Nuclear Physics B Proceedings Supplement 00 (2014) 1–3
Nuclear Physics B Proceedings Supplement
Searches for supersymmetry at CMS in final states with photons
Maximilian Knut Kiesel, on behalf of the CMS collaboration
I. Physikalisches Institut B, RWTH Aachen University, Aachen, Germany
Abstract
Four searches for supersymmetry at CMS in final states with photons are discussed in this article. The data analyzed corresponds to up to 19.7fb−1and was recorded at centre-of-mass energies of 7 and 8 TeV by the CMS experiment.
Searches in final states with photons are sensitive to various scenarios for physics beyond the standard model, espe- cially gauge mediated supersymmetry breaking. To increase the sensitivity for various classes of models, four analyses with different selections and background estimation methods are performed. Wino-like neutralino mixing scenarios are probed in final states with at least one photon and jets, while final states with at least two photons are most sensitive to bino-like neutralino mixing scenarios. A higgsino-like neutralino scenario is studied by selecting two photons with an invariant mass close to the Higgs mass. While all of these analyses explore events with high missing transverse energy, a fourth analysis covers also final states with two photons and low missing transverse energy. No excess of data over the standard model expectation is observed, and upper limits on various signal cross sections are calculated.
Keywords:
search, supersymmetry, photon, CMS, GMSB, higgsino, stealth SUSY
1. Introduction
Searches for supersymmetry (SUSY) in final states with photons are especially sensitive to gauge medi- ated supersymmetry breaking (GMSB). As the lightest neutralino decays into a gravitino ( ˜G) and a standard model (SM) boson, the mixing of the lightest neutralino is important for the resulting final states. Three of the analyses presented here are optimized for the discovery of wino-, bino-, and higgsino-like neutralino scenarios, while the fourth analysis abandons the missing trans- verse energy (6ET) requirement and is sensitive to vari- ous other scenarios for physics beyond the SM. The data is recorded by the CMS experiment [1].
2. Final states with one or two photons and6ET
Events are selected with either a high energetic pho- ton, hadronic activity, jets and6ET, or with two photons
Email address:[email protected](Maximilian Knut Kiesel)
and6ET[2]. The background of jets misidentified as pho- tons and photon-jet production is estimated from a con- trol sample with a photon-like jet instead of the photon.
The ratio of selected events with photons to the control sample is propagated from events with low 6ET to the signal region with high6ET. Kinematic dependencies of this ratio on photonpT or the recoil against the photons are considered.
To estimate the background from electrons misidenti- fied as photons, events with electrons instead of photons are selected and scaled by the probability of an electron faking a photon. This probability is measured using the Z →eeresonance. For the single-photon analysis, ini- tial and final state radiation is estimated using simula- tion. Figure 1 shows the event yields, background pre- diction and two signal scenarios for both signal selec- tions.
No evidence for physics beyond the SM is found, and multiple statistically independent bins in 6ET are used to calculate limits at 95% confidence level using data
Knut Kiesel/Nuclear Physics B Proceedings Supplement 00 (2014) 1–3 2
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Candidate Sample γ
γ
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ET
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Data/Prediction 0.2
0.4 0.6 0.81 1.2 1.4 1.61.8
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ETmissT [GeV]
EmissT [GeV]
E
Figure 1: Total standard model background prediction compared to the number of single-photon events (top) and di-photon events (bottom), including signal benchmark points where the masses (mq˜/m˜g/mχ˜0
1) are given in GeV in the plots.
corresponding to 4.04 fb−1. The event yields are inter- preted for bino- and wino-like neutralino scenarios in the gluino-squark mass space in the general gauge me- diation framework. The exclusion contours are shown in Fig. 2.
3. Final states with a Higgs boson and6ET
Events containing two photons with an invariant mass close to the Higgs mass and two b-jets are selected [3].
To increase the sensitivity, these events are categorized with respect to having an additional b-jet, or the invari- ant mass of two b-jets being close to the Higgs mass.
