The doubly charged scalar:

Transcription

1 The doubly charged scalar: current status and perspectives Margherita Ghezzi Moriond QCD, March 2018 Margherita Ghezzi (PSI) The doubly charged scalar Moriond QCD, 20/03/ / 18

2 Introduction: the doubly charged scalar The doubly charged scalar from the SU(2) L -triplet scalar Type-II see-saw model Yukawa term with the triplet: Majorana mass term for neutrinos: ( ) S + 2S ++ S = 2S 0 S + < S > 0 = ( 0 0 w 0 ) L Y = f ij L T i C 1 iτ 2 SL j + h.c. m ij ν c ilν jl m ij = w f ij = m ji T. P. Cheng and L. F. Li, Phys. Rev. D 22 (1980) 2860 W. Grimus, R. Pfeiffer and T. Schwetz, Eur. Phys. J. C 13 (2000) 125 E. Ma, M. Raidal and U. Sarkar, Nucl. Phys. B 615 (2001) 313 A. G. Akeroyd and M. Aoki, Phys. Rev. D 72 (2005) Margherita Ghezzi (PSI) The doubly charged scalar Moriond QCD, 20/03/ / 18

3 Introduction: the doubly charged scalar The doubly Charged SU(2) L -singlet scalar Zee-Babu model SM + 2 SU(2) L -singlet scalars: a singly charged scalar which couples to left-handed leptons: h ± a doubly charged scalar which couples to right-handed leptons: k ±± It generates mass terms for the neutrinos at two loops: h h k e L e L ν L ν L e R e R H H A. Zee, Nucl. Phys. B 264 (1986) 99 K. S. Babu, Phys. Lett. B 203, 132 (1988) M. Nebot, J. F. Oliver, D. Palao and A. Santamaria, Phys. Rev. D 77 (2008) Margherita Ghezzi (PSI) The doubly charged scalar Moriond QCD, 20/03/ / 18

4 Introduction: the doubly charged scalar The doubly Charged SU(2) L -singlet scalar Minimal model for neutrino masses SM + 1 SU(2) L -singlet doubly charged scalar: S ±± R It couples only with right-handed charged leptons: L = ( D µ S ++) ( D µ S ++) + ( ) λ ab (l R ) c al Rb S ++ + h.c. λ ab consist of 6 independent parameters and allow for LFV processes. S. F. King, A. Merle and L. Panizzi, JHEP 1411 (2014) 124 Margherita Ghezzi (PSI) The doubly charged scalar Moriond QCD, 20/03/ / 18

5 Introduction: the doubly charged scalar The doubly charged SU(2) L -singlet scalar Neutrino mass terms are generated at three loop: Ξ W S l a l b c W S ±± Ξ Ν La Ν Lb c EFT approach: ± W ± ξ Λ 3 S [ H + H + ( D µh 0) ( D µ H 0) 2H + H 0 ( D µh +) ( D µ H 0) + H 0 H 0 ( D µh +) ( D µ H +)] + h.c. S. F. King, A. Merle and L. Panizzi, JHEP 1411 (2014) 124 Margherita Ghezzi (PSI) The doubly charged scalar Moriond QCD, 20/03/ / 18

6 Low energy: current limits Current low-energy experimental limits Br [ τ e e ± e ] Br [ τ µ µ ± µ ] Br [ τ e µ ± µ ] Br [ τ µ e ± µ ] Br [ τ µ e ± e ] Br [ τ e µ ± e ] Br [ µ e e ± e ] P ( ) M M = Br [τ eγ] Br [τ µγ] Br [µ eγ] BR(l ± p l ± r γ) α mp 5 3 (24π 2 ) 2 mφ 4 λ Γp pw λ rw w=1 2 BR(l ± p l ± r l s l ± t ) m5 p λ ps 2 λ rt 2 s rt6(4π) 3 m 4 φ Γp Margherita Ghezzi (PSI) The doubly charged scalar Moriond QCD, 20/03/ / 18

7 ost exclusively to leptons and for high High values energy: of vlhc mostly searches to a pair of W bosons. This case where the H ±± particle decays only into electrons. Direct searches at LHC oration has already published similar results and the most stringent constraints originwhere the lower mass limit of H R ±± (H±± L ) was observed to be 370 GeV (550 GeV) at a.l.) of 95% and with the assumption that Br(H ±±! e ± e ± ) = 100%. Similar searches d by the CMS collaboration [21]. q H ++ `+ `+ ATLAS 7 TeV: Eur.Phys.J. C72 (2012) 2244 q /Z H ` ` iagram of the pair production pp! H ±± H process. The analysis studies only the electron st one of the lepton Signature: pairs are electrons. same-sign lepton CERN-EP pairs Assumptions on the branching ratios Narrow width approximation CMS 7 TeV: Eur.Phys.J. C72 (2012) 2189 ATLAS 13 TeV: CMS 13 TeV: CMS-PAS-HIG Margherita Ghezzi (PSI) The doubly charged scalar Moriond QCD, 20/03/ / 18

