GMp Experiment. M. Eric Christy. Hall A/C Summer Meeting For the GMp Collaboration

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1 GMp Experiment M. Eric Christy For the GMp Collaboration Hall A/C Summer Meeting 2017

2 Overview of GMp Experiment Performed measurements of elastic e-p cross section over a Q2 range of 2-16 GeV2 Improve cross section precision at large Q2 by factor of 3 or better Normalization process for other measurements. Provide insight into scaling behavior of form factors at high Q2 Kinematic coverage is large enough to separate relative normalization from -dependence at large Q2 in a combined analysis with SLAC data Constrain the 2- contribution at high Q2 when combined with form factor ratios from polarization measurements Goal: 2% or better Cross sections 2

3 Experimental Setup Left HRS Right HRS p(e,e')p Scattered electrons were detected in the high resolution spectrometer (HRS) HRS parameters: Acceptance: 4.5%<Δp/p<4.5%, 6 msr Q3 e' Resolution: p/p =0.5 mrad (Horizontal) =1.0 mrad (Vertical) Dipole Beam: A e HRS t Lef Raster To beam dump Target Q2 Q1 BPM and wire scanners Q2 BCM Q1 Scattering chamber Q3 Target: 15 cm view LH2 D Side Q2 Rig ht HRS Det e pac ctor kag e Q3 D Top view or ect Det kage pac Q1 3

4 Experimental Setup Lead glass Counters Scintillators Gas Cherenkov Straw chamber s2m s0 Added for GMp Reduce systematics VDC Scattered particles Side view Scattering chamber To beam dump BCM Raster Target Q2 Q1 BPM and wire scanners Rig ht HRS Det ect o p a c kag r e Q3 D Top view 4

5 Configurations for GMp Reminder GMp is spread over 3 run periods. By far largest fraction of data taken in Fall 2016 (~ 6 months ago). Effectively 4 different spectrometers (2 different Q1 for both L and R HRS). Tuned new Q1 magnets to match B*dl of previous Q1. Still need optics data for all configurations with much poorer quality for LHRS data sets prior to Fall 2016 run. 5

6 Procedure to Extract Elastic Cross Section Cross section: Reduced cross section: Parameters: Ndet: number of scattered elastic electrons detected NBG: events from background processes : Integrated luminosity : Corrections for efficiencies LT: live time correction A(E', ): spectrometer acceptance RC: radiative correction factor E: beam energy θ: Scattering angle A thorough understanding of all these parameters is crucial for a precision cross section measurement 6

7 Elastic Cross Section Extraction (Monte Carlo Ratio Method) (1) Assuming acceptance and ratiative contributions are correctly modeled: Wmax= 1.07 GeV Method for 1st pass cross sections Will cross check with acceptance correction (1) method in future 7

8 Status of Analysis System calibration Beamline component calibration (done) PID detector (Gas cherenkov, calorimeter) calibrations (done) Tracking detector (VDC, straw chamber) calibrations (done) Timing detector (s0, s2m) calibrations (done) Optics calibration (first pass done, need to fine tune for 2% measurement) Data Analysis HRS acceptance studies (ongoing, 75% complete) Tracking, trigger efficiencies, DAQ livetime (done) Target boiling study (done) PID, Time-of-flight (done) First pass data analysis (done) Detailed aperture checks (ongoing) Second pass analysis with a goal of 2% measurement (ongoing) Acceptance correction method with distinct RadCor code in near future 8

9 Lots Already Completed 1st pass optics - All periods Yang Wang(W&M) Improved sieve slit on LHRS for Fall2016 holes closer spaced and larger angle range Procedure developed using MC data to constrain recon Matrix elements for angular regions outside of last visible hole (polynomials will Not behave well!) Beamline Calibrations / target studies Thir Gautam (Hampton U.) Correction factor for LH2 target: ( A Carbon LH2 Q2 point-to-point uncertainty in target density at 60 A: 0.2% I (ua) 9

10 Cosmic Background Reduction Barak Schmookler (MIT) HRS T1 (S0&S2m) trigger cosmics Standard analysis includes PID, tracking, and timing ( ) cuts. 33 hr Cosmic Run Same tracking and Cerenkov cuts as Beam data ~25 Bkgd events Before Calo cuts Use long beam off periods to study cosmic backgrounds. Calorimeter cut reduces contamination passing cut by 1/10, but the exact amount depends on the spectrometer central momentum setting (since the calorimeter cut is on E/p). Remaining amount subtracted from beam data. Lead glass Counters Scintillators Gas Cherenkov Straw chamber VDC Scattered particles 10

11 PID: Hodoscope timing and Track Beta Longwu Ou (MIT) T1 trigger: S0 & S2m scintillators TOF + p => (Requires careful calibrations for t0 and timewalk for each paddle) Allows descrimination of backward tracks Black: before time walk correction Red: after time walk correction Cosmics Electrons 11

12 VDC Tracking Efficiency and Stability Study Bashar Aljawrneh (NC A&T) VDC Tracking efficiency defined as fraction of electron events: = (PID & one-track events) / (PID events) Electron Sample Electron Sample Cer ADC Beam Sample Eliminate Cosmic backgrounds With cut 12

