eA* *physics motivation for an electron-ion collider from a QGP perspective
Strange Quark Matter 2013 Conference 21-27 August, Birmingham, UK
Javier L Albacete Universidad de Granada & CAFPE
1 Two proposed facilities :
Electron-Ion Collider, EIC (RHIC /JLAB)
- EIC white paper , arXiv:1212.1701 e-conveners: T. Ullrich and Y. Kovchegov Also: Spin and 3D structure of the nucleon Talk by Thomas Burton on tuesday
Large Hadron-electron Collider, LHeC (CERN)
- the LHeC Conceptual Design Report, arXiv:1206.2913 small-x conveners: N. Armesto, B. Cole, P. Newman and A. Stasto
Also: Precision QCD, EW physics, new physics at high energy Talk by Paul Newman on tuesday
Not covered in this talk: Accelerator design and challenges, machine performance, detectors...
2 OUTLINE
Quark and gluon structure in nuclei: status and open questions ! (or why a QGP physicist should care) e+A measurements: highlights !- structure functions !- hard diffraction! !- di-hadron production !- exclusive vector meson production !- cold nuclear matter effects
3 RelevantRelevance open questions for in HICthe addressed HI program: by an eA
• (A,b,x,Q2)-dependence of nuclear structure • Initial state fluctuations ● Particle production at • Initial State correlations ● Probing the ●• Small-xNuclear saturation, nPDF’s,the CGC? very beginning: which medium through wave factorisation in pA/eA? energetic particles • Factorization in eA, pA, AA? function at • Initial conditions for isotropization in AA (jet quenching small x: ● How does the system etc.): modification behave as isotropised nuclear ∼ • Hard Probes: Modificationof QCD of QCD radiation structure so fast?: initial radiationconditions (“energy loss”)and and hadronization hadronization functions. for plasma formation (“absorption”) to in a nuclearin the medium nuclear be studied in pA/eA. medium. 4 4 1.4 0 1.3 PHENIX 2007 STAR 2006 + + - 1.2
dAu 1.1 R 1.0 1.4 1.40.9 0 1.3 PHENIX 2007 STAR 2006 + + - 0 1.30.81.2 y=0 EPS09NLOPHENIX 2007 STAR 2006 + + - dAu 1.20.71.1 R 2 4 6 8 10 12 14 16 1.0 dAu 1.1 [GeV] R 0.9 1.0 3 0.8 y=0 EPS09NLO Figure 9: The computed R0.9dAu0.7 (thick black line and blue error band) at y =0forinclusive pion production compared with the2 4 PHENIX 6 8 [28] 10 12 data 14 (open 16 squares). The error bars are the 0.8 y=0 [GeV]/ EPS09NLO the fit at scales di↵erent than the ones used here. In our case,statisticalreported uncertainties, [25] andfor the the yellow prompt bandJ indicateyield the a point-to-point preliminary systematic value errors.of 0.7 The additionalR = 10%. overall. normalization2 4. 6< uncertainty 8y 10 12< in 14 thedataisnotshown.Thedata 16 we are using a partonic cross section evaluated at Born (LO) FigureFB 9: The0 computed66 0RdAu08(thick for black 2 5 line andCM blue error4, band) whereas at y =0forinclusive ALICE has have been multiplied by± the optimized normalization|[GeV]| factor f =1.03, which is an output order. The common practice is thus to employ a LO (n)PDF pionreported production compared [26] a with preliminary the PHENIX [28] value data (open of squRares).FBN The= error0.60 bars are0 the.07 for of ourstatistical analysis. uncertainties, Also the STAR and the data yellow [50] band (open indicate circles) the point-to-point multiplied by systematic a normalization± errors. factor set. Yet, nothing forbids us to use a NLO one as a defaultf =0The3.90 additional< arey shownCM 10%< for overall3 comparison..5 normalization for the inclusive uncertainty in one. thedataisnotshown.Thedata These values are com- FigureN 9: The| computed| RdAu (thick black line and blue error band) at y =0forinclusive ↵ have been multiplied by the optimized normalization factor fN =1.03, which is an output choice. In a sense, any di erence observed, as for instance thepion productionofpatible our analysis. compared with Also the a strong STAR with thedata shadowing. PHENIX [50] (open circles) [28] data multi (openplied by squ aares). normalization The error factor bars are the one between EPS09 LO and NLO on Fig. 2(b), is an indica-statisticalfN =0 uncertainties,We.90 are would shown for and like comparison. thePb to yellow recall band that indicatePb in order the point-to-point to takePb into systematic account errors. The additional 10% overall normalization uncertainty in thedataisnotshown.Thedata ) tion of the uncertainty attributable to the neglect of unknown the transverse-momentum2 1.4 dependence of the shadowing1.4 ef- have been multiplied by the optimizedPb normalization2 Pb 2 factor fPbN =1.03, which is an output higher QCD corrections. fects one1.2 needs to resort toQ a=1.69 model GeV which contains an1.2 explicit of our analysis. Also) the STAR data [50] (open circles) multiplied by a normalization factor 1.02 1.4 1.4 1.0 f =0.90 areUncertainty shown for comparison.on quark and Qgluon2=1.69 GeV2 structure of the nuclei as reflected Finally, the uncertainty spanned by a given nPDF set withN dependence0.81.2 on PT and y. Thanks to the versatility1.2 0.8 of our =1.69 GeV
