1-pass calibration for A1n

Outline

For polarized 3He running in Fall 2019 and Spring 2020, the nominal raster for production is 5mm diameter circular. The nominal triggers used are 3/4 for both HMS and SHMS. Both HMS and SHMS should be taking data (for example if run plan specify one run, it means one run on HMS and one run on SHMS simultaneously). No coincidence trigger will be used/setup.

We will need to do optics calibration, reference cell (cross section and pressure curves), 3He elastic longitudinal asymmetry, and 3He Delta transverse asymmetry measurements.

Beam and raster checkout

 Please refer to 2-pass commissioning procedure, follow:
 - Establish beam in the hall
 - Initial Raster checks
 - Harp scans
 - Target/Beam centering, Raster calibration

Optics Calibration

Optics (angle and ytarg) Calibration

  Goals 
 - To calibration spectrometer optics for 40cm long target at 30 deg. Calibrate angle reconstruction.

 Setup
 - Beam Current:   5-20 uA CW, raster varies
 - HMS setting: 30 degrees, -1.2 GeV/c (electron)
 - SHMS setting: 30 degrees, -1.68 GeV/c (electron)
 - Target:       Multi(7)-foil Carbon Foils

 Procedure
 - Move target to multi-foil position;
 - Move Sieve Slit IN for both HMS and SHMS;
 - Take a short run (2min) at 20uA, verify sieves are both IN;
 - Ask MCC to increase current to 20uA (Max for raster off on this target). Take two runs, 45 minutes each. 
 - Ask MCC to turn raster ON to 5mm diameter, take one run at 20 uA for 45 minutes.
 - Move Sieve Slit OUT for both HMS and SHMS;
 - Take one run at 20 uA for 15 minutes. 
 - Ask MCC to turn raster OFF, take one run at 20 uA for 15 minutes.

 Things to watch for (Expert Analysis)
 - There should be optics expert(s) checking data quality as we go.

Optics (Momentum) Calibration

  Goals 
 - To calibration momentum reconstruction of spectrometers.

 Setup
 - Beam Current:   5--20 uA CW, raster always OFF
 - HMS setting: 11.7 deg, momentum varies (electron)
 - SHMS setting: 8.5 deg, momentum varies (electron)
 - Target:      Double Carbon Foils

 Procedure
 - Move target to Double carbon foil position.

 - To be filled

 Things to watch for (Expert Analysis)
 - There should be optics expert(s) checking data quality as we go.

Polarized 3He and Reference Cell Runs, Delta resonance setting

Polarized 3He Delta Transverse Asymmetry

 Goals 
 - To measure physics transverse asymmetry of Delta resonance to (5-10)% relative on each spectrometer.

 Setup
 - Beam Current:  DAQ rate-limited and up to 30uA, raster always ON (5mm diameter)
 - Beam IHWP: should be switched half-way
 - HMS setting: 12.5 deg, -1.799 GeV/c (electron)
 - SHMS setting: 12.5 deg, -1.799 GeV/c (electron) 
 - Target:      Polarized 3He Cell, Empty Reference Cell
 - Target spin direction: 90 or 270-deg
 - Target coil setting: TBD
 - Detectors: All scintillator bars ON. 
 - Parity check: Inform Hall A prior to taking data to make sure they set the charge asymmetry feedback cutoff at 0.5uA.

 Procedure
 - Set spectrometers at the required settings, target at Reference Cell position, pump the reference cell to empty;
 - Check and make sure all scintillators are ON;
 - Take a short run at 2uA to determine rate and prescale factor. Adjust beam current to reach close to 4.5kHz with PS=1 (but do not exceed 30uA), which means current is probably limited by SHMS rate.
 - Take a five-minute run or until reaching 10,000 events for both HMS and SHMS

 - Move target to Polarized 3He Cell position, spin polarization at either 90 or 270 degrees.
 - Perform one polarimetry measurement before taking data.
 - Take one 1-minute run at 2uA, check rates and adjust beam current and prescale factors. Adjust beam current (but do not exceed 30uA) to reach close to 4.5kHz with PS=1, which means current is probably limited by SHMS rate.
 - Take five 30-minute runs at the optimal current set above, perform one polarimetry measurement after each run. Verify data quality (see below) and verify target is still polarized.
 - Switch beam IHWP position. (may need to inform other halls in advance). For example from IN to OUT or from OUT to IN.
 - Take five 30-minute runs at the optimal current set above, perform one polarimetry measurement after each run. Verify data quality (see below) and verify target is still polarized.

 Things to watch online
 - Apply y or z cuts to isolate events scattered from 3He gas (We do not want events from the glass windows!)
 - Apply 1.1<W<1.35 GeV cut to isolate the Delta resonance.
 - Run online script to ensure we see physics asymmetry. HMS and SHMS should see opposite asymmetries. 

