arXiv subjects

J. Bhom

Publications and source records attributed to J. Bhom.

At least 19 recordsLinked to original sources

arXiv2026

Branching fraction measurements of $\eta$ and $\eta^\prime(958)$ anomalous decays

Branching fractions of $\eta$ and $\eta'(958)$ anomalous decays are measured using $pp$ collision data at a center-of-mass energy of $\sqrt{s}=13\,\text{TeV}$ collected by the LHCb experiment and corresponding to an integrated luminosity of $5.4\,\text{fb}^{-1}$. The measured values and upper limits are \begin{align*} \cal{B}(\eta\to\mu^+\mu^-) &= (5.02\pm0.14\pm0.18\pm0.26)\times10^{-6} , \\ \cal{B}(\eta'(958)\to\mu^+\mu^-) &<1.9\times10^{-7}\textrm{ at 90% CL} , \\ \cal{B}(\eta\to\pi^+\pi^-\mu^+\mu^-) &<5.4\times10^{-7}\textrm{ at 90% CL}, \\ \cal{B}(\eta'(958)\to\pi^+\pi^-\mu^+\mu^-) &= (2.73\pm0.14\pm0.13\pm0.14)\times10^{-5} , \end{align*} where the uncertainties are, respectively, statistical, systematic, and due to the external branching fraction of the $\phi(1020)\to\mu^+\mu^-$ decay, which is used for normalization. This marks the first experimental search for the $\eta'(958)$ decay, and the most precise measurement of the branching fraction $\cal{B}(\eta\to\mu^+\mu^-)$ to date.

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arXiv2026

New measurements of $B^+_c$ decays into single charm final states

Using proton-proton collision data corresponding to an integrated luminosity of $9 \,\textrm{fb}^{-1}$ collected by the LHCb experiment, searches are performed for $B^+_c$ mesons decaying to a charm and a charmless meson pair. Five products of branching fraction, ${\cal B}(B^+_c\!\to DX)$, and fragmentation ratio $f_c\big/f_u$ are reported, \begin{align*} R_{D^+ K^{*0}} &= ( 1.42 \pm 0.23 \pm 0.07 \pm 0.11 ) \times 10^{-6}, \\ R_{D^{*0} K^+} &= (1.46 \pm 0.30 \pm 0.11 \pm 0.05 ) \times 10^{-6}, \\ R_{D^+_s \phi}\ \ \ &= ( 4.0\pm 1.3 \pm 0.2 \pm 0.5) \times 10^{-7 }, \\ R_{D^0 K^+}\ &= ( 9.7 \pm 1.0 \pm 0.4 \pm 0.3 ) \times 10^{-7}, \\ R_{D^0 \pi^+}\ &<\ 1.4 \times 10^{-7}\ \text{at 95\% CL}. \end{align*} In each case, the first uncertainty is statistical, the second is systematic and the third includes external uncertainties. The first result is a first observation, the second and third exhibit clear evidence and the fourth improves the precision of previous measurements by a factor two. Additionally, the $CP$ asymmetry in $B^+_c\!\to D^0 K^+$ decays is measured and found to be compatible with zero.

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arXiv2026

Measurement of CP asymmetries in $\kern 0.18em\overline{\kern -0.18em B}^0 \to D_s^- D^+$ and $\kern 0.18em\overline{\kern -0.18em B}_s^0 \to D_s^+ D^-$ decays

Measurements of the combined CP asymmetries in $\kern 0.18em\overline{\kern -0.18em B}^0 \to D_s^- D^+$ and $\kern 0.18em\overline{\kern -0.18em B}_s^0 \to D_s^+ D^-$ decays are made using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9fb$^{-1}$. The measurements are found to be \begin{aligned} A_{CP}(\kern 0.18em\overline{\kern -0.18em B}^0 \to D_s^- D^+) &= 0.0009 \pm 0.0053 \pm 0.0040, \\ A_{CP}(\kern 0.18em\overline{\kern -0.18em B}_s^0 \to D_s^+ D^-) &= 0.103\phantom{0} \pm 0.053\phantom{0} \pm 0.010, \end{aligned} where the first and second uncertainties are statistical and systematic, respectively. This is the first measurement of this asymmetry in $\kern 0.18em\overline{\kern -0.18em B}_s^0$ decays, and the most precise measurement to date for $\kern 0.18em\overline{\kern -0.18em B}^0$ decays. Both measurements are found to be consistent with CP symmetry.

