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Salvatore Fazio BNL for the BNL EIC Science Task Force

GPDs at an EIC. Salvatore Fazio BNL for the BNL EIC Science Task Force. g *. g. XX International Conference on Deep-Inelastic Scattering and Related Subjects University of Bonn, Germany March 26-30, 2012. p. p. Plan of the talk.

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Salvatore Fazio BNL for the BNL EIC Science Task Force

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  1. GPDs at an EIC Salvatore Fazio BNLfor the BNL EIC Science Task Force g* g XX International Conference on Deep-Inelastic Scattering and Related Subjects University of Bonn,Germany March 26-30, 2012 p p

  2. Plan of the talk • The eRHIC accelerator and an EIC detector capabilities for exclusive diffraction • GPDs and DVCS • Bethe-Heitler subtraction • |t|-differential cross sections • Charge and spin asymmetries • Imaging with an EIC (the impact!) • J/y • Summary See also: D. Mueller’s and M. Diehl’s talks S. Fazio: DIS2012 - Bonn, Germany

  3. The eRHIC collider EIC detector EIC/eRHIC Polarized e-gun eRHIC detector Beam-dump 6 pass 2.5 GeV ERL Coherent e-cooler • 5 - 20 GeV electrons on 100-250 (130) GeV protons (nuclei). Polarization of electrons and protons (nuclei) • Lumi: 0.62 x1033cm-2s-1 (stage 1–eppol) • 3.1 x 1033 cm-2s-1 (stage 1–epunp) • 9.7 x 1033 cm-2s-1 (stage 2-ep) • Important for exclusive DIS: • Dedicated forward instrumentation • High tracker coverage • Very High lumi! ePHENIX • An electron ring will be built at the RHIC facility • The current experiments can be upgraded for ap(A) physics • A new dedicated detector will be built eSTAR S. Fazio: DIS2012 - Bonn, Germany

  4. The EIC detector p/N e FORWARD REAR • General properties: • Hermetic • Asymmetric • Important for exclusive diffraction: • Hermetic Central Tracking Detector (Si pixels) • Good em calorimeter resolution with fine granularity (fibres) • Very forward calorimetry • Roman pots from the early beginning (and with excellent acceptance) S. Fazio: DIS2012 - Bonn, Germany

  5. Direct |t| measurement @ eRHIC Accepted in“RomanPot”(example) at s=20m Plots from J-H Lee 20x250 GeV Quadrupoles acceptance 5x50 GeV Roman Pots at HERA 10s from the beam-pipe L = 27.77 pb-1 55 events (DVCS + BH) • • high‐t acceptance mainly limited by magnet aperture • • low‐t acceptance limited by beam envelop (~10σ) • • t‐resolution limited by • – beam angular divergence ~100μrad for small t • – uncertainties in vertex (x,y,z) and transport • – ~<5-10% resolution in t (RP at STAR) S. Fazio: DIS2012 - Bonn, Germany

  6. Accessing the GPDs ~ ~ • DVCS(g): H, E, H, E • VM(r, w, f): H E • Info on quark flavors via PS mesons (p, h): H E quantum number of final state selects different GPDs: ~ ~ S. Fazio: DIS2012 - Bonn, Germany

  7. Accessing the GPDs Dominated by H slightly dependent on E Angle btw the production and scattering planes Angle btw the scattering plane and the transverse pol. vector Requires a positron beam at eRHIC Dominated by H slightly dependent on E sin(FT-fN) governed by E and H S. Fazio: DIS2012 - Bonn, Germany

  8. γ* V γ IP p p p p Deeply Virtual Compton Scattering VM (ρ, ω, φ, J/ψ, Υ) DVCS (γ) γ* Scale: Q2 + M2 Q2 A GOLDEN MEASUREMENT! • DVCS properties: • Similar to VM production, but γinstead of VM in the final state • Very clean experimental signature • Not affected by VM wave-function uncertainty • Hard scale provided by Q2 • Sensitive to both quarks and gluons S. Fazio: DIS2012 - Bonn, Germany

