Particles

A new type of parametrization for parton distribution functions in the proton, based on their -evolution at large and small x values, is constructed. In our analysis, the valence and nonsinglet parts obey the Gross–Llewellyn–Smith and Gottfried sum rules, respectively. For the singlet quark and gluon densities, momentum conservation is taken into account. Then, using the Kimber–Martin–Ryskin prescription, we extend the consideration to Transverse Momentum Dependent (TMD, or unintegrated) gluon and quark distributions in the proton, which currently plays an important role in a the number of phenomenological applications. The analytical expressions for the latter, valid for both low and large x, are derived for the first time.

PoS

Baikal-GVD is a large underwater neutrino detector currently under construction in Lake Baikal, Russia. With the detector volume already approaching 0.4 km$^3$ and a sub-degree angular resolution, Baikal-GVD is becoming one of the key players in neutrino astronomy. We review the current status of Baikal-GVD and recent results obtained with the partially complete instrument.

PoS

The linear accelerator Linac-200 at JINR is a new facility, constructed to provide electron test beams to carry out particle detectors R&D, to perform studies of advanced methods of electron beam diagnostics, and for applied research. The core of the facility is a refurbished MEA accelerator from NIKHEF. The key accelerator subsystems including controls, vacuum, precise temperature regulation were completely redesigned or deeply modernized. Two test beam channels are available for users: the first one with electron energy in range 5–25 MeV and maximum pulse current 60 mA; and the second one with electron energy in range 40–200 MeV and maximum pulse current 40 mA. The pulse current varies smoothly from the maximum value down to almost zero (single electrons in a pulse). This report presents the status and operation parameters of the facility.

JETP Lett.

The T-odd correlation ${{\xi }_{{\pi e\gamma }}}$, which is the mixed product of the momenta of ${{e}^{ + }}$, ${{\pi }^{0}}$, and γ in the system of rest of the kaon divided by $M_{K}^{3}$, has been measured in the K$^{+}$ → π$^{0}$e$^{+}$ν$_{e}$γ radiative decay among 101 200 candidate events detected at the OKA setup. The asymmetry of the distribution in ${{\xi }_{{\pi e\gamma }}}$ is characterized by the ratio ${{A}_{\xi }} = \frac{{{{N}_{ + }} - {{N}_{ - }}}}{{{{N}_{ + }} + {{N}_{ - }}}}$, where ${{N}_{{ + ( - )}}}$ is the number of events with positive (negative) ξ. The value ${{A}_{\xi }}$ = (+0.1 ± 3.9(stat.) ± 1.7(syst.)) × 10$^{–3}$ or ${\text{|}}{{A}_{\xi }}{\text{|}} < 5.4 \times {{10}^{{ - 3}}}$ (90% C.L.) has been obtained.

Phys.Rev.Lett.

The radiative hyperon decay $\mathrm{\Lambda }\to n\gamma$ is studied using $(10087\pm 44)\times {10}^{6}J/\psi$ events collected with the BESIII detector operating at BEPCII. The absolute branching fraction of the decay $\mathrm{\Lambda }\to n\gamma$ is determined to be $(0.832\pm 0.038_{\mathrm{stat}}\pm 0.054_{\mathrm{syst}})\times {10}^{-3}$, which is a factor of 2.1 lower and 5.6 standard deviations different than the previous measurement. By analyzing the joint angular distribution of the decay products, the first determination of the decay asymmetry ${\alpha }_{\gamma }$ is reported with a value of $-0.16\pm 0.10_{\mathrm{stat}}\pm 0.05_{\mathrm{syst}}$.

Sci. China Phys. Mech. Astron.

We present a search for the lepton flavor violating decay J/ψ → e$^{±}$μ$^{∓}$ using 8.998 × 10$^{9}$J/ψ events collected with the BESIII detector at the BEPCII e$^{+}$e$^{−}$ storage ring. No excess of signal above background is observed; we therefore set an upper limit on the branching fraction of ${\cal B}\left( {J/\psi \to {e^ \pm }{\mu ^ \mp }} \right) < \,4.5 \times {10^{ - 9}}$ at the 90% confidence level. Improving the previous best result by a factor of more than 30, this measurement places the most stringent limit to date on lepton flavor violation in the heavy quarkonium sector.

