JHEP

By analyzing 4.48 × 10$^{8}$ψ(3686) events collected with the BESIII detector, we observe the decays χ$_{cJ}$ → $ {nK}_S^0\overline{\Lambda} $ + c.c. (J = 0, 1, 2) for the first time, via the radiative transition ψ(3686) → γχ$_{cJ}$. The branching fractions are determined to be (6.65 ± 0.26$_{stat}$ ± 0.41$_{syst}$) × 10$^{−4}$, (1.66 ± 0.12$_{stat}$ ± 0.12$_{syst}$) × 10$^{−4}$, and (3.58 ± 0.16$_{stat}$ ± 0.23$_{syst}$) × 10$^{−4}$ for J = 0, 1, and 2, respectively.[graphic not available: see fulltext]

JINST

The Baikal-GVD is a neutrino telescope situated in the deepest freshwater lake in the world — Lake Baikal. The design of the Baikal-GVD trigger system allows also to study the ambient light of the lake. The analysis of the optical light activity of Baikal water, particularly, time and spatial variations of the luminescence activity for data collected in years 2018, 2019, and 2020 is presented. For the first time we observed highly luminescent layer moving upwards with maximal speed of 28 m/day in January 2021.

J.Open Source Softw.

Current neutrino detectors will observe hundreds to thousands of neutrinos from a Galactic supernova, and future detectors will increase this yield by an order of magnitude or more. With such neutrino data sets, the next Galactic supernova will significantly increase our un- derstanding of the explosions of massive stars, nuclear physics under extreme conditions, and the fundamental properties of neutrinos. However, there is a gulf between supernova simu- lations and the corresponding signals in detectors, making comparisons between theory and observation, as well as between different detectors, very difficult. SNEWPY offers a unified interface for hundreds of supernova simulations, a large library of flux transformations on the way towards the detector, and an interface to SNOwGLoBES (Scholberg & SNOwGLoBES Contributors, 2021), allowing users to easily calculate and compare expected event rates from many supernova models in many different neutrino detectors.

JHEP

The production of dark matter in association with Higgs bosons is predicted in several extensions of the Standard Model. An exploration of such scenarios is presented, considering final states with missing transverse momentum and b-tagged jets consistent with a Higgs boson. The analysis uses proton-proton collision data at a centre-of-mass energy of 13 TeV recorded by the ATLAS experiment at the LHC during Run 2, amounting to an integrated luminosity of 139 fb$^{-1}$. The analysis, when compared with previous searches, benefits from a larger dataset, but also has further improvements providing sensitivity to a wider spectrum of signal scenarios. These improvements include both an optimised event selection and advances in the object identification, such as the use of the likelihood-based significance of the missing transverse momentum and variable-radius track-jets. No significant deviation from Standard Model expectations is observed. Limits are set, at 95% confidence level, in two benchmark models with two Higgs doublets extended by either a heavy vector boson Z′ or a pseudoscalar singlet a and which both provide a dark matter candidate χ. In the case of the two-Higgs-doublet model with an additional vector boson Z′, the observed limits extend up to a Z′ mass of 3 TeV for a mass of 100 GeV for the dark matter candidate. The two-Higgs-doublet model with a dark matter particle mass of 10 GeV and an additional pseudoscalar a is excluded for masses of the a up to 520 GeV and 240 GeV for tan β = 1 and tan β = 10 respectively. Limits on the visible cross-sections are set and range from to 0.05 fb to 3.26 fb, depending on the missing transverse momentum and b-quark jet multiplicity requirements.[graphic not available: see fulltext]

JINST

The high-energy muon neutrino events of the IceCube telescope, that are triggered as neutrino alerts in one of two probability ranks of astrophysical origin, “gold” and “bronze”, have been followed up by the Baikal-GVD in a fast quasi-online mode since September 2020. Search for correlations between alerts and GVD events reconstructed in two modes, muon-track and cascades (electromagnetic or hadronic showers), for the time windows ±1 h and ±12 h does not indicate statistically significant excess of the measured events over the expected number of background events. Upper limits on the neutrino fluence will be presented for each alert.

