Kaon_LT Experiment

                Mar 26-27/26 PionLT/KaonLT Analysis Meeting Notes

                -------------------------------------------------

                                (Notes by GH)

                    Today: KaonLT will be discussed first

Thursday: Present

-----------------

Regina - Garth Huber, Nathan Heinrich, Nermin Sadoun, Nacer Hamdi,

   Alicia Postuma, Muhammad Junaid

CUA - Sammer Jain, Chi Kin Tam, Tanja Horn

Virginia - Richard Trotta

Ohio - Julie Roche

Richard

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KaonLT high Q2 LT-sep

- investigating small |t| thetaCM behavior

  - the problem shown last week was that the #events for thetaCM~0 gets large

    in data but not MC

  - implemented Gabriel's suggestion, which was to replace thetaCM with

    sin(thetaCM) in the analysis, but it made no difference

  - followed the crucial clue, which was that the weird behavior is only in

    data, not MC.  Maybe it's caused by pion leakthrough background events?

- modified the background subtraction algorithm for variables other than MM

  - previously, applied to these variables a background scale factor determined

    from the integral of the MM background normalization

  - that method ignores the kinematic correlations between MM and other

    variables

  - new method: on an event-by-event basis, determine a background subtraction

    scale factor to apply to pion leakthrough subtraction events determined

    from where they are in the MM distribution, rather than an average

    normalization factor

  - then fill the other variables (e.g. Q2, W) with this MM-weighted background

    scale factor   

  - the subtraction then takes into account the correlations between MM and

    other kinematic variables for background events

  - fixes the spike at small thetaCM

  - data vs MC comparisons are also now better for variables other than MM,

    Q2-dist is better, SHMS/HMS-delta dists have noticeably better comparisons

    between data and MC

  - *NB* issue yet to be solved: lower end of W-distibution is weirdly cut-off,

    looks artificial

Chi Kin

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KaonLT high Q2 syst unc studies

- varied acceptance cuts

  - changes cut regions in low-epsilon distributions

  - of course, the high-epsilon data have a diamond cut, so changing the

    acceptance cut has no effect

  - SIMC yield, Data yield, average kinematics, will all change

  - still need to calculate new cross sections

  - Tanja: as long as the MC correctly describes the data, the cross sections

    should remain stable

- varying diamond cuts

  - looking to decrease polygon size by 2.5%-15%

  - Garth: this seems too big of a change, the issue primarily is small

    variations on the edges of the diamond where the #events starts dropping

    and there is a small ambiguity on where to place the boundary

    - large diamond changes will affect first and last t-bins much more than

      the others, given where in the diamond these events come from

  - *NB* comparing RT and CKT's diamonds is likely to be more instructive

- rad corr

  - last week: showed that Rad-On/Off gave a huge variation

    - Dave suggested to compare Rad-On/Off for pion case, and use that for the

      systematic

      - CKT not sure how to properly propage this to K+ t-phi bins, GH suggests

        an overall scale factor instead of t-phi dependent

    - Tanja: suggests to check how this was handled in Carmignotto, Mohrning,

      Niculescu theses

    - *NB* Garth: suspect last week's result indicates the MM cut is too

      narrow, see if you can widen the MM cut to reduce the sensitivity

  - Garth: for pi+ analysis, there is very little background underneath the

    neutron peak, so one can unambiguously investigate the rad corr systematic

    - for K+ analysis, there is some ambiguity in the Lambda tail, as it

      depends on how much pion background is subtracted.  Possibly it makes

      more sense to quote a combined background-subtraction/RadCorr systematic,

     rather than separately

- K decay correction in SIMC

  - changed the K+->mu+nu_mu branching ratio in SIMC, made no difference

Sameer

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PionLT Q2=1.6 W=3.08 yield analysis

- replayed data for both high and low epsilon

- initial PID checks

  - CoinTime shows pi+ and K/p bands vs MM

- *NB* Junaid apply cuts in this specific order:

  1) acceptance cut

  2) then CoinTime

  3) then look at other Detectors in various combinations

- *NB* Garth: this is briefly described in the notes following Kathleen's

  presentation of March 13, suggest to look them up

  - Tanja: also look at recent Hall C theses to learn what was done there

- after cuts, will check CoinTime and RF time offsets

Friday: Present

---------------

Regina - Garth Huber, Nathan Heinrich, Alicia Postuma, Muhammad Junaid,

   Nermin Sadoun, Nacer Hamdi

CUA - Chi Kin Tam, Tanja Horn

Virginia - Richard Trotta

JMU - Gabriel Niculescu

Glasgow - Kathleen Ramage, Rachel Montgomery

FIU - Pete Markowitz

Nacer

-----

KaonLT Q2=0.5 LT-sep

- implementing t-shift based on MM-shift, followed by 1 iteration

  - sigL: low -t peak is gone, t-dependence is much flatter now, the issue is

    that the first t-bin is negative by ~1.5sigma

    - no longer an exponential, the fit parameter in the exponent prefers zero

  - sigT: rises to compensate

  - interference terms: basically the same

- iterate 2 more times

  - Data/MC ratios are better than before, generally more flat vs phi

- Richard: they haven't shown their results yet, but after t-shift the

  cross-sections stayed similar to before the shift

  - Later note by GH: the reduced sensitivity could likely be due to the higher

   -t values of the high Q2 data and the correspondingly wider t-bin

- Nacer will change the lower limit of the 1st t-bin a bit, to avoid the

  unphysical region near -tmin

  - *NB* Richard: suggests to plot W,Q2 for each t-bin (summing

    Left,Right,Center SHMS) and compare to the ave-Q2,ave-W values the model is

    calculated at

    - this is how he found the thetaCM problem, the ave-Q2,ave-W values were

      outside the range of the data distribution, now they agree well

- shows plots of -t vs -tmin

  - generally good agreement between edge of distribution and -t=-tmin line

  - shows small #events -t<-tmin

    - Garth: have pion leakthrough been subtracted?  It seems likely these are

      due to mis-identified pions

    - Nacer: indeed no pion leakthrough is subtracted on these plots

- has CoinTime blocking info from Sameer, preparing to replay data to determine

  the correction factors

Alicia

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u-channel analysis

- met w/ Bill on Tuesday for 2hr on shape study

  - he suggested to not worry on exact values of u-bins right now, concentrate

    more on the shape study now and fine-tune the u-bins after that is done

  - seems good advice, concentrating now on getting the MC fits to data to work

    properly

Nathan

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PionLT LT-sep framework checks

- Junaid and Nathan now have exactly matching data yields, moving on to SIMC

  yield comparisons

  - SIMC yields agree to better than 1e-6 for one setting

  - now running other SHMS settings for checks

- after that is done, will compare cross sections

- identified an issue during Data yield comparisons

  - Junaid had defined ROC1 as ROC2 by mistake, due to a copy/paste error in

    python environment setup

  - once this was fixed, ROC2 needs to be defined as ROC2, things agreed

  - Junaid has pushed the fixed version to UTIL_PION

  - *NB* Kathleen, Nermin, Sameer should double check their python environments

    to make sure they did not inherit Junaid's bug

- setting up replay scripts for other settings in x=0.39 scaling scan

Junaid

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PionLT Q2=3.85 W=2.62 LT-sep