 - Expected total rate: To be filled
 - Expected asymmetries (after W and Ytg cuts): To be filled HMS Aphys=4.8% Ameas=2.1% and SHMS Aphys=2.5% Ameas=0.98% if Pt=50%, Pb=85%, N2 dilution 0.92.
 - Expected uncertainties better than dA/A=10% on each of HMS and SHMS.

Polarized 3He and Reference Cell Runs, 3He elastic setting

Spectrometer Setting for All Runs at the 3He Elastic Setting

 - HMS setting: 12.5 deg, -2.1435 GeV/c (electron) 
 - SHMS setting: 12.5 deg, -2.1435 GeV/c (electron) 

Reference Cell Hydrogen (H2) Cross Section

 Goals 
 - To measure hydrogen elastic cross section as a cross check of data quality

 Setup
 - Beam Current: up to 30uA and DAQ rate-limited, raster always ON (5mm diameter)
 - Target:      Reference Cell, filled with H2 and Empty.
 - Detectors: All SC bars on

 Procedure
 - Set spectrometers at the required settings, target at the Reference Cell position;
 - Pump out Reference Cell (to vacuum);
 - Take a short run at 5uA to check rate and prescale factor. We would like to see close to 4.5kHz with PS=1. Decrease the current if necessary but do not drop below 2uA. If rates are too high at 2uA, set a larger PS factor. If rates are too off, stop the run and adjust beam current/PS factor and restart the run. If rates are okay we can continue to next step.
 - Take two five-minute runs, make sure there are no less than 10,000 events for each of HMS and SHMS.

 - Fill Reference Cell to 2 atm of hydrogen gas;
 - Take a short run at 5 uA to determine rate and prescale factor.  We would like to see close to 4.5kHz with PS=1. Decrease the current if necessary but do not drop below 2uA. If rates are too high at 2uA, set a larger PS factor. If rates are too off, stop the run and adjust beam current/PS factor and restart the run. If rates are okay we can continue to next step.
 - Take two five-minute runs, apply ytar or ztar and W cut and make sure H2 elastic events from the H2 gas are no less than 10,000 for each of HMS and SHMS

 Things to watch online
 - Ensure all SC bars are ON
 - For 2atm H2 filled cell, apply ytar or ztar cuts to isolate events scattered from H2 gas (We do not want events from the glass windows!), and apply W cuts to select only H2 elastic. Note the elastic peak is not at dp=0 because the spectrometers are set at 3He elastic. 
 - Run online script to ensure we collect no less than 10,000 H2 elastic (with ytar or ztar and W cuts) for each of HMS and SHMS

Setup Scintillator bars for 3He Elastic Scattering

  Goals 
 - To determine which two SC bars should be turned ON to focus on 3He elastic (suppress quasielastic)
 - Must be done Prior to Polarized 3He Longitudinal Asymmetry and all N2 and 3He reference cell runs at the elastic setting
 
 Setup
 - Beam Current: DAQ rate-limited and up to 30uA, raster always ON (5mm diameter)
 - Target:      Polarized 3He Cell (or Reference Cell filled with 1atm 3He gas if Polarized cell is not available)
 - Detectors:   All SC on to start with 

 Procedure
 - Set spectrometers at the required settings, target at the Polarized 3He Cell position;
 - Take a short run at 1 uA, check focal plane event distribution and determine which two scintillator bars should be kept on to accept the whole 3He elastic peak and to suppress quasielastic and inelastic events. (expert driven).

3He Reference Cell Runs

  Goals 
 - To determine window background for elastic setting
 - To determine yield vs. pressure (pressure curve) for N2, need 5 points at 0.5, 1.0, 2, 4 and 8 atm, 10,000 N2 elastic events for each pressure setting and each spectrometer.
 - To determine yield vs. pressure (pressure curve) for 3He, need 5 points at 1, 2, 4, 6 and 8 atm, 10,000 3He elastic events for each pressure setting and each spectrometer.
 - Reference cell must be filled with 3He last, and do NOT pump the 3He gas out!
 - time: 2 hrs 20min total

 Setup
 - Beam Current: DAQ rate-limited and up to 30uA, raster always ON (5mm diameter)
 - Target:      Reference Cell, Empty, filled with N2, filled with 3He (last)
 - Detectors: We will need to keep only 2 SC bars ON to limit quasi-elastic scattering events. 

 Procedure
 - Set spectrometers at the required settings, target at the Reference Cell position;
 - Make sure the correct 2 SC bars are ON;
 - Pump the reference cell to empty (vacuum);
 
 - Take two 5-minute runs at 5 uA. Ideally this should yield 4.5kHz with PS=1. If rates are too high, lower the current but do not drop below 2uA. If rates are too low, increase current but do not exceed 30uA.

 - Fill Reference Cell with N2 gas to 8.0 atm, take two 5-minute runs at 2 uA. If rates are too high, prescale it down.
 - Pump the cell to 4.0 atm, take two 5-minute runs at 2 uA. If rates are too high, prescale it down.
 - Pump the cell to 2.0 atm, take two 5-minute runs at 2 uA. If rates are too high, prescale it down.
 - Pump the cell (slowly) to 1.0 atm, take two 8-minute runs at 5 uA. If rates are too high, lower the current but do not drop below 2uA. 
 - Pump the cell (slowly) to 0.5 atm, take two 15-minute runs at 5 uA. If rates are too high, lower the current but do not drop below 2uA. 

