DDVCS with Super Big Bite update Alexandre Camsonne

DDVCS with Super. Big. Bite update Alexandre Camsonne June 7 th 2014

Double DVCS g* + p g‘* + p’ l+ + l- Guidal and Vanderhaegen : Double deeply virtual Compton scattering off the nucleon (ar. Xiv: hep-ph/0208275 v 1 30 Aug 2002) Belitsky Radyushkin : Unraveling hadron structure with generalized parton distributions (ar. Xiv: hep-ph/0504030 v 3 27 Jun 2005)

Double Deeply Virtual Compton Scattering D = p 1 -p 2 = q 2 -q 1 p = p 1+p 2 q = ½ (q 1+q 2) Q 2 = - q 2 scattered electron x= scattered proton outgoing virtual photon h= Q 2 2 p. q D. q p. q Q 2= -(k-k’)2 lepton pair from virtual photon xbj= Q 2 2 p 1 q 1

Double DVCS • Detect dilepton pair instead of real photon • Allow to vary skewness h of the reaction • Charged particle in final state can use spectrometer to measure momentum ( less requirement on calorimeter energy resolution)

Double DVCS and Virtual Bethe Heitler • Interference of Double DVCS and virtual Bethe Heitler

Kinematical coverage JLab 11 Ge. V 25 Ge. V 40 Ge. V DVCS h=x Hu(h , x) 2 2 • DVCS only probes h = x line • Example with model of GPD H for up quark • Jlab : Q 2>0 h x • Kinematical range increases with beam energy ( larger dilepton mass )

DDVCS cross section • VGG model • Order of ~0. 1 pb = 10 -36 cm 2 • Virtual Beth and Heitler • Interference term enhanced by BH • Contributions from mesons small when far from meson mass

DDVCS measurement • Need high luminosity – Hall B : 1035 - 1036 cm-2 s-1 – m. EIC : 1. 5 x 1034 cm-2 s-1 – Want 1038 cm-2 s-1 ideally 1039 cm-2 s-1 • Pair detection : clean trigger • Ideally look at muons channel to avoid ambiguity with initial electron ( muon source low luminosity )

DDVCS measurement • Large acceptance to get the whole angular coverage of the pair • Forward angle for increase of Bethe and Heitler interference • Look at asymmetry as a function of phi

Cinematique

Spectrometre Super. Big. Bite Large Dipole 48 in x 48 in Gem trackers Hadronic Calorimeter 20 cm x 100 cm Big Cal Large Angle Calorimeter

0. 5 % momentum resolution at 5 Ge. V

E 12 -09 -018: SIDIS on polarized 3 He @ 12 Ge. V E 12 -09 -018, 11 Ge. V E 12 -09 -018, 8. 8 Ge. V E 06 -010, 5. 9 Ge. V 9/7/2021 Experiment E 12 -09 -018 • Approved by JLab PAC 38 (August 2011), 64 days, A- rating • Spokespersons: • G. Cates (UVA) • E. Cisbani (INFN) • G. Franklin (CMU) • A. Puckett (LANL—currently JLab, near future UConn) • B. Wojtsekhowski (JLab) • In two-months production run, E 1209 -018 will reach ~1000 X statistical FOM of E 06 -010 n, ~100 X HERMES p • Electron arm: Big. Bite at 30 deg as in E 06 -010 + A 1 n detector upgrades • Hadron arm: Super Big. Bite (SBS) at 14 deg. • Target: high-luminosity polarized Helium-3 SBS Summer 2013 Collaboration Meeting 13

Possible HRS/SBS layout

Experimental setup LAC 2 D Micromegas Big Cal HCAL SRC lead wall GEMs

Simulation • 4 body kinematic generator • Need to put cross sections weighting

Kinematic Big. Bite Angle E l 1 E l 2 E 3. 83 4. 84 1. 02 1. 81 0. 74 5. 17 4. 64 0. 94 1. 67 3. 32 0. 39 0. 71 6. 78 4. 42 0. 85 1. 51 8. 42 3. 01 0. 48 0. 69 8. 37 4. 21 0. 77 1. 37 8. 75 8. 03 2. 68 0. 58 0. 67 9. 99 4. 02 1. 81 9. 31 7. 84 2. 50 0. 63 0. 66 10. 2 3. 50 3. 84 0. 51 0. 91 nu 30. 00 11. 00 1. 32 3. 89 9. 68 3. 89 0. 21 0. 77 30. 00 11. 00 1. 72 5. 07 9. 28 3. 64 0. 29 30. 00 11. 00 2. 17 6. 40 8. 83 30. 00 11. 00 2. 58 7. 60 30. 00 11. 00 2. 97 30. 0 3. 16 W x epsilon Qg* Q 2 11. 0 p Q'P max Last line using RHRS

Need • Q’ too low for DDVCS in standard setting current setup does not work • Larger magnet could help • Need to be closer to target – New scattering chamber

Crazy idea • Make magnet bigger • Use additionnal iron and coils • Offset target and rotate magnet L ECA Beam Chicane L HCA Bigbite or HRS Pb • Study of radiation hard cryogenic superconducting tracker SBS

Conclusion • Need dedicated setup • Need to study new field with larger magnet • Look at solution to be closer to target • Will study cost effectiveness using SBS