The background is estimated by a fit in the sidebands of
) [GeV]
~q m(
500 1000 1500
) [GeV]g~m(
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excluded
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Observed
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)2 (GeV/cg~m
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2) = 375 (GeV/c χ∼0
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Observed (theory) σ
±1 Expected
(theory) σ
±1 (experimental) σ
±1 CMS Preliminary
= 8 TeV s -1, dt = 4.04fb
∫L
Excluded
Figure 2: The 95% C.L. observed exclusion contour in gluino-squark mass space for wino-like neutralino for the single photon analysis (top) and for bino-like neutralino for the di-photon analysis (bottom).
the invariant mass spectrum of the di-photon system, as shown in Fig. 3.
The 95% confidence limits are calculated in bins of 6ET and combined for all event categories for higgsino- like neutralinos in the stop-higgsino mass plane. The cross section limit and the exclusion contour is shown in Fig. 4 for data corresponding to 19.7 fb−1. Stop masses of 370 GeV and below are excluded.
4. Final states with two photons
A search without 6ET requirement can be sensitive to extra dimensions, heavy-flavor compositeness, little Higgs, R-parity violation, GMSB and stealth SUSY [4].
Events with two photons, at least four jets and the scalar sumST of the transverse momenta of all jets, photons and6ETlarger than 700 GeV are selected. The signal re- gion is seperated into events with exactly four jets and five or more jets.
Knut Kiesel/Nuclear Physics B Proceedings Supplement 00 (2014) 1–3 3
(GeV)
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Events per GeV
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= 19.7 fb-1
t d
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L = 8 TeV, s CMS,Data Sideband Fit
= 300 GeV
tR
Signal: m~
= 290 GeV
χ∼0
m 2 b-jets
≥
Figure 3: Invariant mass of two photons. Events with an invariant mass smaller than 118 GeV or larger than 133 GeV are used to es- timate the background using a fit. A hypothetical signal is drawn in addition.
(GeV)
tR
m~
200 300 400 500
(GeV)0 1χ∼m
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Observed 95% Cross Section Exclusion (pb)
0 0.5 1 1.5 2 2.5 3 3.5
+ 5 GeV
+ χ∼1 0 = m χ∼2
5 GeV, m
−
+ χ∼1
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0 χ∼1
m
) = 1, Strong and EW Production G~
→ H 0 χ∼1 Br(
Natural GMSB Higgsino model
Observed 95% CLs Limits Theory uncertainty Expected 95% CLs Limits
experimental σ
±1 Expected
= 19.7 fb-1
t d
∫
L = 8 TeV, s CMS,Figure 4: Limits on SUSY production cross sections for different top squark and higgsino masses. The regions to the left of the contours are expected (thick dashed red) and observed (solid black curves) to be excluded at the 95% confidence level.
To estimate the background, two control regions are defined: A “jet multiplicity sideband” (JMSB) composed of events with two or three jets and ST >600 GeV, and a “STsideband” with four or more jets and 600<ST<700 GeV. Since the shape of the ST-spectrum was found to be independent of the jet multiplicity, theSTshape is taken from the JMSB and the normalization is taken from theST sideband. The STdistribution, the background estimation, and a signal are shown in Fig. 5.
In Fig. 6, limits on stealth SUSY [5] cross sections as function of the squark mass are compared to the pre- dicted stealth SUSY cross section for data correspond- ing to 4.96 fb−1 at a centre-of-mass energy of 7 TeV.
(GeV) ST
600 800 1000 1200 1400
Events / (50 GeV)
10 20 30 40
50 CMS4.96 fb-1, s = 7 TeV
4-jets Data, ≥
Expected Background Syst. Uncertainty
=900GeV
q~
M Sideband ST
Figure 5: Observed ST spectrum, background expectation with systematic uncertainty, and predicted signal for a squark mass of 900 GeV in events with four or more jets.
(GeV)
q~
M
500 1000 1500 2000
(fb)σ
1 10 102
CMS
= 7 TeV s
-1, 4.96 fb
q~
×M = 1/2
χ∼0
M
=90GeV
=100GeV, Ms s~
M
) = 1
~s γ
→ χ∼0
BR(
Observed Limit Expected Limit Stealth SUSY
1 SD Expected
±
Figure 6: Stealth SUSY cross-section limit at the 95% CL as a func- tion ofMq˜. The observed limit, median expected limit, and the pre- diction for a stealth SUSY model is shown.
Squark masses below 1400 GeV are excluded in this scenario.
References
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