Rare charm c→uνν¯ dineutrino null tests for e+

Abstract

Rare |∆c| = |∆u| = 1 transitions into dineutrinos are strongly GIM-suppressed and constitute excellent null tests of the standard model. While branching ratios of D → P ν ν, D → P + P − ν ν, P = π, K, baryonic Λ + c → p ν ν, and Ξ + c → Σ + ν ν and inclusive D → Xν ν decays are experimentally unconstrained, signals of new physics can be just around the corner. We provide model-independent upper limits on branching ratios reaching few ×10 −5 in the most general case of arbitrary lepton flavor structure, ∼ 10 −5 for scenarios with charged lepton conservation and few ×10 −6 assuming lepton universality. We also give upper limits in Z and leptoquark models. The presence of light right-handed neutrinos can affect these limits, a possibility that can occur for lepton number violation at a TeV, and that can be excluded with an improved bound on B(D 0 → invisibles) at the level of ∼ 10 −6 , about two orders of magnitude better than the present one. Signatures of c → uν ν modes contain missing energy and are suited for experimental searches at e + e − -facilities, such as BES III, Belle II and future e + e − -colliders, such as the FCC-ee running at the Z.

Lepton-quark fusion at Hadron colliders, precisely

“…Leptoquark collider searches so far were mainly focused on the pair production mechanism driven by QCD interactions, while the role of the defining leptoquark interaction to a quark and a lepton was invoked in decays. However, interesting flavor effects occur when the leptoquark coupling is large(ish) [77][78][79][80][81][82][83][84][85][86][87][88][89][90][91], consequently predicting richer collider phenomenology on the production side. Building on refs.…”

Exploring charm decays with missing energy in leptoquark models

“…There have been various analyses in the past, such as refs. [6][7][8][23][24][25][26][27][28][29][30][31][32][33], looking into the effects of LQs on FCNC charm processes, but c → u / E was covered by only a few [6][7][8]. The outcomes of our work would be complementary to those of the latter.…”

“…Second, as will be demonstrated later on, relative to those with SM fermions alone the LQ-mediated FCNCs that involve the sterile neutrinos and SM quarks might exert considerably enhanced influence on the charm decays of concern, especially if the quarks are also right-handed. This latter LQ feature has not been treated previously in the c → u / E context [6][7][8]. With respect to the predictions of the models to be studied shortly, it will be useful to have some idea about the extent to which they might be accessible by the aforementioned experiments.…”

“…The flavor-changing neutral-current (FCNC) decays of charmed hadrons into a lighter hadron plus missing energy ( / E) have long been anticipated in the literature [1][2][3][4][5][6][7][8][9][10][11][12][13][14] to be among likely environments in which to discover hints of new physics (NP) beyond the standard model (SM). In the SM these processes arise at short distance from the quark transition c → uνν, which emits unobserved neutrinos (νν) and is greatly suppressed because it proceeds from loop diagrams and is subject to very efficient Glashow-Iliopoulos-Maiani cancellation [1].…”

Null test searches for BSM physics with rare charm decays

“…The experimental and theoretical status of rare charm decays is presented in Ref. [5] and increasing and ongoing research interest [1,2,[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] manifests the importance of progress in the field.…”