Phys. Rev. B

We numerically investigate heating-and-cooling quenches taking place entirely in the nonordered phase of the discrete Gross-Pitaevskii equation on a three-dimensional cubic lattice. In equilibrium, this system exhibits a $U\left(1\right)$-ordering phase transition at an energy density which is significantly lower than the minimum one during the quench. Yet, we observe that the postquench relaxation is accompanied by a transient $U\left(1\right)$ ordering, namely, the correlation length of $U\left(1\right)$ fluctuations significantly exceeds its equilibrium prequench value. The longer and the stronger the heating stage of the quench, the stronger is the $U\left(1\right)$ transient ordering. We identify the origin of this ordering with the emergence of a small group of slowly relaxing lattice sites accumulating a large fraction of the total energy of the system. Our findings suggest that the transient ordering may be a robust feature of a broad class of physical systems. This premise is consistent with the growing experimental evidence of the transient $U\left(1\right)$ order in rather dissimilar settings.

Eur. Phys. J. C

The CUPID-Mo experiment to search for 0$\nu \beta \beta$ decay in $^{100}$Mo has been recently completed after about 1.5 years of operation at Laboratoire Souterrain de Modane (France). It served as a demonstrator for CUPID, a next generation 0$\nu \beta \beta$ decay experiment. CUPID-Mo was comprised of 20 enriched $\hbox {Li}_{{2}}^{100}\hbox {MoO}_4$ scintillating calorimeters, each with a mass of $\sim 0.2$ kg, operated at $\sim 20$ mK. We present here the final analysis with the full exposure of CUPID-Mo ($^{100}$Mo exposure of 1.47 $\hbox {kg} \times \hbox {year}$) used to search for lepton number violation via 0$\nu \beta \beta$ decay. We report on various analysis improvements since the previous result on a subset of data, reprocessing all data with these new techniques. We observe zero events in the region of interest and set a new limit on the $^{100}$Mo 0$\nu \beta \beta$ decay half-life of $T_{1/2}^{0\nu }> {1.8}\times 10^{24}$ year (stat. + syst.) at 90% CI. Under the light Majorana neutrino exchange mechanism this corresponds to an effective Majorana neutrino mass of ParseError: KaTeX parse error: Expected group as argument to '\left' at end of input: \left  $<~{(0.28{-}0.49)}$ eV, dependent upon the nuclear matrix element utilized.

Phys.Lett.B

A search for a massive resonance X decaying to a pair of spin-0 bosons ϕ that themselves decay to pairs of bottom quarks, is presented. The analysis is restricted to the mass ranges $m_{\mathrm{\varphi }}$ from 25 to 100 GeV and $m_{\mathrm{X}}$ from 1 to 3 TeV. For these mass ranges, the decay products of each ϕ boson are expected to merge into a single large-radius jet. Jet substructure and flavor identification techniques are used to identify these jets. The search is based on CERN LHC proton-proton collision data at $\sqrt{s}=13\text{TeV}$, collected with the CMS detector in 2016–2018, corresponding to an integrated luminosity of 138${\text{fb}}^{-1}$. Model-specific limits, where the two new particles arise from an extended Higgs sector, are set on the product of the production cross section and branching fraction for $\mathrm{X}\to \mathrm{\varphi }\mathrm{\varphi }\to (\mathrm{b}\bar{\mathrm{b}})(\mathrm{b}\bar{\mathrm{b}})$ as a function of the resonances' masses, where both the $\mathrm{X}\to \mathrm{\varphi }\mathrm{\varphi }$ and $\mathrm{\varphi }\to \mathrm{b}\bar{\mathrm{b}}$ branching fractions are assumed to be 100%. These limits are the first of their kind on this process, ranging between 30 and 1fb at 95% confidence level for the considered mass ranges.

