Transversely Polarized Neutron DVCS with SoLID-SIDIS...
Transcript of Transversely Polarized Neutron DVCS with SoLID-SIDIS...
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Transversely Polarized Neutron
DVCS with SoLID-SIDIS Setup
Zhihong Ye Duke University
05/15/2015, SoLID Collaobration Meeting
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Wigner distributions (Belitsky, Ji, Yuan) (or GTMDs)
5D
3D
1D
(X. Ji, D. Mueller, A. Radyushkin)
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One of the main goal to develop SoLID is the 3D mapping of the nucleon structure, so besides doing TMDs, we should do GPDs!.
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GPD Study @ SoLID
Generalized Parton Distributions (GPD):
Encode Information of the parton distribution in
both the transverse plane and longitudinal direction.
Four GPDs for quarks or gluons:
Connect to FF & PDFs: e.g.
gqgqgqgq EHEH ////~
,~
,,
)(),,(
)(),,(
2
1
0
1
1
0
tFtxEdx
tFtxHdx
qq
qq
0),()0,0,(~
0),()0,0,(
xxqxH
xxqxH
q
q
qq
gqgq
gq
L
xExHxdxJ
1
1
//
/ )]0,,()0,,([2
1
X Longitudinal quark momentum fraction (not experimental accessible)
• ξ Longitudinal momentum transfer. In Bjorken limit:
ξ = xB/(2-xB) • t Total squared momentum transfer
to the nucleon: t = (P-P’)2
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Angular Momentum Sum Rule (Ji’s Sum Rule): (X. Ji, PRL 78, 610 (1997)
)(),,(~
)(),,(~
1
0
1
0
tgtxEdx
tgtxHdx
q
P
q
q
A
q
Quark O.A.M.
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GPD Study @ SoLID
Deeply Virtual Compton Scattering (DVCS):
BH DVCS
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2 BHDVCS
B
IdtddxdQ
d
Interference-Term
),,,(),,(),,( 1
1
1
1tHidx
x
txHPdx
ix
txHDVCS
BH from Nucleon FF, F1 & F2
Compton Form Factor (CFF): Re(H) Im(H)
Can access GPDs via DVCS by measuring the Ф dependence of DVCS & Interference Terms
(similarly for other three)
In the asymmetry: 22BHDVCS I
IA
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2**
BHDVCSBHDVCSI
CFFs access GPDs at x=ξ (DDVCS doesn’t have this limit)
n/p'en/pe
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GPD Study @ SoLID
DVCS with polarized electron beam and targets:
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NH3: Transversely polarized (proton)
He3: Transversely & Longitudinally polarized (neutron)
Polarization Asymmetries CFFs
Longitudinal Beam ALU
Longitudinal Target AUL
Long. Beam + Long. Target
ALL
Transverse Target AUT
Long. Beam +Trans.Targt
ALT
},~
,
},~
,
npn
ppp
EHIm{H
EHIm{H
}~
,,
}~
,
nnn
pp
EEIm{H
HIm{H
}~
,,
}~
,
nnn
pp
EERe{H
HRe{H
},
},
nn
pp
ERe{H
ERe{H
},
},
nn
pp
EIm{H
EIm{H
Suppressed at t0 where F1n0 but should be sensitive at large t
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Beam Energy, E0 = 8.8 / 11.0 GeV
Scattered Electrons & Real Photons :
Large Angle: 3.5
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Trigger Design:
DVCS with Polarized He3
There will be many low-energy photons from secondary scattering, radiations etc.
To remove accidental coincidence triggers, we need to raise the EC threshold (P>2GeV/c is still fine)
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Acceptance
DVCS with Polarized He3
Recoil neutrons: (1) at large angles (2) P~0.4GeV/c It will be very difficult to detect neutrons
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Kinematic Coverage
DVCS with Polarized He3
Integrated Rate:
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DVCS with Polarized He3
21 days on E0=8.8GeV, 48 days on E0=11GeV Binning: 4D
Asymmetries:
Asymmetry Binning and Projection
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Asymmetry Projection:
DVCS with Polarized He3
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21 days on E0=8.8GeV, 48 days on E0=11GeV
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TSA on x at one Q2 bin
Two transversely polarized direction (x->0/180degree, y->90/270 degree), 5-Q2-bins, so: BSAx5, TSAx5x2, DSAx5x2 25 such kind of plots
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Neutron Missing Mass
• The electron resolutions (from GEM tracking reconstruction): δP/P ~ 2%, δθ ~ 0.6mrad, δΦ ~ 5mrad • The photon angular resolutions are determined by the EC position resolution and the electron vertex reconstruction: δx_EC = 1cm, δy_EC=1cm, δz_vertex=0.5cm • For the energy resolution, I used the value now we can archieve: 5% • No exclusive pi0 model yet, so I use the uniform phase space for the pi0 events, and scale the histograms with one common factor (0.01).