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arXiv2026

Improved branching-fraction measurements of $B^0_{(s)} \to K_S^0 h^+ h^{'-}$ decays and first observation of $B^0_{s} \to K_S^0 K^+ K^-$

This paper presents a study of the charmless three-body decays ${B^0_{(s)} \to K_{\mathrm{S}}^0 h^+ h^{\prime -}}$ (where $h^{(\prime)} = \pi, K$), using a sample of $pp$ collision data collected by the LHCb experiment, corresponding to an integrated luminosity of $9\mbox{\,fb}^{-1}$. The decay ${B^0_s \to K_{\mathrm{S}}^0 K^+ K^-}$ is observed for the first time, and the following ratios of branching fractions are measured: \begin{alignat*}{6} &\frac{{\cal B}(B^0 \to K^0_{\mathrm{S}} K^+ K^-)}{{\cal B}(B^0 \to K^0_{\mathrm{S}} \pi^+\pi^-)} &&= 0.578 &&\pm 0.007 &&\pm 0.017\,, &\frac{{\cal B}(B^0 \to K^0_{\mathrm{S}} K^\pm\pi^\mp)}{{\cal B}(B^0 \to K^0_{\mathrm{S}} \pi^+\pi^-)} &&= 0.1363 &&\pm 0.0035 &&\pm 0.0051\,, &\frac{{\cal B}(B^0_s \to K^0_{\mathrm{S}} \pi^+\pi^-)}{{\cal B}(B^0 \to K^0_{\mathrm{S}} \pi^+\pi^-)} &&= 0.269 &&\pm 0.011 &&\pm 0.015 && \pm 0.008\,, &\frac{{\cal B}(B^0_s \to K^0_{\mathrm{S}} K^+ K^-)}{{\cal B}(B^0 \to K^0_{\mathrm{S}} \pi^+\pi^-)} &&= 0.0303 &&\pm 0.0041 &&\pm 0.0025 && \pm 0.0009\,, &\frac{{\cal B}(B^0_s \to K^0_{\mathrm{S}} K^\pm\pi^\mp)}{{\cal B}(B^0 \to K^0_{\mathrm{S}} \pi^+\pi^-)} &&= 1.818 &&\pm 0.021 &&\pm 0.031 && \pm 0.056\,, \end{alignat*} where the uncertainties are statistical, systematic, and due to knowledge of the ratio of hadronisation fractions of the $B^0_s$ and $B^0$ mesons, respectively.

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arXiv2026

A method for luminosity determination based on real-time hit reconstruction with the LHCb silicon pixel detector

The data acquisition system of the upgraded LHCb experiment includes the fast reconstruction of all hits in the vertex locator (VELO) pixel detector at the beam-crossing rate of 40 MHz, implemented as on-the-fly clustering embedded in the firmware of the readout board FPGAs. The availability of a high rate of reconstructed clusters in real time enables a new fast approach for measuring luminosity and monitoring the LHCb luminous region, directly at the detector readout level. This methodology has been implemented as an array of real-time cluster counters in the VELO readout FPGAs and has been in operation since the start of the 2024 physics run of LHCb. This paper describes the methodology and its features and performance, both on proton-proton and lead-lead collision data. The method shows a statistical resolution better than the percent level, and a sensitivity to variable running conditions of the same level. This is achieved with an intrinsic time granularity better than 100 ms , undersampled to 3 s for analysis purposes. Nonlinear behaviour is compatible with zero in a luminosity range including the LHCb Run 3 operating point.

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arXiv2026

Observation of the decay $\chi_{c1}(3872)\rightarrow J\mskip -3mu/\mskip -2mu\psi \mu^+\mu^-$

The first observation of the $\chi_{c1}(3872)\rightarrow J\mskip -3mu/\mskip -2mu\psi \mu^+\mu^-$ decay is reported using proton-proton collision data recorded with the LHCb detector corresponding to an integrated luminosity of $9fb^{-1}$. The decay mode is observed for the first time, with a significance of $6.5\sigma$. Its branching fraction is measured relative to the $\chi_{c1}(3872)\rightarrow J\mskip -3mu/\mskip -2mu\psi \pi^+\pi^-$ decay mode \begin{align*} \frac{\cal{BF}(\chi_{c1}(3872)\rightarrow J\mskip -3mu/\mskip -2mu\psi \mu^+\mu^-)}{\cal{BF}(\chi_{c1}(3872)\rightarrow J\mskip -3mu/\mskip -2mu\psi \pi^+\pi^-)} = \left(1.68\pm 0.32\pm 0.05\right)\times10^{-3}, \end{align*} where the first uncertainty includes both statistical contributions and systematic contributions which are uncorrelated between data-taking periods, and the second represents the systematic contributions that are correlated between data-taking periods.

