CMS-PAS-SUS-19-003

CMS-PAS-SUS-19-003
Search for top squark pair production in a di-tau final state in proton-proton collisions at $\sqrt{s} =$ 13 TeV
CMS Collaboration
May 2019

Abstract: A search for the pair production of the supersymmetric partner of the top quark, the top squark, produced in proton-proton collision events at $\sqrt{s} =$ 13 TeV is presented in final states containing hadronically decaying tau leptons and large missing transverse momentum. These final states are highly sensitive to high $\tan{\beta}$ or higgsino-like scenarios in which decays of electroweak gauginos to tau leptons are dominant. The search uses a dataset corresponding to an integrated luminosity of 77 fb $^{-1}$ which was recorded by the CMS detector during 2016 and 2017. No significant excess is observed with respect to the background prediction, and exclusion limits at 95% confidence level are presented in the top squark and lightest neutralino mass plane within the framework of simplified models. It is found that top squark masses up to 1100 GeV are excluded for a nearly massless neutralino.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, JHEP 02 (2020) 015. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Top squark pair production in proton-proton collisions at the LHC, producing pairs of b quarks and taus accompanied with neutrinos and LSPs in the final state.
png pdf	Figure 1-a: Top squark pair production in proton-proton collisions at the LHC, producing pairs of b quarks and taus accompanied with neutrinos and LSPs in the final state.
png pdf	Figure 1-b: Top squark pair production in proton-proton collisions at the LHC, producing pairs of b quarks and taus accompanied with neutrinos and LSPs in the final state.
png pdf	Figure 1-c: Top squark pair production in proton-proton collisions at the LHC, producing pairs of b quarks and taus accompanied with neutrinos and LSPs in the final state.
png pdf	Figure 1-d: Top squark pair production in proton-proton collisions at the LHC, producing pairs of b quarks and taus accompanied with neutrinos and LSPs in the final state.
png pdf	Figure 2: Distributions of the search variables ${{p_{\mathrm {T}}} ^\text {miss}}$ , ${m_\text {T2}}$ , and ${H_{\mathrm {T}}}$ after baseline selections for data and the predicted background. The distributions for a few representative signal points corresponding to $x =$ 0.5 and [ $m_{\tilde{\mathrm{t}}_{1}}$ , $m_{\tilde{\chi}^0_1}$ ] = [300, 100] GeV, [500, 350] GeV, and [800, 300] GeV are overlaid.
png pdf	Figure 2-a: Distribution of the search variable ${{p_{\mathrm {T}}} ^\text {miss}}$ after baseline selections for data and the predicted background. The distributions for a few representative signal points corresponding to $x =$ 0.5 and [ $m_{\tilde{\mathrm{t}}_{1}}$ , $m_{\tilde{\chi}^0_1}$ ] = [300, 100] GeV, [500, 350] GeV, and [800, 300] GeV are overlaid.
png pdf	Figure 2-b: Distribution of the search variable ${m_\text {T2}}$ after baseline selections for data and the predicted background. The distributions for a few representative signal points corresponding to $x =$ 0.5 and [ $m_{\tilde{\mathrm{t}}_{1}}$ , $m_{\tilde{\chi}^0_1}$ ] = [300, 100] GeV, [500, 350] GeV, and [800, 300] GeV are overlaid.
png pdf	Figure 2-c: Distribution of the search variable ${H_{\mathrm {T}}}$ after baseline selections for data and the predicted background. The distributions for a few representative signal points corresponding to $x =$ 0.5 and [ $m_{\tilde{\mathrm{t}}_{1}}$ , $m_{\tilde{\chi}^0_1}$ ] = [300, 100] GeV, [500, 350] GeV, and [800, 300] GeV are overlaid.
png pdf	Figure 3: The 15 search regions defined in bins of ${{p_{\mathrm {T}}} ^\text {miss}}$ , ${m_\text {T2}}$ , and ${H_{\mathrm {T}}}$ .
png pdf	Figure 4: Plots showing the purities (top), scale-factors (middle), and $\text {SF}^{e \mu} - \text {SF}^{\mu \mu}$ (bottom) in the different bins of the ${\mathrm{t} {}\mathrm{\bar{t}}}$ CR for 2016 (left) and 2017 (right) data.
png pdf	Figure 4-a: Plots showing the purities (top), scale-factors (middle), and $\text {SF}^{e \mu} - \text {SF}^{\mu \mu}$ (bottom) in the different bins of the ${\mathrm{t} {}\mathrm{\bar{t}}}$ CR for 2016 data.
png pdf	Figure 4-b: Plots showing the purities (top), scale-factors (middle), and $\text {SF}^{e \mu} - \text {SF}^{\mu \mu}$ (bottom) in the different bins of the ${\mathrm{t} {}\mathrm{\bar{t}}}$ CR for 2017 data.
png pdf	Figure 5: Event yields in the 15 search bins as defined in Figure 3. The yields for a few representative signal points corresponding to $x =$ 0.5 and [ $m_{\tilde{\mathrm{t}}_{1}}$ , $m_{\tilde{\chi}^0_1}$ ] = [300, 100] GeV, [500, 350] GeV, and [800, 300] GeV are overlaid.
png pdf	Figure 6: The exclusion limits at 95% CL for the pair production of the top squark decaying in a di-tau final state are displayed in the $m_{\tilde{\mathrm{t}}_{1}} \text {-} m_{\tilde{\chi}^0_1}$ plane for $x =$ 0.25 (top left), 0.5 (top right) and 0.75 (bottom), as described in Equation 1. The black (red) lines represent the observed (expected) limits. The solid lines represent the central values, and the dashed lines the one standard deviation variation due to the theoretical or experimental uncertainties around the central values. The colour shading corresponds to the observed limit on the cross section.
png pdf	Figure 6-a: The exclusion limits at 95% CL for the pair production of the top squark decaying in a di-tau final state are displayed in the $m_{\tilde{\mathrm{t}}_{1}} \text {-} m_{\tilde{\chi}^0_1}$ plane for $x =$ 0.25, as described in Equation 1. The black (red) lines represent the observed (expected) limits. The solid lines represent the central values, and the dashed lines the one standard deviation variation due to the theoretical or experimental uncertainties around the central values. The colour shading corresponds to the observed limit on the cross section.
png pdf	Figure 6-b: The exclusion limits at 95% CL for the pair production of the top squark decaying in a di-tau final state are displayed in the $m_{\tilde{\mathrm{t}}_{1}} \text {-} m_{\tilde{\chi}^0_1}$ plane for $x =$ 0.5, as described in Equation 1. The black (red) lines represent the observed (expected) limits. The solid lines represent the central values, and the dashed lines the one standard deviation variation due to the theoretical or experimental uncertainties around the central values. The colour shading corresponds to the observed limit on the cross section.
png pdf	Figure 6-c: The exclusion limits at 95% CL for the pair production of the top squark decaying in a di-tau final state are displayed in the $m_{\tilde{\mathrm{t}}_{1}} \text {-} m_{\tilde{\chi}^0_1}$ plane for $x =$ 0.75, as described in Equation 1. The black (red) lines represent the observed (expected) limits. The solid lines represent the central values, and the dashed lines the one standard deviation variation due to the theoretical or experimental uncertainties around the central values. The colour shading corresponds to the observed limit on the cross section.

