Dihadron correlations at e RHIC and Monte Carlo

Dihadron correlations at e. RHIC and Monte Carlo development Liang Zheng BNL/IOPP, CCNU 7/31/2012 RBRC Forward physics workshop

Outline • Motivation • RHIC forward d. Au program • Dihadron correlation at future e. RHIC – Monte Carlo results – Compared with CGC prediction – The power of Monte Carlo • Summary and Prospects 7/31/2012 RBRC Forward physics workshop 2

Motivation • e. A program will investigate the nuclei structure with great precision • – Probing gluon dynamics, establish the existence of the saturation regime. – Study cold nuclear medium effect with parton propagation and hadronization in nuclear matter. – Image nuclear gluon structure. dihadron correlation is a key measurement in the e. A program to help us explore the saturation physics. 7/31/2012 RBRC Forward physics workshop 3

RHIC forward d. Au program Nuclear modification factor PRL 97 (2006), 152302 PHENIX |h| < 0. 35 STAR, BRAHMS Forward h PRL 98 (2007), 172302 p 0 meson Rd. A ~ 1 at mid rapidity Rd. A<1, Single hadron production suppressed at forward rapidity. Cold Nuclear Matter (CNM) effect. Probing small x region. 7/31/2012 RBRC Forward physics workshop 4

Dihadron correlation at RHIC forward d. Au program Guzey, Strikman, Vogelsang, PL B 603, 173 Eur. Phys. J. C 43: 427 -435, 2005 The rapidity of associate particle correlated with the x of struck gluon. From the Pythia 2 ->2 process Probably onset of saturation. Constrain x range. 7/31/2012 Approach to smaller mean x RBRC Forward physics workshop 5

Dihadron correlation measurement CY ( Conditional Yield ) Beam view or transverse plane Phys. Rev. Lett. 91 072304 trigger (usually leading pt) Df associate Nearside peak: delivers jet fragmentation information Awayside peak: medium k. T kick both from initial and final state 7/31/2012 RBRC Forward physics workshop pp d. Au dihadron correlation are similar at mid rapidity, suppression in Au. Au collision is dominated by final state interaction 6

Dihadron correlation measurement Dihadron pair nuclear modification factor PHENIX ar. Xiv: 1109. 2133 v 1 Forward-Forward 7/31/2012 RBRC Forward physics workshop Mid-Forward 7

Dihadron correlation at RHIC side-view beam-view forward d. Au program p ar. Xiv: 1008. 3989 v 1 π p. A Low gluon density (pp): p. QCD predicts 2→ 2 process ⇒ back-to-back di-jet High gluon density (p. A): 2 → many process ⇒ expect broadening of away-side 7/31/2012 Multiple emissions de-correlate the away side peak forward-forward di-pion correlation. Gluon densities saturate first in the center of the nucleus. RBRC Forward physics workshop 8

Dihadron correlation at RHIC forward d. Au program CGC model ar. Xiv: 1005. 4065 v 1 Albacete, Marquet Bowen et al. 2012 7/31/2012 RBRC Forward physics workshop 9

Dihadron correlation at RHIC forward d. Au program Multiple parton interaction (Non CGC formalism) Kang, Vitev, Xing, ar. Xiv: 1112. 6021 v 1 7/31/2012 RBRC Forward physics workshop 10

Dihadron correlation at e. RHIC EIC: – Extract the spatial multi-gluon correlations and study their non-linear evolution – Control final state • essential for understanding the transition from a deconfined into a confined state. (in AA) Advantage over p(d)A: – e. A experimentally much cleaner • no “spectator” background to subtract • Access to the exact kinematics of the DIS process (x, Q 2) 7/31/2012 RBRC Forward physics workshop 11

DIS kinematics Event wise variables: Particle wise variables: p. T is defined with respect to virtual photon 7/31/2012 RBRC Forward physics workshop 12

theoretical prediction from CGC L ~ A 1/3 Probe interacts coherently with all nucleons example bin 7/31/2012 Bin: 0. 5<Q 2<1. 5 Ge. V 2, 0. 6<y<0. 8 <x>=1. 01 x 10 -4, <y>=0. 69, <Q 2>=0. 84 Ge. V 2, <W 2>=8322 Ge. V 2, <nu>=4434 Ge. V RBRC Forward physics workshop 13

theoretical prediction from CGC Bowen, Dominguez, Yuan 2011/2012 ep: Q 2>Qs 2, dilute system. y=0. 7 zh 1 = zh 2 = 0. 3 e. Au: Q 2<Qs 2, dense system. p 1 T>2 Ge. V 1 Ge. V < p 2 T < p 1 T A factor ~ 2 suppression from ep to e. Au at EIC energy. Probing x range as low as 10 -4 7/31/2012 RBRC Forward physics workshop 14

Our Monte Carlo approach for the e. A simulation A hybrid model consisting of DPMJet and PYTHIA with n. PDF EPS 09. e- Nuclear geometry by DPMJet and n. PDF provided by EPS 09. e- σ A A’ Parton level interaction and jet fragmentation completed in PYTHIA. Nuclear evaporation ( gamma dexcitation/nuclear fission/fermi break up ) treated by DPMJet Energy loss effect from routine by Salgado&Wiedemann to simulate the nuclear fragmentation effect in cold nuclear matter (under development). 7/31/2012 RBRC Forward physics workshop 15

Dihadron correlation at e. RHIC PGF Resolved Dominant process: Photon Gluon Fusion (PGF), sensitive to the property of strong gluon field. QCDC 67% Q 2=4 Ge. V 2 from PYTHIA simulation 22% 11% 7/31/2012 RBRC Forward physics workshop 16