Nucl. Instrum. Meth. A

The Calorimeter of the Mu2e experiment is a complicated detector made of crystal scintillators with dedicated read-out electronics per crystals. The compactness of the Front-End Units matrix, the complexity of the necessary services, and the limited space available after detector installation in the experimental hall make access, manipulation and maintenance of the Front-End Units very hard. This paper reports on the conceptual mechanical design of a robotic arm composed of a gantry structure for $xyz$ positioning on the desired Front-End Unit and equipped with custom-designed grippers to perform the necessary maintenance operations. This includes the optimization of the Front-End Units cables routing.

JHEP

A simultaneous measurement of the three components of the top-quark and top-antiquark polarisation vectors in t-channel single-top-quark production is presented. This analysis is based on data from proton–proton collisions at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 139 fb$^{−1}$, collected with the ATLAS detector at the LHC. Selected events contain exactly one isolated electron or muon, large missing transverse momentum and exactly two jets, one being b-tagged. Stringent selection requirements are applied to discriminate t-channel single-top-quark events from the background contributions. The top-quark and top-antiquark polarisation vectors are measured from the distributions of the direction cosines of the charged-lepton momentum in the top-quark rest frame. The three components of the polarisation vector for the selected top-quark event sample are ${P}_{x^{\prime }}$ = 0.01 ± 0.18, ${P}_{y^{\prime }}$ = −0.029 ± 0.027, ${P}_{z^{\prime }}$ = 0.91 ± 0.10 and for the top-antiquark event sample they are ${P}_{x^{\prime }}$ = −0.02 ± 0.20, ${P}_{y^{\prime }}$ = −0.007 ± 0.051, ${P}_{z^{\prime }}$ = 0.79 ± 0.16. Normalised differential cross-sections corrected to a fiducial region at the stable-particle level are presented as a function of the charged-lepton angles for top-quark and top-antiquark events inclusively and separately. These measurements are in agreement with Standard Model predictions. The angular differential cross-sections are used to derive bounds on the complex Wilson coefficient of the dimension-six $\mathcal{O} _{tW}$ operator in the framework of an effective field theory. The obtained bounds are C$_{tW}$ ∈ [−0.9, 1.4] and C$_{itW}$ ∈ [−0.8, 0.2], both at 95% confidence level.[graphic not available: see fulltext]

Eur.Phys.J.C

The decay $D \rightarrow K^-\pi ^+$ is studied in a sample of quantum-correlated $D{\bar{D}}$ pairs, based on a data set corresponding to an integrated luminosity of 2.93 fb$^{-1}$ collected at the $\psi (3770)$ resonance by the BESIII experiment. The asymmetry between $C\!P$-odd and $C\!P$-even eigenstate decays into $K^-\pi ^+$ is determined to be ${{\mathcal {A}}}_{K\pi } = 0.132 \pm 0.011 \pm 0.007$, where the first uncertainty is statistical and the second is systematic. This measurement is an update of an earlier study exploiting additional tagging modes, including several decay modes involving a $K^0_L$ meson. The branching fractions of the $K^0_L$ modes are determined as input to the analysis in a manner that is independent of any strong phase uncertainty. Using the predominantly $C\!P$-even tag $D\rightarrow \pi ^+\pi ^-\pi ^0$ and the ensemble of $C\!P$-odd eigenstate tags, the observable ${{\mathcal {A}}}_{K\pi }^{\pi \pi \pi ^0}$ is measured to be $0.130 \pm 0.012 \pm 0.008$. The two asymmetries are sensitive to $r_D^{K\pi }\cos \delta _D^{K\pi }$, where $r_D^{K\pi }$ and $\delta _D^{K\pi }$ are the ratio of amplitudes and phase difference, respectively, between the doubly Cabibbo-suppressed and Cabibbo-favoured decays. In addition, events containing $D \rightarrow K^-\pi ^+$ tagged by $D \rightarrow K^0_{S,L} \pi ^+\pi ^-$ are studied in bins of phase space of the three-body decays. This analysis has sensitivity to both $r_D^{K\pi }\cos \delta _D^{K\pi }$ and $r_D^{K\pi }\sin \delta _D^{K\pi }$. A fit to ${{\mathcal {A}}}_{K\pi }$, ${{\mathcal {A}}}_{K\pi }^{\pi \pi \pi ^0}$ and the phase-space distribution of the $D \rightarrow K^0_{S,L} \pi ^+\pi ^-$ tags yields $\delta _D^{K\pi }= \left( 187.6 {^{+8.9}_{-9.7}}{^{+5.4}_{-6.4}} \right) ^{\circ }$, where external constraints are applied for $r_D^{K\pi }$ and other relevant parameters. This is the most precise measurement of $\delta _D^{K\pi }$ in quantum-correlated $D{\bar{D}}$ decays.