2 1.0 1.0 0.6 by nuclear-PDF parametrizations 0.6 error may not encompass curves which can be obtained by Glauber, 0.8 code, such computation can also be done0.8 including =1.69 GeV 2 ( 0.40.6 Pb Pb Pb0.6 0.4 , fits from di↵erent groups. This is, for instance, the case the impact-parameterPb valence dependencesea alonggluon with involved pro- 0.2( 0.4 0.4 0.2 Pb ) of nDSg and EPS09 LO, whose shadowing magnitudes are duction2 1.4 0.2 mechanisms containing a non-trivial PT0.2-dependence.1.4
) 1.4 2 2 1.4
2 Q2 =1.69 GeV2
1.2) 1.4 Q =100 GeV 1.4 1.2 roughly the same unlike the anti-shadowing one as it can be We1.22 emphasise that the e2 ↵ect2 of the P cut shown on1.2 Fig. 4 1.2 Q =100 GeV T 1.2 1.01.0 1.01.0 seen on Fig. 2(c). Yet, to be rigorous, we should have derived is not0.8 related1.0 to any Cronin e↵ect which is not1.0 taken0.8 into =1.69 GeV
2 0.80.8 0.8 0.8 =100 GeV =100 GeV 2 0.62 0.6 an error band from the EPS09 eigen sets. The error band may account, 0.60.6 here. It simply comes from the increase0.6 of0.6x2 and , , ( 0.4 0.4 ThisThis work, work, EPS09NLO EPS09NLO 0.4 0.4 0.4( 0.4 ( Pb HKN07HKN07 (NLO) (NLO) have then been closer to the nDSg for instance. mT (PTPb )0.2 for increasingnDS (NLO) PT . In particular, the anti-shadowing0.2 Pb 0.20.2 nDS (NLO) 0.20.2 0.0 -4 -3 -2 -1 -4 -3 -2 -1 -4 -3 -2 -1 0.0 In addition to the uncertainties from the nPDF and their im- peak is0.0 shifted-410 10-3 10 to-2 less10 -1 10 negative-410 -310 10-2 rapidities10-1 10 -4 10 which-310 -21 modifies-1 0.0 RFB
) 1.4 1.4
2 10 10 10 10 10 10 2 10 210 10 10 10 10 1 plementation, we also has to consider the e↵ect of a break-up at large1.2 yCM . Q =100 GeV 1.2 • These uncertainties1.0 | | propagate to the calculation of pretty much any1.0 hard process probability on the nuclear-modification factor as in Fig. 2(d). Figure 10: Comparison of the average valence and sea quark, and gluon modifications at 2 0.8 2 2 2 0.8 Q =1.69=100 GeV GeV and Q =100GeV for Pb nucleus from the NLO global DGLAP analyses Figure 10: 2 Comparison0.6 of the average valence and sea quark, and gluon modifications0.6 at 2 pPb EPS09NLO.2
2 HKN07 [5],, nDS [6] and2 this work, Q =1.69 GeV and QThis=100GeV work, EPS09NLO for Pb nucleusFerreiro from the et NLO al global DGLAP analyses
0.4 R 0.4 HKN07 [5], nDS( [6] andHKN07 this (NLO) work, EPS09NLO. Pb 0.2 0.2 nDS (NLO) 1 pPb FB 1 pPb FB 1 0.0 -4 -3 -2 -1 -4 -3 -2 -1 -4 -3 -2 -1 0.0 10 10 10 10 10 10 10 10 10 10 10 10 1 R R J/Psi in pPb: J/ψ pPb 5 TeV, p > 6 GeV T EPS09 LO18 central set 0.8 0.8 EPS09 LO min. EMC 0.5 EPS09 LO max. EMC Figure 10: Comparison of the averageEPS09 valence LO min.18 shadowing and sea quark, and gluon modifications at 2 2 EPS09 LO max. shadowing 0.6 0.6 Q2 =1.69 GeV and Q2 =100GeV nDSgfor LO Pb nucleus from the NLO global DGLAP analyses J/ψ pPb 5 TeV, EPS09 J/ψ pPb 5 TeV, EPS09 LO central set, LO HKN07 [5], nDS [6] and this work, EPS09NLO. central set -4 -2 0 2 4 central set, NLO y 0.4 min. shadowing 0.4 CM max. shadowing 5 0 1 2 3 4 50 2 4 |y | |y | pPb FB 1
CM CM R 18 (a) EPS09 LO scale uncertainty (b) EPS09 LO vs. EPS09 0.8 NLO J/ψ pPb 5 TeV, p > 6 GeV T EPS09 LO central set 0.6 EPS09 LO min. EMC EPS09 LO max. EMC EPS09 LO min. shadowing EPS09 LO max. shadowing nDSg LO 0.4 pPb FB 1 pPb FB 1 0 1 2 3 4 5
R R |y | CM
0.8 0.8 FIG. 4: (Colour online) J/ nuclear modification factor (up) and J/ψ pPb 5 TeV EPS09 LO central set its forward-to-backward (down) ratio in pPb collisions, at psNN = J/psi pPb 5 TeV, EPS09 LO EPS09 LO min. EMC 0.6 0.6 central set EPS09 LO max. EMC central set, σ = 1.5 mb 5 TeV versus y using 5 extremal curves of the EPS09LO nPDF set EPS09 LO min. shadowing abs central set, σ = 2.8 mb EPS09 LO max. shadowing abs > nDSg LO and nDSg with a cut PT 6 GeV. 0.4 0.4 0 1 2 3 4 50 1 2 3 4 5 |y | |y | Conclusions.— We have provided predictions for the J/ CM CM nuclear modification factors in pPb collisions and its forward- to-backward ratio, R , at ps = 5 TeV as functions of y (c) EPS09 vs. nDSg (d) EPS09 LO with abs FB NN for low and mid PT , which can be compared to the ALICE and LHCb preliminary data and the forthcoming ATLAS and FIG. 3: (Colour online) Same as Fig. 2 for RFB CMS one taken during the 2013 LHC pPb run. Unless there is an unexpectedly large anti-shadowing, the All these e↵ects also impact the forward-to-backward ratio measured values of RFB support the presence of a significant RFB as can be seen on Fig. 3. Their impact remains signifi- shadowing –of a magnitude stronger than the central value of cant, except for the break-up probability. Its e↵ect on RFB (see EPS09LO. This should be taken into account in the interpre- Fig. 3(d)) is much smaller than on RpPb and can in practice be tation the PbPb data. disregarded. We would like to thank R. Arnaldi, Z. Conesa del Valle, K. Eskola, These values can be compared to the preliminary measure- C. Hadjidakis, J. He, F. Jing, N. Matagne, I. Schienbein, R. Vogt and ments by the LHCb and ALICE collaborations. LHCb has Z. Yang for stimulating and useful discussions. 1.4 0 1.3 PHENIX 2007 STAR 2006 + + - 1.2
dAu 1.1 R 1.0 0.91.4 1.4 0 1.3 PHENIX 2007 0.8 y=0 EPS09NLO+ - 0 1.3 STAR 2006PHENIX+ 2007 1.2 + - 0.7 STAR 2006 + dAu 1.21.1 2 4 6 8 10 12 14 16 R