8 High energy: LHC searches Current limits from LHC CMS searches ( ) S + 2S ++ Search for a scalar triplet S = 2S 0 S + with degenerate masses fb 1 of integrated luminosity at 13 TeV Channels: Pair production with decays S ++ S l + l + l l Associated production with decays S ±± S l ± l ± l ν l + I l + I q Z 0 /γ Φ ++ l + J q W ± Φ ++ l + J q Φ l K q Φ l K l L ν L CMS-PAS-HIG Margherita Ghezzi (PSI) The doubly charged scalar Moriond QCD, 20/03/ / 18

9 High energy: LHC searches Current limits from LHC CMS searches S ±± L decaying at 100% to ee, µµ, ττ, eµ, eτ, µτ; Benchmark points: Lower bounds on the mass of the S ±± L - observed (expected) 95% CL: S ±± R may have similar kinematic properties, but potentially very different production cross sections. No associate production. CMS-PAS-HIG Margherita Ghezzi (PSI) The doubly charged scalar Moriond QCD, 20/03/ / 18

10 Current limits from LHC ATLAS searches 36.1 fb 1 of integrated luminosity at 13 TeV. Scenarios: larger than that for H R H R, because of di erent couplings to the Z boson [19]. Alon High energy: LHC searches decay, the doubly-charged Higgs particle can decay into a pair of W bosons as well. T for the doubly-charged Higgs particle to decay into a pair of W bosons compared to th a pair of leptons depends on the vacuum expectation value (v ) of the Higgs triplet [9, of v it decays almost exclusively to leptons and for high values of v mostly to a pair analysis studies the case where the H ±± particle decays only into electrons. The ATLAS collaboration has already published similar results and the most stringent ate from Ref. [20], where the lower mass limit of H R ±± (H±± L ) was observed to be 370 G confidence level (C.L.) of 95% and with the assumption that Br(H ±±! e ± e ± ) = 100% were also performed by the CMS collaboration [21]. q i,j=e,µ B(S ±± l i l j ) = 100% m ( S ±± ) L between 770 GeV and % C.L. m ( S ±± ) R between 660 GeV and % C.L. q /Z H ++ Figure 1: Feynman diagram of the pair production pp! H ±± H process. The analysis stud channel, where at least one of the lepton pairs are electrons. H `+ `+ ` ` B(S ±± l i l j > 10% (decays to τ and W are possible) m ( S ±± ) L larger than % C.L. m ( S ±± ) R larger than % C.L. 2 CERN-EP Margherita Ghezzi (PSI) The doubly charged scalar Moriond QCD, 20/03/ / 18

11 High energy: LHC searches Width effects No production decay approximation; some topologies that are negligible in the NWA can become relevant; assumption: gauge sector not modified, i.e. S ±± R coupling; Γ S is considered as a free parameter and ab,cd Γpart S coupling to Z is not a free Γ S σ PP l + a l + b l c l d (M S, Γ S, λ ab, λ cd ) = λ 2 abλ 2 cd ˆσ(M S, Γ S ) λmax /MS++ ΓS (%) Crivellin, MG, Panizzi, Pruna, Signer, in preparation Margherita Ghezzi (PSI) The doubly charged scalar Moriond QCD, 20/03/ / 18

12 High energy: LHC searches Width effects: results Very good approximation for light leptons: σ PP l + a l + b l c l d (M S, Γ S, λ ij ) = κ ab,cd λ 2 ab λ2 cd ˆσ PP 2e + 2e (M S, Γ S ) σ [pb] for pp e + e + e - e - (σfw-σnwa)/σnwa [%] for pp e + e + e - e - (Preliminary plot) 7.5% 2.5% 60% 30% 50% % -10% 5% 20% 10% 40% 5 5-5% /MS++ ΓS (%) /MS++ ΓS (%) 1-2.5% 0% MS [GeV] ++ MS [GeV] Cross-section corresponding to the maximum coupling values; relative ratio between cross-sections in the FW regime and NWA. Crivellin, MG, Panizzi, Pruna, Signer, in preparation Margherita Ghezzi (PSI) The doubly charged scalar Moriond QCD, 20/03/ / 18

