Upload
earl
View
34
Download
0
Tags:
Embed Size (px)
DESCRIPTION
A photon sample selection from Z ll decay. Alexey Antonov * , Evgeny Yu Soldatov * * Moscow Engineering Physics Institute (MEPHI). “Physics&Computing in ATLAS” – 22/09/2010. Outline:. Motivation True level Signal Background Reconstruction level control plots - PowerPoint PPT Presentation
Citation preview
E. Soldatov Pure photon sample selection 1
A photon sample selection from Zll decay
Alexey Antonov*, Evgeny Yu Soldatov*
*Moscow Engineering Physics Institute (MEPHI)
Outline:
•Motivation
•True level Signal Background
•Reconstruction level control plots
•Reconstruction Signal/Background optimization
•Results for Z -> ee•Results for Z -> •Conclusions
“Physics&Computing in ATLAS” – 22/09/2010
E. Soldatov Pure photon sample selection 2
Photon sample selection using Z->llprocess
Truth M(Z->ee)
M(ee) [GeV]
SignalBackground
Idea is to obtain pure photon sample from known physics process with distinctive kinematical feature - -M(ee) and dR(e) -M() and dR()
One of a problems is a small production cross section.
-ISR-Brem-Jets
Main goal of the analysis is to find the signal selection method - check Signal to Background ratio - and statistical yield
-FSR
E. Soldatov Pure photon sample selection 3
MC sample and preselection
Public FullSim MC samples - 5M events ~4.5 fb
Public Analysis code rel. 15.6.1
-1
Z -> mc08.106051.PythiaZmumu_1Lepton.merge.AOD.e347_a84_t53_tid061356
Z -> ee mc08.106050.PythiaZee_1Lepton.recon.AOD.e347_s462_r541_tid028253
Et() > 5 GeV;
Pt(e) > 15 GeV; Pt() > 15 GeV;
|| (e)| < 2.5; || ()| < 2.5;
E. Soldatov Pure photon sample selection 4
Z -> ee signal and signal and backgrounds (truth backgrounds (truth
level)level)
4
E. Soldatov Pure photon sample selection 55
R distribution for signal and all backgrounds (TRUTH)
Signal (FSR) ISR
Brem
-to-closest lepton angle
Jets treated as
22 R
E. Soldatov Pure photon sample selection 6
Remaining statistics & efficiency of photon reconstruction vs. R cut.
6
R>0.2always used
further
Remaining signal
statistics vs. R cut
FSR Efficiency
R
R cut selection
R>0.2
22 R
E. Soldatov Pure photon sample selection 7
TRUTH invM(eeee) for FSR, ISR and Jets (as photon)
FSR ISR Jets
JetsISRFSR
For bottom plots 80GeV < invM(eeee) < 100GeV
0.9K events 148K events52K events
M(eeee) [GeV]M(eeee) [GeV]
M(eeee) [GeV]M(eeee) [GeV]M(eeee) [GeV]
M(eeee) [GeV]
E. Soldatov Pure photon sample selection 8
Z -> ee Reconstruction levelReconstruction level
8
E. Soldatov Pure photon sample selection 9
Control plots for reconstructed FSR photons (signal)
- with tight cut
9
ET (), MeV
Efficiency vs.
()
Et() distribution
ET (), MeV() distribution
- no tight cut
Efficiency vs. Et ()
E. Soldatov Pure photon sample selection 10
Bkg.
all Z-> eeee events Signal/Background
M(eeee) [GeV]
Optimal M((eeee) window is 82<M(eeee)<95 GeV (see backup slides)
Reconstructed invM(eeee)
FSR – 26k
M(eeee) [GeV]
M(eeee) [GeV]
M(eeee) [GeV]
- Tight cut- No Tight cut
- Tight cut- No Tight cut
- Tight cut- No Tight cut- Tight cut
- No Tight cut
E. Soldatov Pure photon sample selection 11
eeee selection optimization
Photon tight cut
Mass window 82<M(eeee)<95 GeV window
Usual selection:
Mass window for invariant M(ee)ee);
Photon ET cut;
Upper R cut.
Extra cuts:
All these cuts will be applied sequentially to the signal with initial statistics 26139 events.
E. Soldatov Pure photon sample selection 12
eeee mass selection optimization
E. Soldatov Pure photon sample selection 13
Reconstructed invM M(eeee) - 82<M(eeee)<95 GeV window
Bkg.FSR
Signal/Background
Bkg.
