What prospects for Supersymmetry at the Large Hadron Collider ?

1. What prospects for Supersymmetry at the Large Hadron Collider ? Some of the techniques with which ATLAS and CMS intend to constrain Supersymmetry Christopher.Lester @ cern.ch

2. What are we going to cover? • Not a results talk! (WMAP etc) • Briefly look at supersymmetry • Look at RPV / RPC distinction from point of view of experiment • In no partiular order: look at a few • inclusive/widely applicable experimental techniques, also • less general but perhaps more powerful experimental techniques HCP2005 : SUSY at the LHC : Christopher.Lester@cern.ch

3. Supersymmetry – Extra particles • To stabilise the higgs mass NEED: • A scalar partner for every fermion • squark, slepton, (stop, sbottom, selectron, smuon, sneutrino, etc) • A fermion partner for ever boson: • gluino, • photino, wino, zino, higgsino • (mix to form 4 neutralinos) • Inexact symmetry – broken somehow HCP2005 : SUSY at the LHC : Christopher.Lester@cern.ch

4. Two main SUSY scenarios: (RPV/RPC) RP-Conserving RP-Violating R-Parity: Conservation/Violation • R=+1 for Standard Model particles • R= -1 for SUSY particles (L.S.P. = “lightest SUSY particle”) HCP2005 : SUSY at the LHC : Christopher.Lester@cern.ch

5. What do events look like? RPV RPV (Lepton number violating) (Baryon number violating) RPC RPC

6. So main signatures are: • Lots of jets • Lots of leptons • Lots of missing energy (RPC) • More on these a little later • ATLAS Trigger: ETmiss > 70 GeV, 1 jet>80 GeV. (or 4 lower energy jets). Gives 20Hz @ low luminosity. HCP2005 : SUSY at the LHC : Christopher.Lester@cern.ch

7. M.S.S.M. Squark masses (12) The gluino mass (1) Slepton masses (9) Neutralino masses (4) Chargino masses (2) Spins (?) Mixing matrices (?) Phases (?) ….. (plenty) Other models: RP-Violating M.S.S.M. RPV couplings (45) mSUGRA model m0, m1/2, A0, tan β, sgn μ (5) A.M.S.B. model m0, m3/2, tan β, sgn μ (4) G.M.S.B. model λ, Mmes, N5, tan β, sgn μ, Cgrav (6) What do we want to know? There is no shortage of parameters which need to be determined! HCP2005 : SUSY at the LHC : Christopher.Lester@cern.ch

8. The kinds of measurements which can be made, very much depend on the SUSY model which nature has chosen! Two very different approaches: (1) General techniques (2) Non general .. specific techniques Look at some specific RPV scenarios first What can we measure? “Lots, but it depends…” HCP2005 : SUSY at the LHC : Christopher.Lester@cern.ch

9. R-Parity Violation RPV L.S.P. = lightest SUSY particle • Easier than RPC? • The L.S.P. decays! • No missing energy, so reconstruct full event! • Case 1: Decays into leptons: • Multi-lepton signature • Case 2: Decays into jets: • Multi-jet signature • Case 3: Long lifetime: • looks like RPC scenario • Sparticles may be produced singly! HCP2005 : SUSY at the LHC : Christopher.Lester@cern.ch

10. Case 1: Lepton number violating RPV λ’ijk couples a slepton to two quarks Can have resonant sneutrino production Cross section can place lower bound on λ’ijk Expect to observe (within 3 years) either 900 GeV sneutrino if λ’211>0.05 350 GeV sneutrino if λ’211>0.01 (present limit: ) Reconstructed neutralino mass peak in mjjμ invariant mass distribution λ’ijk =0.09 HCP2005 : SUSY at the LHC : Christopher.Lester@cern.ch

11. Case 2: Baryon number violating RPV • Each L.S.P. decays to three quarks (u,d,s) forming three jets (jjj) • Require 2 leptons and at least 8 jets: (j+jjj)+(j+ll+jjj) • Look for L.S.P. / chargino peak in mjjj / m jjjll plane msquark L = 638 ± 5 ±12 GeV mneutralino 2 = 212 ± 0.3 ± 4 GeV mslepton R = 155 ± 3 ± 3 GeV mneutralino 1 = 117 ± 3 ± 3 GeV HCP2005 : SUSY at the LHC : Christopher.Lester@cern.ch

12. R-Parity Conservation RPC L.S.P. = lightest SUSY particle • L.S.P. stable and weakly interacting, and so “goes missing” • Missing energy signature • Usually incomplete event reconstruction • Need to rely on long decay chains and kinematic variables (endpoints and distributions) • Sparticles are only produced in pairs • Double the trouble  • Missing information in BOTH halves of event!  • More general techniques available! Half an event HCP2005 : SUSY at the LHC : Christopher.Lester@cern.ch

13. Inclusive reach in mSUGRARPC CMS 100 fb-1 (~3 years) (Slide stolen from G.Polesello – SUSY2004) HCP2005 : SUSY at the LHC : Christopher.Lester@cern.ch