dAu 1.11.0 [GeV] R 0.9 1.0 0.8 y=0 EPS09NLO Figure 9: The computed R0.9dAu (thick black line and blue error band) at y =0forinclusive 0.7 pion production compared with2 the 4 PHENIX 6 8 [28] 10 12 data 14 (open 16 squares). The error bars are the 0.8 y=0 EPS09NLO statistical uncertainties, and the yellow band[GeV] indicate the point-to-point systematic errors. 0.7 The additional 10% overall normalization2 4 6 uncertainty 8 10 12 in 14 thedataisnotshown.Thedata 16 haveFigure been multiplied 9: The computed by theRdAu optimized(thick black normalization line and[GeV] blue error factor band)f at=1y =0forinclusive.03, which is an output pion production compared with the PHENIX [28] data (open squares).N The error bars are the of ourstatistical analysis. uncertainties, Also the STAR and the data yellow [50] band (open indicate circles) the point-to-point multiplied bysystematic a normalization errors. factor fN =0The.90 additional are shown 10% for overall comparison. normalization uncertainty in thedataisnotshown.Thedata Figure 9: The computed RdAu (thick black line and blue error band) at y =0forinclusive pion productionhave been multiplied compared by the with optimized the PHENIX normalization [28] data factor (openfN =1 squ.03,ares). which is The an output error bars are the of our analysis. Also the STAR data [50] (open circles) multiplied by a normalization factor Pb Pb Pb statisticalfN =0 uncertainties,.90 are shown for and comparison. the yellow band indicate the point-to-point systematic errors. The additional 10% overall normalization uncertainty in thedataisnotshown.Thedata ) 2 1.4 1.4 have been multiplied by the optimizedPb normalization2 Pb 2 factor fPbN =1.03, which is an output 1.2 Q =1.69 GeV 1.2
of our analysis. Also) the STAR data [50] (open circles) multiplied by a normalization factor 1.02 1.4 1.4 1.0 Uncertainty on quark and gluon2 structure2 of the nuclei as reflected fN =0.90 are shown0.81.2 for comparison. Q =1.69 GeV 1.2 0.8 =1.69 GeV by nuclear PDF-parametrizations 2 0.61.0 1.0 0.6 , 0.8 0.8 =1.69 GeV ( 2 0.4 Pb Pb Pb 0.4
Pb 0.6 0.6 , valence sea gluon 0.2( 0.4 0.4 0.2 Pb ) 2 1.4 0.2 0.2 1.4
) 1.4 2 2 1.4 2 Q2 =1.69 GeV2
1.2) 1.4 Q =100 GeV 1.4 1.2
1.22 1.2 Q2=100 GeV2 1.01.01.2 1.2 1.01.0 0.8 1.0 1.0 0.8 =1.69 GeV 0.8 0.8 2 0.8 0.8 =100 GeV =100 GeV 2
0.62 0.6 , 0.60.6 0.6 0.6 , , ( 0.4 0.4 ThisThis work, work, EPS09NLO EPS09NLO 0.4 0.4 0.4( 0.4 ( Pb HKN07HKN07 (NLO)
Pb 0.2 nDS (NLO) 0.2 Pb 0.20.2 nDS (NLO) 0.20.2 0.0 -4 -3 -2 -1 -4 -3 -2 -1 -4 -3 -2 -1 0.0 0.0 10-4 10-3 10-2 10 -1 10 -410 -310 10-2 10-1 10 -4 10 -310 -21 -1 0.0
) 1.4 1.4
2 10 10 10 10 10 10 2 10 2 10 10 10 10 10 1 1.2 Q =100 GeV 1.2 1.0 1.0 Figure 10: Comparison of the average valence and sea quark, and gluon modifications at 2 0.8Constrained2 by2 DIS 2 • Situation specially dramatic for small-x gluons0.8 Q =1.69=100 GeV GeV and Q =100GeV for Pb nucleus from the NLO global DGLAP analyses Figure 10: 2 Comparison of the average(where valence most of and the particles sea quark, produced and gluonin a HIC mo comedifications from) at HKN07 [5],0.6Constrained nDS [6] and by this DY work, EPS09NLO. 0.6 2 , 2 2 2 Q =1.69 GeV0.4and QThis=100GeV work, EPS09NLO for Pb nucleus from the NLO global DGLAP0.4 analyses ( Constrained by sum rules HKN07 [5], nDS [6] andHKN07 this (NLO) work, EPS09NLO. Pb 0.2 0.2 AssumptionsnDS i.c. (NLO)(=Guessed. Complete absence of empiric constraints) 0.0 0.0 10-4 10-3 10-2 10-1 10-4 10-3 10-2 10-1 10-4 10-3 10-2 10-1 1
18 6
Figure 10: Comparison of the average valence18 and sea quark, and gluon modifications at Q2 =1.69 GeV2 and Q2 =100GeV2 for Pb nucleus from the NLO global DGLAP analyses HKN07 [5], nDS [6] and this work, EPS09NLO.
18 Small-x = High gluon densities
2 saturation Qs(Y) Saturation: At sufficiently small-x region • QCD evolution becomes non-linear Geometric • particle production becomes non-linear Scaling • QCD stays weakly coupled 1 gluonBK/JIMWLK emission BFKL ladder CGC evolution: BFKL ladder fusion linear non-linear Y = ln 1/x BFKL DGLAP non-perturbative region
2 2 ΛQCD ln Q αs ~ 1 αs << 1
• The Color Glass Condensate effective theory has emerged as the most solid candidate to approximate QCD in the small-x regime.
• CGC provides a consistent description of data at small-x in a variety of colliding systems: e+p, p+p, p(d)-A, AA. However alternative descriptions exist in all cases
• Coherence effects at small-x are essential for the description of HIC data. They appear under different names in the literature: shadowing, percolation, transverse momentum cut-offs in event generators, re-summation of multiple scatterings etc
7 Small-x = High gluon densities. Theory open questions
• Does collinear factorization + DGLAP evolution hold to arbitrarily small-x? If so, are would one be hiding relevant dynamics in the initial conditions for DGLAP evolution?
• Transition from the saturation to the high-pT (leading-twist) regime
2 2 CGC evolution (down in x) does not contain RpPb(y=6) rcBK-MC-hyb 1.8 EPS09 nPDF 1.8 the DGLAP limit, hence after some evolution 1.6 1.6
(at forward rapidities), RpA predictions reach 1.4 1.4 unity only at unrealistically large values of pT 1.2 1.2 1 1
0.8 0.8
how RpA goes back towards unity at high-pT ? 0.6 0.6 0.4 0.4
0.2 0.2
2 4 6 8 10 pt (GeV) • The transition from the saturation regime to confinement
how does it happen ? does the coupling run with Qs ? are classical fields still the right degrees of freedom ?