Signal/Background
FSR
No tight CUT
Tight CUT
15.8k 3.9k events
11.4k events21.1k
Max s/b ~ 7
Max s/b ~ 3.3
M(eeee) [MeV]
M(eeee) [MeV]M(eeee) [MeV]
M(eeee) [MeV] M(eeee) [MeV]
M(eeee) [MeV]
E. Soldatov Pure photon sample selection 14
Reconstructed invM(eeee) @ 82<M(eeee)<95 GeV & 50<M(eeee)<82 GeV
NO Tight cut
Tight cut
M(eeee) [MeV]
- 96% of background rejected if M(eeee) and M(eeee) window cuts applied
FSR
12.7k events
Bkg.
Bkg.FSR
2.k events
16.7k events 6.1k events
<S/B>~6.2
<S/B>~2.75
- 50% signal reduction (with tight cut)
M(eeee) [MeV] M(eeee) [MeV]
M(eeee) [MeV]
E. Soldatov Pure photon sample selection 15
Upper R cut (Tight and Mee cuts applied))
S/B ratio
15
With the cut R<1.6 the S/B ratio reaches level of 7.47 with remaining statistics 39% of the initial one.
R R
Remaining statistics
Remaining signal statistics and averaged s/b ratio (integral from 0.2 to upper R cut) as a function of the upper R cut with Mee and tight cut.
E. Soldatov Pure photon sample selection 16
Remaining statistics
16
For ET>9 GeV averaged S/B=10.45 can be achieved and statistics is 31% from the initial one.
S/B ratio
Effect of the low Et cut for photons (all previous cuts applied)Effect of the low Et cut for photons (all previous cuts applied)
From ET distribution, it is clear, that low ET cut can give an
effect
ET, MeV
- Signal- Background
ET, MeV
ET, MeV
E. Soldatov Pure photon sample selection 17
Mee, MeV
S/B ratio
Differential distributions of s/b ratio as a function of InvMee for all previously presented cuts and with addition of the tight cut
17
For black line averaged S/B=7.18 and remaining statistics is 39% from the initial one. For green – it was given on the previous slide (10.45 and 31%
accordingly).
- all presented all presented cuts - extra tight cut
Ratio of S/B for selection w/o TightCut to selection with TightCut
Z->ee could be useful for the tight cut efficiency validation
E. Soldatov Pure photon sample selection 18
Z -> ee Selections Summary
18
SelectioSelectionn
S/B ratio
Statistics from initial
Number of signal events
No cuts 0.18 100% 26139
Inv Mee<95 GeV
1.40 89% 23221
+ Inv Mee>82
GeV
1.87 82% 21499
+ Tight cut 4.22 62% 16112
+ Inv Mee<82 GeV
5.58 53% 13770
+ Inv Mee>50 GeV
6.19 50% 13004
+ R<1.6 7.47 39% 10318
+ ET>9 GeV 10.45 31% 8187
E. Soldatov Pure photon sample selection 19
Z -> Reconstruction levelReconstruction level
19
E. Soldatov Pure photon sample selection 20
Reconstructed invM() @ 80<M()<96 GeV & 15<M()<80 GeV
- Tight cut has marginal effect on selection if M() and M() cuts applied
NO Tight cut
Tight cut
M() [MeV]
- 99% of background rejected if M() and M() cuts applied
FSR
15k.events
Bkg.
Bkg.FSR
1290 events
16k.events 1348 events
<S/B>~11.6
<S/B>~11.9
- 30% signal reduction
M() [MeV]M() [MeV]
M() [MeV]
Same R>0.2 used
E. Soldatov Pure photon sample selection 21
Differential Signal to Background Ratio as a function of
invM()
Tight cut has a marginal effect on selection if M() and M() cuts applied
NO Tight cut
Tight cut
<S/B>~11.9
<S/B>~11.6
80<M()<96 GeV & 15<M()<80 GeV
M() [MeV]M() [MeV]
No TightCut/TightCut Ratio
Z-> could be useful for the tight cut efficiency validation..
