Cross-section Measurements with HRS and Septum

Transcription

1 Cross-section Measurements with HRS and Septum Vincent Sulkosky The College of William and Mary Hall A Analysis Workshop January 6 th, 27 Hall A Analysis Workshop p.1/16

2 Overview of Experiment E97-11 Precise measurement of generalized GDH integral at low Q 2,.2 to.3 GeV 2, see J. Singh s talk. Inclusive experiment: 3 He( e,e )X Measured polarized cross section differences Seven different beam energies from 1.1 GeV to 4.4 GeV were used and two angles. The spectrometer momentum was varied from.5 GeV/c to 3.1 GeV/c. 2 2 Q (GeV ) threshold W (GeV) Hall A Analysis Workshop p.2/16

3 Measured Observables Asymmetries: A, = 1 f N2 P tg P beam N + Q + LT + N Q LT N + Q + LT + + N Q LT Cross-sections: σ o = N cuts N inc ρε det LT Acc. 2ρ N 2 ρ + ρ N2 σ N2 σ, = 2A, σ o g 1, g 2 g 1, g 2 : spin dependent structure functions Hall A Analysis Workshop p.3/16

4 Analysis Procedure Detector Eff., deadtime Acceptance and target density N 2 dilution σ o = N cuts N inc ρε det LT Acc. 2ρ N 2 ρ + ρ N2 σ N2 σraw σ o Radiative Corrections Data σ, g1, g2 GDH + N N A raw A A PID and Acceptance cuts Charge & Deadtime Pt, Pb and N 2 dilution A, = 1 f N2 P tg P beam N + Q + LT + N Q LT N + Q + LT + + N Q LT Hall A Analysis Workshop p.4/16

5 Spectrometer Acceptance What is acceptance? The geometrical efficiency of a spectrometer. Acceptance is crucial in measuring absolute cross sections. Acceptance = 1 Ω E Z Hall A Analysis Workshop p.5/16

6 Spectrometer Acceptance What is acceptance? The geometrical efficiency of a spectrometer. Acceptance is crucial in measuring absolute cross sections. Acceptance = 1 Ω E Z Ω - solid angle (sr). E - spectrometer momentum bite (MeV/c). Z - target length (cm). Hall A Analysis Workshop p.5/16

7 Determining the acceptance The magnetic elements of the spectrometer result in a complicated acceptance shape that is dependent on the target variables. The acceptance shape is determined by comparing a simulation to the data. A ray tracing program, SNAKE, is used to generate trajectories through a model of the spectrometer. 1 Ω E Z = N mc N mc tot accp Ω mc E mc Z mc Hall A Analysis Workshop p.6/16

8 Determining the acceptance Quadrupole 3 Septum Magnet Quadrupole 1 Target Focal Plane Quadrupole 2 Dipole Hall A Analysis Workshop p.6/16

9 Hall A Monte-Carlos MCEEP - standard Hall A tool. SIMC - Hall C code modified for HRS. G1 - GEANT based code. HRS transfer functions - SNAKE model of the spectrometers. SAMC - Single Arm Monte-Carlo (A. Deur). More info can be found at Hall A Analysis Workshop p.7/16

10 Single Arm Monte-Carlo (SAMC) Developed by Alexandre Deur for E94-1. Used for inclusive 3 He experiments in Hall A. Various versions exists for different experiments. Most recent version adapted for use with the septum magnet. More info can be found at Hall A Analysis Workshop p.8/16

11 Single Arm Monte-Carlo (SAMC) Includes: Inclusive measurements. Point and extended targets. Raster. Elastic radiative correction (internal + external). Landau Straggling. Multiple scattering. More info can be found at Hall A Analysis Workshop p.8/16

12 Single Arm Monte-Carlo (SAMC) Reactions: Unpolarized elastic: 3 He, 4 He, Carbon, Nitrogen. Polarized elastic: 3 He. Polarized quasi-elastic: 3 He. Mott/phase space. More info can be found at Hall A Analysis Workshop p.8/16

13 E97-11 Experimental Setup Septum magnet Low Q 2 requires forward angles. Minimum spectrometer angle is The septum magnet allows detection of electrons with scattering angles of 6 and 9. Designed for the spectrometers to retain their resolution and have comparable acceptance. Hall A Analysis Workshop p.9/16

14 E97-11 Experimental Setup Collimators: target and sieve slit Target collimators remove the glass windows from the acceptance. Three different collimator configurations were used. Sieve collimator removes background from outside the target region. Sieve collimator centered at sieve slit W x H = 5.5 x 9.9 cm 2. Hall A Analysis Workshop p.9/16

