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!
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