13 High energy: future colliders Perspective of searches at future colliders S = N s Ns +N b Beamstrahlung Standard acceptance cuts: Significance = 5 Muon pair production at CLIC (Preliminary plot) E(µ ± ) > 10 GeV cos(θ) < 0.95 log( 12) Integrated luminosities: 350 GeV 380 GeV 1.5 TeV 3 TeV 100 fb fb fb fb CLIC 350 GeV CLIC 380 GeV CLIC 1500 GeV CLIC 3000 GeV MS (GeV) e + e γ µ µ + e + e Z µ µ + e + e H µ µ + e + S ++ µ e µ + Crivellin, MG, Panizzi, Pruna, Signer, in preparation Margherita Ghezzi (PSI) The doubly charged scalar Moriond QCD, 20/03/ / 18

14 High energy: future colliders Perspective of searches at future colliders The polarization of the beams increases the sensitivity CLIC will have the option to polarize the electron beam P e = 0.4 P e + = 0 Muon pair production at CLIC Muon pair production with R-polarized beams Significance = Significance = log( 12) log( 12) CLIC 350 GeV CLIC 380 GeV CLIC 1500 GeV CLIC 3000 GeV MS (GeV) CLIC 350 GeV CLIC 380 GeV CLIC 1500 GeV CLIC 3000 GeV MS (GeV) Crivellin, MG, Panizzi, Pruna, Signer, in preparation Margherita Ghezzi (PSI) The doubly charged scalar Moriond QCD, 20/03/ / 18

15 High energy: future colliders Perspective of searches at future colliders Measurements with polarized beams allow to distinguish between S ±± L and S ±± R T. Nomura, H. Okada and H. Yokoya, Nucl. Phys. B 929 (2018) 193 (Preliminary plot) e + e e + e : λ 11 P e = 0.4, P e + = 0 cos(θ) < 0.5 e + e e ± µ : λ 12, λ 11 No SM background log( 11) Electron pair production with R-polarized e- beam Significance = 5 cos <0.5 CLIC 350 GeV CLIC 380 GeV CLIC 1500 GeV CLIC 3000 GeV MS (GeV) Crivellin, MG, Panizzi, Pruna, Signer, in preparation Margherita Ghezzi (PSI) The doubly charged scalar Moriond QCD, 20/03/ / 18

16 High energy: future colliders Limits from low energy and discovery power of LC Limits from SINDRUM + discovery power at CLIC prototypes 0 (Preliminary plot) 1 log10( 12) m =500 GeV, CLIC 380 m = 1 TeV, CLIC 380 m = 2 TeV, CLIC 380 m =500 GeV, CLIC 1500 m = 1 TeV, CLIC 1500 m = 2 TeV, CLIC 1500 m =500 GeV, CLIC 3000 m = 1 TeV, CLIC 3000 m = 2 TeV, CLIC 3000 m =500 GeV, SINDRUM m =1 TeV, SINDRUM m =2 TeV, SINDRUM log 10 ( 11 ) Crivellin, MG, Panizzi, Pruna, Signer, in preparation Margherita Ghezzi (PSI) The doubly charged scalar Moriond QCD, 20/03/ / 18

17 High energy: future colliders Direct production Single production at ILC (Preliminary plot) 0.0 L 10 λ 11 e + e φ + + e e (Boson Fusion, 1 TeV) 100 fb e + e φ ++ e e fb e e fb S ab ab e + e 1 ab 100 zb m φ [GeV] Crivellin, MG, Panizzi, Pruna, Signer, in preparation Margherita Ghezzi (PSI) The doubly charged scalar Moriond QCD, 20/03/ / 18

18 Summary Summary Doubly charged scalars arise in many BSM models, in triplets or singlets under SU(2) L, often in connection with the neutrino masses; LFV low energy processes set strong limits on combination of the DCS couplings to leptons; future e + e colliders can provide complementary bounds; due to the production of the DCS in the t-channel, future e + e colliders can be sensitive to mass scales of several TeV; direct searches have been performed at LHC by both ATLAS and CMS, setting limits on the DCS mass in the range (320, 870) GeV depending on the assumptions; a moderately large width (Γ S /m S few%) can have 10-20% effect on the cross section compared to the NWA; further investigations of the DCS phenomenology are ongoing and the results will be published soon. Margherita Ghezzi (PSI) The doubly charged scalar Moriond QCD, 20/03/ / 18