Eur.Phys.J.C

A search for the pair production of heavy leptons as predicted by the type-III seesaw mechanism is presented. The search uses proton–proton collision data at a centre-of-mass energy of 13 TeV, corresponding to $139\,\text {fb}^{-1}$ of integrated luminosity recorded by the ATLAS detector during Run 2 of the Large Hadron Collider. The analysis focuses on final states with three or four electrons or muons from the possible decays of new heavy leptons via intermediate electroweak bosons. No significant deviations above the Standard Model expectation are observed; upper and lower limits on the heavy lepton production cross-section and masses are derived respectively. These results are then combined for the first time with the ones already published by ATLAS using the channel with two leptons in the final state. The observed lower limit on the mass of the type-III seesaw heavy leptons combining two, three and four lepton channels together is 910 GeV at the 95% confidence level.

Phys. Rev. D

A measurement of the $CP$-even fraction of the decay $D^0\to {\pi }^{+}{\pi }^{-}{\pi }^{+}{\pi }^{-}$ is performed with a quantum-correlated $\psi (3770)\to D\overline{D}$ data sample collected by the BESIII experiment, corresponding to an integrated luminosity of $2.93{\mathrm{fb}}^{-1}$. Using a combination of $CP$ eigenstates, $D\to {\pi }^{+}{\pi }^{-}{\pi }^0$ and $D\to K_{S,L}^0{\pi }^{+}{\pi }^{-}$ as tagging modes, the $CP$-even fraction is measured to be $F_{+}^{4\pi }=0.735\pm 0.015\pm 0.005$, where the first uncertainty is statistical and the second is systematic. This is the most precise determination of this quantity to date. It provides valuable model-independent input for the measurement of the angle $\gamma$ of the Cabibbo-Kobayashi-Maskawa matrix with $B^{\pm }\to D{K}^{\pm }$ decays, and for time-dependent studies of $CP$ violation and mixing in the $D^0\text{-}{\overline{D}}^0$ system.

Phys. Rev. D

By analyzing $e^{+}{e}^{-}$ annihilation data with an integrated luminosity of $2.93{\mathrm{fb}}^{-1}$ collected at the center-of-mass energy $\sqrt{s}=3.773\mathrm{GeV}$ with the BESIII detector, we present the first absolute measurements of the branching fractions of twenty Cabibbo-suppressed hadronic $D^{0(+)}$ decays involving multiple pions. The highest four branching fractions obtained are $\mathcal{B}(D^0\to {\pi }^{+}{\pi }^{-}{\pi }^0)=(1.343\pm 0.013_{\mathrm{stat}}\pm 0.016_{\mathrm{syst}})\%$, $\mathcal{B}(D^0\to {\pi }^{+}{\pi }^{-}2{\pi }^0)=(1.002\pm 0.019_{\mathrm{stat}}\pm 0.024_{\mathrm{syst}})\%$, $\mathcal{B}(D^{+}\to 2{\pi }^{+}{\pi }^{-}{\pi }^0)=(1.165\pm 0.021_{\mathrm{stat}}\pm 0.021_{\mathrm{syst}})\%$, and $\mathcal{B}(D^{+}\to 2{\pi }^{+}{\pi }^{-}2{\pi }^0)=(1.074\pm 0.040_{\mathrm{stat}}\pm 0.030_{\mathrm{syst}})\%$. The $CP$ asymmetries for the six decays with highest signal yields are also determined and found to be compatible with zero.

