[d2n-analysis-talk] d2n Collaboration Analysis Meeting notes from May 23 at JLab (Brad)
Brad Sawatzky
brads at jlab.org
Thu Jul 19 16:31:52 EDT 2012
Hi all,
I'm sorry for the (absurdly) long delay in posting these to the list. I
hope it's better late then never...
-- Brad
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* d2n collaboration analysis meeting on May 23 at JLab
**********************************************************
Temple: Matt, Dave, Zein-Eddine
CMU: Gregg, Vahe
JLab: Brad, JP, Zhiwen
- Mark Dalton (UVa) present for the full morning session Vince (MIT) around
for most of morning session, Kalyan and others in and out
- JP and Zhiwen in for morning target session
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Top Priorities based on our discussions throughout the meeting
----------------------------------------------------------------------------
- Understanding pair-symmetric backgrounds
- simulation will let us understand the bend-up vs. bend-down differences
(ie. is it all "geometry")
- get the simulated data ROOT files available (Vahe?)
- generate plots and show data vs. simulation to see if the
trends match
- bend-down e+ : bend-up e+ vs. x (or momentum, etc)
- bend-up e+ : bend-up e- vs. x (or momentum, etc)
- investigate trackless events
- only ~15% of our T2 triggers have a track --- why?
- Kalyan comments that Transversity analysis thinks that the bulk of the
trackless events are really pi0 decays
- details are in a long-note and/or Transversity ELOG entries by
Xin/Kalyan
- could be a handle on pi0 related backgrounds
- we sometimes conflate the pion rejection ratio with "contamination"
- we should be be able to look at the pion leakage into the electron spectrum
and get an electron:pion ratio from BigBite data (we've done this in the past)
- Matt should look back in his talks for prior pion-rejection studies
- get pions rates (ie. real e-:pion ratios) from the HRS and then apply our
rejection ratio
- also need to understand pi+ contamination in positron sample
- this was significant for Transversity setup
- target corrections
- Brad will pass his notes on to Matt (see Matt's "Target Talk" notes below)
- LHRS cross sections
- investigate how the acceptance corrections are being applied
- general systematic studies on cuts, etc
- Radiative Corrections
- generally under control
- uncertainties associated with the model input to the corrections probably
over-estimated
- False Asymmetries (BigBite)
- beam charge asyms (done as part of beam polarization analysis -- need to
confirm -- Diana will look back)
- need to verify that beam charge asym is being controlled run-by-run
- ie. feedback fails for some reason
- add to our systematic check plots
- any false asyms that might driven by transverse beam component?
- should be small, but we can check
- have a short run period that can be used to investigate this
- extract live time asymmetries for BigBite data
- Kalyan notes we can pull these data from both the helicity-gated scalers
and the ungated scalers (ie. sort in the analyzer using helicity state)
- Timelines
- Graduation dates for Matt, Dave?
- shooting for completion within the next year
- graduation May 2013
- confirm thesis topics/scope is clear
- Matt: focus on d2/g2
- Dave: 5-pass A1
* Present some nearly final results at the Fall APS/DNP
- Matt and Dave will generate a semi-detailed milestone list to get there
and present at our meeting on June 12 (Tues)
* move regular meeting day to Tuesdays at 2:30pm
- Publication topics / proposed papers
- push for A1n, d2n paper out around Jan. 2013
- NIM/equiv on BigBite Cherenkov
? status of BigBite electron stack paper (Xin is working on it)
- Brad set target for July 4
- A1n paper
- need to think about how to present the physics
- Phys Rev C?
- quark flavor contributions -- might be good hook for higher-impact paper?
- need to handle the DIS and resonance data in clear fashion
- can we make any statements regarding Duality with our data?
- incorporate g1 (3He and n) into this paper
- d2n paper (highest impact?, priority)
- first pub
- can just move directly from asyms to d2 (corrections are less complicated)
- ie. 3He to neutron correction on the moment is smaller and less prone
to systematics than A1(x), etc
- incorporate g2 (3He and n) into this paper
- ie. x^2(g2 - g2_ww)
- E06-014 archival paper
- pion double-spin asyms?
