arXiv subjects

M. Becker

Publications and source records attributed to M. Becker.

At least 19 recordsLinked to original sources

arXiv2026

Observation of the $T_{c\bar{c}1}(4430)^-$ state in $B^0\to D^{*-}D^0K^+$ decays

A study of resonant structures in $B^0 \to D^{*-}D^0K^+$ decays is presented. The analysis uses proton-proton collision data collected by the LHCb experiment at center-of-mass energies of $\sqrt{s} = 7$, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb$^{-1}$. The analysis demonstrates that the existing known excited $D_s^+$ resonances in the $D^0K^+$ spectrum are insufficient to describe the data. The inclusion of the tetraquark state $T_{c\bar{c}1}(4430)^-$ improves the description of the data with a statistical significance exceeding $5σ$. This corresponds to the first observation of the $T_{c\bar{c}1}(4430)^- \to D^{*-} D^0$ decay. The measured properties of the $T_{c\bar{c}1}(4430)^-$ state are consistent with those previously measured in its decay to the $ψ(2S)π^-$ final state.

hep-ex↗

arXiv2026

Stringent limits on $C\!PT$- and Lorentz-invariance violation from $B_s^0$ meson decays

Tests of fundamental symmetries, such as $C\!PT$ and Lorentz invariance, provide sensitive probes of physics beyond the standard quantum-field-theory framework. Possible violations of these symmetries are investigated through interference effects in decays of $B_s^0$ mesons to $D_s^-π^{+}$ states. The analysis uses proton-proton collision data collected with the LHCb detector in 2015-2018 at a centre-of-mass energy of $13~\mathrm{TeV}$, corresponding to an integrated luminosity of $6~\mathrm{fb}^{-1}$. The results are interpreted within the Standard Model Extension framework, yielding sensitivities to the Lorentz-violating parameter $Δa_μ$ at the ${\cal O}(10^{-14})\,\mathrm{GeV}$ level. Without assuming Lorentz-invariance violation, the $C\!PT$-violating parameter $z$ in the $B_s^0$ system is measured to be $\mathcal{R}e(z) = 0.018 \pm 0.016 \pm 0.003$ and $\mathcal{I}m(z) = 0.003 \pm 0.004 \pm 0.002$, where the first uncertainties are statistical and the second systematic. These results represent the most precise constraints on $C\!PT$ violation in the $B_s^0$ system.

hep-ex↗

arXiv2026

Observation of the ${Ξ_b^-\to Ξ^-μ^+μ^-}$ and study of the ${Ξ_b^-\toΞ^-ψ(2S)}$ decays

The rare decay ${Ξ_b^-\toΞ^-μ^+μ^-}$ is observed for the first time using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of $7$, $8$ and~$13~\text{TeV}$, corresponding to integrated luminosities of $1$, $2$ and $6~\text{fb}^{-1}$, respectively. Its branching fraction is reported in intervals of the dimuon invariant mass squared. The integrated value of ${\cal{B}}(Ξ_b^-\toΞ^-μ^+μ^-)$ is measured to be ${ (118 \pm 24 \pm 7 \pm 38 ) \times 10^{-8}}$, where the first uncertainty is statistical, the second is systematic and the third uncertainty arises from the normalisation branching fraction ${\cal{B}}(Ξ_b^-\toΞ^-J/ψ)$, whose uncertainty is dominated by SU(3)-breaking effects. In addition, the ratio of the branching fractions of the ${Ξ_b^-\toΞ^-ψ(2S)}$ and the ${Ξ_b^-\toΞ^-J/ψ}$ decays is measured to be ${ 0.491 \pm 0.041 \pm 0.019 }$.

hep-ex↗

arXiv2026

Measurement of the local and nonlocal amplitudes in $B^{+}\to K^{+}μ^{+}μ^{-}$ decays