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arXiv2026

Machine learning techniques for jet reconstruction at LHCb and application to the search for $H \to b \bar{b}$ and $H \to c \bar{c}$ in $\sqrt{s}=13$ TeV $pp$ collisions

Two machine learning techniques for jet measurements at the LHCb experiment are presented: a regression-based method for jet-energy calibration and a deep neural network algorithm for jet flavour tagging, distinguishing between $b$-quark, $c$-quark, and light parton jets. These techniques are applied to a search for inclusive $H \to \bbbar$ and $H \to c\barcc$ decays using a LHCb dataset corresponding to an integrated luminosity of 1.6\invfb. The observed (expected) 95\% confidence level upper limits correspond to 6.6 (11.1) times the SM cross-section for the $H \to b\bar b$ process, and 1003 (1834) times the SM cross-section for the $H \to c\bar c$ process.

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arXiv2026

Search for lepton-number-violating $B^-\to D^{(*)+}\mu^-\mu^-$ decays

A search is performed for lepton-number-violating $B^-\to D^{(*)+}\mu^-\mu^-$ decays, using data collected by the LHCb experiment in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb$^{-1}$. No significant signal is observed, and upper limits are set on the branching fractions, ${\cal B}(B^-\to D^{+}\mu^-\mu^-) < 4.6 \times 10^{-8}$ and ${\cal B}(B^-\to D^{*+}\mu^-\mu^-) < 5.9 \times 10^{-8}$, at the 95% confidence level.

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arXiv2025

Comprehensive analysis of the $B^0\to K^{*0}\mu^+\mu^-$ decay

An analysis of the $B^{0}\rightarrow K^{*0}(\to K^+ \pi^-)\mu^{+}\mu^{-}$ decay is presented using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 8.4 fb$^{-1}$. The full set of $CP$-averaged and $CP$-asymmetric angular observables is determined in bins of the invariant mass squared of the dimuon system, as well as the branching fraction relative to the $B^{0}\rightarrow J/\psi(\to\mu^{+}\mu^{-})K^+\pi^-$ decay. For the first time, the full set of observables pertaining to the $K^+\pi^-$ S-wave contribution to the final state are presented and consideration is given to effects arising from the mass of the muons. The measurements of the $CP$-averaged observables and the branching fractions continue to exhibit the pattern of tensions with the Standard Model predictions that have been seen in previous analyses that use part of the dataset considered in this Letter.

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arXiv2025

Search for heavy neutral leptons in B-meson decays

A search for long-lived heavy neutral leptons produced in B-meson decays and decaying to a $ \mu^\pm \pi^\mp$ final state is performed with data collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $5\,\mathrm{fb}^{-1}$. The results are interpreted in both lepton-number-conserving and lepton-number-violating scenarios. No significant excess is observed. Constraints are placed on the squared mixing element $|U_{\mu N}|^2$ to the active muon neutrino, under the assumption that couplings to other lepton flavours are negligible, in the mass range of $1.6$-$5.5$ GeV.

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arXiv2025

Measurement of the branching fractions and longitudinal polarisations of $B^0_{(s)} \to K^{0} \kern 0.18em \overline{\kern -0.18em K}{}^{0}$ decays

A time- and flavour-integrated amplitude analysis of $B^0$ and $B^0_s$ decays to the $(K^+\pi^-)(K^-\pi^+)$ final state in the $K^*(892)^0 \kern 0.18em \overline{\kern -0.18em K}{}^{*}(892)^0$ region is presented, using $pp$ collision data recorded with the LHCb detector in 2011--2018, corresponding to an integrated luminosity of $9\,\text{fb}^{-1}$. The branching fractions of the $B^0$ and $B^0_s$ decays are measured relative to the $B^0 \to D^-\pi^+$ and $B^0_s \to D^-_s \pi^+$ modes, respectively. The corresponding longitudinal polarisation fractions are found to be $f_L^{d} = 0.600 \pm 0.022 \pm 0.017$ and $f_L^{s} = 0.159 \pm 0.010 \pm 0.007$, where the uncertainties are statistical and systematic, respectively. The theory-motivated ratio of the squared $B^0_s$ to $B^0$ longitudinally polarised decay amplitudes is found to be $L_{K^{*0} \kern 0.18em \overline{\kern -0.18em K}{}^{*0}} = 4.92 \pm 0.55 \pm 0.48 \pm 0.02 \pm 0.10$, 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 polarisation in $B \to VV$ decays at the level of 4.4 standard deviations.

