Physics with Photons and Missing Energy at ATLAS

DOE Site VisitWednesday July 27, 2011

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

In collaboration with Liverpool, DESY, Annecy, Tokyo Tech, La Plata

*Ph.D. June 2011

ATLAS MET-Based AnalysesAnalyses are signature-based:

• Monojets*

• Zero-Lepton• One-Lepton• Two-Lepton• Multi-Lepton• Photon(s)* (our focus)• Inclusive • B Jet(s)

* Co-analysis with Exotics group (that’s a different physics group altogether)

Red indicates some form of public result

available on full 2010 data sample (36 pb-1)

Models Used (for inspiration and/or analysis)

• mSUGRA / Constrained MSSM

• “24-parameter” MSSM

• Generic MSSM parameter space (four degenerate light quarks, gluino octet, LSP)

• Generic GMSB (“GGM”) space (light gluino octet, light Bino NLSP, gravitino)

• Non-contextual SUSY partners (tau sneutrino, stop+sbottom, hadronizing scolored particles)

Largely redundant

model spaces

Independent; may appear

only in photons+MET

Hidden gauge sector breaks SUSY via weakly-coupled messenger interactions

LSP is light (< 1 GeV) gravitino

NLSP is typically Bino-like neutralino 01,

which decays with ~75% BF to photon-gravitino

Two photons + missing transverse energy (MET) is effective signature.

Gauge Mediation

Strong production: • gluino/gluino or squark/squark• dominates when colored sparticles are accessible

Weak production:• 1

20 or 1

1

• dominates when only EW-charged particles are accessible

In both cases, decay proceeds through NLSP 10

Little additional activity in limit that produced state is degenerate with NLSP.

Production Mechanisms

Based on “minimal” SPS8 model designed for ‘Snowmass’-type comparitive studies

• Essentially one single phenomenological parameter, often cast as MBino

• Strong partner mass tied to 10 scale, and is

high (~ TeV)Luminosity (lower-mass EW states) trumps energy for SPS8 analyses

For 6.3 fb-1, D0 finds M > 170 GeV at 95% CL, out of reach of 36 fb-1 2010 ATLAS sample

Tevatron (2 TeV) Analyses

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)

Production cross-section (7TeV)

Bino - like Neutralino: |M1| << and |M1| < |M2|; M of Neultralino NLSP ~ M1, Neultralino NLSP + Gravitino (76%)

For Bino-like neutralino, two photons + MET is most promisingbut lose coverage if hadronic activity is required (jets, HT, etc.)

No visible jet activity when

Mg ~ M

Thanks to Shih/Ruderman, ArXiv 0911.4130

SPS8 Trajectory

D0 Limit

“Recast” D0 result in terms of GGM; compare to expected LHC reach (Ruderman & Shih, arXiv:1103.6083)

GGM Reach: Tevatron vs. LHC

2010 analysis (36 pb-1) breaks significant new ground

Avoid inefficiencies with very simple selection:

• One photon with Et > 30 GeV

• Another photon with Et > 20 GeV

• MET > 125 GeV

2010 (36 pb-1) Analysis

Signal Region

MET

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)

More selective trigger (2g20) forces higher Pt cuts

• Two photons with Et > 25 GeV

• MET > 125 GeV still

Estimated backgrounds above MET=125:

QCD 2.3 0.9

EW 2.4 1.3

Total 4.8 1.5

2011 (~1 fb-1) Analysis

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!

1 fb-1 paper in preparation 3-4 fb-1 (full 2011 run) analysis will follow

But, progress with 2+MET to be incremental

• Background limited (re-optimization?)

• Steep mass dependence

Explore other channels• Photon + (b)jet + MET (Kuhl)• Photon + MET (Kim; dedicated trigger)• Photon + lepton + MET• Non-pointing photons

2011 Analysis: What Next?

• SCIPP playing leadership (and major technical) role in central SUSY analysis

• One +MET paper in press (36 pb-1), one in preparation (1 fb-1), a third in planning (3-4 fb-1).

• Beginning to explore/develop complementary single-photon channels

• Talks by Bangert (Cargese 2010) Mitrevski (West-Cost Forum, SLAC) and Schumm (SUSY Recast, Davis)

Photon(s) + MET Summary