This paper presents a thorough study of the local and nonlocal amplitudes in $B^+ \to K^+μ^+μ^-$ transitions through an amplitude analysis of the dimuon mass spectrum of the decay. The analysis is based on $pp$ collision data corresponding to an integrated luminosity of 8.4fb$^{-1}$ collected by the LHCb experiment. This measurement employs a model that describes both one-particle and two-particle nonlocal amplitudes across the entirety of the dimuon mass spectrum, enabling the determination of both short- and long-distance contributions to the decay. The compatibility of the Wilson coefficient combinations $C_9+C_9'$ and $C_{10}+C_{10}'$ with the Standard Model prediction is found to vary between $1.6\,σ$ and $4\,σ$, depending on the choice of local form factors.

hep-ex↗

arXiv2026

Evidence for the decay $B^0_s\toϕη'$

Using a dataset corresponding to an integrated luminosity of $9 \,\textrm{fb}^{-1}$ collected in proton-proton collisions between 2011 and 2018 by the LHCb experiment, evidence is found for the decay $B^0_s\toϕη'$ with $3.5 σ$ significance. The branching ratio relative to the $B^0_s\toϕϕ$ decay is determined to be $R=(3.56 \pm 0.79\pm 0.18\pm 0.06)\times10^{-2}$. This corresponds to a branching fraction, $B(B^0_s\toϕη')=(0.66 \pm 0.15 \pm 0.03 \pm 0.02) \times 10^{-6}$ where, in both cases, the first uncertainty is statistical, the second systematic, and the third due to external branching fractions.

hep-ex↗

arXiv2026

Branching fraction measurement of the $B^0\to K^+π^-μ^+μ^-$ decay at high dihadron mass

This Letter presents the first measurement of the $B^{0} \to K^{+}π^{-}μ^{+}μ^{-}$ differential branching fraction in the region of the dihadron $K^+π^-$ mass, $m_{Kπ}$, $1000< m_{Kπ} < 1835\,\text{MeV}/c^{2}$. This decay mode is mediated by the quark-level transition $b \to s\ell^{+}\ell^{-}$, for which the measured effective couplings show tensions with Standard Model predictions. The analysis is performed using proton-proton collision data collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of $8.4\,\text{fb}^{-1}$. The differential branching fraction is determined across different regions of dimuon mass squared, $q^2$, in the interval $0.1 < q^2 < 18.0\,\text{GeV}^2/c^{4}$, as well as in different regions of $ m_{Kπ}$ in the interval $1.1 < q^2 < 6.0\,\text{GeV}^2/c^{4}$. The results represent the first differential measurement of the branching fraction across $m_{Kπ}$ within the selected dihadron-mass region, and the first observation of the decay within this region above the $J/ψ$ resonance.

hep-ex↗

arXiv2026

Energy-energy correlators within $Z$-tagged jets in proton-proton collisions at $\sqrt{s}$ = 13 TeV

Energy-energy correlators probe perturbative and nonperturbative QCD regimes of jet formation through momentum-weighted angular correlations between hadrons. First measurements in light-quark-enriched jets are presented for inclusive, like-sign, and opposite-sign charged-hadron pairs, using proton-proton collisions at LHCb. The results support universality of the confinement scale for light-quark-initiated jets across collision systems and the reported transverse momentum scale of the jet. In the charge-dependent measurements, opposite-sign correlations are enhanced as angular separation decreases down to the confinement-scale region, a behavior that is well described by simulations.

hep-ex↗

arXiv2026

Measurement of the ratio of branching fractions $\mathcal{B}(B_c^+ \to J/ψτ^+ ν_τ)/\mathcal{B}(B_c^+ \to J/ψμ^+ ν_μ)$

A measurement of the ratio of semileptonic branching fractions $\mathcal{R}(Jψ)$, defined as $\mathcal{R}(J/ψ) \equiv \mathcal{B}(B_c^+ \to J/ψτ^+ ν_τ)/\mathcal{B}(B_c^+ \to J/ψμ^+ ν_μ)$, is reported using a sample of proton-proton collision data corresponding to an integrated luminosity of 5.4 fb$^{-1}$ recorded by the LHCb experiment in 2016--2018 at a center-of-mass energy of 13 TeV. The measured value is found to be $\mathcal{R}(J/ψ) = 0.51 \pm 0.12\text{(stat)} \pm 0.08\text{(syst)}$, which is within 1.8 standard deviations of the predictions from the Standard Model assuming lepton flavor universality.

