JINST

Measurements and searches performed with the ATLAS detector at the CERN LHC often involve signatures with one or more prompt leptons. Such analysesare subject to `fake/non-prompt' lepton backgrounds, where either a hadron or a lepton from a hadron decay or an electron from a photon conversion satisfies the prompt-leptonselection criteria. These backgrounds often arise within a hadronic jet because of particle decays in the showering process, particle misidentification or particleinteractions with the detector material. As it is challenging to model these processes with high accuracy in simulation, their estimation typically uses data-driven methods.Three methods for carrying out this estimation are described, along with their implementation in ATLAS and their performance.

JHEP

A search is performed for exclusive high-mass γγ → WW and γγ → ZZ production in proton-proton collisions using intact forward protons reconstructed in near-beam detectors, with both weak bosons decaying into boosted and merged jets. The analysis is based on a sample of proton-proton collisions collected by the CMS and TOTEM experiments at $ \sqrt{s} $ = 13 TeV, corresponding to an integrated luminosity of 100 fb$^{−1}$. No excess above the standard model background prediction is observed, and upper limits are set on the pp → pWWp and pp → pZZp cross sections in a fiducial region defined by the diboson invariant mass m(VV) > 1 TeV (with V = W, Z) and proton fractional momentum loss 0.04 < ξ < 0.20. The results are interpreted as new limits on dimension-6 and dimension-8 anomalous quartic gauge couplings.[graphic not available: see fulltext]

Nucl. Instrum. Meth. A

With the HL-LHC upgrade of the LHC machine, an increase of the instantaneous luminosity by a factor of five is expected and the current detection systems need to be validated for such working conditions to ensure stable data taking. At the CERN Gamma Irradiation Facility (GIF++) many muon detectors undergo such studies, but the high gamma background can pose a challenge to the muon trigger system which is exposed to many fake hits from the gamma background. A tracking system using RPCs is implemented to clean the fake hits, taking profit of the high muon efficiency of these chambers. This work will present the tracking system configuration, used detector analysis algorithm and results.

JHEP

This paper presents measurements of charged-hadron spectra obtained in pp, p+Pb, and Pb+Pb collisions at $ \sqrt{s} $ or $ \sqrt{s_{\textrm{NN}}} $ = 5.02 TeV, and in Xe+Xe collisions at $ \sqrt{s_{\textrm{NN}}} $ = 5.44 TeV. The data recorded by the ATLAS detector at the LHC have total integrated luminosities of 25 pb$^{−1}$, 28 nb$^{−1}$, 0.50 nb$^{−1}$, and 3 μb$^{−1}$, respectively. The nuclear modification factors R$_{pPb}$ and R$_{AA}$ are obtained by comparing the spectra in heavy-ion and pp collisions in a wide range of charged-particle transverse momenta and pseudorapidity. The nuclear modification factor R$_{pPb}$ shows a moderate enhancement above unity with a maximum at p$_{T}$ ≈ 3 GeV; the enhancement is stronger in the Pb-going direction. The nuclear modification factors in both Pb+Pb and Xe+Xe collisions feature a significant, centrality-dependent suppression. They show a similar distinct p$_{T}$-dependence with a local maximum at p$_{T}$ ≈ 2 GeV and a local minimum at p$_{T}$ ≈ 7 GeV. This dependence is more distinguishable in more central collisions. No significant |η|-dependence is found. A comprehensive comparison with several theoretical predictions is also provided. They typically describe R$_{AA}$ better in central collisions and in the p$_{T}$ range from about 10 to 100 GeV.[graphic not available: see fulltext]

Phys.Rev.Lett.