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arXiv2025

Observation of the rare baryonic decay $B^{+}\rightarrow p \bar{\it{\Lambda}}$ and measurement of its weak decay parameter

The first observation of the decay $B^{+}\rightarrow p \bar{\it{\Lambda}}$ is presented, using proton-proton collision data collected by the LHCb experiment between 2016 and 2018 at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $5.4\,\mathrm{fb}^{-1}$. The signal significance exceeds seven standard deviations. Using the $B^{+} \rightarrow K^{\mathrm{0}}_{\mathrm{S}} \pi^{+}$ decay as a normalization channel, the branching fraction is measured and combined with previous LHCb results based on data collected at 7 and 8 TeV in 2011 and 2012, yielding $\mathcal{B}(B^{+}\rightarrow p \bar{\it{\Lambda}})=(1.24\pm 0.17\pm 0.05\pm 0.03)\times 10^{-7}$, where the first uncertainty is statistical, the second is systematic, and the third comes from the uncertainty on the branching fraction of the normalization channel. The $B^{+}\rightarrow p \bar{\it{\Lambda}}$ weak decay parameter is measured to be $\alpha_B = 0.87_{-0.29}^{+0.26} \pm 0.09$, indicating the presence of comparable S-wave and P-wave decay amplitudes.

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arXiv2025

Differential decay rate of $B^+ \to J/\psi K^+$ with the LHCb Upgrade I experiment

The normalised decay rate of $B^+ \to J/\psi(\to \mu^+\mu^-) K^+$ is measured as a function of the lepton helicity angle using a data sample corresponding to an integrated luminosity of $1.1 \text{fb}^{-1}$ collected during October 2024 with the upgraded (Upgrade I) LHCb detector. This angular distribution can be parameterised by two coefficients, the forward-backward asymmetry, $A_{FB}$, and the flatness parameter, $F_{H}$, whose values are constrained by conservation of angular momentum. These coefficients are measured both integrated and differentially across various kinematic and detector-response variables, and the results are found to be in good agreement with expectations. These measurements show that the detector response of the LHCb Upgrade I experiment is understood to the precision required to reliably extract the angular coefficients associated with rare $b \to s \mu^+\mu^-$ and $b \to d \mu^+\mu^-$ transitions, which are particularly sensitive to physics beyond the Standard Model.

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arXiv2025

Branching fraction measurement of the $\mathit{\Lambda} \to p \mu^- \overline{\nu}_{\mu}$ decay

A measurement of the branching fraction for the decay $\mathit{\Lambda} \to p \mu^- \overline{\nu}_{\mu}$ is presented using $\textit{pp}$ collision data collected by the LHCb experiment at a centre-of-mass energy of 13 TeV. The analysis is based on data recorded between 2016 and 2018, corresponding to an integrated luminosity of $5.4 \ \text{fb}^{-1}$. The result is obtained using $\mathit{\Lambda} \to p \pi^-$ decays as a normalisation channel. The measured branching fraction is $B(\mathit{\Lambda} \to p \mu^- \overline{\nu}_{\mu})= (1.462 \pm 0.016 \pm 0.100 \pm 0.011 ) \times 10^{-4}$, where the uncertainties are statistical, systematic, and due to the limited knowledge of the normalisation mode branching fraction, respectively. This result improves the precision of the branching fraction measurement by a factor of two compared to the previous best measurement and sets a more stringent bound on lepton flavour universality in $s \to u$ quark transitions. It is consistent with previous measurements, and the extracted lepton flavour universality test observable, $R^{\mu e} = \frac{\Gamma(\mathit{\Lambda} \to p \mu^- \overline{\nu}_\mu)}{\Gamma(\mathit{\Lambda} \to p e^- \overline{\nu}_e)} = 0.175 \pm 0.012$, agrees with the Standard Model prediction.