hep-ex↗

arXiv2026

$π$-QCD; Proposal for Experiments at the GSI Pion Beam Facility

We propose to investigate the dynamics of hadronic matter in the strong QCD regime using the pion-beam facility at GSI in conjunction with HADES. This program will study hadron physics through elementary pion-nucleon interactions up to $\sqrt{s}\approx$2.35 GeV, bridging cold matter research with detailed analyses of exclusive reactions. Our goals include exploring baryon resonance formation and their electromagnetic structures. This will complement photo-production experiments (e.g., ELSA) and enhance our understanding of emissivity in dense, hot hadronic matter. Key topics include examining baryon couplings to mesons and virtual photons, analyzing hyperon weak decays in exclusive reactions, and using Partial Wave Analyses with differential cross sections and polarization observables to achieve unprecedented precision in baryon-meson coupling data ($ρ$N, $ω$N). Furthermore, e$^{+}$e$^{-}$ production measurements off nucleons will provide insight into the electromagnetic transition form factors of baryons in the time-like region, revealing the role of vector mesons ($ρ$, $ω$). Reactions on nuclear targets allow for detailed studies of hadron properties, including vector-meson line shapes and strengths in cold nuclear matter. These measurements provide a critical reference for the interpretation of results from the hot and dense environment created in $A+A$ collisions. This research also has broader implications. It will contribute to the modeling of neutrino-nucleus interactions, facilitate unprecedented investigations into hypernuclei formation, and enhance our understanding of strong interaction dynamics across different energy regimes.

nucl-ex↗

arXiv2026

Angular analysis of the $B^+\toπ^+μ^+μ^-$ decay

This paper presents the first measurement of the forward-backward asymmetry, $A_{\rm FB}$, and the flat term, $F_{H}$, that parameterise the angular distribution of the $B^+\toπ^+μ^+μ^-$ decay. The proton-proton collision dataset used in the analysis corresponds to an integrated luminosity of 9 fb$^{-1}$, collected with the LHCb experiment between 2011 and 2018. The analysis is performed in two intervals of dimuon mass squared, one above and one below the region containing the $J\mskip -3mu/\mskip -2muψ$ and $ψ(2S)$ narrow charmonium resonances. The Standard Model predictions lie within the obtained $68\%$ confidence level interval in the high-mass and within the $99\%$ interval in the low-mass region.

hep-ex↗

arXiv2026

First measurement of the forward rapidity dependence of $W$ boson transverse helicity fractions

The transverse helicity fractions of $W$ bosons are measured as a function of the $W$ boson rapidity, $y_{W}$, in the range $0 \leq y_{W} \leq 5$ using $W\toμν_μ$ decays in $pp$ collisions at $\sqrt{s}$ = 13 TeV recorded by the LHCb experiment and corresponding to an integrated luminosity of $5.1$ fb$^{-1}$. The fractions are extracted from a template fit to the muon transverse momentum and pseudorapidity. The results show a strong rapidity dependence and agree with next-to-leading-order Standard Model predictions, providing the first determination of the transverse helicity fractions of $W$ bosons in the forward region.

hep-ex↗

arXiv2026

Search for $τ^-\to μ^-μ^+μ^-$ decays at the LHCb experiment with Run 2 data

A search for the lepton-flavour-violating decay $τ^-\to μ^-μ^+μ^-$ is carried out using data collected by the LHCb experiment between 2016 and 2018 in proton-proton collisions at the LHC at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb$^{-1}$. An upper limit of $1.9\,(2.3)\times 10^{-8}$ is set at the 90% (95%) confidence level on the branching fraction of the decay.

