SUSY Discovery at 10TeV? SUSY working group meeting 21 st May 2008 Claire Gwenlan, UCL

Introduction 10 TeV run coming soon (2-3 months? 100 pb -1 possible?) Studies show that, if SUSY is relatively light, it could be discovered very early at the LHC (based on 14 TeV Monte Carlo) 2 EG: 0-lepton + 2-Jet + MET inclusive SUSY search (CSC5)  so what about at 10 TeV – could we hope to see something?

Currently no MC… BUT can re-weight existing 14 TeV samples hadronic cross section given by: hadronic cross section given by: For a particular kinematic configuration with s, t, u, should just need to change the probability that incoming partons *had* that configuration i.e. just a PDF re-weight PDFs  from 14TeV  10TeV proton PDFs Plot from James Stirling: DIS08 ^ ^ ^ ^ ^ ^ x i : x of parton i at 14TeV; x i ’: x of parton i at 10TeV Re-weight MC to 10 TeV using: 3 hard subprocess cross section

Check of Method Good agreement between re-weighted and 10 TeV samples (bkgs also checked) EG: sample of SU3 SUSY events generated in ATLFAST Effective Mass example weights (all < 1) 4 PDF weights p T Jet,1,2 >150,100 GeV M eff = p T Jet,1 + p T Jet,2 + MET [GeV] Good agreement between re-weighted and 10 TeV samples (bkgs also checked) method rather general  can re-weight to any CM energy < 14 TeV method rather general  can re-weight to any CM energy < 14 TeV

Check of Method Good agreement between re-weighted and 10 TeV samples (bkgs also checked) EG: sample of SU3 SUSY events generated in ATLFAST Effective Mass example weights (all < 1) 5 PDF weights p T Jet,1,2 >150,100 GeV M eff = p T Jet,1 + p T Jet,2 + MET [GeV] Good agreement between re-weighted and 10 TeV samples (bkgs also checked) method rather general  can re-weight to any CM energy < 14 TeV method rather general  can re-weight to any CM energy < 14 TeV

Cut No. 2  Jet + MET Analysis Cuts 0 J70_XE70 trigger 1 p T Jet,1 > 150 GeV 2 p T Jet,2 > 100 GeV 3 MET > max(100,0.3*M eff ) 4 |phi(Jet1,2)-phi(MET)| > no isolated lepton SUSY analysis “Generic search for R- parity conserving SUSY in the inclusive 2-Jet + MET+0- lepton channel” Effective Mass: M eff = ∑ p T Jet,i + MET [sum runs over two highest-p T jets] 6 EG: CSC5-style, inclusive 2- and 3-Jet analyses (full details in note) results shown in main part of talk are for the 2-Jet case (3-Jet results in backups) results shown in main part of talk are for the 2-Jet case (3-Jet results in backups) no optimisation of cuts for 10 TeV – i.e. just a simple repeat of CSC5 analysis

Results: SU3 vs. SM bkg Integrated L = 100 pb -1 BEFORE reweighting  EG: CSC5 2  Jet + MET + 0  lepton SUSY analysis: 7 NOTE: all MC predictions shown at LO (i.e. no k-factors applied)

Results: SU3 vs. SM bkg Integrated L = 100 pb -1 BEFORE reweighting  AFTER reweighting  14 TeV  10 TeV:  SU3 signal reduced by ~ 2.9  SM bkg reduced by ~ QCD reduced by ~ QCD reduced by ~ tt reduced by ~ tt reduced by ~ W/Z reduced by ~ 2 - W/Z reduced by ~ 2 - diboson reduced by ~ diboson reduced by ~ EG: CSC5 2  Jet + MET + 0  lepton SUSY analysis: NOTE: all MC predictions shown at LO (i.e. no k-factors applied)