14. events Signal S.M. Background Squark/gluon mass scale RPC What you measure: Peak of Meff distribution correlates well with SUSY scale “as defined above” for mSUGRA and GMSB models. (Tovey)

15. Kinematic edges: l+l-edge RPC • EXAMPLE: • l+l-edge • The l+l- invariant mass from the decay chain (right) has akinematic endpoint. • For 100 fb-1, edge measured at 109.10±0.13(stat) GeV • Dominant systematic error on lepton energy scale also ~0.1% • Maximum dilepton invariant mass is related to sparticle masses HCP2005 : SUSY at the LHC : Christopher.Lester@cern.ch

16. Plenty of other kinematic endpoints! RPC Sequential Branched HCP2005 : SUSY at the LHC : Christopher.Lester@cern.ch

17. Edge positions

18. Fitted distributions ll llq ll llq S5 lq high lq low lq high lq low O1 llq Xq llq Xq

19. Endpoint structure … What different invariant mass distributions look like for a selection of plausible supersymmetric models. ( hep-ph/0410303 ) Note that some edges are not simple! HCP2005 : SUSY at the LHC : Christopher.Lester@cern.ch

20. Coverage of edges / Problems RPC However ... … different processes can produce the same final state. • Can the process be identified? • Detailed study of the shape of the distributionscan provide clues • Likely coverage? • Lepton edge observable over significant region of m0, m1/2 parameter space (CMS plot left) • See also hep-ph/0410303 and hep-ph/0501033 for more detailed analysis • Likely outcome? • Precise sparticle mass differences – 1% if lucky with which chains are open • When chains are long enough, resolution on absolute mass scale improves and can measure mass of L.S.P. HCP2005 : SUSY at the LHC : Christopher.Lester@cern.ch

21. The sort of measurement you get HCP2005 : SUSY at the LHC : Christopher.Lester@cern.ch

22. Measuring spins in SUSY hep-ph/0405052 • pp-collider! • Protons have more quarks than antiquarks • So LHC will make more squarks than antisquarks! • Spin-1/2 neutralino can tell the difference between: • q+l or qbar+lbar, and • q+lbar or qbar+l • Look for asymmetry between 1. and 2. • Asymmetry not washed out (completely) by lepton ambiguity! 5 years’ data 500 fb-1 1.5 years data (HL) 150 fb-1 HCP2005 : SUSY at the LHC : Christopher.Lester@cern.ch

23. Non-edge RPC methods • For LONG enough decay chains (4 or more 2-body decays) kinematics of decaying system are over-constrained by observed momenta • So can determine masses from small sample of events • O(N) events needed to determine N unknown masses • “Mass Relation Method” -- proof of principle using 1000 events (hep-ph/0402295) For LONG decay chains. At least 4 decays. Mass relation method HCP2005 : SUSY at the LHC : Christopher.Lester@cern.ch

24. mother (0 to 1000 GeV) mneutralino (0 to 600 GeV) Mass Relation Method Results Gluino Squark Neutralino2 Slepton Very good measurements of mass differences < 1% Correlations still make overall mass scale hard to determine, without input from LC or say some other independent LHC technique Reconstructed sparticle masses as function of reconstructed LSP mass HCP2005 : SUSY at the LHC : Christopher.Lester@cern.ch

25. Putting it all together! • Want to make fewer model assumptions • Huge parameter spaces / model spaces need to be explored • Have large number of different measurements we can make • Need Markov Chain techniques to explore likelihood surfaces efficiently HCP2005 : SUSY at the LHC : Christopher.Lester@cern.ch

26. Exploring non-linear experimental constraints upon susy model spaces HCP2005 : SUSY at the LHC : Christopher.Lester@cern.ch

27. LHC & Supersymmetry • What can the LHC provide if SUSY exists? • DISCOVERY ? ………………………………. YES! • Excellent prospects • Might even be “easy” ! • Largely model-independent • PRECISE MEASUREMENTS ? …….... Plenty! • but more likely to be model-dependent HCP2005 : SUSY at the LHC : Christopher.Lester@cern.ch

28. We can expect ATLAS and CMS to Observe squarks and gluons below 2.5 TeV andobserve sleptons below 300 GeV in inclusive measurements. Accurately measure squark, slepton and neutralino masses using cascade decays (provided chains are sufficiently long and rates are favourable) Determine spin of neutralinos Success is expected in both RPV and RPC scenarios Precise measurements: many can be made in principle, but which of them can measured in practice will depend strongly on the model which nature has chosen Other areas of completed and ongoing research which there was not time to discuss: N.L.S.P. lifetime in G.M.S.B. models (Non-pointing photons / slow heavy leptons) A.M.S.B. models Lepton flavour violation (via slepton mixing) Measuring the gaugino mixing matrix Direct slepton production Non-minimal models SUSY Higgs sector Everything else which I have forgotten to mention ... CMS The End HCP2005 : SUSY at the LHC : Christopher.Lester@cern.ch

29. Missing energy – early reachRPC ATLAS (Slide stolen from G.Polesello – SUSY2004)

30. Cross sections and rates HCP2005 : SUSY at the LHC : Christopher.Lester@cern.ch