8 Fluctuations and correlations. • The main source of error in the extraction of medium parameters (e.g η/s) is our insufficient understanding of the initial state and its fluctuations
Initial Sate models: Large uncertainties for initial eccentricities MC-Event Generators, Glauber, 0.13 0.14 0.5 ε2 ε3 ε4 CGC-based approaches etc 0.4 0.07 0.08 0.3 0.13 0 0.03 0.2 0.1 0.07 0 0.03 0 M. Luzum & 0.16 0.18 0.1 0.2 0.3 0.4 0.5 0.5 ε5 ε6 J.Y Ollitrault 0.4 0.09 0.09 Glauber (discs) 0.3 MC-KLN Glauber (points) 0.2 DIPSY 0.1 UrQMD MCrcBK (NB fluct) 0 0 0.1 0.2 0.3 0.4 0.5 0 0.1 0.2 0.3 0.4 0.5 0.6 Centrality Centrality
Figure 1: (Color online) RMS eccentricities versus centrality for several models of initial conditionsε in 1% centralitybins. Centrality was selected according to multiplicity or entropy, as appropriate for each model, and6 the transverse densityof • CGC dynamics builds up “initial state”the correlations same quantity was used to calculate that eccentricities. compete Inset plots magnify with the mostthe central hydro 3% of collisions. The models shown are: PHOBOS MC-Glauber [6] [Glauber (points)], MC-KLN[7]v3.43anditsGlauberimplementation[Glauber interpretation of data. (discs)], mckt-v1.25 with negative binomial fluctuations [8] (MCrcBK (NB)), DIPSY [9], and UrQMD [10]. E.g ridge in pPb • Surprising ridge well as preliminary results on such an extractionstructures including aquantitativeerrorbarobtainedby observed in systematic study of all known sources of uncertainty. high multiplicity pPb 2. Ultra-central collisions events have been In a standard picture of a heavy-ion collision,attributed the asymmetric region to ofsaturation overlap in a collision between two nuclei results in a anisotropy in the transverse density of the system at early times. Over time, this spatial anisotropy is transformedeffects into a mom (CGCentum anisotropy …) by a collective response that is well described by (viscous) hydrodynamics.Infact,theellipticflowcoefficient v2 is (to a good approximation) directly proportional to this initial eccentricity in a given colli- 2 2iφ 2 sion event: v2 ∝ ε2 ≡ |#r e $|/#r $.Theproportionalityconstantdependssensitivelyonthe• Flow characteristics in viscosity of the medium, However, poor knowledge of the earliest stages of the collision result in significant uncertainty in ε2 See, for example,pPb the top (mass left panel ordering of Fig. 1, which showsat root- 1 9 mean-square values of ε2 from a number of commonly-used models for initial conditions .The resulting uncertainty in v2 has been the largest sourcelow ofp uncertaintyT) resembles when determining thatη/s from data [2]. Though there has been much recent study concerning the physics of the early stages of acollision[8,9],itisnotyetpossibletomakeareliablestin PbPbatement … aboutascribed what range to of values of initial eccentricity are within the realm of possibility.hydrodynamics. It is now known that quantum fluctuations are also a significantsourceofanisotropyinthe initial state, and therefore anisotropic flow. This is especially apparent from the presence of large “A lot more needs to be 1 Most vn measurements are sensitive to the rms value of the event-by-event distribution of vn understood2 about our pA baseline” 18 k' Deep Inelastic Scattering: e+A -> e+X Experimental Advantages k • Precise: Direct access to parton-level kinematics q • Clear: Absence of initial state effects • CleannPDFs: No spectator backgroundeA inclusive pX● F2 data substantially reduce Theoretical the uncertainties Advantages in DGLAP analysis; • Well understood at (N)NLO accuracy inclusion of charm, beauty and FL also produce improvements.
2 2 photon virtuality: Q = (k k0) > 0 Q2 Bjorken-x: x = 2p q ·
• Four orders of magnitude increase in kinematic range over previous DIS experiments
- LHeC: smaller-x, larger Q2
- EIC: variety of nuclei
10 15 Inclusive structure functions: F2 and FL
Q2/x y = s M 2 measured quark distributions gluon distribution • PrecisionnPDFs: nuclear PDF’s eA : x,Qinclusive2 and A-dependence and flavour decomposition (u,d,s,c,b) ● F data substantially • Possibility reduce to distinguish the uncertainties evolution schemes: in DGLAP DGLAP analysis; vs GCG (or others) 2 • High precision tests of collinear factorization. Simultaneous fit of F2 and FL? inclusion of charm, beauty and F also produce improvements. Heavy• p-Pb willflavor do PDFsa lot here. inL nuclei LHeC/EIC: unconstrained. Better handle of kinematics, systematics, A-coverage LHeC Pb Pb Pb
) EIC 2 LHeC 1.4 1.2 LHeC F2 + FEPS09NLO2c,b + FL 1.2 1.4 Q2 = 2.7 GeV2, x = 10-3 Fit 1 stat. errors enlarged (× 50) Q2 = 2.7 GeV2, x = 10-3 stat. errors enlarged (× 5) 1.2 Valence sys. uncertainty bar to scaleGlue 1.2 sys. uncertainty bar to scale 1.0 1 1 1.0 0.8 Sea 0.8 =1.69 GeV 2 ) 0.6 ) 0.6 p p L 2
, 0.8 0.8
( 0.4 Q2=1.69 GeV2 0.4 Pb /(A F /(A 0.2 F /(A 0.2 A A L 2 0.6 F2 only 0.6 Beam Energies A ∫Ldt = F = = F =
) 1.4 -1 1.4 L 2 EPS09NLO
2 5 on 50 GeV 2 fb 0.4 0.4 R 1.2 R 5 on 75 GeV 4 fb-1 Fit 1 rcBK 1.2 5 on 100 GeV 4 fb-1 EPS09 (CTEQ) Beam Energies A ∫Ldt 1.0 1.05 on 50 GeV 2 fb-1 0.2 0.2 -1 rcBK 0.8 Si Cu Au 0.85 on 75 GeV 4 fb -1 =100 GeV F2 only 5 on 100 GeV 4 fb EPS09 (CTEQ) 2 0.6 0.6
, 0 0 0.4 2 12345672 0.41234567 ( Q =100 GeV
Pb 0.2 A¹⁄³ 0.2 A¹⁄³ 0.0 0.0 10-4 10-3 10-2 10-1 10-4 10-3 10-2 10-1 10-4 10-3 10-2 10-1 1 11 15 Figure 3.15: Left: The ratio R2 of the F2 structure function in a nucleus over that of the proton scaled by mass number A as a function of A1/3. The predictions from a CGC based calculation (rcBK) [142] and from a linear evolution using the latest nuclear PDFs (EPS09) and CTEQ6 for the proton are shown [167, 153]. Right: The same for the longitudinal structure function FL (see text for details). uses the linear NLO DGLAP evolution in error bars are scaled up by a factor of 50 for pQCD resulting in the nuclear parton dis- R2 and a factor of 5 for RL; as the statistical tribution set EPS09 [167, 153]: it exhibits a errors are clearly small, the experimental er- broader error band, similar to the case of RG rors will be dominated by the systematic un- in Fig. 3.11. Even in linear DGLAP evolu- certainties shown by the orange bars drawn tion, non-linear e↵ects may be absorbed into to scale in the two panels of Fig. 3.15. As the the non-perturbative initial conditions for exact EIC detector design has not been de- the nuclear PDFs, where the A-dependence termined yet, the systematic errors were esti- is obtained through a fit to available data, mated based on normalization uncertainties resulting in the ability of DGLAP-based ap- achieved by HERA. These measurements at proaches to indiscriminately describe a broad an EIC (both stage-I and stage-II) will have range of nuclear data. This leads to the a profound impact on our knowledge of nu- wide error bands of EPS09, especially for clear structure functions (especially FL and FL, clearly demonstrating the lack of exist- the gluon distribution) as can be easily seen ing nuclear structure function data. Due to from the size of the statistical and system- these large theoretical error bars, the mea- atic errors bars for stage-I shown in Fig. 3.15. 