n DVCS using TDIS setup Alexandre Camsonne SBS

n. DVCS using TDIS setup Alexandre Camsonne SBS meeting January 31 st 2018

Overview • n. DVCS • TDIS setup • n. DVCS with TDIS setup

Deeply Virtual Compton Scattering Simplest hard exclusive process involving GPDs k’ k factorization p q’ p’ GPDs The GPDs enter the DVCS amplitude as an integral over x : GPDs appear in the real part through a PP integral over x GPDs appear in the imaginary part at the line x=±ξ Mueller, Radyushkin, Ji Collins, Freund, Strikman

Deeply Virtual Compton Scattering Using a polarized electron beam: Asymmetry appears in Φ The cross-section difference accesses the Imaginary part of DVCS and therefore GPDs at x=±ξ Purely real and fully calculable Twist-3 term Twist-2 term Bilinear combinations of GPDs The total cross-section accesses the real part of DVCS and therefore an integral of GPDs over x Kroll, Guichon, Diehl, Pire …

Deeply Virtual Compton Scattering A. V. Belitsky, D. Muller, A. Kirchner, Nucl. Phys. B 629, 323 (2002). Combination to be extracted from the data GPDs n-DVCS experiments provide different linear combinations of GPDs than p. DVCS experiments. n-DVCS experiments have different flavor sensitivity than p-DVCS experiments.

E 03 -106 experimental apparatus and kinematics Beam energy = 5. 75 Ge. V Beam polarization = 75% Beam current = ~ 4 μA Luminosity = 4. 1037 cm-2. s-1 nucleon-1 Polarized Electron Beam t Sca LH 2 / LD 2 target tr lec E ed r e t on Left HRS DVCS events are identified with MX 2 g Electromagnetic Calorimeter

DVCS on coherent deuteron With a Deuterium target one can have 3 different DVCS processes p n d d p-DVCS (incoherent) n-DVCS (incoherent) d d d-DVCS (coherent) Access deuteron GPDs Impulse approximation :

Analysis method Mx 2 cut = (MN+Mπ)2 p-DVCS and n-DVCS MN Contamination by 2 d-DVCS MN 2 +t/2 N + mesons (Resonnant or not) accidentals

TDIS

Tagged n. DVCS • same technique : • no need to detect neutron ( no loss of efficiency because of neutron detector ) • unambiguously identify coherent DVCS on deuterium

SBS for TDIS

TPC

n. DVCS with TDIS • Add calorimeter to TDIS setup (Eric Fuchey)

Kinematical coverage

TDIS to do • Geometry / detector – add TPC magnetic field – LAC implementation – m. TPC implementation – straw target – beamline • Background study – LAC trigger rate, background and pion rejection – RICH background and pion rejection Signal study. TDIS event generator • TDIS event generator

n. DVCS to do list • DVCS event generator • Background study in calorimeter – moller coming out from target – how bad is background : distance, size of calorimeter • Missing mass resolution • Observables and counting rates DVCS – crossection and difference of crossections as function of phi

Conclusion • n. DVCS with TDIS setup seems doable • need to study rate in calorimeter • straighforward setup : trying to put a proposal this year • could allow to have both n. DVCS and d. DVCS on deuterium