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TRANSCRIPT
Amandeep Kalsi1, A. Gurrola2 , Nitish Dhingra1, J. B. Singh1, T. Kamon3, V. Bhatnagar1
XX DAE-BRNS High Energy Physics Symposium, 13-18 Jan 2013, Visva-Bharati, Santiniketan (India)
Analysis Strategy
Based on searches performed so far, gluinos and 1st/2nd generationsquarks are likely heavy with the masses >~ 1.5 TeV while thebounds on the masses of charginos /neutralinos and thirdgeneration SUSY particles are less constrained in those searches.
SUSY in VBF processes - complementary to searches for direct production for EWKinos or sleptons, providing a way to probe them through direct production.
Does not require cascade decays of heavier colored particles in classic SUSY searches.
Selecting and triggering events with a VBF-like topology provides a way to probe scenarios with compressed spectra and small mass splittings.
VBF production provides a very strong handle on backgroundsby selecting two forward jets with mass M(jj) ~1 TeV.
Cross-section of slepton production via Drell-Yan and VBF processes becomes almost comparable atMstau ~ 500 GeV.
B. Dutta et al., “Vector Boson Fusion Processes as a Probe of Supersymmetric Electroweak Sectors at the LHC”, arXiv: 1210.0964 [hep-ph]M. Carena et. al, “Light Stau Phenomenology and the Higgs→γγ Rate”, arXiv: 1205.5842 [hep-ph]
Supersymmetry (SUSY) is one of the best studied theories for physics beyond the Standard Model (SM) .
Provides natural solution to hierarchy problem, origin of dark matter and many other unsolvedproblems.
In SUSY, to each fermion (boson) of SM, there corresponds a supersymmetric boson (fermion).Minimal Supersymmetric Standard Model (MSSM) is the simplest extension of the SM that includesSUSY.
MSSM involves five Higgs bosons (h0, H0, A0, H±) along with four neutralinos (χ͂01, χ0͂2, χ0͂
3, χ0͂4) and four
charginos (χ͂±1, χ±͂2) produced from mixing of gaugino and higgsino states.
No experimental evidence of SUSY particles found till date, which implies it is a broken symmetry withsparticles masses large enough to evade current experimental bounds.
SUSY models involving conservation of R-parity, resulting in pair-production of SUSY particles witha stable Lightest SUSY particle (LSP) which is considered as a Dark Matter candidate.
VBF as SUSY probe
Introduction
References
CMS Detector
Signal and Background Processes
pp → jf jf χ1͂± χ1͂
± → jf jf (χ1͂0τ±ν) (χ1͂
0τ±ν)
pp →jfjf χ2͂0 χ1͂
± → jf jf (χ1͂0τ+τ- ν) (χ1͂
0τ±ν)
Signal Process :
Standard Model Backgrounds :
QCD : Multijets fake hadronic taus. Z→τ τ: Two real taus decay hadronically. Z →µµ/ee : µ/e can fake hadronic taus.W+Jets : Isolated leptons combined with non-isolated jets. ttbar : Two W’s from top decay provide jets (fake τ’s) along with b-jets.
Central Selections: Standard TauID selections. Central selections expected to be well simulated by MC. Whenever possible, obtain background enriched control regions. Obtain Data-to-MC correction factor in these control regions.
VBF Selections: Select at least one pair of high pT jets with large separation (Δη) and large invariant
mass. VBF selections provides background suppression of the order of ~10-3-10-4.Mis-modelling of background rate in the Signal Region is expected to come from VBF
selections. Measure the efficiency of VBF selections directly from the collision data. Extrapolate to the signal region
using equation:
Analysis Strategy
Background Estimation & Control Plots
Z→τ τ Background Estimation
For additional validation, obtained a semi-clean enriched sample of Z →ττ background by requiring opposite-signtau-pair to have invariant mass < 90 GeV.
Enhances confidence in the understanding of Tau ID selections and double-Tau trigger.
Data-to-MC scale factor ~ 1.07 ± 0.17. Negligible Bkg. contribution in the Signal Region.
QCD Background Estimation
QCD multijet is the dominant background for fully hadronic final state. The MC statistics is not sufficient to model it properly so fully data-driven approach is used. Keep the same central selections, BUT invert the opposite-sign requirement i.e. select like-sign ττ pairs (No VBF selections). Subtract the like-sign non-QCD MC backgrounds from the like-sign data (contamination from like-sign non-QCD MC
backgrounds is very very small ~ 1%). ROS/LS is measured using a sample of non-isolated taus. Extract the shapes and QCD contribution by applying ROS/LS to the like-sign region.
τ+(-) τ-(+)τ –(+) τ-(+)
ROS/LS = 1.22 ± 0.03
VBF KinematicsBenchmark Point: M(χ͂1+)~M(χ͂20) = 180 GeV, M(χ1͂
0) = 90GeV, M(τ͂1+)-M(χ1͂
0) = 30GeV
arXiv:1210.0964 hep-ph
The SM backgrounds can be controlled by VBF cuts ( 2 energetic forward jets) to probe light EWKino and slepton sectors.
Searches for EWKinos and sleptons via VBF processes are complementary to existing SUSY searches.
SUMMARY
arXiv:1210.0964 hep-ph
1Panjab University2Vanderbilt University
3Texas A & M University
On the behalf of CMS Collaboration