GMp Experiment (E ): An update

Transcription

1 GMp Experiment (E ): An update Kalyan Allada MIT Hall A/C Summer Meeting, Jefferson Lab 17th July 2015

2 Motivation Accurately measure e-p elastic cross section in kinematics similar to other JLab form factor measurements (Q2 = 7 17 GeV2) Improve accuracy of the cross section by as much as a factor of 5 (< 2%) over previous measurements Key input to all form factor experiments, and many of other experiments where elastic scattering is used for normalization Approved for 24 PAC days

3 Kinematic Coverage and Expected Precision Requires very good control on : - beam energy - target density - scattering angle Goal: 2 % or less total uncertainty

4 Kinematics Will be revised based on the available beam energy and the limitation on HRS magnet current

5 GMp Commissioning Activities Fall 2014: Eb = 7.3 GeV, only L-HRS working Installed new EDTM system in L-HRS Improved light collection on HRS Gas Cherenkov with WLS paint Collected optics data and one elastic point at Q 2 = 7.7 GeV2 Large uncertainties in beam energy, beam charge and position Spring 2015: Eb = 9.6 GeV, then Eb = 2.2 GeV Commissioning of SOS quad on R-HRS New raster commissioning, BPM/harp and BCM calibration Beam energy measurement Collected HRS optics data - L-HRS was mostly used by the DVCS expt. Target boiling studies e-p elastic data at Q2 = 1.0 GeV2 for cross-check No physics, only calibration data was collected

6 Event Reconstruction from Fall 2014 Ebeam=7.29 GeV Elastic e-p scattering σ=0.035 GeV2

7 HRS Detector Configuration Two VDCs at focal plane to determine particle direction Straw chamber as an auxiliary tracking detector Scintillator paddles S0 and S2m as primary trigger detectors Particle ID: Cherenkov counters lead-glass shower+preshower

8 RHRS Q1 Magnet The HRSs (RHRS and LHRS) are QQDQ spectrometers. Quadrupole 1 (Q1) focuses in the dispersive (i.e. bend) plane, while Q2 and Q3 focus in the non-dispersive direction For the RHRS Q1, a rapid, non-linear voltage increase across the two leads was observed with an increase in current Because of this, Q1 has been removed from the RHRS and replaced with Hall C SOS quad Repairs of R-HRS Q1 are planned for this Fall

9 SOS Quad Front View SOS quad mounted in R-HRS

10 Pole-Tip Field vs Current in SOS Quad Nominal current in SOS quad (after matching Bdl to original Q1) is 213 Amp/GeV

11 Simulation Studies of the RHRS The program COSY Infinity was used to model the magnetic elements of the spectrometer Used an idealized quad magnet with limited fringe-field effects for these simulations. More complete simulations using field-maps may be forthcoming in the near future.. Position and momentum variables after the magnetic element are determined by summing the product of matrix elements to a given order Simulations performed by Barak Schmookler (MIT)

12 COSY Infinity Ray-Tracing: RHRS with SOS Quad, Non-Dispersive Plane Barak Schmookler (MIT)

13 Acceptance Comparison: (e,e ) Elastic Simulation SOS Quad set to match field integral (Bdl) of Q1 Barak Schmookler (MIT)

14 SOS Quad Tune: Data with Optics Target Right Q1 current = + 10 % of nominal Reconstruction using old matrix Multi-foil carbon target Try to match to the old tune by removing slope in foil position vs phi Did not try to maximize the acceptance need to look at focal plane variables

15 SOS Quad Tune: Data with Optics Target Right Q1 current = - 4 % of nominal -4 % gave the best match to the old tune

16 HRS Optics Data Optics data collected during the commissioning run Fall 2014 Spring 2015 HRS Sieve Target θhrs Ebeam (GeV) P0 (GeV) Comment L-arm Yes Five-foil Carbon No survey Yes Five-foil Carbon θ, φ, y optimization (-4%) (-2%) (2%) (4%) Dp optimization R-arm No LH

17 R-HRS: sieve pattern from center carbon foil

18 Right HRS Optics (θ HRS 48 deg.) θ, φ optimization results: D H = 0.28 mm D V = 0.93 mm D = average of the absolute value of the difference between the mean of Gaussian fit and corrected hole position GMp requirement: DH = 0.18mm Current issue: Yang Wang (W&M) - not enough sieve holes visible - moving R-HRS to smaller angles will help with acceptance DV = 0.35 mm

19 Right HRS Optics (θ HRS 48 deg.) Target y (horizontal) optimization results - Spring 2015 data = 0.75 mm (GMp requirement) Yang Wang (W&M)

20 Straw Chamber One Straw Chamber installed in each HRS 3 U and 3 V planes U-V angle: 450 to horizontal 170 straws per plane Wire spacing: cm Help resolve ambiguous tracks from VDC Determine VDC efficiency Straw chamber VDC

21 Event Display er t s lu c e On M VDC VDC i-c t l u straw chamber Longwu Ou (MIT) t n e ev er t s lu n e v e S2m t PRL1 PRL2