We present a new determination of the smallest neutrino mixing angle ${\theta }_{13}$ and the mass-squared difference $\mathrm{\Delta }{m}_{32}^2$ using a final sample of $5.55\times {10}^6$ inverse beta-decay (IBD) candidates with the final-state neutron captured on gadolinium. This sample is selected from the complete dataset obtained by the Daya Bay reactor neutrino experiment in 3158 days of operation. Compared to the previous Daya Bay results, selection of IBD candidates has been optimized, energy calibration refined, and treatment of backgrounds further improved. The resulting oscillation parameters are ${\sin }^{2}2{\theta }_{13}=0.0851\pm 0.0024$, $\mathrm{\Delta }{m}_{32}^2=(2.466\pm 0.060)\times {10}^{-3}{\mathrm{eV}}^2$ for the normal mass ordering or $\mathrm{\Delta }{m}_{32}^2=-(2.571\pm 0.060)\times {10}^{-3}{\mathrm{eV}}^2$ for the inverted mass ordering.

Eur.Phys.J.C

Cross-sections for the production of a Z boson in association with two photons are measured in proton–proton collisions at a centre-of-mass energy of 13 TeV. The data used correspond to an integrated luminosity of 139 fb$^{-1}$ recorded by the ATLAS experiment during Run 2 of the LHC. The measurements use the electron and muon decay channels of the Z boson, and a fiducial phase-space region where the photons are not radiated from the leptons. The integrated $Z(\rightarrow \ell \ell )\gamma \gamma $ cross-section is measured with a precision of 12% and differential cross-sections are measured as a function of six kinematic variables of the $Z\gamma \gamma $ system. The data are compared with predictions from MC event generators which are accurate to up to next-to-leading order in QCD. The cross-section measurements are used to set limits on the coupling strengths of dimension-8 operators in the framework of an effective field theory.

Phys.Part.Nucl.Lett.

The behavior of the gluon density in nuclei is investigated in the framework of the rescaling model.

Phys. Rev. Lett.

A search for the standard model (SM) Higgs boson ($H$) produced with transverse momentum ($p_T$) greater than 450 GeV and decaying to a charm quark-antiquark ($c\bar{c}$) pair is presented. The search is performed using proton-proton collision data collected at $\sqrt{s} = 13$ TeV by the CMS experiment at the LHC, corresponding to an integrated luminosity of 138 fb$^{−1}$. Boosted $H \to c\bar{c}$ decay products are reconstructed as a single large-radius jet and identified using a deep neural network charm tagging technique. The method is validated by measuring the $Z \to c\bar{c}$ decay process, which is observed in association with jets at high $p_T$ for the first time with a signal strength of $1.00^{+0.17}_{−0.14}$ (syst) $\pm 0.08$ (theo) $\pm 0.06$ (stat), defined as the ratio of the observed process rate to the SM expectation. The observed (expected) upper limit on $\sigma (H){\cal B}(H \to c\bar{c})$ is set at 47 (39) times the SM prediction at 95\% confidence level.

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.

Eur.Phys.J.C

The flavour-tagging algorithms developed by the ATLAS Collaboration and used to analyse its dataset of $\sqrt{s} = 13$ TeV pp collisions from Run 2 of the Large Hadron Collider are presented. These new tagging algorithms are based on recurrent and deep neural networks, and their performance is evaluated in simulated collision events. These developments yield considerable improvements over previous jet-flavour identification strategies. At the 77% b-jet identification efficiency operating point, light-jet (charm-jet) rejection factors of 170 (5) are achieved in a sample of simulated Standard Model $t\bar{t}$ events; similarly, at a c-jet identification efficiency of 30%, a light-jet (b-jet) rejection factor of 70 (9) is obtained.

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.

