Exploring Gluonic Matter with Electron-Ion Collisions Outline - PowerPoint PPT Presentation

Exploring Gluonic Matter with Electron-Ion Collisions Outline • Gluon, Saturation • Electron-Ion Collider • Signals of saturation/Selected key measurements in eA J.H. Lee Brookhaven National Laboratory QM2012, Washington D.C. 1

Glue in matter: What do we know HERA I+II inclusive, jets, charm PDF Fit (x) 1 1 1 x=6.32 10 -5 xf x=0.000102 June 2011 HERA F 2 2 10 Q = 10 GeV x=0.000161 2 -log x=0.000253 ZEUS NLO QCD fit x=0.0004 em HERAPDF1.7 (prel.) x=0.0005 2 F 5 0.8 0.8 0.8 x=0.000632 H1 PDF 2000 fit exp. uncert. x=0.0008 model uncert. H1 94-00 HERAPDF Structure Function Working Group x=0.0013 parametrization uncert. xu H1 (prel.) 99/00 v 0.6 0.6 0.6 x=0.0021 ZEUS 96/97 HERAPDF1.6 (prel.) 4 BCDMS x=0.0032 E665 NMC x=0.005 0.4 0.4 0.4 xg ( 0.05) xd × v x=0.008 3 x=0.013 0.2 0.2 0.2 xS ( 0.05) × x=0.021 x=0.032 2 -3 -4 -2 -1 10 10 10 10 1 x x=0.05 x=0.08 • Gluons responsible for the visible mass and drive the vacuum x=0.13 structure x=0.18 1 • x=0.25 NLO QCD and the measurement “broadly similar”: limited success x=0. 4 • For smaller values of x, structure function F 2 rises strongly with Q 2 : x=0.65 Simple quark-parton model Bjorken scaling breaks 0 2 3 4 5 1 10 10 10 10 10 • Gluons dominate at low-x, but the underlying dynamics and the 2 2 Q (GeV ) evolution is not well established d 2 σ ep → eX = 4 πα 2 1 − y + y 2 F 2 ( x, Q 2 ) − y 2 ⇤� ⇥ ⌅ e.m. 2 F L ( x, Q 2 ) dxdQ 2 xQ 4 2 2

How gluons grow and saturate 1/3 % & # 2 A A ) 2 ≈ cQ 0 10 ( Q s ( P a r t o n G a s $ x ' Q 2 (GeV 2 ) 1 EIC Coverage Gold Calcium 0.1 Proton Color Glass Condensate Λ 2 QCD Confinement Regime 200 120 10 -5 4 10 -4 0 10 -3 10 -2 A x • Saturation regime, where parton splitting is balanced by multi- gluon fusion between self-interacting gluons, arises naturally through non-linear BK/JIMWLK evolution • in the Color Glass Condensate (CGC) framework • characterized by saturation momentum Q S (x,A) • Experimental establishment on the “theoretical evidence” of saturation regime is fundamentally important for understanding of gluonic dynamics - strong interaction 3

Electron-Ion Collider (EIC) Exploring gluons (and sea quarks) - beyond HERA • e + Ion : nuclear enhanced (~x300) effective small-x reach - deeply into saturation regime 10 3 Measurements with A ≥ 56 (Fe): • wide energy range: kinematic eA/ μ A DIS (E-139, E-665, EMC, NMC) ν A DIS (CCFR, CDHSW, CHORUS, NuTeV) coverage with great leverage for DY (E772, E866) 10 2 EIC √ s=90 GeV measuring gluon distribution F L Q 2 (GeV 2 ) EIC √ s=45 GeV ( √ s A =~20-100 GeV) 10 • high luminosity (~x500 of Q 2 s , q u ark A u , m e d i a n b HERA) : rare and precision probe 1 C a , for gluonic properties: heavy me d i an b p , m flavor, exclusive measurements, ... e d i a n b 0.1 10 -4 10 -3 10 -2 10 -1 1 • polarized e and p: gluonic x contribution to spin degree of freedom of nucleon 4

