l/t separation in the 3 he(e,e’p) reaction at parallel kinematics freija descamps supervisors: ron...

L/T separation in the 3He(e,e’p) reactionat parallel kinematics

Freija Descamps

Supervisors:Ron GilmanEric Voutier

Co-supervisor:Jean Mougey


• Motivations• Quasi-elastic scattering

• 3He(e,e’p) cross section• L/T separation

• Experimental setup• Cross section extraction

• Experimental data• Normalization• Monte Carlo simulation• Results

• L/T separation• Status report

• Conclusion and prospects

Motivations

E89-044 experiment: December 1999! April 2000

Free nucleon Bound nucleonChange in structure?

Study bound nucleon by (e,e’p) quasi-elastic scattering

Extract electromagnetic response functions for various transfered four-momenta Q (i.e. various probing resolutions).

•High Q2 : unexplored domain•Variable Q2 •High precision measurements

Quasi-elastic scattering: 3He(e,e’p)B

Bpm ppqp

BpHeBpm TTMmmE 3*

Missing momentum : undetected momentum

Missing energy : separation energy

GeV/c5.1 ppqGeV837.0

Leptonic plane

Hadronic plane

• Only e’ and p are detected

• Residual system B:

Quasi-elastic: 12

2

pm

Qx

Parallel: 0pq

pm ≈ 0

• Kinematical regime

2 body break-up peak2-bbu

3 body break-up threshold3-bbu

Quasi-elastic scattering

3He(e,e’p)d cross section

)2(cos)(cos)2( 3

5

TTTTLTLTTTLLM

pp

pff

RVRVRVRVREp

dddEd

),,,( TTLTTL RRRR : Nuclear response functions

R: Recoil factor

σM: Mott cross section

),,,( TTLTTL VVVV : Kinematic electron coupling coefficients

L/T separation:

•Separation of longitudinal/transverse response functions

•Interference terms ! 0 if pq! 0 (parallel kinematics)

•Averaging over out-of-plane angle: ! 0Separation using Rosenbluth method:

•Extraction of the 3He(e,e’p)d cross section at different kinematic settings

•Keep same hadronic vertex and change leptonic vertex.

TL RR and

)cos(2),cos(

)2(cos)(cos)2( 3

5

TTTTLTLTTTLLM

pp

pff

RVRVRVRVREp

dddEd

KIN01≠ KIN03 change photon polarization

2 points in space

T

M

VR,

Experimental setup

Jefferson Laboratory (CEBAF, Newport News, USA), continuous electron beam : •Beam Energy up to 6 GeV•Beam Intensity up to 200 A

•Recirculation arcs

•0.6 GeV LINAC

•67 MeV injector

•3 experimental areas

•Extraction elements

Experimental setup

e He3

p

e

d, np

Experimental setup

Experimental setup

Electron Arm Hadron Arm

TOF

p

0

Electron Arm Hadron ArmTracking Vertical Drift Chamber (2 planes) Vertical Drift Chamber (2 planes)

Triggers S1, S2 scintillator planes (Čerenkov) S1, S2 scintillator planes (S0)

PID Čerenkov, Shower countersS1, S2 ! TOF

S0S1, S2 ! TOF

Experimentaldata

1

Raw Data

Coincidence

events

Real coincidence

events

Filter

Background rejection

Accidental coincidence

rejection

Experimental YieldIn pm and Em bins

1 Experimental Data: Background rejectionSome examples...

Electron ArmHadron and Electron Arm

• Events that are not reconstructed atthe same point by each spectrometer • Pion contamination

Demand |zlabh-zlabe| < 0.02. Demand hit in Čerenkov counter.

1 Experimental Data: Accidental coincidences

Bin experimental data in pm

Per pm bin: bin in Em

First bin in Em = 2-bbu bin

Substract flat background:

BininEm

Experimental yield per pm, Em binAccidental coincidences

Luminosity2

Raw Data

All

events

Detector Efficiencies

Efficiency study

total deadtimetarget density

Normalizationfactor

2 Luminosity: Scintillator efficiency study

Scintillator efficiency study

Kin 03: S1-study in Hadron arm

Start losing ‘good events’!

2 Luminosity: target density monitoring

Target density monitoring: Single rates

Kin 03: Single rates vs. Run number

Increase in

target density

Monte Carlosimulation

3

Experimentalconditions

Input

Raw simulatedevents

Resolutions,Offsets,

Target density

Monte Carlo

Acceptance cuts

Simulated YieldIn pm and Em bins

3 Monte Carlo simulation: matrix-method

Em

VertexEm

Asymptotic

Binning in EmV

BinningIn

EmA

Radiation effects

Resolution effects

Weights associated to each vertex

bin

3 Monte Carlo simulation: example

Em

VertexEm

Asymptotic

Binning in EmV

BinningIn

EmA

Radiation effects

Resolution effects

Eventdrawn in 2nd bin

Vertex

Resolution effect to

1st asymptotic binContribution

to N12

3 Monte Carlo simulation: example

Em

VertexEm

Asymptotic

Binning in EmV

BinningIn

EmA

Radiation effects

Resolution effects

Eventdrawn in 2nd bin

Vertex

Resolution effect to

1st asymptotic binContribution

to N12

Eventdrawn in 2-bbu bin

Vertex (1)

Radiation to

3rd asymptotic binContribution

to N31

Cross section results

1w

Kin 03 Kin 01Previous AnalysisCurrent Analysis


Kin 01Previous AnalysisCurrent Analysis

Why this difference?

Bq

pq

qp

mp

Bq > 90° Bq < 90°

Current analysis: no angle selection


Previous AnalysisCurrent Analysis

pq

pq

Bq

Bq

Pm>0(<0)! Bq<45°(>135°)

pq<2°

L/T Separation: status report

• Kin01, Kin03: keep same hadronic vertex

•ω/q and pm/q phase spaces need to be matched

•Mean values have to be checked to be equal for Kin01 and Kin03

•Extract 2-bbu cross sections for the two kinematics at the average kinematic point.

q vs ω for Kin01 and Kin03

L/T Separation: status report

TTLLMpp RVRVREp 3333

3

)2(

)2(cos)(cos)2( 3

5

TTTTLTLTTTLLM

pp

pff

RVRVRVRVREp

dddEd

σ

TTLLMpp RVRVREp 1113

1

)2(

Conclusion and prospects

• Next steps?• Generalization of the matrix-method to deconvolute radiative effects between pm bins

• Additional binning in Q2

• Cross section extractions and L/T separations for the remaining Q2 at parallel kinematics

• Good understanding of efficiencies• Optimization of good-event-selection

• Matrix method• Gain in statistics• Iteration of matrix method • Results consistent with previous analysis

• Understanding of the different aspects concerning the separation• First results seem reasonable

• Detector in-beam efficiency study

• 3He(e,e’p)d Cross section extraction

• Preliminary L/T separation

l/t separation in the 3 he(e,e’p) reaction at parallel kinematics freija descamps supervisors: ron...

Documents