  9. Scanning the phase space… DVCS |t|-slope @ HERA EIC lumi: ~10 fb-1/year @ stage 1 – 5x100 ~10 fb-1/month @ stage 2 – 20x250 • EIC will provide sufficient lumito bin in multi-dimensions • wide x and Q2 range needed to extract GPDs 20 X 250 5 X 100 … we can do a fine binning in Q2 and W… and even in |t| S. Fazio: DIS2012 - Bonn, Germany

  10. DVCS phase-space Stage 2 Stage 1 S. Fazio: DIS2012 - Bonn, Germany

  11. MC simulation Written by E. Perez, L Schoeffel, L. Favart[arXiv:hep-ph/0411389v1] The code MILOU is Based on a GPDs convolution by: Freund and M. McDermott [All ref.s 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: • 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 Q2: • Proton dissociation (ep → eγY) can be included • Other non-GPD based models are implemented like FFS, DD S. Fazio: DIS2012 - Bonn, Germany

  12. DVCS BH e  e  p p DVCS - BH • sample: no tracksmatchingto the • second candidate (DVCS+BH) esample: a track match to the second candidate (BH+bkgd) Wrong-sign sample: a negative track match to the second candidate (bkgd) BH is “precisely” known but to certain level! Uncertainty on proton form factor uncertainty on BH xsec ~ 3% (at LO) S. Fazio: DIS2012 - Bonn, Germany

  13. BH rejection Eel Eγ Eel Eγ Eel Eγ Eel Eγ BH electron has very low energy (often below 1 GeV) Photon for BH (ISR) goes often forward (trough the beam pipe) Important: em Cal must discriminate clusters above noise down to 1 GeV S. Fazio: DIS2012 - Bonn, Germany

  14. BH rejection BH and DVCS BH dominated In DVCS most of the photon are less “rear” Than the electrons: (θel-θg) > 0  rejects most of the BH S. Fazio: DIS2012 - Bonn, Germany

  15. BH fraction Stage 2 BH subtraction will be not an issue for y<0.6 S. Fazio: DIS2012 - Bonn, Germany

  16. BH fraction Stage 1 BH subtraction will be relevant in stage 1, at large y, depending on the x-Q2 bin BUT… Stage 1-2 overlapping: x-sec. measurements in stage 2 at low-y can cross-check the BH subtrac. made in stage 1 S. Fazio: DIS2012 - Bonn, Germany

  17. Data simulation & selection • 0.01 < |t| < 0.85 GeV2 • (Low-|t| sample) • Very high statistics • Systematics will dominate! • Within Roman pots acceptance • Acceptance criteria • for Roman pots: 0.03< |t| < 0.88 GeV2 • for |t| > 1GeV2 detect recoil proton in main detector • 0.01 < y < 0.85 GeV2 • h< 5 • BH rejection criteria (applied to x-sec. measurements) • y < 0.6 • (θel-θg) > 0 • Eel>1GeV2; Eel>1GeV2 • Events smeared for expected resolution in t, Q2, x • Systematic uncertainty assumed to be ~5% (having in mind experience from HERA) • Overall systematic uncertainty from luminosity measurement not taken into account • 1.0 < |t| < 2.0 GeV2 • (Large-|t| sample) • Xsec goes down exponentially • requires a year of data taking @ 20x250 GeV(stage 2) • Main detector can be used in measuring |t| Stage 1: 5 X 100 GeV~10 fb-1 (~ a year) Stage 2: 20 X 250 GeV~100 fb-1 (~ a year) S. Fazio: DIS2012 - Bonn, Germany

  18. dσ/d|t|- Stage 1 b=5.6 • Specifications: • Statistical error down to 1% • It uses smeared t values (5% momentum resol.) • |t|-binning –> 3 * resolution (or • higher) Smearing of momenta and energies accordig to… (~ 10 months EIC) S. Fazio: DIS2012 - Bonn, Germany

