Spectrometer Optics Calibration for g2p Experiment. Chao Gu University of Virginia On Behalf of the E Collaboration

Transcription

1 Spectrometer Optics Calibration for g2p Experiment Chao Gu University of Virginia On Behalf of the E Collaboration Hall A/C Analysis Workshop, Dec 18th, 2013

2 HRS Optics: Overview HRS has a series of magnets 3 quadrupoles to focus and 1 dipole to disperse on momentums Optics study will provide a matrix to transform VDC readouts to kinematics variables which represents the effects of these magnets 0 y 1 C A tg = 0 h xi h i h xi h i hy yi h yi First Order Matrix hy i h i 1 0 C A x y 1 C A Q3 VDC Target Q1 Q2 Dipole 2

3 Optics Goal The g2p experiment will measure the proton structure function g 2 in the low Q 2 region ( GeV 2 ) for the first time Goal: 5% systematic uncertainty when measuring cross section Optics Goal: <1.0% systematic uncertainty of scattering angle, which will contribute <4.0% to the uncertainty of cross section! 1/ sin 4 ( /2) Momentum uncertainty is not as sensitive, but it is not hard to reach 10-4 level 3

4 Optics for g2p Septa magnet Target magnetic field Optics matrix will cover septa magnet Target magnetic field will break the focusing nature of the spectrometer so more difficult 0 y 1 C A tg = 0 h xi h i h xi h i hy yi h yi First Order Matrix hy i h i 1 0 C A x y 1 C A Q3 VDC Target Septa Q1 Q2 Dipole 4

5 Angle Calibration Determine the center scattering angle Survey: ~1mrad Idea: Use elastic scattering on different target materials E 0 E E! = 1+ E M 1 (1 cos ) 1+ E M 2 (1 cos ) Data taking: Carbon foil in LHe, or CH 2 foil Two elastic peak took at the same time He Peak Septa Center Angle θ0 Target The accuracy to determine this difference is <50KeV -> <0.5mrad C Peak E 5

6 Matrix Calibration Calibrate the angle and momentum matrix elements: Use carbon foil target and point beam Use sieve slit to get the real scattering angle from geometry Angle: Fit with data which we already know the real scattering angle Momentum: Use the real scattering angle to calculate elastic scattering momentum of carbon target Target Sieve slit Septa A B C D E F G 6

7 Matrix Calibration: Angle LHRS Before Calibration After Calibration Resolution: 1.4mrad (RMS) 7

8 Matrix Calibration: Angle RHRS Before Calibration After Calibration Resolution: 1.6mrad (RMS) 8

9 Matrix Calibration: Momentum LHRS Before Calibration After Calibration Relative momentum RMS: 1.4x10-4 Relative momentum 9

10 Matrix Calibration: Momentum RHRS Before Calibration After Calibration Relative momentum RMS: 1.7x10-4 Relative momentum 10

11 Optics Study with Target Field To include target field Normal sieve slit method is not useful Idea: separate reconstruction process to 2 parts: Use HRS optics matrix to do the reconstruction from VDC to sieve slit Use the target field map to do a ray trace of the scattered particle from sieve slit to target VDC Sieve slit Septa Q1 Q2 Q3 Target Dipole 11

12 Optics Study with Target Field Recalibrate the angle matrix elements: Start with the transform matrix without target field To fit the matrix element, need to know the effective theta and phi angle Use a modified SAMC simulation to get these effective angles Side View Effective theta angle used to fit HRS angle matrix Beam Reaction point Real theta angle x Sieve z 12

13 Optics Study with Target Field Reconstruct the scattering angle: Use the HRS transform matrix to get the effective target variables Project the effective target variables to sieve slit Use the field map to calculate the trajectory of the scattered electron, which will tell us the real scattering angle Side View Effective beam x position Beam Reaction point BPM readout x Sieve z 13

14 Optics Study with Target Field Run simulation to decide the effective theta and phi Assuming point beam Beam energy 2.254GeV, Target field 2.5T Initial angle in simulation Effective angle to do the fitting 14

15 Optics Study with Target Field Sieve pattern after calibration Use carbon foil target and point beam Sieve pattern is decided by both the beam position and the reconstructed angle Directly use BPM readout to provide beam position here 15

16 Optics Study with Target Field Compare reconstructed target theta and phi angle with the calculated result Calculated theta and phi Reconstructed theta and phi 16

17 Conclusion Optics study without target field works well Optics study with target field The reconstructed procedure is designed with help of simulation The method is tested with 1 set of the data and could do the reconstruction Will test the method on different settings 17

18 E Collaboration Spokespeople Alexander Camsonne (JLab) J.P. Chen (JLab) Don Crabb (UVA) Karl Slifer (UNH)! Post Docs Kalyan Allada Elena Long James Maxwell Vince Sulkosky Graduate Students Toby Badman Melissa Cummings Chao Gu Min Huang Jie Liu Pengjia Zhu Ryan Zielinski!!! Jixie Zhang

19 Thanks I would like to thank the following people for their guidance and helpful discussions! Min Huang and Ryan Zielinski who also did many calibration work Jian-ping Chen Nilanga Liyanage Jixie Zhang, Vince Sulkosky John Lerose Jie Liu, Jin Huang, Xin Qian, Yi Qiang, Kiad Saenboonruang, Zhihong Ye

20 Backups

21 BPM Issue BPM issue in g2p New BPM electronics does not seem to work very well during the no-targetfield optics Sieve hole z z New method: Assume the beam hits only one point on the target Ideally the reconstructed trajectories should intersect at this target point Actually it will not perfectly intersect, each trajectory will give an intersection with the target foil The standard deviation of these intersections will give us a reference to do a fit and get the optics matrix for phi angle x y BPM x Transport Coords Hall Coords 21

22 Experiment Setup Hall A High Resolution Spectrometer High momentum resolution: 10-4 level over a range of GeV/c High momentum acceptance: δp/p < 4.5% Wide range of angular settings: 12.5 ~150 for left arm, 12.5 ~130 for right arm Angular acceptance: ±30 mrad (Horizontal) and ±60 mrad (Vertical) HRS HRS HRS