CMS-PAS-FTR-18-029

CMS-PAS-FTR-18-029
Search for excited leptons in $\ell \ell \gamma$ final states in proton-proton collisions at the HL-LHC
CMS Collaboration
December 2018

Abstract: A search for excited leptons (electrons and muons) is presented, using simulation of the upgraded CMS detector at the High-Luminosity LHC (HL-LHC). Excited leptons are predicted by many theories beyond the standard model (SM) where quarks and leptons are not elementary but instead are themselves composite objects. Excited leptons ($\ell^* = e^$, $\mu^$) in $\ell\ell\gamma$ ($\ell=$ e, $\mu$) final states where the excited lepton decays to a SM lepton and a photon ($\ell^*\rightarrow\ell\gamma$) are studied. The main background is Drell-Yan production in association with a photon. The HL-LHC environment (a centre of mass energy of 14 TeV and an integrated luminosity of 3000 fb$^{-1}$) allows for an extension of the discovery potential for excited leptons. The analysis is optimised for HL-LHC conditions, and indicates that 5$\sigma$ discovery of excited leptons is possible for masses up to 5.1 TeV. If no significant discrepancies are seen in the data, excited leptons with masses below 5.8 TeV could be excluded at 95% confidence level.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: The Feynman diagram of the production of excited leptons in $\ell \ell \gamma $ final states.
png pdf	Figure 2: 2D $ {m_{\ell \gamma}^\text {max}} $ versus $ {m_{\ell \gamma}^\text {min}} $ distribution after full selection with $ {\mathrm {Z}} \gamma$ background (blue circles) and signal ${e}^{}$ and ${\mu}^{}$ samples of ${m_{\ell ^*}} =$ 3.5 TeV (orange triangles) in the electron channel (left) and muon channel (right). The dashed green line indicates the lower bound of the search window.
png pdf	Figure 2-a: 2D $ {m_{\ell \gamma}^\text {max}} $ versus $ {m_{\ell \gamma}^\text {min}} $ distribution after full selection with $ {\mathrm {Z}} \gamma$ background (blue circles) and signal ${e}^{}$ and ${\mu}^{}$ samples of ${m_{\ell ^*}} =$ 3.5 TeV (orange triangles) in the electron channel. The dashed green line indicates the lower bound of the search window.
png pdf	Figure 2-b: 2D $ {m_{\ell \gamma}^\text {max}} $ versus $ {m_{\ell \gamma}^\text {min}} $ distribution after full selection with $ {\mathrm {Z}} \gamma$ background (blue circles) and signal ${e}^{}$ and ${\mu}^{}$ samples of ${m_{\ell ^*}} =$ 3.5 TeV (orange triangles) in the muon channel. The dashed green line indicates the lower bound of the search window.
png pdf	Figure 3: The product of signal acceptance and efficiency as a function of the generated resonance mass for the $ {\mathrm {e}} {\mathrm {e}}\gamma $ (lower) and $ {{\mu}} {{\mu}}\gamma $ (upper) channels. Each marker denotes the value measured from the simulated signal sample at a given mass point.
png pdf	Figure 4: Discovery significance for excited electrons (left) and muons (right) with 3000 fb$^{-1}$ at the HL-LHC.
png pdf	Figure 4-a: Discovery significance for excited electrons with 3000 fb$^{-1}$ at the HL-LHC.
png pdf	Figure 4-b: Discovery significance for excited muons with 3000 fb$^{-1}$ at the HL-LHC.
png pdf	Figure 5: Exclusion limits for excited electrons (left) and muons (right) on the product of cross section and branching fraction.
png pdf	Figure 5-a: Exclusion limits for excited electrons on the product of cross section and branching fraction.
png pdf	Figure 5-b: Exclusion limits for excited muons on the product of cross section and branching fraction.

Tables
png pdf	Table 1: Summary of the systematic uncertainties.

Summary

The search for excited leptons in final states with two leptons and a photon in proton-proton collisions at the High-Luminosity LHC (HL-LHC) is studied. The HL-LHC environment (a centre of mass energy of 14 TeV and an integrated luminosity of 3 ab$^{-1}$) allows for an extension of the discovery potential for excited leptons. The results are optimised for HL-LHC conditions, and it is found that excited leptons masses up to 5.5 (5.1) TeV can be excluded (discovered), for both excited electrons and excited muon states. Excited leptons could be excluded for masses below 5.8 TeV, at 95% confidence level.

