DiPhoton + MET: Towards Unblinding of the 5 fb-1 Analysis

• Reminder about 1 fb-1 analysis• New strategy: A B C analyses• Optimization• MET Blues• Background estimates• Unblinding of A, preparation for B unblinding

Bruce Schumm29 Feb 2012

1 fb-1 Analysis: Thumbnail Sketch

(First-order) signal selection straightforward:• 2 tight isolated photons with ET 25 GeV

• ETmiss 125 GeV

Optimization based only on ETmiss cut value

Optimization geared towards high-mass Gluino for broad range of bino masses (50 GeV to Mgluino)

Analysis Improvements

Overlap Criteria- Reverse /e overlap criterion (have medium e kill )- e fake rate goes from 0.049-0.168 to 0.025-0.075- 13% signal efficiency loss

Conversion pixel requirements- Conversion tracks can have no pixel hits- e backgrounds reduced by 43% (42% for events with one conversion; 61% for events with two conversions)- 13% signal efficiency loss

Conversion categories- Division into three conversion categories suggested- No benefit if background is ~0

Two scales characterize GMSB production/decay

• Missing energy (mostly bino mass; also bino boost) MET

• Total energy, including photons (sparticle mass) HT

Analysis A: High-mass sparticle, high-mass binoLarge MET, moderate HT

Analysis B: High-mass sparticle, low-mass binoModerate MET, large HT

Analysis C: SPS8 (direct gaugino production; sparticles too heavy)Moderate-to-large MET; NO HT (most like 1 fb-1 analysis)

Also: 1 fb-1 backgrounds observed to have photons close to MET (photon to MET) cut explored for A,B,C analsyes

Optimization: General Principles

C

Optimization of A, B, C Points: Results

Optimization results:All use photon ET > 50 GeV.

Figure of merit rather flat in use either 0.5 or no cut

Drop unjustified significant digits

Target Model

ETmiss HT

A (900,800) 200 600 0.5

B (900,50) 100 1100 ---

C SPS8 170 125 --- 0.5

Background: Definition of “QCD” Control Samples

We model the ETmiss distribution of selected events with

no intrinsic missing energy via two control samples: QCDg and QCDgg.

A “control photon” satisfies the loose, but not the tight, selection requirement for two shower quantities: the shower shape in the shower core {fracs1} and the shower width {weta1} in the first sampling of the electromagnetic calorimeter.

QCDg has one such control photon; QCDgg has two.

QCDg, QCDgg, and gg – MET_SimpRefFinal

2/16/2012 10

No resemblance of control sample eT

miss shape to that of the signal

QCDg, QCDgg, and gg – MET_LocHadTopo

2/16/2012 11 Propose to use LocHadTopo for ET

miss

N.B.: Studies with +Njets MC suggest high-ET

miss tails a bit larger for SimpMetRefFinal

BACKGROUNDS

QCDgControl Sample(DESY)

E- Control Sample(Penn)

Overlap ?(DESY)

Missed?(SCIPP)

EW Background from e- control sample Brig, Jack

N.B.: “Signal” is e-

Scale factors from Ze/ZeeMultiply these by “signal” numbers on previous page

Pseudo-photon control sample (Peter, Martin)

• QCDg distribution provides shape and tails

• scale to signal (gamma-gamma) in low-MET region (ET

miss<20 GeV)

SIGNAL BLINDED FOR MET > 100 GEV

SIGNAL BLINDED FOR MET > 100 GEV

SIGNAL BLINDED FOR MET > 100 GEV

Background Summary

QCD EW TOTA 0.10 0.10 0.03 0.03 0.13 0.13

B 0+0.38-0.0 0.03 0.03 0.03+0.41

-0.03

C 0.7 ? 1.2 ? 1.9 ?

1 fb-1 0.8 0.7 3.1 1.5 4.1 1.7*

*Includes a 0.2 event contribution from “irreducible” backgrounds (two real photons) that are negligible in A

and B regions; needs to be checked for C

Missed/Overlapped backgrounds study: No significant corrections suggested (up to smallish uncertainties)

A:ggm_900_800 -> LL: 142.4, sig: 16.9, #S: 21.3, #B 0.01ggm_1000_800 -> LL: 39.8, sig: 8.9, #S: 7.1, #B 0.01ggm_1100_800 -> LL: 10.8, sig: 4.7, #S: 2.4, #B 0.01ggm_1200_800 -> LL: 3.4, sig: 2.6, #S: 0.9, #B 0.01