Phys.Rev.D

Using a sample of $(448.1\pm 2.9)\times {10}^6\psi (3686)$ decays collected with the BESIII detector at BEPCII, we report an observation of ${\mathrm{\Xi }}^{-}$ transverse polarization with a significance of $7.3\sigma$ in the decay $\psi (3686)\to {\mathrm{\Xi }}^{-}{\overline{\mathrm{\Xi }}}^{+}$ (${\mathrm{\Xi }}^{-}\to \mathrm{\Lambda }{\pi }^{-}$, ${\overline{\mathrm{\Xi }}}^{+}\to \overline{\mathrm{\Lambda }}{\pi }^{+}$, $\mathrm{\Lambda }\to p{\pi }^{-}$, $\overline{\mathrm{\Lambda }}\to \overline{p}{\pi }^{+}$). The relative phase of the electric and magnetic form factors is determined to be $\mathrm{\Delta }\mathrm{\Phi }=(0.667\pm 0.111\pm 0.058)\mathrm{rad}$. This is the first measurement of the relative phase for a $\psi (3686)$ decay into a pair of ${\mathrm{\Xi }}^{-}{\overline{\mathrm{\Xi }}}^{+}$ hyperons. The ${\mathrm{\Xi }}^{-}$ decay parameters (${\alpha }_{{\mathrm{\Xi }}^{-}}$, ${\varphi }_{{\mathrm{\Xi }}^{-}}$) and their conjugates (${\alpha }_{{\overline{\mathrm{\Xi }}}^{+}}$, ${\varphi }_{{\overline{\mathrm{\Xi }}}^{+}}$), the angular-distribution parameter ${\alpha }_{\psi }$, and the strong-phase difference ${\delta }_p-{\delta }_s$ for $\mathrm{\Lambda }{\pi }^{-}$ scattering are measured to be consistent with previous BESIII results.

Nucl.Instrum.Meth.A

The COMET experiment at J-PARC aims to search for a lepton-flavour violating process of muon to electron conversion in a muonic atom, $\mu$-e conversion, with a branching-ratio sensitivity better than $10^{-16}$, 4 orders of magnitude better than the present limit, in order to explore the parameter region predicted by most well-motivated theoretical models beyond the Standard Model. The need for such an excellent sensitivity places several stringent requirements on the detector; (i) good momentum resolution, $<2\text{\%}$, for 100 MeV/$c$ electron, which is primarily limited by multiple scattering effect for this momentum region; and (ii) high rate capability, up to $5\times 10^9{\mu }^{-}$/s muon beam enabled by J-PARC. In order to fulfil such requirements a vacuum-compatible, ultra-thin-wall straw tracker has been designed, and a $20\mathrm{\mu }\mathrm{m}$-thick Mylar straw with 70 nm Al cathode has been developed employing an ultrasonic-welding technique. The detector performances such as detection efficiency and intrinsic spatial resolutions were investigated with test-beam experiments and confirmed to be acceptable for the COMET experiment. The construction of the straw tracker for COMET Phase-I has been completed. In parallel to the construction of present tracker a thinner $12\mathrm{\mu }\mathrm{m}$-thick straw has been developed with joint collaboration among KEK, JINR and CERN. During this R&D, it was noticed that the current technology cannot achieve tubes much smaller than 5 mm in diameter or walls much thinner than $12\mathrm{\mu }\mathrm{m}$. We also launched a brand-new project to realize the graphite-textile straw which has a potential to realize an extremely low material tracker. In this article, a brief report on detector construction with a present $20\mathrm{\mu }\mathrm{m}$-thick straw, R&D on a new $12\mathrm{\mu }\mathrm{m}$-thick straw, and a brand-new graphite straw, is provided.

Phys. Rev. Lett.

