The plots shown here are from NA62 2016 data and are produced by modifications of code written by Giuseppe Ruggiero and Connor Graham.
The plots show comparisons of data with MC for
K+ -> pi+ + pi0
Data - black, MC - green. Plots are shown only when there are entries in both data and MC.
The object of this study is to compare the data and MC distributions and to compare
the effects of the event selections on data and MC at a stage in the analysis
when a reasonably clean selection of the K+ -> Pi+ Pi0 decay channel has been made.
COMPARISON of DATA WITH MC after K+ -> Pi+ Pi0 selection
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Comparison plots are here: KaonEventAnalysis
The plots have been made in the function KaonEventAnalysis::PiP0Analysis
The plots 214 - 222 show the fMMiss ( missing mass squared to K+ Pi+ ) at the
following points in code: at start of code, and after the following cuts: time ,
beam kinematics, Z-vertex, highToT, interaction, CHANTI, kinematic tails.
The number of events is reduced from 435 ( plot 214) to 326 (plot 221)
by these cuts.
Within statistics, the shape of the data MM distributions agree well with those
produced by the MC.
Subsequently, the following selection (S) is made:
if (fTrigControl && !isPhoton && !positron && !muonRA && !isEarly
&& fIsOneParticle && !isSegment && !isBadMMiss && isRICHLikePion
&& isRingCandidate && isFinalBeam && isKineCut) {
The number of events rejected by each of these cuts is shown in Plots 223 - 229.
For example, plot 225 shows that 81 events are rejected by the muonRA cut.
The plots show the missing mass distributions for the rejected events.
This selection, S, reduces the number of events from 326 to 164, see
plots 204 - 209, 212 which compare data and MC. Plots 212, 213 show the
fMMiss distributions for selected and rejected events, respectively.
Evidently the selection, S, rejects good Pi+ Pi0 events;
there is some evidence for increased tails in the missing
mass distribution for rejected events.
Finally, plots 204 - 211 compare data and MC for different variables.
In all cases there is good agreement between data and MC. Notice that
the Pi0 mass is better estimated using the gammas than using the K+,Pi+
(compare 204 , 205).
Summary of effect of cuts
DATA MC
cuts Events fraction Events fraction
start 435 6938 <- events at input to PiP0Analysis()
first set 326 0.75 5547 0.8 <- events remaing after first cuts
trigger 1 0 <- events rejected by cuts 'S'
photon 45 0.10 231 0.03 |
e+ 5 0.01 139 0.02 |
muonRA 81 0.19 1239 0.18 V
one particle 14 0.03 0
segment 20 0.05 0
RICHpion 52 0.12 388 0.06
Ringcand. 30 0.07 645 0.09
finalbeam 6 0.01 27 0.004
KineCut 10 0.02 89 0.01
data MC
total selected(all cuts) 164 3549
rejected by cuts 'S' 162 1998
Data Missing mass squared accepted
Data Missing mass squared rejected
MC Missing mass squared accepted
MC Missing mass squared rejected
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COMPARISON Of DATA WITH MC after K+ -> MU+ nu selection
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The Table below shows the numbers of events either remaining or
rejected after cuts in the function Kmu2Analysis; ~50000 muons have been input from MC.
This version of Kmu2Analysis does not use Connors latest muon selection.
Initial cuts are: beam kinematics, beam background cut, kinematic tails.
This is followed by the 15-35 muon momentum selection and
if (!isPhoton && !positron && !isEarly && fIsOneParticle && !isSegment && isRICHLikeMuon && muon && fTrack->GetIsMip() && !isMult && isFinalBeam){
( cut "S" )
Cut Data fraction MC Fraction
Start 12220 24650 No 15 -35 cut.
initial cuts 8135 0.67 17770 0.72 number after intial cuts
photon (plot 227) 1554 (473) 13 this and the numbers following
positron 167 39 are the numbers of events rejected by the selections
early 15 2 in cut "S" (including the 15-35 cut)
onepart 247 (133) 0
segment 218 (117) 0
rich 893 (65) 13 numbers in () are the number of
muon 816 166 events in the mu missing mass peak.
mip 1418 (496) 1208
mult 833 (166) 120
beam 63 (36) 0
mu final 745 3887 final number of muons
mu rej 2035 1396 number rejected
Data Missing mass squared accepted
Data Missing mass squared rejected
Remove "mip" requirement since , for MC, it rejects good muon events.
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After removal of the "Mip" requirement:
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Apply selection:
if (!isPhoton && !positron && !isEarly && fIsOneParticle && !isSegment && isRICHLikeMuon && muon && !isMult && isFinalBeam){
( cut "S" )
Fig. 1 Data Missing mass squared accepted 1000 muons accepted ( plot 235 Fig 5)
Fig. 2 Data Missing mass squared rejected ~ 690 good muons rejected (plot 236 Fig 6)
Fig. 3 MC Missing mass squared accepted 4893 muons accepted
Fig. 4 MC Missing mass squared rejected 356 good muons rejected
Overall numbers from Figs 1 and 2:
data MC
mu final 1000 4893
rej 1780 390
Figs 5. Comparison plots data/MC data - black , MC - green
Plots 227 -234 show the missing mass spectra of rejected events
for each of the rejections isPhoton, positron etc (cuts "S" above).
In most cases, rejected events have a component that shows a good
muon missing mass peak that is also in time with the trigger -
see next plots.
Figs 6. Data time plots see plots 107 -113: accepted events,
plots 114 -120: rejected events with missing mass**2 < 0.01 GeV**2
and selections as defined above. Times are for GTK, Ktag etc.
Note time similarity of accepted and rejected events.
Some out-of-time events are present for both accepted and rejected events.
There is a 1 ns time shift for the LKr relative to FineTriggerTime.
MUON SUMMARY
Fig. 1 shows that for data, 1000 muons are accepted.
Fig 2 shows the corresponding mass spectra for events that are rejected by cuts "S" (defined above with no "mips" rejection). Of the rejected events, 697 events appear to be good muon events (have missing mass**2 < 0.01, implying that ~40% of good muon events are rejected by the cuts "S". This is is reasonable agreement with G.R.'s estimate of the random veto (~30%).
Figs. 3 and 4 show the corresponding results for MC events. For MC, 7% of good muon events are rejected by the cuts.
The time plots of Figs 5 and 6 show a well defined peak, slightly shifted off zero, with low-level tails of off-time events. The rejected events have larger tails than the accepted events but are otherwise identical.
Details of photon rejection for muons
Two-constraint Kmu2 missing mass fits
4 constraint Kpi2 fits - comparison of data and MC