hep-ex↗

arXiv2026

Discovery of an unexpectedly light and narrow beauty-strange state

As the essential building blocks of visible matter, hadrons have traditionally been classified by the quark model as mesons composed of quark-antiquark pairs and baryons built from three valence quarks. Yet, this classical picture does not account for the intricate chiral dynamics of the strong force and the emergence of exotic multi-quark hadrons. While experimental evidence for such unconventional dynamics has surfaced in the charm sector, the open-beauty system remains the long-sought frontier for testing the universality of these mechanisms. Here the observation of a new resonance in the beauty-strange sector with a global significance exceeding seven standard deviations is reported using proton-proton collision data recorded by the Large Hadron Collider beauty (LHCb) experiment at the European Organization for Nuclear Research (CERN). It exhibits a narrow natural width and a substantial mass deficit compared to the conventional quark model predictions. This result marks the first observation of a nonconventional single-beauty hadron, providing crucial insights into the chiral dynamics of the strong interaction and heavy-quark spin symmetry in the exotic domain.

hep-ex↗

arXiv2026

Measurement of the $Ω_b^-$ baryon lifetime

The lifetime ratio ${r_τ\equivτ_{Ω_b^-}/τ_{Ξ_b^-}}$ between the ${Ω_b^-}$ and ${Ξ_b^-}$ baryons is measured using a sample of $pp$ collision data corresponding to an integrated luminosity of 6 fb$^{-1}$ and collected by the LHCb experiment during LHC Run 2 (2015$-$2018). The ratio $r_τ$ is measured in two sets of decays modes, ${ {(Ω_b^-,Ξ_b^-)\to(Ω_c^0π^-,Ξ_c^0π^-)}}$ and ${(Ω_b^-,Ξ_b^-)\to(J/ψΩ^-, J/ψΞ^-)}$, with ${(Ω_c^0,Ξ_c^0)\to pK^-K^-π^+}$, ${(Ω^-,Ξ^-)\to(Λ^0 K^-,Λ^0π^-)}$, ${Λ^0\to pπ^-}$ and $J/ψ\toμ^+μ^-$. The measured $r_τ$ values are averaged and combined with Run 1 (2011$-$2012) measurements in the same decay modes to obtain ${r_τ = 1.109\pm0.055\pm0.010}$. Multiplying by the known ${Ξ_b^-}$ lifetime results in the ${Ω_b^-}$ lifetime ${τ_{Ω_b^-} = 1.751\pm0.089\pm0.022~{\rm ps}}$, where the uncertainties are statistical and systematic. This measurement improves on the precision of the $Ω_b^-$ lifetime by about a factor of two over the previous world average. The value of $r_τ$ is in agreement with the most recent theoretical predictions from the heavy quark expansion framework.

hep-ex↗

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 $h^{(\prime)} = π, K$), using a sample of $pp$ collision data collected by the LHCb experiment during Runs 1 and 2 of the LHC, corresponding to an integrated luminosity of $9\,\mathrm{fb}^{-1}$. 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}} π^+π^-)} &&= 0.578 &&\pm 0.007 &&\pm 0.017\,, &\frac{{\cal B}(B^0 \to K^0_{\mathrm{S}} K^\pmπ^\mp)}{{\cal B}(B^0 \to K^0_{\mathrm{S}} π^+π^-)} &&= 0.1363 &&\pm 0.0035 &&\pm 0.0051\,, &\frac{{\cal B}(B^0_s \to K^0_{\mathrm{S}} π^+π^-)}{{\cal B}(B^0 \to K^0_{\mathrm{S}} π^+π^-)} &&= 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}} π^+π^-)} &&= 0.0303 &&\pm 0.0041 &&\pm 0.0025 && \pm 0.0009\,, &\frac{{\cal B}(B^0_s \to K^0_{\mathrm{S}} K^\pmπ^\mp)}{{\cal B}(B^0 \to K^0_{\mathrm{S}} π^+π^-)} &&= 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.