Integrated L = 100 pb -1 Comparison of some other SUSY benchmark points (SUX) all are mSUGRA, but cover quite a wide range of phenomenologies all are mSUGRA, but cover quite a wide range of phenomenologiesSU1 coannihilation region SU2 focus point region SU3 bulk region SU4 low mass point SU6 funnel region SU8.1 coannihilation region Results: other mSUGRA points 9 EG: CSC5 2  Jet + MET + 0  lepton SUSY analysis:

Statistical Significance (S/√B) 14 TeV 10 TeV SU12312 SU2 < 1 SU33922 SU SU6168 SU82412 Statistical Significances 100 pb -1 Numbers are maximum significances (taken above some M eff threshold) 10

Discovery Significances 100 pb -1 Discovery Significance (Z n ) * 14 TeV 10 TeV SU SU2<1<1 SU SU SU SU * Z n is a measure of the significance (as used in CSC5) which tries to take into account systematic uncertainties on the bkg measurements. Numbers in the table are calculated assuming 50% uncertainty on QCD and 20% on all other bkgs – these are not the “right” numbers – dedicated bkg studies needed for those! 11 Numbers are maximum significances (taken above some M eff threshold) (don’t take too much notice of the actual values – it’s just to get a (very) rough feeling)

Summary Is there potential for discovery with small amounts of 10 TeV data?  YES – there does at least seem to be potential! A 5x increase in centre-of-mass energy compared to previous experiments is still a lot !!! – and the discovery of light SUSY may not need much data (it doesn’t take much to give large S/  B values for the models considered here) BUT that data still needs to be understood BUT that data still needs to be understood This was really just a quick look for fun – to see if anything is even potentially feasible! It looks like it could be, but the limiting factor will of course be how well we can determine and understand the backgrounds with the small amount of data we expect. 12 Bonus Extra – method could be useful to allow studies to proceed before 10 TeV MC available? Or as an alternative for samples that will not be re-generated?

BackUps

Integrated L = 100 pb -1 Results: other mSUGRA points 14Cut 3-Jet Analysis Cuts 0 J70_XE70 trigger 1 p T Jet,1 > 150 GeV 2 p T Jet,3 > 100 GeV 3 MET>max(100,0.25*M eff ) 4 |phi(Jet1,2,3)-phi(MET)| > no isolated lepton EG: CSC5 3  Jet + MET + 0  lepton SUSY analysis:

mSUGRA Points m0m1/2A0 tan  Region SU > 0 Coannihilation SU Focus point SU > 0 Bulk SU Low mass SU > 0 Funnel SU Coannihilation More details on the mSUGRA points considered 15

MC Bkg Samples Sample CSC ID  (pb) N T K TTbar K J4MET K J5MET K J6MET K J7MET K J8MET x K WW K WZ K ZZ K Zee K Zmumu K Ztautau K Znunu K Wenu K Wmunu K Wtaunu K 16

some other example checks  all show good agreement (within statistical limitations) Method: Some Bkg Checks CSCID: CSCID: CSCID: CSCID:

Some Bkg Weight Examples T1 Wenu Znunu WW Zee SU3 Weights for all processed events i.e. no cuts imposed J5MET J8MET SU4

Sensitivity to choice of Q 2 s, t, u are the usual Mandelstam variables Re-weighting technique not very sensitive to choice of factorisation scale M eff = p T Jet,1 + p T Jet,2 + MET [GeV]

EG. Re-weighting to Other  s Values M eff = p T Jet,1 + p T Jet,2 + MET [GeV] Should be able to re-weight to any CM energy < 14 TeV but *not* to higher beam energies, since some regions of phase space but *not* to higher beam energies, since some regions of phase space accessible at higher  s, will not be populated in the 14 TeV Monte Carlo 5 TeV 7 TeV

21 “Commissioning to 10 TeV should be fast, no quench being anticipated, giving us confidence that the experiments will be recording data at record high energies by the summer. In 1989, it was only a matter of weeks before LEP produced its first profound result – a measurement of the number of light neutrino families. In this respect at least, history will not be repeating itself. The LHC is a discovery machine, and the discoveries it is chasing will require a little more patience.” Robert Aymar, on the 10TeV run