Results for Q 2=1 Ge. V 2 Scattered electron pseudo-rapidity For ep 30 x 100: Bin : 0. 5<Q 2<1. 5, 0. 6<y<0. 8 Scattered e- : <E>=9. 00 Ge. V, <θ>=176. 51 o η<0 η>0 Leading particle span p e- Trigger/associate particle cut: |η|<4 ( 2<θ<178 deg ), p. TTrig>2, 1<p. TAsso<2 0. 15<z Trig, Asso<0. 45 7/31/2012 RBRC Forward physics workshop 17

Results for Q 2=1 Ge. V 2 ep Near s=0. 431± 0. 007 Away s=0. 555± 0. 008 30+100 Ge. V 10 M events 0. 5<Q 2<1. 5, 0. 6<y<0. 8 |η|<4 ( 2<θ<178 deg), p. TTrig>2, 1<p. TAsso<2 0. 15<z Trig, Asso<0. 45 e. Au Nuclear PDF gives no strong suppression effect Near s=0. 452± 0. 007 Away s=0. 593± 0. 008 Suppression factor: 0. 861 7/31/2012 RBRC Forward physics workshop 18

Compare with CGC prediction EIC white paper Results from our Monte Carlo, no saturation included. A good discrimination of different models with a few months running. Prediction from CGC calculation. 7/31/2012 RBRC Forward physics workshop 19

Compare with CGC prediction Theoretical results from Bowen Similar to Jd. A we can define a Je. A here. The absence of nuclear effect would correspond to Je. A=1. Je. A <1 would signify suppression of dihadron correlation. Well controlled kinematics, pronounced signal between sat and non-sat. 7/31/2012 RBRC Forward physics workshop 20

The power of Monte Carlo 2 2 back to back parton Intrinsic k. T smears parton back to back correlation Fragmentation p. T introduce p. T with respect to jet axis for hadrons. Parton shower affects the parton p. T imbalance and the jet profile. Medium energy loss effect ep 30 x 100 Ge. V Additional radiation (Parton shower) Fragmenation p. T MC approach Theoretical model Intrinsic k. T PARP(91)=0. 4<Qs 2<0. 6 Ge. V 2 Fragmentation p. T PARJ(21)=0. 4 <p. T 2>=0. 2 Ge. V 2 Parton shower 7/31/2012 Intrinsic kt IS/FS RBRC Forward physics workshop Not available 21

The power of Monte Carlo With only intrinsic kt, no fragmentation pt, no Parton Shower Additional radiation (PS) Intrinsic kt MC side Theory side Intrinsic k. T = 0. 4 Ge. V 0. 4<Qs 2<0. 6 Ge. V 2 Theoretical prediction Fragmenation pt MC results ep 30 x 100 Ge. V MC cuts: Theoretical input: 3. 5<Q 2<4. 5 Q 2=4 0. 65<y<0. 75 y=0. 7 pt trig>2 Ge. V p. T trig>2 Ge. V 1<p. T asso<p. T trig 0. 25<z 1, z 2<0. 35 7/31/2012 z 1=z 2=0. 3 Theoretical curves from B. W. Xiao RBRC Forward physics workshop 22

The power of Monte Carlo Intrinsic kt + fragmentation pt, no Parton Shower Additional radiation (PS) Intrinsic kt MC side Theory side Intrinsic k. T = 0. 4 Ge. V Frag p. T = 0. 4 Ge. V 0. 4<Qs 2<0. 6 Ge. V 2 <p. T 2> = 0. 2 Ge. V 2 Theoretical prediction Fragmenation pt MC results Seeing the fact that we have different treatment to PDF and fragmentation process, we have come to an agreement in ep for these two approaches. Theoretical curves from B. W. Xiao 7/31/2012 RBRC Forward physics workshop 23

The power of Monte Carlo Intrinsic kt + fragmentation pt, with Parton Shower on Additional radiation (PS) Intrinsic kt MC side Theory side Intrinsic k. T = 0. 4 Ge. V Frag p. T = 0. 4 Ge. V Parton shower on 0. 4<Qs 2<0. 6 Ge. V 2 <p. T 2> = 0. 2 Ge. V 2 Theoretical prediction Fragmenation pt MC results with PS As parton shower in MC can be used as a good way to compensate theory results. Stretch theoretical curve of e. Au based on the PS effect on ep. Theoretical curves from B. W. Xiao 7/31/2012 RBRC Forward physics workshop 24

Energy loss effect under development Possible to include some final energy loss effect. According to Py. QM developed by Raphael. The probability for a parton to loose energy ∆E is given by Salgado & Wiedemann PRD 68, 014008 (2003) path length L hard parton This radiation spectrum usually depends on the length of medium L, and the transport coefficient 7/31/2012 RBRC Forward physics workshop 25

Energy loss effect under development Comparison with Hermes data 27. 6 Ge. V e. Xe vs e. D 7/31/2012 RBRC Forward physics workshop Black: Hermes data Blue: MC results 26

Summary & Prospects • Dihadron correlation is a very important measurement in the future e. RHIC e. A program. • A generic Monte Carlo generator design based on p. QCD calculation in the vacuum with flexible nuclear effects added on. • Energy loss effect in cold nuclear medium to be included in this Monte Carlo. • Can be utilized to understand d. A or p. A data and extract the model parameters as an input in our e. Au simulation. 7/31/2012 RBRC Forward physics workshop 27

7/31/2012 RBRC Forward physics workshop 28