

• Rad. and Coll. E-loss g=2.0
• Rad. and Coll. E-loss g=2.2

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 0.5 1 1.5 2

γ + jet √s = 5.02 TeV 0 − 10% 1 σγ dσJγ dxJγ

xJγ

ATLAS p+p prel. ATLAS Pb+Pb prel. 0 − 10% PYTHIA-8 p+p

• Rad. and Coll. E-loss g=2.0
• Rad. and Coll. E-loss g=2.2

19

0.5 1 1.5 2 50 100 150 200 250

γ + jet, √s = 5.02 TeV R = 0.3, |yJ| < 1.6, |yγ| < 1.44 40 < pγ

T < 50 GeV

50 100 150 200 250

50 < pγ

T < 60 GeV

50 100 150 200 250

60 < pγ

T < 80 GeV

50 100 150 200 250

80 < pγ

T < 100 GeV

IAA pJ

T(GeV) CMS prel. 0-30%

pJ

T(GeV)

• Rad. E-loss g=2.0
• Rad. and Coll. E-loss g=2.0
• Rad. E-loss g=2.2
• Rad. and Coll. E-loss g=2.2

pJ

T(GeV)

pJ

T(GeV)

Nuclear modification factor IAA (photon+jet)

• larger suppression at the LHC along the main diagonal
• enhancement in the region of pT J < pT V and suppression in the region of pT J > pT V,

which is characteristic of in-medium tagged-jet dynamics. § Kinematic cuts play a role

IAA =

dσAA dpV

T dpJ T

hNbini

dσpp dpV

T dpJ T

20

0.5 1 1.5 2 40 50 60 70 80 90 100 110 120

Z + jet, √s = 5.02 TeV R = 0.3, |yJ| < 1.6 40 < pZ

T < 50 GeV

40 50 60 70 80 90 100 110 120

50 < pZ

T < 60 GeV

40 50 60 70 80 90 100 110 120

60 < pZ

T < 80 GeV

40 50 60 70 80 90 100 110 120

80 < pZ

T < 100 GeV

IAA pJ

T(GeV)

pJ

T(GeV)

• Rad. E-loss g=2.0
• Rad. and Coll. E-loss g=2.0
• Rad. E-loss g=2.2
• Rad. and Coll. E-loss g=2.2

pJ

T(GeV)

pJ

T(GeV)

Prediction of IAA for Z+jet

§ Knowledge of initial states - pp baseline § Jet-medium interaction SCETG § Medium evolution

What’s next?

21

Outlook – precision calculation of p+p baseline

§ NNLO Z+jet

Excellent agreement of NNLO results with CMS data over the entire PTj1 range, not

• nly the overall normalization, but the shape which is significant for the

implementation of parton energy loss effect Boughezal, Liu, Petriello, PRL, PLB 2016

10−5 10−4 10−3 10−2 10−1 100 101 100 200 300 400 500 600 700

Z+jet, √s = 7 TeV R = 0.5, |yJ| < 2.4 71 < mℓℓ < 111 GeV |pℓ

T| > 20 GeV, |yℓ| < 2.4

dσ/dpJ

T [pb/GeV]

pJ

T CMS PYTHIA-8 p+p

22

Outlook - evolution of jet transport parameter

§ Factorization at NLO in cold nuclear matter

• J. Casalderrey-Solana and X.-N. Wang (2008)

Tqg(xB, 0, 0, µ2

f) ≈

Nc 4π2αs fq/A(xB, µ2

f)

Z dy−ˆ q(µ2

f, y−)

µ2 ∂ ∂µ2 Tqg(xB, 0, 0, µ2

f) =

αs 2π Z 1

xB

dx x  Pqq(ˆ x)Tqg(x, 0, 0, µ2) + ∆P qg→qg(ˆ x) ⊗ Tqg + Pqg(ˆ x)Tgg(x, 0, 0, µ2)

• qhat evolution (scale dependence)

Kang, Wang, HX, PRL 2014 Kang, Qiu, Wang, HX, PRD 2016

dh`2

hT i

dzh / Dq/h(z, µ2) ⌦ HLO(x, z) ⌦ Tqg(x, 0, 0, µ2) + ↵s 2⇡ Dq/h(z, µ2) ⌦ HNLO(x, z, µ2) ⌦ Tqg(gg)(x, 0, 0, µ2)

§ qhat evolution

23

Summary

§ The enhancement of particle produced in backward rapidity in pA collisions can be well explained by incoherent multiple scattering. § Strong medium modification effects as observed in XJV and IAA distributions can be explained by energy loss effects. The V+jet production in heavy ion collisions provide us good opportunities to constrain the light quark energy loss mechanism.

24

Summary

§ The enhancement of particle produced in backward rapidity in pA collisions can be well explained by incoherent multiple scattering. § Strong medium modification effects as observed in XJV and IAA distributions can be explained by energy loss effects. The V+jet production in heavy ion collisions provide us good opportunities to constrain the light quark energy loss mechanism.

Thanks!