arXiv subjects

S. Bhattacharya

Publications and source records attributed to S. Bhattacharya.

At least 19 recordsLinked to original sources

arXiv2026

Regularity of core coupled high-spin structure in neutron-rich $^{196-202}$Au isotopes approaching N $=126$

Excited states built upon long-lived high-spin isomers in hard-to-reach neutron-rich Au ($Z=79$) isotopes were populated using multi-nucleon transfer reactions between $^{136}$Xe and $^{198}$Pt at 7 MeV/u. These states in $^{196,\,198-202}$Au were identified for the first time using the powerful combination of the VAMOS++ spectrometer, the CATLIFE detection system, and the AGATA $γ$-ray tracking array. Their measured energies exhibit remarkable regularity as a function of neutron number and are seen to be inherited from the energies of yrast-band members in the corresponding Hg ($Z=80$) isotope. Large-scale shell-model calculations reproduce the observed regularity and show that these states arise from the unique-parity orbitals $\pi0h_{11/2}$ and $\nu0i_{13/2}$ coupled to the Hg core. This regularity is due to the dominant proton configurations of the Hg and Au isotopes, where the level energies are almost independent of different neutron-orbital occupancies. The calculated Au wave functions show significant higher-spin components of the corresponding Hg core, unlike what is expected in the conventional interpretation in terms of the weak-coupling/decoupling limits of the particle-core coupling model.

nucl-ex↗

arXiv2026

First evidence of the decay $B^+\toπ^+ e^+ e^-$

The first evidence for the decay $B^+\toπ^+ e^+ e^-$ is reported using proton-proton collision data recorded by the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fb$^{-1}$. A signal excess with a significance of 3.2$σ$ is observed and the branching fraction is measured to be $\cal{BR}(B^+\toπ^+ e^+ e^-) = (2.4\,{}^{+0.9}_{-0.8} \,{}^{+0.4}_{-0.2}) \times 10^{-8}$, where the first set of uncertainties is statistical and the second is systematic. The result is consistent with the Standard Model expectation.

hep-ex↗

arXiv2026

Evidence for the decay $B^0 \to μ^+ μ^-$ and improved measurements of the decay $B^0_s \to μ^+ μ^-$

The first single-experiment evidence for the rare decay $B^0 \to μ^+ μ^-$ and the world's most precise measurements of the $B^0_s \to μ^+ μ^-$ branching fraction and effective lifetime are reported. The results are obtained using Run 3 proton-proton collision data corresponding to an integrated luminosity of 18 fb$^{-1}$ recorded with the LHCb Upgrade I detector at a centre-of-mass energy of $13.6$ TeV between 2024 and 2025. Their combination with the Run 1 and Run 2 LHCb results further improves the precision. All measurements are found to be in agreement with the Standard Model expectations.

hep-ex↗

arXiv2026

Search for $\mathrm{GeV}$-scale axion-like particles in PbPb collisions

A search is performed for the production of axion-like particles with masses in the range 3-10 GeV using PbPb collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of $0.228~\mathrm{nb}^{-1}$ and a nucleon-nucleon centre-of-mass energy of $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV. This is the first search for axion-like particles produced exclusively by two photons ($γγ\to a\toγγ$) in the forward direction. It extends sensitivity to previously unexplored regions of the parameter space, probing axion-like particle masses and couplings down to 3.0 GeV and $3.2\times10^{-4}~\mathrm{GeV}^{-1}$, respectively. This result provides the most stringent limits to date on the production of axion-like particles from exclusive photon-photon fusion processes with masses between 3 and 5 GeV.

hep-ex↗

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

Chemical abundance patterns at z=1-7: Carbon, Nitrogen, Neon, Sulphur, and Argon abundances from JWST spectroscopy

The relative abundances of chemical elements in the interstellar medium (ISM) trace the history of star formation and chemical enrichment in galaxies. We investigate the abundance patterns of carbon (C), nitrogen (N), neon (Ne), sulfur (S), and argon (Ar) in star-forming galaxies at z=1-7, combining ultra-deep JWST/NIRSpec observations from the MARTA survey with archival spectroscopy. We assemble 244 galaxies with [OIII]4363 detections and derive direct Te-based abundances. New empirical strong-line calibrations for N/O, Ne/O, S/O, and Ar/O extend the analysis to an additional 514 galaxies. We find distinct abundance-metallicity trends. N/O is enhanced by 0.18 dex in median relative to local galaxies, with a stronger enhancement at low metallicity. Direct measurements reveal decreasing S/O and Ar/O with increasing metallicity, while strong-line measurements suggest a flattening at higher metallicities, especially for S/O. We also identify a stellar-mass dependence in the O/Ar-Ar/H plane, with lower-mass galaxies exhibiting lower O/Ar at fixed Ar/H, consistent with differences in star-formation efficiency and delayed SNe Ia enrichment. Ne/O remains approximately constant up to 12+log(O/H)=8.2, with a mild increase at higher metallicities and no significant redshift evolution. C/O tentatively increases with metallicity, broadly following the local relation. Finally, a forward model shows that observational selection affects the abundance ratios differently: it mainly restricts the accessible metallicity range for Ne/O and Ar/O, but preferentially selects galaxies with enhanced N/O at low metallicity, with a weaker effect for S/O. These results provide new constraints on chemical enrichment at high redshift and highlight the importance of accounting for selection effects when interpreting abundance-metallicity trends.

astro-ph.GA↗

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

Evolution of high-spin states in neutron-rich $^{195-202}$Au isotopes approaching the $N=126$ shell closure

\textbf{Background: } The nuclear structure in the region southwest of the doubly magic $^{208}$Pb is important to benchmark theoretical models relevant for neutron-rich heavy element formation and for the origin of the $A\approx195$ peak in the mass abundance distribution. Although neutron-rich Pb, Tl, and Hg ($Z=80-82$) isotopes are relatively well studied, experimental data for neutron-rich Au isotopes ($Z=79$) remain largely limited due to experimental challenges. \textbf{Purpose: } The purpose of this work is to investigate the evolution of the high-spin structure in neutron-rich Au isotopes near the $N=126$ shell closure and to characterize the underlying shell-model configurations, with a particular focus on the roles of the high-$j$ unique-parity $πh_{11/2}$ and $νi_{13/2}$ orbitals. \textbf{Methods: } Neutron-rich $^{195-202}$Au isotopes were produced using multi-nucleon transfer reactions of $^{198}$Pt($^{136}$Xe, $^{x}$I)$^{y}$Au at a beam energy of 7 MeV/u. %between a 7 MeV/u $^{136}$Xe beam and a $^{198}$Pt target at GANIL. Prompt and delayed $γ$-ray spectroscopy of isotopically identified reaction products was performed with a unique experimental setup combining the VAMOS++ large acceptance magnetic spectrometer, the AGATA HPGe $γ$-ray tracking array, and the CATLIFE detection system.

nucl-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

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↗