CMS-PAS-EXO-16-016

CMS-PAS-EXO-16-016
Search for heavy neutrinos and third-generation leptoquarks in final states with two hadronically decaying $\tau$ leptons and two jets in proton-proton collisions at $\sqrt{s} =$ 13 TeV
CMS Collaboration
June 2016

Abstract: A search for heavy, right-handed neutrinos, $N_{l}$, and right-handed $W_{R}$ bosons, which arise in the left-right symmetric extensions of the standard model, has been performed. The search focuses on the scenario where the $W_{R}$ and $N_{l}$ decay chains result in a pair of high-$p_{\mathrm{T}}$ $\tau$ leptons which decay hadronically, in addition to two high-$p_{\mathrm{T}}$ jets and missing transverse energy from the $\tau$ lepton decays. The analysis is performed using 2.1 fb$^{-1}$ of data collected by the CMS experiment in 2015 at $\sqrt{s} = $ 13 TeV. For models with strict left-right symmetry, and assuming only $N_{\tau}$ flavor contributes significantly to the $W_{R}$ decay width, $W_{R}$ masses below 2.35 (1.63) TeV are excluded at a 95% confidence level, assuming the $N_{\tau}$ mass is 0.8 (0.2) times the mass of $W_{R}$ boson. To illustrate the sensitivity of this analysis to other new physics models, focus is also placed on pair production of third-generation scalar leptoquarks with decay into $\tau\tau \mathrm{bb}$. Third-generation scalar leptoquarks with masses below 740 GeV are excluded, assuming a 100% branching fraction for the leptoquark decay to a $\tau$ lepton and a bottom quark.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, JHEP 03 (2017) 077. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png	Figure 1-a: QCD shape closure test in $N_{j}< $ 2 data, which shows that the mass shape in non-isolated $\tau _{h}\tau _{h}$ control sample correctly models the ``true" shape in the isolated region (``Data").
png	Figure 1-b: QCD closure test of the ABCD method applied in $N_{j} < $ 2 data, which shows there is a good agreement between the nominal yield/shape and the predicted yield/shape.
png	Figure 1-c: QCD closure test in $N_{j} \geq$ 2 data, which shows the mass shape in non-isolated $\tau _{h}\tau _{h}$ control samples (``QCD" in the legend) correctly models the ``true" shape in the isolated region (``Data" in the legend).
png	Figure 1-d: QCD closure test in $N_{j} \geq$ 2 data, which shows the $S_{T}$ shape in non-isolated $\tau _{h}\tau _{h}$ control samples (``QCD" in the legend) correctly models the ``true" shape in the isolated region (``Data" in the legend).
png	Figure 2-a: $m(\tau _{h},\tau _{h},j,j, {E_{\mathrm {T}}^{\text {miss}}} )$ distribution in the SR.
png	Figure 2-b: $S_{T}$ distribution in the SR.
png	Figure 3-a: a: Expected and observed limits, at 95% confidence level, as functions of $m(W_{R})$ mass. b: Expected and observed limits, at 95% confidence level, as functions of LQ mass. The bands on the expected limits represent the one and two standard deviations obtained using a large sample of pseudo-experiments based on the background-only hypothesis for each bin of the mass and $S_{T}$ distributions.
png	Figure 3-b: a: Expected and observed limits, at 95% confidence level, as functions of $m(W_{R})$ mass. b: Expected and observed limits, at 95% confidence level, as functions of LQ mass. The bands on the expected limits represent the one and two standard deviations obtained using a large sample of pseudo-experiments based on the background-only hypothesis for each bin of the mass and $S_{T}$ distributions.
png	Figure 4: Observed and expected 95% CL upper limits on the production cross section for the ratio between $m(N_{\tau })$ and $m(W_{R})$ as a function of $m(W_{R})$.

Tables
png pdf	Table 1: Number of observed events in data and estimated background and signal rates in the SR.

Summary

A search is performed for physics beyond the SM in events with two energetic $\tau$ leptons, two energetic jets, and large momentum imbalance, using data corresponding to an integrated luminosity of 2.1 fb$^{-1}$ collected by the CMS detector in proton-proton collisions at $\sqrt{s}=$ 13 TeV. The search focuses on two benchmark new physics scenarios: (1) production of heavy right-handed neutrinos, $N_{l}$, and right-handed $W_{R}$ bosons which arise in the left-right symmetric extensions of the SM and where the $W_{R}$ and $N_{l}$ decay chains result in a pair of high-$p_{\mathrm{T}}$ $\tau$ leptons; (2) pair production of third-generation scalar leptoquarks which decay to $\tau\tau$bb. The observed $m(\tau_{h},\tau_{h},j,j,E_{\mathrm{T}}^{\text{miss}})$ and $S_{T}$ distributions do not reveal any evidence for new physics. Assuming only $N_{\tau}$ flavor contributes significantly to the $W_{R}$ decay width, $W_{R}$ masses below 2.35 (1.63) TeV are excluded at a 95% confidence level, assuming the $N_{\tau}$ mass is 0.8 (0.2) times the mass of $W_{R}$ boson. This is the first LHC result for $N_{l}$ searches with $\tau$ leptons. This analysis is the first to focus on searches for pair production of third-generation scalar leptoquarks using the $\tau_{h}\tau_{h} jj$ final state, resulting in an expected 95% CL exclusion of $m($LQ$)<$ 790 GeV and an observed exclusion of approximately 740 GeV.

