Study of Neutron Structure via Far-Forward Tagging of eD ...skipper.physics.sunysb.edu/~abhay/2014/EICUM/Talks/06272014-Det/5_Park.pdf · D = 100 GeV, cross-angle: 50 mrad, p R(rest

Study of Neutron Structure via Far-Forward Tagging ofeD → e ′NX in EIC

Kijun Park 1

1Old Dominion University/Jefferson Lab

June 27, 2014

K.Park (ODU/JLAB) Neutron Structure via Tagging June 27, 2014 1 / 12

Electron Ion Collider → Spectator Tagging

x-410 -310 -210 -110 1

-0.2

-0.1

0

0.1

0.2

0.3 (x))d∆(x)-u∆x(

HERMES 5 Flavor

EIC 5 on 50

EIC 5 on 50 GeV100 days, 10^33Kinney, Seele 2008

No Free Neutron Target- Neutron Structure (flavor decomposition of quark-spin, sea quarks, gluon pol.)

- Spectator Nucleon Tagging (forward detection/unique for collider)

- ~D (a well understood wave function/pol. neutron spin/limited FSI/coherence N = 2,...)

Neutron structure function- Gluon and sea quark (transverse) imaging of the nucleon

- Nucleon Spin (∆G vs. logQ2, transverse momentum)

- Nucleon QCD (gluons in nuclei, quark/gluon energy loss)

- QCD vacuum and Hadron Structure and formation


Spectator Tagging → Extrapolating Neutron Structure

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X

D

R RTpα ,

−t p p )(= R D2

p

n ��

��

��

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t(−

MN)2

mN2

0.1∼ GeV2

on−shell pointF

dd

[..]

∗σ/

2n ( x, Q )2∼

− t[by courtesy of C. Weiss]

Light-Cone parallel to ~q + ~PD

Light-Cone momentum fraction, Transverse momentum of recoil proton:

αR = 2ER + pz

R

MD

, ~pRT

Cross-section in the IA

dσ

dxdQ2dαRd3pR/ER

= fFlux × SD(αR , pRT )× F2n

(

x

2− αR

,Q2

)

On-shell extrapolation: t → M2N

or (t −M2N) ≡ t′ → 0

- Free neutron structure at pole

- Model-independent method


MC Simulation

Ee = 5 GeV, ED = 100 GeV, cross-angle: 50 mrad, pR(rest frame)= 300 MeV

Normal. Emittances: dp/p = 3× 10−4, dθ = 2× 10−4,

Luminosity= 1033cm−2sec

−1, Time= 106(sec)

⇓ ⇓

Cross-section Comparison between MC and Analytic calculation (±5% bin-center)

MEIC Beam Emittance effect << ±1%, even with fine binning

Sufficient t′ resolution for the extrapolation

F2D structure function on-shell extrapolation with experimental uncertaintyestimation

dσ

dxdQ2dαRd3pR/ER

= fFlux × Fn2D (xBj , αR , pRT ) = fFlux × SD (αR , pRT ) × F2n

(

x

2 − αR

,Q2

)

∆σMC =∑

Ni∆t′

dσ

dxdQ2dt′Γ · J/N0 , count = L · T · ∆σMC , σ(∆σMC ) =

∆σMC√count

=

√

∆σMC

L · T

[See Backup Slide]


MC Simulation → F2D(x ,Q2, αR , t

′)

htSEntries 26880

Mean -0.0003975

RMS 0.005271

-0.1 -0.08 -0.06 -0.04 -0.02 0 0.02 0.04 0.06 0.08 0.10

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

2.2 htSEntries 26880

Mean -0.0003975

RMS 0.005271

Actual Distributionof tPrime at vertex

Delta tPrime

x=0.01-0.05

Q2=15-20GeV2

t′ = (pS − pD)2−M2

N

Intrinsic momentum spread in Ionbeam smears recoil momentumDominant uncertainty for MEIC

Effect on t′ (angular spread)

Smearing < t′ bin-size

F2D vs. t′ : take out fFluxαR : cut around 1 ± 0.02

Excellent resolution allows to reachsmaller t′

Feasible on-shell extrapolation

Blue vertical dash line =t′min = 0.00416 GeV2

≈ 2MNBD

High resolution in pR permits finebinning in t′


F2D → F2n/SD(αR , pRT )

F2D × (t′)2 vs. t′ : take out a pole term contribution in spectral function; SD(αR , pRT )

RES = Res(ψd (Tpol )) =C

2√2πMN

GeV−1/2

Extrapolation with Error evaluation from ”quadratic fit”: 0.3902± 0.0048


Far-Forward Detection in EIC

Good acceptance for all ion fragments - rigidity different from beam- Large magnet apertures (small gradients a fixed maximum peak field)

Good acceptance for low-pT recoils - rigidity similar to beam- Small beam size detection point (downstream focus, efficient cooling)- Large dispersion (generated after the IP, D=D′=0 the IP)

Good momentum and angular resolution- Longitudinal dp/p ≈ 4 · 10−4

- Angular in θ, for all φ: ≈ 0.2mrad- pRT ≈ 15MeV/c resolution for tagged nucleon in 100GeV deuterium beam- Long, instrumented drift space (no apertures, magnet, ...)

Sufficient beam line separation (≈ 1m)

[Talk: P. Nadel-Turonski]


Sample Tracks in Detector Simulation [GEMC]

10 events from eD → e ′psX

Figure : Examples of physics event eD → e′psX , red color rays: spectator protons, light-bluerays: scattered electrons

[Talk: M. Ungaro]


GEMC Acceptance @ Far-Forward Region

Figure : pR (GeV) vs. αR : (left: Generated, middle: Accepted, right Cross section weighted)on the 2nd Dipole Exit Window


Summary

1 The MEIC will be an excellent tool to provide unique and precisenuclear physics measurements.

- Kinematics / Polarized D & 3He / Forward nucleon tagging

2 Nucleon tagging is an excellent tool to study parton structure

- Free neutron structure function (F2) from on-shell extrapolation

3 Optimize energy, luminosity, and detector/IR in MC for deep exclusiveand SIDIS processes

- MC simulation will provide more realistic requirement of experimentaldetectors

4 R&D in progress to establish methods

- Theoretical : Polarization(~e, ~D), FSI, Shadowing,...- Experimental : MC simulation, Particle Tracking, Systematics, ...


MC simulation

[BackUp slide #1]

Left Comparison between MC and Analytic calculation (±5% bin-centering effect)

Middle Initial State Smearing (ISS) is << ±1%

Right Intrinsic MC Statistical Uncertainty is ∼ 0.3%


Spectator Tagging: Coherent Effects

[BackUp slide #2]

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+

interference

X

X

n

p

n

p

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Shadowing effect important in inclusiveDIS x << 0.1Diffractive scattering on single nucleon

Interference between scattered p and n

[Talk: C. Weiss]

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X

pT

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S

Shadowing in Tagged DIS

Coherent effect is clean (N = 2)

Systematics is important (unpol./pol.)in p-n

FSI between p and n → distortion ofpT , spin


Documents

Study of Neutron Structure via Far-Forward Tagging of eD ...skipper.physics.sunysb.edu/~abhay/2014/EICUM/Talks/06272014-Det/5_Park.pdf · D = 100 GeV, cross-angle: 50 mrad, p R(rest