1. Salvatore Fazio BNL University of Washington – INT Seattle, WA – USA November 1-13, 2010 Simulation of DVCS with an EIC using MILOU pp  

2. Planing of the talk  The eRHIC accelerator and an EIC detector compared to HERA  Strategy of a DVCS measurement  Hera results  Extension to EIC  DVCS simulation for an EIC  Summary Nov. 9, 20102 S. Fazio: INT-workshop, Univ. of Washington, Seattle

3.  27.5 GeV electrons/positrons on 920 GeV protons → √s=318 GeV  2 colliding experiments: H1 and ZEUS  Total lumi collected at HERA: 500 pb -1, polarization of electrons/positrons at HERA II Detectors not originally designed for forward physics, Roman pots added later From HERA to an EIC collider  20 - 30 GeV electrons on 325 (125) GeV protons (nuclei). Polarization of electrons and protons (nuclei)  Lumi: 1.4 x 10 34 cm -2 s -1 For exclusive diffraction the concept is similar to HERA but: Dedicated forward instrumentation Higher tracker coverage Very High lumi! STAR ePHENIX 6 pass 2.5 GeV ERL Coherent e-cooler Beam- dump Polarized e- gun eRHIC detector EIC/eRHIC HERA Nov. 9, 20103 S. Fazio: INT-workshop, Univ. of Washington, Seattle

4. Important (as respect of HERA) improvements: Central Tracking Detector better em calorimeter resolution Very forward calorimetry Rear Trackers! Roman pots from the early biginning The EIC detector e p/N FORWARD REAR Nov. 9, 20104 S. Fazio: INT-workshop, Univ. of Washington, Seattle Similarities with HERA detectors: Hermetic Asymmetric 2 468 10 2.5 m 3.5 m 1214 90 mm 5.75 m 16 IP Dipole: 2.5 m, 6 T  =18 mrad 4.5 m  =18 mrad  =10 mrad Estimated  * ≈ 8 cm  =44 mrad 6.3 cm ZDC p c /2.5 15.7 cm 6 mrad 11.2 cm 4.5 cm neutrons p c /2.5 e Quad Gradient: 200 T/m

5. Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 5 0.44 m 90 m 10 mrad 0.329 m 3.67 mrad 60 m 10 20 30 0.188036 m 18.8 m 16.8 m 6.33 mrad 4 m Dipole © D.Trbojevic 30 GeV e - 325 GeV p 125 GeV/u ions Spinrotator

6. GPD p p γ γ* Deeply Virtual Compton Scattering VM (ρ, ω, φ, J/ψ, Υ)DVCS (γ) Q2Q2 Q 2 + M 2 Scale: DVCS properties: Similar to VM production, but γ instead of VM in the final state No VM wave-function involved Important to determine Generalized Parton Distributions sensible to the correlations in the proton GPD s are an ingredient for estimating diffractive cross sections at LHC IP pp V γ* Nov. 9, 20106 S. Fazio: INT-workshop, Univ. of Washington, Seattle

7. Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 7  theoretically very clean DVCS (  ): H, E, H, E DVCS (  ): H, E, H, E  VM (  H E  info on quark flavors PS mesons (  : H E PS mesons (  : H E~ ~~ ~ quantum number of final state selects different GPDs: 00 2  u  d  2  u  d ρ0ρ0 2u  d, 9g/4 ω 2u  d, 3g/4  s, g ρ+ρ+ udud J/ψg Accessing the GPDs

8. Nov. 9, 20108 BHDVCS p p   e e Wrong-sign sample: a negative track match to the second candidate  sample: no tracks matching to the second candidate e sample: a track match to the second candidate (DVCS+BH) (BH+ d ilepton + J/  ) (dilepton + J/  ) DVCS @ ZEUS - Strategy S. Fazio: INT-workshop, Univ. of Washington, Seattle

9. Q 2 dependence for the W slope not clear within the uncertainties! ZEUS: JHEP05(2009)108 H1: Phys.Lett.B659:796-806,2008 Nov. 9, 20109 S. Fazio: INT-workshop, Univ. of Washington, Seattle Fit: σ ~ W δ DVCS @ HERA t measured indirectly: No evidence for W dependence of bby roman pots!