15 E97-11 Experimental Setup Hall A Analysis Workshop p.9/16

16 Target Coordinates Scattered electron y sieve z tg y tg L Sieve plane φ tg Θ y tg D Spectrometer central ray Beam z react Hall center Hall A Analysis Workshop p.1/16

17 SAMC: Modifications and Issues Changes for E97-11: Update transfer functions for septum + HRS (J. LeRose). Add target and sieve slit collimators. Use exact scattering angle formula. cos θ sc = cos θ φ tg sin θ 1+θtg 2 +φ2 tg θ sc θ ± φ tg Hall A Analysis Workshop p.11/16

18 SAMC: Modifications and Issues Changes for E97-11: Update transfer functions for septum + HRS (J. LeRose). Add target and sieve slit collimators. Use exact scattering angle formula. Discovered Issues: Transfer functions fit withtoo small x tg range: ± 3 mm. δ acceptance is larger for model compared to data. Hall A Analysis Workshop p.11/16

19 Issues Problem: x tg range vertical axis: x fp and horizontal axis: x fp Hall A Analysis Workshop p.12/16

20 Issues Problem: extra δ acceptance Can reduce Q3 exit aperature radius to 28 cm. Also seen in MCEEP, see JLab-TN-1-25 by Paul Ulmer. Hall A Analysis Workshop p.12/16

21 Carbon Elastic Data and MC Comparison W - M Acceptance θ tg Acceptance Elastic Data 7 Simulation σ (µ barns) σ (µ barns) Elastic Data Simulation W - M( C) Absolute Comparison! θ tg Hall A Analysis Workshop p.13/16

22 Carbon Elastic Data and MC Comparison φ tg Acceptance y tg Acceptance 1 Elastic Data Simulation Elastic Data Simulation 8 12 σ (µ barns) 6 4 σ (µ barns) φ tg Absolute Comparison! y tg Hall A Analysis Workshop p.13/16

23 3 He Target Acceptance Run 291, 1.79 GeV Run 291, 1.79 GeV y tg y tg φ tg θ tg 1 5 Run 291, 1.79 GeV Run 291, 1.79 GeV θ tg δ φ tg θ tg 5 Hall A Analysis Workshop p.14/16

24 3 He Target Acceptance Background: Enhanced peak at negative θ tg. Possibly due to scrapping off the bore cooler. Unfortunately leaves a hole once background is removed. Collimator punch-thru events. Both effects can be removed with tighter acceptance cuts. Hall A Analysis Workshop p.14/16

25 3 He Target Acceptance 3 Black GeV, Polarized He 3 Black GeV, Polarized He GeV/c Data With σ Mott δ θ tg 3 Black GeV, Polarized He 3 Black GeV, Polarized He φ tg y tg Hall A Analysis Workshop p.14/16

26 3 He Target Acceptance 3 Black GeV, Polarized He 1 3 Black GeV, Polarized He GeV/c Data 6 4 With σ Mott δ θ tg 3 Black GeV, Polarized He 14 3 Black GeV, Polarized He φ tg y tg Hall A Analysis Workshop p.14/16

27 3 He Target Acceptance Empty Reference Cell, Run # θ tg Hall A Analysis Workshop p.14/16

28 Acceptance Cuts Run 292, 1.79 GeV/c Run 292, 1.79 GeV/c y tg 4 δ φ tg θ tg θ tg Run 292, 1.79 GeV/c φ tg δ Run 292, 1.79 GeV/c φ tg Hall A Analysis Workshop p.15/16

29 Acceptance Cuts 3 Black GeV, Polarized He 3 Black GeV, Polarized He GeV/c Data With σ Mott δ θ tg 6 3 Black GeV, Polarized He 6 3 Black GeV, Polarized He φ tg y tg Hall A Analysis Workshop p.15/16

30 Remaining Items and Summary Collimator Background A full simulation is underway (T. Holmstrom). SAMC interfaced with QFS to calculate inelastic cross-sections (K. Slifer). Important and necessary to extract cross-sections differences. If background is unpolarized, then it will cancel in the difference. If polarized, then a lot more work may be required. Summary Acceptance determination is crucial for cross-section analyses. For E97-11, SAMC code was used for the spectrometer acceptance. Major hurdle from collimator background. Hall A Analysis Workshop p.16/16

31 Remaining Items and Summary GeV, 6 Degrees sr -1 ) -1 (nb MeV σ Preliminary W (MeV) Hall A Analysis Workshop p.16/16