1 Dmitriy Toporkov Budker Institute of nuclear physics Novosibirsk OLYMPUS collaboration meeting DESY 31/08/2010 Measurement of e+e- scattering cross section ratio off proton

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 2 List of participants J. Arrington a, L.M. Barkov b, V.F. Dmitriev b, V.V. Gauzshtajn c, R.A. Golovin b A.V. Gramolin b, R.J. Holt a, V.V. Kaminsky b, B.A. Lazarenko b, S.I. Mishnev b, N.Yu. Muchnoi b, V.V. Neufeld b, D.M. Nikolenko b, A.V. Osipov c, I.A. Rachek b, R.Sh.Sadykov b, Yu.V. Shestakov b, V.N. Stibunov c, D.K. Toporkov b, H.de Vries d, S.A. Zevakov b and V.N. Zhilich b. a ANL, Argonne, USA, b BINP, Novosibirsk, Russia, c INP TPU, Tomsk, Russia, d NIKHEF, Amsterdam, The Netherlands

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 3 Form factor ratio – polarized and unpolarized data

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 4 The problem caused the appearance of many new theoretical work performed in the various approaches P.A.M. Guichon, M. Vanderhaeghen. Phys. Rev. Lett. 91, (2003) P.G. Blunden, W. Melnitchouk and J.A. Tjon. Phys. Rev. Lett. 91, (2003) M.P, Rekalo and E.Tomasi-Gustafson. Eur. Phis. Jour. A22, 331 (2004) Y.C. Chen et al., Phys. Rev. Lett. 93, (2004) A.V. Afanasev and N.P. Merenkov. Phys. Rev. D70, (2004) A.V. Afanasev et al.. Phys. Rev. D72, (2005) P.G. Blunden, W. Melnitchouk and J.A. Tjon. Phys. Rev. C72, (2005) Y.C. Chen et al.. Phys. Rev. C72, (2005) S. Kondratyuk et al.. Phys. Rev. Lett. 95, (2005) D. Borisyuk and A. Kobushkin. Phys. Rev. C78, (2008) N.Kivel and M.Vanderhaeghen. Phys. Rev. Lett. 103 (2009) etc. as well as the suggestions of new experiments for the determination of two-photon exchange contribution through the measurement of R e+/e− ratio, since the old data of 60th are not accurate enough. Novosibirsk/VEPP-3 operated OLYMPUS: DORIS/BLAST data taking 2012 TJNAF/CLAS/PR04-116

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 5 How to measure TPE R measures the real part of the two-photon amplitude

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 6

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 7 10 – – – – – – e  Q 2 (GeV/c) 2 N + events R/R %  R =  (e+) /  ( e - ), E=1600 MeV Systematic errors Different energy of e +, e - beams (  for three intervals 0.1, 0.2, 0.2 % / MeV) Different position of beams (  for three intervals 5.0, 1.4, 0.9 % / mm) Drift of the efficiency over the time of experiment Drift of the target thickness during the experiment Difference of the radiation corrections for electrons and positrons

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 8 VEPP-3 Energy : 2000 MeV Lifetime : s Av. curren : 100 mA Bunch : 0.7x0.3 mm VEPP-3 VEPP-4M COLLIDER, NOVOSIBIRSK

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 9 Schematic side view of the particle detection system

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 10 Middle angle scattering Large angle scattering Small angle scattering Moller/Bhabha monitor

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 11 VEPP-3 Straight Section with Internal Target

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 12 Storage cell cooled by cold head

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 13

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 14 Typical picture of the e+/e− currents in VEPP-3 storage ring during the data taking.

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 15 Initial current of the e+e- beams during the time of experiment

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 16 Beam Integral Collected in shifts during the experiment at VEPP-3

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 17 Accumulation of integral beam current VEPP-3 during the experiment.

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 18 Compton back-scattering energy monitor

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 19 Spectrun fragment near w max Back Compton scattering set up for measurement energy of e+/e- beams.