hep-ex↗

arXiv2026

Observation of the doubly charmed baryon $\varOmega^+_{cc}$

A search for the doubly charmed baryon $\varOmega^+_{cc}$ in the $\varOmega^0_cπ^+$ decay channel is performed using proton-proton collision data corresponding to an integrated luminosity of $6.3\text{fb}^{-1}$, collected with the upgraded LHCb detector in 2024 at a center-of-mass energy of 13.6$\text{TeV}$. A peaking structure with a global significance of $8.7σ$ is observed in the $\varOmega^0_cπ^+$ mass spectrum, where the $\varOmega^0_c$ baryon is reconstructed in the $pK^-K^-π^+$ final state. The structure is consistent with originating from a weakly decaying particle and is identified as the doubly charmed baryon $\varOmega^+_{cc}$. Its mass is determined to be $3725.9 \pm 1.0 \,(\mathrm{stat}) \pm 0.2 \,(\mathrm{syst}) \pm 0.4 \,(\mathrm{lifetime}) \pm 0.6 \,(\mathrm{ext})\,\text{MeV/}c^2$, where the third uncertainty arises from the dependence of the selection-induced bias on the unknown $\varOmega^+_{cc}$ lifetime, and the fourth is due to the uncertainties on the masses of the $\varOmega^0_c$, $\varXi^+_c$, and $\varXi^{++}_{cc}$ baryons.

hep-ex↗

arXiv2026

Weak Lensing Mass Calibration of the ACT DR5 Galaxy Clusters with the DES Year 3 Weak Lensing Data

We use weak gravitational lensing measurements from Year 3 Dark Energy Survey data to calibrate the masses of 443 galaxy clusters selected via the Sunyaev-Zel'dovich effect from Atacama Cosmology Telescope Data Release 5 maps. We incorporate redshift and SZ measurements for individual clusters into a hierarchical model for the stacked lensing signals and perform Bayesian analyses to constrain hydrostatic mass bias of the clusters. Our treatment of systematic uncertainties includes a prescription for measuring and accounting for the weak lensing boost factor, consideration of a miscentering effect, as well as marginalization over uncertainties in the source galaxy photometric redshift distributions and shear calibration. The constraints on the normalization of the mass-observable relation have a precision of 7%, with the mean WL halo mass $M_{\rm 500c} = 5.4 \times 10^{14} M_{\odot}$. We measure the bias between the true cluster mass and the mass estimated from the SZ signal assuming hydrostatic equilibrium, to be $1-b = 0.74^{+0.06}{-0.05}$ over the full sample. When splitting the clusters into high and low redshift bins, we measure $1-b = 0.58^{+0.06}{-0.05}$ and $0.81^{+0.08}{-0.06}$, respectively. When introducing additional freedom in redshift and mass to the hydrostatic bias model, we find that $1-b$ decreases with redshift (with the power law of $-1.8^{+0.5}{-0.6}$, 99.95% confidence), consistent with findings from other recent studies, while we do not find any significant trend in mass. We also demonstrate that our result is robust against various systematics such as a scale cut, priors on baryonic and miscentering parameters, and degree of scatter in mass-observable relation. The weak-lensing mass calibration presented in this study will be a useful tool for using the ACT clusters as probes of astrophysics, and as a step towards using their abundance as a cosmological probe.

astro-ph.CO↗

arXiv2026

Measurement of the $W$-boson production cross-sections in $pp$ collisions at $\sqrt{s}$ = 13 TeV in the forward region

A precision measurement of the $W$-boson production cross-section is performed using the $W \to μν$ decay channel, based on a sample of proton-proton collision data collected by the LHCb experiment at $\sqrt{s}$ = 13 TeV and corresponding to an integrated luminosity of 5.1 $fb^{-1}$. The cross-section is measured for muons with transverse momentum between 25 and 55 GeV and pseudorapidity between 2.0 and 4.5. The integrated production cross-sections of $W$ bosons are measured to be $$ \begin{array}{lcl} σ_{W^+ \to μ^+ν} &=& 1754.2 \pm 1.5 \pm 11.9 \pm 35.1\text{ pb} \\ σ_{W^- \to μ^-\barν} &=& 1178.1 \pm 1.3 \pm 9.7 \pm 23.6\text{ pb} \end{array} $$ where uncertainties are statistical, systematic, and due to the luminosity determination, respectively. Results are in good agreement with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics. This measurement is significantly more precise than previous results in this kinematic regime.

hep-ex↗