m. eric christy€¦ · june 22, 2017 eric christy - hall a/c summer meeting 2 performed...

GMp Experiment

M. Eric Christy

Hall A/C Summer Meeting 2017

For the GMp Collaboration

June 22, 2017 Eric Christy - Hall A/C Summer Meeting 2

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.

Overview of GMp Experiment

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


BCM Raster BPM andwire scanners

TargetTo beam dump

Left H

RS

Top view

Scattering chamber

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

Resolution: p/p≤2×104

=0.5 mrad (Horizontal)=1.0 mrad (Vertical)

Q1

Q2

Q3

D

Detector

package

Right HRS

Q1 Q2

Q3

D

Detector package

Side view

Beam: 15-70ATarget: 15 cm LH2

Right HRS

Left HRS

Q1 Q2

Dipole

Q3

e'

e

Experimental Setup


Experimental Setup

BCM Raster BPM andwire scanners

Target

To beam dump

Top view

Scattering chamber

Right HRS

Q1 Q2

Q3

D

Detector package

Side view

VDC

Straw chamber

Gas Cherenkov

Lead glass Counters

Scattered particles

Scintillators

Added for GMpReduce systematics

s0

s2m


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.


Cross section:

● Ndet

: number of scattered elastic electrons detected

● NBG

: events from background processes

● : Integrated luminosity ● : Corrections for efficiencies

Parameters:

A thorough understanding of all these parameters is crucial for a precision cross section measurement

● LT: live time correction● A(E',): spectrometer acceptance● RC: radiative correction factor● E: beam energy● θ: Scattering angle

Reduced cross section:

Procedure to Extract Elastic Cross Section


Elastic Cross Section Extraction (Monte Carlo Ratio Method)

Assuming acceptance and ratiative contributions are correctly modeled:

→ Method for 1st pass cross sections→ Will cross check with acceptance correction (1) method in future

(1)

Wmax

= 1.07 GeV


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


Correction factor for LH2 target:(2.70.4)% @ 100 A

Q2 point-to-point uncertainty in target density at 60 A: 0.2%

Lots Already Completed

Thir Gautam (Hampton U.) Carbon

LH2

I (uA)

Beamline Calibrations / target studies

1st pass optics - All periodsYang 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!)


Cosmic Background Reduction

• HRS T1 (S0&S2m) trigger cosmics

• Standard analysis includes PID, tracking, and timing () cuts.

• Use long beamoff 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.

VDC

Straw chamber

Gas Cherenkov

Lead glass Counters

Scattered particles

Scintillators

33 hr Cosmic Run

Same tracking and Cerenkov cuts as Beam data

~25 Bkgd eventsBefore Calo cuts

Barak Schmookler (MIT)


● T1 trigger: S0 & S2m scintillators

→ TOF + p =>

(Requires careful calibrations for t0 and

timewalk for each paddle)

● Allows descrimination of backward tracks

PID: Hodoscope timing and Track Beta Longwu Ou (MIT)

Black: before timewalk correctionRed: after timewalk correction

Cosmics Electrons


VDC Tracking Efficiency and Stability Study

• VDC Tracking efficiency defined as fraction of electron events:

= (PID & one-track events) / (PID events)

Bashar Aljawrneh (NC A&T)

Electron Sample

Eliminate Cosmic backgroundsWith cut

Beam Sample

Electron Sample

Cer ADC


Stability Study: VDC Tracking Efficiency (L-HRS)

LHRS

RHRS

Bashar Aljawrneh (NC A&T)


● 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.

S0 efficiency Barak Schmookler (MIT)

→ Typical efficiency > 99.8%

→ No significant position variation


S2 Efficiency

(Reduces multiple scattering bias)



Stability Study: Total T1 trigger Efficiency (LHRS)

• 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

Bashar Aljawrneh (NC A&T Univ)

LHRS

RHRS


Magnet Stability Study Longwu Ou (MIT)

→ Similar for other magnets

→ Can adjust field ratios in MonteCarlo to account for small variations if necessary.


● 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 p

0 > 3 GeV/c and results in

deteriorated resolution in reconstructed W peak

● Will use simulation to evaluate the effect on extracted cross section

7% drop in field strength at 4 GeV/c

Red: simulationBlue: data

Invariant mass

p0 = 2.67 GeV/c p0 = 3.69 GeV/c

Q1 saturation Longwu Ou (MIT)


SIMC Aperture Checks with ‘Old’ Q1

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.



SIMC Aperture Checks with ‘New’ Q1

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.



e-p elastic Data / Monte Carlo studies

With SIMC


e-p Elastic: Data vs SIMC, Q2 ~ 6 (GeV/c)2

Thir Gautam (HU)

Thir Gautam (Hampton U.)

Arbitrary Offset ~2.4 mrad

Arbitrary Offset ~ -5 MeV

Raster correctionImplemented soon


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

Longwu Ou (MIT)


Acceptance / cross section Studies for 12C TargetWith COSY Single-Arm MC

(“effective” white spectra scans)


12C Inelastic: Data vs MC (Fall 2016)

● 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/MC = 1.0269

Thir Gautam (HU)

Systematic shift consistent with elastics

Data deficit consistent with elastics


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

Thir Gautam (HU)

Charge symmetic bkgds not include in MC


12C 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


Data/MC = 1.0212

→ 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

Thir Gautam (HU)


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)


Acceptance studies ongoingTable 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.

June 22, 2017 Eric Christy - Hall A/C Summer Meeting 31Longwu Ou (MIT)

Preliminary Results (Data / MC method)


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 2018


Graduate students:

Thir Gautam (Hampton)

Longwu Ou (MIT)


Yang Wang (W&M) - defended Ph.D June 2017 (2015 low Q2 )

Bashar Aljawrneh (NCA&T)

PostDoc: Kalyan Alyada (MIT)

Credits


Backup Slides


Selection of elastic electrons

Compare data to MC using global fit to existing 12C data (E.C., T. Gautam, A. Bodek)

> 0.612C 27Al < 0.4

m. eric christy€¦ · june 22, 2017 eric christy - hall a/c summer meeting 2 performed...

Documents