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 20 Positrons Electrons E, MeV Energy of e+/e- beams being measured during one shift with the use of Back Compton scattering monitor time

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 21 Energy of e+/e- beams being measured with the use of Back Compton scattering monitor during the experiment

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 22 Selection of the elastic e-p scattering events

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 23  E e /E e =14% DATA-blue GEANT4-red  ev LA Energy in LA calorimeter Event selection MeV

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 24 Information on the beams positions comes from: Beam position monitors of VEPP-3. They are located rather far from the target center and give only information on beams stability Four beam scrapers. They are located close to the target and provide information about absolute position of the beams. But they are rarely used because with them data taking should be interrapted Coordinate systems of the detector give the possibility off-line to determine both the horizontal and vertical relative shift of the electron or positron beams with an accuracy of ~ 0.1 mm

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 25 The measurement of differences in the vertical position of e+/e+ beams on the events of SA scattering. N run

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 26 Dependence of counting rate of the detectors vs. vertical shift of the beam x10 2 N ev MA, GEANT4x10 2 N ev LA, GEANT4

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 27 Dependence of counting rate of SA detector vs. vertical shift of the beam x10 2 N ev SA, GEANT4 Absolute pozition mm with  Z e+/e- = 0.1 mm  (N1+N2)/(N1+N2)=0.12%

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 28 Raw ratio R e+/e− (no corrections) for MA are monitoring to SA. Preliminary result R=

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 29 Raw ratio R e+/e− (no corrections) for LA are monitoring to SA. Preliminary result Q 2 =1.43 (ГэВ/с) 2  R=

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 30 Radiative corrections Ispecially important for the determination of the difference of the e + e - elastic scattering off proton

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 31 Born elastic electron vertex correction vacuum polarization box diagram proton vertex correction crossed-box diagram box diagram

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 32 Bremsstrahlung initial electron radiation final electron radiation initial proton radiation final proton radiation

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 33 Radiative corrections J. Schwinger, Phys.Rev. 76, 790(1949) D. R. Yennie, S. Frautschi and Suura, Ann.Phys. 13,379(1961) L. M. Mo and Y.S.Tsai, Rev.Mod.Phys. 41,205(1968) L. C. Maximon and J. A. Tjon, Phys. Rev. C, v.62, (2000) M. Vanderhaeghen et al., Phys. Rev. C, v. 62 (2000) R. Ent et al. Phys. Rev. C, v.64 (2001) F. Weissbach et al. Eur. Phys. J. A 30, (2006) E. Tomasi-Gustafsson, Phys. of Part. and Nucl. Lett. 2007, Vol. 4, p. 281

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 34 Reaction: where k, k’ initial and final lepton four-momenta, p, p’ proton four-momenta, w - photon four-momentum. The total cross section for single-photon bremsstrahlung is given by where is Born electron-proton cross section. The first and third terms in brackets have different signs in the case of e - p and e + p scattering. Soft Photon Approximation

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 35 Angular distribution of first order bremsstrahlung photons Soft Photon Approximation E e = 1.6 GeV  e = 60 0 E   > 100 MeV 

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 36 Radiative corrections with real photons emission integrated over photon angles E e =1.6 GeV

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 37 SPA, LA, GEANT4. R dependence vs. cuts More correct calculation of radiative corrections (V.Fadin and A.Feldman,Private communication) with no restriction on the photon energy and proton form factor taken into account will be performed soon

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 38 Preliminary result for R e+/e− in comparison with calculations of P.G. Blunden et al.  =0.50 Q 2 =1.43 GeV 2

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 39 Рicture from Kivel talk PNPI Winter school 09

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 40 N. Kivel, private communication (Preprint MKPH-T-10-06)

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 41 Future plans To apply new radiative corrections Make corrections on the beam’s position To repeat the experiment at the energy of 1000 MeV with larger scattering angle

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 42 Part of participants VEPP-3

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 43

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 44

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 45

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 46

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 47

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 48 Parameters under control during the data taking

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 49

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 50 e+/e scattering off proton at JLab

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 51 1% Range of momentum transfer and expected accuracy at JLab

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 52

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 53 OLYMPUS:

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 54 The BLAST Detector Left-right symmetric Large acceptance: 0.1 < Q 2 /(GeV/c) 2 < o <  < 80 o, -15 o <  < 15 o COILS B max = 3.8 kG DRIFT CHAMBERS Tracking, PID (charge)  p/p=3%,  = 0.5 o CERENKOV COUNTERS e/  separation SCINTILLATORS Trigger, ToF, PID (  /p) NEUTRON COUNTERS Neutron tracking (ToF) DRIFT CHAMBERS CERENKOV COUNTERS SCINTILLATORS NEUTRON COUNTERS TARGET BEAM COILS All the advantages of VEPP-3 expt. –Pure beam, well defined energy Q 2,  coverage close to CLAS Coincidence measurement –Could do (e,e’n), other reactions

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 55

Toporkov, DESY 31/08/10 Measurement of e+e- scattering cross section ratio off proton 56