1/3 surements of R2 and RL as functions of A This measurement, together with the ones may not allow one to directly distinguish be- described below, will constrain models to tween a non-linear (saturation) and linear such an extent that the “true” underlying (DGLAP) evolution approaches at a stage- evolution scheme can be clearly identified. It IEIC. is also possible that stage-I data would de- Shown along the line at unity by vertical crease the error band of DGLAP-based pre- notches in Fig. 3.15 are the statistical error dictions, allowing for the R2 and RL mea- bars for an EIC stage-I measurement calcu- surement in stage-II at a smaller x to dis- lated using the Rosenbluth separation tech- criminate between saturation and DGLAP nique. The statistical error bars were gen- approaches. However it is also possible that, 1 erated from a total of 10 fb /A of Monte on its own, the R2 and RL measurements Carlo data, spread over three beam energies may turn out to be insu cient to uniquely (see plot legend for details). The statistical di↵erentiate between DGLAP-based models
78 Di↵ractive Scattering
Di↵ractive scattering has made a spectacular comeback with the observation of an unex- pectedly large cross-section for di↵ractive events at the HERA e+p collider. At HERA, hard di↵ractive events, e(k)+N(p) e (k )+N(p )+X, were observed where the proton ! 0 0 0 remained intact and the highly virtual photon fragmented into a final stateDi↵Xractivethat was sep- Scattering arated from the scattered proton by a large rapidity gap without any particles. These events are indicative of a color neutralDi↵ exchangeractive in the Scatteringt-channel between the virtual photon and the proton over several units in rapidity.Di↵ Thisractive color scattering singlet exchange has made has a historically spectacular been comeback with the observation of an unex- called the pomeron, which had a specificpectedly interpretation large cross-section in Regge theory. for di An↵ractive illustration events of at the HERA e+p collider. At HERA, Dia↵ractive hard di↵ scatteringractive event has is made shown a in spectacular Fig. 3.2. comeback with the observation of an unex- hard di↵ractive events, e(k)+N(p) e0(k0)+N(p0)+X, were observed where the proton pectedly large cross-section for di↵ractive events at the HERA e+p collider.! At HERA, remained intact and2 the highly virtual photon fragmented into a final state X that was sep- hard di↵ractive events, e(k)+N(p) e (k )+tN=((pp)+pX0), wereis the observed square of where the momentum the proton k' ! arated0 0 from0 the scattered proton by a large rapidity gap without any particles. These events remained intact and the highly virtual photon fragmentedtransfer into at a the final hadronic state X vertex.that was The sep- are indicative of a color neutral exchange in the t-channel between the virtual photon and arated from the scattered proton by a large rapidity gapvariable withoutt here any is particles. identical These to the events one the proton over several units in rapidity. This color singlet exchange has historically been are indicativek of a color neutral exchange in the t-channelused in between exclusive the processes virtual photon and gen- and q called the pomeron, which had a specific interpretation in Regge theory. An illustration of the proton over several units in rapidity. This coloreralised singlet exchange parton distributions has historically (see thebeen Max hard di↵ractive event is shown in Fig. 3.2. called the pomeron, which had a specific interpretationSidebar in Regge on page theory. 43). An illustration of a hard di↵ractive event is shown in Fig. 3.2. 2 M 2 =(p p + k k )2 is the squaredt =(p p0) Hardis the Diffraction square of the in momentum DIS gap X 0 0 k' transfer at the hadronic vertex. The t =(pmassp ) of2 theis the di↵ squareractive of final the state. momentum p k' 0 • A surprising feature of QCD at HERA (e+p): A proton p' transfer at the hadronic vertex. The variable t here is identical to the one k⌘ = ln(tan(✓/2)) is the pseudorapidityin its of restused frame in exclusive hit by a 25 processes TeV electron and gen- remains intact variable t hereq is identical to the one a particle whose momentum has a15 rel- % oferalised the time parton distributions (see the k used in exclusive processesM and gen- Figure 3.2: Kinematicq quantities for the de- ative angle ✓ to the proton beamx axis. Sidebar on page 43). scription of a di↵ractive event. eralised parton distributions (see the Mx For ultra-relativistic particles the pseu-• Mediated by colorless exchange -- “pomeron” The kinematic variables are similar to colorlessdorapiditySidebar on is page equal 43). to the rapidity, ⌘ 2 2 rapiditygap M⇠ X =(p p0 + k k0) is the squared those for DIS with the following additions: exchangey =1/2ln((E + pLgap)/(E + pL)). • Nuclei: - Coherent (nucleus intact): b-imaging of nuclei gap M 2 =(p p + k k )2 is theDi↵ractive squared Scatteringmass of the di↵ractive final state. Xp 0 0 - Incoherent (nucleus breakup): Saturation At HERA, gaps of several units in rapidity havemass been observed. of the di↵ Oneractive finds finalp' that state. roughly p Di↵ractive scattering has made a spectacular⌘ = comebackln(tan( with the✓ observation/2)) is of an the unex- pseudorapidity of 15% of the deep inelastic cross-sectionp' corresponds to hard di↵pectedlyractive large events cross-section with for invariant di↵ractive events at the HERA e+p collider. At HERA, hard di↵ractive events, e(k)+N(p) e0(k0)+N(p0)+aX particle, were observed whose where the momentum2 proton 2 has a rel- masses MX > 3 GeV. The remarkable nature⌘ of= thisln(tan( result✓/ is2)) transparentis the pseudorapidity in the proton! of Q = 5 GeV Figure 3.2: Kinematicremained quantities intact and for the highly the virtual de- photon fragmented into a final state X that was sep-× -3 rest frame: a 50 TeV electron slams into the protona and particle15%arated whose of from the the momentum time, scattered the proton proton by has a large a rapidity rel- is gapative without angle any particles.