- talk to Andreas Metz
========================================================
NOTE: What follows are some miscellaneous notes that I took during the various
sessions.
CAVEATS:
- These were mixed up with some other weekly notes that I keep in a way that
would have been confusing to others. I did some significant culling of the
older notes to leave the newer stuff -- not sure if what is left is useful
to others or not.
- Take them for what they're worth. There may be confusing/wrong information
here...
========================================================
--------------------------------------------------------
- Wally's overview/summary
--------------------------------------------------------
- complicated regions are where gamma is large
- ie. Q2 small (low-x: below 0.1) and
high-W (high-x: above 0.8)
- WM question is "what neutron model should we use" ie. MAID + "leading twist"?
- focus on comparing A1n at DIS with Xiaochao
- focus on comparing A1n in Resonance with Patricia
- June, July timeframe
? what can be done to manage correction in the resonance region?
--------------------------------------------------------
- Matt's Report
--------------------------------------------------------
- Target talk
- JP comments that the temp differences on the pumping chamber varied with
the target polarization state because the laser light struck the RTDs
differently in the different configurations
- JP reports that the Transversity guys did a study that corrected the RTD
temps to get the "real" internal cell temps rather than a straight
average
- also looked at the associated density effects
- need to better understand the 3He density corrections associated with
temperatures (work was done by Lamiaa and Yawei)
- need to find errors associated with the chamber densities
- Yawei working on it now
- the nominal 1% uncertainties could be low (slide 15; Yawei working on it)
- ie. transfer tube uncertainty can be a driving error in the pumping
cell to target cell diffusion equation
- need to be careful that we distinguish between the "short-tube"
results from GeN which showed a small polarization difference between
the pumping and target cells, our transfer tubes were longer --
effect can be 10% change between top and bottom
- note that we have some new information from Yawei that is *not* reflected
in today's presentation
- EPR calculation
? some question as to which kappa_0 value to use
- old value vs. new value results in a systematic few percent shift
- there is uncertainty associated with the temperature correction to this value
- this is one of the driving uncertainties in the EPR calculation
- would be better to just measure kappa_0 at the temps we used, won't
happen for our results though...
- can cross check this with water data though, so we should be OK
- gradient effects?
- ie. BB field on vs. off (needs to confirm BigBite field status water
calibration runs)
- BigBite Talk
- some discussion on maybe publishing the pion asymmetry data?
- note that the "positron asym" correction is really the "pi0
pair-produced electron contamination" correction
- we should update our internal terminology for this correction to make
the above fact clearer
- there is some confusion over how to interpret the different e+/e-
ratios between the HRS, BigBite(standard field), BigBite(reverse field)
- do we understand what is driving the difference
- do we understand why the CLAS ratio matches the HRS ratio?
- different targets, very different geometries
- are e+/e- rates really insensitive to these details?
--------------------------------------------------------
- Dave's Report
--------------------------------------------------------
- LHRS update
- acceptance corrections (SAMC)
- logic between the acceptance weight calculation was reworked
! energy loss and multi-scattering calculations are now omitted
* not sure where they get input now..
- this is now built into the Radiative Correction code(?) -- energy
piece is in here, at least in part
- still don't know how the multiple scattering is treated
- don't want to "double count" correlated the straggling+energy loss
effects
- Brad needs to read the lectures of 1975 by Mo and Tsai
- statement was made that they are accounted for in the independent
radiative correction factor, not sure this makes sense
- new acceptance is very flat vs. momentum
- uncertainties on the weighting are much larger than the point-to-
point
- need to double-check systematic effects due to cuts on the acceptance
- ZE comments that dp/p has some discrepancy that we might be able to
improve (slide 23/51)
- should update cross section model to use same F1F209 model that we're
using in the radiative correction code
- also want to run the sims longer to remove any pseudo-data statistical
uncertainties (ie. simulated curves should be smooth)
o SAMC aperture study (older notes)
- SAMC shows that 17--20% of electrons that run down the magneto-optical
axis do _not_ transport to the focal plane. Why?
