Searches for heavy neutrinos and high-mass ditau resonances with CMS

Transcription

1 Searches for heavy neutrinos and high-mass ditau resonances with CMS Wang Feng On behalf of IHEP CMS group

2 Outline Introduction A new model with heavy composite Majorana neutrino and its search Search for heavy neutrinos, from the left-right model, with taus Search for high-mass ditau resonances (IHEP Beijing) Pag 2 / 16

3 Introduction People involved in the measurements (IHEP Beijing) Pag 3 / 16

4 Introduction Introduction Standard model (SM) of elementary particle physics Theory that can explain many experimental observations, but with un-resolved issues: experimental: neutrino masses, dark-matter/energy, gravity, baryogenesis theoretical: why SU SM : SU(3)xSU(2)xU(1), hierarchy problem Use the large hadron collider (LHC) to test the SM LHC results have shown a good agreement between data and expectations Few measurements has reported a mild excess during Run I (IHEP Beijing) Pag 4 / 16

5 2 Introduction Run I CMS anomalies in the eejj final state with 19.7 fb 1 Heavy neutrino search from the Left-Right model N(Events) (0.0)/(bin width) (pb) σ β 1st generation Lepto-Quark search CMS Preliminary s = 8 TeV Data, 19.6 fb LQ, M = 650 GeV, β Z + jets tt (from Data) Other backgrounds QCD multijets = S T (GeV) [LQ M = 650 selection] LQ LQ eejj ATLAS exclusion (1.03 fb, 7 TeV) CMS exclusion (5.0 fb, 7TeV) CMS exclusion (19.6 fb, 8 TeV) 2 σ theory β with unc., (β=1) Expected 95% CL upper limit Observed 95% CL upper limit CMS 2012 Preliminary M LQ (GeV) s = 8 TeV 2.5 σ effect in the eejj channel Independent excesses in the 2 analyses We studied a new model to interpret these results No excess in the µµjj channels No searches in the ττjj channels We performed a measurement in this final state Excess also in search for LeptoQuark of 1st Gen in eνjj (IHEP Beijing) Pag 5 / 16

6 Introduction Composite models for quarks and leptons (Ref: arxiv: ) Compositness of leptons and quarks is one possible scenario beyond the Standard Model If quarks and leptons are composite we expect Contact interaction: a residual interaction of the internal dynamics which should become manifest at some sufficiently high-energy scale, Λ Excited states of quarks and leptons Among the composite models we consider the weak isospin model It doesn t rely to the internal dynamics Fermion compositness trough weak isospin symmetry analogy with strong isospin prediction of hadronic states before the discovery of quarks and gluons (IHEP Beijing) Pag 6 / 16

7 Introduction Excess in eejj channel in our model The composite model scenario can take into account the HN eejj Run I excess via the production of a heavy composite (excited) neutrino. and can qualitatively reproduce the shape of the CMS excess in the M(eejj) distribution 1/N(dN/dM) (bin width GeV) signal Λ=TeV, m*=1250gev background tt - background W + W + W M(e,e,jet,jet) (GeV) It can reproduce also the absence of the excess in the µµjj channel and the predominance of opposite sign on same sign di-leptons events (see backup) (IHEP Beijing) Pag 7 / 16

8 Heavy composite Majorana nuetrino Heavy composite Majorana neutrino search with 2 leptons and 2 jets (Ref: CMS-EXO6-026) Consider ee+jj, µµ+jj channels ll: pt>1,35(50,30) GeV for ee(µµ), η < fat jet: pt>190 GeV, η < 2.4 Bkg estimation done consistently among channels Drell-Yan From simulation after data/mc correction taken from Z-peak Multijet From loose leptons weighted by probability of jet to be misidentified as leptons t t From eµ data scaled to the 2lep same-flavor region Events CMS Preliminary tt+tw DY Other Bkg stat. data 2.3 fb syst. (13 TeV) Events CMS Preliminary tt+tw DY Other Bkg stat. data 2.3 fb syst. Λ 5, M 2.5 [TeV] (13 TeV) 20 Λ 5, M 2.5 [TeV] Λ 5, M 3.5 [TeV] 20 Λ 5, M 3.5 [TeV] M(eeJ) (GeV) M(µµJ) (GeV) No excesses compared to the SM expectations (IHEP Beijing) Pag 8 / 16

