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Daniel Teyssier RWTH Aachen University

Searches for non-standard SUSY signatures in CMS

on behalf of the CMS collaboration

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Outline :

- physics goals- the CMS detector- two photons searches in GMSB- HSCP searches- conclusion

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Physics goals

• mGMSB (minimal Gauge Mediated Supersymmetry Breaking) model, with SUSY breaking transmitted via gauge interactions (from hidden sector to visible sector), alternative to mSUGRA

• 6 parameters to define the model : – Λ (SUSY breaking scale)

– Mm (messenger mass scale)

– Nm (number of SU(5) messenger multiplets)

– Cgrav (NLSP lifetime)

– tanβ

– sign(µ)

• Some sets of parameters give the neutralino as the NLSP and the gravitino as LSP, with BR(χ → γ) > 80% : as sparticles are produced in pairs, final states contain γγ with high pT

γγ final states in GMSB

G~ ~

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Physics goals HSCP (Heavy Stable Charged Particles), τ, g, t

• Other sets of parameters in mGMSB model predict quasi-stable sleptons (stau) with masses greater than hundred GeV• UED (Universal Extra Dimension) model predicts also such quasi-stable sleptons, called KK (Kaluza-Klein) states, with cross-sections of the order of few fb• split SUSY (model with high scalar masses) permits the existence of long lived gluino• MSSM allows light stop to be the NLSP, with the only possible decay t->cХ and then a long lived stop

• g and t hadronize to form R-hadrons : R-baryons (gqqq, t1qq), R-mesons (gqq, t1q) and R-gluonball gg

~ ~

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~ ~ ~

~ ~

~ ~ ~_ _

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CMS detector

Tracker :

σpT/pT ≈ 1.5 ∙10-4 pT(GeV) + 0.5%

ECAL :

σE/E ≈ 2.9%/√E(GeV) + 0.5%

HCAL :

σE/E ≈ 120%/√E(GeV) + 6.9%

Muons :

σpT/pT ≈ 5% for 1 TeV muons

Performances of the detector :

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γγ GMSB

• Signature : 2 high pT photons, large transverse missing energy (gravitino) and high pT jets

• Selection based on :

– high level trigger used : single γ

– photon isolation criteria

– pT (γ) > 80 GeV

– pTmiss > 160 GeV

– pT4j > 50 GeV

g q χ+

q q ν

l

l

χ0

γ

G

~ ~~ ~ ~~

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γγ GMSB• Main background :

– QCD multijets and γ+jets : fake MET from mismeasured jets

– tt and W+jets : electron could be misidentified as a photon, and possible large MET from neutrinos

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dataset selection non-pointing pointing

GMSB Λ=140 TeV 402.3 2.96 289.4

Z+jets 0.65 0.00 0.37

W+jets 2.76 0.00 1.46

QCD 54.9 0.27 2.32

TTbar (incl.) 16.3 0.00 6.13

Sum background 74.7 0.27 10.27

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γγ GMSB• Significance estimated using likelihood ratio and toy experiments

∫Ldt to get 5 σ

for =140 TeV

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HSCP : detection techniquesMuon-like signature but : - β lower than high relativistic muons (for both lepton-like and R-hadrons) - charge flipping for R-hadrons (trajectory modified and neutral R-hadrons not visible) R-hadrons do not shower

in calorimeters :

Average R-hadron energy loss per nuclear interaction according to different models

hep-ph/0611040

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HSCP : β measurement

dE/dx using inner tracker :

Non Relativistic Non Relativistic ParticleParticle

β-2 ≈ k dE/dX in 0.1<βγ<0.9 region k measured from proton sample

Z → µµ sample used as control sample

TOF (Time Of Flight) using muon system :

Non Relativistic Non Relativistic ParticleParticle

RPC (Resistive Plate Chamber) usedto confirm the track, and reject the background, mainly badly measured muons and cosmic muons

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HSCP selection

SM SM backgroundbackground

tt11 500GeV 500GeV

Samples used :Samples used :

• Signal : g, t1, mGMSB τ1, KK τ1 (full Geant4 and specific simulation for R-hadrons interactions : R Mackeprang, A Rizzi : Eur.Phys.J.C50:353-362,2007)

• SM background : QCD, W/Z+jets, tt

Selection criteria :Selection criteria :

• Muon : pT >30 GeV

• Tracker : β-1tk>1.1, Nhits>8, χ²/ndof < 5

• Combined : β-1DT > 1.25, β-1

tk> 1.25 with mavg > 100 GeV

Mass measurement :

• β taken as the average between (βtk,βDT) and momentum measured in muon system

• the HSCP mass is calculated

~ ~ ~ ~

β-1 tk

β-1 DT

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β-1 tk

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CMS AN-2007/049

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HSCP results

mGMSB mGMSB ττ

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KK KK ττ11 tt11

• SM background and cosmic muons negligible• gluino and stop channels to be easily seen after the start-up • stau and KK states channels need more integrated luminosity

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√s=14 TeV

√s=14 TeV

∫Ldt to get 5 σ

gg

Mass spectrum

Mass (GeV) Mass (GeV)

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Conclusion

• γγ GMSB :

- discovery possible at startup of the LHC

- to cover models up to Λ~200 (300) TeV would need an integrated luminosity of 1 (100) fb-1

• HSCP :

- high cross-sections and discovery potential from the startup at LHC

- mGMSB staus or R-hadrons up to few hundred GeV could be seen in the first 100 pb-1

- KK states more challenging but feasible with more than 1fb-1

- other searches exist on stopped HSCP, that are decaying up to few hours/days after the production

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BACKUP

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Cross-sections