CP violation in rare lepton-number-violating W decays at the LHC

Abstract

Some models of leptogenesis involve a quasi-degenerate pair of heavy neutrinos N1,2 whose masses can be small, O(GeV). Such neutrinos can contribute to the rare lepton-number-violating (LNV) decay $$ {W}^{\pm}\to {\mathrm{\ell}}_1^{\pm }{\mathrm{\ell}}_2^{\pm }{\left({q}^{\prime}\overline{q}\right)}^{\mp } $$ W ± → ℓ 1 ± ℓ 2 ± q ′ q ¯ ∓ . If both N1 and N2 contribute, there can be a CP-violating rate difference between the LNV decay of a W− and its CP-conjugate decay. In this paper, we examine the prospects for measuring such a CP asymmetry ACP at the LHC. We assume a value for the heavy-light neutrino mixing parameter |BℓN|2 = 10−5, which is allowed by the present experimental constraints, and consider 5 GeV ≤ MN≤ 80 GeV. We consider three versions of the LHC — HL-LHC, HE-LHC, FCC-hh — and show that small values of the CP asymmetry can be measured at 3σ, in the range 1% ≲ ACP ≲ 15%.

CP violation in $B_s$ decays mediated by two nearly-degenerate Majorana neutrinos

“…Another significant difference is that in our result A CP reaches maximum when y is around 1 while in Ref. [54] y is between 0.3-0.5. See Ref.…”

“…Ref. [54] studies CP violation of similar mechanism in W boson decays and it shows that under the condition that m N1 equals 5 GeV, 10 GeV, 20 GeV and 60 GeV, A CP shows considerable differences. Another significant difference is that in our result A CP reaches maximum when y is around 1 while in Ref.…”

“…[46] in LNV B meson decays. CP-violating LNV processes induced by similar mechanisms in the decays of other mesons [46][47][48][49][50][51], τ leptons [52,53] as well as W boson [54] were also studied in detail in literature. Besides, the existence of two nearly degenerate Majorana neutrinos together with the CP violating phases can lead to significant difference between the decay width of the LNV meson decays and that of the lepton-number-conserving ones [55,56], which is contrary to the common hypothesis.…”

Measuring CP violation in rare $W$ decays at the LHC

“…Recently, Ref. [47] explored the CP violation in rare W decays at the LHC, but the CP violation effect produced in this case is influenced by the initial parton distribution functions in proton. To evade this conflict, in a recent work [48],…”

CP violation in top quark decay via heavy Majorana neutrinos at the LHC

“…There have been a great number of theoretical works on examining the prospects for observing CP violation via lepton-number-violating processes, where the CP violation can be measured in the decays of mesons [40][41][42][43][44][45][46][47] and tau leptons [48,49]. Recently, the possibility for measuring CP violation in W + and W − decay at the LHC is explored [50]. However, the CP violation effect is influenced by the initial parton distribution functions (PDF), which leads to the different production cross section of W + and W − .…”