CMS logoCMS event Hgg
Compact Muon Solenoid
LHC, CERN

CMS-PAS-SUS-17-003
Search for pair production of tau sleptons in $\sqrt{s}= $ 13 TeV pp collisions in the all-hadronic final state
Abstract: A search for direct tau slepton pair production in pp collisions at a center-of-mass energy of 13 TeV is presented. The data correspond to an integrated luminosity of 35.9 fb$^{-1}$ collected with the CMS detector at the Run-2 of the CERN LHC in 2016. The search is performed using events with two hadronically decaying tau leptons and a large imbalance in the measured transverse momentum of the event. The results are interpreted as upper limits on the cross section for tau slepton pair production in different helicity scenarios.
Figures & Tables Summary Additional Figures & Tables References CMS Publications
Additional information on efficiencies needed for reinterpretation of these results are available here.

Additional technical material for CMS speakers can be found here.
Figures

png pdf
Figure 1:
Simplified model for direct stau pair production followed by each stau decaying to a $\tau $ lepton and an LSP.

png pdf
Figure 2:
The $\Sigma {M_{\mathrm {T}}} $ (left) and $ {M_{\mathrm {T2}}} $ (right) distributions after the baseline selection. The signatures of stau pair production with different stau masses are shown. A requirement of large $ {M_{\mathrm {T2}}} $, while efficient at reducing the SM background, greatly reduces the signal acceptance for low stau masses. We therefore define additional search regions with moderate $ {M_{\mathrm {T2}}} $ and use $\Sigma {M_{\mathrm {T}}} $ as a discriminating variable to target smaller stau masses. Three signal hypotheses in the maximally-mixed scenario are overlaid, with the first number indicating the stau mass and the second the LSP mass.

png pdf
Figure 2-a:
The $\Sigma {M_{\mathrm {T}}} $ distribution after the baseline selection. The signatures of stau pair production with different stau masses are shown. A requirement of large $ {M_{\mathrm {T2}}} $, while efficient at reducing the SM background, greatly reduces the signal acceptance for low stau masses. We therefore define additional search regions with moderate $ {M_{\mathrm {T2}}} $ and use $\Sigma {M_{\mathrm {T}}} $ as a discriminating variable to target smaller stau masses. Three signal hypotheses in the maximally-mixed scenario are overlaid, with the first number indicating the stau mass and the second the LSP mass.

png pdf
Figure 2-b:
The $ {M_{\mathrm {T2}}} $ distribution after the baseline selection. The signatures of stau pair production with different stau masses are shown. A requirement of large $ {M_{\mathrm {T2}}} $, while efficient at reducing the SM background, greatly reduces the signal acceptance for low stau masses. We therefore define additional search regions with moderate $ {M_{\mathrm {T2}}} $ and use $\Sigma {M_{\mathrm {T}}} $ as a discriminating variable to target smaller stau masses. Three signal hypotheses in the maximally-mixed scenario are overlaid, with the first number indicating the stau mass and the second the LSP mass.

png pdf
Figure 3:
(Left) Closure test for the fake rate method in a data control region where the $ {M_{\mathrm {T2}}} $ or $\Sigma {M_{\mathrm {T}}} $ requirements are inverted. The predicted and observed yields show good agreement. (Right) The visible mass spectrum is used to validate our modeling of Drell-Yan backgrounds. A minimum di-$ {\tau _\mathrm {h}} $ ${p_{\mathrm {T}}}$ of 50 GeV is required to reduce the QCD multijet background. Data and simulation agree within the experimental uncertainties.

png pdf
Figure 3-a:
Closure test for the fake rate method in a data control region where the $ {M_{\mathrm {T2}}} $ or $\Sigma {M_{\mathrm {T}}} $ requirements are inverted. The predicted and observed yields show good agreement.

png pdf
Figure 3-b:
The visible mass spectrum is used to validate our modeling of Drell-Yan backgrounds. A minimum di-$ {\tau _\mathrm {h}} $ ${p_{\mathrm {T}}}$ of 50 GeV is required to reduce the QCD multijet background. Data and simulation agree within the experimental uncertainties.

png pdf
Figure 4:
The excluded stau pair production cross section as a function of the stau mass for the three different helicities: left-handed (left), maximally-mixed (middle), right-handed (right). The plots in the top row assume a fixed LSP mass of 1 GeV, the ones on the middle row 20 GeV, and the ones on the bottom row 50 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis.

png pdf root
Figure 4-a:
The excluded stau pair production cross section as a function of the stau mass for left-handed helicity. The plot assumes a fixed LSP mass of 1 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis.