9 Heavy composite Majorana nuetrino Heavy composite Majorna neutrino limits with 2 leptons and 2 jets σ(pp en) BR(N ejj) (pb) CMS 2 Preliminary fb Observed Expected ± Expected ± 1σ 2σ Theory (Λ 5 TeV) Theory uncertainty (13 TeV) σ(pp µn) BR(N µjj) (pb) CMS 2 Preliminary fb Observed Expected ± Expected ± 1σ 2σ Theory (Λ 5 TeV) Theory uncertainty (13 TeV) N mass (TeV) N mass (TeV) Exclusions for a heavy composite Majorana neutrinos for masses up to 4.35 (4.5) TeV in the eejj (µµjj) channel (IHEP Beijing) Pag 9 / 16

10 Left-right heavy neutrino Heavy neutrino search, from left-right model, with 2 taus and 2 jets (Ref: CMS-EXO6-016) No searches with 3rd generation lepton in Run I looking for heavy neutrinos from the left-right model we performed a new search to investigate this case Consider τ h τ h jj channel τ h : pt>70 GeV, η < 2.1 j: pt>50 GeV, η < 2.4 E T > 50 GeV, no b-jet M(τ h, τ h ) >0 GeV Drell-Yan ditau part well modelled, for dijet side take data/mc correction from Z µµ+jets Multijet data events with loose τ h isolation weighted by tight-to-loose τ h efficiencies measured with E T <30 t t From simulation, after validation in high-multiplicity b-jet region No excess compared to the SM expectations (IHEP Beijing) Pag / 16

11 Left-right heavy neutrino Heavy neutrino limits, from left-right model, with 2 taus and 2 jets W R masses below 2.35 (1.63) TeV are excluded at a 95% confidence level, assuming the HN τ mass is 0.8 (0.2) times the mass of W R boson (IHEP Beijing) Pag 11 / 16

12 No excesses compared to the SM expectations (IHEP Beijing) Pag 12 / 16 High-mass ditau High-mass ditau search Ref: CMS-EXO6-008 We further performed a search for new physics with two taus, which is an important signature due to the increase in s at LHC Consider τ h τ h, µτ h, eτ h, eµ channels l: pt>20,30,35,60 (τ h, µ, e, τ h in τ h τ h ) GeV, η < 2.1 E T > 30 GeV Opposite charge, no b-jets, τ pair consistent with ditau topology Event for M(τ 1, τ 2, E T ) > 300 GeV Bkg estimation done consistently among channels Drell-Yan taken from Monte-Carlo (MC) after correction/validation w.r.t. data W+jets using data control region weighted by the efficiencies to derive signal region contribution Multijet using data considering like-sign events

13 High-mass ditau High-mass ditau mass distributions (IHEP Beijing) Pag 13 / 16

14 High-mass ditau limits High-mass ditau Results w.r.t. Z Sequential Standard Model Z < 2.1 TeV, world best limit (IHEP Beijing) Pag 14 / 16

15 Conclusions Conclusions LHC results have not shown any clear sign of new physics so far Some Run I results have modest excesses we have focused on them at the beginning of Run II: we have studied a new model to interpret them, based on heavy composite Majorana neutrinos we have looked for heavy composite Majorana neutrinos we have also looked for heavy neutrinos (left-right model) in the tau channel We have further searched for new physics with two high-mass ditau, which is an important signature due to the increase in s at LHC Again we have not found relevant discrepancies between data and expectations much more data are coming in order to set more stringent conclusions on these searches (IHEP Beijing) Pag 15 / 16

