Difference between revisions of "Tuesday, Jun 25, 2013 11:00am EDT"

Latest revision as of 12:42, 25 June 2013

Agenda

• http://solid.physics.umass.edu/~seamus/riordan_molltrack_20130625.pdf

Minutes

• Attendance: David A., Wouter, Seamus, Mark Pitt, Rupesh, KK
• David A:
  • Defining what the tracking system needs to do
  • Some simulation progress so far..

• KK:
  • What is needed for MIE?
  • Nilanga agreed to write the MIE tracking section
  • No breakdown in MIE proposal for tracking systematics. We just claim that we will get 0.5%.
  • Old MIE proposal has some argument for 0.5%, but need more work.
  • Want to get something more concrete and construct a systematic error table.

• KK:
  • Monte Carlo task: move collimator around, and observe how APV varies -> Use this as geometry argument.

• David A:
  • In the simulation, need a correct central theta, beam energy, and distribution.

• KK:
  • We need to come up with a nomenclature so that we can put this in MIE, and starting using this moving forward. Perhaps, dig up E158, and see what was used here.

• David A:
  • Tracking system is not trying to measure absolute central angle. Tracking system is used to understand acceptance around this: radiation losses, acceptances around this, acceptances in the detector etc.
  • Reply on survey to give us a central angle about the collimator, and use the simulation to understand the acceptances/distributions.
  • With the thick target (can never get the kinematics at the scattering vertex), can only get some effective kinematics.

• Seamus:
  • Need an effective acceptance function (somewhat similar to what we did in PREX)
  • First order uncertainty: move collimator around, vary magnetic field, and observe how it affects APV.
  • Distribution matching: various distributions
  • r,r',phi,phi' describes a track - GEM measurements
  • Move GEMs closer to detector - resolution improves
  • Direction variables more important for reconstruction
  • Mollers: theta_CM vs r: basically all the theta_CM are focused at one point in r <- spectrometers designed to focus Mollers to a point in r.
  • Mollers: theta_CM vs r': theta_CM more spread in r',
  • eps: theta_ver vs r and theta_ver vs r': different than Mollers, and more features <- perhaps quadratic? theta_ver vs r' has strong correlation, and can be very useful for tracking.

• KK: need to isolate these events
  • point target of size Z where elastic will dominate
  • very high radiation length tiny calorimeter that can slide up and down, in order to pick up tracks.

• David A:
  • radial separation between eps and Mollers will allow us to pick out ep or Mollers cleanly by putting a cut on r.
  • perhaps something similar on phi, but less interesting.

• tracking:
  • st. line fits to GEMs, and get the correlations at the target variables
  • do not need anything as complicated as in QWEAK.

• Seamus:
  • need some information upstream of the magnet: either from survey, GEMs or something..
  • because we need some absolute calibration

• Seamus:
  • Inelastics occupy a large phase-space, but not sure that we can gain anything useful for tracking here. Most of the tracking info is probably going to come from ep.

• KK:
  • why it is that we can get away without any tracking information upstream of magnets?
  • Eprime: we don't need to measure Eprime event by event
  • we can get away without measuring Eprime, but need to justify why we can do this

• David A:
• can't measure Eprime because of radiative tail.

• KK:
  • think about thin target, sieve hole, movable collimator: whatever are needed to get the correlations cleanly

• Seamus:
  • Carbon foils, sieve holes spaced cleanly: to map out the phase space
  • What do the magnetic fields do to the acceptances (especially at the edges)?

• David A:
  • acceptance is defined by collimator, spectrometers, detector locations.
  • If acceptance has mag field & main detector location to it, which it does with the radiative tail, then we get some distributions with simulation & slightly different distributions in data, how do we quantify our error due to mismatch in distributions?
  • we adjust the knobs like theta, Ep etc in simulation and try to quantify this error.

• KK:
  • carbon foil, sieve: gives us kinematic factor that multiplies the asymmetry: perhaps can use this.
• Seamus:
  • there are always going to be some mismatch between simulation and data, and ..

• Mark Pitt:
  • basically measuring an acceptance function:
  • QWEAK: theta, Eprime distribution and match data. But for Moller we can't do this.

