Discovering and Exploring the New World SUSY Searches with ATLAS Alan Barr, UCL

Signature-based hunts Astro/cosmo motivation for model-independent signatures We’re pretty sure there are WIMPs out there LHC produces Dark Matter + something visible Invisible particle could be: Lightest SUSY particle Lightest KK particle Lightest generic parity-odd particle Signature: Missing energy + Xvis + Xvis Benefit: Same search finds multiple different models Drawback: You ain’t so sure what you’ve got when you find it

(S)particles SM SUSY quarks (L&R) leptons (L&R) neutrinos (L&?) squarks (L&R) sleptons (L&R) sneutrinos (L&?) Spin-1/2 Spin-0 After Mixing  Z0 W± gluon B W0 Bino Wino0 Wino± gluino Spin-1 4 x neutralino Spin-1/2 gluino h0 H0 A0 H± ~ H0 H± ~ 2 x chargino Spin-0 Extended higgs sector (2 doublets)

SUSY Dark Matter mSUGRA A0=0, tan(b) = 10, m>0 Slepton Co-annihilation region: LSP ~ pure Bino. Small slepton-LSP mass difference makes measurements difficult. 'Focus point' region: significant h component to LSP enhances annihilation to gauge bosons ~ Ellis et al. hep-ph/0303043 Disfavoured by BR (b  s) = (3.2  0.5)  10-4 (CLEO, BELLE) c01 t1 t g/Z/h ~ 'Bulk' region: t-channel slepton exchange - LSP mostly Bino. 'Bread and Butter' region for LHC Expts. c01 l lR ~ Also 'rapid annihilation funnel' at Higgs pole at high tan(b), stop co-annihilation region at large A0 0.094    h2  0.129 (WMAP)

Example SUSY spectrum Assume R-parity “Standard search” Look for: Mass (GeV) Assume R-parity “Standard search” Look for: Jets from squark & gluino decays Leptons from gaugino & slepton decays Missing energy from (stable) LSPs Enhanced taus at large tan beta Enhanced b-jets at large tan beta “Typical” SUSY spectrum

An Event

Lots of channels to look at Below the lines = discovered Different final states CMS Physics TDR vol II makes good reading!

https://twiki.cern.ch/twiki/bin/view/Atlas/CscSusyNotes Where are we now? https://twiki.cern.ch/twiki/bin/view/Atlas/CscSusyNotes SUSY1: Data-driven Estimation of Z/W backgrounds to SUSY SUSY2: Data-driven Estimation of top Backgrounds to SUSY SUSY3: Data-driven Estimation of QCD Backgrounds to SUSY SUSY4: Estimation of Heavy Flavor backgrounds and associated systematic SUSY5: Searches and inclusive studies for SUSY events SUSY6: Exclusive measurements for SUSY events SUSY7: Gaugino direct productions SUSY8: Studies for Gauge mediated SUSY Reconstruction Detector response Model backgrounds Measure backgrounds

Importance of detailed detector understanding Et(miss) Lesson from the Tevatron GEANT simulation already shows events with large missing energy Jets falling in “crack” region Calorimeter punch-through Vital to remove these in missing energy tails Large effort in physics commissioning

First landfall? Inclusive distributions Trigger on jets + missing energy Plot “effective mass” Look for non-SM physics at high mass Signal BG

Precise measurement of SM backgrounds: the problem SM backgrounds are not small There are uncertainties in Cross sections Kinematical distributions Detector response

Standard Model backgrounds: measure from LHC DATA Measure in Z -> μμ Use in Z -> νν R: Z -> nn B: Estimated Example: SUSY BG Missing energy + jets from Z0 to neutrinos Measure in Z -> μμ Use for Z ->  Good match Useful technique Statistics limited Go on to use W => μ to improve

Observation on measuring backgrounds “from the data”

Independent variables?