✓ to Thesex the = events 3.3 proton10 beam axis. Figure 3.2: Kinematic quantities for thescription de- of a di↵ractive⇡ are indicative event. of a color neutral exchange in the t-channelFor between ultra-relativistic the2.5 virtual photoneAu andstage-I particles the pseu- una↵ected, even though the virtual photon impartsobservableative a high angle momentum subjectthe✓ protonto over theto transfer severalstrong proton units on innon-linear beam rapidity. a quark axis. This color singlet exchange has historically been scription of a di↵ractive event. The kinematic variablescalled the pomeron, are which similar had a specific to interpretationdorapidity in Regge theory. is An equal illustration to of the rapidity, ⌘ or antiquark in the target. A crucial question in di↵ractionFor ultra-relativistic is thea hard nature di↵ractive of event particles the2 is color shown in the neutral Fig. pseu-3.2. effects even with Q values 2 2 x x ⇠ those for DIS with the following additions: y =1/2ln((E2 + p )/(E + p )). exchangeThe kinematic between variables the proton are and similar the virtual to photon.dorapidity This interaction is equal to probes, the rapidity, in a2 novel⌘ 2 M M L L significantly bigger than Qk'S t =(p p0) is the square of the momentum ⇠ /d /d saturation model thosefashion, for DIS the withnature the of following confining interactionsadditions: within hadrons.y =1/2ln((E + pL)/(E + pL)). transfer at the hadronic vertex. The Au variable t herediff isdiff identical to the one The cross-section can be formulated analogouslyAt HERA, to gaps inclusive of several DISk by units defining in rapiditythe di↵rac- haveused been in exclusive observed.σ σ processes One and gen- finds that roughly d d 1.5
q D D eralised parton distributions (see the tiveAtstructure HERA, gaps functions of severalF and unitsF inas rapidity15% of the haveat deep HERA been inelastic observed. the NLO cross-section OneDGLAP finds description that corresponds roughlyM to hard) di↵) ractive events with invariant 2 L x Sidebar on page 43). non-saturation model (LTS) Au pp 2 2 tot tot
15% of the deep inelastic cross-section correspondsmasses MXbreaks to> hard3 GeV. down di↵ractive Thealready remarkable events at Q with ~ 8 nature invariantGeV of this resultσ σ is transparent in the proton 4 2 2 2 M 2 =(p p + k k )2 is the squared d 4⇡↵ y y gap X 0 0 1 D,4 D,4 (1/ ------(1/ masses MX > 3 GeV.= The remarkable1 y + rest natureF frame:(x, of Q this a2,M 50 result2 TeV,t) electron is transparentF ( slamsx, Q2,M into in2 the,t the) proton. protonmass and of the di↵15%ractive final of state.the time, the proton is 2 2 6 2 X L p X dxB dQ dM dt Q 2 2 p' ⇡ rest frame: a 50X TeV electron✓ slams intouna◆ the↵ected, proton even and though15% the of the virtual time, photon the proton imparts⌘ is= aln(tan( high✓/2)) momentumis the pseudorapidity transfer of on a quark ⇡ -1 a particle whose momentum0.5 ∫Ldt has a= rel- 10 fb /A una↵ected, even though the virtual photonor antiquark impartsclean in a high theand target. momentumunambiguousFigure 3.2: AKinematic crucial transfer signal quantities question on of for a thesaturation quark in de- di↵ractionative angle ✓ isto the the proton nature beam axis. of the color neutral2 In practice, detector specifics may limit the measurements of di↵ractive events to those errors enlarged (× 20) M or antiquark in the target. A crucial questionexchange in di between↵raction the is thescription proton nature of a di and↵ ofractive the the event. color virtual neutral photon.For ultra-relativistic This interaction particles the pseu- probes, in a novelcc where the outgoing proton (nucleus) is not tagged, requiring insteadThe kinematic a large variables rapidity are similar gap to dorapidity is equal to the rapidity, ⌘ ⇠ exchange ⌘ in the between detector. thet protoncan then and only the befashion, virtual measured photon. the for nature particular This of interactionthose confining final for DIS states with interactions probes, theX following, e.g. in additions: for a withinJ/ novel hadrons.y =1/2ln((E + pL)/(0E + pL)). -1 fashion,mesons, the whose nature momentum of confining can interactions be reconstructedThe within cross-section very hadrons. precisely. canAt be HERA, formulated gaps of several units analogously in rapidity have beento inclusive observed. One finds DIS10 that by roughly defining the1 di↵rac- 10 15% of the deep inelastic cross-section corresponds to hard di↵ractive events with invariant The cross-section can be formulated analogously to inclusive DISD by definingD the di↵rac- M 2 (GeV2) tive structure functionsmassesF2MXand> 3 GeV.FL Theas remarkable nature of this result is transparent in the proton x D D rest frame: a 50 TeV electron slams into the proton and 15% of the time, the proton is tive structure functions F2 and FL as ⇡ 12 4 una↵2ected, even though the2 virtual photon imparts a high momentum transfer2 on a quark d 4⇡↵or antiquark in the target.y A crucial questionD,4 in di↵raction2 is2 the nature ofy the colorD,4 neutral 2 2 4 2 2 62 = exchange2 between1 y the+ proton andF the virtual(x, photon. Q ,M This interaction,t) probes,F in a( novelx, Q ,M ,t) . d 4⇡↵ y D,4 2 2 6y D,4 2 X L X = 1 y + dxFB dQ(x,dM Q2X,Mdt2 ,t) Qfashion,F the nature (x, of Q confining2,M2 2 interactions,t) . within hadrons. 2 2 2 Q6 2 2 X 2The✓ cross-sectionL can be formulated◆X analogously to inclusive DIS by defining the di↵rac- dxB dQ dMX dt D D ✓ ◆ In practice, detectortive specificsstructure functions mayF2 and limitFL as the measurements of di↵ractive events to those 4 2 2 2 d 4⇡↵ y D,4 2 2 y D,4 2 2 In practice, detector specifics may limit the measurements of di2↵ractive2 = 6 events1 y + to thoseF2 (x, Q ,MX ,t) FL (x, Q ,MX ,t) . where the outgoing protondxB dQ dM (nucleus)dt Q is not2 tagged, requiring 2 instead a large rapidity gap where the outgoing proton (nucleus) is not tagged, requiring insteadX a large✓ rapidity◆ gap ⌘ in the detector. t canIn practice, then detectoronly specificsbe measured may limit the measurements for particular of di↵ractive final events states to those X, e.g. for J/ ⌘ in the detector. t can then only be measured for particularwhere final the outgoing states protonX, (nucleus) e.g. for is notJ/ tagged, requiring instead a large rapidity gap mesons, whose momentum ⌘ in the can detector. bet can reconstructed then only be measured very for particular precisely. final states X, e.g. for J/ mesons, whose momentum can be reconstructed very precisely.mesons, whose momentum can be reconstructed very precisely.
