1 the LHC Jet & MET Searches Adam Avakian PY898 - Special Topics in LHC Physics 3/23/2009

2 Overview SUSY summary Production and Decay Modes Dijet CMS

3 The Standard Model L = L gauge + L matter + L Yukawa + L higgs 19 parameters total (masses, couplings, etc.) Describes nearly all accelerator data Still leaves plenty of mysteries

4 Symbol Description Value m e Electron mass 511 keV m μ Muon mass 106 MeV m τ Tauon mass 1.78 GeV m u Up quark mass1.9 MeV m d Down quark mass 4.4 MeV m s Strange quark mass87 MeV m c Charm quark mass 1.32 GeV m b Bottom quark mass 4.24 GeV m t Top quark mass172.7 GeV θ 12 CKM 12-mixing angle θ 23 CKM 23-mixing angle θ 13 CKM 13-mixing angle δ CKM CP-violating Phase g 1 U(1) gauge coupling g 2 SU(2) gauge coupling g 3 SU(3) gauge coupling θ QCD QCD Vacuum Angle ~0 μ Higgs quadratic coupling Unknown λ Higgs self-coupling strength Unknown Parameters of the Standard Model

5 What’s wrong with the Standard Model? It fails to explain: –Neutrino masses and mixing angles –Baryogenesis –Dark Matter –Dark Energy

6 SUSY (SUperSYmmetry) “Standard way beyond the Standard Model” - Altarelli & Feruglio Spacetime symmetry (“square root” of a translation) Stable theory from M weak (10 3 GeV) to M GUT (10 16 GeV) New “superpartner” particles MSSM (Minimal Supersymmetric SM) is the simplest SUSY extension to SM

7 MSSM (Minimal Supersymmetric SM) Construct Lagrangian that changes only by total derivative under SUSY (action is invariant) Add all “soft SUSY breaking” terms –Same physics at UV, symm. broken in IR Minimal extension has 124 parameters instead of 19 now!

8 More SUSY models mSUGRA (minimal SUperGRAvity) –5 basic parameters (m 0, m 1/2, A 0, tan , sign(  )) determine phenomenology at LHC scale GMSB (Gauge-Mediated Symmetry Breaking) AMSB (Anomaly-Mediated Symmetry Breaking) etc.

9 Mass Spectra under mSUGRA Note that all scalar masses converge and all spin 1/2 masses converge

10 Superpartners Each SM particle has a superpartner New conserved charge/quantum number Naming conventions for “sparticles”: –Fermions: prepend with “s”, e.g. squark –Bosons: add “-ino” suffix, e.g. gluino –  Spin = Spin § 1/2

11 List of sparticles

12 Where are the sparticles? Produced at higher energy scales than previous colliders have achieved Lightest Supersymmetric Particle (LSP) is stable and must be weakly interacting –mSUGRA: bino/wino/higgsino/gravitino? –GMBS: gravitino –AMSB: wino It would be a strong candidate for Dark Matter WIMP

13 LSP (Lightest Supersymmetric Particle) If LSP is weakly interacting, how can we produce and observe such particles? - Indirectly! Higher energy sparticles need not be weakly interacting They can be produced in sparticle/anti-sparticle pairs and decay to LSP LSP is observed indirectly as an MET signature

14 SUSY Events We always expect MET from LSPs The other particles produced in the sparticle decays may hadrons, leptons, etc. Events generally classified based on the number of leptons produced

15 SUSY Candidate Event M. Spiropulu [Eur. Phys. J. C (2009) 59: 445–462]

16 Gluino Pair Production

17 Squark Pair Production

18 Squark-Gluino Associated Production

19 Sparticle Production Cross-Sections and dominate SUSY signatures at LHC if 1 TeV

20 Sparticle Production Tevatron LHC

21 Gluino Decay Modes

22 Squark Decay Modes

23 Gluino Decays

24 Particle Cascade Decays Ultimately, we expect something more like this Run MC simulations (ISAJET, PYTHIA) for multiple points in parameter space and try to match the LHC data

25 Sample LHC SUSY Event Source: Baer

26 Rough Estimate of squark/gluino masses from M eff ATLAS TDR (F. Paige) M eff = MET + E(jet 1 ) + E(jet 2 ) + … + E(jet n )

27 Missing MET & H T distributions M. Spiropulu [Eur. Phys. J. C (2009) 59: 445–462]

28 Dijet Event CMS Works best in parameter space squarks have large branching decay to LSP

29 –2 jets + MET –Search for events with exactly two jets above certain threshold –Require minimum MET Dijet Event Process

30 Dijet Background QCD dijet events (MET due to mismeasurement, cracks, etc.) Z + Jet (Z  )

31 Dijet Event Preselection Cuts

32 Dijet Event -  cut CMS Collaboration [CMS PAS SUS ]  < 2  /3 cuts out almost the entire QCD background

33 New variables for cuts: ,  T

34 Dijet Event Search CMS Collaboration [CMS PAS SUS ]

35 The additional cuts M eff > 500 GeV  < 2  /3  or  T > 0.55

36 Dijet Event Search CMS Collaboration [CMS PAS SUS ]

37 Prospects for the LHC Center-of-mass energy = 14 TeV Should be able to produce sparticles at a rate high enough to determine signal over background We may see sparticles for the first time!

38 LHC Reach vs. earlier experiments Baer, Belyaev, Krupovnickas, Tata: JHEP 0402, 007 (2004)

39 Reach of LHC at fb Baer, Balasz, Belyaev, Krupovnickas, Tata: JHEP 0306, 054 (2003)

40 Reach of CMS for various Integrated Luminosities We’re maybe just a couple of years from seeing evidence of SUSY!

41 Conclusion If SUSY exists and squarks and gluinos have a mass under 3 TeV, then we should be able to see evidence within of few years of taking data at the LHC If they have a mass of about 1 TeV, then we should see them much sooner, possibly in the dijet signature