Eur. Phys. J. C

The Baikal Gigaton Volume Detector (Baikal-GVD) is a km$^3$-scale neutrino detector currently under construction in Lake Baikal, Russia. The detector consists of several thousand optical sensors arranged on vertical strings, with 36 sensors per string. The strings are grouped into clusters of 8 strings each. Each cluster can operate as a stand-alone neutrino detector. The detector layout is optimized for the measurement of astrophysical neutrinos with energies of $\sim $ 100 TeV and above. Events resulting from charged current interactions of muon (anti-)neutrinos will have a track-like topology in Baikal-GVD. A fast $\chi ^2$-based reconstruction algorithm has been developed to reconstruct such track-like events. The algorithm has been applied to data collected in 2019 from the first five operational clusters of Baikal-GVD, resulting in observations of both downgoing atmospheric muons and upgoing atmospheric neutrinos. This serves as an important milestone towards experimental validation of the Baikal-GVD design. The analysis is limited to single-cluster data, favoring nearly-vertical tracks.

Eur. Phys. J. C

A flavour-tagged time-dependent angular analysis of ${{B} ^0_{s}} \!\rightarrow {{J /\psi }} \phi $ decays is presented where the ${J /\psi }$ meson is reconstructed through its decay to an $e ^+e ^-$ pair. The analysis uses a sample of pp collision data recorded with the LHCb experiment at centre-of-mass energies of 7 and $8\text {\,Te V} $, corresponding to an integrated luminosity of $3 \text {\,fb} ^{-1} $. The $C\!P$-violating phase and lifetime parameters of the ${B} ^0_{s} $ system are measured to be ${\phi _{{s}}} =0.00\pm 0.28\pm 0.07\text {\,rad}$, ${\Delta \Gamma _{{s}}} =0.115\pm 0.045\pm 0.011\text {\,ps} ^{-1} $ and ${\Gamma _{{s}}} =0.608\pm 0.018\pm 0.012\text {\,ps} ^{-1} $ where the first uncertainty is statistical and the second systematic. This is the first time that $C\!P$-violating parameters are measured in the ${{B} ^0_{s}} \!\rightarrow {{J /\psi }} \phi $ decay with an $e ^+e ^-$ pair in the final state. The results are consistent with previous measurements in other channels and with the Standard Model predictions.

Eur. Phys. J. C

A search for R-parity-violating supersymmetry in final states characterized by high jet multiplicity, at least one isolated light lepton and either zero or at least three b-tagged jets is presented. The search uses ${139}\,{\text {fb}^{-1}}$ of $\sqrt{s} = {13}\hbox { TeV}$ proton–proton collision data collected by the ATLAS experiment during Run 2 of the Large Hadron Collider. The results are interpreted in the context of R-parity-violating supersymmetry models that feature gluino production, top-squark production, or electroweakino production. The dominant sources of background are estimated using a data-driven model, based on observables at medium jet multiplicity, to predict the b-tagged jet multiplicity distribution at the higher jet multiplicities used in the search. Machine-learning techniques are used to reach sensitivity to electroweakino production, extending the data-driven background estimation to the shape of the machine-learning discriminant. No significant excess over the Standard Model expectation is observed and exclusion limits at the 95% confidence level are extracted, reaching as high as 2.4 TeV in gluino mass, 1.35 TeV in top-squark mass, and 320 (365) GeV in higgsino (wino) mass.