Tables
png pdf	Table 1: Relative systematic uncertainties from different sources on signal and background yields in 2016 and 2017 combined. These values are the weighted (by the yields in the respective bins) averages of the relative uncertainties in the different search bins. For the asymmetric uncertainties, the upper (lower) entry is the uncertainty due to the upward (downward) variation. The numbers in box brackets in the heading indicate the top squark and LSP masses in GeV, respectively.
png pdf	Table 2: Event yields along with statistical and systematic uncertainties in 2016 and 2017 combined, for different background sources in the 15 search bins as defined in Figure 3. The notation used here is, $\text {yield} ^{+\text {stat} +\text {syst}}_{-\text {stat}-\text {syst}}$ .

Summary

The signature of top squark pair production in final states with two tau leptons has been explored in data collected by the CMS detector during 2016 and 2017, corresponding to integrated luminosities of 35.9 fb

$^{-1}$ and 41.3 fb

$^{-1}$ , respectively. The search was performed in a final state containing an oppositely charged hadronic tau lepton pair, at least one jet identified as likely to contain a b hadron, and missing transverse momentum. The dominant standard model backgrounds were found to originate from top quark pair production and processes where jets were misidentified as hadronic tau lepton decays. Data driven techniques were followed to estimate these backgrounds, while other backgrounds were estimated using simulations.

