Salvatore Fazio BNL University of Washington – INT Seattle, WA – USA November 1-13, 2010 Simulation of DVCS with an EIC using MILOU pp
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, S. Fazio: INT-workshop, Univ. of Washington, Seattle
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 GeV electrons on 325 (125) GeV protons (nuclei). Polarization of electrons and protons (nuclei) Lumi: 1.4 x 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, S. Fazio: INT-workshop, Univ. of Washington, Seattle
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, S. Fazio: INT-workshop, Univ. of Washington, Seattle Similarities with HERA detectors: Hermetic Asymmetric m 3.5 m 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 / cm 6 mrad 11.2 cm 4.5 cm neutrons p c /2.5 e Quad Gradient: 200 T/m
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle m 90 m 10 mrad m 3.67 mrad 60 m m 18.8 m 16.8 m 6.33 mrad 4 m Dipole © D.Trbojevic 30 GeV e GeV p 125 GeV/u ions Spinrotator
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, S. Fazio: INT-workshop, Univ. of Washington, Seattle
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: 00 2 u d 2 u d ρ0ρ0 2u d, 9g/4 ω 2u d, 3g/4 s, g ρ+ρ+ udud J/ψg Accessing the GPDs
Nov. 9, 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/ ) ZEUS - Strategy S. Fazio: INT-workshop, Univ. of Washington, Seattle
Q 2 dependence for the W slope not clear within the uncertainties! ZEUS: JHEP05(2009)108 H1: Phys.Lett.B659: ,2008 Nov. 9, S. Fazio: INT-workshop, Univ. of Washington, Seattle Fit: σ ~ W δ HERA t measured indirectly: No evidence for W dependence of bby roman pots!
Nov. 9, 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
W-dependence: summary Summary of the W,t-dependence for all VMs + DVCS measured at HERA Nov. 9, S. Fazio: INT-workshop, Univ. of Washington, Seattle Fit: σ ~ W δ Exclusive production of VMs can be a golden measurement for an EIC
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 ZEUS: σ(p T )/p T =0.0058p T ⊕ ⊕ /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 ZEUS DVCS/BHBH Always measure a track when we can -> better momentum resolution but not only… More acceptance for DVCS! Nov. 9, S. Fazio: INT-workshop, Univ. of Washington, Seattle
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 = pb events (DVCS + BH) for eRHIC: * E p /325 cm -2 s -1 assuming 50% operations efficiency one week corresponds to: L(1 w)= 0.5 * (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, S. Fazio: INT-workshop, Univ. of Washington, Seattle EIC lumi
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 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
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle MILOU Based on: Frankfurt, Freund and Strikman (FFS) [Phys. Rev. D 67, (1998). Err. Ibid. D (1999)] FFS GPDs-based Based on: A. Freund and M. McDermott All ref. in: 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/ v1]
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
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 1.5 < Q 2 < 100 GeV < x < < y < < |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)= nb (FFS_ALLM) ep -> e p)= 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.
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 18 vs E 30 X 325
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 19 vs E 20 X 250
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 20 vs E 10 X 100
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 21 vs E 5 X 50
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 30x325 Precision enormously improved Roman pots acceptance not yet included in the simolation 1.5 < Q 2 < 100 GeV < x < < y < 0.8
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 23 t-xsec GPDs conv X < Q 2 < 100 GeV < x < < y < 0.8 Systematics will dominate!!
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle X 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!
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 25 Scanning the phase space… Logarithmic bins: 1 < Q 2 < 100 GeV < x < 0.1 y = 0.85 y = 0.01 y = 0.85 y = X X X X 50
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 = X X X 1005 X 50
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 27 30x325-t-xsec Veri precice scan! y = 0.85 y = 0.01
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
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 29 10x100 5x50 t-xsec y = 0.85
The phi angle DVCS: the beam-charge asymmetry At EIC: Possible if a positron beam Thanks to a good tracker coverage Nov. 9, S. Fazio: INT-workshop, Univ. of Washington, Seattle Interference term: Beam charge asymmetry: DVCS and BH: identical final state → they Interfere
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
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, S. Fazio: INT-workshop, Univ. of Washington, Seattle
Back up Nov. 9, S. Fazio: INT-workshop, Univ. of Washington, Seattle