13 Stability Study: VDC Tracking Efficiency (L-HRS) Bashar Aljawrneh (NC A&T) LHRS RHRS 13

14 S0 efficiency Barak Schmookler (MIT) The main trigger for the GMp Experiment consists of a coincidence between the two scintillator detectors (s0 and s2). By using other triggers, the efficiency of the both scintillators can be determined. Once the positions of the scintillators relative to the spectrometer central ray were determined, the efficiencies across the detector planes could be determined. Typical efficiency > 99.8% No significant position variation 14

15 S2 Efficiency Barak Schmookler (MIT) (Reduces multiple scattering bias) 15

16 Stability Study: Total T1 trigger Efficiency (LHRS) Bashar Aljawrneh (NC A&T Univ) The trigger T1 is used to calculate the total scintillator efficiency. Clean electron sample (NT) selected from either T2 or T3 triggers => check if T1 is present (NT1) T1 = NT1 / NT LHRS RHRS 16

17 Magnet Stability Study Longwu Ou (MIT) Similar for other magnets Can adjust field ratios in MonteCarlo to account for small variations if necessary. 17

18 Q1 saturation Longwu Ou (MIT) A pair of identical resistive quads were used in the place of old Q1 during fall 2016 run The field strength of all magnets were measured and monitored by probes during data taking A saturation of the Q1 field is observed at p0 > 3 GeV/c and results in deteriorated resolution in reconstructed W peak 7% drop in field strength at 4 GeV/c Will use simulation to evaluate the effect on extracted cross section Invariant mass p0 = 2.67 GeV/c Red: simulation Blue: data p0 = 3.69 GeV/c 18

19 SIMC Aperture Checks with Old Q1 Barak Schmookler (MIT) We checked that all aperture checks in SIMC were consistent with the HRS technical drawing. We added missing circular aperture after Q3. When the collimator box is operated in the open position, there is still an aperture that limits the acceptance. We added this aperture to the simulation. 19

20 SIMC Aperture Checks with New Q1 Barak Schmookler (MIT) Right HRS Q1: Spring 2016 Modified the simulation to account for the aperture changes that accompanied the installation of the new Q1. => Reduced acceptance compared to 'old' Q1 That's a good thing. 20

21 e-p elastic Data / Monte Carlo studies With SIMC 21

22 e-p Elastic: Data vs SIMC, Q2 ~ 6 (GeV/c)2 Thir Gautam (Hampton U.) Arbitrary Offset ~ -5 MeV Raster correction Implemented soon Arbitrary Offset ~2.4 mrad Thir Gautam (HU) 22

23 e-p Elastic: Data vs SIMC, Q2 ~ 7 (GeV/c)2 Longwu Ou (MIT) 23

24 Acceptance / cross section Studies for 12C Target With COSY Single-Arm MC ( effective white spectra scans) 24

25 12 C Inelastic: Data vs MC (Fall 2016) Thir Gautam (HU) Took data on single foil carbon target to study the acceptance of the spectrometer Use uniform phase space illumination single-arm MC Apply physics weighting with fully radiated model, which matches well to existing data. Data deficit consistent with elastics Systematic shift consistent with elastics Data/MC =

26 LHRS 12C Carbon pointing runs (Fall 2016) LHRS 12C point runs (E' = 1 GeV at all Ebeam and angles) Used with HRS pointing surveys at sampling of angles to determine pointing at all angles Charge symmetic bkgds not include in MC Thir Gautam (HU) 26

27 12 C Cross Section Ratios (Fall 2016) Thir Gautam (HU) systematic shape in p/p clearly visible Reduction in data events for p/p>3.5% consistent with elastics 27

28 Thir Gautam (HU) x'_tar data distribution looks narrower than MC, also shift is still there reduced data width partly due to poorly constrained optics at the edge of x'_tar using old sieve with fewer holes Data/MC =

29 C12 Inelastic: Data to MC Cross section ratios (Spring 2015) Drop off at dp/p > 3.5% is still evident Slight slope still evident Additional drop off at dp/p<~-3%, which might be related to the mismatch between data/mc Thir Gautam (HU) 29

30 Acceptance studies ongoing Table from Y. Wang (W&M) Look for mismatches In hard edges defined by apertures Study sensitivity of acceptance to modelling of forward Transport. adjust integral B*dl of magnets as above. => most sensitive to Quad 2 adjust aperture positions by +/- 1 mm (exhaustive table not shown) Expect smaller sensitivity with new Q1 Final optimization of cuts to minimize sensitivity ongoing. 30

31 Preliminary Results (Data / MC method) Longwu Ou (MIT) 31

32 Summary Beamline and detector calibrations mostly complete Optics for much of data set (Q2 < 12) complete Optics correction for Q1 saturation being studied Detailed acceptance studies well underway Preliminary 5% cross sections extracted Expect final < 2% cross secction in Spring / Summer

33 Credits Graduate students: Thir Gautam (Hampton) Longwu Ou (MIT) Barak Schmookler (MIT) Yang Wang (W&M) - defended Ph.D June 2017 (2015 low Q 2 ) Bashar Aljawrneh (NCA&T) PostDoc: Kalyan Alyada (MIT) 33

34 Backup Slides 34

35 Selection of elastic electrons 35

36 Compare data to MC using global fit to 12 existing C data (E.C., T. Gautam, A. Bodek) C 12 < 0.4 > 0.6 Al 27