png pdf root
Figure 4-b:
The excluded stau pair production cross section as a function of the stau mass for maximally-mixed helicity. The plot assumes a fixed LSP mass of 1 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis.

png pdf root
Figure 4-c:
The excluded stau pair production cross section as a function of the stau mass for right-handed helicity. The plot assumes a fixed LSP mass of 1 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis.

png pdf root
Figure 4-d:
The excluded stau pair production cross section as a function of the stau mass for left-handed helicity. The plot assumes a fixed LSP mass of 20 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis.

png pdf root
Figure 4-e:
The excluded stau pair production cross section as a function of the stau mass for maximally-mixed helicity. The plot assumes a fixed LSP mass of 20 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis.

png pdf root
Figure 4-f:
The excluded stau pair production cross section as a function of the stau mass for right-handed helicity. The plot assumes a fixed LSP mass of 20 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis.

png pdf root
Figure 4-g:
The excluded stau pair production cross section as a function of the stau mass for left-handed helicity. The plot assumes a fixed LSP mass of 50 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis.

png pdf root
Figure 4-h:
The excluded stau pair production cross section as a function of the stau mass for maximally-mixed helicity. The plot assumes a fixed LSP mass of 50 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis.

png pdf root
Figure 4-i:
The excluded stau pair production cross section as a function of the stau mass for right-handed helicity. The plot assumes a fixed LSP mass of 50 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis.
Tables

png pdf
Table 1:
The largest systematic uncertainties in the analysis for the signal models and the different SM background predictions. For the signal models the uncertainties are re-evaluated for the different mass hypotheses.

png pdf
Table 2:
Final predicted and observed event yields in all SRs with all statistical and systematic uncertainties combined. For the background estimates with no events in the sideband or the simulated sample, the 68% statistical upper limit is presented. For the total background estimate the central value and the uncertainties are extracted from the full pre-fit likelihood.
Summary
A search for tau sleptons in the all-hadronic final state was performed in pp collisions at a center-of-mass energy of 13 TeV using three complementary search regions. The data sample corresponds to an integrated luminosity of 35.9 fb$^{-1}$. No excess was observed in any of the search regions. Upper limits on the cross section of direct tau slepton (stau) pair production are derived, for each stau decaying to a tau lepton and an LSP. The analysis is most sensitive to left-handed staus. For a left-handed stau of 125 GeV decaying to a massless LSP the observed limit is 1.5 times the expected production cross section in the simplified model.
Additional Figures

png pdf
Additional Figure 1:
Misidentification rate as a function of $\tau$ $p_{\mathrm {T}}$ for various parton types without any cut on the isolation (left) or after applying a loose isolation requirement as done in the analysis (right). The variation across parton types is greatly reduced by applying such a requirement. After applying the loose isolation requirement, a systematic uncertainty of 30% is assigned to the misidentification rate to cover the jet parton dependence as this analysis does not determine the jet parton type.

png pdf
Additional Figure 1-a:
Misidentification rate as a function of $\tau$ $p_{\mathrm {T}}$ for various parton types without any cut on the isolation. The variation across parton types is greatly reduced by applying such a requirement.

png pdf
Additional Figure 1-b:
Misidentification rate as a function of $\tau$ $p_{\mathrm {T}}$ for various parton types after applying a loose isolation requirement as done in the analysis. The variation across parton types is greatly reduced by applying such a requirement. After applying the loose isolation requirement, a systematic uncertainty of 30% is assigned to the misidentification rate to cover the jet parton dependence as this analysis does not determine the jet parton type.

png pdf
Additional Figure 2:
Illustration showing the complementarity of the different search and control regions.

png pdf
Additional Figure 3:
The excluded cross sections for stau pair production as a function of the stau mass for a model where the left-handed and right-handed staus are considered to be mass degenerate. The plots are shown for a fixed LSP mass of 1 GeV (left), 20 GeV (middle), and 50 GeV (right). The inner (green) band and the outer (yellow) band indicate the regions containing 68% (1 s.d.) and 95% (2 s.d.), respectively, of the distribution of limits expected under the background-only hypothesis. Several mass hypotheses are just excluded in this model.

png pdf
Additional Figure 3-a:
The excluded cross sections for stau pair production as a function of the stau mass for a model where the left-handed and right-handed staus are considered to be mass degenerate. The plots are shown for a fixed LSP mass of 1 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68% (1 s.d.) and 95% (2 s.d.), respectively, of the distribution of limits expected under the background-only hypothesis. Several mass hypotheses are just excluded in this model.