- applying t-shift based on MM-shift

  - MM-shifts were in different directions for lo, hi epsilon, t-shifts

    similarly will be in opposite directions

  - also some of the MM-shifts were fairly large, ~10 MeV

  - this is the "worst case" scenario in terms of sensitivity to t-shift

- shows plots of -t vs -tmin after t-shift applied

  - before t-shift, had events -t<-tmin

  - hi eps: after t-shift, events move away from -t=-tmin line, now events have

    -t>-tmin

  - lo eps: before t-shift, there was a small gap between data and -t=-tmin

    line, after t-shift the gap is gone, events come right to the line

  - this confirms the respective t-shifts are applied with correct sign

- LT-sep after t-shift

  - very large effect, sigT now has a steep rise in cross section at low -t,

    while sigL is fairly flat

    - more distressing: sigL is now negative by ~1.5sigma at low -t

  - plots of unsep cross sections vs phi also indicate this, the gap between

    high and low epsilon is much smaller after t-shift

  - Data/MC ratios do not look good, particularly at low -t, where they are 2

    and higher, this at least tells us that the data are not consistent with

    this new behavior

  - for a test, applies t-shifts with same sign for hi,lo epsilon, rather than

    opposite sign.  sigL is much better behaved

- *NB* Garth: are we sure the MM offsets are correct?  We should take a closer

   look at them given this info, maybe we can reduce some of the MM-shifts

- *NB* Nacer: suggests to change the low -t bin lower limit, to exclude events

   very close to -tmin

Kathleen

--------

LD+ yield for Q2=1.6 W=3.08 6.4GeV (2022) data

- last week: looked at detector cuts in more detail

- Random Subtraction: selecting 3 peaks on either side of prompt, with a gap of

  2 away from prompt peak (i.e. peaks 3-5 on either side)

  - Garth: some evidence that the 5th peak is a bit smaller than peaks 2,3,4 on

    both sides.  Possibly they are getting close to the edge of the coincidence

    timing window.  Suggest to use peaks 2-4 rather than 3-5, as their heights

    are more uniform

- Dummy Target Subtraction:

  - calculated target thickness factor f=4.009 from target group report

  - normalized by total beam charge as a quick test

  - *NB* Nacer: need to form Qeff from the detector efficiencies and livetimes

    - the relevant information should be in the report files

- MM plot after Random and Dummy subtractions

  - Nacer: to minimize sensitivity to the MM cut, put the cut in the

    plateau between the neutron peak and Delta-rise

  - *NB* Alicia: your next step should be to compare the MM peak to SIMC, to

    see how well they agree, that will also guide where to place the MM cut

Next steps:

- calculate Qeff from detector efficiencies, livetimes

- will clean up macros used to make plots

- will present a poster at IOP conference, will distribute a draft for comments

Nermin

------

PionLT 9.117GeV Q2=1.6 W=3.08 SHMS=6deg detector efficiencies

- SHMS Aerogel:

  - Last week: LD+ aerogel eff was 97%

    - added a HGC cut to the aerogel efficiency calculation to reduce K/p

      contamination, now the efficiency is 99%

  - new LD- detector efficiencies

    - using cuts on SHMS calorimeter, acceptance, CoinTime, obtained aerogel

      efficiency of 98%

    - after adding HGC, aerogel eff improved to 99%

- HMS Cherenkov:

  - coin efficiency is lower for LD- than LD+

  - this means HMS calorimeter is not removing all pi- from the electron sample

    used to calculate the efficiency

  - tightened the calorimeter cut, efficiency improved

- HMS Calorimeter:

  - applied acceptance, CoinTime, Cherenkov cuts, got eff=0.978 +/- 1e-4

  - tightened the Cherenkov cut, nothing improved

  - Garth: the issue when calculating the HMS calorimeter efficiency is that it

    is very difficult to remove all of the pi- contamination in the electron

    sample

  - Ali ended up using dedicated Heep runs with minimal pi- contamination in

    his HMS calorimeter efficiency study, and then apply this efficiency to the

    physics data

  - *NB* Junaid: he has done the HMS calorimeter efficiency study for HMS

    momenta from 1-4 GeV/c.  Please check the HMS momentum for your setting,

    and if it is within this range then you can use his efficiencies (and

    uncertainties) directly

    - Junaid will send his slides on this

Next steps:

- Lumi study for LD2 cryotarget

   Next Meetings

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- Thurs: Apr 2 @ 16:00 Eastern/14:00 Regina

  - PionLT will go first

- Fri: Apr 3 @ 11:00 Eastern/9:00 Regina

  - NO MEETING DUE TO EASTER (GOOD FRIDAY) HOLIDAY