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PoS(EPS-HEP2015)128 http://pos.sissa.it/ ∗† [email protected] Speaker. On behalf of the CMS and ATLAS collaborations Hints of new in B-physics sectorand have lepton lead flavor to violating considerable observables at interests the onthe LHC. the Standard Searches flavor Model physics for particles or lepton new flavor heavy violating particlesexperiment. decays have This of been talk conducted summarizes at Run the ATLAS 1 and searchesphysics CMS for in lepton multi-lepton/photon flavor final violating states. phenomena and new † ∗ Copyright owned by the author(s) under the terms of the Creative Commons c The European Physical Society Conference on22–29 High July Energy 2015 Physics Vienna, Austria Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). Shilpi Jain Searches for new phenomena in multileptonstates final with the ATLAS and CMS detectors National Central University, Taiwan E-mail: PoS(EPS-HEP2015)128 ] 9 which µ e Shilpi Jain ], and Peter → process. One 3 Z , µ pairs consistent 2 e ] and ATLAS [ µ 8 e → ] via one-loop decays Z 10 . CMS uses data-driven tech- ττ → ]. Z 14 on the branching ratio of region. With this analysis, CMS places a 7 − Z 10 × 5 2 . ] searched for oppositely charged ] in the neutral sector motivates the search for lepton 7 13 and heavy resonances. is predicted to be negligibly small [ Z µ e and new heavy resonances Z → ] and CMS [ Z etc. The first place to observe LVF decays is in 12 0 Z ], with and Richard Hagen [ 1 and ATLAS places a limit of 7 region and then extrapolating it in the 7 decays − Z ]. The properties of the observed Higgs are like the ones which are predicted 6 ]. Both ATLAS [ Z 10 mass. Dominant background to this analysis is , 5 11 × Z , , 4 10 The branching fraction of In spite of the absence of an underlying symmetry, lepton flavor is explicitly conserved in the The success of Run I of LHC is marked by the discovery of the which was 1. Study of LVF in decays of 2. Compositeness in the lepton sector 3. Type III seesaw models 4. New phenomena with multi-photon final state 2.1 LVF in limit of 7 look for signature of LVF in decays of with the niques to estimate the backgrounds, whereas,excluding ATLAS the estimated the background by fitting the data is one order of magnitude better than the results from LEP [ flavour violation in the chargeda sector clear as well. indication of Ifin new LVF in which physics charged such beyond sector signatures the is canheavy SM. observed, occur, neutral gauge it for There boson would e.g., are be R-parity other violating many SUSY, models new with physics an scenarios additional can observe the LVF signature in not yet observed heavy resonances. Both CMS [ with flavour-oscillating neutrinos, thus rendering itsiment. detection impossible Many in new any physics near models, future forcan exper- e.g., increase Dirac the or branching Majorana fraction neutrinos,LHC of [ R-parity lepton violating flavour SUSY violating Z decays which can be detected at 2. Search for LVF decays SM. The observation of neutrino oscillation [ within the Standard Modelunanswered (SM) by of the particle SM, for physics.leptons e.g., are we Still fundamental, do there neutrino not oscillation,study are yet etc. many of know the questions lepton Observation origin of which flavour ofstates neutrino are violating dark are oscillation (LVF) matter, rich makes sector if probes the the to interesting.can look quarks be for and Multi-lepton studied new physics in and beyond multi-lepton multi-photonprocesses, the and which final SM. includes multi-photon There the final following: are states. various processes This which paper focuses on few of those predicted in three papers written independentlyof in Higgs 1964. boson, known The as theory the whichwith Brout-Englert-Higgs predicted mechanism, Robert the was existence Brout proposed by [ Francois Englert Searches for new phenomena in multilepton final states in ATLAS and CMS 1. Introduction Higgs [ PoS(EPS-HEP2015)128 , ) s γ 0 ]. 0 = µ γ e `` `` Max ` , 21 e , 0 311 Λ = 20 s or 2 , ` 0 Shilpi Jain µ 19 , ] allowing for 01. 18 . (where 15 s or 4 0 0 [ γ e ) at a characteristic 0 = ∗ Z `` ` 132 and jets are assumed to Λ giving a final state of ν γ and then decaying to a SM ` , ATLAS constructs a 3 body is coming from the decay of a ∗ 01 and ` τ . and a 0 in RPV SUSY. This is for ` ) and leptons ( τ ˜ = ∗ ν q 0 311 is boosted (it being coming from decay Λ Z , two invariant masses are possible (M in SSM. ∗ 0 ` in case of search in ATLAS. Since ATLAS Z ] searched for excited electrons and muons in µτ which has missing transverse momentum in the 23 s). This gives a final state of 4 3 0 ] search for LVF in broad range spectrum of had µ and τ 17 τ decays to 2 jets. In case of CMS, for the decay mode in Quantum black hole production. e produced along with a SM Z , th s or 2 ∗ 0 µ ` e M ( e are collinear since 0 ] and CMS [ ` Z 2 and its decay further to a SM 22 ` ` ] and CMS [ 16 ) would reduce the signal efficiency by a large factor. To maintain the e 07. From CMS it is 1.3 TeV for . , collinear neutrino approximation is used where 0 τ Since there are two same flavour leptons in the final state without the knowl- ν ) and performs a cut and count analysis. Whereas, in case of CMS following = γ decaying to either 2 `` 132 along with SM in case of CMS and Z ), whereas, CMS looked for a wider spectrum of final states: Λ ∗ ` µ µ e , e is final state: , with = 0 , the decay products from γ 11 and Z ` . Since such excited states couple to the SM , these can be produced and further . `` Z `` edge of which lepton comes from the decay of 0 ` Λ As already mentioned above, new physics scenarios can increase the branching ratio of LVF SM of does not provide any explanation for three generations of fam- s. CMS also studied the case where 1. 