10. Nov. 9, 201010 b = 4.5 ± 1.3 ± 0.4 d σ /dt measured for the first time by a direct measurement of the outgoing proton 4-momentum using the LPS spectrometer The ZEUS result is in agreement with H1 …nevertheless it seems to suggest a lower trend! t dependence S. Fazio: INT-workshop, Univ. of Washington, Seattle

11. W-dependence: summary Summary of the W,t-dependence for all VMs + DVCS measured at HERA Nov. 9, 201011 S. Fazio: INT-workshop, Univ. of Washington, Seattle Fit: σ  ~ W δ Exclusive production of VMs can be a golden measurement for an EIC

12. To successfully measure t indirectly from the electron and photon candidates it is important:  Tracker coverage (tracker has higher momentum resolution than Cal!) Reso of the CTD @ ZEUS: σ(p T )/p T =0.0058p T ⊕ 0.0065 ⊕ 0.0014/p T  High resolution em calorimetry (crucial! Remember that one particle is a photon!) For ZEUS it was σ(E)/E=0.18/√E Measuring t indirectly with an EIC CTD acceptance @ ZEUS DVCS/BHBH Always measure a track when we can -> better momentum resolution but not only… More acceptance for DVCS! Nov. 9, 201012 S. Fazio: INT-workshop, Univ. of Washington, Seattle

13. Direct t measurement at EIC But… is an indirect measurement of t really an issue for EIC? We’ll get roman pots in the forward region at EIC! L = 27.77 pb -1 55 events (DVCS + BH) for eRHIC: 1.4 10 34 * E p /325 cm -2 s -1 assuming 50% operations efficiency one week corresponds to: L(1 w)= 0.5 * 604800(s in a week) * (1.4x10 34 cm -2 s -1 ) = 4*10 39 cm -2 = 4000pb -1 + Roman Pots ~ 8000 events/week !! assuming the same acceptance ad LPS (~2%) Calculations are absolutely not rigorous! But give an idea… Silicon micro-strips resolution: 0.5% for P L ; 5 MeV for P T Nov. 9, 201013 S. Fazio: INT-workshop, Univ. of Washington, Seattle EIC lumi

14. t vs proton scattering angle Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 14 4 GeV el x 50 GeV prot 4 x 100 4 x 250 very strong correlation between t and “recoiling” proton angle  Roman pots need to be very well integrated  resolution on t! t=(p 4 -p 2 ) 2 = 2[(m p in.m p out )-(E in E out - p z in p z out )] t=(p 3 –p 1 ) 2 = m ρ 2 -Q 2 - 2(E γ* E ρ -p x γ* p x ρ -p y γ* p y ρ -p z γ* p z ρ ) 14

15. Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle MILOU Based on: Frankfurt, Freund and Strikman (FFS) [Phys. Rev. D 67, 036001 (1998). Err. Ibid. D 59 119901 (1999)] FFS GPDs-based Based on: A. Freund and M. McDermott All ref. in: http://durpdg.dur.ac.uk/hepdata/dvcs.html GPDs, evolved at NLO by an indipendent code which provides tables of CFF - at LO, the CFFs are just a convolution of GPDs: 15 Old model: written before data came out! Used by H1 and ZEUS for their DVCS measurements The ALLM parametrization for F 2 is used The code MILOU contains two different models for DVCS simulation: Written by E. Perez, L Schoeffel, L. Favart [arXiv:hep-ph/0411389v1]

16. provide the real and imaginary parts of Compton form factors (CFFs), used to calculate cross sections for DVCS and DVCS-BH interference. The B slope is allowed to be costant or to vary with Q 2 : Proton dissociation (ep → eγY) can be included Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 16 MILOU

17. Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 1.5 < Q 2 < 100 GeV 2 10 -4 < x < 0.1 0.01 < y < 0.85 0 < |t| < 1.5 GeV 2 Radiative corrections: OFF t slope: B = 5.00 (costant) GPDs evolved at NLO ALLM param. used for F 2 (FFS model) 30 X 325: E_el = 10 GeV  ep -> e  p)= 0.186 nb (FFS_ALLM)  ep -> e  p)= 0.376 nb (GPDs) 20 X 250: E_el = 5 GeV  ep -> e  p)= 0.16 nb (FFS_ALLM)  ep -> e  p)= 0.32 nb (GPDs) 10 X 100: E_el = 0 GeV  ep -> e  p)= 8.1*10 -2 nb (FFS_ALLM)  ep -> e  p)= 0.16 nb (GPDs) 17 5 X 50: E_el = 0 GeV  ep -> e  p)= 8.1*10 -2 nb (FFS_ALLM)  ep -> e  p)= 0.16 nb (GPDs) Phase space eRHIC Luminosity 100 k event generated for each config.

18. Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 18   vs E  30 X 325

19. Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 19   vs E  20 X 250

20. Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 20   vs E  10 X 100

21. Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 21   vs E  5 X 50

22. Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 22 t-xsec (ep ->  p) FFS - 30 X 325 by roman pots! L = 0.54 fb -1 EIC lumi: 4 fb -1 /month @ 30x325 Precision enormously improved Roman pots acceptance not yet included in the simolation 1.5 < Q 2 < 100 GeV 2 10 -4 < x < 0.1 0.01 < y < 0.8

23. Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 23 t-xsec GPDs conv. - 30 X 325 1.5 < Q 2 < 100 GeV 2 10 -4 < x < 0.1 0.01 < y < 0.8 Systematics will dominate!!

24. Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 24 20 X 25010 X 1005 X 50 t-xsec  dominated by gluon contributions  EIC will provide sufficient luminosity to bin in multi-dimensions  wide x and Q 2 range needed to extract GPDs … we can do a fine binning in Q2 and W!

25. Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 25 Scanning the phase space… Logarithmic bins: 1 < Q 2 < 100 GeV 2 10 -4 < x < 0.1 y = 0.85 y = 0.01 y = 0.85 y = 0.01 20 X 250 10 X 100 30 X 325 5 X 50

26. Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 26 Scanning the phase space… y = 0.01 y = 0.85 y = 0.01 y = 0.85 30 X 32520 X 250 10 X 1005 X 50

27. Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 27 30x325-t-xsec Veri precice scan! y = 0.85 y = 0.01

28. Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 28 20x250-t-xsec GPD FFS y = 0.01 y = 0.85 y = 0.01 y = 0.85

29. Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 29 10x100 5x50 t-xsec y = 0.85

30. The phi angle DVCS: the beam-charge asymmetry At EIC: Possible if a positron beam Thanks to a good tracker coverage Nov. 9, 201030 S. Fazio: INT-workshop, Univ. of Washington, Seattle Interference term: Beam charge asymmetry: DVCS and BH: identical final state → they Interfere

31. 31  How does the nuclear environment modify parton-parton correlations?  How do nucleon properties change in the nuclear medium? (Bethe-Heitler)  Nuclear GPDs ≠ GPDs of free nucleon  Enhancement of effect when leaving forward limit?  caused by transverse motion of partons in nuclei?  important role of mesonic degrees of freedom?  manifest in strong increase of real part of τ DVCS with atomic mass number A?  DVCS in coherent region: new insights into ‘generalized EMC effect’? new insights into ‘generalized EMC effect’? Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle DVCS on nuclear targets MC simulation for DVCS on nuclei coming soon thanks to an updated version of MILOU code

32. Summary  A lot of experience carried over from HERA  Simulation shows how an EIC forward program can sensibly improve HERA results and go beyond  Uncertainties will be dominated by systematics  Large potential for diffractive-DIS studies using polarized and unpolarized protons and nuclei Outlook:  Simulation of asymmetries  Simulation of DVCS on nuclei  Updating the MILOU code to status of art (Re_Amp, NNLO…) Nov. 9, 201032 S. Fazio: INT-workshop, Univ. of Washington, Seattle

33. Back up Nov. 9, 201033 S. Fazio: INT-workshop, Univ. of Washington, Seattle