Characterizing glue in matter with EIC • Precisely mapping momentum and space-time distribution of gluons in nuclei in wide kinematic range e including saturation regime through: k' k • Inclusive measurements of structure functions q X p X (F 2 ,F L , F 2D , F LD ): eA → eX, eA → eX+gap e • Semi-inclusive measurements of final state k' k distributions: eA → eA{ π ,K, Φ ,D,J/ Ψ ...}X q Mx } • Exclusive final states: eA → eA{ ρ , Φ ,J/ Ψ , γ }+gap gap gap p A p' • Multiple controls: x, Q 2 , t, M X2 for light and heavy nuclei 5

Selected Key Measurement I: Integrated gluon distribution: non-linear QCD in F L F A L ( x, Q 2 ) ∝ x G A ( x, Q 2 ) proton Au (A=197) 0 0 -2 -2 leading twist )/F L leading twist )/F L -4 -4 (F L - F L (F L - F L -6 -6 -8 -8 3 3 -10 -10 2 2 -5 -5 log 10 (Q 2 ) log 10 (Q 2 ) -4 1 -4 1 -3 -3 log log -2 (x) (x) -2 1 1 0 0 Bartels, ¡Golec-­‑Biernat, ¡Motyka, ¡PRD ¡ ¡81 ¡(2010) • Saturation signal in nuclear structure function: F LA is sensitive to higher twist (non-linear) effects at low Q 2 / small-x - correction to leading-twist DGLAP • Higher twist effect cancelation in F 2 (=F L +F T ) • Based on saturation inspired model (GBW) describing HERA ep data • wide energy range of EIC is essential for the measurement 6

Integrated gluon distribution at EIC: F 2 and F L 2 ( x, Q 2 ) − y 2 Q 2 =sxy σ r ( x, Q 2 ) = F A Y + F A L ( x, Q 2 ) 1.2 1.2 Q 2 = 2.7 GeV 2 , x = 10 -3 Q 2 = 2.7 GeV 2 , x = 10 -3 errors to scale stat. errors enlarged ( × 50) sys. uncertainty bar to scale 1 1 p ) p ) 0.8 0.8 A /(A F 2 A /(A F L 0.6 0.6 R 2 = F 2 R L = F L 0.4 0.4 rcBK Beam Energies A ∫ Ldt Beam Energies A ∫ Ldt EPS09 (CTEQ) 2 fb -1 2 fb -1 5 on 50 GeV 5 on 50 GeV 0.2 0.2 rcBK 4 fb -1 4 fb -1 5 on 75 GeV 5 on 75 GeV Cu Au 4 fb -1 4 fb -1 5 on 100 GeV 5 on 100 GeV EPS09 (CTEQ) 0 0 1 2 3 4 5 6 7 1 2 3 4 5 6 7 A ¹ ⁄ ³ A ¹ ⁄ ³ • F 2,LA extracted from pseudo-data generated at 3 EIC energies (2-4 fb -1 ) • 5+50 GeV 5+75 GeV 5+100 GeV • Data, with errors, added to theoretical expectations from EPS09 PDF and rcBK • at Q 2 = 2.7 GeV 2 x=10 -3 7