No significant excess was observed, and exclusion limits on top squark masses in terms of neutralino masses were set at 95% confidence level, within the framework of simplfied models where the top squark decays via a chargino to final states including tau leptons. In such models, top squark masses have been excluded up to 1100 GeV for an almost massless LSP, and LSP masses up to 450 GeV have been excluded for a top squark mass of 900 GeV. These results are very useful in probing a region of the supersymmetric parameter space corresponding to high

$\tan\beta$ and higgsino-like scenarios.

References
1	P. Ramond	Dual Theory for Free Fermions	PRD3 (1971) 2415--2418
2	\relax Yu. A. Golfand and E. P. Likhtman	Extension of the Algebra of Poincare Group Generators and Violation of p Invariance	JEPTL 13 (1971) 323--326.[Pisma Zh. Eksp. Teor. Fiz.13,452(1971)]
3	A. Neveu and J. H. Schwarz	Factorizable dual model of pions	NPB31 (1971) 86--112
4	J. Wess and B. Zumino	A Lagrangian Model Invariant Under Supergauge Transformations	PL49B (1974) 52
5	P. Fayet	Supergauge Invariant Extension of the Higgs Mechanism and a Model for the electron and Its Neutrino	NPB90 (1975) 104--124
6	G. 't Hooft	Naturalness, chiral symmetry, and spontaneous chiral symmetry breaking	NATO Sci. Ser. B 59 (1980) 135--157
7	R. K. Kaul and P. Majumdar	Cancellation of Quadratically Divergent Mass Corrections in Globally Supersymmetric Spontaneously Broken Gauge Theories	NPB199 (1982) 36
8	H. P. Nilles	Supersymmetry, Supergravity and Particle Physics	PR 110 (1984) 1--162
9	S. P. Martin	A Supersymmetry primer		hep-ph/9709356
10	J. R. Ellis, K. Enqvist, D. V. Nanopoulos, and F. Zwirner	Observables in Low-Energy Superstring Models	MPLA1 (1986) 57
11	R. Barbieri and G. F. Giudice	Upper Bounds on Supersymmetric Particle Masses	NPB306 (1988) 63--76
12	H. Baer et al.	Collider phenomenology for supersymmetry with large tan Beta	PRL 79 (1997) 986--989	hep-ph/9704457
13	M. Guchait and D. P. Roy	Using $\tau$ polarization as a distinctive SUGRA signature at LHC	PLB541 (2002) 356--361	hep-ph/0205015
14	J. Alwall, P. Schuster, and N. Toro	Simplified Models for a First Characterization of New Physics at the LHC	PRD79 (2009) 075020	0810.3921
15	LHC New Physics Working Group Collaboration	Simplified Models for LHC New Physics Searches	JPG39 (2012) 105005	1105.2838
16	CMS Collaboration	Search for top squark pair production in pp collisions at $\sqrt{s}=$ 13 TeV using single lepton events	JHEP 10 (2017) 019	CMS-SUS-16-051 1706.04402
17	CMS Collaboration	Search for top squarks and dark matter particles in opposite-charge dilepton final states at $\sqrt{s}=$ 13 TeV	PRD97 (2018), no. 3, 032009	CMS-SUS-17-001 1711.00752
18	CMS Collaboration	Search for top-squark pair production in the single-lepton final state in pp collisions at $\sqrt{s} =$ 8 TeV	EPJC73 (2013), no. 12	CMS-SUS-13-011 1308.1586
19	CMS Collaboration	Search for direct pair production of scalar top quarks in the single- and dilepton channels in proton-proton collisions at $\sqrt{s}=$ 8 TeV	JHEP 07 (2016) 027	CMS-SUS-14-015 1602.03169
20	CMS Collaboration	Search for top squark pair production in compressed-mass-spectrum scenarios in proton-proton collisions at $\sqrt{s} =$ 8 TeV using the $\alpha_T$ variable	PLB767 (2017) 403--430	CMS-SUS-14-006 1605.08993
21	CMS Collaboration	Searches for pair production of third-generation squarks in $\sqrt{s}=$ 13 TeV pp collisions	EPJC77 (2017), no. 5, 327	CMS-SUS-16-008 1612.03877
22	CMS Collaboration	Search for direct production of supersymmetric partners of the top quark in the all-jets final state in proton-proton collisions at $\sqrt{s}=$ 13 TeV	JHEP 10 (2017) 005	CMS-SUS-16-049 1707.03316
