Эксперимент OLYMPUS и форм факторы протона С.Белостоцкий

ЭкспериментЭксперимент

OLYMPUSOLYMPUSии

форм факторы форм факторы протонапротона

С.БелостоцкийС.Белостоцкий

FF definition and observables

2

Mott p

2 2 2 2E M

2e

d d 1 Q, ,

d d (1 ) 4M

1, 0 1.

1 2(1 ) tan (

G (Q ) G (Q )

/ 2)photon polarization

pk'pk

ek 'ek

q

pJ

eJ

' 'e e e p p p2

p

2 21 2

1 1M e u k u k F (Q ) F (Q )e u k i q u k

q 2M

In plane wave Born (OPE) approximation e-p scattering invariant amplitud

e

pJeJ

Unpolarized cross section

under study for decades

2 2 2 2( ) ( )E Mr G Q G Q

Theoretical interpretation

Белостоцкий сессия ОФВЭ 2012

22 2

2 2D 2 2

G Q , Q qQ

0.84GeVwith

not ideal but acceptableparameterization

2 2p E

2 2M

G (Q )1

G (Q )

It was commonly

accepted that

Direct measurements Rosenbluth separation

Extraction of FFs from unpolarized e-p elastic scattering


JLAB measurements of recoil proton polarization

2p E

2M

G (Q )???

G (Q )

2E

2M

along recoil proton momentum,

perp. to recoil prot

P

on momentum

in scat.plane

G (Q ) P (1 )

P 2G )

P

(Q

Polarized JLAB measurements

Direct measurements:


*2

2

4 ( )Re( ( ))( )1

( ) ( )

e pBorn e ee

core pe Born e

M MQED

M

Two photon exchange TPE and beam charge asymmetry

Beam charge asymmetry sensitive to TPE:

must be measured

Most likely explanation

2 2p E MG (Q ) / G (Q )

Second order corrections affect strongly extracted from unpolarized experiments

keeping intact polarized data


TPE or some other explanations ???

VEPP-3 Novosibirsk

CLAS-JLAB OLYMPUS

Experiment


Российские участникиOLYMPUS collaboration

ПИЯФ С.БелостоцкийГ.ГавриловД.ВеретенникоковА.ИзотовА.КиселевО.МиклухоЮ.Нарышкин Отдел трековых детекторовА.Крившич, В Андреев, Е.Иванов,... Лаборатория радиоэлектроникиЛ.УваровВоронежский государственный университет (студенты)К.Суворов, К.Байбуз


OLYMPUS at DORIS, DESY

Hydrogen target region

BPM1BPM2

Target cell elliptical 9x16mm**2.length 60mm,Beam sizes 0.6x0.1mm**2

15 28 10 atoms cm

collimator

Study of elastic scattering in identical conditions @ 2 GeV

e p,e p

Doris storage ring 2-4.5 GeV2 GeV beams, 100 mA, change daily,Beam energy stability 0.5 MeVBeam position 0.1mm quasi continuous beam ( “topup” mode)

OLYMPUS

e ,e


33 2 1Luminosity 2 10 cm s

Olympus detector

ep elastic event selection: TOF correlation, energy deposit in TOF counters,ep vertices correlation, co-planarity requirement, angular/momentum kinematic correlations

Positron vertex distribution

co-planarity


12 deg. Luminosity monitor

e p / e p ratio must be 1 as TPE expected to be small at low Q**2

Energy deposit in TOF scintillation barfor recoil protons in coincidence with 12 deg. leptons

e p / e p 1.0067 0.0008 close to unity

Sci. counters SiPMs, MWPCs, PNPI readout, GEMs

Target density measurementGood agreement with MC


Symmetric Meoller /Bhabha monitor

symm.at 2GeV (e e ,e e ) 1.3deg.