16 Conclusions Thanks for the attention! (IHEP Beijing) Pag 16 / 16

17 Backup: Heavy composite Majorana Neutrinos Extended weak isospin model I W Multiplet I W Multiplet 0 E ( ) 0 U, D( ) E 0 U 1/2 ɛ E 1/2 Ψ D 1 ɛ E 0 U + U E (5/3) 1 U U, D D E D D (4/3) E + U + 3/2 ɛ M E 0 (5/3) E 3/2 Ψ M U D E D (4/3) (IHEP Beijing) Pag 17 / 16

18 Backup: Heavy composite Majorana Neutrinos Gauge and Contact interactions q j l + q j Gauge l + q j Contact l + = W + q i N q i N q i N L G = 1 2Λ φσ µν ( gf τ 2 W µν + g f YB µν ) φ L + h.c. L C = g 2 2 j µ j µ j µ = η L φ L γ µ φ L + η L φ L γ µφ L + η L φ L γ µφ L + h.c. + (L R) Λ 2 1 where g = 4π, η = 1 and f, f = 1 (IHEP Beijing) Pag 18 / 16

19 Backup: Heavy composite Majorana Neutrinos Production cross section σ(pp N l) (fb) Λ=5TeV contact gauge mass of N (TeV) σ(pp N l) (fb) Λ=15TeV contact gauge mass of N (TeV) (IHEP Beijing) Pag 19 / 16

20 Backup: Heavy composite Majorana Neutrinos Excess in eejj channel in our model The composite model scenario can explain this excess via the production of a heavy composite (excited) neutrino. Two processes are possible q i q j N q k l + l + q l q j q i N l + l + q l q k Exchange of virtual heavy Majorana neutrino (left) HEP equivalent of neutrinoless double β-decay Resonant production of heavy Majorana neutrino (right) σ(p p e + e + q q - ) (fb) Λ=TeV The resonant production is the dominant process m* (TeV) (IHEP Beijing) Pag 20 / 16

21 Backup: Heavy composite Majorana Neutrinos Excess in eejj channel in our model In our model is possible to have the excess in the eejj channel and not in the µµjj channel assuming excited µ state heavier than excited e state It is also possible to take into account the predominance of opposite sign on same sign di-leptons. Two possible explanations: processes giving only opposite sign: pp e + L e + e jj, pp e L ++ e e + jj existence of an additional neutrino with a slightly different mass, the interference between the two states can depress same sign. (arxiv: [hep-ph]., arxiv: [hep-ph] ) (IHEP Beijing) Pag 21 / 16

22 Backup: Heavy composite Majorana Neutrinos Excess in ep/ T jj channel CMS reported an excess in a search of lepto-quarks in the channel ep/ T jj for s = 8 TeV ( ) This can be explained by our model with processes like pp ln lνz lνjj The absence of the excess in µp/ T jj channel can be explained assuming that the excited muon state is heavier than excited electron state (IHEP Beijing) Pag 22 / 16

23 Backup: Heavy composite Majorana Neutrinos Excess in di-boson search Recently ATLAS observed an excess around 2 TeV in a search for high-mass diboson resonances with boson-tagged jets at s = 8 TeV ( We can produce a pair of charged excited fermions that could form a 1S bound state wich could decay in a pair of gauge bosons Example: pp L + L 1SBoundstate W + W (IHEP Beijing) Pag 23 / 16

24 Backup: Heavy composite Majorana Neutrinos Events at di-jet mass 5 TeV CMS and ATLAS observed few events at 5 TeV in the di-jet mass at Run II of the LHC (CMS-PAS-EXO5-001, ATLAS-CONF ) [pb / GeV] dσ/ dm jj 1-2 CMS Preliminary data background fit to data QCD MC q* (4.5 TeV) 42 pb (13 TeV) Events ATLAS Preliminary s=13 TeV, 80 pb y* < η < 2.5, Δη < 1.3 M jj > 1.1 TeV Wide Jets 1 Data Fit Statistical uncertainty on fit Function choice uncertainty (Data-Fit)/σ Dijet Mass (GeV) Dijet Mass [GeV] Rel. Uncert m [TeV] jj If they are confirmed by higer statistics and result in an excess, this could be interpreted as the first hadronic resonance in a composite scenario (IHEP Beijing) Pag 24 / 16