Transversely Polarized Neutron

DVCS with SoLID-SIDIS Setup

Zhihong Ye Duke University

05/15/2015, SoLID Collaobration Meeting

Wigner distributions (Belitsky, Ji, Yuan) (or GTMDs)

5D

3D

1D

(X. Ji, D. Mueller, A. Radyushkin)

2

One of the main goal to develop SoLID is the 3D mapping of the nucleon structure, so besides doing TMDs, we should do GPDs!.

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

3

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.

GPD Study @ SoLID

Deeply Virtual Compton Scattering (DVCS):

BH DVCS

22

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

4

2**

BHDVCSBHDVCSI

CFFs access GPDs at x=ξ (DDVCS doesn’t have this limit)

n/p'en/pe

GPD Study @ SoLID

DVCS with polarized electron beam and targets:

5

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

Beam Energy, E0 = 8.8 / 11.0 GeV

Scattered Electrons & Real Photons :

Large Angle: 3.5

7

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)

Acceptance

DVCS with Polarized He3

Recoil neutrons: (1) at large angles (2) P~0.4GeV/c It will be very difficult to detect neutrons

Kinematic Coverage

DVCS with Polarized He3

Integrated Rate:

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10

DVCS with Polarized He3

21 days on E0=8.8GeV, 48 days on E0=11GeV Binning: 4D

Asymmetries:

Asymmetry Binning and Projection

Asymmetry Projection:

DVCS with Polarized He3

11

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

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

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 …

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,

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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