62 62 62 p J/ + p
103 H1
(nb) ZEUS Elastic VM production inLHeC ep: Simulation b−Sat (eikonalised) b−Sat (1−Pomeron) LHeC central values from Exclusive vector mesonextrapolating HERAproduction: data: e+AEe = 150 ->GeV e+A+V 0.721 Ee = 100 GeV 2 ( p) = (2.96 nb)(W/GeV) E = 50 GeV 10 e • Similar to diffraction (b-imaging and saturation)Ee = 20 GeV • Easier and cleaner identification of final state Vertical (dotted) lines indicate values of W = s = 4E E • Bonus track: Constraint on VM wave functionsmax e p at the LHeC with Ep = 7 TeV.
10 102 103 104 ● transverseElastic J/ψ momentum production dependence energy dependence W (GeV)
∫Ldt = 10 fb-1/A coherent - no saturation ∫Ldt = 10 fb-1/A coherent - no saturation p J/ + p 4 appears5 as a candidate to 10 1 < Q2 < 10 GeV2 incoherent - no saturation 10 1 < Q2 < 10 GeV2 incoherent - no saturation 1200 x < 0.01 coherent - saturation (bSat) x < 0.01 coherent - saturation (bSat) LHeC central values from
) |η(edecay)| < 4 incoherent - saturation (bSat) |η(Kdecay)| < 4 incoherent - saturation (bSat) H1 signal) saturation effects 2 extrapolating HERA data: p(edecay) > 1 GeV/c 2 4 p(Kdecay) > 1 GeV/c 3 10 (nb) ZEUS 0.721 10 δt/t = 5% δt/t = 5% 1000 ( p) = (2.96 nb)(W/GeV) at work!!! LHeC Simulation b−Sat (eikonalised) 103 incoherent 102 800 b−Sat (1−Pomeron) 1 z saturation
) − (1 z)!r /dt (nb/GeV /dt ) /dt (nb/GeV /dt ψ −
φ 2 10 γ∗ !r E J/Psi @ LHeC 10 z 600
10 x x! e’ e’ Au’+ Linear,+ Non-linear, e’ e’ Au’+ + J/ !b → Ee = 150 GeV → 400 1 sensitivity saturation.Ee = 100 GeV 1 Ee = 50 GeV (e + Au(e + (e + Au(e + Ee = 20 GeV σ
σ 2
d 200 d -1 to (xg) ɸ. @ EIC Vertical (dotted) lines indicate values of 10 -1 p coherent p 10 ! W = s = 4E E at the LHeC with E = 7 TeV. J/ψ max e p p φ 0 10-2 10-2 0 500 1000 1500 2000 2500 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 34 W (GeV) |t | (GeV2) |t | (GeV2)
Figure 3.20: d /dt distributions for exclusive J/ (left) and (right) production in coherent andFigure 4.23: LHeC exclusive J/ photoproduction pseudodata, as a function of the p incoherent events in di↵ractive e+Au collisions. Predictions from saturationb-imaging: and non-saturation throughcentre-of-mass a Fourier energy transformation,W , plotted on a (top) log–log scale and (bottom) linear–linear scale. models are shown. one can extractThe the di↵ erencespatial between gluon the distribution solid and dashed (and curves indicates the size of unitarity corrections correlations). according to the b-Sat dipole model. a color-neutral exchange, which is dominated neutrons emitted by the nuclear breakup in by two gluons at the lowest order. It is pre- the incoherent case. Again, we compare to 13 cisely this two gluon exchange which yields a predictions of saturation and non-saturation di↵ractive measurement of the gluon density models. Just as for the previous figures, the in a nucleus. curves were generated with the Sartre event Experimentally the key to the spatial generator and had to pass through an ex- gluon distribution is the measurement of the perimental filter. The experimental cuts are 139 d /dt distribution. As follows from the op- listed in the figures. tical analogy presented in Sec. 3.2.1, the As the J/ is smaller than the , one Fourier-transform of (the square root of) this sees little di↵erence between the saturation distribution is the source distribution of the and no-saturation scenarios for exclusive J/ object probed, i.e., the dipole scattering am- production but a pronounced e↵ect for the 2 plitude N(x, rT ,bT ) on the nucleus with rT , as expected. For the former, the statisti- 2 2 ⇠ rd 1/(Q + MV ), where MV is the mass of the cal errors after the 3 minimum become ex- vector meson [165] (see also the Sidebar on cessively large requiring substantially more page 43). than the simulated integrated luminosity of 1 Figure 3.20 shows the d /dt distribution 10 fb /A. The situation is more favorable for J/ on the left and mesons on the for the , where enough statistics up to the right. The coherent distribution depends on 4th minimum are available. The ⇢ meson has the shape of the source while the incoher- even higher rates and is also quite sensitive ent distribution provides valuable informa- to saturation e↵ects. However, it su↵ers cur- tion on the fluctuations or “lumpiness” of rently from large theoretical uncertainties in the source [176]. As discussed above, we the knowledge of its wave-function, making are able to distinguish both by detecting the calculations less reliable.
85 Di-hadron azimuthal correlations: e+A -> e+h1+h2+X
• CGC prediction: At small-x, back-to-back correlations strongly suppressed trigger 1 dNpair ➡ Coincidence probability CP( )= Ntrig d
RHIC d+Au forward data Predictions for the EIC 0.18 Central dAu collisionsQ2 = 1 GeV2 EIC stage-II ptrigger > 2 GeV/c ep T 0.026 0.16 0.2 -1 assoc trigger STAR Preliminary CGC calculations ∫ Ldt = 10 fb /A 1 < pT < pT 0.14 pt < 2 GeV/c <ηt> = 3.2 Stasto et al |η|<4 0.024 pt > pa > 1 GeV/c <ηa>=3.2 Albacete-Marquet 0.15
0.12 ) "non-CGC" calculations ) 0.022 ) eAu - nosat eCa Kang et al 0.1 Δϕ ( ΔΦ Δϕ
0.02 0.08 Au 0.1 C( e CP( C 0.06 0.018 0.04 eAu 0.05 0.016 eAu - sat 0.02
0.014 0 0 -1 0 12 2.52 33 3.54 4 4.55 22.533.544.5 ΔΦ Δϕ Δϕ Background subtraction, vicinity to the kinematic limit, K-factors, double parton eA colliders: smoking gun for saturation Figurescattering 3.16: Left: prevent A saturation interpretation model as a CGC prediction of the coincidence signal versus azimuthal angle dieffect↵erence ' between two hadrons in e+p, e+Ca, and e+A collisions [169, 170]. Right: A comparison of saturation model prediction for e+A collisions with calculations from conven- 14 tional non-saturated model for EIC stage-II energies. Statistical error bars correspond to 10 1 fb /A integrated luminosity.