JHEP

A measurement of prompt photon-pair production in proton-proton collisions at $ \sqrt{s} $ = 13 TeV is presented. The data were recorded by the ATLAS detector at the LHC with an integrated luminosity of 139 fb$^{−1}$. Events with two photons in the well-instrumented region of the detector are selected. The photons are required to be isolated and have a transverse momentum of $ {p}_{\mathrm{T}{,}_{\gamma 1(2)}} $> 40 (30) GeV for the leading (sub-leading) photon. The differential cross sections as functions of several observables for the diphoton system are measured and compared with theoretical predictions from state-of-the-art Monte Carlo and fixed-order calculations. The QCD predictions from next-to-next-to-leading-order calculations and multi-leg merged calculations are able to describe the measured integrated and differential cross sections within uncertainties, whereas lower-order calculations show significant deviations, demonstrating that higher-order perturbative QCD corrections are crucial for this process. The resummed predictions with parton showers additionally provide an excellent description of the low transverse-momentum regime of the diphoton system.[graphic not available: see fulltext]

JHEP

A search is presented for new particles produced at the LHC in proton-proton collisions at $ \sqrt{s} $ = 13 TeV, using events with energetic jets and large missing transverse momentum. The analysis is based on a data sample corresponding to an integrated luminosity of 101 fb$^{−1}$, collected in 2017–2018 with the CMS detector. Machine learning techniques are used to define separate categories for events with narrow jets from initial-state radiation and events with large-radius jets consistent with a hadronic decay of a W or Z boson. A statistical combination is made with an earlier search based on a data sample of 36 fb$^{−1}$, collected in 2016. No significant excess of events is observed with respect to the standard model background expectation determined from control samples in data. The results are interpreted in terms of limits on the branching fraction of an invisible decay of the Higgs boson, as well as constraints on simplified models of dark matter, on first-generation scalar leptoquarks decaying to quarks and neutrinos, and on models with large extra dimensions. Several of the new limits, specifically for spin-1 dark matter mediators, pseudoscalar mediators, colored mediators, and leptoquarks, are the most restrictive to date.[graphic not available: see fulltext]

JHEP

A measurement of four-top-quark production using proton-proton collision data at a centre-of-mass energy of 13 TeV collected by the ATLAS detector at the Large Hadron Collider corresponding to an integrated luminosity of 139 fb$^{−1}$ is presented. Events are selected if they contain a single lepton (electron or muon) or an opposite-sign lepton pair, in association with multiple jets. The events are categorised according to the number of jets and how likely these are to contain b-hadrons. A multivariate technique is then used to discriminate between signal and background events. The measured four-top-quark production cross section is found to be $ {26}_{-15}^{+17} $ fb, with a corresponding observed (expected) significance of 1.9 (1.0) standard deviations over the background-only hypothesis. The result is combined with the previous measurement performed by the ATLAS Collaboration in the multilepton final state. The combined four-top-quark production cross section is measured to be $ {24}_{-6}^{+7} $ fb, with a corresponding observed (expected) signal significance of 4.7 (2.6) standard deviations over the background-only predictions. It is consistent within 2.0 standard deviations with the Standard Model expectation of 12.0 ± 2.4 fb.[graphic not available: see fulltext]

JHEP

JUNO is a massive liquid scintillator detector with a primary scientific goal of determining the neutrino mass ordering by studying the oscillated anti-neutrino flux coming from two nuclear power plants at 53 km distance. The expected signal anti-neutrino interaction rate is only 60 counts per day (cpd), therefore a careful control of the background sources due to radioactivity is critical. In particular, natural radioactivity present in all materials and in the environment represents a serious issue that could impair the sensitivity of the experiment if appropriate countermeasures were not foreseen. In this paper we discuss the background reduction strategies undertaken by the JUNO collaboration to reduce at minimum the impact of natural radioactivity. We describe our efforts for an optimized experimental design, a careful material screening and accurate detector production handling, and a constant control of the expected results through a meticulous Monte Carlo simulation program. We show that all these actions should allow us to keep the background count rate safely below the target value of 10 Hz (i.e. ∼1 cpd accidental background) in the default fiducial volume, above an energy threshold of 0.7 MeV.[graphic not available: see fulltext]

