PREX Q2Analysis

Kiadtisak Saenboonruang

University of Virginia

Hall A Analysis Workshop

December 8, 2010

PREX

“Pb Radius Experiment”

Experiment Overview• A clean measurement of the neutron skin of 208Pb through

parity violating electron scattering

• Run from March-June 2010

• For PREX(elastic scattering of 208Pb target),

� ��~0.009��

� spectrometer angle �~88 ���

�� Analysis• �� is the square of the four-momentum transferred from

the incident electron to the target proton

• �� � ��� � �������� �

• For elastic scattering, �, ��, � are related

• Four ways of calculating ��(elastic scattering)

1. �� � 2��� 1 � cos �2. �� � 2��"#�1 � cos � �3. �� � 2�′�"′#�1 � cos � �4. �� � 2 �� � ��� where m is target nucleus mass

where "# �'

'(�)

*��'+,-. / �

and "′# �'

'+�)0

*��'+,-. / �

Challenges in �� determination

For Eq 4: �� � 2 �� � ���, • � � ��~201• 2�~2001 and 2�′~2001• 2 � � �� ~2801 → 1400% uncertainty

THIS EQUATION WILL NOT WORK!!!

For Eq 1-3: �� � ������5���5����, ��

• 2�� � �678

692���:�

678

69�2�′��:�

678

6/2���

• 2�and2��contribute~0.002% uncertainty

• Most uncertainty is from �• Spectrometer angle from survey gives δ�~0.8mrad

•F78

78 � 2F/

/→ δ�� � 2%

• We need δ�� G 1% → 2� G 0.5%or0.4 ���

Pointing Measurement• A way to measure spectrometer angle with better accuracy

than survey

• Using the fact that;

� for different scattering angles, scattering energy

is different.

� for different mass, the same scattering angle, scattering

energy is different.

�� �� � �I�1 :

�I2JK

�

1 :2�LMN��

�2�

JK

How do we do pointing?With waterfall target (for several OP settings)

� Select events from central sieve slit’s hole

� Find the separation of 16O and 1H ground state energies

� Find central angle � using the least χ2 method

16O16O

1H

1H

Pointing Results • Angles between target and central sieve slit’s hole

• These angles give scattering energies to be better than 50 keV

• Given that we have 3 settings to use, 2�~351 → δ�~0.35 ���• 2�~0.4% → 2��~0.8% (within required 1% uncertainty)

LHRS 88.4 mrad

RHRS 86.1 mrad

P0 ∆R�STUT� ∆R�VWXYUXYZ� Difference

1.063 GeV 4.217 MeV 4.229 MeV 12 keV

1.058 GeV 4.185 MeV 4.220 MeV 35 keV

1.047 GeV 4.245 MeV 4.199 MeV 46 keV

0.0855

0.0860

0.0865

0.0870

0.0875

0.0880

0.0885

0.0890

Angle (rad)

Spectrometer

Analysis Values

Survey ValuesLHRS RHRS

Central Angle Comparison

Optics Reconstruction• With pointing measurement, we can have accurate �� for central hole

• Need to consider �� for the whole acceptance � Optics Reconstruction

• Optics Reconstruction

� Transform focal plane variables (x,y,θ,φ) to target variable (δ,y, θ,φ)

Note: 2 �[+[\

[\

Angle Reconstruction

LHRS

RHRS

Momentum Reconstruction• Crucial for pointing measurement (need to be better than 40 keV)

• Look at energy difference of 12C ground state and first excited state

Note: Nominal value is 4.44 MeV

Preliminary Q2 Analysis• Cut used

� Single hit

(“L.tr.n==1”)

� Trigger type

(“P.evtype ==1 or P.evtype==5”)

� Angle cut

(“abs(L.tr.tg_th)<0.07 and abs(L.tr.tg_ph)<0.07”)

� Particles hit PREX detector

(“P.loQadcL > pedestal and P.upQadcL > pedestal”)

Q2 Dependence on Trigger Type• 2 triggers used:

1. T1: Trigger above VDC planes

2. T5: S0 Trigger above PREX detectors

• By average, T5 gives Q2 ~0.2% higher than T1

LHRS RHRS

T1

T1

T1

T1

T1

T1

T5

T5

T5

T5

T5

T5

Q2 Dependence on Trigger Rate

LHRS RHRS

500kHz 150kHz

57kHz 9.3kHz

1.6kHz 0.3kHz

500kHz 150kHz

57kHz 9.3kHz

1.6kHz 0.3kHz

• VDC fails to perform for high rates

• In normal operation, VDC can work up to ~101]^/` �

• For PREX, the active area on VDC is 20 cm2

• For high rates, GEM will solve the problem

0.008800

0.009000

0.009200

0.009400

0.009600

0.009800

0.010000

0.010200

1 10 100 1000 10000 100000 1000000

Q2

Rate (Hz)

Q2 vs Rate

500 kHz

150 kHz

57 kHz9.3 kHz300 Hz

Gas Electron Multiplier (GEM)• Gaseous ionization detector

• Perform up to 10 MHz/cm2

• Resolution ~70b

VDC Projection on GEM Correlation

Q2 by Geometric Cut• To ensure the hit on PREX detector, cut on PREX detector’s ADC values

• However, for some runs, PREX detectors didn’t perform well� Geometric Cut

• Geometric cut: VDC projection on PREX detector and cut on the size of

the detector

• By average, Q2 by ADC cut is ~0.3% higher

Preliminary Q2 Results

0.0085

0.0087

0.0089

0.0091

0.0093

0.0095

0.0097

0.0099

0.0101

0 5 10 15 20 25

Q2

Run

Q2RHRS (whole)

LHRS (whole)

500 kHz

Thin Pb

150 kHz

• Q2 deviates in opposite direction can be due to the beam shifted by 0.5 mm

• Due to the low beam current, the fast feedback was turned off.

Date Target LHRS Run Q2 RHRS Run Q2

1 4/3/2010 Pb/D #3 27257 0.009292 - -

2 4/18/2010 Pb/D #3 27421 0.009361 6714 0.008775

3 4/18/2010 Pb/D #3 27422 0.009378 6715 0.008773

4 4/18/2010 Pb/D #3 27423 0.009345 6716 0.008771

5 4/18/2010 Pb/D #3 27424 0.010110 6717 0.009383

6 4/18/2010 Pb/D #3 27425 0.010120 6718 0.009380

7 4/18/2010 Pb/D #3 27426 0.009318 6719 0.008765

8 4/18/2010 Pb/D #3 27427 0.009358 6720 0.008772

9 4/25/2010 Pb/D #3 27506 0.009403 6740 0.008849

10 4/25/2010 Pb/D #3 27507 0.009324 6741 0.008799

11 4/25/2010 Pb/D #3 27508 0.009296 6742 0.008786

12 4/25/2010 Pb/D #3 27511 0.009336 6745 0.008770

13 5/7/2010 Pb/D #2 27610 0.009405 - -

14 5/19/2010 Pb/D #2 27697 0.009413 6823 0.008721

15 5/19/2010 Pb/D#2 - - 6824 0.008734

16 5/19/2010 Pb/D #2 27698 0.009340 6825 0.008725

17 5/19/2010 Pb/D #3 27700 0.009364 6826 0.008784

18 5/19/2010 Pb/D #3 27701 0.009371 6827 0.008787

19 5/19/2010 Pb/D #3 - - 6828 0.008782

20 6/4/2010 Pb/D #3 27722 0.009328 6839 0.008749

21 6/4/2010 Pb/D #3 27723 0.009334 6840 0.008747

22 6/12/2010 Thin Pb 27824 0.009260 6906 0.008796

23 6/12/2010 Thin Pb 27825 0.009250 6907 0.008793

24 6/12/2010 Thin Pb 27826 0.009242 6908 0.008795

25 6/18/2010 Pb/D #1 - - 6965 0.008828

Future Plans• GEM Analysis

• Explanation of the 1% fluctuation in Q2

• Table of errors