  19. Asymmetries Plots from D. Mueller S. Fazio: DIS2012 - Bonn, Germany

  20. Imaging Plots from D. Mueller …FIT… Errors are extrapolated for: |t| 0 ; |t| > 1.5 GeV2 S. Fazio: DIS2012 - Bonn, Germany

  21. Imaging • A global fit over all mock data was done, based on the GPDs-based model: • [K. Kumerički, D Müller, K. Passek-Kumerički 2007] • Known values q(x), g(x) are assumed for Hq, Hg (at =0, t=0 forward limits Eq, Egare unknown) • Excellent reconstruction of Hsea, Hseaand good reconstruction of Hg(from dσ/dt) Plots from D. Mueller See also: D. Mueller’s talk for details M. Diehl’s talk for an overview S. Fazio: DIS2012 - Bonn, Germany

  22. J/ψ • g*p -> J/yp • pseudo-data generated using a version of Pythia tuned to J/y data from HERA • wave function uncert. (non-relativistic approximation) • mass provides hard scale • Sensitive to gluons • Both photo- and electro-production can be computed Plots from E. Aschenauer S. Fazio: DIS2012 - Bonn, Germany

  23. Summary • A lot of experience carried over from HERA • Simulation shows how an eRHIC can much improve our knowledge of GPDsa.r.o. HERA • A fine binning of x-sec and symmetries will be possible, uncertainties mostly dominated by systematics • Large potential for an accurate 2+1D imaging of the polarized and unpolarized quarks and gluons inside the hadrons (and nuclei!) S. Fazio: DIS2012 - Bonn, Germany

  24. Back up S. Fazio: DIS2012 - Bonn, Germany

  25. DVCS @ HERA Fit: σ ~ Wδ Q2 dependence for the W slope not clear within the uncertainties! ZEUS: JHEP05(2009)108 H1: Phys.Lett.B659:796-806,2008 tmeasured indirectly: by roman pots! No evidence for W dependence of b S. Fazio: DIS2012 - Bonn, Germany

  26. qgvsEg 20 X 250 S. Fazio: DIS2012 - Bonn, Germany

  27. qgvsEg 10 X 100 S. Fazio: DIS2012 - Bonn, Germany

  28. BH BH DVCS DVCS • BH dominates at large y. • DVCS dropes with y S. Fazio: DIS2012 - Bonn, Germany

  29. BH fraction - overall Effect of the cuts The effect of the cut for the 20x250 conf. is that BH never exceeds 70% of the sample S. Fazio: DIS2012 - Bonn, Germany

  30. BH fraction - overall for the 5x100 conf. is that BH can be a problem at large y and large t, depending on the bin S. Fazio: DIS2012 - Bonn, Germany

  31. t-xsec (ep -> gp) Selection criteria: 0.01 < y < 0.6 θγ < 2x10-2 radθel< 2x10-2radEγ > 1 GeVEel > 1 GeVb=5.6 GeV-2 HERA eRHIC 10 x-bins ; 5 Q2-bins S. Fazio: DIS2012 - Bonn, Germany

  32. dσ/d|t|- Stage 2 b=5.6 (~ 3.5 weeks EIC) S. Fazio: DIS2012 - Bonn, Germany

  33. dσ/d|t|- Stage 2 b=5.6 • Resolution: uniform assumed ~20% • Large-|t| -> |t| is reconstructed using the main detector (~ 1 year EIC) S. Fazio: DIS2012 - Bonn, Germany

  34. Crucial! Our em cal must distinguish two clusters within the order of 1 deg More studies on-going… • Electron and photon clusters are ofter very close! • can affect the phi distribution reconstruction! S. Fazio: DIS2012 - Bonn, Germany

  35. DVCS in coherent region: • new insights into ‘generalized EMC effect’? (Bethe-Heitler) DVCS on nuclear targets • How does the nuclear environment modify parton-parton correlations? • How do nucleon properties change in the nuclear medium? • 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 τDVCS with atomic mass number A? MC simulation for DVCS on nuclei coming soon thanks to an updated version of MILOU code S. Fazio: DIS2012 - Bonn, Germany

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