1 Rutherford Appleton Laboratory The 13th Annual International Conference on Supersymmetry and Unification of the Fundamental Interactions Durham, 2005

1

Rutherford Appleton Laboratory

The 13th Annual International Conference on Supersymmetry and Unification of the Fundamental Interactions

Durham, 2005

SUSY Discovery Potential at CMS using Two Same Sign Muons

C. H. Shepherd-ThemistocleousRutherford Appleton Laboratory, UK

SUSY05, Durham, UK 2

Introduction

Generic search for SUSY Determine CMS reach shortly after start up ( ∫ L dt up to 10 fb-1 )

Inclusive search within mSUGRA Exploit clean signature

– same sign di-muons plus jets• Rejection of SM background

• High trigger efficiency

• 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


mSUGRA

em

old cosmological constraint 0.1 < < 0.3 WMAP cosmological constraint 0.094 < < 0.129 require that is the LSP excluded by favoured by at 2-σ level

01

b s2g

2xh

2xh

J.Ellis et al., hep-ph/0303043

Perform study within mSUGRA. Only 5 free parameters: m0, m1/2, tanβ, A0, sign(μ))

Example of allowed regions. A0 = 0, tanβ = 10, μ > 0


SUSY points considered in this study

m12 m0 tanβ

1 500 107 102* 300 1330 103 700 149 104 210 150 105 850 181 106 285 210 107 700 2155 108 360 230 109 900 2530 10

10 240 330 2011 400 85 1012 300 1200 3513 500 1620 3514 1000 2520 3515 1000 2715 1016* 1500 3442 1017 2000 4192 1018 2500 4942 1019 250 60 1020 300 65 10

- negligible σ

Selected set of points with A0 = 0, sign() > 0. Updated post-WMAP benchmark point

(hep-ph/0306219) [* - with modification] Additional points

– (calculated by A.Birkedal (Cornell), K.Matchev (UF))

Six of the points (high mass) are found to have negligible cross-sections

0

1000

2000

3000

4000

5000

6000

0 500 1000 1500 2000 2500 3000m1/2

m0

18

15

12

14

17

97

16

5

4,6,8,10,11,19,20

2

1 3

13


Cross sections & simulation

SUSY coupling constants and cross sections determined at LO using ISAJET

http://www.phy.bnl.gov/~isajet/

NLO corrections for SUSY processes determined using PROSPINO (v1)hep-ph/9611232

Cross sections for standard model processes determined using PYTHIA 6.220 and CompHEP 4.2 (Z/b b, single top).

NLO corrections used for ( t t, ZZ, Z b b )

All hadronization done using PYTHIA 6.220

Full CMS detector simulation was used (CMSIM, ORCA)


Standard Model Backgrounds

• Other potential background considered at generator level only (using CompHEP)

pb 0.212* 5.17* 0.129* 3.03* 18(NLO) 26.2 70.2 886(NLO) 232(NLO)*N1 2,120 51,700 1,290 30,300 180,000 262,000 702,000 8,860,000 2,320,000N2 112 1,798 71 1,067 256 727 39.7 142,691 12,924 160,000

tb tqb tb tqb ZZ ZW WW tt Zbb All

- negligible contribution

pb 0.129 0.0979 0.0305 0.00994 0.000574 0.000706 0.000442 0.000572 0.0000161N1 1,290 979 305 99.4N2 <15 <10 <3 <1

pb 0.556 0.65 neg. neg. neg.N1 5,560 6,500N2 <200 <200

WWW ZWW ZZW ZZZ WWWW ZWWW ZZWW ZZZW ZZZZ

ttW ttZ ttWW ttZW ttZZ

• Full detector simulation for main backgrounds

N1 – total number of expected events for integral luminosity of 10fb-1

N2 – number of events after pre-selection (two same sign muons with PT>10 GeV & ||<2.5)


SUSY cross sections

Notation:

– N1 – total number of expected events for integral luminosity of 10fb-1

– N2 – number of events after pre-selection (two same sign muons, PT>10 GeV)

– Significance, (S.I.Bityukov,N.V.Krasnikov)

– S/B – ratio:

12 2 S B BS N N N /S BN N

1 2 3 4 5 6 7 8 9 10, pb 1.21 2.43 0.161 83.2 0.0511 17.6 0.0354 5.21 0.00911 31.8N1 1,210 24,300 1,610 832,000 511 176,000 354 52,100 91 318,000N2 (NLO) 470 1470 66 14,600 20.7 4,330 18,3 1,520 2.71 11,700Significance 1.2 3.6 0.16 35.8 0.05 10.8 0.04 3.8 28.8S/B 0.0029 0.0092 0.00041 0.091 0.00013 0.027 0.00011 0.0095 0.073

SUSY point number:

11 12 13 14 15 16 17 18 19 20, pb 2.27 2.77 0.214 0.00527 0.00504 0.00048 0.00006 0.000008 40.8 15.9N1 22,700 27,700 2,140 52.7 50.4 4.8 0.6 0.08 408,000 159,000N2 (NLO) 961 2,210 188 9,200 4,570Significance 2.4 4.6 0.46 22.6 11.4S/B 0.006 0.014 0.0012 0.058 0.029

SUSY point number:

- excluded points


Signature

Example signal Example Background

Variables for cuts:

– Missing ET

– Jets ET

– Muon PT, Muon Impact Parameter

– Plus: Muon Isolation, Muon η, Jet η, number of jets/muons, …

Lpp gu X 1 d

L

01

1t t1 b

L 01

pp tt X W b

Y

W b


Examples Distributions (1)

mSUGRA point 11m0=85 GeV, m1/2=400 GeV, tanβ = 10, A0 = 0, signμ > 0

After preselection cuts: two same sign muons with PT>10 GeV & ||<2.5


Example Distributions (2)

mSUGRA point 11m0=85 GeV, m1/2=400 GeV, tanβ = 10, A0 = 0, signμ > 0

After preselection cuts: two same sign muons with PT>10 GeV & ||<2.5


Example Distributions (3)

mSUGRA point 3

m0=149 GeV,

m1/2=700 GeV

tanβ = 10

A0 = 0

sign(μ) > 0


Analysis Cuts

Simple 1d cuts based analysis Variables considered

– Missing ET, ETjet1, ETjet3, PTμ1, PTμ2, d0 (μmin ) , d0 (μmax)

Range of values of cuts for each variable considered

Missing ET: 0 - 500 GeVETjet1: 0 - 400 GeVETjet3: 0 - 250 GeVPTμ1: 10 - 150 GeV/cPTμ2: 10 - 80 GeV/cd0 (μmin ) : 0.005 - 0.0005 cm and no cutd0 (μmax) : 0.1 - 0.005 cm and no cut

Set of cuts optimized at each SUSY point ~ 176k sets of cuts considered Values of significance, S/B and Ntot for 10fb-1 determined


Selection of set of cuts


Final analysis cuts Two sets of cuts chosen which have high significance and S/B for all SUSY

points

– Set #1: • Missing ET > 200 GeV,

• ETjet3 > 170 GeV,

• PTμ1 > 20 GeV

– Set #2: • Missing ET > 100 GeV,

• ETjet1 > 300 GeV,

• ETjet3 > 100 GeV

These cuts are applied in addition to the preselection cuts:

– 2 same sign muons, both with PT > 10 GeV & Results were obtained for all SUSY points for each of the above sets of cuts

Trigger cuts

L1: single with Pt > 14 GeV di- with Pt > 3 GeV HLT: di- with Pt > 7 GeV


Results for 2nd set of cuts

Monte Carlo statistical errors shown for number of events after all cuts (N final)

SET 2 SM 1 2 3 4 5 6N final 432 ± 8.8 184 ± 9.3 560 ± 29 30.4 ± 1.4 1590 ± 152 9.6 ± 0.45 1030 ± 67Signif 8.06 21.4 1.44 48.4 0.46 35S/B 0.43 1.3 0.07 3.7 0.002 2.4

SET 2 7 8 9 10 11 12 13N final 8.31 ± 0.39 530 ± 28 n/a 1950 ± 151 322 ± 18 781 ± 42 86.9 ± 4Signif 0.4 20.5 n/a 56.1 13.4 28.1 4S/B 0.019 1.2 n/a 4.5 0.75 1.8 0.2

SET 2 14 15 16 17 18 19 20N final n/a n/a n/a n/a n/a 1220 ± 106 996 ± 67Signif n/a n/a n/a n/a n/a 39.8 34S/B n/a n/a n/a n/a n/a 2.8 2.3


Results: Significance

Total number of points out of reach (Significance < 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 > 5

– S/B > 0.4 (excess of 40% or more over expected number of SM events)

SET 1 SET 21 9.05 8.062 20.8 21.43 2 1.444 25 48.45 0.77 0.466 20.6 357 0.78 0.48 15.5 20.59 n/a n/a10 31.7 56.111 12.1 13.412 27.1 28.113 6 414 n/a n/a15 n/a n/a16 n/a n/a17 n/a n/a18 n/a n/a19 25.6 39.820 20.6 34

Significance


Results: Reach for 10fb-1

0

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0 500 1000 1500 2000 2500 3000m1/2

m0

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97

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4,6,8,10,11,19,20

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1 3

130

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190 240 290 340 390 440

4

68

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1119 20

Many points will be visible for ∫L<<10 fb-1

Significance for many points >> 5 for ∫L=10 fb-1


A First Estimate of Systematic Effects

To estimate the stability of the results, the effect of varying the cuts and the number of SM and SUSY events was investigated:

– Uncertainty in signal acceptance and background variation• 30% decrease in no. of SUSY events + 30% increase in no. of SM events

– Energy and momentum scale uncertainty• shift of all cuts by + or – 20% simultaneously

Only one "SUSY discovery" point (#13) goes out of reach

Above probably pessimistic scenario– 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%

tt


Summary

Study performed based on the mSUGRA model tanβ=10,20,35, sign(μ)>0, A0=0

Full detailed simulation, trigger emulation and reconstruction was used

Excess of mSUGRA events over SM processes is statistically significant for many benchmark points for ∫L<<10fb-1

up to 600 GeV in m1/2 and at least up to 1600 GeV in m0

Results are optimistic for SUSY discovery


Backup slides


Location in parameter space

Variety of SUSY decay chains possible Mix depends on where one is in SUSY parameter space.

– e.g. for point 5, 42% of decay chains (PYTHIA) follow the form of the previous diagram.

Where m0 < m1/2 m(sleptons) < m (

two body decays to lepton final states open up.


Previous CMS studyFast detector simulation onlyIntegrated Lumi 100 fb-1

Documents

1 Rutherford Appleton Laboratory The 13th Annual International Conference on Supersymmetry and Unification of the Fundamental Interactions Durham, 2005