1. ATLAS puts a limit of 2.0 TeV on the invariant mass of 2. ATLAS puts a limit of 2.5 TeV on3. the massCMS of puts a limit of 3.6 TeV on 0 → and a µ ∗ ` 2 ` of a heavy particle). In suchthe a case, decayed applying product the (e.g. standard isolation in calorimeter or tracker around invariant mass (M is done for the two different cases: efficiency in this case, relaxed isolation is applied. To search for scale decay via contact interactions toSM other gauge fermions boson. or Both via ATLAS gauge [ interactions to a SM fermion and a (where (which is the same as ATLAS), 2 Such models predict the existence of excited states of quarks ( Run I produced via contactproduction interactions of and decay via gauge interactions. ATLAS looked for the LVF decays. Both ATLAS [ decays. Such models predict the existence of a heavy neutral gauge boson Searches for new phenomena in multilepton final states in ATLAS and CMS 2.2 LVF decays of heavy resonances where searches for LVF decays in the final state of heavy resonance). This technique significantlyare improves the the limits mass from resolution. LHC: This way following final state, it becomes tough to reconstructmomentum the vector mass of of the heavy resonance. To reconstruct the four be collinear (based on the fact that if heavy resonance exists, then ilies. There are many physics modelsOne which of attempt to such explain family the observed ofthe hierarchy models observed of quarks which fermions. and leptons try are to composite explain objects of this fundamental observed constituents [ phenomena by postulating that 3. Search for excited leptons PoS(EPS-HEP2015)128 e γ 87, Max ` − . 0 τ . Here for any ∗ = ]. There ` Shilpi Jain µ ) channel. γ 24 Min ` V µ ) channel. ( / e µ ). Exactly the e ( V γ e Min ` and M ]); or weak-triplet 33 γ 0 and , Max ` . Assuming only and M 32 6 = , − τ γ V Max ` 31 10 , = 30 τ , V 29 = µ V = used in the excited lepton analysis in CMS. e V γ Min ` . This is further followed by the decay of heavy − 4 Σ + and M ] have searched for type III heavy-lepton partners of Σ γ 36 Max ` → Z ]); weak-triplet scalars ([ → 28 is reconstructed, one again is left with two same flavour leptons , q Z q 27 ) two invariant masses are possible (M , γ ] and CMS [ and `` 26 , 35 ± final state: masses below 2.35 (2.38) TeV are excluded in Σ 25 0 Z final state: masses below 2.45 (2.48) TeV are excluded in Once the Σ γ `` ) which can be produced through quark-annihilation via a virtual boson as `` − → in Σ 0 , in ± f gives an inverted “L-shape” feature for the signal, whereas, the background lies 0 0 ). Since one of the combinations is right (for an event), a 2-D scatter plot of M f Σ W − , ]). ATLAS [ γ γ shows the 2-D scatter plot M Min ` Min ` + = = → final state: 1 34 Σ 0 f f q which are the mixing angles between the SM and the triplet state. With this analysis, ` q 2 τ ` V and M and M also (as in the case of same procedure is followed as above by scanning the 2-D region of M 2 in the final state without the knowledge of which lepton comes from the decay of flat in this 2-D space.a In particular CMS, such signal an mass “L-shape” point, ismass a feature hypothesis 2-D is and region exploited that inverted for region “L-shape” is this region scanned search. is for For formed any around excess the above the SM expectation. excess above the SM expectation. , Observation of neutrino oscillation is a direct indication that neutrinos have mass [ There are many new physics scenarios (essentially extensions of SM) that can result in final In CMS also, cut and count analysis is performed. Both ATLAS and CMS did not see any Figure µ 2. For 1. For 2. V , e follows: state of three or more photons.more Following photons: are some of the models which predict a final state of 3 or 4. Heavy-lepton partners of neutrinos (Type III seesaw) are many models which can explain thisintroduces observation. new Among them heavy is the particles seesawaccounting that mechanism for which couple both the both neutrino toweak-singlet masses fermions the and ([ leptons their smallness. andfermions These to new ([ the heavy Higgs particles could doublets,neutrinos be thus ( mixing, CMS excludes mass of heavy resonance below 320 GeV. 5. New phenomena with multi-photon ATLAS excludes mass of the heavy resonance below 335 GeV for excess above the SMexcludes expectation massed and below 2.2 limits TeV, whereas, are CMS placed has the on following the limits: mass of excited lepton. ATLAS It also shows the 3-body invariant mass used for search in ATLAS. fermions to SM and leptons.ATLAS CMS looks searches for for a final 2 state isolated of 3 leptons leptons and and MET, whereas, at least 2 jets andwhereas, CMS MET. excludes Parameters masses of below the 280 theory GeV for are Searches for new phenomena in multilepton final states in ATLAS and CMS V PoS(EPS-HEP2015)128 +jets ) which [GeV] [GeV] [GeV] γ γγγ h eeeeee Shilpi Jain , W+ mmm t with scalars a ) = (0.2, 10) TeV ) = (0.5, 10) TeV ) = (0.8, 10) TeV Λ Λ Λ , , , γ e* e* e* Data 2012 Z + jets, diboson, t Bkg. uncertainty (m (m (m Z + -1 ) that can also decay to 2 photons. H = 8 TeV L dt = 13 fb loop or fermion loop. This decay is s ∫ ATLAS ± 200200200 400 400 400 600 600 600 800 800 800 1000 1000 1000 1200 1200 1200 1400 1400 1400 444 333 222 111 -1-1-1

