update on the diphoton + met analysis
DESCRIPTION
Update on the Diphoton + MET Analysis. Bruce Schumm, channeling Ben Auerbach (Argonne), Osamu Jinnouchi (Tokyo Tech), Susan Fowler (Penn) UC Santa Cruz / SCIPP 6 March 2014 SUSY General Analysis Meeting. Conference Note public in early January: - PowerPoint PPT PresentationTRANSCRIPT
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Update on the Diphoton + MET Analysis
Bruce Schumm, channeling Ben Auerbach (Argonne), Osamu
Jinnouchi (Tokyo Tech), Susan Fowler (Penn)
UC Santa Cruz / SCIPP
6 March 2014 SUSY General Analysis Meeting
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06 March 2014 2
Conference Note public in early January:
Search for Supersymmetry in Diphoton Events with Large MissingTransverse Momentum in 8 TeV pp Collision Data with the ATLASDetector
ATLAS-CONF-2014-001
List of Tasks generated to move from note to paper…
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04 June 2013 3
First: MC performance on tight-tight sample
LocHadTopo has slightly larger tails than MetRefFinal
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04 June 2013 4
• QCDtg+Iso close to tight-tight (signal) distribution proxy for high MET• QCDtg provides good representation of tight-tight MET distribution• QCDg+Iso also looks good but statistics are low.
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04 June 2013 5
• For LocHadTopo, both QCDtg and QCDg seen to provide a good representation of the tight-tight MET distribution (again, using QCDtg-Iso as a proxy at high MET)
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16 July 2013 6
Next: Signal Regions
We define five signal regions, for:
• Strong production, high and low bino mass (SP1,SP2)• Weak production, high and low bino mass (WP1,WP2)• Choose MET cut to suppress backgrounds (MIS)
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04 June 2013 7
Direct Background Estimate Methodology
A CB
e.g. for signal region WP2
Estimate = C*(A/B)
Nominal control sample is QCDtg_50_noIso
This is METRefFinal; can also look at QCDtg and QCDg of LocHadTopo
Met
Ref
Fin
al
Met
Ref
Fin
al
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19 December 2012 8
Nominal QCD Background
Control Region Study
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19 December 2012 9
We have performed the WP2 QCD background estimate without the \dphij cut, finding that the expected background rises from $0.90 \pm 0.35$ to $1.7 \pm 0.5$. It should be noted that the background would be expected to rise with the removal of the \dphij cut; if the `gg' distribution of Fig.~\ref{fig:dphij} is the correct distribution of the WP2 QCD background, this increase would be about 20\%, to 1.1 events. The observed value of 1.7 events is approximately 50% higher than this, which we interpret as an additional 50% systematic uncertainty on both the WP2 and MIS QCD background estimates.
DPHI_JET_MET SYSTEMATIC
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19 December 2012 10
QCDg+Iso Comparison
LocHadTopo Comparison
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16 July 2013 11
SP1 Meff
Extrapolations
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16 July 2013 12
SP2 Meff
Extrapolations
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16 July 2013 13
Combining all the above information yields the following overall result for
QCD background(See Note for justifications…)
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04 June 2013 14
Electroweak Backgrounds (W, ttbar, etc.)
~75% involve e fake; much of remainder incorporatedin QCD backgrounds
Reconstruct e sample; scale by measured e fake rate
+/- 25% uncertainty from non e fake processes
+/- 10% uncertainty from fake rate measurement
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04 June 2013 15
e Fake Rate Results
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04 June 2013 16
e Sample Statistics and EW Background Estimates
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04 June 2013 17
Irreducible Backgrounds
Z; Z
• Small contribution • NLO K-factor 2.0 +/- 0.3 (well understood) Estimate directly from MC
W; Wl
• Larger contribution• NLO K-factor 3.0 +/- 3.0• Dominant background systematic Constrain with new data-driven study
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04 June 2013 18
W K Factor
http://arxiv.org/pdf/1103.4613v1.pdf
LO “radiation zero” eliminated at NLOGrows with hardness of radiation Rapidly-varying function of W system recoil
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04 June 2013 19
Can we constrain the W K factorwith an lgg (l = e,) sample?
Ben Auerbach
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04 June 2013 20
Choose study region to be • 50 < MET < 250 (leave MIS signal region blind)
• PT(l) > 100
Ben Auerbach
Nexpected = 7.4 (6.5 W)
Nobserved = 7.0
K factor of 3.0 +\- 1.2
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16 July 2013 21
Irreducible background results
And then putting it all together…
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16 July 2013 22
60 < MET < 100 Sideband Studies – No Dphi cut
100 < MET < 150 Sideband Studies – No Dphi cut
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16 July 2013 23
60 < MET < 100 Sideband – Dphi_g_MET > 0.5
100 < MET < 150 Sideband – Dphi_g_MET > 0.5
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16 July 2013 24
Wrap-Up
• Preliminary estimates of background completed
• Note updated with new background studies (nearly done) ATL-COM-PHYS-2013-109
• Addressing comments from prior review (before p1328/p1181 MET changes that threw us back)
• Starting to build toward request for unblinding
• In the mean time, are developing limit-setting approach, and beginning to evaluate signal systematics
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04 June 2013 25
MET Issues
• Are latest (“post-Moriond”?) object definitions included in p3128 EGamma10NoTauLoose MET?
• We will need in any case to assemble our own “fluctuated” EGamma10NoTauLoose in order to do systematic studies
• But for now, background estimates largely insensitive to MET systematics (data-driven), so could use intrinsic p1328 variable if “approved”
• Will definitely need to be able to assemble EGamma10NoTauLoose from scratch soon though.