References
1	O. W. Greenberg and C. A. Nelson	Composite models of leptons	PRD 10 (1974) 2567
2	J. C. Pati, A. Salam, and J. A. Strathdee	Are quarks composite?	PLB 59 (1975) 265
3	O. W. Greenberg and J. Sucher	A quantum structure dynamic model of quarks, leptons, weak vector bosons, and Higgs mesons	PLB 99 (1981) 339
4	H. Terazawa, M. Yasu\`e, K. Akama, and M. Hayshi	Observable effects of the possible substructure of leptons and quarks	PLB 112 (1982) 387
5	M. Abolins et al.	Testing the Compositeness of Quarks and Leptons	in Elementary Particles and Future Facilities (Snowmass 1982), p. 274 1982eConf C8206282
6	E. Eichten, K. D. Lane, and M. E. Peskin	New Tests for Quark and Lepton Substructure	PRL 50 (1983) 811
7	H. Harari	Composite models for quarks and leptons	Physics Reports 104 (1984) 159
8	U. Baur, M. Spira, and P. M. Zerwas	Excited quark and lepton production at hadron colliders	PRD 42 (1990) 815
9	S. Bhattacharya, S. S. Chauhan, B. C. Choudhary, and D. Choudhury	Search for excited quarks in $ q\overline{q} {\rightarrow} {\gamma} {\gamma} $ at the CERN LHC	PRD 76 (2007) 115017	0705.3472
10	S. Bhattacharya, S. S. Chauhan, B. C. Choudhary, and D. Choudhury	Quark Excitations Through the Prism of Direct Photon Plus Jet at the LHC	PRD 80 (2009) 015014	0901.3927
11	G. Apollinari et al.	High-Luminosity Large Hadron Collider (HL-LHC) : Preliminary Design Report
12	CMS Collaboration	Technical Proposal for the Phase-II Upgrade of the CMS Detector	CMS-PAS-TDR-15-002	CMS-PAS-TDR-15-002
13	CMS Collaboration	The Phase-2 Upgrade of the CMS Tracker	CDS
14	CMS Collaboration	The Phase-2 Upgrade of the CMS Barrel Calorimeters Technical Design Report	CDS
15	CMS Collaboration	The Phase-2 Upgrade of the CMS Endcap Calorimeter	CDS
16	CMS Collaboration	The Phase-2 Upgrade of the CMS Muon Detectors	CDS
17	CMS Collaboration	Expected performance of the physics objects with the upgraded CMS detector at the HL-LHC	CDS
18	ATLAS Collaboration	Search for excited leptons in proton-proton collisions at $ \sqrt{s} = $ 7~TeV with the ATLAS detector	PRD 85 (2012) 072003	1201.3293
19	ATLAS Collaboration	Search for excited electrons and muons in $ \sqrt{s} = $ 8~TeV proton-proton collisions with the ATLAS detector	New J. Phys. 15 (2013) 093011	1308.1364
20	ATLAS Collaboration	A search for an excited muon decaying to a muon and two jets in pp collisions at $ \sqrt{s} = $ 8 TeV with the ATLAS detector	New J. Phys. 18 (2016) 073021	1601.05627
21	CMS Collaboration	Search for excited leptons in $ pp $ collisions at $ \sqrt{s}= $ 7 TeV	PLB 720 (2013) 309	CMS-EXO-11-034 1210.2422
22	CMS Collaboration	Search for excited leptons in proton-proton collisions at $ \sqrt{s} = $ 8~TeV	JHEP 03 (2016) 125	CMS-EXO-14-015 1511.01407
23	CMS Collaboration	Search for excited leptons in $ {\ell \ell \gamma} $ final states in proton-proton collisions at $ \sqrt{s} = $ 13 TeV	CMS-PAS-EXO-18-004	CMS-PAS-EXO-18-004
24	ALEPH Collaboration	Search for excited leptons at 130--140 GeV	PLB 385 (1996) 445
25	DELPHI Collaboration	Search for composite and exotic fermions at LEP 2	EPJC 8 (1999) 41	hep-ex/9811005
26	OPAL Collaboration	Search for unstable heavy and excited leptons at LEP 2	EPJC 14 (2000) 73	hep-ex/0001056
27	L3 Collaboration	Search for excited leptons at LEP	PLB 568 (2003) 23	hep-ex/0306016
28	H1 Collaboration	Search for excited electrons in $ ep $ collisions at HERA	PLB 666 (2008) 131	0805.4530
29	CDF Collaboration	Search for Excited and Exotic Electrons in the $ e\gamma $ Decay Channel in $ \rm {p}\overline{\rm p} $ Collisions at $ \sqrt{s} = $ 1.96 TeV	PRL 94 (2005) 101802	hep-ex/0410013
30	CDF Collaboration	Search for Excited and Exotic Muons in the $ \mu\gamma $ Decay Channel in $ \rm {p}\overline{\rm p} $ Collisions at $ \sqrt{s} = $ 1.96 TeV	PRL 97 (2006) 191802	hep-ex/0606043
31	D0 Collaboration	Search for excited muons in $ {p}\overline{p} $ collisions at $ \sqrt{s} = $ 1.96 TeV	PRD 73 (2006) 111102	hep-ex/0604040
32	D0 Collaboration	Search for excited electrons in $ {p}\overline{p} $ collisions at $ \sqrt{s} = $ 1.96 TeV	PRD 77 (2008) 091102	0801.0877
33	T. Sjostrand, S. Mrenna, and P. Z. Skands	PYTHIA 6.4 physics and manual	JHEP 05 (2006) 026	hep-ph/0603175
34	J. Alwall et al.	MadGraph 5: going beyond	JHEP 06 (2011) 128	1106.0522
35	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
36	J. de Favereau et al.	DELPHES 3, A modular framework for fast simulation of a generic collider experiment	JHEP 02 (2014) 057	1307.6346
37	CMS Collaboration	Constraints on the Higgs boson self-coupling from ttH + tH, H $ \rightarrow \gamma\gamma $ differential measurements at the HL-LHC	CMS-PAS-FTR-18-020	CMS-PAS-FTR-18-020
38	CMS Collaboration	Projected performance of Higgs analyses at the HL-LHC for ECFA 2016	CDS
39	T. Junk	Confidence level computation for combining searches with small statistics	NIMA 434 (1999) 435	hep-ex/9902006
40	A. L. Read	Presentation of search results: the $ CL_s $ technique	JPG 28 (2002) 2693