C:sps8_170 -> LL: 22.2, sig: 6.7, #S: 11.9, #B 0.9sps8_180 -> LL: 14.5, sig: 5.4, #S: 8.9, #B 0.9sps8_200 -> LL: 6.6, sig: 3.6, #S: 5.3, #B 0.9sps8_220 -> LL: 2.7, sig: 2.3, #S: 3.0, #B 0.9sps8_240 -> LL: 1.2, sig: 1.5, #S: 1.8, #B 0.9

B:ggm_900_50 -> LL: 45.1, sig: 9.5, #S: 10.3, #B 0.05ggm_1000_50 -> LL: 13.6, sig: 5.2, #S: 4.0, #B 0.05ggm_1100_50 -> LL: 2.7, sig: 2.3, #S: 1.2, #B 0.05ggm_1200_50 -> LL: 0.4, sig: 0.85, #S: 0.3, #B 0.05

A word on the 5 fb-1 reach (not fully-optimal analyses)

Limits for 1 fb-1 about 820 GeV

for analysis-A-like scenario and ~145

TeV for SPS8 trajectory

Unblinding Procedures

1) Obtain Ed-Board approval (done 2/21/12)

2) Examine HT sidebands to build confidence in background modeling, especially without the cut (B analysis)

3) Since B sidebands (up to HT=1100 GeV) are almost A signal region (HT > 600 GeV) explore and unblind A before exploring B sidebands

HT Sidebands for Analysis A: 200 < HT < 400

MET Cut

Includes cut

HT Sidebands for Analysis A: 400 < HT < 600

MET Cut

Includes cut

Analysis A Unblinded

No signal for MET > 200;Should set strong limit for high Bino mass (note that 200 GeV cut has avoided one background event)

Includes cut

Analysis B Blinded

HT > 1100No cut

HT Sidebands for Analysis B: 500 < HT < 800

500 < HT < 800 No cut

HT Sidebands for Analysis B: 800 < HT < 1100

800< HT < 1100No cut

How well do we understand these backgrounds? Should

we fear not using the cut?

e- Control Sample (EW Bkgds); No Cut

Scale by e rate to get expected background

e- Control Sample (EW Bkgds); No Cut

Scale by e rate to get expected background

MET 50-75 75-100 100-200 > 200

EW 6.6 1.6 2.2 0.15

QCD 60.0 5.9 1.8 0.26

Exp. Bkgd 66.6 7.5 4.0 0.41

events 64 5 3 0

200 < HT < 1100 Sideband: Expected (assuming no signal) vs. Observed Rates

With cut

MET 50-75 75-100 100-200 > 200

EW 7.2 2.0 2.5 0.18

QCD 84.4 7.7 2.6 0.31

Exp. Bkgd 91.5 9.6 5.1 0.49

events 82 8 3 2

cut removed

200 < HT < 1100 Sideband: Expected (assuming no signal) vs. Observed Rates

Summary

Three analyses geared towards high&low mass bino, SPS8

High-mass bino analysis: 0 signal events

Low-mass bino ready to unblind; SPS8 requires further background studies (underway)

Verbatim 2011 analysis applied to 5 fb-1 150-200 GeV increase in limits

2012 analysis improvements 250-400 GeV increase

CMS did better than ATLAS with 1 fb-1 because of• More favorable interpretation of GGM model• Luck

but per fb-1, our analysis was more sensitive

BACKUP

Also: Limit of > 145 TeV set on SPS8 SUSY Breaking scale

Analysis background-limited; sparticle cross section goes as ~M-9

reoptimize!

Photon Et Optimization (1 fb-1 Analysis) Helenka

Choose Cut of50/50

Cross-check with MET distribution from Zee (background real ?)

No QCDg above 100 GeV Less than 1 event at 95% CL

Martin

Overlap Between QCDg and EW backgrounds

Missed Backgrounds (?)

• Since our “QCD” backgrounds are estimated by normalizing control samples (QCDg, Zee) to low-MET signal, they should be comprehensively accounted for

• “EW” (W,top) backgrounds estimated via e- control sample Assumes all W,top contributions have at least one e fake

• Is this true? If not, what is character of the “missed” component?

• Might the “missed” component in fact be incorporated into the QCD control sample (pseudo-photon) estimate?

Dan

According to MC, what fraction of EW background is due to e fakes?

MC

Of the 25% that is “missed”No e With e

+ 18.9 0.0

+ jet 47.5 5.0

+ 3.0 2.9

+ W l 22.9 0.0

18.9% + 47.5% = 66.4% 2/3 is expected to be reflected in the pseudo-photon sampleThis 2/3 may well be the source of the “EW-contamination” in the pseudo-photon sample (cross-check underwayThis component is neither missed nor double-counted! Add “QCD” and “EW” backgrounds linearly (values and errors)