The light invisible boson in FCNC decays of B and $$B_c$$ mesons

Li, Geng; Wang, Tianhong; Zhang, Jingbo; Wang, Guoli

doi:10.1140/epjc/s10052-021-09333-z

“…These processes are further divided into 2-body decays with a single new particle and 3-body decays with a pair of new particles. All the 2-body channels plus the 3-body decay with a pair of new fermions have been extensively studied before [8][9][10][11][12][13][14][16][17][18][19][20]. 1 The table indicates with a double-checkmark processes that have not received much attention, namely three body modes with a pair of vector particles.…”

Section: Jhep03(2023)037mentioning

confidence: 99%

FCNC B and K meson decays with light bosonic Dark Matter

He

¹

,

Ma

²

,

Valencia

³

2023

J. High Energ. Phys.

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We consider decays of B and K mesons into a pseudo-scalar or vector meson plus missing energy. Within the SM, these modes originate from flavor changing neutral current (FCNC) processes with two neutrinos in the final state. In this paper we consider the experimental upper bounds on these modes and interpret the difference between these bounds and the SM prediction as a window into new light invisible particles. In particular we consider the case where some new symmetry requires the new particles to be produced in pairs. We first construct the general low energy effective Lagrangian coupling an FCNC with two dark sector particles of spin zero, one-half and one. We then present numerical estimates for the constraints that can be placed on these interactions, finding that an effective new physics scale from $$ \mathcal{O} $$ O (10)-$$ \mathcal{O} $$ O (1011) GeV can be probed, with the exact value strongly depending on the interaction structure as well as the mass of the invisible particle. For "Image missing" we incorporate into our constraints the effect of using only the signal regions of NA62, and for "Image missing" the q2-dependent efficiency of Belle II.

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Deciphering the Belle II data on $$ B\to K\nu \overline{\nu} $$ decay in the (dark) SMEFT with minimal flavour violation

Hou,

Li,

Shen

et al. 2024

J. High Energ. Phys.

0

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Recently, the Belle II collaboration announced the first measurement of the branching ratio $$ \mathcal{B}\left({B}^{+}\to {K}^{+}\nu \overline{\nu}\right) $$ B B + → K + ν ν ¯ , which is found to be about 2.7σ higher than the Standard Model (SM) prediction. We decipher the data with two new physics scenarios: the underlying quark-level $$ b\to s\nu \overline{\nu} $$ b → sν ν ¯ transition is, besides the SM contribution, further affected by heavy new mediators that are much heavier than the electroweak scale, or amended by an additional decay channel with undetected light final states like dark matter or axion-like particles. These two scenarios can be most conveniently analyzed in the SM effective field theory (SMEFT) and the dark SMEFT (DSMEFT) framework, respectively. We consider the flavour structures of the resulting effective operators to be either generic or satisfy the minimal flavour violation (MFV) hypothesis, both for the quark and lepton sectors. In the first scenario, once the MFV assumption is made, only one SM-like low-energy effective operator induced by the SMEFT dimension-six operators can account for the Belle II excess, whose parameter space is, however, excluded by the Belle upper bound of the branching ratio $$ \mathcal{B}\left({B}^0\to {K}^{\ast 0}\nu \overline{\nu}\right) $$ B B 0 → K ∗ 0 ν ν ¯ . In the second scenario, it is found that the Belle II excess can be accommodated by 22 of the DSMEFT operators involving one or two scalar, fermionic, or vector dark matters as well as axion-like particles. These operators also receive dominant constraints from the B0 → K*0 + inv and Bs → inv decays. Once the MFV hypothesis is assumed, the number of viable operators is reduced to 14, and the B+ → π+ + inv and K+ → π+ + inv decays start to put further constraints on them. Within the parameter space allowed by all the current experimental data, the q2 distributions of the B → K(*) + inv decays are then studied for each viable operator. We find that the resulting prediction of the operator $$ {\mathcal{Q}}_{q\chi}=\left({\overline{q}}_p{\gamma}_{\mu }{q}_r\right)\left(\overline{\chi}{\gamma}^{\mu}\chi \right) $$ Q qχ = q ¯ p γ μ q r χ ¯ γ μ χ with a fermionic dark matter mass mχ ≈ 700 MeV can closely match the Belle II event distribution in the bins 2 ≤ q2 ≤ 7 GeV2. In addition, we, for the first time, calculate systematically the longitudinal polarization fraction FL of K* in the B → K* + inv decays within the DLEFT. By combining the decay spectra and FL, almost all the DSMEFT operators are found to be distinguishable from each other. Finally, the future prospects at Belle II, CEPC and FCC-ee are also discussed for some of these FCNC processes.

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FCNC charmed-hadron decays with invisible singlet particles in light of recent data

Li,

Tandean

2023

J. High Energ. Phys.

1

0

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The flavor-changing neutral current (FCNC) decays of charmed hadrons with missing energy (Ɇ) can serve as potentially promising hunting grounds for hints of new physics, as the standard-model backgrounds are very suppressed. A few of such processes have been searched for in recent experiments, specifically D0→ Ɇ by Belle and D0→ π0Ɇ and $$ {\Lambda}_c^{+} $$ Λ c + → pɆ by BESIII, resulting in upper bounds on their branching fractions. We consider them to illuminate the possible contributions of the quark transition c → uɆ with a couple of invisible spinless bosons carrying away the missing energy, assuming that they are not charge conjugates of each other and hence can have unequal masses. We find that these data are complementary in that they constrain different sets of the underlying operators and do not cover the same ranges of the bosons’ masses, but there are regions not yet accessible. From the allowed parameter space, we show that other D-meson decays, such as D → ρɆ, and the charmed-baryon ones Ξc → (Σ, Λ)Ɇ can have sizable branching fractions and therefore may offer further probes of the new-physics interactions. We point out the importance of D0 → γɆ which are not yet searched for but could access parts of the parameter space beyond the reach of the other modes. In addition, we look at a scenario where the invisibles are instead fermionic, namely sterile neutrinos, and a scalar leptoquark mediates c → uɆ. We discuss the implications of the aforesaid bounds for this model. The predictions we make for the various charmed-hadron decays in the different scenarios may be testable in the near future by BESIII and Belle II.

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The light invisible boson in FCNC decays of B and $$B_c$$ mesons

Cited by 5 publications

References 52 publications

FCNC B and K meson decays with light bosonic Dark Matter

FCNC B and K meson decays with light bosonic Dark Matter

Deciphering the Belle II data on $$ B\to K\nu \overline{\nu} $$ decay in the (dark) SMEFT with minimal flavour violation

FCNC charmed-hadron decays with invisible singlet particles in light of recent data

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