References
1	M. Lindner, T. Ohlsson, and G. Seidl	Seesaw mechanisms for Dirac and Majorana neutrino masses	PRD65 (2002) 053014	hep-ph/0109264
2	P. Minkowski	$ \mu \to e\gamma $ at a Rate of One Out of $ 10^{9} $ Muon Decays?	PLB67 (1977) 421--428
3	R. N. Mohapatra and G. Senjanovic	Neutrino Mass and Spontaneous Parity Violation	PRL 44 (1980) 912
4	CMS Collaboration	Search for heavy neutrinos and $ \mathrm {W} $ bosons with right-handed couplings in proton-proton collisions at $ \sqrt{s} = 8\,\text {TeV} $	EPJC74 (2014), no. 11	CMS-EXO-13-008 1407.3683
5	J. Pati and A. Salam	Lepton number as the fourth color	PRD 10 (1974) 275
6	B. Gripaios	Composite leptoquarks at the LHC	JHEP 02 (2010) 045
7	H. Georgi and S. Glashow	Unity of All Elementary-Particle Forces	PRL 32 (1974) 438
8	CMS Collaboration	Search for heavy neutrinos and $ \mathrm {W} $ bosons with right-handed couplings in proton-proton collisions at $ \sqrt{s} = 8\,\text {TeV} $	EPJC74 (2014), no. 11	CMS-EXO-13-008 1407.3683
9	ATLAS Collaboration	Search for heavy neutrinos and right-handed $ W $ bosons in events with two leptons and jets in $ pp $ collisions at $ \sqrt{s}=7 $ TeV with the ATLAS detector	EPJC72 (2012) 2056	1203.5420
10	CMS Collaboration	The CMS experiment at the CERN LHC	JINST 03 (2008) S08004	CMS-00-001
11	CMS Collaboration	Commissioning of the Particle-Flow Reconstruction in Minimum-Bias and Jet Events from pp Collisions at 7~TeV
12	M. Cacciari, G. P. Salam, and G. Soyez	The Anti-k(t) jet clustering algorithm	JHEP 04 (2008) 063	0802.1189
13	CMS Collaboration	Pileup Jet Identification	Technical Report CMS-PAS-JME-13-005, CERN, Geneva
14	CMS Collaboration	Determination of jet energy calibration and transverse momentum resolution in CMS	JINST 6 (2011) 11002	CMS-JME-10-011 1107.4277
15	CMS Collaboration	Identification of b-quark jets with the CMS experiment	JINST 8 (2013) P04013
16	CMS Collaboration	Identification of b-quark Jets at the CMS Experiment in the LHC Run2 Startup
17	CMS Collaboration	Performance of muon identification in pp collisions at $ \sqrt{s}=7 $ TeV	JINST 07 (2012) P10002
18	CMS Collaboration	Performance of $ \tau $-lepton reconstruction and identification in CMS	JINST \bf 07 (2012) P01001
19	J. Alwall et al.	MadGraph 5 : Going Beyond	JHEP 06 (2011) 128	1106.0522
20	T. Sj\"ostrand, S. Mrenna, and P. Z. Skands	PYTHIA 6.4 Physics and Manual	JHEP 05 (2006) 026	hep-ph/0603175
21	Z. Was et al.	TAUOLA the library for tau lepton decay	NPPS 98 (2001) 96	hep-ph/0011305
22	GEANT4 Collaboration	GEANT4: A Simulation toolkit	NIM\bf A506 (2003) 250
23	M. Kramer, T. Plehn, M. Spira, and P. M. Zerwas	Pair production of scalar leptoquarks at the CERN LHC	PRD 71 (2005) 057503
24	CMS Collaboration	Measurement of the inclusive Z cross section via decays to tau pairs in pp collisions at $ \sqrt{s} = 7 $ TeV	JHEP 08 (2011) 117
25	CMS Collaboration	CMS Luminosity Measurement for the 2015 Data Taking Period
26	S. Alekhin et al.	The PDF4LHC Working Group Interim Report		1101.0536
27	M. Botje et al.	The PDF4LHC Working Group Interim Recommendations		1101.0538
28	P. M. Nadolsky et al.	Implications of CTEQ global analysis for collider observables	PRD 78 (2008) 013004	0802.0007
29	A. D. Martin, W. J. Stirling, R. S. Thorne, and G. Watt	Update of parton distributions at NNLO	PLB 652 (2007) 292
30	M. Ubiali	NNPDF1.0 parton set for the LHC	NPPS 186 (2009) 62
31	G. Nanava et al.	How to use SANC to improve the PHOTOS Monte Carlo simulation of bremsstrahlung in leptonic W-Boson decays	Acta Phys. Polon. B34 (2003) 4561	hep-ph/0303260
32	G. Miu et al.	W Production in an Improved Parton-Shower Approach	PLB449 (1999) 313