Searching for Supersymmetry with Final- State Photons at ATLAS

Searching for Supersymmetry with Final-

State Photons at ATLAS

UC Davis High-Energy

Physics Seminar

November 6, 2012

Bruce A. Schumm

Santa Cruz Institute for Particle Physics

University of California, Santa Cruz

Searches for SUSY with photons at ATLAS 2Bruce Schumm

SUSY States

SUSY posits a complete set of mirror states with SSUSY = |SSM – ½|

• Stabilize Higgs mass for GUTs

• Can provide reasonable dark-matter candidate

• Minimum of two Higgs doublets


To avoid lepton/baryon number violation can require that “SUSYness” is conserved, i.e., preserves a multiplicative “parity” quantum number R such that RSM = +1; RSUSY = -1

If you can’t get rid of SUSYness, then the lightest super-symmetric particle (LSP) must be stable dark matter, missing energy

LSP is typically a “neutralino” (dark matter must be neutral); admixture of ,known as “1

0 ”, whose identity is not that relevant to phenomenology

R Parity

00 ~,

~,

~HW 0B


But we know that SUSY is broken…

SUGRA: Local supersymmetry broken by supergravity interactions

Phenomenology: LSP (usually 10) carries missing energy.

GMSB: Explicit intermediate-scale “messenger” gauge couplings to some number of “secluded” superfields mediate SUSY breaking.

Phenomenology: Gravitino ( ) LSP; NLSP is 10 or . Content of 1

0 germane.

AMSB: Higher-dimensional SUSY breaking communicated to 3+1 dimensions via “Weyl anomaly”.

Phenomenology: LSP tends to be , with 1+, 1

0 nearly degenerate.

SUSY Breaking

G~ ~

W~


Minimal GMSB has five parameters:

: Scale at which SUSY “kicks in” to cure quadratic divergences

Mmess: Scale of new gauge interactions

Nmess: Number of fields in secluded sector

tan: Ratio of <vev>s of two Higgs doublets

sgn(): Sign of SUSY Higgs mass parameter

“Minimal” (Standard) GMSB Phenomenology

Over most of GMSB parameter space, NLSP is a bino-like

neuatralino, i.e., the partner of the U(1) gauge boson


If the 10 NLSP is bino-like,

then it decays to -gravitino with BF cos2W.

Since SUSY states come in pairs (R-parity) this produces a striking + + ET

Miss signature

Photon Signatures in GMSB

For minimal GMSB (SPS8)

mgluino msquark >> m

“EW production” Associated leptons, jets

“SPS8 Trajectory” of GMSBSingle free parameter • tan = 15 • Mmess = 2• Nmess = 1• > 0


Strong vs. Electroweak Production

SUSY Breaking Scale (TeV)

probe high mass scale steep mass dependence (~M-8) beam energy vs. luminosity lower backgrounds; “scale chasing”

probe intermediate mass scales higher backgrounds benefit from high L.dt

mGMSB

EW

Strong

STRONG COUPLING

ELECTROWEAK COUPLING

However: if colored states are decoupled, EW production will dominate• Dedicated EW prod. analyses• Pure-EW simplified models (new!)

5 fb-1 reach

s = 7 TeV


• Preserve basic phenomen-ology (gravitino LSP and bino-like NLSP)

• Decouple everything else except for one higher-mass state that governs production (total transverse energy scale)

• Bino NLSP governs final decay step (ET

Miss, ET scales)

• For existing analyses, high-mass state is colored (gluino, squark)

Strong production

High mass scale

Generalized Gauge Mediation Scenarios

Start w/ minimal GMSB and decouple

most states


The high-mass (strongly-coupled) state can be either gluino or squark

Set limits in gluino-bino (squark-bino) plane

GGM Parameter Space

7 TeV Strong-Production Cross Sections


Further, one can relax assumption that 10 NLSP is bino-like.

What about a wino-Like NLSP?

Degenerate triplet 1, 1

0 Final state + lepton + ET

Miss

Both EW and strong production

Even-More Generalized Scenarios: Wino NLSP

EW Production at Wino (1 1

0) scaleStrong Production at gluino scale


If 10 is pure higgsino, no photons in final state

For certain range of admixture with bino, + bjet + MET is best channel

And Also: Higgsino-Like NLSP

Bino Mass

Br(χ->H+G)

Br(χ-> γ+G)

Br(χ-> Z+G)

B+MET Signif.

B+γ+MET Signif.

γγ+MET Signif.