Using a sample of $(10.09\pm 0.04)\times {10}^{9}J/\psi$ events collected with the BESIII detector operating at the BEPCII storage ring, a partial wave analysis of the decay $J/\psi \to \gamma \eta {\eta }^{\prime }$ is performed. The first observation of an isoscalar state with exotic quantum numbers $J^{PC}=1^{-+}$, denoted as ${\eta }_1(1855)$, is reported in the process $J/\psi \to \gamma {\eta }_1(1855)$ with ${\eta }_1(1855)\to \eta {\eta }^{\prime }$. Its mass and width are measured to be $(1855\pm 9_{-1}^{+6})\mathrm{MeV}/c^2$ and $(188\pm {18}_{-8}^{+3})\mathrm{MeV}$, respectively, where the first uncertainties are statistical and the second are systematic, and its statistical significance is estimated to be larger than $19\sigma$.

J.Radioanal.Nucl.Chem.

To find a high purity flux for low background experiments is one of the most challenging problems. In this work, we report the production process of a highly purified ammonium acetate flux solution for low background experiments. A sub-distilled method has been used to purify initial precursors from contamination for the syntheses of final product. As a result, a high purity ammonium acetate solution was synthesized with a minimum content of elements which collectively represent the main source of background radiation (K  < 2.3 × 10$^{–8}$ g/g, Th  < 2.6 × 10$^{–11}$ g/g and U  < 1 × 10$^{–11}$ g/g). An Estimation of the impurity content of the product has been performed with Instrumental neutron activation analysis, inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry.

Phys. Rev. Lett.

Using $e^{+}{e}^{-}$ annihilation data corresponding to an integrated luminosity of $6.32{\mathrm{fb}}^{-1}$ collected at center-of-mass energies between 4.178 and 4.226 GeV with the BESIII detector, we perform the first amplitude analysis of the decay $D_s^{+}\to K_S^0{K}^{+}{\pi }^0$ and determine the relative branching fractions and phases for intermediate processes. We observe an $a_0$-like state with mass of 1.817 GeV in its decay to $K_S^0{K}^{+}$ for the first time. In addition, we measure the ratio $\{\mathcal{B}[D_s^{+}\to {\overline{K}}^{*}(892{)}^0{K}^{+}]/\mathcal{B}[D_s^{+}\to {\overline{K}}^0{K}^{*}(892{)}^{+}]\}$ to be ${2.35}_{-0.23\mathrm{stat}}^{+0.42}\pm 0.10_{\mathrm{syst}}$. Finally, we provide a precision measurement of the absolute branching fraction $\mathcal{B}(D_s^{+}\to K_S^0{K}^{+}{\pi }^0)=(1.46\pm 0.06_{\mathrm{stat}}\pm 0.05_{\mathrm{syst}})\%$.

JINST

The Mu2e experiment at Fermilab will search for the CLFV neutrino-less coherent conversion of a muon into an electron in the field of an aluminum nucleus. The observation of this process would be the evidence of physics beyond the Standard Model. Mu2e comprises a straw-tracker, an electromagnetic calorimeter and an external veto for cosmic rays. The calorimeter provides electron identification, a fast trigger and aids track reconstruction. It is a state-of-the-art crystal calorimeter and employs 1340 pure CsI crystals readout by UV-extended SiPM and fast electronics. The design consists of two identical annular disks positioned at the relative distance of 70 cm downstream the target.The hostile Mu2e conditions (total ionizing dose of 12 krad and a neutron fluence of 5 × 10$^{10}$ n/cm$^{2}$ @ 1 MeVeq (Si)/y, 1 T magnetic field and vacuum level of 10$^{−4}$ Torr) posed tight constraints on the mechanical structures and materials choice. The support structure of the two crystal matrices employs two aluminum hollow rings and parts made of open-cell vacuum-compatible carbon fiber. SiPMs and front-end electronics for each crystal are assembled in one mechanical unit inserted in a machined copper holder. The units are supported by a plate made of vacuum-compatible material. The plate integrates the cooling system made of a network of copper lines flowing a low temperature fluid and placed in thermal contact with the copper holders. The DAQ is hosted in aluminum crates positioned on the lateral surface of the disks. The crates also integrate the DAQ electronics cooling system. We review the constraints on the calorimeter structures design, the development of all the structural components, including the simulations that have determined the materials and technological choices and the specifications of the cooling station, components production and quality assurance tests, the procedures for detector assembly, transportation and installation in the experimental area.

