supersymmetric particle reconstructions at cms

Supersymmetric Particle Supersymmetric Particle Reconstructions at CMSReconstructions at CMS

Massimiliano ChiorboliMassimiliano Chiorboli

INFN CataniaINFN Catania

7 May 2003 PRS-SUSY meeting Massimiliano Chiorboli

Up to a couple of years ago, most of Up to a couple of years ago, most of attention devoted to inclusive studiesattention devoted to inclusive studies

I started working in the Physics group on I started working in the Physics group on sparticle reconstructionsparticle reconstruction

Sbottom, squark ad gluino mass peaks in Sbottom, squark ad gluino mass peaks in 3 mSUGRA points3 mSUGRA points


Decay ChainsDecay Chains

2 high pt isolated leptons OS

(leptons = e,)

2 high pt non-b jets

missing Et

2 high pt isolated leptons OS

(leptons = e,)

2 high pt b jets

missing Et

g~ pp

b~02

~

qq~ g~ pp

q~02

01

~~

SM bkg: tt, Z+jet, W+jet, ZZ, WW, ZW, QCD jets

p

p

g~

b~

b

b

01

~02

~~

bb~

01

~


Generation and SimulationGeneration and Simulation

SUSY events generated with ISAJET SUSY events generated with ISAJET 7.51 + PYTHIA 6.1587.51 + PYTHIA 6.158

SM bkg events (tt, Z+jet, W+jet, ZZ, WW, SM bkg events (tt, Z+jet, W+jet, ZZ, WW, ZW, QCD jets) generated with PYTHIA ZW, QCD jets) generated with PYTHIA 6.1586.158

Detector simulated with CMSJET 4.801Detector simulated with CMSJET 4.801


Benchmark PointsBenchmark PointsProposed Post-LEP Benchmarks for Supersymmetry, M. Battaglia Proposed Post-LEP Benchmarks for Supersymmetry, M. Battaglia et alet al. (hep-ph/0106204). (hep-ph/0106204)

Rather low mRather low m00 and m and m1/21/2 values in order to have high values in order to have high SUSY cross sectionSUSY cross section

Three different tanThree different tan values values (tan (tan = 10, 20, 35) since = 10, 20, 35) since BR(BR(22

00 l l++ll- - 1100) depends on ) depends on

tantan


Reconstruction MethodReconstruction Method

p

p

g~

b~

b

b

01

~

02

~ ~

• assuming M(assuming M(1100) known) known

•Selecting events “in edge”Selecting events “in edge”

• Combining the Combining the 2200 obtained from obtained from

the two leptons with the most the two leptons with the most energetic b-jet in the eventenergetic b-jet in the event

p

M

M1p

01

02

~

~

At the end-point:At the end-point:

GeV 80 )M( GeV 65

2 isolated leptons, pT>15 GeV, ||<2.4

2 b-jets, pT>20 GeV, ||<2.4


Reconstruction MethodReconstruction Method

SM bkg can be reduced cutting on ESM bkg can be reduced cutting on ETTmissmiss

The main problem is combinatorialThe main problem is combinatorial

Once the sbottom (or the squark) is reconstructed:Once the sbottom (or the squark) is reconstructed:

p

p

g~

b~

b

b

01

~

02

~ ~


Results @ Point BResults @ Point B

0A

)(sign

10tan

100m

250m

0

0

21

SUSYSUSY = 57.77 pb = 57.77 pb

GeV 906σ

GeV 10536q)χ~M( 02

Result of the fit:Result of the fit:

GeV 0.537)c~(M)u~M(

GeV 8.542)s~(M)d~

M(

LL

LL

Generated valuesGenerated values1 fb-1

squarksquark

%44.16)~~(BR 0

2 → dilepton edge well visible

pb 4.1)chain decayq~pp(BR pb 5.0)chain decayq~g~pp(BR

Result of the fit:Result of the fit:

GeV 542σ

GeV 7500b)χ~M( 02

10 fb-1

sbottomsbottom

b~

g~pp

pb 1.0)chain decayb~

pp(BR

GeV 1.955)g~M( Generated value:Generated value:

10 fb-1

sbottom sbottom chainchain

GeV 742

GeV 7495bb)~M( 02

GeV 575

GeV 7295qq)~M( 02

10 fb-1

squark squark chainchain

gluinogluino

Squark mass peaks can be reconstructed in the first Squark mass peaks can be reconstructed in the first few weeks (resolution few weeks (resolution ~~12%)12%)

