Elastic Electron Scattering off He and He (E04-018)

Elena Khrosinkova

Kent State University

Hall A Collaboration Meeting

Jefferson Lab, June 2008

3 4

Objective

Elastic scattering off helium's stable isotopes at large momentum transfers

Extraction of He3 charge and magnetic and He4 charge form factors

3

Jefferson Lab, June 2008 2/17

Experimental Apparatus

Coincidence experiment using TOF method 20 cm helium cells

Jefferson Lab, June 2008 3/17

Elastic Electron-Helium Scattering

He charge and magnetic form factors:

,

He charge form factor:

2

sin2

cos

2sin4

' 2222

43

22

QQ

E

EZ

d

dA B

2Q const

1

222222 QFQF

Q MC 2222 2 QFQ MA B

22

43

222

2sin4

2cos'

QFE

EZ

d

dC

3

4

Jefferson Lab, June 2008 4/17

2sin4 22

EEQ

Data range

Jefferson Lab, June 2008 5/17

Data range

Jefferson Lab, June 2008 6/16

Data range

Jefferson Lab, June 2008 7/17

Analysis projectsCurrent Calibration

2 current calibrations Normalization of the current

at the injector cavity to the

Faraday cup

Cross-check with the Unser

current

Jefferson Lab, June 2008 8/17

Normalization of the

two BCM cavities to

the calibrated injector

cavity

Analysis projectsCurrent Calibration

Jefferson Lab, June 2008 9/17

Normalization of the

scalers frequency

(right, left) to the

average value of the

calibrated injector

cavity current

Analysis projectsCurrent Calibration

Jefferson Lab, June 2008 10/17

Analysis projectsCalorimeter calibration

6x6 blocks

calibration

MC simulation for energy deposited in first and second layers

1222 – 1273 runs

ep elastic, 2.13 GeV

E/p vs E

E/p

Co

un

ts

Jefferson Lab, June 2008 11/17

Cerenkov sum corrected

Analysis projectsCerenkov Gain Equalization

With cuts on >99% of total

light in one particular tube

Number of photoelectrons > 6

Cerenkov efficiency

close to 100%

1222 – 1273 runs

ep elastic, 2.13 GeV

7.9NL.cer.a_p[4]

L.cer.a_p[5]C

ou

nts

1.9N

7.9N

Jefferson Lab, June 2008 12/17

Analysis projectsTiming Offsets Correction

1232 – 1233 runs,

ep elastic

2.34 GeV

Jefferson Lab, June 2008 13/17

tof, uncorrected

tof, corrected

Co

un

tsC

ou

nts

Analysis projectsScintillators ADC Equalization

L.s1.ra_p[3]

L.s1.ra_p[2]

L.s1.la_p[3]

L.s1.la_p[2]

L.s1.la_c[*] + L.s1.ra_c[*]

Jefferson Lab, June 2008 14/17

1222 – 1273 runs ep elastic, 2.13 GeV

Analysis projectsEvent Display

Jefferson Lab, June 2008 15/17

3D event display

For all tracks from the analyzer

LHRS and RHRS

Cuts for “fired” blocks

In progress

Elastic stripe

= 40 fm , e He2Q 2 3

Jefferson Lab, June 2008 16/17

Left, m

Rig

ht, m

Summary

Finalization of the detector calibrations

Improving tracking routine

Ready for mass analysis

Jefferson Lab, June 2008 17/17