Instruments

The Mu2e experiment at Fermi National Accelerator Laboratory will search for the charged-lepton flavour-violating neutrinoless conversion of negative muons into electrons in the Coulomb field of an Al nucleus. The conversion electron with a monoenergetic 104.967 MeV signature will be identified by a complementary measurement carried out by a high-resolution tracker and an electromagnetic calorimeter, improving by four orders of magnitude the current single-event sensitivity. The calorimeter—composed of 1348 pure CsI crystals arranged in two annular disks—has a high granularity, 10% energy resolution and 500 ps timing resolution for 100 MeV electrons. The readout, based on large-area UV-extended SiPMs, features a fully custom readout chain, from the analogue front-end electronics to the digitisation boards. The readout electronics design was validated for operation in vacuum and under magnetic fields. An extensive radiation hardness certification campaign certified the FEE design for doses up to 100 krad and 10 n/cm and for single-event effects. A final vertical slice test on the final readout chain was carried out with cosmic rays on a large-scale calorimeter prototype.

Nature Phys.

Since the discovery of the Higgs boson in 2012, detailed studies of its properties have been ongoing. Besides its mass, its width—related to its lifetime—is an important parameter. One way to determine this quantity is to measure its off-shell production, where the Higgs boson mass is far away from its nominal value, and relating it to its on-shell production, where the mass is close to the nominal value. Here we report evidence for such off-shell contributions to the production cross-section of two Z bosons with data from the CMS experiment at the CERN Large Hadron Collider. We constrain the total rate of the off-shell Higgs boson contribution beyond the Z boson pair production threshold, relative to its standard model expectation, to the interval [0.0061, 2.0] at the 95% confidence level. The scenario with no off-shell contribution is excluded at a p-value of 0.0003 (3.6 standard deviations). We measure the width of the Higgs boson as ${{{\varGamma }}}_{{{{{{\rm{H}}}}}}}={3.2}_{-1.7}^{+2.4}\,{{{{{\rm{MeV}}}}}}$, in agreement with the standard model expectation of 4.1 MeV. In addition, we set constraints on anomalous Higgs boson couplings to W and Z boson pairs.

JINST

The T2K experiment widely uses plastic scintillator as a target for neutrino interactions and an active medium for the measurement of charged particles produced in neutrino interactions at its near detector complex. Over 10 years of operation the measured light yield recorded by the scintillator based subsystems has been observed to degrade by 0.9–2.2% per year. Extrapolation of the degradation rate through to 2040 indicates the recorded light yield should remain above the lower threshold used by the current reconstruction algorithms for all subsystems. This will allow the near detectors to continue contributing to important physics measurements during the T2K-II and Hyper-Kamiokande eras. Additionally, work to disentangle the degradation of the plastic scintillator and wavelength shifting fibres shows that the reduction in light yield can be attributed to the ageing of the plastic scintillator. The long component of the attenuation length of the wavelength shifting fibres was observed to degrade by 1.3–5.4% per year, while the short component of the attenuation length did not show any conclusive degradation.

Eur. Phys. J. C

Liquid argon time projection chamber detector technology provides high spatial and calorimetric resolutions on the charged particles traversing liquid argon. As a result, the technology has been used in a number of recent neutrino experiments, and is the technology of choice for the Deep Underground Neutrino Experiment (DUNE). In order to perform high precision measurements of neutrinos in the detector, final state particles need to be effectively identified, and their energy accurately reconstructed. This article proposes an algorithm based on a convolutional neural network to perform the classification of energy deposits and reconstructed particles as track-like or arising from electromagnetic cascades. Results from testing the algorithm on experimental data from ProtoDUNE-SP, a prototype of the DUNE far detector, are presented. The network identifies track- and shower-like particles, as well as Michel electrons, with high efficiency. The performance of the algorithm is consistent between experimental data and simulation.