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

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…

04 June 2013 3

First: MC performance on tight-tight sample

LocHadTopo has slightly larger tails than MetRefFinal

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.

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)

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)

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

19 December 2012 8

Nominal QCD Background

Control Region Study

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

19 December 2012 10

QCDg+Iso Comparison

LocHadTopo Comparison

16 July 2013 11

SP1 Meff

Extrapolations

16 July 2013 12

SP2 Meff

Extrapolations

16 July 2013 13

Combining all the above information yields the following overall result for

QCD background(See Note for justifications…)

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

04 June 2013 15

e Fake Rate Results

04 June 2013 16

e Sample Statistics and EW Background Estimates

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

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

04 June 2013 19

Can we constrain the W K factorwith an lgg (l = e,) sample?

Ben Auerbach

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

16 July 2013 21

Irreducible background results

And then putting it all together…

16 July 2013 22

60 < MET < 100 Sideband Studies – No Dphi cut

100 < MET < 150 Sideband Studies – No Dphi cut

16 July 2013 23

60 < MET < 100 Sideband – Dphi_g_MET > 0.5

100 < MET < 150 Sideband – Dphi_g_MET > 0.5

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

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.