Eur.Phys.J.C

This paper presents a search for dark matter, $\chi $, using events with a single top quark and an energetic W boson. The analysis is based on proton–proton collision data collected with the ATLAS experiment at $\sqrt{s}=$ 13 TeV during LHC Run 2 (2015–2018), corresponding to an integrated luminosity of 139 fb$^{-1}$. The search considers final states with zero or one charged lepton (electron or muon), at least one b-jet and large missing transverse momentum. In addition, a result from a previous search considering two-charged-lepton final states is included in the interpretation of the results. The data are found to be in good agreement with the Standard Model predictions and the results are interpreted in terms of 95% confidence-level exclusion limits in the context of a class of dark matter models involving an extended two-Higgs-doublet sector together with a pseudoscalar mediator particle. The search is particularly sensitive to on-shell production of the charged Higgs boson state, $H^{\pm }$, arising from the two-Higgs-doublet mixing, and its semi-invisible decays via the mediator particle, a: $H^{\pm } \rightarrow W^\pm a (\rightarrow \chi \chi )$. Signal models with $H^{\pm }$ masses up to 1.5 TeV and a masses up to 350 GeV are excluded assuming a $\tan \beta $ value of 1. For masses of a of 150 (250) GeV, $\tan \beta $ values up to 2 are excluded for $H^{\pm }$ masses between 200 (400) GeV and 1.5 TeV. Signals with $\tan \beta $ values between 20 and 30 are excluded for $H^{\pm }$ masses between 500 and 800 GeV.

Chin. Phys. C

Using data taken at 29 center-of-mass energies between 4.16 and 4.70 GeV with the BESIII detector at the Beijing Electron Positron Collider corresponding to a total integrated luminosity of approximately 18.8 , the process is observed for the first time with a statistical significance of . The average Born cross sections in the energy ranges of (4.160, 4.380) GeV, (4.400, 4.600) GeV and (4.610, 4.700) GeV are measured to be fb, fb and fb, respectively, where the first uncertainties are statistical and the second are systematic. The line shapes of the and invariant mass spectra are consistent with phase space distributions, indicating that no hexaquark or di-baryon state is observed.

Chin.Phys.C

We report a search for a heavier partner of the recently observed state, denoted as , in the process , based on collision data collected at the center-of-mass energies of , 4.682 and 4.699 GeV with the BESIII detector. The is of interest as it is expected to be a candidate for a hidden-charm and open-strange tetraquark. A partial-reconstruction technique is used to isolate recoil-mass spectra, which are probed for a potential contribution from (). We find an excess of () candidates with a significance of , after considering systematic uncertainties, at a mass of . As the data set is limited in size, the upper limits are evaluated at the 90% confidence level on the product of the Born cross sections () and the branching fraction () of , under different assumptions of the mass from 4.120 to 4.140 MeV and of the width from 10 to 50 MeV at the three center-of-mass energies. The upper limits of are found to be at the level of pb at each energy. Larger data samples are needed to confirm the state and clarify its nature in the coming years.

Phys.Lett.B

We search for an axion-like particle (ALP) a through the process $\psi (3686)\to {\pi }^{+}{\pi }^{-}J/\psi$, $J/\psi \to \gamma a$, $a\to \gamma \gamma$ in a data sample of $(2.71\pm 0.01)\times {10}^9$$\psi (3686)$ events collected by the BESIII detector. No significant ALP signal is observed over the expected background, and the upper limits on the branching fraction of the decay $J/\psi \to \gamma a$ and the ALP-photon coupling constant $g_{a\gamma \gamma }$ are set at 95% confidence level in the mass range of $0.165\le m_a\le 2.84\text{GeV}/c^2$. The limits on $\mathcal{B}(J/\psi \to \gamma a)$ range from $8.3\times {10}^{-8}$ to $1.8\times {10}^{-6}$ over the search region, and the constraints on the ALP-photon coupling are the most stringent to date for $0.165\le m_a\le 1.468\text{GeV}/c^2$.

