David Futyan Moriond QCD and Hadronic Interactions

1

Moriond QCD and Hadronic Interactions, La Thuile,
Italy, 17th March 2005
First Detailed Study on the SUSY Discovery
Potential at CMS using Two Same Sign Muons in
the mSUGRA Model
David Futyan University of California, Riverside,
USA
Principal contributors Alexey Drozdetskiy, Darin
Acosta, Guenakh Mitselmakher University of
Florida, Gainesville, USA
2
Introduction

• Inclusive search within framework of the mSUGRA
  model
• Aim is to determine reach within mSUGRA parameter
  space for potential discovery of supersymmetry
  soon after LHC start-up (?L10fb-1)
• Use same sign muon signature
• First detailed look

3
mSUGRA parameter space

• mSUGRA is a popular simplification of the MSSM
  (GUT sub-model)
• Only 5 free parameters (m0, m1/2, tanß, A0,
  sign(µ))

A0 0,
J.Ellis et al., hep-ph/0303043
4
SUSY points considered in this study
m0
18
4,6,8,10,11,19,20
17
16
15
9
7
14
13
2
12
3
5
1
m1/2

• Updated post-WMAP benchmark points
• (hep-ph/0306219) - with modification
• More points
• (calculated by A.Birkedal (Cornell), K.Matchev
  (UF))
• Six of the points (high mass) are found to have
  negligible cross-sections

5
Signature choice

• For this study the "2 Same Sign Muons" signature
  was chosen, based on
• Theoretical studies for Tevatron
• hep-ph/9904282, "Supersymmetry Reach of the
  Tevatron via Trilepton, Like-Sign Dilepton and
  Dilepton plus Tau Jet Signatures", K.T.Matchev,
  D.M.Pierce
• Simple, very clean signature
• High trigger efficiency
• Reduced number of background events/processes in
  comparison to "multi-jets only" signatures

6
Analysis overview
7
Tools

• Calculation of coupling constants, cross sections
  for SUSY processes ISAJET
• http//www.phy.bnl.gov/isajet/
• Calculation of NLO corrections for SUSY
  processes PROSPINO
• hep-ph/9611232
• Event generation CompHEP (Z/?bB, Single-top
  processes), PYTHIA (SUSY, tt, ZZ, ZW, WW)
• hep-ph/9908288 (CompHEP)
• http//www.thep.lu.se/torbjorn/Pythia.html
• Full CMS detector simulation was used in this
  study CMSIM, ORCA
• http//cmsdoc.cern.ch/cmsim/cmsim.html
• http//cmsdoc.cern.ch/cmsreco/

8
Cross sections, number of events SM processes

• Other processes considered at generator level
  only (CompHEP)
• Estimate of preselected events based on s.BR

main contribution into background

• Notations
• N1 total number of expected events for integral
  luminosity of 10fb-1
• N2 number of events after pre-selection (two
  same sign muons, each with PTgt10 GeV,
  hlt2.5)

9
Cross sections, number of events SUSY processes

• Notations
• N1 total number of expected events for integral
  luminosity of 10fb-1
• N2 number of events after pre-selection (two
  same sign muons, PTgt10 GeV)
• Significance,
  (S.I.Bityukov,N.V.Krasnikov)
• S/B ratio

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Example signal and background processes

• Signal
  Background
• Cut variables
• Missing ET
• Jet ET
• Muon PT, Muon impact parameter
• Plus Muon isolation, Muon ?, Jet ?, Number of
  jets/muons,

11
Event kinematics (example)

• SUSY point (3)
• m0149 GeV, m1/2700 GeV, tanß 10, A0 0,
  signµ gt 0

12
Analysis cuts

• For the chosen cut variables, a set of values was
  chosen for optimization
• Missing ET 0, 100, 150, 200, 250, 400, 500 GeV
• ETjet1 0, 70, 100, 200, 300, 400 GeV
• ETjet3 0, 30, 50, 80, 100, 170, 250 GeV
• PTµ1 10, 20, 30, 60, 100, 150 GeV/c
• PTµ2 10, 15, 20, 50, 80 GeV/c
• IPµmin N/A, 0.005, 0.0015, 0.0005 cm
• IPµmax N/A, 0.1, 0.03, 0.01, 0.005 cm
• For each possible combination of the above cuts
• Values of Significance, S/B and expected no. of
  events (NFinal) for 10 fb-1 are calculated
• Total of about 176,000 combinations
• Final sets of cuts selected through an iterative
  optimization procedure

