backgrounds to the diphoton + met analysis
DESCRIPTION
Backgrounds to the Diphoton + MET Analysis. Bruce Schumm, channeling Ben Auerbach (Argonne) and Osamu Jinnouchi (Tokyo Tech) UC Santa Cruz / SCIPP 04 June 2013 SUSY Background Forum Meeting. Three background sources: QCD (gamma-gamma, gamma-jet, jet-jet; no primary MET) - PowerPoint PPT PresentationTRANSCRIPT
Backgrounds to the Diphoton + MET Analysis
Bruce Schumm, channeling Ben Auerbach (Argonne) and Osamu
Jinnouchi (Tokyo Tech)
UC Santa Cruz / SCIPP
04 June 2013 SUSY Background Forum Meeting
04 June 2013 2
Three background sources:
• QCD (gamma-gamma, gamma-jet, jet-jet; no primary MET)• Electroweak (W-gamma, ttbar; usually with e fake)• Irreducible (W, Z; with neutrinos in decay)
Start with QCD background
Recall: 2x2x2=8 considered control samples, defined by data with one pseudophoton, with• Zero (QCDg) or one (QCDtg) tight isolated photon• 50 or 75 GeV ET cut on pseudophoton• pseudophoton isolated or not
Nominal MET is standard MetRefFinal, but also look at LocHadTopo as cross-check
Which of all of these are useful?
04 June 2013 3
First: MC performance on tight-tight sample
LocHadTopo has slightly larger tails than MetRefFinal
04 June 2013 4
• Statistics are limited: must make use of 50 GeV ET cut, no-iso if possible• QCDtg+Iso close to tight-tight (signal) distribution proxy for high MET• QCDtg provides good representation of tight-tight MET distribution
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)
04 June 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)
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
04 June 2013 8
Direct Background Results and Systematics
LocHadTopo QCDtg and QCDg provide good systematic check
MetRefFinal QCDg expected to be a bit high; ignore
SP1, SP2 statistics a bit poor complement with extrapolation technique
04 June 2013 9
SP1 Meff
Extrapolations
04 June 2013 10
SP2 Meff
Extrapolations
04 June 2013 11
Combining all the above information yields the following overall result for
QCD background(See Note for justifications…)
04 June 2013 12
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
04 June 2013 13
e Fake Rate Results
04 June 2013 14
e Sample Statistics and EW Background Estimates
04 June 2013 15
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
04 June 2013 16
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
04 June 2013 17
Can we constrain the W K factorwith an lgg (l = e,) sample?
Ben Auerbach
04 June 2013 18
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
04 June 2013 19
Irreducible background results
And then putting it all together…
04 June 2013 20
Wrap-Up
• Preliminary estimates of background completed
• Updating the Note with new background studies (nearly done)
• Addressing comments from prior review (before p1328/p1181 MET changes that threw us back)
• When end is in sight, will request Ed Board meeting to discuss unblinding
• In the mean time, are developing limit-setting approach, and beginning to evaluate signal systematics
04 June 2013 21
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.