measurement of the hard photodisintegration of a proton-pair in the 3 he nucleus. running now in...
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Measurement of the Hard photodisintegration of a proton-pair in the 3He nucleus.
Running now in JLab, hall A
E03-101:GamPP n
p
p
Ishay Pomerantz, Tel-Aviv University
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Hard photodisintegration: A process in which a high energy photon is absorbed by
a nucleon pair, resulting in two nucleons with large transverse momenta.
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1-5 GeV
3He
1.5-2.5 GeV/c
”Spectator” neutron
1.5-2.5 GeV/c
γ
_ 3 He _ p _high pt__ p _high p
t__ n_slow_
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Motivation: Significant time has been devoted by JLab to investigate
the hard photodisintegration of the Deuteron. The breakup of a pp pair is a direct continuation of this study.
Deuteron results indicates that the quarks are the relevant degrees of freedom in describing these interactions, yet pQCD fails to describe them. Several quark models have been formulated, and their validity requires testing.
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Two possible mechanisms can explain the high Pt:
Breaking a transverse compact object
(Initial state)
Hard rescattering
(Final state)
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Breaking a transverse compact object: The high Pt Results from initial state correlation. A very minute part of the pair wave function.
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γ
QGS
Quark Gluon String ModelV. Yu Grishina et al. EUR.J.Phys.A10,355(2000)
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RNA
Reduced Nuclear AmplitudesS.J. Brodsky, J.R. Hiller,Phys. Rev. C 28 (1983) 475
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Hard rescattering: One proton absorbs the photon, and then interacts with
the other member of the pair. Also a rare case (large c.m. scattering angle).
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HRM
γ
ψpp
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T PP_ PP
Hard Rescattering ModelL.L. Frankfurt, G.A Miller,M.M. Sargasian, M.I Strikman , Phys. Rev. Lett.84,3045(2000)
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Experimental setup
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Electrons3He
Radiator Target
HRS
HRS
Photons
Protons
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The radiator
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Planned measurements: Scaling of the cross section with s Oscillations The light cone momentum distribution of the spectator
neutron Polarization transfer
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Scaling of the cross section with s: constituent counting rule predicts:
For the case of:
N =1(ɣ)+6(pp)+3(p)+3(p)-2=11
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d_dt AB _ CD
_ S_ _N=n
A+n
B+n
C+n
D-2_
f _ts
_
_ pp _ p_highpt _ _ p_high pt _
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Oscillations: A unique feature of hard rescattering
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d_dt
__ pp _ pp__d_dt
_ pp _ pp_
HRM
γ
ψpp
p
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T PP_ PP
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The light cone momentum distribution of the spectator neutron:
The width of the distribution The asymmetry around
αn=1 indicates the s
dependence.
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_ n=AEn_ pnz
EA_ pAz
~En_ pnz
mnCompact object
Rescattering
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Polarization transfer:
At the moment, doesn't
seem feasible because
of low rates at high
energy and priority
considerations.
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Deu
tero
n da
ta
X. Jiang et al. Phys. Rev. Lett. 98, 182302 (2007)
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Offline analysis: Full kinematic reconstruction. Application of cuts. Comparison of the various reconstructed kinematic
variables with a simulation. Inspection of the Events/Unit charge ratio. Extraction of the scaled cross section and αn.
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Full kinematic reconstruction.
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Full kinematic reconstruction.
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Neutron momentum Reaction point Photon energy
Gev/c Gevm
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Applying cuts on: Coincidence events. Detector acceptance. Reaction point within the
target. An energy bin of 200MeV
from the photon end point.
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Gev
Photon energy at beam energy 2.1GeV
EndPoint
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Comparison of the various reconstructed kinematic variables with a simulation.
Simulation is used to evaluate coincidence efficiency
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Red – Generated events(scaled) Black- events that fall within acceptance
Gev/c Gev/c m
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Events/Unit charge as a function of the run no.
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With radiator
W/o radiator
Eγ=3.1GeV
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Inspection of the No. events/charge ratio. Oops – a pressure drop !
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IOC reboot
Fixed
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Extraction of the scaled cross section and αn.
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Very Preliminary (online) results:
Points at 1.1 GeV 2.1GeV 3.1GeV 4.1GeV
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Very Preliminary (online) results:
Possible interpretation
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?
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Plans for next week 1.65 GeV 2.4 GeV 4.72 GeV Maybe 0.8 GeV
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Summary In Hard photodisintegration two protons are found to have
large transverse momentum. The goal of the experiment is to find the origin of this
momentum. We look at features of the cross section, and the light cone
momentum distribution to establish an explanation. We found high cross section point at 2.1GeV that we'll
further investigate, and we plan to continue to 4.7GeV.
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