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arXiv2025

Measurement of charged-hadron distributions in heavy-flavor jets in proton-proton collisions at $\sqrt{s}$=13 TeV

Charged-hadron distributions in heavy-flavor jets are measured in proton-proton collisions at a center-of-mass energy of $\sqrt{s}$ = 13 TeV collected by the LHCb experiment. Distributions of the longitudinal momentum fraction, transverse momentum, and radial profile of charged hadrons are measured separately in beauty and charm jets. The distributions are compared to those previously measured by the LHCb collaboration in jets produced back-to-back with a $Z$ boson, which in the forward region are primarily light-quark-initiated, to compare the hadronization mechanisms of heavy and light quarks. The observed differences between the heavy- and light-jet distributions are consistent with the heavy-quark dynamics expected to arise from the dead-cone effect, as well as with a hard fragmentation of the heavy-flavor hadron as previously measured in single-hadron fragmentation functions. This measurement provides additional constraints for the extraction of collinear and transverse-momentum-dependent heavy-flavor fragmentation functions and offers another approach to probing the mechanisms that govern heavy-flavor hadronization.

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arXiv2025

Search for $K_{\mathrm{S(L)}}^{0} \rightarrow \pi^{+}\pi^{-}\mu^{+}\mu^{-}$ decays at LHCb

A search for $K_{\mathrm{S(L)}}^{0} \rightarrow \pi^{+}\pi^{-}\mu^{+}\mu^{-}$ decays is performed using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of $13\,\mathrm{TeV}$, corresponding to an integrated luminosity of $5.4\,\mathrm{fb^{-1}}$. No $K_{\mathrm{S(L)}}^{0} \rightarrow \pi^{+}\pi^{-}\mu^{+}\mu^{-}$ signals are found and upper limits are set for the first time on the branching fractions $\mathcal{B}(K_\text{S}^{0} \rightarrow \pi^{+}\pi^{-}\mu^{+}\mu^{-}) < 1.4 \times 10^{-9}$ and $\mathcal{B}(K_\text{L}^{0} \rightarrow \pi^{+}\pi^{-}\mu^{+}\mu^{-}) < 6.6 \times 10^{-7}$, at the 90% confidence level.

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arXiv2025

Measurement of $C\!P$ asymmetry in $D^0 \to K^0_{\rm S} K^0_{\rm S}$ decays with Run 3 data

A measurement of $C\!P$ asymmetry in $D^0 \to K^0_{\rm S} K^0_{\rm S}$ decays is reported, based on a data sample of proton-proton collisions collected with the LHCb detector in 2024 at a centre-of-mass energy of $13.6\,$TeV, corresponding to an integrated luminosity of $6.2\,\mathrm{fb}^{-1}$. The $D^0 \to K^0_{\rm S} \pi^+ \pi^-$ decay is used as calibration channel to cancel residual detection and production asymmetries. The time-integrated $C\!P$ asymmetry for the $D^0 \to K^0_{\rm S} K^0_{\rm S}$ mode is measured to be $$ {\cal A}^{C\!P} (D^0 \to K^0_{\rm S} K^0_{\rm S}) = (1.86 \pm 1.04\pm 0.41)\%, $$ where the first uncertainty is statistical, and the second is systematic. This measurement represents the most precise single-experiment determination of this quantity to date.

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arXiv2025

Searches for $B^0\to K^+\pi^-\tau^+\tau^-$ and $B_s^0\to K^+K^-\tau^+\tau^-$ decays

The first searches for $B^0\to K^+\pi^-\tau^+\tau^-$ and $B^0_s\to K^+K^-\tau^+\tau^-$ decays at the LHCb experiment are conducted with $pp$ collision data corresponding to an integrated luminosity of $5.4\textrm{ fb}^{-1}$. The tau leptons are reconstructed using the $\tau^+\to \mu^+\overline{\nu}_\tau\nu_\mu$ decay and the results are presented in bins of $K^+\pi^-$ 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 $B^0\to K^+\pi^-\tau^+\tau^-$ decays outside the $K^*(892)^0$ region in $K^+\pi^-$ mass and the first limits for $B^0_s\to K^+K^-\tau^+\tau^-$ decays. The searches are recast into limits on the decays $B^0\to K^*(892)^0\tau^+\tau^-$ and $B^0_s\to \phi(1020)\tau^+\tau^-$, yielding $2.8\times10^{-4}$ ($2.5\times10^{-4}$) and $4.7\times10^{-4}$ ($4.1\times10^{-4}$) at the $95\%$ ($90\%$) confidence level, respectively. For the decay $B^0\to K^*(892)^0\tau^+\tau^-$, this result improves on the current best upper limit by an order of magnitude.

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