23	CMS Collaboration	Search for supersymmetry in proton-proton collisions at 13 TeV using identified top quarks	PRD97 (2018), no. 1, 012007	CMS-SUS-16-050 1710.11188
24	ATLAS Collaboration	Search for direct top squark pair production in final states with two leptons in $\sqrt{s} =$ 13 TeV pp collisions with the ATLAS detector	EPJC77 (2017), no. 12, 898	1708.03247
25	ATLAS Collaboration	ATLAS Run 1 searches for direct pair production of third-generation squarks at the Large Hadron Collider	EPJC75 (2015), no. 10, 510	1506.08616
26	ATLAS Collaboration	Search for top squark pair production in final states with one isolated lepton, jets, and missing transverse momentum in $\sqrt s = 8 TeV pp$ collisions with the ATLAS detector	JHEP 11 (2014) 118	1407.0583
27	ATLAS Collaboration	Search for direct top-squark pair production in final states with two leptons in pp collisions at $\sqrt{s} =$ 8TeV with the ATLAS detector	JHEP 06 (2014) 124	1403.4853
28	ATLAS Collaboration	Search for top squarks in final states with one isolated lepton, jets, and missing transverse momentum in $\sqrt{s}=$ 13 TeV pp collisions with the ATLAS detector	PRD94 (2016), no. 5, 052009	1606.03903
29	ATLAS Collaboration	Search for top squarks decaying to tau sleptons in $pp$ collisions at $\sqrt{s}=$ 13 TeV with the atlas detector	PRD 98 (Aug, 2018) 032008
30	CMS Collaboration	The CMS experiment at the CERN LHC	JINST 3 (2008) S08004	CMS-00-001
31	CMS Collaboration	The CMS trigger system	JINST 12 (2017) P01020	CMS-TRG-12-001 1609.02366
32	C. Oleari	The powheg box	Nuclear Physics B - Proceedings Supplements 205-206 (2010) 36 -- 41, . Loops and Legs in Quantum Field Theory
33	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
34	T. Sjostrand, S. Mrenna, and P. Z. Skands	PYTHIA 6.4 Physics and Manual	JHEP 05 (2006) 026	hep-ph/0603175
35	CMS Collaboration	Event generator tunes obtained from underlying event and multiparton scattering measurements	CDS
36	CMS Collaboration	Extraction and validation of a new set of CMS PYTHIA8 tunes from underlying-event measurements		CMS-GEN-17-001 1903.12179
37	GEANT4 Collaboration	GEANT4: A Simulation toolkit	NIMA506 (2003) 250--303
38	W. Beenakker, R. Hopker, M. Spira, and P. M. Zerwas	Squark and gluino production at hadron colliders	NPB 492 (1997) 51	hep-ph/9610490
39	A. Kulesza and L. Motyka	Threshold resummation for squark-antisquark and gluino-pair production at the LHC	PRL 102 (2009) 111802	0807.2405
40	A. Kulesza and L. Motyka	Soft gluon resummation for the production of gluino-gluino and squark-antisquark pairs at the LHC	PRD 80 (2009) 095004	0905.4749
41	W. Beenakker et al.	Soft-gluon resummation for squark and gluino hadroproduction	JHEP 12 (2009) 041	0909.4418
42	W. Beenakker et al.	Squark and gluino hadroproduction	Int. J. Mod. Phys. A 26 (2011) 2637	1105.1110
43	A. Giammanco	The Fast Simulation of the CMS Experiment	J. Phys. Conf. Ser. 513 (2014) 022012
44	CMS Collaboration	Particle-flow reconstruction and global event description with the cms detector	JINST 12 (2017) P10003	CMS-PRF-14-001 1706.04965
45	M. Cacciari, G. P. Salam, and G. Soyez	The anti- $k_t$ jet clustering algorithm	JHEP 04 (2008) 063	0802.1189
46	M. Cacciari, G. P. Salam, and G. Soyez	FastJet user manual	EPJC 72 (2012) 1896	1111.6097
47	CMS Collaboration	Jet energy scale and resolution in the CMS experiment in pp collisions at 8 TeV	JINST 12 (2017) P02014	CMS-JME-13-004 1607.03663
48	CMS Collaboration	Identification of heavy-flavour jets with the CMS detector in pp collisions at 13 TeV	JINST 13 (2018) P05011	CMS-BTV-16-002 1712.07158
49	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