Phys.Rev.C

We have evaluated pseudoscalar and scalar neutral pion photoproduction in $\vec{\gamma }p\to {\pi }^{0}p$ and $a_0^{0}p$ above the resonance region and within Regge phenomenology. Our fit, including GlueX $\mathrm{\Sigma }$ pseudoscalar photoproduction data, shows that previous Stanford Linear Accelerator Center (SLAC) $\mathrm{\Sigma }$ measurements for $\vec{\gamma }p\to {\pi }^{0}p$ above $E_{\gamma }=4\mathrm{GeV}$ vary substantially from SLAC data with more recent measurements made by GlueX in the vicinity of $E_{\gamma }=9\mathrm{GeV}$. The Regge model predicts that the beam polarization asymmetry $\mathrm{\Sigma }$ of the scalar meson is opposite to that of pseudoscalar meson photoproduction; however, the cross sections are similar. While the natural parity vector meson exchange is dominant in both cases, the contribution of the unnatural parity pseudovector meson exchange is very small. Using Regge phenomenology, we predicted high-energy behavior for double polarized observables $\mathbb{E}$, $\mathbb{F}$, $\mathbb{G}$, and $\mathbb{H}$ for the reactions $\gamma p\to {\pi }^{0}p$ and $a_0^{0}p$.

Phys. Rev. C

The ATLAS detector at the Large Hadron Collider has been used to measure jet substructure modification and suppression in $\mathrm{Pb}+\mathrm{Pb}$ collisions at a nucleon–nucleon center-of-mass energy $\sqrt{s_{{}_{NN}}}=5.02\mathrm{TeV}$ in comparison with proton–proton ($pp$) collisions at $\sqrt{s}=5.02\mathrm{TeV}$. The $\mathrm{Pb}+\mathrm{Pb}$ data, collected in 2018, have an integrated luminosity of $1.72{\mathrm{nb}}^{-1}$, while the $pp$ data, collected in 2017, have an integrated luminosity of $260{\mathrm{pb}}^{-1}$. Jets used in this analysis are clustered using the anti-$k_t$ algorithm with a radius parameter $R=0.4$. The jet constituents, defined by both tracking and calorimeter information, are used to determine the angular scale $r_{\mathrm{g}}$ of the first hard splitting inside the jet by reclustering them using the Cambridge–Aachen algorithm and employing the soft-drop grooming technique. The nuclear modification factor, $R_{AA}$, used to characterize jet suppression in $\mathrm{Pb}+\mathrm{Pb}$ collisions, is presented differentially in $r_{\mathrm{g}}$, jet transverse momentum, and in intervals of collision centrality. The $R_{AA}$ value is observed to depend significantly on jet $r_{\mathrm{g}}$. Jets produced with the largest measured $r_{\mathrm{g}}$ are found to be twice as suppressed as those with the smallest $r_{\mathrm{g}}$ in central $\mathrm{Pb}+\mathrm{Pb}$ collisions. The $R_{AA}$ values do not exhibit a strong variation with jet $p_{\mathrm{T}}$ in any of the $r_{\mathrm{g}}$ intervals. The $r_{\mathrm{g}}$ and $p_{\mathrm{T}}$ dependence of jet $R_{AA}$ is qualitatively consistent with a picture of jet quenching arising from coherence and provides the most direct evidence in support of this approach.

Phys. Rev. Lett.

Based on electron positron collision data collected with the BESIII detector operating at the BEPCII storage rings, the differential cross sections of inclusive $\pi^0$ and $K^0_S$ production as a function of hadron momentum, normalized by the total cross section of the $e^{+}e^{-} \to$ hadrons process, are measured at six center-of-mass energies from 2.2324 to 3.6710 GeV. Our results with a relative hadron energy coverage from 0.1 to 0.9 significantly deviate from several theoretical calculations based on existing fragmentation functions, especially at lower energies.

