Study of $$ {\mathrm{B}}_{\mathrm{c}}^{+} $$ decays to charmonia and three light hadrons

Using proton-proton collision data, corresponding to an integrated luminosity of 9 fb−1 collected with the LHCb detector, seven decay modes of the $$ {\mathrm{B}}_{\mathrm{c}}^{+} $$ B c + meson into a J/ψ or ψ(2S) meson and three charged hadrons, kaons or pions, are studied. The decays $$ {\mathrm{B}}_{\mathrm{c}}^{+} $$ B c + → (ψ(2S) → J/ψπ+π−)π+, $$ {\mathrm{B}}_{\mathrm{c}}^{+} $$ B c + → ψ(2S)π+π−π+, $$ {\mathrm{B}}_{\mathrm{c}}^{+} $$ B c + → J/ψK+π−π+ and $$ {\mathrm{B}}_{\mathrm{c}}^{+} $$ B c + → J/ψK+K−K+ are observed for the first time, and evidence for the $$ {\mathrm{B}}_{\mathrm{c}}^{+} $$ B c + → ψ(2S)K+K−π+, decay is found, where J/ψ and ψ(2S) mesons are reconstructed in their dimuon decay modes. The ratios of branching fractions between the different $$ {\mathrm{B}}_{\mathrm{c}}^{+} $$ B c + decays are reported as well as the fractions of the decays proceeding via intermediate resonances. The results largely support the factorisation approach used for a theoretical description of the studied decays.

Impact of $$b \rightarrow s \ell \ell $$ anomalies on rare charm decays in non-universal $$Z'$$ models

In this work, we study the impact of $$b \rightarrow s \ell \ell $$ b → s ℓ ℓ , $$B_s - \bar{B_s}$$ B s - B s ¯ mixing and neutrino trident measurements on observables in decays induced by $$c \rightarrow u $$ c → u transition in the context of a non-universal $$Z'$$ Z ′ model which generates $$C^{\mathrm{NP}}_{9} <0$$ C 9 NP < 0 and $$C^{\mathrm{NP}}_9 = - \,C^{\mathrm{NP}}_{10} $$ C 9 NP = - C 10 NP new physics scenarios at the tree level. We inspect the effects on $$D^0 \rightarrow \pi ^0 \nu {\bar{\nu }}$$ D 0 → π 0 ν ν ¯ , $$D^+ \rightarrow \pi ^+ \nu {\bar{\nu }}$$ D + → π + ν ν ¯ and $$B_c \rightarrow B^+ \nu {\bar{\nu }} $$ B c → B + ν ν ¯ decays which are induced by the quark level transition $$c \rightarrow u \nu {\bar{\nu }}$$ c → u ν ν ¯ . The fact that the branching ratios of these decays are negligible in the standard model (SM) and the long distance effects are relatively smaller in comparison to their charged dileptons counterparts, they are considered to provide genuine null-tests of SM. Therefore the observation of these modes at the level of current as well as planned experimental sensitivities would imply unambiguous signature of new physics. Using the constraints on $$Z'$$ Z ′ couplings coming from a combined fit to $$b \rightarrow s \ell \ell $$ b → s ℓ ℓ , $$\varDelta M_s$$ Δ M s and neutrino trident data, we find that any meaningful enhancement over the SM value is ruled out in the considered framework. The same is true for $$D - {\bar{D}}$$ D - D ¯ mixing observable $$\varDelta M_D$$ Δ M D along with $$D^0 \rightarrow \mu ^+ \mu ^-$$ D 0 → μ + μ - and $$D^+ \rightarrow \pi ^+ \mu ^+ \mu ^-$$ D + → π + μ + μ - decay modes which are induced through $$c \rightarrow u \mu ^+ \mu ^-$$ c → u μ + μ - transition.

Moderately suppressed dimension-five proton decay in a flipped SU(5) model

We study colored Higgsino-mediated proton decay (dimension-five proton decay) in a model based on the flipped SU(5) GUT. In the model, the GUT-breaking 10, $$ \overline{\mathbf{10}} $$ 10 ¯ fields have a GUT-scale mass term and gain VEVs through higher-dimensional operators, which induces an effective mass term between the color triplets in the 5, $$ \overline{\mathbf{5}} $$ 5 ¯ Higgs fields that is not much smaller than the GUT scale. This model structure gives rise to observable dimension-five proton decay, and at the same time achieves moderate suppression on dimension-five proton decay that softens the tension with the current bound on Γ(p → K+$$ \overline{\nu} $$ ν ¯ ). We investigate the flavor dependence of the Wilson coefficients of the operators relevant to dimension-five proton decay, by relating them with diagonalized Yukawa couplings and CKM matrix components in MSSM, utilizing the fact that the GUT Yukawa couplings are in one-to-one correspondence with the MSSM Yukawa couplings in flipped models. Then we numerically evaluate the Wilson coefficients, and predict the distributions of the ratios of the partial widths of various proton decay modes.

