Kaon_LT Experiment

                Dec 18-19/25 PionLT/KaonLT Analysis Meeting Notes

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                                (Notes by GH)

                    Today: KaonLT will be discussed first

Thursday: Present

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Regina - Garth Huber, Alicia Postuma, Nathan Heinrich, Vijay Kumar,

   Nermin Sadoun, Muhammad Junaid

CUA - Sameer Jain, Chi Kin Tam, Tanja Horn

Virginia - Richard Trotta

Ohio - Julie Roche

FIU - Pete Markowitz

JLab - Dave Gaskell

Richard

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KaonLT Q2=3.0 W=2.32 LT-sep

- using same paramterization and parameters as Q2=4.4 so far, no iterations yet

- looking at outliers in Exp/MC Ratios bin-by-bin, either high or low

- low epsilon, -t=0.46, phi=30deg

  - some possible undersubtraction of background underneath Lambda region

- low epsilon, -t=0.546, phi=150deg

  - oversubtraction of background, also some issues with propagation of

    uncertainties when no backgrounds remain after subtraction

- other bins shown: similar issues

- new Exp/MC ratios (no parameter changes) after fixes

  - still a few outliers remain, but others now more in line, some with

    substantially larger (but correct) error bars

  - higher -t bins show a hump in the Exp/MC ratio near phi=0, which would be

    an LT issue, lower -t bins are flatter

Chi Kin

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KaonLT Q2=3.0 W=3.14 LT-sep

- looking at background subtractions as well

  - background subtraction was not properly applied for some low epsilon bins

  - changed to:

    SIMC(Lambda)+exp(Cheybshev)*(x-xmin)*(xmax-x)

  - this results in an oversubtraction

- one issue is due to SIMC underprediction of Lambda peak width

  - Dave: this could be caused by SHMS saturation effect

    - setting has: P_HMS=4.2 GeV/c, P_SHMS=6.8 GeV/c

    - *NB* suggests to plot MM vs delta_SHMS

    - *NB* also suggests to double-check that low momentum HMS matrix elements

      are being used, rather than high momentum ones

    - DG and Tennessee students recently stumbled upon an unforeseen SHMS

      optics effect

      - W resolution was surprisingly bad

      - discovered a step function in W-reconstruction, different values for

        yptar<0 and yptar>0 like a step function

	- possibly a HB effect not properly taken into account in the optics

          reconstruction?

      - *NB* suggests to plot MM vs yptar_SHMS

  - investigated changes to the resmult factor that Ali had tuned for his data

    - Lambda peak width consistently wider at high epsilon than low epsilon

    - *NB* Dave: before trying to tune the resmult factor to your data, it's

      better to look first at correlations in the data and try to understand

      the optics first

      - whether things change with setting, depend on the origin of the effect

        e.g. in the 6 GeV era, there was an observed rate-dependence to the

        tracking resolution that traced as due to bad hits in the DC at high

        rate

- the SIMC Lambda resolution mismatch causes some background oversubtraction

  (i.e. the SIMC Lambda is fit and subtracted from the data to yield a flatter

  distribution that is then fit for the background subtraction, if this peak

  subtraction has problems, the background that is fit is too large)

  - temporary solution: add a Gaussian smearing function to SIMC when doing the

    background fit

  - hasn't checked Exp/MC ratios yet

- the uncertainty in the background subtraction is calculated as:

  - fit the polynomial bkd and normalized SIMC to data

    - use MINUIT params: vol, cov sampled from multivariable normal dist

    - discard regions where the uncertainty explodes

  - Richard: we eventually will want a discussion on the best way to do the

    background subtraction, since RT and CKT have different methods

    - Garth: if they're both reasonably valid, we should take the difference

      between them as a systematic

- a full replay of KaonLT data will be done over the break, including new HMS

  0th order matrix offsets that Nacer identified, and CoinBlocking correction

Sameer

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KaonLT CoinBlocking correction for 10.6 GeV data

- shows plot of correction vs CoinRate

  - 3 plateaus observed, different correction values for <1kHz, 1.0-2.5kHz, >2.5kHz

  - obtained corrections of ~0.94 for >2.5kHz CoinRate, SHMS-Left setting

- Dave: are these rates corrected for the beam off periods?