Selected Key Measurement II: Di-hadron correlation: Measurements at RHIC y y p p x x q q p+p → π 0 π 0 + X, √ s = 200 GeV d+Au → π 0 π 0 + X, √ s = 200 GeV d+Au → π 0 π 0 + X, √ s = 200 GeV Uncorrected Coincidence Probability (rad -1 ) 0.03 0.016 p T,L > 2 GeV/c, 1 GeV/c < p T,S < p T,L p T,L > 2 GeV/c, 1 GeV/c < p T,S < p T,L p T,L > 2 GeV/c, 1 GeV/c < p T,S < p T,L 〈η L 〉 =3.2, 〈η S 〉 =3.2 〈η L 〉 =3.2, 〈η S 〉 =3.2 〈η L 〉 =3.1, 〈η S 〉 =3.2 0.02 0.014 0.025 CGC+offset 0.012 0.15 0.02 0.01 0.008 0.015 0.01 0.006 0.01 0.004 Peaks 0.05 Peaks Peaks Δφ σ Δφ σ Δφ σ p+p d+Au peripheral 0.005 d+Au central 0 0.44 ± 0.02 0.002 0 0.41 ± 0.01 0 0.46 ± 0.02 π 1.63 ± 0.29 STAR Preliminary STAR Preliminary STAR Preliminary π 0.68 ± 0.01 π 0.99 ± 0.06 0 0 0 -1 0 1 2 3 4 -1 0 1 2 3 4 5 -1 0 1 2 3 4 5 Δφ Δφ Δφ 20 • Multiple scattering in the dense nucleus at forward in dAu lead to mono-jet (decorrelation at ΔΦ = π ) in CGC frame work ( J. Albacete and C. Marquet, PRL 105 (2010)) • Alternative interpretation: Multiple parton scattering (Energy loss+dynamical shadowing) without saturation at “moderate” x (Kang, Vitev, Xing PRD85 (2012)) • Estimated x A in dAu at RHIC ~ 10 -3 8

Di-hadron correlation at EIC 0.18 Q 2 = 1 GeV 2 trigger < 2 GeV/c EIC stage-II p T ep 0.2 ∫ Ldt = 10 fb -1 /A 0.16 assoc < p T trigger 1 < p T | η |<4 0.14 0.15 0.12 C e Au ( Δϕ ) eAu - nosat C( Δϕ ) eCa 0.1 0.1 0.08 0.06 sampling eAu 0.04 0.05 eAu - sat 0.02 0 0 2 2.5 3 3.5 4 4.5 2 2.5 3 3.5 4 4.5 Δϕ Δϕ Bowen, Dominguez, Yuan 2011/2012 • EIC reach small-x regime with clean kinematic control in di-hadron correlation measurement • EIC expected data from10 fb -1 integrated luminosity at 30(e)x100(p/Au) GeV • Factor of ~2 suppression expected in eAu/ep with saturation compared with non-saturation model: Pythia+nPDF+DPMJETIII • Q 2 =1 GeV 2 <x>=1x10 -4 • hadron p T cut: trigger / associate = 2 / 1 GeV/c • Systematic differential measurement: crossing onset of saturation using √ s, Q 2 , A 9

Di-hadron correlation vs x at EIC: Nuclear modification J eAu Data:Phenix RHIC dAu, √ s = 200 GeV 1 mid-forward forward-forward eAu - nosat EIC stage-II 1 ∫ Ldt = 10 fb -1 /A J eAu J dAu Q 2 = 1 GeV 2 eAu - sat trigger > 2 GeV/c p T assoc < p T trigger peripheral 1 < pT 10 -1 | η |<4 central 10 -3 10 -2 -3 -2.5 -2 -1.5 -1 frag x A log 10 (x g ) • J eAu - relative yield of di-hadrons produced in e Au compared to ep collisions • Curves from saturation model (B. Xiao (2012) ) 10

Selected Key measurement III: Gluon spatial distribution and correlations in exclusive diffractive Vector Meson production e e e e gap gap p n coherent incoherent A A A A’ • Novel “strong” probe to investigate gluonic structure of nuclei: color dipole coherent and incoherent diffractive interaction: Sensitive to saturation (s,b,A) • Large σ diff / σ total in e+A (~25-40%) compared to e+p (~10-15%) • Coherent: Access to spatial distribution of gluons • Precise transverse imaging of the gluons • Modification due to small-x evolution • Tagging with vetoing spectator neutrons in Zero Degree Calorimeter • Incoherent: Gluon correlations in the transverse plane 11