13
Illustration of cut optimization procedure

• Plot Significance for all sets of cuts
• Then choose an "optimal" region several
  iterations
• Finally, choose a particular set

14
Analysis cuts

• Two sets of cuts chosen which have high
  significance and S/B for all SUSY points
• Set 1
• Missing ET gt 200 GeV,
• ETjet3 gt 170 GeV,
• PTµ1 gt 20 GeV
• Set 2
• Missing ET gt 100 GeV,
• ETjet1 gt 300 GeV,
• ETjet3 gt 100 GeV
• These cuts are applied in addition to the
  "signature cut"
• 2 same sign muons, both with PT gt 10 GeV
• Results were obtained for all SUSY points for
  each of the above sets of cuts

15
Results cut set 2

• Monte Carlo statistical errors shown for number
  of events after all cuts (N final)
• All final events accepted by L1 and HLT
• L1 single µ with PTgt14 GeV, di-µ with PT gt 3 GeV
• HLT di-µ with PTgt7 GeV

16
Results significance

• Total number of points out of reach (Significance
  lt 5) for 10 fb-1
• 9 for cut set 1
• 10 for cut set 2
• Remainder are potential "discovery points" for 10
  fb-1 of integrated luminosity
• Significance gt 5
• S/B gt 0.4 (excess of 40 or more over expected
  number of SM events)

17
Results sensitive area at 10 fb-1
m0
m1/2

• Many points will be visible with ?Lltlt10 fb-1
• Significance for many points gtgt 5 for ?L10 fb-1

18
First estimate of systematic effects

• To estimate the stability of the results, the
  effect of varying the no. of SM and SUSY events
  was investigated
• Apply simultaneously
• 30 decrease in no. of SUSY events
• 30 increase in no. of SM events
• Only one background process survives after all
  cuts
• Precision to which cross-section is expected to
  be known for this process (including theoretical
  systematics) is about 10
• Only one "SUSY discovery" point (13) goes out of
  reach

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Summary

• Study performed based on the mSUGRA model
• tanß10,20,35, sign(µ)gt0, A00
• Full detailed simulation, trigger emulation and
  reconstruction was used
• Excess of mSUGRA events over SM processes is
  statistically significant for many benchmark
  points for ?Lltlt10fb-1
• up to 600 GeV in m1/2 and at least up to 1600 GeV
  in m0
• Results are optimistic for SUSY discovery

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Prospects

• Further optimization
• Investigation of use of additional cut variables
  for S/B and Significance optimization, e.g.
• µ isolation
• b-tagging
• ? of jets, ? of muons
• Possible extension of sensitivity area
• Additional backgrounds
• QCD multi-jet production (4b, 4c, 2b2c, Wcc, Zcc,
  Wbb) has been found to contribute significantly
  to the background
• Investigation of additional points at high m0,
  low m1/2 to determine extent of sensitive region
  in m0
• Detailed study of systematic errors
• Possibility to study discovery potential for
  other SUSY models

21
Acknowledgements

• Principal Contributors
• Alexey Drozdetskiy
• Darin Acosta University
  of Florida
• Guenakh Mitselmakher
• Thanks also to
• Salavat Abdullin (ITEP/FNAL)
• Andreas Birkedal (Cornell)
• Nancy Marinelli (University of Athens)
• Konstantin Matchev (UF)
• Luc Pape (CERN)
• Albert de Roeck (CERN)
• Alexander Sherstnev (MSU)
• Michael Spira (PSI)
• Grzegorz Wrochna (Soltan Institute for Nuclear
  Studies)

22
BACKUP SLIDES
23
Results, Cuts Set 1
24
SUSY points considered in this study
m0
m1/2

• Updated post-WMAP benchmark points
• (hep-ph/0306219) - with modification
• More points
• (calculated by A.Birkedal (Cornell), K.Matchev
  (UF))
• Six of the points (high mass) are found to have
  negligible cross-sections

25
Results sensitive area at 10 fb-1
m0
m1/2

• Many points will be visible with ?Lltlt10 fb-1
• Significance for many points gtgt 5 for ?L10 fb-1