The fate of $$\mathbf{V}_\mathbf{1}$$ vector leptoquarks: the impact of future flavour data

Motivated by the recent experimental progress on the B-meson decay anomalies (in particular the angular observables in $$B\rightarrow K^*\mu \mu $$ B → K ∗ μ μ ), we rely on a simplified-model approach to study the prospects of vector leptoquarks in what concerns numerous flavour observables, identifying several promising decay modes which would allow to (indirectly) probe such an extension. Our findings suggest that the confirmation of the B-meson decay anomalies, in parallel with positive signals (at Belle II or LHCb) for $$\tau \rightarrow \phi \mu $$ τ → ϕ μ , $$B_{(s)}$$ B ( s ) -meson decays to $$\tau ^+ \tau ^-$$ τ + τ - and $$\tau ^+ \mu ^-$$ τ + μ - ($$\tau ^+ e^-$$ τ + e - ) final states, as well as an observation of certain charged lepton flavour violation decays (at COMET or Mu2e), would contribute to strengthen the case for this scenario. We also illustrate how the evolution of the experimental determination of $$R_{D^{(*)}}$$ R D ( ∗ ) could be instrumental in falsifying an explanation of the anomalous B-meson decay data via a vector $$V_1$$ V 1 leptoquark.

Reheating after inflation by supersymmetry breaking

We study reheating after the end of inflation in models where the inflaton is the superpartner of goldstino and is charged under a gauged U(1) R-symmetry. We consider two classes of models – one is small field characterized by an almost flat Kähler space, and the other large field characterized by a hyperbolic Kähler space SU(1, 1)/U(1), while in both cases the inflaton superpotential is linear due to the R-symmetry. The inflationary observables of our models fit within 2$$\sigma $$ σ CMB values. Upon coupling the inflaton sector to the (supersymmetric) Standard Model, we compute the MSSM parameters, mass spectrum, and decay modes of the inflaton, with the resulting reheating temperature around $$10^8$$ 10 8 GeV. We also find that both models can accommodate superheavy LSP dark matter, depending on the parameter choice.

Updated search for $$ {B}_c^{+} $$ decays to two charm mesons

A data set corresponding to an integrated luminosity of 9 fb−1 of proton-proton collisions collected by the LHCb experiment has been analysed to search for $$ {B}_c^{+}\to {D}_{(s)}^{\left(\ast \right)+}{\genfrac{}{}{0pt}{}{\left(\hbox{---} \right)}{D}}^{\left(\ast \right)0} $$ B c + → D s ∗ + — D ∗ 0 decays. The decays are fully or partially reconstructed, where one or two missing neutral pions or photons from the decay of an excited charm meson are allowed. Upper limits for the branching fractions, normalised to B+ decays to final states with similar topologies, are obtained for sixteen $$ {B}_c^{+} $$ B c + decay modes. For the decay $$ {B}_c^{+}\to {D}_s^{+}{\overline{D}}^0 $$ B c + → D s + D ¯ 0 , an excess with a significance of 3.4 standard deviations is found.

Analysis of W± + 4γ in the 2HDM Type-I at the LHC

We analyse a light charged Higgs boson in the 2-Higgs Doublet Model (2HDM) Type-I, when its mass satisfies the condition MH±< Mt + Mb and the parameter space is consistent with theoretical requirements of self-consistency as well as the latest experimental constraints from Large Hadron Collider (LHC) and other data. Over such a parameter space, wherein the Standard Model (SM)-like state discovered at the LHC in 2012 is the heaviest CP-even state of the 2HDM, it is found that the decay modes of the charged Higgs boson are dominated by H±→ W±(∗)h. Furthermore, the light neutral Higgs boson h dominantly decays into two photons. Under these conditions, we find that the production and decay process pp → H±h → W±(∗)hh → ℓνℓ + 4γ (ℓ = e, μ) is essentially background free. However, since the W±(∗) could be largely off-shell and the h state is very light, so that both the lepton coming from the former and the photons coming from the latter could be rather soft, we perform here a full Monte Carlo (MC) analysis at the detector level demonstrating that such a W± + 4γ signal is very promising, as it would be yielding significant excesses at the LHC with an integrated luminosity of L = 300 fb−1 at both $$ \sqrt{s} $$ s = 13 and 14 TeV.

Electrodisintegration of Deuteron into Dark Matter and Proton Close to Threshold

We discuss an investigation of the dark matter decay modes of the neutron, proposed by Fornal and Grinstein (2018–2020), Berezhiani (2017, 2018) and Ivanov et al. (2018) for solution of the neutron lifetime anomaly problem, through the analysis of the electrodisintegration of the deuteron d into dark matter fermions χ and protons p close to threshold. We calculate the triple-differential cross section for the reaction e−+d→χ+p+e− and propose to search for such a dark matter channel in coincidence experiments on the electrodisintegration of the deuteron e−+d→n+p+e− into neutrons n and protons close to threshold with outgoing electrons, protons, and neutrons in coincidence. An absence of neutron signals should testify to a detection of dark matter fermions.

Collider signatures of coannihilating dark matter in light of the B-physics anomalies

Motivated by UV explanations of the B-physics anomalies, we study a dark sector containing a Majorana dark matter candidate and a coloured coannihilation partner, connected to the Standard Model predominantly via a U1 vector leptoquark. A TeV scale U1 leptoquark, which couples mostly to third generation fermions, is the only successful single-mediator description of the B-physics anomalies. After calculating the dark matter relic surface, we focus on the most promising experimental avenue: LHC searches for the coloured coannihilation partner. We find that the coloured partner hadronizes and forms meson-like bound states leading to resonant signatures at colliders reminiscent of the quarkonia decay modes in the Standard Model. By recasting existing dilepton and monojet searches we exclude coannihilation partner masses less than 280 GeV and 400 GeV, respectively. Since other existing collider searches do not significantly probe the parameter space, we propose a new dedicated search strategy for pair production of the coloured partner decaying into bbττ final states and dark matter particles. This search is expected to probe the model up to dark matter masses around 600 GeV with current luminosity.