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Abstract:

The collinear and transverse-momentum-dependent jet fragmentation function and the radial profile for $B^{Â\pm }$ mesons in jets are measured. The $B^{Â\pm }$ mesons are reconstructed through the $J/\mathrm{ψ}(→{\mathrm{μ}}^{+}{\mathrm{μ}}^{−})K^{Â\pm }$ decay channel using proton-proton collision data collected during 2016–2018 with the LHCb detector at a center-of-mass (c.m.) energy of $\sqrt{s}=13\mathrm{TeV}$ , corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{−1}$ . The results complement recent measurements of jet fragmentation functions for heavy-flavor hadrons and suggest a growing contribution of gluon fragmentation to $B^{Â\pm }$ mesons as the jet transverse momentum increases.

Abstract:

An amplitude analysis of the B0→ηc(1S)K+π-$${{{B} ^0} \!\rightarrow {\eta _{c}} (1S) {{K} ^+} {{\pi } ^-}} $$ decays with ηc(1S)→pp¯$${\eta _{c}} (1S) \rightarrow {p} {\overline{{p}}} $$ is performed using a sample corresponding to an integrated luminosity of 9fb-1$$\,\text {fb} ^{-1}$$ of p$$p $$p$$p $$ collision data collected by the LHCb detector at centre-of-mass energies of s$$\sqrt{s}$$ = 7, 8 and 13TeV$$\,\text {Te\hspace{-1.00006pt}V}$$. The data are described with a model including only intermediate contributions from known K∗0$${K} ^{*0}$$ resonances. Evidence for an exotic resonance in the ηc(1S)π-$${\eta _{c}} (1S) {{\pi } ^-} $$ system, reported in a previous analysis of this decay channel, is not confirmed. The inclusive branching fraction of the B0→ηc(1S)K+π-$${{B} ^0} \rightarrow {\eta _{c}} (1S) {{K} ^+} {{\pi } ^-} $$ decays is measured to be B(B0→ηc(1S)K+π-)=(5.82±0.20±0.23±0.55)×10-4,$$\begin{aligned}&\mathcal {B}({{B} ^0} \rightarrow {\eta _{c}} (1S) {{K} ^+} {{\pi } ^-}) \\&\quad = (5.82 \pm 0.20 \pm 0.23 \pm 0.55) \times 10^{-4}, \end{aligned}$$where the first uncertainty is statistical, the second systematic, and the third arises from the limited knowledge of external branching fractions.

Abstract:

The first searches for $B^0→K^{+}{\mathrm{π}}^{−}{\mathrm{τ}}^{+}{\mathrm{τ}}^{−}$ and $B_s^0→K^{+}{K}^{−}{\mathrm{τ}}^{+}{\mathrm{τ}}^{−}$ decays at the LHCb experiment are conducted with $pp$ collision data corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{−1}$ . The tau leptons are reconstructed using the ${\mathrm{τ}}^{+}→{\mathrm{μ}}^{+}{\stackrel{¯}{\mathrm{ν}}}_{\mathrm{τ}}{\mathrm{ν}}_{\mathrm{μ}}$ decay and the results are presented in bins of $K^{+}{\mathrm{π}}^{−}$ or $K^{+}{K}^{−}$ mass. No signal is observed and upper limits are set on the branching fractions. The searches result in the first upper limits for $B^0→K^{+}{\mathrm{π}}^{−}{\mathrm{τ}}^{+}{\mathrm{τ}}^{−}$ decays outside the $K^{*}(892{)}^0$ region in $K^{+}{\mathrm{π}}^{−}$ mass and the first limits for $B_s^0→K^{+}{K}^{−}{\mathrm{τ}}^{+}{\mathrm{τ}}^{−}$ decays. The searches are recast into limits on the decays $B^0→K^{*}(892{)}^0{\mathrm{τ}}^{+}{\mathrm{τ}}^{−}$ and $B_s^0→\mathrm{ϕ}(1020){\mathrm{τ}}^{+}{\mathrm{τ}}^{−}$ , yielding $2.8×{10}^{−4}$ ( $2.5×{10}^{−4}$ ) and $4.7×{10}^{−4}$ ( $4.1×{10}^{−4}$ ) at the 95% (90%) confidence level, respectively. For the decay $B^0→K^{*}(892{)}^0{\mathrm{τ}}^{+}{\mathrm{τ}}^{−}$ , this result improves on the current best upper limit by an order of magnitude.

Abstract:

The first search for the $B_s^0→K^{−}{\mathrm{Ï€}}^{+}\mathrm{γ}$ decay in the range $796<m(K^{−}{\mathrm{Ï€}}^{+})<1800\mathrm{MeV}/c^2$ is performed using data from proton-proton collisions collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{−1}$ . The photons are reconstructed through their conversion into an electron-positron pair, which significantly improves the mass resolution of the reconstructed decays with respect to decays with an unconverted photon. A signal excess with a significance of 3.5 standard deviations is measured, constituting the first experimental evidence for this decay. In the range $796<m(K^{−}{\mathrm{Ï€}}^{+})<996\mathrm{MeV}/c^2$ , the ratio $\mathcal{R}$ between the branching fractions of the signal decay and the favored ${\stackrel{¯}{B}}^0→K^{−}{\mathrm{Ï€}}^{+}\mathrm{γ}$ decay is measured to be $\mathcal{R}=(3.7Â\pm 1.2Â\pm 0.4)×{10}^{−2}$ where the first uncertainty is statistical and the second is systematic. This measurement is consistent with the value predicted in the Standard Model. In the range $996<m(K^{−}{\mathrm{Ï€}}^{+})<1800\mathrm{MeV}/c^2$ , the ratio $\mathcal{R}=(0.2Â\pm 2.7Â\pm 1.3)×{10}^{−2}$ is measured.

Abstract:

A time- and flavor-integrated amplitude analysis of $B^0$ and $B_s^0$ decays to the $(K^{+}{\mathrm{Ï€}}^{−})(K^{−}{\mathrm{Ï€}}^{+})$ final state in the $K^{*}(892{)}^0{\stackrel{¯}{K}}^{*}(892{)}^0$ region is presented, using $pp$ collision data recorded with the LHCb detector in 2011–2018, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{−1}$ . The branching fractions of the $B^0$ and $B_s^0$ decays are measured relative to the $B^0→D^{−}{\mathrm{Ï€}}^{+}$ and $B_s^0→D_s^{−}{\mathrm{Ï€}}^{+}$ modes, respectively. The corresponding longitudinal polarization fractions are found to be $f_L^d=0.600Â\pm 0.022Â\pm 0.017$ and $f_L^s=0.159Â\pm 0.010Â\pm 0.007$ , where the uncertainties are statistical and systematic, respectively. The theory-motivated ratio of the squared $B_s^0$ to $B^0$ longitudinally polarized decay amplitudes is found to be $L_{K^{*0}{\stackrel{¯}{K}}^{*0}}=4.92Â\pm 0.55Â\pm 0.48Â\pm 0.02Â\pm 0.10$ , where the uncertainties are statistical, systematic, due to uncertainty of external mass and lifetime measurements, and due to knowledge of the fragmentation fraction ratio, respectively. This confirms the previously reported tension between experimental determinations and theoretical predictions of longitudinal polarization in $B→VV$ decays at the level of 4.4 standard deviations.