Phys.Rev.D

The decay ${\eta }_c(2S)\to {\pi }^{+}{\pi }^{-}\eta$ is searched for through the radiative transition $\psi (3686)\to \gamma {\eta }_c(2S)$ using 448 million $\psi (3686)$ events accumulated at the BESIII detector. The first evidence of ${\eta }_c(2S)\to {\pi }^{+}{\pi }^{-}\eta$ is found with a statistical significance of $3.5\sigma$. The product of the branching fractions of $\psi (3686)\to \gamma {\eta }_c(2S)$ and ${\eta }_c(2S)\to {\pi }^{+}{\pi }^{-}\eta$ is measured to be $\mathrm{Br}(\psi (3686)\to \gamma {\eta }_c(2S))\times \mathrm{Br}({\eta }_c(2S)\to {\pi }^{+}{\pi }^{-}\eta )=(2.97\pm 0.81\pm 0.26)\times {10}^{-6}$, where the first uncertainty is statistical and the second one is systematic. The branching fraction of the decay ${\eta }_c(2S)\to {\pi }^{+}{\pi }^{-}\eta$ is determined to be $\mathrm{Br}({\eta }_c(2S)\to {\pi }^{+}{\pi }^{-}\eta )=(42.4\pm 11.6\pm 3.8\pm 30.3)\times {10}^{-4}$, where the third uncertainty is transferred from the uncertainty of the branching fraction of $\psi (3686)\to \gamma {\eta }_c(2S)$.

Phys. Rev. D

A theoretical description of photon-pair production in polarized positron-electron annihilation is presented. Complete one-loop electroweak radiative corrections are calculated taking into account the exact dependence on the electron mass. Analytical results are derived with the help of the SANC system. The relevant contributions to the cross section are calculated analytically using the helicity amplitude approach. The cases of unpolarized and longitudinally polarized fermions in the initial state are investigated. Calculations are realized in the Monte Carlo integrator MCSANCee and generator ReneSANCe which allow one the implementation of any experimental cuts used in the analysis of $e^{+}{e}^{-}$ annihilation data of both low and high energies.

Eur. Phys. J. C

A measurement of ${{D}} ^0$ meson production by the LHCb experiment in its fixed-target configuration is presented. The production of ${{D}} ^0$ mesons is studied with a beam of 2.5 $\,\text {Te\hspace{-1.00006pt}V}$ protons colliding on a gaseous neon target at rest, corresponding to a nucleon–nucleon centre-of-mass energy of $\sqrt{s_{\scriptscriptstyle \text {NN}}} = 68.5\,\,\text {Ge\hspace{-1.00006pt}V} $. The sum of the ${{D}} ^0$ and ${\hspace{0.0pt}\overline{\hspace{0.0pt}{D}}} {}^0$ production cross-section in $p\text {Ne}$ collisions in the centre-of-mass rapidity range $y^{\star }\in [-2.29, 0]$ is found to be $\sigma _{D^{0}}^{y^\star \in [-2.29, 0]} = 48.2 \pm 0.3 \pm 4.5 \,\upmu \text {b}/\text {nucleon}$ where the first uncertainty is statistical and the second is systematic. The ${{{D}} ^0}-{{\hspace{0.0pt}\overline{\hspace{0.0pt}{D}}} {}^0} $ production asymmetry is also evaluated and suggests a trend towards negative values at large negative $y^{\star }$. The considered models do not account precisely for all the features observed in the LHCb data, but theoretical predictions including 1$\%$ intrinsic charm and 10$\%$ recombination contributions better describe the data than the other models considered.

Eur.Phys.J.C

The measurement of charmonium states produced in proton-neon ($p\text {Ne}$) collisions by the LHCb experiment in its fixed-target configuration is presented. The production of ${{J} \hspace{-1.66656pt}/\hspace{-1.111pt}\psi }$ and $\psi {(2S)}$ mesons is studied with a beam of 2.5$\mathrm{\,Te\hspace{-1.00006pt}V}$ protons colliding on gaseous neon targets at rest, corresponding to a nucleon-nucleon centre-of-mass energy $\sqrt{s_{\scriptscriptstyle \text {NN}}} =68.5\mathrm{\,Ge\hspace{-1.00006pt}V} $. The data sample corresponds to an integrated luminosity of $21.7\pm 1.4 $ nb$^{-1}$. The ${{J} \hspace{-1.66656pt}/\hspace{-1.111pt}\psi }$ and $\psi {(2S)}$ hadrons are reconstructed in $\mu ^+\mu ^-$ final states. The ${{J} \hspace{-1.66656pt}/\hspace{-1.111pt}\psi }$ production cross-section per target nucleon in the centre-of-mass rapidity range $y^\star \in [-2.29, 0]$ is found to be $506 \pm 8 \pm 46 \text { nb/nucleon}$. The ratio of ${{J} \hspace{-1.66656pt}/\hspace{-1.111pt}\psi }$ and $D^0$ cross-sections is evaluated to $(1.06 \pm 0.02 \pm 0.09)\%$. The $\psi {(2S)}$ to ${{J} \hspace{-1.66656pt}/\hspace{-1.111pt}\psi }$ relative production rate is found to be $(1.67 \pm 0.27\pm 0.10)\%$ in good agreement with other measurements involving beam and target nuclei of similar sizes.