E. Soldatov Pure photon sample selection 22
Statistics reduction
Integral S / B
For Et() >10 GeV; => <S/B>~25;
Cost – 15% of signal events and Et() range
Low Et() selection @ 80<M()<96 GeV & 15<M()<80 GeV
-Signal (FSR)- All Background
ET () MeV
ET () MeV
ET () MeV
E. Soldatov Pure photon sample selection 23
Z -> selections Summary
Selection <S/B> ratio
Remaining events
Number of signal events
No Cuts 0.25 100% 33173
80<M()<96
GeV 2.4 86% 28523
+ Tight cut 6.7 65% 21516
15<M()<80 GeVNo Tight cut
11.9 48% 16055
15<M()<80 GeV+Tight cut
11.6 45% 14992
+Et() >10 25 41% 13600
Public FullSim MC sample of Z -> - 5M events ~4.5 fb-1
E. Soldatov Pure photon sample selection 24
About real data (I)
After all Z-boson note (ATL-COM-PHYS-2010-701) cuts for 310 nb-1 (runs 161520-161948) we have:
E. Soldatov Pure photon sample selection 25
About real data (II)
Probability of considering process is ~0.5% of Z decays to two leptons. (For previous slide picture – 0 such events).
Expecting integral luminosity this year: ~60 pb-1 ~20k of Z (~100 our photons);
Expecting luminosity next year: ~1 fb-1 ~1M of Z (~5000 our photons).
So in the end of this year there will be necessary statistics for start of the analysis such process. But good analysis and good photon sample to obtain (there will be losses of statistics due to cuts) will be possible in the next year.
E. Soldatov Pure photon sample selection 26
- All in all, about ~22k pure photons from ~4.5 fb can be selected using Z boson decays to electrons and muons using proposed method. Analysis of the real data statistics has been done.
-Selection of a pure photons in the process Z -> ee & Z -> has been studied using 5M (~4.5 fb ) events MC samples.
Conclusions
- Tight cut has a marginal effect on selection if M() and M() applied. Means that Tight cut can be studied using Z -> .
- Z -> : set of cuts 80<M(ee)<96 GeV & 15<M(ee)<82 GeV & Et() >10 GeV & 0.2<R provides ~13600 photons with purity ~96%
- Tight cut allows to identify 62% of photons with the signal-to-background ratio of 4.2 (ee ) and 6.7() in the invariant mass range 82-95 GeV.- Z -> ee : set of cuts 82<M(ee)<95 GeV & 50<M(ee)<82 GeV & Et() >9 GeV & 0.2<R<1.6 provides ~8200 photons with purity ~90%
-1
-1
E. Soldatov Pure photon sample selection 27
Backup slides
27
E. Soldatov Pure photon sample selection 28
Resolution of reconstructed invM(eeee), FSR only
trutheeZ
trutheeZ
recoee
M
MM
28
E. Soldatov Pure photon sample selection 29
EETT andand distributions for reconstructed ISR photons distributions for reconstructed ISR photons (background) matched with truth and reconstruction (background) matched with truth and reconstruction
efficiencyefficiencyET Efficiency
- without tight cut
- with tight cut
29
EfficiencyET, MeVET, MeV
E. Soldatov Pure photon sample selection 3030
With the cut Mee<95 GeV averaged S/B=1.4 and statistics is 89% of the initial one.
Mee, MeVMee, MeV
S/B ratioRemaining statistics
A choice of the mass window for A choice of the mass window for ZZeeeegg - decay study - decay study (I)(I)
Here presented the remaining signal statistics and averaged s/b ratio (integral from 0 to Mee limit) as a function of the upper Mee limit.
E. Soldatov Pure photon sample selection 3131
Further interval mass 82< Mee<95 GeV, with averaged S/B=1.87 will be used for analysis (statistics is 82% of the initial one).
Mee, MeVMee, MeV
S/B ratio
A choice of the mass window for A choice of the mass window for ZZeeeegg - decay study (II)- decay study (II)Here presented the remaining signal statistics and averaged s/b ratio Here presented the remaining signal statistics and averaged s/b ratio (integral from bottom M(integral from bottom Meeee limit limit to 95 GeV) as a function of bottom Mto 95 GeV) as a function of bottom Meeee
limit.limit.
Remaining statistics
E. Soldatov Pure photon sample selection 3232
- with tight cut
- without tight cut
S/B ratio
Differential distributions of s/b ratio as a function Differential distributions of s/b ratio as a function of InvMof InvMeeee for InvM for InvMeeee
With the tight cut averaged S/B ratio in the chosen mass window is 4.22. Remaining statistics is 62% of initial.