390 0.129 0.703 0.167 0.53σ 3.38σ 6.61σ

395 0.208 0.634 0.158 0.763σ 3.95σ 6.87σ

400 0.32 0.537 0.144 0.754σ 3.27σ 5.1σ

405 0.449 0.425 0.126 0.971σ 3.22σ 4.31σ

410 0.57 0.322 0.109 1.07σ 3.14σ 2.78σ

415 0.666 0.24 0.094 1.12σ 2.29σ 1.9σ

420 0.738 0.179 0.083 1.13σ 1.83σ 1.35σ

425 0.789 0.136 0.075 1.25σ 1.74σ 0.923σ

430 0.826 0.105 0.069 1.31σ 1.23σ 0.543σ

435 0.853 0.082 0.065 1.23σ 0.941σ 0.531σ


For bino/higgsino state, choice > 1 suppresses 10 h + gravitino

Generic Single-Photon Signature

Signature:

• Single photon • ET

miss • Njets

Value of N under study (3?)


For all cases, c < 1 mm (photons point back towards origin)

A separate group is look at standard bino-like case for which c is a free parameter (not disfavored by cosmological considerations)

Requires a new photon reconstruction, more background-prone This is an analysis for which ATLAS is particularly well-suited ( segmentation of first layer of CAL)This analysis is not included in this talk! (but…)

Prompt vs. Non-Prompt Photons


Overall status of SUSY searches with photons:

No 2012 (8 TeV) results yet; 7 TeV results as follows:• Diphoton + MET: 35 pb-1,

35 pb-1, 1 fb-1 published, 5 fb-1 in pressAnnecy, Argonne, DESY, La Plata, Tokyo Tech, UCSC

• Photon + lepton + MET: 5 fb-1 conference resultUCSC

• Photon + bjet + MET: 5 fb-1 conference result in preparationUCSC, Technion

• Photon + Njet + MET: Just getting underwayLa Plata, UCSC

Summary of four signatures, and status


The ATLAS Detector

Non-prompt tracksPhoton conversions


The 2011 ATLAS Data Set

A total of 4.7 fb-1 deemed to be adequate for SUSY analyses


Expect 25-30 fb-1 at 8 TeV for 2012

2012 (8 TeV) Data is Accumulating Fast


The basic search: Strong (gluino) production, bino decay

36 pb-1 Analysis:

• Require two stiff, isolated photons (ET1 > 30 GeV, ET2 > 20 GeV)

Diphoton + MET: Strong Production

• Then ETmiss > 125 GeV separates signal from the backgrounds


Mi

Strong-Production “Scale Chasing”

With GGM gluino (squark) mass constrained to be high (> 500 GeV) a two-scale system emerges

• Bino mass sets ETmiss scale

m = 275 GeVm = 450 GeV


• Gluino mass sets total transverse energy scale ~ 1 TeV

Strong-Production “Scale Chasing”

HT does not include missing energy (wanted to maintain observational independence)

mgluino = 1000 GeVElectroweakproduction


Jet mireconstruction can

• Introduce fake photons

• Lead to large ETmiss

(,ETmiss)

Resulting ETmiss often

in direction of

(Small) sensitivity improvement from cutting on (,ET

miss)(,ET

miss) > 0.5


Strong Production• HT large• High-mass bino More ET

miss, less HT, larger (,ETmiss)

• Low-mass bino Less ETmiss, more HT, small (,ET

miss)

EW Production• HT small• Moderate ET

miss

• Larger (,ETmiss)

Diphoton + MET Singal Regions (A,B, and C)

A

C

B


“QCD” Backgrounds• (probably not dominant)• + jet; jet misreconstruction• Estimate from loose-photon sample scaled to data at low ET

miss

“EW” Backgrounds• W; W e; e misreconstruction• tt; t be; e misreconstruction• Estimate from e data rate, with e fake rate also from data

“Irreducible” Backgrounds• W; W e• Z; Z • Estimate directly from MC simulation

Diphoton + MET Backgrounds


Expected Background and Observed Signal

C

• Analysis nearly background-free in SRs A,B

• 2 events in SR C, consistent with background expectation (no HT cut for EW production search)


Define two control samples:• QCD: One loose-but-not-tight photon (dominated by EM-like jets)• QCD: One loose, one loose-but-not-tight photonNormalize to diphoton sample for 0 < ET

miss < 20 GeV

Estimating QCD Backgrounds

Normalization region

Background estimate

5 fb-1 control samples (no HT cut)


• Dominated by e misidentification• ET

miss distribution from data e sample• Scale by measured fake rate from (Ze)/(Zee)

Estimating Electroweak Backgrounds

5 fb-1 e sample (no HT

cut)

Just a reminder!


