1. Alan Barr 7 June 2007 What can we say about what we’ve found? Was it really SUSY? How can we discovery SUSY at LHC? Just find SM Higgs Alan Barr

2. 7 June 2007 Extended higgs sector (2 doublets) Your mission… SMSUSY quarks (L&R) leptons (L&R) neutrinos (L&?) squarks (L&R) sleptons (L&R) sneutrinos (L&?)  Z 0 W ± gluon BW0BW0 h0H0A0H±h0H0A0H± H0H±H0H± 4 x neutralino 2 x chargino After Mixing gluino Spin-1/2 Spin-1 Spin-0 Spin-1/2 Spin-0 Bino Wino 0 Wino ± gluino ~ ~

3. Alan Barr 7 June 2007 Features of R P SUSY? RPV as a conserved QN: Events build from blobs with 2 “exotic legs” A pair of cascade decays results Complicated end result RPV as a conserved QN: Events build from blobs with 2 “exotic legs” A pair of cascade decays results Complicated end result Time standard 2 exotics Production part Time standard heavy exotic lighter exotic Decay part Time Complete event = exotic = standard

4. Alan Barr 7 June 2007 General features “typical” susy spectrum (mSUGRA) Complicated cascade decays –Many intermediates Typical signal –Jets Squarks and Gluinos –Leptons Sleptons and weak gauginos –Missing energy Undetected LSP Model dependent –Various ways of transmitting SUSY breaking from a hidden sector LHC Pt5

5. Alan Barr 7 June 2007 What do we see? Lifetimes short -> look for Standard Model decay relics + missing energy

6. Alan Barr 7 June 2007 Example of a search topology SIGNAL topology q q _ squark q LSP q _ (and similar) BACKGROUND topology (QCD) No unique choice of sensitive topology –Complementary information/sensitivity Expect SM backgrounds with similar characteristics to signal –Need to search for excesses No unique choice of sensitive topology –Complementary information/sensitivity Expect SM backgrounds with similar characteristics to signal –Need to search for excesses

7. Alan Barr 7 June 2007 Practical Problems See only SM decay products –Expect short lifetimes Lose information about order of decays –Jets (other than b and t) indistinguishable Loose flavour information for other squarks “Missing momentum” from neutralinos only determined perpendicular to beam –Individual LSP momenta not individually measurable –Z-momentum of initial state unknown (PDFs) –Can’t reconstruct from final state Forward jets lost down beam pipe –Can’t form “invariant masses” of sparticles No “clean” mass peaks for resonances

8. Alan Barr 7 June 2007 Precise measurement of SM backgrounds: the problem SM backgrounds are not small There are uncertainties in –Cross sections –Kinematical distributions –Detector response Lower backgrounds Higher backgrounds “Rediscover” “Discover” ZZ WW

9. Alan Barr 7 June 2007 Just look for jets? Big QCD background Scalar sum of transverse energy / GeV

10. Alan Barr 7 June 2007 Add some missing energy Look for events with jets and missing energy Cuts  at least two jets with:  E T Jet1,2 > 150,100 GeV  |  Jet1,2 | < 2.5 Meff =  Jets p T i + MET But with addition of some other cuts…  Missing transverse momentum > 100 GeV  cuts based on   i = |  ( Jet,i )-  ( MET )|):  R 1 =  (  2 2 +(  -  1 ) 2 ) > 0.5 rad  R 2 =  (  1 2 + (  -  2 ) 2 ) > 0.5 rad  no jet with  i < 0.5 rad Kill events with missing energy from miss-measured jets QCD dijets “SUSY”

11. Alan Barr 7 June 2007 Two-Jet No M T2 Dijet cuts + MET +  Scalar sum of transverse energy / GeV Expect discovery distribution to be of something like this form: Excess of “some sort” of new physics about SM backgrounds.