• David A:
  • radiative losses make it very difficult to know theta, Ep at the target.
  • thin targets, wire targets with rastered/unrastered beam

• Acceptance function:
  • fit theta vs r horizontal slices, and compare this distribution to data.
• Dave:
  • link dr, r to theta_ver with a functional fit, but how are we going to get the uncertainty?

• Seamus:
  • big question: GEM resolution

• David A:
  • GEMs are probably overkill
  • no point in getting more resolution than the resolution of the spectrometers
  • real reason that we need resolution is to identify real/good tracks

• Seamus:
  • 5mrad resolution will probably suffice. much better than what GEMs can do.

• KK: naive model:
  • combination of foil target, sieve hole to validate field and acceptance function
  • use H2 gas run to demonstrate that we can calculate cross-section
  • run with LH2 production target and look at radiative effects.

• KK:
  • for MIE, if we stick with 3 GEMs upstream of the detectors, as long as we do not need a larger lever arm, we can do away with the Roman pot.

• David A:
  • prefer 4 GEM planes better: redundancy, efficiency headroom.

• KK:
  • can always reduce the GEM surface area, and rotate more.

• rotation system:
  • most of our sensitivity are going to be in radial direction
  • if we do not know phi GEM position much, then not a big deal
  • radius on a rotator is much easier
  • radial survey much easier than phi - and more precise?

• KK:
  • not so sure about this.
  • phi defocusing completely dominates in some regions.

• KK:
  • tie the GEMs together for rotation? over 5 m?

• David A:
  • 4 GEM planes: self calibration easy.
  • if the main detectors are surveyed very well, then we can use the main detectors to

• KK:
  • need some crude trigger scintillator, that can come off or turned off to trigger for charged particles.

• Mark Pitt/David A:
  • need to move scintillator out of the way, to prevent radiation damage.

• David A:
  • use thin detectors as trigger?
• KK:
  • useful to have thin detectors by itself.

• David A:
  • have trigger scintillator housed on the GEM housing, so it rotates with the GEMs?

• KK:
  • 3 or 4 GEM planes.

• David A:
  • all GEMs locked together locked tougher much easier to deal with.

• KK:
  • 2 GEMs couple together, 1 m apart?
  • 4 GEMs

• Mark Pitt:
  • pairs of VDCs, HDCs in QWEAK: relatively stable during rotation
  • GEMs in vacuum: worried about exit window thickness?

• KK:
  • can make the exit window thin enough

• David A:
  • sieve collimator?

• KK:
  • roll in/out in front of the acceptance collimator
  • prefer to do it for all 7 collimator

• David A:
  • needs to be surveyed as well, as well as the primary collimator.

• KK:
  • during E158, did a similar thing, and repeatedly used this sieve collimator

• Dave:
  • need to completely block out primary collimator?
  • very useful in QWEAK for background studies.

• KK:
  • need to think this through.

• Seamus:
  • What is the dependence on the magnetic field?
  • position uncertainties,

• David A:
  • how does the radial distribution of eps change when we move the coil?
  • what does r' do when the coil is moved?

• Seamus:
  • need slopes for this

• David A:
  • slopes for the absolute magnetic field
  • slopes for beam position on the target - first order cancellation around the sextants, but won't have perfect symmetry.

• Seamus:
  • need to consider raster as well, the plots in the document discussed in this meeting was generated with the raster turned on.

• KK:
  • can do this only with optics target?

• David A/Seamus:
  • need eps because the phase space is different for different tragets/processes.

• Seamus:
  • elastic C might even be better for this?? need to think this through..

• KK:
  • Work on Near term, longer term plan.
  • Near term: what goes into MIE.

• David A:
  • Do we have Al or carbon elastic generator?
  • Does a nuclear target give us any advantage??
  • Can we trust anything without any radiative effects included?

• David A:
  • need to see the affects in asymmetry, to r' distribution as we move collimator.

_________________________________________ _________________________________________

• David A:
  • would probably want main detectors in event mode, because we would want to look at pulse height distributions.

• Mark Pitt:
  • QWEAK used two different PMT bases, because of 10^6 difference in rates between current and event mode.

• KK:
  • PREX used the same base, modified PMT voltages between current and event mode running.
  • PREX production voltage 600 V, tracking voltage 2000V; lost only 1 of 7-8 PMTs: could do something similar.