png pdf
Additional Figure 3-b:
The excluded cross sections for stau pair production as a function of the stau mass for a model where the left-handed and right-handed staus are considered to be mass degenerate. The plots are shown for a fixed LSP mass of 20 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68% (1 s.d.) and 95% (2 s.d.), respectively, of the distribution of limits expected under the background-only hypothesis. Several mass hypotheses are just excluded in this model.

png pdf
Additional Figure 3-c:
The excluded cross sections for stau pair production as a function of the stau mass for a model where the left-handed and right-handed staus are considered to be mass degenerate. The plots are shown for a fixed LSP mass of 50 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68% (1 s.d.) and 95% (2 s.d.), respectively, of the distribution of limits expected under the background-only hypothesis. Several mass hypotheses are just excluded in this model.
Additional Tables

png pdf
Additional Table 1:
Cut-flow for different mass points of the left-handed stau sample for all three search regions corresponding to 35.9 fb$^{-1}$ of integrated luminosity for various signal model points, given as the mass pair ($\tilde{\tau }$,$\tilde{\chi }_1^{0}$). The yields are normalized to the theoretical cross sections. The baseline selection requires exactly two hadronic tau candidates passing the kinematic and trigger requirements and no additional electrons or muons.
References
1 G. 't Hooft Naturalness, chiral symmetry, and spontaneous chiral symmetry breaking NATO Sci. Ser. B 59 (1980)135
2 E. Witten Dynamical breaking of supersymmetry Nucl. Phys. B 188 (1981) 513
3 M. Dine, W. Fischler, and M. Srednicki Supersymmetric technicolor Nucl. Phys. B 189 (1981) 575
4 S. Dimopoulos and S. Raby Supercolor Nucl. Phys. B 192 (1981) 353
5 S. Dimopoulos and H. Georgi Softly broken supersymmetry and SU(5) Nucl. Phys. B 193 (1981) 150
6 R. K. Kaul and P. Majumdar Cancellation of quadratically divergent mass corrections in globally supersymmetric spontaneously broken gauge theories Nucl. Phys. B 199 (1982) 36
7 J. Wess and B. Zumino Supergauge transformations in four-dimensions Nucl. Phys. B 70 (1974) 39
8 G. R. Farrar and P. Fayet Phenomenology of the Production, Decay, and Detection of New Hadronic States Associated with Supersymmetry PLB 76 (1978) 575
9 C. Boehm, A. Djouadi, and M. Drees Light scalar top quarks and supersymmetric dark matter PRD 62 (2000) 035012 hep-ph/9911496
10 C. Bal\'azs, M. Carena, and C. E. M. Wagner Dark matter, light stops and electroweak baryogenesis PRD 70 (2004) 015007 hep-ph/403224
11 G. Jungman, M. Kamionkowski, and K. Griest Supersymmetric dark matter PR 267 (1996) 195 hep-ph/9506380
12 G. Hinshaw and et al. Nine-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Parameter Results The Astrophysical Journal Supplement Series 208 (2013) 19 1212.5226
13 K. Griest and D. Seckel Three exceptions in the calculation of relic abundances PRD 43 (1991) 3191
14 D. A. Vasquez, G. Belanger, and C. Boehm Revisiting light neutralino scenarios in the MSSM PRD 84 (2011) 095015 1108.1338
15 S. King, J. Roberts, and D. Roy Natural Dark Matter in SUSY GUTs with Non-universal Gaugino Masses JHEP 10 (2007) 106 0705.4219
16 J. Ellis, T. Fak, K. A. Olive, and M. Srednicki Natural Dark Matter in SUSY GUTs with Non-universal Gaugino Masses Astropart. Phys. 13 (2000) 181 9905481
17 LEP SUSY Working Group Notes LEPSUSYWG/04-01.1
18 ATLAS Collaboration Search for the direct production of charginos, neutralinos and staus in final states with at least two hadronically decaying taus and missing transverse momentum in pp collisions at $ \sqrt{s} = $ 8 TeV with the ATLAS detector JHEP 10 (2014) 96 1407.0350
19 ATLAS Collaboration Search for the electroweak production of supersymmetric particles in $ \sqrt{s} = $ 8 TeV pp collisions with the ATLAS detector PRD 93 (2016) 052002 1509.07152