It’s not just ETMiss! Potential large object reco systematics in busy environment Jet reconstruction Lepton isolation B-jet efficiencies Tau reconstruction Jet veto for gauginos … Trigger We need to measure these separately TTbar is “nearest thing” in many cases

Triggers? Pb-1 Recall that we are interested in only one event in a billion

R-hadrons in detectors Signatures: High energy tracks (charged hadrons) High ionisation in tracker (slow, charged) Characteristic energy deposition in calorimeters Large time-of-flight (muon chambers) Charge may flip Trigger: Calorimeter: etsum or etmiss Time-of-flight in muon system Overall high selection efficiency Reach up to mass of 1.8 TeV at 30 fb-1 GEANT simulation of pair of R-hadrons (gluino pair production)

GMSB: non-pointing g event h cluster (1st layer – IP) h rec poiting (egamma obj) g G ~ c01 ~

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What might we have found out? Assume we have MSSM-like SUSY with m(squark)~m(gluino)~600 GeV See excesses in these distributions Can’t say “we have discovered SUSY” Can say some things: Undetected particles produced missing energy Some particles mass ~ 600 GeV, couplings similar to QCD Meff & cross-section Some of the particles are coloured jets Some of the particles are Majorana excess of like-sign lepton pairs Lepton flavour ~ conserved in first two generations e vs mu numbers Possibly Yukawa-like couplings excess of third generation Some particles contain lepton quantum numbers opposite sign, same family dileptons … Fun for later! Slide based on Giacomo’s

Imperatives Concentrate on: CSC notes! Understanding the systematics Detector, trigger, reconstruction Measuring the backgrounds Many to consider Optimising the search strategies Power + credibility! Exercising your sea-legs CSC notes!

Told you we’d find India!

Some sources CMS Physics TDR, Volume II (recent) CERN-LHCC-2006-021 ATLAS Physics TDR (older) CERN-LHCC-99-015 Physics at the LHC 2006 Programme SLAC School 06 Polesello, Hinchliffe SUSY06 Polesello, Spiropulu Missing ET tails: Paige SM background Okawa et al, WMAP constraints Ellis et al SUSY mass extraction Gjelsten et al SUSY Spin: Barr Exotic SUSY Parker Dark Matter Nojiri et al R-hadrons Kraan et al Hellman et al WW scattering Stefanidis GMSB Zalewski, Prieur RS Graviton: Allanach et al, Traczyk Black Holes Charybdis, Tanaka, Brett, Lester Stephanidis

Extra rations

SUSY mass scale

SUSY mass measurements Try various decay chains Extracting parameters of interest Difficult problem Lots of competing channels Can be difficult to disentangle Ambiguities in interpretation Experiments have been studying this for ~ a decade Lots of effort has been made to find good techniques Look for sensitive variables (many of them) Extract masses

SUSY production cross-sections

Constraining masses with cross-section information edges inclusive cross-section ptmiss > 500 combined Combine with Markov Chain MC Edges best for mass differences Formulae contain differences in m2 Overall mass- scale hard at LHC Cross-section changes rapidly with mass scale Use inclusive variables to constrain mass scale E.g. >500 GeV ptmiss Lester, Parker, White hep-ph/0508143

Focus point Lari et al Heavy Scalars Light gluino, gaugino 300 fb-1

More on GMSB Negligible contribution from the SM backgrounds (consistent with TDR)  Trigger efficiencies of the signal is crucial for the discovery potential (background rejection, rate estimates would be the next step) G1a (L=90TeV) G1a (L=90TeV) <After Requiring> Meff > 400GeV EtMiss>0.1Meff two leptons BG Total BG Total g1 g2 Leading Photon Pt (GeV) 2nd Leading Photon Pt (GeV)

Baryonic R-Parity Violation Decay via allowed where m( ) > m( ) Use extra information from leptons to decrease background. Sequential decay of to through and producing Opposite Sign, Same Family (OSSF) leptons Test point

Leptonic R-Parity Violation RPV has less missing Et Neutralino -> stau tau stau -> tau mu qq Large rate of taus - smoking gun Stau LSP Phillips

Light stops Lari, Polesello Stop pair production: 412 pb (PROSPINO, NLO) Dominant (~100%) stop decay: t → c+ b → c01 W* b Final state is very similar to top pair production events. 4 jets, 2 of which b-jets, one isolated lepton, missing energy All of them softer (on average) than in top pair production Invariant mass combinations will not check out with top, W masses Lari, Polesello M(bjj) 1.8 fb-1 M(bl) 1.8 fb-1 GeV GeV Points: simulated data Histograms: signal events (MC truth)