Lepton Number Violation in Higgs Decay at LHC

Abstract

We show that within the Left-Right symmetric model, lepton number violating decays of the Higgs boson can be discovered at the LHC. The process is due to the mixing of the Higgs with the triplet that breaks parity. As a result, the Higgs can act as a gateway to the origin of heavy Majorana neutrino mass. To assess the LHC reach, a detailed collider study of the same-sign di-leptons plus jets channel is provided. This process is complementary to the existing nuclear and collider searches for lepton number violation and can probe the scale of parity restoration even beyond other direct searches.PACS numbers: 14.80. Bn, 13.35.Hb The discovery of the Higgs boson [1,2] allows to test the mechanism of elementary particle mass generation at the LHC [3]. Compared to this success, the problem of neutrino mass in the Standard Model (SM) appears acute. Neutrinos may be their own antiparticles [4], and lead to lepton number violation (LNV). The canonical way of searching for LNV, neutrino-less double beta decay (0ν2β) [5], can be induced by light Majorana neutrinos or by new physics [6]. The latter, needed for neutrino mass, can be provided by the celebrated seesaw mechanism [7][8][9][10][11]. In particular, Left-Right symmetric models (LRSM) [12], designed to explain parity violation of weak interactions [13], embed naturally the seesaw [7,8].With the left-right (LR) scale in the TeV range, 0ν2β may be dominated by heavy Majorana neutrino (N ) exchange [14,15], which may become favored in view of the cosmological bound on light neutrino masses.A direct strategy for LNV searches at hadron colliders was suggested in [16] by Keung and Senjanović (KS) [17]. The KS production of heavy Majorana neutrinos would reveal LNV and relate directly to 0ν2β [15,18] and lepton flavor violation (LFV) [19,20]. The Dirac mass is predicted [21] and may be tested at the LHC through LNV decays, uncovering the underlying seesaw mechanism and connecting to electric dipole moments [21,22]. Indirect constraints [23][24][25][26][27] played an important role and comprehensive analyses [28,29] allow the LR scale well within the ∼ 6 TeV reach of the LHC [30].In this Letter we show that LHC can probe a new channel, connecting Higgs physics to restoration of parity. We exploit the fact that the SM Higgs can have a sizeable mixing with the triplet that breaks spontaneously LR symmetry and provides a mass to N . Through this mixing the Higgs can decay to a pair of N [31]. Therefore, it can probe their Yukawa couplings via a LNV final state with two same or opposite sign charged leptons and four jets, as shown on Fig. 1. The relevant range of N masses * amaiezza@ific.uv.es † miha.nemevsek@ijs.si ‡ fabrizio.nesti@irb.hr FIG. 1. Dominant diagram leading to LNV Higgs decay.typically leads to displaced vertices. Higgs decay to RH neutrinos was mentioned in [32] and studied in [33] with effective operators, pointing out the LNV character and vertex displacement. Here, in the LRSM, the LNV decay is probing the origin of N masses, just as the standard decays te...

Majorana Higgses at colliders

“…Higgs decay to heavy sterile neutrinos was mentioned also in [60] and analyzed in [61,62] with effective operators. Recently, a more detailed collider study of the LNV decays of the SM Higgs to N N within the LRSM was done in [63]. Here, we extend the analysis to the phenomenology of the RH triplet at colliders: section 2 gives a short review of LRSM features, the decay and production channels of the Higgses of interest are computed in section 3 and section 4.…”

“…In both e and µ channels the same cuts as in [63] are imposed to further enhance the sensitivity. Their impact is seen in table 1, here we describe them in a bit more detail.…”

Displaced vertex searches for sterile neutrinos at future lepton colliders

“…[12][13][14][15][16][17][18][19][20], which derived a constraint on the squared active-sterile mixing angle |θ| 2 < 10 −5 for heavy neutrino masses ∼ 20 GeV, and prospects for a sensitivity of |θ| 2 ∼ 10 −7 for 300 fb −1 . Estimates for the sensitivity reach of long-lived heavy neutrinos via displaced vertices have been made for the Z-pole run of the Future Circular electron positron Collider (FCC-ee) in ref.…”

Leptogenesis constraints on B − L breaking Higgs boson in TeV scale seesaw models

“…Therefore, a detailed study of its properties is likely to provide another window to the physics behind the neutrino masses. The collider signatures of this B − L breaking scalar have been studied in some recent papers [17][18][19][20][21]. In this paper, we study some cosmological implications of this new scalar for the dynamical generation of matterantimatter asymmetry in the early universe.…”