12. Alan Barr 7 June 2007 Importance of detailed detector understanding 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 Lesson from the Tevatron Et(miss) Rare occurrences hurt

13. Alan Barr 7 June 2007 Inclusive reach in mSUGRA parameter space  Map of discovery potential corresponding to a 5σ excess above background in mSUGRA m 0 – m 1/2 parameter space for the ATLAS experiment. jets + E T miss channel L = 10 33 cm -2 s -1 ~1 year → ~2200 GeV ~1 month → ~1800 GeV few days (< one week) → ~1300 GeV Health warning: expecting SUSY discovery in a few days will seriously damage your credibility

14. Alan Barr 7 June 2007 Different searches We will be looking in many different channels –n jets + m leptons + missing energy –+- b-jets (common at large tan β) –+- tau-jets (“ “ “) –Charged stable particles –NLSP -> photon gravitino (GMSB) –R-parity violating modes –R-hadrons –…

15. Alan Barr 7 June 2007 What might we then know? 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 have mass ~ 600 GeV, with couplings similar to QCD M eff & 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 –…–… Slide based on Polesello

16. Alan Barr 7 June 2007 Mapping out the new world Some measurements make high demands on: –Statistics (=> time) –Understanding of detector –Clever experimental technique LHC Measurement SUSY Extra Dimensions Masses Breaking mechanism Geometry & scale Spins Distinguish from ED Distinguish from SUSY Mixings, Lifetimes Gauge unification? Dark matter candidate?

17. Alan Barr 7 June 2007 Constraining masses Mass constraints Invariant masses in pairs –Missing energy –Kinematic edges Observable:Depends on: Limits depend on angles between sparticle decays Frequently- studied decay chain

18. Alan Barr 7 June 2007 Mass determination Basic technique –Measure edges –Try with different SUSY points –Find likelihood of fitting data Event-by-event likelihood –In progress Measure edges Variety of edges/variables Try various masses in equations C.G. Lester Narrow bands in ΔM Wider in mass scale Improve using cross- section information

19. Alan Barr 7 June 2007 SUSY mass measurements Extracting parameters of interest –Difficult problem –Lots of competing channels –Can be difficult to disentangle –Ambiguities in interpretation –Lots of effort has been made to find good techniques Try various decay chains Look for sensitive variables (many of them) Extract masses

20. Alan Barr 7 June 2007 SUSY mass measurements: LHC clearly cannot fully constrain all parameters of mSUGRA –However it makes good constraints Particularly good at mass differences [ O (1%)] Not so good at mass scales [ O (10%) from direct measurements] Mass scale possibly best “measured” from cross- sections –Often have >1 interpretation What solution to end-point formula is relevant? Which neutralino was in this decay chain? What was the “chirality” of the slepton “ “ “ ? Was it a 2-body or 3-body decay?

21. Alan Barr 7 June 2007 SUSY spin measurements The defining property of supersymmetry –Distinguish from e.g. similar-looking Universal Extra Dimensions Difficult to measure @ LHC –No polarised beams –Missing energy –Indeterminate initial state from pp collision Nevertheless, we have some very good chances…

22. Alan Barr 7 June 2007 Measuring spins of particles Basic recipe: –Produce polarised particle –Look at angular distributions in its decay spin θ

23. Alan Barr 7 June 2007 Left Squarks -> strongly interacting -> large production -> chiral couplings mass/GeV Revisit “Typical” sparticle spectrum Some sparticles omitted  1 0 –> Stable -> weakly interacting Right slepton (selectron or smuon) -> Production/decay produce lepton -> chiral couplings LHC point 5  2 0 = neutralino 2 –> (mostly) partner of SM W 0  1 0 = neutralino 1 –> Stable -> weakly interacting Right slepton (selectron or smuon) -> Production/decay produce lepton -> chiral couplings

24. Alan Barr 7 June 2007 Spin projection factors Approximate SM particles as massless -> okay since m « p P S Chiral coupling

25. Alan Barr 7 June 2007 Spin projection factors Approximate SM particles as massless -> okay since m « p P S S Σ=0 Spin-0 Produces polarised neutralino

