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July 10/25 PionLT/KaonLT Analysis Meeting Notes
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-----------------------------------------------
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(Notes by GH)
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Today: KaonLT will be discussed first
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Please remember to post your slides at:
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https://redmine.jlab.org/projects/kltexp/wiki/Kaon_LT_Meetings
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Present
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-------
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Regina - Garth Huber, Nathan Heinrich, Alicia Postuma, Muhammad Junaid,
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Ivan Zhenchuk, Nacer Hamdi
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Virginia - Richard Trotta
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Ohio - Julie Roche
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Richard
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-------
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Q2=4.4 W=2.74 LT-separations
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- now using the same simpler parameterization for all settings
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- only showing Center SHMS settings right now
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- in the parameterization, t_av is the average t-value over all data, while |t|
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is the central value for a given t-bin
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- pion background was adjusted for all t-phi bins
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- previously was doing a fit of the pi+n region to determine the integral for
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normalization, now just summing over channels in the neutron MM-range
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- this gives the correct normalization now, while we noticed some obvious
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over subtraction last week
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- for pion subtraction, using 0.88<mpi<0.94 integration range, in
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- as a result, the oscillations in phi are smaller now
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- with this smaller pion subtraction, still has some background underneath
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the Lambda peak that needs investigation
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- will look at improving the HGC hole cut, particularly at 10.6GeV, to reduce
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pion leakthrough
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- some t-phi bins are barely populated for Center setting (not unexpected)
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- however, for these settings, can't normalize to nonexistent pi+n peak
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- *NB* Garth: suggest to fit by hand the pion background in the Delta
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region to the background underneath the Lambda for these cases, taking
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care to avoid negative counts, should use the SIMC peak shape as a guide
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for how much to subtract
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- *NB* Nacer: if there is background remaining after pion subtraction,
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suggest to fit a simple polynomial to subtract it off
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Nacer
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-----
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KaonLT Low Q2 LT-sep
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- wrote 2 scripts to fit the functional params
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- sig_uns obtained using Koltenuk ratios, but fitting the parameters using
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Tanja's Fpi-2 parameterization
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- one script uses ROOTfit and the other uses Python, comparing them to check
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for consistency
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- results the same, except for sigL param(6) which fit more stably with
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ROOT than Python
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- Nacer is giving initial params in the fit to be about 1, rather than
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using Tanja's thesis values
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- long discussion about the need to properly initialize the fit params, as
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fitting algorithms often find false minima
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- Richard: it is quite possible to end up with Ratios near 1, but in a false
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chi-square minimum
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- this is because the Ratios are based on the integrals of the
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distributions
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- *NB* to really be sure you have the correct fit, you need to compare
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Data and MC distributions of focal plane and physics variables. They
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will converge when you have the correct fit
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- Nacer's code made the mistake of feeding degree values into sin(thetacm)
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rather than radians for LT and TT, so the fits weirdly oscillate
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- Garth: there is no guarantee the equations from Tanja's thesis will be what
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eventually gives a good fit to the data, so pay attention to what the fits
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give you, so we can figure out what to eventually adjust
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Junaid
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------
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Q2=3.85 W=2.62 LT-sep
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- fitting Tanja's Fpi-2 parameterization as well, using Python
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- in sigL, keeping param(8),param(9) in denominator fixed for now, and only
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allowing the 3 parameters in the numerator to float
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- reran SIMC w/Fpi-2 parameterization
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- initial values in the fit were taken from Tanja's thesis, not ~1 as Nacer
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did
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- has fits, but hasn't looked at the new parameters yet
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- Garth: suggests to take a look at the parameters and see how they have
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changed, that can tell you which params to fix and which to let float or
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set to zero
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- working on a Weight recalculation script, meetings planned with Richard and
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Bill next week
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Nathan
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------
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PionLT deadtime investigations
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- still following up on weird timing shifts identified a few months ago
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- changed pTRIG.ROC1,2 pTRIG4_ROC1,2 PT2 timing window ranges
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- the changes are small, e.g. pTRIG1.ROC1 changed from 5100-6200 to 5000-6000
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- now T.coin.pTRIG1_ROC1_tdcTimeRaw shows a multiple peak structure
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- will make different versions of plot for different multiplicities to see
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what is going on
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- with this change, CT vs xfp shows that the weird timing shift has gone away
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- not sure why, maybe ONLINE params are being called somehow?
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- doing a new replay to be sure
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- CT offset has also shifted, shouldn't have, indicates that something else
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has changed that shouldn't have
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- still trying to debug code, to be sure correct DBASE are being used
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- not sure if last week's plots (showing no change) are right or not
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- maybe the explicit call to TCOIN.param had a typo? Unfortunately, did not
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keep a record so no way to know
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Alicia
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------
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u-channel background fitting
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- had a discussion with Henry Klest re Pythia generator
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- also had a discussion with Bill last week
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- he things it's uncorrelated 3-pi background, suggests to modify the
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phase-space SIMC routine rather than use Pythia
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- *NB* Garth: suggest to look at Appendix in Ambrozewicz thesis to figure
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out what to change in his derivation
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Ivan
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----
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KaonLT K+ and pi+ BSA analysis
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- random subtraction is messed up for K+, need to look at it again
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- also messed up for pi+
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- the issue was that the reals window is shifted between pi+ and K+ and the
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randoms normalization factor was not calculated correctly
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- this affected pi+ BSA, and since pi+ is also used for background
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subtraction for K+, it also affects K+ BSA
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- anticipating the BSA will be closer to zero, with less randomness when
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randoms fixed, but of course there is no guarantee of this
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- *NB* Garth: suggests to try a separate pion subtraction factor for each
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t-bin, not a global factor at each Q2
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- *NB* same comments regarding background underneath the Lambda that are in
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Nacer comments above apply
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- starting preparations for systematic error studies
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Next Meeting
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-------------
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- Thur July 17 @ 15:30 Eastern/13:30 Regina
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- PionLT will go first
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