Early SUSY discoveryAlan Barr

Claire Gwenlan

29th February 2007UK SUSY/Exotics

How to best use early data• poor knowledge of multi-jet backgrounds• incomplete measurement of other backgrounds• limited detector understanding

How to best use early data• poor knowledge of multi-jet backgrounds• incomplete measurement of other backgrounds• limited detector understanding

We wont be able to find SUSY quickly in the “16 jets + 4 leptons” channel!We wont be able to find SUSY quickly in the “16 jets + 4 leptons” channel!

Robust topologies

SIGNAL topology

q

q_

squarkq

LSP

q_

LSP(and similar)

BACKGROUND topology(QCD)

Small Njets + ET

• Select a small number of high PT jets– Large signal cross-section– Large control statistics– Relatively well known SM backgrounds

• Relatively model independent– Does not rely on leptonic cascades– Does not rely on hadronic cascades

• Use kinematics rather than “busyness of event” to pick out SUSY

Selection• Keep it simple

– Two jets

– ET (J1,2) > 150 GeV; |η1,2| < 2.5

– Plot MT2

– N.B. MT2 → 0 if:• ET → 0

• ET parallel to either jet

• Jet ET → 0

Characteristics of backgrounds

)2(j(2)TT

)1(j(1)TT

T)2()1(T2 ,,,max

minpppp

ppp

mmM

J.Phys.G29:2343-2363,2003, Phys.Lett.B463:99-103,1999

Sample discrimination

1 fb-1 !1 fb-1 !

Full sim CSC AODsFull sim CSC AODs

Requirements

• Need:– Some understanding of ET and energy scale

• Degree needs to be determined

– Some lepton ID• Estimate Z→νν from Z→ μμ

– Some idea of ttbar background

• Do not need:– B-tagging– Detailed understanding of jet resolution tails– Missing ET tails from multi-jets– To know much about loss of energy in cracks etc

Summary & next steps

• Idea– Use simple topology for rapid discovery of light

sparticles– 2 jets + missing energy– Kinematic plot of MT2 gives good discrimination– Backgrounds under control– Excellent prospects if SUSY is light

• Next:– QCD background from Alpgen (rather than

Pythia)– Trigger– Backgrounds from control regions

Backups

Samples

• CSC 11.0.x AODs (Full Simulation)

SUSY (SU3): 5403 herwig (+jimmy)Jets (J1-J8): 5010->5017 pythiattbar (no all-hadronic): 5200 MC@NLO (+jimmy)ttbar (only all-hadronic): 5204 MC@NLO (+jimmy)Zee : 5152 MC@NLOZmumu: 5151 MC@NLOWenu: 5100 herwig (+jimmy)

More to add when R12 AODs available…