JHEP

A measurement of the cross section of the associated production of a single top quark and a W boson in final states with a muon or electron and jets in proton-proton collisions at $ \sqrt{s} $ = 13 TeV is presented. The data correspond to an integrated luminosity of 36 fb$^{−1}$ collected with the CMS detector at the CERN LHC in 2016. A boosted decision tree is used to separate the tW signal from the dominant t$ \overline{\mathrm{t}} $ background, whilst the subleading W+jets and multijet backgrounds are constrained using data-based estimates. This result is the first observation of the tW process in final states containing a muon or electron and jets, with a significance exceeding 5 standard deviations. The cross section is determined to be 89 ± 4 (stat) ± 12 (syst) pb, consistent with the standard model.[graphic not available: see fulltext]

Phys. Rev. Lett.

This Letter reports results from the first long-baseline search for sterile antineutrinos mixing in an accelerator-based antineutrino-dominated beam. The rate of neutral-current interactions in the two NOvA detectors, at distances of 1 and 810 km from the beam source, is analyzed using an exposure of $12.51\times {10}^{20}$ protons-on-target from the NuMI beam at Fermilab running in antineutrino mode. A total of 121 of neutral-current candidates are observed at the far detector, compared to a prediction of $122\pm 11(\mathrm{stat}.)\pm 15(\mathrm{syst}.)$ assuming mixing only between three active flavors. No evidence for ${\overline{\nu }}_{\mu }\to {\overline{\nu }}_s$ oscillation is observed. Interpreting this result within a $3+1$ model, constraints are placed on the mixing angles ${\theta }_{24}<25°$ and ${\theta }_{34}<32°$ at the 90% C.L. for $0.05{\mathrm{eV}}^2\le \mathrm{\Delta }{m}_{41}^2\le 0.5{\mathrm{eV}}^2$, the range of mass splittings that produces no significant oscillations at the near detector. These are the first $3+1$ confidence limits set using long-baseline accelerator antineutrinos.

Phys. Lett. B

Searches for new resonances in the diphoton final state, with spin 0 as predicted by theories with an extended Higgs sector and with spin 2 using a warped extra-dimension benchmark model, are presented using 139 fb⁻¹ of $\sqrt{s}=13$ TeV pp collision data collected by the ATLAS experiment at the LHC. No significant deviation from the Standard Model is observed and upper limits are placed on the production cross-section times branching ratio to two photons as a function of the resonance mass.

JHEP

A search for a heavy Higgs boson H decaying into the observed Higgs boson h with a mass of 125 GeV and another Higgs boson h$_{S}$ is presented. The h and h$_{S}$ bosons are required to decay into a pair of tau leptons and a pair of b quarks, respectively. The search uses a sample of proton-proton collisions collected with the CMS detector at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 137 fb$^{−1}$. Mass ranges of 240–3000 GeV for m$_{H}$ and 60–2800 GeV for $ {m}_{{\mathrm{h}}_{\mathrm{S}}} $ are explored in the search. No signal has been observed. Model independent 95% confidence level upper limits on the product of the production cross section and the branching fractions of the signal process are set with a sensitivity ranging from 125 fb (for m$_{H}$ = 240 GeV) to 2.7 fb (for m$_{H}$ = 1000 GeV). These limits are compared to maximally allowed products of the production cross section and the branching fractions of the signal process in the next-to-minimal supersymmetric extension of the standard model.[graphic not available: see fulltext]

JHEP

This paper describes a measurement of light-by-light scattering based on Pb+Pb collision data recorded by the ATLAS experiment during Run 2 of the LHC. The study uses 2.2 nb$^{−1}$ of integrated luminosity collected in 2015 and 2018 at $ \sqrt{s_{\mathrm{NN}}} $ = 5.02 TeV. Light-by-light scattering candidates are selected in events with two photons produced exclusively, each with transverse energy $ {E}_{\mathrm{T}}^{\gamma } $> 2.5 GeV, pseudorapidity |η$_{γ}$| < 2.37, diphoton invariant mass m$_{γγ}$> 5 GeV, and with small diphoton transverse momentum and diphoton acoplanarity. The integrated and differential fiducial cross sections are measured and compared with theoretical predictions. The diphoton invariant mass distribution is used to set limits on the production of axion-like particles. This result provides the most stringent limits to date on axion-like particle production for masses in the range 6–100 GeV. Cross sections above 2 to 70 nb are excluded at the 95% CL in that mass interval.[graphic not available: see fulltext]

Nature Phys.

