Dmitriy Toporkov Budker Institute of nuclear physics Novosibirsk OLYMPUS collaboration meeting

Toporkov, DESY 31/08/10

Measurement of e+e- scattering cross section ratio off proton

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Dmitriy ToporkovDmitriy ToporkovBudker Institute of nuclear physicsBudker Institute of nuclear physics

NovosibirskNovosibirsk

OLYMPUS collaboration meetingOLYMPUS collaboration meetingDESY 31/08/2010DESY 31/08/2010




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List of participantsJ. Arringtona, L.M. Barkovb, V.F. Dmitrievb,

V.V. Gauzshtajnc , R.A. Golovinb A.V. Gramolinb, R.J. Holta, V.V. Kaminskyb, B.A. Lazarenkob,

S.I. Mishnevb, N.Yu. Muchnoib, V.V. Neufeldb, D.M. Nikolenkob, A.V. Osipovc , I.A. Rachekb,

R.Sh.Sadykovb, Yu.V. Shestakovb, V.N. Stibunovc , D.K. Toporkovb, H.de Vriesd, S.A. Zevakovb

and V.N. Zhilichb.

a ANL, Argonne, USA, b BINP, Novosibirsk, Russia, c INP TPU, Tomsk, Russia, d NIKHEF, Amsterdam, The Netherlands



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Form factor ratio – polarized and unpolarized data



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The problem caused the appearance of many new theoretical work performed in

the various approachesP.A.M. Guichon, M. Vanderhaeghen. Phys. Rev. Lett. 91, 142303 (2003)P.G. Blunden, W. Melnitchouk and J.A. Tjon. Phys. Rev. Lett. 91, 142304 (2003)M.P, Rekalo and E.Tomasi-Gustafson. Eur. Phis. Jour. A22, 331 (2004)Y.C. Chen et al., Phys. Rev. Lett. 93, 122301 (2004)A.V. Afanasev and N.P. Merenkov. Phys. Rev. D70, 073002 (2004)A.V. Afanasev et al.. Phys. Rev. D72, 013006 (2005)P.G. Blunden, W. Melnitchouk and J.A. Tjon. Phys. Rev. C72, 034612 (2005)Y.C. Chen et al.. Phys. Rev. C72, 034642 (2005)S. Kondratyuk et al.. Phys. Rev. Lett. 95, 172503 (2005)D. Borisyuk and A. Kobushkin. Phys. Rev. C78, 025206 (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 Re+/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



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How to measure TPE

R measures the real part of the two-photon amplitude



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/R R

10 –12 0.98 0.08–0.11 8.7.106 ----

19 – 27 0.91

0.26–0.47 3.1.106 0.07

60 – 80 0.40 1.40–1.76 1.5.104 1.00

e

Q2(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



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VEPP-3Energy : 2000 MeVLifetime : 30000 sAv. curren : 100 mABunch : 0.7x0.3 mm

VEPP-3 VEPP-4M COLLIDER, NOVOSIBIRSK



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Schematic side view of the particle detection system



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Middle anglescattering

Large anglescattering

Small anglescattering

Moller/Bhabhamonitor



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VEPP-3 Straight Section with Internal Target



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Storage cell cooled by cold head



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Typical picture of the e+/e− currents in VEPP-3 storage ring during the data taking.



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Initial current of the e+e- beams during the time of experiment



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Beam Integral Collected in shiftsduring the experiment at VEPP-3



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Accumulation of integral beam current VEPP-3

during the experiment.



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Compton back-scattering energy monitor



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Spectrun fragment near wmax

Back Compton scattering set up for measurementenergy of e+/e- beams.



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PositronsElectrons

E, MeV

Energy of e+/e- beams being measured during one shift

with the use of Back Compton scattering monitor

time



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Energy of e+/e- beams being measured with the use of Back Compton scattering monitor during the experiment



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Selection of the elastic e-p scattering events



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Ee/Ee=14%DATA-blueGEANT4-red

ev LA

Energy in LA calorimeter

Event selection

MeV



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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 stabilityFour beam scrapers. They are located close to thetarget and provide information about absolute position of the beams. But they are rarely used because with them data taking should be interraptedCoordinate 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



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The measurement of differences in the vertical position

of e+/e+ beams on the events of SA scattering.

Nrun



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Dependence of counting rate of the detectorsvs. vertical shift of the beam

x102 Nev MA, GEANT4 x102 Nev LA, GEANT4



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Dependence of counting rate of SA detector

vs. vertical shift of the beamx102 Nev SA, GEANT4 Absolute pozition 0.5+-0.2 mm

with Ze+/e- = 0.1 mm

(N1+N2)/(N1+N2)=0.12%



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Raw ratio R e+/e− (no corrections) for MA are monitoring to SA.

Preliminary result

R=1.00412 +- 0.00094



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Raw ratio R e+/e− (no corrections) for LA are monitoring to SA.

Preliminary result

Q2=1.43 (ГэВ/с)2 R=1.057 +- 0.011



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Radiative corrections

Ispecially important for the determinationof the difference of the e+e- elasticscattering off proton



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Born elastic

electron vertex correction

vacuumpolarization

boxdiagram

protonvertex correction

crossed-boxdiagram

boxdiagram



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Bremsstrahlung

initial electron radiation

final electron radiation

initial proton radiation

final proton radiation



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Radiative correctionsJ. 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) 054320M. Vanderhaeghen et al., Phys. Rev. C, v. 62 (2000) 025501R. Ent et al. Phys. Rev. C, v.64 (2001) 054610F. Weissbach et al. Eur. Phys. J. A 30, 477-487 (2006)E. Tomasi-Gustafsson, Phys. of Part. and Nucl. Lett. 2007, Vol. 4, p. 281



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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



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Angular distribution of first order bremsstrahlung photons Soft Photon ApproximationEe = 1.6 GeV

e = 600

E> 100 MeV



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Radiative corrections with real photons emission integrated over photon angles

Ee=1.6 GeV



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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



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Preliminary result for R e+/e− in comparison with calculations of P.G. Blunden et al.

=0.50 Q2=1.43 GeV2



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Рicture from Kivel talkPNPI Winter school 09



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N. Kivel, private communication (Preprint MKPH-T-10-06)



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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



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Part of participants

20.11.2009. VEPP-3



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Parameters under control during the data taking



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e+/e scattering off proton at JLab



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1%

Range of momentum transfer and expectedaccuracy at JLab



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OLYMPUS: BLAST@DORIS



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The BLAST Detector

Left-right symmetric

Large acceptance:0.1 < Q2/(GeV/c)2 < 0.820o < < 80o, -15o < < 15o

COILS Bmax = 3.8 kG

DRIFT CHAMBERSTracking, PID (charge)p/p=3%, = 0.5o

CERENKOV COUNTERSe/ separation

SCINTILLATORSTrigger, ToF, PID (/p)

NEUTRON COUNTERSNeutron tracking (ToF)

DRIFT CHAMBERS

CERENKOVCOUNTERS

SCINTILLATORS

NEUTRON COUNTERS

TARGETBEAM

BEAM

COILS

• All the advantages of VEPP-3 expt.– Pure beam, well defined energy

• Q2, coverage close to CLAS

• Coincidence measurement– Could do (e,e’n), other reactions



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Dmitriy Toporkov Budker Institute of nuclear physics Novosibirsk OLYMPUS collaboration meeting