Physics with Photons and Missing Energy at ATLAS

DOE Site VisitThursday June 14, 2012

Damiani*, Kim, Kuhl, Litke, Mitrevski, Nielsen, Schumm (convener)

Collaborators: Annecy, DESY, La Plata, Liverpool, Penn, Tokyo Tech, Wiezmann

*Ph.D. June 2012

SCIPP Roles Played• Diphoton + MET (flagship photon + MET analysis)

Schumm convener, cast of ~ dozen Damiani thesis

• Photon + Bjets + MET Nielsen, Kuhl, with Weizmann

• Photon + Lepton + MET Mitrevski

• Overall Photon(s) + X + MET Schumm is contact person

PapersSearch for Diphoton Events with Large Missing Transverse Momentum in 1 fb-1 of 7 TeV Proton-Proton Collision Data with the ATLAS Detector

Phys. Lett. B710 (2012) 519-537

Search for Diphoton Events with Large Missing Transverse Momentum in 36 pb-1 of 7 TeV Proton-Proton Collision Data with the ATLAS Detector

Eur. Phys. J. C71 (2011) 1744

Full 2011 diphoton + MET result (5 fb-1) in Collaboration-

Wide Review for ICHEP and then

Phys. Lett. B

ATLAS Recognition• Invited Talks

Mitrevski: Photons+MET, SUSY11, Aug 2011 Schumm: SUSY @ ATLAS, CIPANP, May 2012

• US Talks Schumm: SUSY @ ATLAS, SUSY Recast (Davis), April 2011 Mitrevski: Photons+MET, BNL SUSY Workshop, May 2011

Photon(s) + MET: MotivationATLAS searches defined by signature, motivated by one or more BSM physics scenario.

Photon(s) + MET Motivations:

• Gauge-Mediated SUSY Breaking (GMSB) New “hidden” gauge/messenger sector protects flavor symmetry Photons from gaugino gravitino decay

• Universal Extra Dimensions (UED) Weak gravity excused by leaking into extra dimensions Gravity-mediated KK photon decay KK + G(KK)

Hidden gauge sector breaks SUSY via weakly-coupled messenger interactions

LSP is light (<< 1 GeV) gravitino

NLSP is typically neutralino 01

Bino-like neutralino is natural, which decays with ~75% BF to photon-gravitino

2 photons + missing transverse energy (MET)

01 could also be admixture of Wino, Higgsino

Photon + (lepton, bjets) + MET

GMSB Phenomonology

5 fb-1 Diphoton+MET Strategy• Tighter photon selection suppresses backgrounds

• Three analysis regions targeting

A: High-mass (strong) production, heavy 01

B: High-mass production, light 01

C: Low-mass (electroweak) production

Analysis Cuts

Expected Background

Observed Signal

5 fb-1 Diphoton+MET Results

• Tighter photon selection (no pixel hits for conversions)• Optimized signal regions & highter photon ET thresh

~100 GeV greater reach than CMS (like x3 stats):

New Analysis I: + bjets + MET

+ bjet + MET Motivation and Search

Shih, Ruderman

• One photon, ET > 125 GeV

• MET > 150 GeV

• 2 ET > 50 jets, one b-tagged

• min > 0.4

• MT(,MET) > 100 GeV

• Lepton veto

+ bjet + MET: Prospects

For 01 ~50/50 h/B mix,

can approach mg ~ 700 GeV when m > ~200 GeV

Target: SUSY2012Beijing, Aug 13-18

First analysis of cascade involving

photon + bjet

New Analysis II: Photon + Lepton + MET

“Lead” is Jovan Mitrevski •Target EW production, and bino/wino admixture for 0

1)

• Start with l = to avoid jet (QCD) backgrounds

• Backgrounds (order of size): W, tt(+), W+jets, Z + (,jets)

Only existing result is CMS, 35 pb-1

EW Production

Shih, Ruderman

Wino-like NLSP

+ Lepton + MET Prospects

SRQCDXR1

XR2

TCR

Background approach nearing completion

Systematics ~ next week

Histogram-fit limits ~ 2weeks

Hope to make SUSY12

WCRW

SCIPP playing leading role in multi-signature arena

Attentive analysis yields very aggressive limits

2011 (5 fb-1)Two papers published, one in CWR, two more in analysis stage

2012 (20 fb-1 @ 8 TeV)Expect 10-15% improvement from each of higher energy, statistics 25% increase in reach (?)

Beyond14 TeV will open up a whole new window

Photon(s) + MET Summary

BACKUP

The “minimal” SPS8 model is ad hoc, selected somewhat arbitrarily as a concrete model for which different facilities could be compared

In particular, no reason why EW and colored partner scales need be coupled

Generalize model so that one strong partner, one EW partner are light, all other partner masses are high (~1.5 TeV)

Free parameters are gluino, Bino-like 10 masses:

General Gauge Mediation (GGM)

Two major sources:

MET Distribution from QCD Sources • Loose photon control sample• Z e+e- to model events

MET from EW Sources (Ws, ttbar)• e control sample from data, MC• Scale to contribution with e fake rate from Z ee studies

Data-Driven Background Estimate

Nothing there with 36 pb-1, so we set limits…

ISO: New Physics!

Signal region

ATLAS has better photon reconstruction than CMS (conversions)

Observed, Expected Limits

7/25/11: Accepted (pending small revisions)

Observed in Signal Region vs.

Expected Background

20101 (~1 fb-1) Analysis

2010

201130x increase in data sample size

12x improvement in cross-section limit

But: 1/M9 forMgluino

~ 900 GeV!