The complicated structure of the neutron cannot be calculated using first-principles calculations due to the large colour charge of quarks and the self-interaction of gluons. Its simplest structure observables are the electromagnetic form factors1, which probe our understanding of the strong interaction. Until now, a small amount of data has been available for the determination of the neutron structure from the time-like kinematical range. Here we present measurements of the Born cross section of electron–positron annihilation reactions into a neutron and anti-neutron pair, and determine the neutron’s effective form factor. The data were recorded with the BESIII experiment at centre-of-mass energies between 2.00 and 3.08 GeV using an integrated luminosity of 647.9 pb−1. Our results improve the statistics on the neutron form factor by more than a factor of 60 over previous measurements, demonstrating that the neutron form factor data from annihilation in the time-like regime is on par with that from electron scattering experiments. The effective form factor of the neutron shows a periodic behaviour, similar to earlier observations of the proton form factor. Future works—both theoretical and experimental—will help illuminate the origin of this oscillation of the electromagnetic structure observables of the nucleon.

JHEP

An angular analysis of the rare decay $ {B}_s^0 $→ ϕμ$^{+}$μ$^{−}$ is presented, using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of 8.4 fb$^{−1}$. The observables describing the angular distributions of the decay $ {B}_s^0 $→ ϕμ$^{+}$μ$^{−}$ are determined in regions of q$^{2}$, the square of the dimuon invariant mass. The results are consistent with Standard Model predictions.[graphic not available: see fulltext]

Eur. Phys. J. C

The OSIRIS detector is a subsystem of the liquid scintillator filling chain of the JUNO reactor neutrino experiment. Its purpose is to validate the radiopurity of the scintillator to assure that all components of the JUNO scintillator system work to specifications and only neutrino-grade scintillator is filled into the JUNO Central Detector. The aspired sensitivity level of $10^{-16}\hbox { g/g}$ of $^{238}\hbox {U}$ and $^{232}\hbox {Th}$ requires a large ($\sim 20\,\hbox {m}^3$) detection volume and ultralow background levels. The present paper reports on the design and major components of the OSIRIS detector, the detector simulation as well as the measuring strategies foreseen and the sensitivity levels to U/Th that can be reached in this setup.

Eur. Phys. J. C

A combination of searches for top squark pair production using proton–proton collision data at a center-of-mass energy of 13$\,\text {Te}\text {V}$ at the CERN LHC, corresponding to an integrated luminosity of 137$\,\text {fb}^{-1}$ collected by the CMS experiment, is presented. Signatures with at least 2 jets and large missing transverse momentum are categorized into events with 0, 1, or 2 leptons. New results for regions of parameter space where the kinematical properties of top squark pair production and top quark pair production are very similar are presented. Depending on the model, the combined result excludes a top squark mass up to 1325$\,\text {Ge}\text {V}$ for a massless neutralino, and a neutralino mass up to 700$\,\text {Ge}\text {V}$ for a top squark mass of 1150$\,\text {Ge}\text {V}$. Top squarks with masses from 145 to 295$\,\text {Ge}\text {V}$, for neutralino masses from 0 to 100$\,\text {Ge}\text {V}$, with a mass difference between the top squark and the neutralino in a window of 30$\,\text {Ge}\text {V}$ around the mass of the top quark, are excluded for the first time with CMS data. The results of theses searches are also interpreted in an alternative signal model of dark matter production via a spin-0 mediator in association with a top quark pair. Upper limits are set on the cross section for mediator particle masses of up to 420$\,\text {Ge}\text {V}$.

