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Эксперимент OLYMPUS и форм факторы протона С.Белостоцкий. FF definition and observables. Theoretical interpretation. Unpolarized cross section. under study for decades. Белостоцкий сессия ОФВЭ 2012. Extraction of FFs from unpolarized e-p elastic scattering. Direct measurements. - PowerPoint PPT Presentation
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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
Белостоцкий сессия ОФВЭ 2012
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:
Белостоцкий сессия ОФВЭ 2012
*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
Белостоцкий сессия ОФВЭ 2012
TPE or some other explanations ???
VEPP-3 Novosibirsk
CLAS-JLAB OLYMPUS
Experiment
Белостоцкий сессия ОФВЭ 2012
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
Белостоцкий сессия ОФВЭ 2012
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
Белостоцкий сессия ОФВЭ 2012
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
Белостоцкий сессия ОФВЭ 2012
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
Белостоцкий сессия ОФВЭ 2012
Symmetric Meoller /Bhabha monitor
symm.at 2GeV (e e ,e e ) 1.3deg.
Белостоцкий сессия ОФВЭ 2012
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
Белостоцкий сессия ОФВЭ 2012
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
Белостоцкий сессия ОФВЭ 2012
“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)
S.Belostotski Seminar HEPD, May 05 2009
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
S.Belostotski Seminar HEPD, May 05 2009
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
S.Belostotski Seminar HEPD, May 05 2009
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
S.Belostotski Seminar HEPD, May 05 2009
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
S.Belostotski Seminar HEPD, May 05 2009
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
S.Belostotski Seminar HEPD, May 05 2009
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