GeV2. The highest transverse momentum power of these measurements. In fact, al- hadron in the di-hadron correlation func- ready with a fraction of the statistics used tion is called the “trigger” hadron, while here one will be able to exclude one of the the other hadron is referred to as the “asso- scenarios conclusively. ciate” hadron. The “trigger” hadrons have The left panel of Fig. 3.17 depicts the pre- trig transverse momenta of pT > 2 GeV/c and dicted suppression through JeAu, the relative the “associate” hadrons were selected with yield of correlated back-to-back hadron pairs assoc trig 1 GeV/c < pT 80 from [282] and, in order to illustrate their e↵ect, di↵erent nuclear PDFs [167,326] and both ordinary [515,516] and modified [518]13 fragmentation functions. Cuts have been applied as in the H1 study [519]14 whose data are well reproduced by the NLO calculation: angle of the 0 ⇡ from the proton in the laboratory ✓ [5 , 25 ], pion energy fraction x = E /E > 0.01 ⇡ 2 ⇡ ⇡ p and pion transverse momentum 2.5 2 1 dN k 1 dN k Q v = photon energy Rk (⌫,z,Q2)= A p , (4.31) = A N e d⌫dz N e d⌫dz 2Mx z = fraction taken by the hadron A p e 1.50 D0 mesons (lower energy)2 with N the number of scattered electrons at aPions given (lower⌫ energy)and Q i.e. the DIS cross section. large v : in-medium parton propagation At LO and for a single quark flavour, this doubleD0 mesons ratio (higher becomes energy) the ratio of fragmentation functions in eA over ep, see [337]. Usually, the energyPions (higher of the energy) lepton-hadron/nucleus collisions - Energy and path-length dependence of D0 (10% less energy loss) are the same in numerator1.30 and denominator, andWang, the pions collisions (lower energy) in the denominator are eD partonic energy loss and pT-broadening in order to suppress isospin e↵ects as much as possible.Wang, pions (higher energy) In order to estimate the nuclear modifications of fragmentation functions for the case of the LHeC, we compute1- this pion double ratio. For the numerator,1- we D0 consider ePb collisions at 1.10 systematic systematic 60+2750 GeV while foruncertainty the denominator we take ep collisionsuncertainty at 60+7000 GeV. We follow the model in [520] which considers the energy loss of the parent parton though radiative processes15 plus formation time arguments which make the e↵ective length of traversed nu- 0.90 clear matter L smaller at small ⌫ than the geometrical one Lmax. We use the LO nucleon PDFs in [282] andMultiplicity Ratio the nucleon fragmentation functions in [515,516], and also considered the nuclear modification of PDFs in [167]. We employ a value of the transport coe cient char- acterising the strength0.70 of the interaction of a quark with nuclear matterq ˆ =0.7 GeV2/fm 16. ~ Ratio of FF’s The results for ⇡0 production are shown in Fig. 4.57. Several conclusions can be drawn. First, the e↵ect of0.50 the di↵erence in energy between numerator and denominator, and of isospin, are very small. Second, 0.01 < y < 0.85, nuclear x > 0.1, 10 e↵ fbects-1 on fragmentation are larger for smaller ⌫, 2 2 2 as expected in a model Higher in which energy: 25 the GeV energy 15 177 Jets in e+A • Large ET even in eA • Useful for studies of parton dynamics in nuclei and photon and jet structure • Studies of backgroundJets subtraction in andeA: reconstruction pending Jets in eA: EIC LHeC proton nucleus Access to large-x values of the gluon distribution. Complementary to F2 data to constrain nPDF’s ● Jets: large ET even in eA. ● Jets: large ET● evenUseful infor eA. studies of parton dynamics in nuclei (hard probes), and 16 ● Useful for studiesfor photon of structure.parton dynamics in nuclei (hard probes), and for photon structure.● Background subtraction, detailed reconstruction pending. 17 ● Background subtraction, detailed reconstruction pending. 17 Conclusions - A high-energy eA collider would be to the QGP program the same as HERA for the pp program at the LHC. - QGP properties cannot be precisely extracted from data without a proper understanding of the initial state: eA collisions would provide access to a precise picture: • Unprecedented access to small-x nPDF’s • Novel sensitivity to physics beyond standard pQD. • High precision test of factorization • Transverse scan of the hadron at small-x • Detailed information on parton energy loss and hadronization dynamics - Many more processes and observables still to be investigated - Many thanks to EIC and LHeC working groups for their input! Thank you! 17 Back up slides 18 eA • New effects likely to be revealed in tensions between eA and pA, AA, ep (breakdown of factorisation) • Detailed precision understandingTalk by Paul Newman likely on tuesday to come from eA - LHeC offers access to lower x than is realistically achievable in pA at the LHC 15 - Clean final states / theoretical control to (N)NLO in QCD 19 (p , y >>0) pPb. Moving forward: Testing the evolution t h 2 2 2 2 pPb rcBK-MC rcBK-MC 1.8 R (y=0) RpPb(y=2) EPS09 nPDF 1.8 1.8 EPS09 nPDF 1.8 rcBK 1.6 rcBK-MC-hybrid IPSat 1.6 1.6 1.6 1.4 1.4 1.4 1.4 1.2 1.2 1.2 1.2 1 1 1 1 0.8 0.8 0.8 0.8 0.6 0.6 0.6 0.6 0.4 0.4 0.4 0.4 0.2 Preliminary results. JLA-Dumitru-Fujii-Nara0.2 2 4 6 8 10 2 4 6 8 10 pt (GeV) pt (GeV) nPDF EPS09 results by P Quiroga 2 2 2 2 RpPb(y=4) rcBK-MC-hyb RpPb(y=6) rcBK-MC-hyb 1.8 EPS09 nPDF 1.8 1.8 EPS09 nPDF 1.8 1.6 1.6 1.6 1.6 1.4 1.4 1.4 1.4 1.2 1.2 1.2 1.2 1 1 1 1 0.8 0.8 0.8 0.8 0.6 0.6 0.6 0.6 0.4 0.4 0.4 0.4 0.2 0.2 0.2 2 4 6 8 10 pt (GeV) 2 4 6 8 10 pt (GeV) 20 b-dependence proton: Well modelling! constrained by :) Nucleus abundant HERA data :( 21 EIC: eRHIC, ELIC eRHIC, ERL MEIC, polarized pA@LHC and eA at an EIC: 4. Future opportunities and facilities. 40 22 LHeC@CERN: LHeC, ERL 41 23 Kinematics: LHC vs. EIC/LHeC (Ee=140GeV*and* E =7TeV) ● Existing ep: p pp@LHC at y=0; eA: not even dAu@RHIC. ● LHeC: clean scan of Salgado the LHC x- Q2 domain. ● EIC: complements HERA with eA. pA@LHC and eA at an EIC: 4. Future opportunities and facilities. 42 24