 - Pump the cell to vacuum
 - Fill the cell to 1 atm with 3He gas, take two 5-minute runs at 5 uA. If rates are too high, lower the current but do not drop below 2uA. 
 - Fill the cell to 2 atm with 3He gas, take two 5-minute runs at 5 uA. If rates are too high, lower the current but do not drop below 2uA. 
 - Fill the cell to 4 atm with 3He gas, take two 5-minute runs at 5 uA. If rates are too high, lower the current but do not drop below 2uA.
 - Fill the cell to 6 atm with 3He gas, take two 5-minute runs at 4 uA. If rates are too high, lower the current but do not drop below 2uA.
 - Fill the cell to 8 atm with 3He gas, take two 5-minute runs at 3 uA. If rates are too high, lower the current but do not drop below 2uA.

 - Important: After these runs are completed, do NOT pump out the 3He gas!

 Things to watch for
 - These reference cell runs must be taken with exactly the same spectrometer and scintillator settings as polarized 3He elastic asymmetry runs (see next)
 - For each gas pressure setting (except for empty cells), need 10,000 events from gas alone (apply ytar or ztar cuts) for each of HMS and SHMS.

Polarized 3He Elastic Longitudinal Asymmetry

  Goals 
 - To measure physics longitudinal asymmetry of 3He elastic scattering to (2-3)% relative, cross check PbPt from Moller and Target Polarimetry

 Setup
 - Beam Current: DAQ rate-limited and up to 30uA, raster always ON (5mm diameter)
 - HMS setting: 12.5 deg, -2.1435 GeV/c (electron) 
 - SHMS setting: 12.5 deg, -2.1435 GeV/c (electron) 
 - Target:      Polarized 3He Cell, Reference Cell
 - Target spin direction: 0-deg, 180-deg
 - Target coil settings: TBD
 - Detectors: We will need to keep only 2 SC bars ON to limit quasi-elastic scattering events. 
 - Parity check: Inform Hall A prior to taking data to make sure they set the charge asymmetry feedback cutoff at 0.5uA.

 Procedure
 - Set spectrometers at the required settings, target at the Reference Cell position;
 - Pump the reference cell to empty (vacuum in the cell);
 - Take one 1-minute run at 1 uA, check focal plane event distribution and determine which two scintillator bars should be kept on. (expert driven).
 - Once scintillators are set, take another short run at 1uA to determine rate and prescale factor. Adjust beam current to reach close to 4.5kHz with PS=1 (but do not exceed 30uA), which means current is probably limited by SHMS rate.
 - Take a five-minute run or until reaching 10,000 events for both HMS and SHMS

 - Move target to Polarized 3He Cell position, spin polarization at either 0 or 180 degrees.
 - Perform one polarimetry measurement before taking data.
 - Make sure the same two SC bars are on as the Reference Cell, 
 - Take one 1-minute run at 1 uA, check focal plane event distribution and determine which two scintillator bars should be kept on. (expert driven).
 - Once scintillators are set, take one 1-minute run at 2uA, check rates and adjust prescale factor. Ideally we want 4.5kHz on each of HMS/SHMS with PS=1.
 - Take three 30-minute (TBD) runs at the optimal current set above, perform one polarimetry measurement after each run. Verify data quality (see below) and verify target is still polarized.
 - Rotate target spin direction from 0 to 180 deg (or from 180 to 0 deg)
 - Take three 30-minute runs at the optimal current set above, perform one polarimetry measurement after each run. Verify data quality (see below) and verify target is still polarized.
 - Call MCC and ask beam IHWP to be inserted (or taken out). Need to inform other halls prior to the switch.
 - Take xxx runs ... (repeat above)

 Things to watch online
 - Ensure the correct SC bars are on (We need elastic events! One SC bar is in principle enough but we keep TWO on)
 - Apply y or z cuts to isolate events scattered from 3He gas (We do not want events from the glass windows!)
 - Apply W cuts to isolate elastic events from others.
 - Run online script to ensure we see physics asymmetry. HMS and SHMS should see the same asymmetry. Asymmetry should flip sign with beam IHWP switch.

 - Expected total rate: (To be updated) HMS at 1uA total 1.8KHz 3He gas elastic 240Hz; SHMS at 1uA total 27.7kHz Prescaled by 15 to 3He gas elastic 740Hz
 - Expected asymmetries (after W and Ytg cuts): (To be updated) HMS Aphys=4.8% Ameas=2.1% and SHMS Aphys=2.5% Ameas=0.98% if Pt=50%, Pb=85%, N2 dilution 0.92.
 - Expected uncertainties dA/A=2% (goal) or 3% (minimum) on each of HMS and SHMS.