Sbottom and gluino in the first year (resolution Sbottom and gluino in the first year (resolution ~~66÷8%)÷8%)

Two independent gluino mass measurementsTwo independent gluino mass measurements The resolution can be improved with larger statistics The resolution can be improved with larger statistics

((~5~5÷6% at 300 fb÷6% at 300 fb-1-1))

Sbottom ChainSbottom Chain Squark ChainSquark Chain

10 fb-1 60 fb-1 300 fb-1 10 fb-1 60 fb-1 300 fb-1

M(sbottom)M(sbottom) 500±7 502±4 497±2 M(squark) 536±10 532±2 536±1

(sbottom)(sbottom) 42±5 41±4 36±3 (squark) 60±9 36±1 31±1

M(gluino)M(gluino) 594±7 592±4 591±3 M(gluino) 592±7 595±2 590±2

(gluino)(gluino) 42±7 46±3 39±3 (gluino) 75±5 59±2 59±2


10 fb-1

Results @ Point GResults @ Point GWith respect to the Point B:With respect to the Point B:

Lower total SUSY cross section (8.25 pb)Lower total SUSY cross section (8.25 pb)

Lower BR’s of useful decaysLower BR’s of useful decays

Higher BR’s of competitive decaysHigher BR’s of competitive decays

Lower BR of the last decayLower BR of the last decay

16.44%) Bpoint (

%26.2)~~(BR 0

2

%)48.27 Bintpo(

%58.26)bb~

g~(BR %)7.326 Bintpo(

%92.59)qq~g~(BR

%)19.2 Bintpo(

%52.21)Wt~b~

(BR 2

B)point at allowed(not

%83.7)W~~(BR 011

300 fb-1


Results @ Point GResults @ Point G

gluinogluinosquarksquark

sbottomsbottom gluinogluino

Sbottom ChainSbottom Chain

300 fb-1

M(sbottom)M(sbottom) 720±26

(sbottom)(sbottom) 81±18

M(gluino)M(gluino) 851±40

(gluino)(gluino) 130±43

Squark ChainSquark Chain

300 fb-1

M(squark) 774±9

(squark) 84±9

M(gluino) 853±11

(gluino) 126±11

300 fb-1


Point IPoint I

%25.0)~~(BR 0

2

BBGG

300 fb-1

The tau channel is the main one The tau channel is the main one also in the other pointsalso in the other points

Tau-pair edge is not as sharp as Tau-pair edge is not as sharp as in the e and in the e and case, but could case, but could help to cover points in which the help to cover points in which the reconstruction is problematicreconstruction is problematic

It could be exploited in regions It could be exploited in regions with too low leptonic BRwith too low leptonic BR

Neutralino BR’sNeutralino BR’s

B G I

BR(BR(2200→ll)→ll) 16.44 2.26 0.25

BR(BR(2200→→ 83.22 75.88 98.13

II


ConclusionsConclusions Supersymmetric Spectroscopy Supersymmetric Spectroscopy has been has been

attemptedattempted CMS will be capable to reconstruct sparticles CMS will be capable to reconstruct sparticles

with favourable parameterswith favourable parameters Point BPoint B

squark in the first few weeks (1 fbsquark in the first few weeks (1 fb-1-1)) sbottom and gluino in the first year (10 fbsbottom and gluino in the first year (10 fb-1-1))

Point GPoint G squark, sbottom and gluino with 300 fbsquark, sbottom and gluino with 300 fb-1-1

Point IPoint I no recontruction possible with the lepton channel, but it no recontruction possible with the lepton channel, but it

could be useful to investigate other decay chains (e.g. could be useful to investigate other decay chains (e.g. →→

CMS Note in preparationCMS Note in preparation


Future perspectivesFuture perspectives

What can be done…What can be done… Re-run the analysis in full simulationRe-run the analysis in full simulation Try to look fo other sparticles in the Try to look fo other sparticles in the

same pointssame points stopstop non-strongly interacting sparticlesnon-strongly interacting sparticles

Investigate other decay channelsInvestigate other decay channels →→ at Point I (high tan at Point I (high tan points) points)

Explore reconstruction capability at Explore reconstruction capability at different pointsdifferent points

supersymmetric particle reconstructions at cms

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