For example: SRB, low-mass Bino:• Acceptance ~20%• For background-free analysis, 95% CL is 3 events• 3/0.2 less than 15 events produced, or for 5 fb-1, < 3 fb

Assembling GGM Cross-section limits

Signal Acceptance (%)


And sure enough…

Derived GGM Cross-Section Limits


3 fb corresponds to production of ~1100 GeV gluino scale of limit

GGM Mass Limits

Choice of signal region (A or B) based on best expected limit (depends only on expectation from data-driven backgrounds and signal MC)


300 GeV (35%) limit increase from 1 fb-1 5 fb-1 (New signal regions, plus greater rejection of e fakes)

Gluino-bino and Squark-bino Mass Limits

Squark limits somewhat lower (lower cross-section)


• SPS8: Similar efficiency but higher background: < 5 fb-1

• NNLSP/NLSP scale 550/300 GeV• Hard to glean general sense from constrained model• 2012 analysis will include “EW grid” with Wino NNLSP and bino NLSP• Grid strategy developed with David Shih (Rutgers theory)• Optimization underway; will likely include to SRs (C,D) for high/low mass bino

SPS8 Limits and Electroweak Production


Single selection geared towards both EW and strong production

Make use of “transverse mass” (similar role to HT)

• High ET photon: ET > (100,85) GeV for (e,) channel

• Lepton with pT > 25 GeV

Photon + Lepton + MET Analysis


• Most backgrounds estimable from MC constrained by independent measurements (W, tt, tt, …).•Misreconstruction (jet,e ) plays smaller role• 15e, 11 channel events observed• 13e, 15 channel events expected

• BFs less favorable• Acceptance smaller (~5%)• Backgrounds higher Significantly weaker limits!

Photon + Lepton + MET Event Rates

Electron Channel

Muon Channel


Lepton + + MET Signal Region Distributions

Electron Channel Muon Channel

ElectroweakProduction

StrongProduction


Mi

Lepton + + MET Mass Limits (Wino NLSP)

ElectroweakProduction

StrongProduction


Wrap-up (Page 1)

Other two analyses still under development…• Photon + bjet + MET: Nearing completion for conference result• Photon + Njet + MET: Still exploring

Plan to have complete slate of analyses for 2012 analysis• Diphoton + MET: Moriond 2013, including EW grid (underway)• Photon + lepton + MET: Moriond 2013; multiple SRs• Photon + bjet + MET: Summer 2013• Photon + Njet + MET: Summer 2013


Naïve Projection for Diphoton + MET (25 fb-1 @ 8 TeV)

• 8 TeV / 7 TeV = 1.14 10% improvement in limit?• ~ M-8 x5 statistical gain 22% gain in limit?• Overall 30% gain in limit (???) would push gluino to ~1500 GeV and squarks to ~1250 GeV (seems a little optimistic?)

But clearly an interesting step forward.

For 14 (13?) TeV running

• Include c as third experimental parameter (along with production scale mass and NLSP mass)• ???

Wrap-Up (Page 2)


Back-Up


Mi

“


GGM (General GMSB): Diphoton Search

GGM and the Diphoton+ETmiss Analysis

Everything decoupled except• Gluino octet• Bino-like NLSP; B(0 G) ~ 1

Require two photons, ETmiss > 125 GeV

Observe: 5 eventsExpect: 4.1 0.6 (syst.) events

Mgluino > 805 GeV

for 50 < M0 < Mgluino

1 fb-1

Phys Lett. B 710 (2012), 519


Wrap-Up

Vibrant and expanding program of SUSY searches No discoveries claimed At 5 fb-1, colored sparticle limits above 1 TeV for some contexts Non-colored partner limits in 300-400 GeV range Increased consideration of “simplified” models (especially EW) Many analyses have yet to update to 5 fb-1

Speculation about 2012 reach (assume 20 fb-1 at s = 8 TeV) ~10% gain from increased s colored M-8 ~10% gain from statistics (background-limited)

• Somewhat better for EW production (not on PDF tails)• Ingenuity, “scale-chasing”

Guesstimate: ~25% increase in sensitive range (e.g. 1000 GeV limits increase to 1250 GeV if SUSY doesn’t exist at that scale)

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Searching for Supersymmetry with Final- State Photons at ATLAS