Mee, MeV
E. Soldatov Pure photon sample selection 3333
Mee, MeV Mee, MeV
Remaining statistics S/B ratio
Bottom cut for theBottom cut for the Invariant Mass of Invariant Mass of two two electrons. electrons. Upper cut is 82 GeV Upper cut is 82 GeV (additional to the tight cut)(additional to the tight cut)
Here presented the remaining signal statistics and averaged s/b ratio Here presented the remaining signal statistics and averaged s/b ratio (integral from bottom M(integral from bottom Meeee limit limit to 82 GeV) as a function of bottom Mto 82 GeV) as a function of bottom Meeee
limit.limit.
For the cut Mee>50 GeV averaged S/B=6.19 and remaining statistics is 50% from the initial one.
E. Soldatov Pure photon sample selection 34
- with 50<InvM50<InvMeeee<82 cut only<82 cut only
- with tight cut addition
S/B ratio
34
Mee, MeV
For black line averaged S/B=2.75 and remaining statistics is 65% from the initial one. For green – it was given on the previous slide (6.19 and 50% accordingly).
Differential distributions of s/b ratio as a function of Differential distributions of s/b ratio as a function of InvMInvMeeee for 50<InvM for 50<InvMeeee<82 cut only and with addition of the <82 cut only and with addition of the
tight cuttight cut
E. Soldatov Pure photon sample selection 35
Comparison of the s/b ratio for Comparison of the s/b ratio for tight cut tight cut onlyonly with the s/b ratio for with the s/b ratio for 50<InvM50<InvMeeee<82 <82
cut onlycut only
- Tight cut
InvMInvMee ee cut / Tight cutcut / Tight cutS/B ratio
Mee, MeVMee, MeV
- Mee cut
35
It could be useful for the tight cut efficiency validation.It could be useful for the tight cut efficiency validation.
E. Soldatov Pure photon sample selection 3636
S/B ratio
Differential distributions of s/b ratio as a function of InvMee for 50<InvMee<82 and DR<1.6 cuts and with addition of the tight
cut
Mee, MeV
For black line averaged S/B=3.98 and remaining statistics is 51% from the initial one. For green – it was given on the previous slide (7.47 and 39%
accordingly).
- with 50<InvM50<InvMeeee<82 <82 and DR<1.6 cuts - with tight cut addition
E. Soldatov Pure photon sample selection 37
Comparison of the s/b ratio for Comparison of the s/b ratio for tight cut onlytight cut only with the s/b with the s/b ratio for ratio for 50<InvM50<InvMeeee<82 and <82 and R<1.6 cuts onlyR<1.6 cuts only
- tight cut only
- InvMInvMeeee&&RRupup cuts only cuts only
InvMInvMeeee&&RRupup cuts / Tight cut cuts / Tight cutS/B ratio
Mee, MeVMee, MeV
37
It could be useful for the tight cut efficiency validation.It could be useful for the tight cut efficiency validation.
E. Soldatov Pure photon sample selection 38
EfficiencyTruth JetsReco JetsET, MeV ET, MeV
EETT and and distribution of the truth and reconstructed (in distribution of the truth and reconstructed (in
photon container) jets and efficiency of such reconstructionphoton container) jets and efficiency of such reconstruction
EfficiencyTruth JetsReco Jets
ET, MeV
38
E. Soldatov Pure photon sample selection 3939
Mee, MeV
Mee, MeV
Truth signal, background and ratio of s/b ratio as a function of Truth signal, background and ratio of s/b ratio as a function of invariant mass eeinvariant mass ee in full area and in window in full area and in window
FSR - Signal
Mee, MeV Mee, MeV
Mee, MeV Mee, MeV
Truth Jets Truth S/B ratio
E. Soldatov Pure photon sample selection 40
EETT and and distributions of all reconstructed photons (with distributions of all reconstructed photons (with and without tight cut)and without tight cut)
The peak in ET distributions around half Z-boson mass corresponds to an error in the reconstruction of the conversion photon from one of the Z-boson’s electron.
40
ET
With tight cut
With tight cut
ET, MeV
ET ET, MeV
E. Soldatov Pure photon sample selection 41
Backup slides Z ->
41
E. Soldatov Pure photon sample selection 42
RR distributions for signal and background (TRUTH)
Signal (FSR) ISR
Brem Jets treated as
R
R
R
R -to-closest lepton angle22 R
E. Soldatov Pure photon sample selection 43
Resolution of reconstructed M()
t r u t he eZ
t r u t he eZ
r e c oe e
M
MM
E. Soldatov Pure photon sample selection 44
Control plots for reconstruction - Z ->
FSR photons reconstruction
Efficiency vs Et()Et() distribution
Efficiency vs) ) distributionEt() [MeV] Et() [MeV]
) )
Tight Cut