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/ 100 GeV GeV GeV 100 100 100 / / / ee ee ee γ γ γ into two photons, thus giving a final state of ) with couplings to the Higgs boson ( a a used in the excited lepton analysis. Once can see the 5 ). Such models can have coupling of γ 1200 γ 4 Min ` M → 1 of LHC data at 8 TeV. It did not observe any excess (8 TeV) (GeV) ]. This branching ratio can be enhanced by the presence − -1 γ ]. Plot on the right shows the 3-body invariant mass used for aa VS 1000 e, min 37 23 M → )[ γ Data Background Signal 200 GeV Signal 1000 GeV Max ` 19.7 fb h 10 M − 800 ]. 10 22 × 5 600 ∼ ), with the subsequent decay of 400 a boson can decay into three photons via Z shows the Feynman diagrams of such processes. ATLAS performed a search in events 200 2 CMS Preliminary Plot on the left shows the

can further decay to photons ( which have masses different from the SM Higgs boson ( 3 photons. of some new physics. scalar boson ( negligibly small (

400 200 800 600

max Figure 1000 1200 M (GeV)

3. In SM, 1. Models which predict pseudo-scalar particles ( 2. Models which have additional gauge bosons that can decay to a photon and a new pseudo- e, γ “inverted L-shape” feature in the signal [ with at least three photons using 20.3 fb Figure 1: excited lepton search in ATLAS [ Searches for new phenomena in multilepton final states in ATLAS and CMS PoS(EPS-HEP2015)128 , Phys. , Phys. Shilpi Jain , Sci.China ] which is one 38 [ 6 − 10 ]. , Phys. Rev. Lett. (1964), × 39 , Phys. Rev. Lett. (1964), 2 . )[ 2 5 − , Phys. Rev. Lett. (1964), , Phys. Rev. Lett. (1967), < 10 , JINST 3:S08003 (2008) , Phys. Rev. Lett. (1964), ) < γ 3 , JINST 3:S08004 (2008) → Z ( BR , Phys. Rev. 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