Eur. Phys. J. C

The first measurement of ${{J}/\psi }$ and ${{D}} ^0$ production in PbNe collisions by the LHCb experiment in its fixed-target configuration is reported. The production of ${{J}/\psi }$ and ${{D}} ^0$ mesons is studied with a beam of lead ions with an energy of 2.5$\,\text {TeV}$ per nucleon colliding on gaseous neon targets at rest, corresponding to a nucleon-nucleon centre-of-mass energy of $\sqrt{s_{\scriptscriptstyle \text {NN}}} =68.5\,\text {GeV} $. The ${{J}/\psi }$/${{D}} ^0$ production cross-section ratio is studied as a function of rapidity, transverse momentum and collision centrality. These data are compared with measurements from $p\text {Ne}$ collisions at the same energy and show no difference in the observed ${{J}/\psi }$ suppression trend when comparing $p\text {Ne}$ and PbNe peripheral collisions with PbNe central collisions.

Phys.Rev.D

Using data samples with a total integrated luminosity of approximately $18{\mathrm{fb}}^{-1}$ collected by the BESIII detector operating at the Beijing Electron-Positron Collider II, the process $e^{+}{e}^{-}\to \mathrm{\Lambda }\overline{\mathrm{\Lambda }}\eta$ is studied at center-of-mass energies between 3.5106 and 4.6988 GeV. The Born cross section for the process $e^{+}{e}^{-}\to \mathrm{\Lambda }\overline{\mathrm{\Lambda }}\eta$ is measured. No significant structure is observed in the Born cross section line shape. An enhancement near the $\mathrm{\Lambda }\overline{\mathrm{\Lambda }}$ mass threshold is observed for the first time in the process. The structure can be described by an $S$-wave Breit-Wigner function. Neglecting contribution of excited $\mathrm{\Lambda }$ states and potential interferences, the mass and width are determined to be $(2356\pm 7\pm 15)\mathrm{MeV}/c^2$ and $(304\pm 28\pm 54)\mathrm{MeV}$, respectively, where the first uncertainties are statistical and the second are systematic.

Phys. Lett. B

Measurements of joint-polarisation states of W and Z gauge bosons in $W^{\pm }Z$ production are presented. The data set used corresponds to an integrated luminosity of 139 fb⁻¹ of proton–proton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. The $W^{\pm }Z$ candidate events are reconstructed using leptonic decay modes of the gauge bosons into electrons and muons. The simultaneous pair-production of longitudinally polarised vector bosons is measured for the first time with a significance of 7.1 standard deviations. The measured joint helicity fractions integrated over the fiducial region are $f_{\mathrm{00}}=0.067\pm 0.010$, $f_{\mathrm{0T}}=0.110\pm 0.029$, $f_{\mathrm{T0}}=0.179\pm 0.023$ and $f_{\mathrm{TT}}=0.644\pm 0.032$, in agreement with the next-to-leading-order Standard Model predictions. Individual helicity fractions of the W and Z bosons are also measured and found to be consistent with joint helicity fractions within the expected amounts of correlation. Both the joint and individual helicity fractions are also measured separately in $W^{+}Z$ and $W^{-}Z$ events. Inclusive and differential cross sections for several kinematic observables sensitive to polarisation are presented.