20 CMS Collaboration Search for electroweak production of charginos in final states with two tau leptons in pp collisions at $ \sqrt{s}=$ 8 TeV JHEP 04 (2017) 018 CMS-SUS-14-022
1610.04870
21 CMS Collaboration Particle-flow reconstruction and global event description with the CMS detector Submitted to JINST CMS-PRF-14-001
1706.04965
22 M. Cacciari, G. P. Salam, and G. Soyez The anti-$ k_t $ jet clustering algorithm JHEP 04 (2008) 063 0802.1189
23 M. Cacciari, G. P. Salam, and G. Soyez FastJet user manual EPJC 72 (2012) 1896 1111.6097
24 CMS Collaboration Study of pileup removal algorithms for jets CMS-PAS-JME-14-001 CMS-PAS-JME-14-001
25 CMS Collaboration Identification of b-quark jets with the CMS experiment JINST 8 (2013) P04013 CMS-BTV-12-001
1211.4462
26 CMS Collaboration Identification of b quark jets at the CMS experiment in the LHC Run 2 CMS-PAS-BTV-15-001 CMS-PAS-BTV-15-001
27 CMS Collaboration Reconstruction and identification of $ \tau $ lepton decays to hadrons and $ \nu_\tau $ at CMS JINST 11 (2016) P01019 CMS-TAU-14-001
1510.07488
28 CMS Collaboration Performance of reconstruction and identification of tau leptons in their decays to hadrons and tau neutrino in LHC Run-2 CMS-PAS-TAU-16-002 CMS-PAS-TAU-16-002
29 CMS Collaboration Performance of electron reconstruction and selection with the CMS detector in proton-proton collisions at $ \sqrt{s} = $ 8 TeV JINST 10 (2015) P06005 CMS-EGM-13-001
1502.02701
30 CMS Collaboration Performance of CMS muon reconstruction in $ pp $ collision events at $ \sqrt{s} = $ 7 TeV JINST 7 (2012) P10002 CMS-MUO-10-004
1206.4071
31 J. Alwall et al. The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations JHEP 07 (2014) 079 1405.0301
32 NNPDF Collaboration Parton distributions for the LHC Run II JHEP 04 (2015) 040 1410.8849
33 P. Nason A new method for combining NLO QCD with shower Monte Carlo algorithms JHEP 11 (2004) 040 hep-ph/0409146
34 S. Frixione, P. Nason, and C. Oleari Matching NLO QCD computations with Parton Shower simulations: the POWHEG method JHEP 11 (2007) 070 0709.2092
35 S. Alioli, P. Nason, C. Oleari, and E. Re A general framework for implementing NLO calculations in shower Monte Carlo programs: the POWHEG BOX JHEP 06 (2010) 043 1002.2581
36 E. Re Single-top $ Wt $-channel production matched with parton showers using the POWHEG method EPJC 71 (2011) 1547 1009.2450
37 T. Sjostrand et al. An introduction to PYTHIA 8.2 CPC 191 (2015) 159 1410.3012
38 GEANT4 Collaboration GEANT4 --- a simulation toolkit NIMA 506 (2003) 250
39 S. Abdullin et al. The fast simulation of the CMS detector at LHC J. Phys. Conf. Ser. 331 (2011) 032049
40 B. Fuks, M. Klasen, D. R. Lamprea, and M. Rothering Revisiting slepton pair production at the Large Hadron Collider JHEP 01 (2014) 168 1310.2621
41 C. G. Lester and D. J. Summers Measuring masses of semiinvisibly decaying particles pair produced at hadron colliders PLB 463 (1999) 99 hep-ph/9906349
42 A. Barr, C. Lester, and P. Stephens m(T2): The truth behind the glamour JPG 29 (2003) 2343 hep-ph/0304226
43 CMS Collaboration Interpretation of searches for supersymmetry with simplified models PRD 88 (2013) 052017 CMS-SUS-11-016
1301.2175
44 J. Alwall, P. Schuster, and N. Toro Simplified models for a first characterization of new physics at the lhc PRD 79 (2009) 075020
45 J. Alwall, M.-P. Le, M. Lisanti, and J. Wacker Model-independent jets plus missing energy searches PRD 79 (2009) 015005
46 LHC New Physics Working Group, D. Alves et al. Simplified models for LHC new physics searches JPG 39 (2012) 105005 1105.2838
47 T. Junk Confidence level computation for combining searches with small statistics NIMA 434 (1999) 435 hep-ex/9902006
48 A. L. Read Presentation of search results: the $ CL_{S} $ technique JPG 28 (2002) 2693
49 ATLAS and CMS Collaborations, LHC Higgs Combination Group Procedure for the LHC Higgs boson search combination in Summer 2011 ATL-PHYS-PUB 2011-11, CMS NOTE 2011/005
50 G. Cowan, K. Cranmer, E. Gross, and O. Vitells Asymptotic formulae for likelihood-based tests of new physics EPJC 71 (2011) 1554 1007.1727
Compact Muon Solenoid
LHC, CERN