  - SJ checks the code, and indeed the rate is not corrected for this

  - *NB* need to apply a beam threshold when incrementing the clock, to get a

    more accurate rate

    - lumi studies typically apply a higher threshold than physics analysis, in

      order to get a higher resolution rate number

- overall, the correction values themselves look reasonable, but we need a more

  accurate rate dependence in order to compare to Nathan's results at similar

  rate

- shows some CoinTimeRaw plots and applied cuts, apparently there are some

  differences setting-by-setting

  - Nathan: provided the electronic setup is unchanged, find a set of cuts that

    work with your widest set of data and use that for all runs in that setting

Friday

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Regina - Garth Huber, Nathan Heinrich, Alicia Postuma, Vijay Kumar

York - Stephen Kay

CUA - Sameer Jain, Tanja Horn, Chi Kin Tam

Virginia - Richard Trotta

JMU - Gabriel Niculesu, Ioana Niculescu

Alicia

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KaonLT u-channel Q2=3.0 W=2.32 Pythia model

- suppressing rho and rho-diffractive processes did not fix the MM double bump

  issue, can make the bump bigger, but not go away

  - turning off charged rho production makes the bump worse, as it suppresses

    featureless background from pi+pi0 production

  - is there someone more familiar with Pythia that she should contact?

    - *NB* Gabriel suggests Harut Avakian from Hall B, either he will know, or

      can put in contact with a grad student who is familiar

- other options if this doesn't work

  - could try running SIMC rho MC and subtract it from Pythia when doing

    background fit

  - could try fitting a higher W-setting Pythia to these data

    - the model cross section will have the wrong angular distribution, but

      since the background is fit separately for each t-phi bin, the

      normalization error would not matter

Vijay

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Low Q2 PionLT LT-sep

- started working on systematic uncertainty studies

  - PID cut is determined with CoinTime and RFTime, not HGC Aerogel

  - CoinTime cut systematics: will vary cut width by +/-0.1ns (10% of cut

    width) and evaluate the difference in sig_uns at low, med, high epsilon

- draft PRL manuscript

  - made progress on experiment section

Nathan

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PionLT Q2=3.85 W=2.62 LT-sep

- comparing his results with Junaid's

  - separate data replay but what should be the same scripts

  - found that the Exp/MC ratio is a bit different

    Nathan: 0.973 +/- 0.060

    Junaid: 0.952 +/- 0.059

    - apparently the SIMC iterations are not the same, which is easily fixed

    - also finds small differences in the MM peak distribution

  - Gabriel: this is a dual-purpose exercise

    1) cross-check of steps in analysis

    2) if alternate analses are equivalent, we have to treat it as a systematic

  - Nathan: would like to know what the source of the difference is first

    before deciding how to handle it

    - strongly suspects cut difference in LT-sep Python package

    - expects to have a conclusion at the next meeting in January

- TrackingEff systematic studies

  - Dave had suggested to plot Normalized Yield vs S1X rate instead of 3/4 rate

    - indeed finds the spread of points to be smaller against S1X, so Dave is

      right, S1X is the better rate to use

    - will make the Mean of Deviations from the trend as a scale systematic

    - and the Standard Deviation as a random systematic

Gabriel

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KaonLT Sigma0 Lambda* analysis

- follow-up about using HallC:p as the beam energy

  - found the deviation in HallC:p at the time of the Arc Energy Measurement

    - about 1.5 MeV at 10.6 GeV, more for lower beam energies

    - has incorporated this

- has a question about the beam energy spread

  - SIMC has a flat beam energy spread about the peak energy, unchanged from 6

    GeV era

    - CEBAF Accelerator paper says the Hall C energy spread is 5E-4 RMS at 10.6

      GeV

    - *NB* should switch to a Gaussian beam energy distribution, with width

      corresponding to the RMS values from the Accelerator paper

      - can have a flag in the input file to use either the current or new beam

        energy spead code

      - Gabriel will follow-up

Next Meetings

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- we will continue with the current meeting schedule for now, can adjust once

  people better know their 2026 timetables

- Thurs: Jan 8 @ 16:00 Eastern/15:00 Regina

  - PionLT will go first

- Fri: Jan  9 @ 11:00 Eastern/10:00 Regina

  - we will continue where we left off