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Neutron Missing Mass
• The electron resolutions (from GEM tracking reconstruction): δP/P ~ 2%, δθ ~ 0.6mrad, δΦ ~ 5mrad • The photon angular resolutions are determined by the EC position resolution and the electron vertex reconstruction: δx_EC = 1cm, δy_EC=1cm, δz_vertex=0.5cm • For the energy resolution, I used the value now we can archieve: 5% • No exclusive pi0 model yet, so I use the uniform phase space for the pi0 events, and scale the histograms with one common factor (0.01).
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We will learn from the new Hall-A 12GeV-DVCS data.
From Marco Carmignotto in Hall-A DVCS
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From LOI to Proposal
These are my naïve personal points of view: a) Need to make clear how strong the physics case are
Will be the first trans-polarized n-DVCS, how important? GPD-En Flavor Decomposition quark OMA (Ji’s Rum rule) Nucleon Spin, and what is more? What asymmetries are most important (or feasible to measure )? BSA, TSA, DSA, Cross Sections … Need a fitting model to get CFFs from asymmetries Helps from Michel Guidal & Marie Boer will be essential.
b) Need to make sure the exclusivity of the measurement Hardware/trigger/DAQ requirements for photon detection? We try a lot of efforts to reject photons in SIDIS but how about keeping them? What resolutions are needed to cleanly identify neutrons? Do we need a better EC design to improve missing mass spectrum? Do we need a recoil neutron detector? >60degrees & < 0.4GeV/c
c) Need to understand backgrounds and how to handle then How to detect pi0 events and subtract them from missing mass? How to evaluate and deal with proton-channel from He3? What other channels can mix in?
d) Need to evaluate systematic errors e) More …
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Summary
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Director Review committee strongly recommended to develop GPD programs.
No approved experiment on transversely polarized neutron-DVCS at Jlab.
SoLID-SIDIS can be directly used for the DVCS measurement:
a) Electron+Photon coincidence trigger (instead of electron+hardron in SIDIS)
b) Need to reconstruct neutron missing mass spectrum to make sure the exclusivity
c) Need a better EC resolution to detect photons and hence controll backgrounds
d) May need additinal callibration runs or more beam time to improve precision and
reduce systematics.
Still a lot of work are needed to be done before we have the actual proposal next year!
Highly welcome colleagues to join and help us!
If we develop this physics case, more DVCS experiments can be followed up:
Longitudinal neutron DVCS, Transverse proton DVCS,
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Backup Slides
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Beam-Spin Asymmetr (ALU):
∆𝜎𝐿𝑈∝ sin 𝜑 𝐼𝑚 𝐹1ℋ + 𝜉 𝐹1 + 𝐹2 ℋ + 𝑘𝐹2ℰ 𝑑𝜑
Longitudinal Target-Spin Asymmetry (AUL):
∆𝜎𝑈𝐿∝ sin 𝜑 𝐼𝑚 𝐹1ℋ + 𝜉 𝐹1 + 𝐹2 ℋ + 𝑘𝐹2ℰ 𝑑𝜑
Longitudinal Double-Spin Asymmetry (ALL):
∆𝜎𝐿𝐿∝ (𝐴 + 𝐵cos 𝜑) 𝑅𝑒 𝐹1ℋ + 𝜉 𝐹1 + 𝐹2 ℋ +𝑥𝐵2
ℰ 𝑑𝜑
Transverse Target-Spin Asymmetry (AUT):
∆𝜎𝑈𝑇∝ sin 𝜑 𝐼𝑚 𝑘(𝐹2ℋ − 𝐹1ℰ) + … 𝑑𝜑
Transverse Double-Spin Asymmetry (ALT):
𝐼𝑚 𝓗𝒑, ℋ 𝑝, ℰ𝑝
𝐼𝑚 𝓗𝒏, ℋ 𝑛, ℰ𝑛
𝐼𝑚 𝓗𝒑, 𝓗 𝒑,
𝐼𝑚 𝓗𝒏, ℰ𝑛, ℰ 𝑛
𝑅𝑒 𝓗𝒑, 𝓗 𝒑,
𝑅𝑒 𝓗𝒏, ℰ𝑛, 𝓔 𝑛
𝐼𝑚 𝓗𝒑, 𝓔𝒑 𝐼𝑚 𝓗𝒏
GPD Study @ SoLID
DVCS with polarized electron beam and targets:
Re 𝓗𝒑, 𝓔𝒑 Re 𝓗𝒏
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