26. Alan Barr 7 June 2007 Spin projection factors Approximate SM particles as massless -> okay since m « p θ*θ* p S Scalar Fermion Polarised fermion

27. Alan Barr 7 June 2007 Spin projection factors Approximate SM particles as massless -> okay since m « p θ*θ* p S m ql – measure invariant mass P S

28. Alan Barr 7 June 2007 l near q invariant mass (1) m/m max = sin ½ θ* Back to back in  2 0 frame θ*θ* quark lepton Phase space -> factor of sin ½ θ* Spin projection factor in |M| 2 : l + q -> sin 2 ½ θ* l - q -> cos 2 ½ θ* l+l+ l-l- Phase space Probability Invariant mass

29. Alan Barr 7 June 2007 Production Asymmetry Twice as much squark as anti-squark pp collider  Good news! Squark Anti-squark Note opposite shapes in distributions

30. Alan Barr 7 June 2007 After detector simulation (ATLFAST) l+l+ l-l- Change in shape due to charge- blind cuts parton-level * 0.6 -> Charge asymmetry survives detector simulation -> Same shape as parton level (but with BG and smearing) detector-level Invariant mass Charge asymmetry, spin-0 Events  detector effects  cuts to greatly reduce SM SUSY

31. Alan Barr 7 June 2007 Interesting questions Can we test gaugino universality? –Can we constrain the neutralino mass mixing matrix? Can we measure sparticle splittings? –JMR: Htt coupling interesting Can we “predict”/confirm dark matter density? Can we measure mass scale to better than ~10% –Precision measurement/prediction for cross- sections? Can we confirm spin(s)?

32. Alan Barr 7 June 2007 Extras

33. Alan Barr 7 June 2007 Standard Model backgrounds: measure from LHC DATA Example: SUSY BG –Missing energy + jets from Z 0 to neutrinos –Measure in Z -> μμ –Use for Z -> Good match –Useful technique Statistics limited –Go on to use W => μ to improve   Measure in Z -> μμ Use in Z -> νν R: Z  B: Estimated R: Z  B: Estimated

34. Alan Barr 7 June 2007 W contribution to no-lepton BG Use visible leptons from W’s to estimate background to no-lepton SUSY search Oe, Okawa, Asai

35. Alan Barr 7 June 2007 Normalising not necessarily good enough Distributions are biased by lepton selection  Distributions are biased by lepton selection 

36. Alan Barr 7 June 2007 Need to isolate individual components…

37. Alan Barr 7 June 2007 Then possible to get it right… Similar story for other backgrounds – control needs careful selection

38. Alan Barr 7 June 2007 Direct slepton spin determination Spin important in slepton production –Occurs through s-channel spin-1 process only –Characteristic angular distribution in production q q _ e+e+ e-e- Z/γ e+e+ e-e- ~ ~ l-l- l+l+ θ*θ* qq _ ~ ~

39. Alan Barr 7 June 2007 Distributions @ parton level black=SUSY Parallel Perpendicular to beam Spin-0 –SUSY –Sleptons –“perpendicular” to beam Spin-½ –UED –KK leptons –“parallel” to beam l-l- l+l+ θ qq _ ~ ~ red=UED blue=PS σ total not to scale

40. Alan Barr 7 June 2007 Sensitive variables? cos θ lab –Good for linear collider –Not boost invariant Missing energy means Z boost not known @ LHC Not sensitive @ LHC Δη –Boost invariant –Sensitive –Not easy to compare with theory cos θ ll * –1-D function of Δη: –All benefits of Δη –Interpretation as angle in boosted frame –Easier to compare with theory l1l1 l2l2 θ 2 lab θ 1 lab l1l1 l2l2 η 2 lab η 1 lab Δη l1l1 l2l2 θl*θl* θl*θl* (A) (B) (C) N.B. ignores azimuthal angle boost

41. Alan Barr 7 June 2007 “Data” = inclusive SUSY after cuts “SPS5” point –Below: spectrum –Right: results –Good stat. discrimination Some results