Tuesday, Jun 25, 2013 11:00am EDT
Agenda
Minutes
- Attendance: David A., Wouter, Seamus, Mark Pitt, Rupesh, KK
- 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.
- Mark Pitt:
- KK: Monte Carlo task: move collimator around, and observe how APV varies -> Use this as geometry argument.
- Dave 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. Dave A: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: Walking through his slides: - 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 1. point target of size Z where elastic will dominate 2. very high radiation length tiny calorimeter that can slide up and down, in order to pick up tracks. Dave 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 Dave 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)?
Dave 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? Dave: 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.
Dave 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
Dave: 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.
Dave: - 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?
Dave: - 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/Dave: need to move scintillator out of the way, to prevent radiation damage.
Dave: use thin detectors as trigger? KK: useful to have thin detectors by itself.
Dave - have trigger scintillator housed on the GEM housing, so it rotates with the GEMs?
KK: - 3 or 4 GEM planes.
Dave: - 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
Dave: sieve collimator?
KK: - roll in/out in front of the acceptance collimator - prefer to do it for all 7 collimator
Dave: - 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,
Dave: - 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
Dave: - 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
KK: - can do this only with optics target?
Dave/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..