22 Tracking with VDC and Straw Chamber Analysis of multi-cluster events in VDC: Select events with one cluster in bottom VDC and straw chambers but more than one clusters in top VDC Reconstruct track using clusters in bottom VDC and straw chambers (disregarding clusters in top VDC) Reconstructed track is then used to calculate target and kinematic variables Fraction of one cluster events in VDC: Nsingle/Ntotal= Longwu Ou (MIT)

23 Detector Performance: S0 S0 consists of a single scintillator paddle with a PMT at each end One of main trigger detectors for GMp experiment Track projection on S0 (X vs Y) All events No TDC hit on at least one PMT σ=0.75 ns No TDC hit on both PMTs About 2.5% of total events are lost due to finite geometrical acceptance of S0 Longwu Ou (MIT)

24 Detector Performance: S2m S2m consists of 16 scintillator paddles in a plane One of main trigger detectors for GMp experiment One photo-electron peak for each ADC channel is aligned Geometrical acceptance of S2m is found to be 99.4% σ=0.89 ns Longwu Ou (MIT)

25 Detector Peformance: Gas Cherenkov All 20 PMTs are covered with wavelength-shifting paint (WLS) The effect of WLS paint was tested in Spring % increase in #p.e. was observed (results in K. Allada et al., NIM A 782 (2015) 87 ) Typically p.e. were detected in GC after application of WLS paint No time dependence observed on the # p.e yield with WLS for over a period of ~ 1 year No time dependence observed

26 Detector Performance: Lead-glass Calorimeter Two layers of lead glass blocks Gain matching of all ADC channels Particle ID (with GC counter) Energy resolution: LHRS: 3GeV RHRS: 1GeV

27 E = GeV: Low-Q2 elastic checks LHRS at 25, 35, 45 deg. RHRS at 48 deg. After correcting for preliminary vertical beam position: -6 mm 2.8 MeV LHRS: Wpeak - Mp = 3.7, 3.7, 3.2 MeV RHRS: Wpeak - Mp = 3.8 MeV - Consistent with random θ < 0.4 mrad - Conservative uncertainty on beam energy ~1x10-3 Eric Christy/Thir Gautam (Hampton)

28 Beam Charge Calibration Multiple current measurements: Unser/BCM/Faraday Cup, need to cross-calibrate Standard BCMs receivers: upstream (x1, x3) and downstream (x1, x3, x10) Two new receivers are also available: upstream and downstream linear over wide range of currents Status: Unser calibrated against known current gain stable within 0.4 % Gain and temperature changes observed after the Spring power outage event BCM calibrated against Unser both Left and RHRS BCMs agree

29 Beam Charge Calibration Calibration of u1 (upstream x1) BCM against Unser current Non-linear below 15 ua, only used for higher current Thir Gautam (Hampton)

30 Beam Charge Calibration Calibration of d3 (downstream x3) BCM against Unser current Saturates above 14 ua, only used for lower current Thir Gautam (Hampton)

31 BPM/Harp Calibration BPMs calibrated against Harp - good agreement between Left and Right HRS Results of BPM vs Harp positions Thir Gautam (Hampton)

32 Target Boiling Studies Work in progress investigating carbon yield drifts Very Preliminary Thir Gautam (Hampton)

33 Manpower Spokespeople: Postdoc: J.Arrington, E.Christy, S.Gilad, B.Moffit, V.Sulkosky, B.Wojtsekhowski (contact) Kalyan Allada (MIT) Graduate Student: Thir Gautam (Hampton Univ) Longwu Ou (MIT) Barak Schmookler (MIT) Yang Wang (W&M) Acknowledgments: The Hall A physics and technical staff The DVCS and Hall A collaborators for taking a lot of shifts

34 Summary Commissioned the GMp experiment during Fall 2014/Spring 2015 No physics data beam energy limited to 2.2 GeV Commissioning activities: HRS detector check-out and calibrations Tuning new quad on R-HRS Beamline commissioning Target boiling studies Data analysis: Optics: angle optimization done, dp optimization (on-going) Systematic studies: target boiling, deadtime etc. (on-going) Low Q2 e-p elastic cross-section as a cross-check (not done yet) Remaining checkout items: wire target for angle measurement Next physics run in Spring 2016 run with 11 GeV beam

35 Spare Slides

36 Detector Performance: Lead-glass Calorimeter New electronics for EDTM (electronic dead-time measurement) was implemented on the LHRS last summer Attenuated logical EDTM pulses are mixed with signals from the Gas Cherenkov, S0 and S2m detectors The number of 'tagged' EDTM pulses that are recorded in scalers is monitored Electronic dead-time was measured and found to be negligible, but more test is needed in very high-rate situation

37 Acceptance in the Focal Plane Acceptance in the focal plane at different quad currents with LH2 target

38 Q1 (SOS) current = - 10% Q1 (SOS) current = + 10% Q1 (SOS) current = - 4%

39 RHRS Q1: Voltage Across Leads Voltage Drop Over Leads Current in Magnet