Data taking

Planned for 3.6 1/fb

Two period of data taking in 2012 Febr and Oct.-Nov.Dec.-Janu 2.Doris full stop in 2013

accumulated by December 18


Outlook

2013 Survey, upgrade of geometrical file for MC Toroid field mapping Setup disassembly Data analysis: Finalize tracking Dedicated computer (available) Two analysis groups: MIT and PNPI cross-check

2014 Data analysis, consensus, publication


“Experimental and theoretical aspects of the proton form factors”

symposium 9-13 July 2012, St.Petersburg, Gatchina, Petersburg Nuclear Physics Institute (PNPI)

• Multi-photon effects in charge lepton proton scattering;

• Form factors in QCD. Lattice calculations;

• Beam charge asymmetry in electron/positron proton elastic scattering: overview of current experiments and data analysis;

• Proton form factors and recoil proton polarization experiments;

• Proton structure at large momentum transfer;

• Charge lepton proton elastic scattering at low momentum transfer, proton radius;

• Form factors in time-like region.

http://hepd.pnpi.spb.ru/hepd/olympus_2012/Белостоцкий сессия ОФВЭ 2012

BACKUP SLIDES

Systematic error 0.3% (not shown)

CLAS-JLAB preliminary

Rosenbluth separation (L-T separation)

2 2 2 2E M

2

r

2

2pe

2 ' 2 'ee e e e e

G (Q ) G (Q )

Q q

1

4E E sin E ,(E ),

Q

4M1 2

2 ,

(1 ) ta

02

1

n ( / 2)

scalar photon fr

scan at fixed

action

E

S.Belostotski Seminar HEPD, May 05 2009

2 2 2 2E M

2 2

2

p

r

E

2

G (Q ) G (Q )

0 1

Q0 15

2M

G (Q )

Q

Under study

Note that

while

problems to extract

at high

Extraction of FFs from Unpolarized Elastic e-p ScatteringExtraction of FFs from Unpolarized Elastic e-p Scattering

Proton electric form factor

Additional problem →cross section normalizationuncertainty (included in errorbars)


JLAB Polarization Transfer experiment (V.Punjabi, C.F.Perdrisat, et al. Phys.Rev. C71, 2005)

dipoleHRSp

protonpolarimeter

Vertical bending ΘB=45 deg.

dipoleHRSe

EMC

'ek

pk

ep

Polarized e-beam Pe ~0.4-0.6,0.934-4.091 GeV, 5-15 μA.

P

P

JLAB Hall A two-arm spectrometer (top view)

eP

p B

P

P

1)

transvesre component no precession,

longitudinal component precesses

w

angle (ith t he

2 2 '

ep

E2

e2M

eG (Q )

G

E Etan( / 2)

2( ) MPQ

P


JLAB Polarization Transfer Results (V.Punjabi, C.F.Perdrisat, et al. Phys.Rev. C71, 2005)

This experiment

O.Gayou et al. phys.Rev.Lett. 88, 2002

disagreement with LT separation results

Fits to LT separation world data subset of world (LT) data


TPE

ep ep e pM e e

Radiative Corrections & TPE graphs

p bremm

2 22 2 * *ep ep e p Born e p Born 2 e p e bremmM e e M 2e e M Re M 2e e M M

*e p Born 2 transverse2e e M Im M P

perpendicular to the production

plane, not related neither b

another indi

eam

nor tar

cation of

get helicity (spontanious)

small, not measured

T

PE

yet

Contribution from two photon exchange diagram not taken into account in traditional analysis may be an explanation


2 *Born e p Born e p e bremstr p bremstr

2 *Born e p Born e p e bremstr p bremst

*2

*2 r

M 2e e M 2e e Re(M M )

M 2e e M 2e e Re(M

Re(M )

R (M )) Me

P.A.M. Guichon and M. Vanderhaeghen, PRL91, 142303 (2003)

P.G. Blunden, W. Melnitchouk, and J.A. Tjon, PRC72, 034612 (2005), PRL91, 142304 (2003)

M.P. Rekalo and E. Tomasi-Gustafsson, EPJA22, 331 (2004)

Y.C. Chen et al.,PRL93, 122301 (2004)

A.V. Afanasev and N.P. Merenkov, PRD70, 073002 (2004)

……….

Intermediate state contributions → model dependent calculations

Charge asymmetry

Charge asymmetry & TPE graph theoretical calculations


VEPP-3 experiment

Ee=1.6 GeV (up to 2 GeV)electron current ~ 30mA, positron current limited to ~ 9mA HERMES type gas target 1015 atoms/cm2, L≈1031cm-2s

Planned for 2009-11


JLAB Polarization Transfer Results

Hall B, CLAS spectrometer, primary 5.7Gev e-beam 1ϻA→ γ-beam → e+e- beam 250 pA→thick hydrogen target→L=1.3x1033 cm-2sec-1

Major challenge hard background conditions related to e+e- production target

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Эксперимент OLYMPUS и форм факторы протона С.Белостоцкий