- seems to be all due to energy loss in the glass wall of the target cell
* big effect, kind of like radiative corrections -- how to handle in
final analysis?
- SAMC might be able to do this 'as-is' (ie. expand the momentum range
in the generator), but need to make sure the 'weight' function is
computed in a rational way (a lot of effects are convoluted together
now)
- identified a set of cuts that are fairly stable regarding transport
fractions
- Systematic uncertainty studies
- dominated by (ie. most sensitive to) cuts on target kinematic variables
at the ~2% level
- Radiative correction studies
- using F1F209 model (Bosted)
- some phenomenological scaling used so model comes into (better) agreement
with other data sets at lower Q2
- overall, the model is doing quite well
- preliminary systematics associated with RC are at the 2--4% level
- 2--6% in the limit, but this is probably an over-estimate(?)
- should remove any "uncertainties" associated with the number of F1F209
input spectra to the radiative corrections (ie. the N_sigma column on
slide 43(?))
--------------------------------------------------------
- Diana's Report
--------------------------------------------------------
- TODO for A1, A2
- Radiative Corrections
- work in progress to evaluate the polarized radiative corrections
(ie. PolRad; Matt)
- Background subtraction
- charged pion asyms (very small ppm level)
- pair production asyms
- negl. for high-x
- unclear for low-x; ie. x<=0.2 is very tricky
- final target polarization
- systematic cut study
- nuclear corrections
- questions about transverse beam-related asymmetry (from Dalton)
- there is a nominal 10--15% beam-related asymmetry(?)
- we DO have a run period from during the 4.7 GeV period where we had
20% long. polarization -- that could give us a measure/bound of the
transverse beam-related asymmetry
- For a1n
- Vince notes that the glass can rescatter back into the acceptance
- larger effect for forward angles, maybe not for us at 45deg
- not sure if transversity looked at it directly
* can cross check with empty reference cell runs, I don't think we've
done this yet
- electron beam polarization
- 1.6% total uncertainty on polarization for each run period
- weighted ave of all Compton and any Moller in each run period
- Target polarization (see Matt's talk for more info)
- measured via NMR and EPR
- NMR is being measured in pumping chamber, EPR is in target chamber
- N2 dilution factor
- some obvious outliers, not fully understood, but much more data available
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- Simulation report (Vahe)
---------------------------------------------------------------------
- detailed model of BigBite magnet coils, yoke, and pole faces
- field map has been updated to use map from MAFIA (Vladimir Nelyubin)
- detector materials are all in the sim
- Drift chambers are just gas volumes
- no gas windows or wires
- Calorimeter
- accurate materials, but no optical photon tracking
- Cherenkov
- accurate materials, optical Cherenkov photons produced in gas are
logged at some level
- Shower, PSh simulated results look quite good in electron regime;
differences appear where we expect pion to be significant
- simulation does not have a realistic pion production model(?)
- has a DIS cross section from Bosted fit w/ radiative corrections included
- using pion (0,+,-) xsecs from Wiser parametrization
- events into BB are weighted according to differential cross sections
- need to verify that the Wiser codes are believable in our kinematics
- Dalton notes that Wiser only measured pi+, pi- yields and then inferred
the pi0 yields from those -- could be significant uncertainties
- parent particle is recorded
- allows us to study positron:electron ratio versus electron energy
--
Brad Sawatzky, PhD <brads at jlab.org> -<>- Jefferson Lab / Hall C / C111
Ph: 757-269-5947 -<>- Fax: 757-269-5235 -<>- Pager: brads-page at jlab.org
The most exciting phrase to hear in science, the one that heralds new
discoveries, is not "Eureka!" but "That's funny..." -- Isaac Asimov
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