Phys. Rev. Lett.

The first measurements of diboson production cross sections in proton-proton interactions at a center-of-mass energy of 5.02 TeV are reported. They are based on data collected with the CMS detector at the LHC, corresponding to an integrated luminosity of $302{\mathrm{pb}}^{-1}$. Events with two, three, or four charged light leptons (electrons or muons) in the final state are analyzed. The $WW$, $WZ$, and $ZZ$ total cross sections are measured as ${\sigma }_{WW}=37.0_{-5.2}^{+5.5}(\mathrm{stat}{)}_{-2.6}^{+2.7}(\mathrm{syst})\mathrm{pb}$, ${\sigma }_{WZ}=6.4_{-2.1}^{+2.5}(\mathrm{stat}{)}_{-0.3}^{+0.5}(\mathrm{syst})\mathrm{pb}$, and ${\sigma }_{ZZ}=5.3_{-2.1}^{+2.5}(\mathrm{stat}{)}_{-0.4}^{+0.5}(\mathrm{syst})\mathrm{pb}$. All measurements are in good agreement with theoretical calculations at combined next-to-next-to-leading order quantum chromodynamics and next-to-leading order electroweak accuracy.

Phys. Rev. D

Based on a data sample of (1.0087±0.0044)×1010  J/ψ events collected by the BESIII detector at the BEPCII accelerator, the absolute branching fraction (BF) of the decay J/ψ→γη is measured with high precision using events in which the radiative photon converts to e+e−. Using the measured absolute BF of J/ψ→γη, the absolute BFs of four dominant η decay modes are measured for the first time. The results are B(J/ψ→γη)=(1.067±0.005±0.023)×10−3, B(η→γγ)=(39.86±0.04±0.99)%, B(η→π0π0π0)=(31.96±0.07±0.84)%, B(η→π+π−π0)=(23.04±0.03±0.54)%, and B(η→π+π−γ)=(4.38±0.02±0.10)%, where the first and second uncertainties are statistical and systematic, respectively. The results are consistent with the world average values within two standard deviations.

Phys. Rev. D

Using $(448.1\pm 2.9)\times {10}^6$ $\psi (3686)$ events collected with the BESIII detector and a single-baryon tagging technique, we present the first observation of the decays $\psi (3686)\to \mathrm{\Xi }(1530{)}^0\overline{\mathrm{\Xi }}(1530{)}^0$ and $\mathrm{\Xi }(1530{)}^0{\overline{\mathrm{\Xi }}}^0$. The branching fractions are measured to be $\mathcal{B}(\psi (3686)\to \mathrm{\Xi }(1530{)}^0\overline{\mathrm{\Xi }}(1530{)}^0)=(6.77\pm 0.14\pm 0.39)\times {10}^{-5}$ and $\mathcal{B}(\psi (3686)\to \mathrm{\Xi }(1530{)}^0{\overline{\mathrm{\Xi }}}^0)=(0.53\pm 0.04\pm 0.03)\times {10}^{-5}$. Here, the first and second uncertainties are statistical and systematic, respectively. In addition, the parameter associated with the angular distribution for the decay $\psi (3686)\to \mathrm{\Xi }(1530{)}^0\overline{\mathrm{\Xi }}(1530{)}^0$ is determined to be $\alpha =0.32\pm 0.19\pm 0.07$, in agreement with theoretical predictions within one standard deviation.

Phys. Rev. D

Analyzing $(448.1\pm 2.9)\times {10}^6\psi (3686)$ events collected with the BESIII detector at the BEPCII collider, the $\psi (3686)\to \omega K_S^0{K}_S^0$ decay is observed for the first time. The branching fraction for this decay is determined to be ${\mathcal{B}}_{\psi (3686)\to \omega K_S^0{K}_S^0}=(7.04\pm 0.39\pm 0.36)\times {10}^{-5}$, where the first uncertainty is statistical and the second is systematic.