50	CMS Collaboration	Performance of the CMS muon detector and muon reconstruction with proton-proton collisions at $\sqrt{s} =$ 13 TeV	JINST 13 (2018) P06015	CMS-MUO-16-001 1804.04528
51	M. Cacciari and G. P. Salam	Pileup subtraction using jet areas	Physics Letters B 659 (2008), no. 1, 119 -- 126
52	CMS Collaboration	Performance of missing transverse momentum reconstruction in proton-proton collisions at $\sqrt{s} =$ 13 TeV using the CMS detector	Submitted to: JINST (2019)	CMS-JME-17-001 1903.06078
53	CMS Collaboration	Technical proposal for the Phase-II upgrade of the Compact Mon Solenoid	CMS-PAS-TDR-15-002	CMS-PAS-TDR-15-002
54	CMS Collaboration	Performance of reconstruction and identification of $\tau$ leptons decaying to hadrons and v $_\tau$ in pp collisions at $\sqrt{s}=$ 13 TeV	Journal of Instrumentation 13 (Oct, 2018) P10005--P10005
55	C. G. Lester and D. J. Summers	Measuring masses of semiinvisibly decaying particles pair produced at hadron colliders	PLB463 (1999) 99--103	hep-ph/9906349
56	A. Barr, C. Lester, and P. Stephens	m(T2): The Truth behind the glamour	JPG29 (2003) 2343--2363	hep-ph/0304226
57	A. J. Barr and C. Gwenlan	The Race for supersymmetry: Using m(T2) for discovery	PRD80 (2009) 074007	0907.2713
58	CMS Collaboration	Search for heavy neutrinos and third-generation leptoquarks in hadronic states of two $\tau$ leptons and two jets in proton-proton collisions at $\sqrt{s} =$ 13 TeV	JHEP 03 (2019) 170	CMS-EXO-17-016 1811.00806
59	CMS Collaboration	Search for supersymmetry in events with a $\tau$ lepton pair and missing transverse momentum in proton-proton collisions at $\sqrt{s} =$ 13 TeV	JHEP 11 (2018) 151	CMS-SUS-17-003 1807.02048
60	CMS Collaboration	Measurement of the differential Drell-Yan cross section in proton-proton collisions at $\sqrt{s} =$ 13 TeV	Submitted to: JHEP (2018)	CMS-SMP-17-001 1812.10529
61	CMS Collaboration	Measurements of $\mathrm{t\overline{t}}$ differential cross sections in proton-proton collisions at $\sqrt{s}=$ 13 TeV using events containing two leptons	JHEP 02 (2019) 149	CMS-TOP-17-014 1811.06625
62	CMS Collaboration	Measurement of the WW cross section pp collisions at sqrt(s)=13 TeV	CMS-PAS-SMP-16-006	CMS-PAS-SMP-16-006
63	CMS Collaboration	Measurement of top quark pair production in association with a Z boson in proton-proton collisions at $\sqrt{s} =$ 13 TeV	CMS-PAS-TOP-18-009	CMS-PAS-TOP-18-009
64	CMS Collaboration	Measurement of differential cross sections and charge ratios for t-channel single top quark production at 13 TeV	CMS-PAS-TOP-17-023	CMS-PAS-TOP-17-023
65	CMS Collaboration	Measurements of the pp $\to$ WZ inclusive and differential production cross section and constraints on charged anomalous triple gauge couplings at $\sqrt{s} =$ 13 TeV	JHEP 04 (2019) 122	CMS-SMP-18-002 1901.03428
66	CMS Collaboration	Measurement of the differential cross sections for the associated production of a $W$ boson and jets in proton-proton collisions at $\sqrt{s}=$ 13 TeV	PRD96 (2017), no. 7, 072005	CMS-SMP-16-005 1707.05979
67	T. Junk	Confidence level computation for combining searches with small statistics	Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 434 (1999), no. 2, 435 -- 443
68	A. L. Read	Presentation of search results: the CLs technique	Journal of Physics G: Nuclear and Particle Physics 28 (sep, 2002) 2693--2704
69	The ATLAS Collaboration, The CMS Collaboration, The LHC Higgs Combination Group Collaboration	Procedure for the LHC Higgs boson search combination in Summer 2011
70	G. Cowan, K. Cranmer, E. Gross, and O. Vitells	Asymptotic formulae for likelihood-based tests of new physics	EPJC71 (2011) 1554	1007.1727