JHEP

A search for a pair of neutral, scalar bosons with each decaying into two W bosons is presented using 36.1 fb$^{−1}$ of proton-proton collision data at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider. This search uses three production models: non-resonant and resonant Higgs boson pair production and resonant production of a pair of heavy scalar particles. Three final states, classified by the number of leptons, are analysed: two same-sign leptons, three leptons, and four leptons. No significant excess over the expected Standard Model backgrounds is observed. An observed (expected) 95% confidence-level upper limit of 160 (120) times the Standard Model prediction of non-resonant Higgs boson pair production cross-section is set from a combined analysis of the three final states. Upper limits are set on the production cross-section times branching ratio of a heavy scalar X decaying into a Higgs boson pair in the mass range of 260 GeV ≤ m$_{X}$ ≤ 500 GeV and the observed (expected) limits range from 9.3 (10) pb to 2.8 (2.6) pb. Upper limits are set on the production cross-section times branching ratio of a heavy scalar X decaying into a pair of heavy scalars S for mass ranges of 280 GeV ≤ m$_{X}$ ≤ 340 GeV and 135 GeV ≤ m$_{S}$ ≤ 165 GeV and the observed (expected) limits range from 2.5 (2.5) pb to 0.16 (0.17) pb.

Phys.Rev.D

We report a study of the decay D0→K¯0π-e+νe based on a sample of 2.93  fb-1 e+e- annihilation data collected at the center-of-mass energy of 3.773 GeV with the BESIII detector at the BEPCII collider. The total branching fraction is determined to be B(D0→K¯0π-e+νe)=(1.434±0.029(stat.)±0.032(syst.))%, which is the most precise to date. According to a detailed analysis of the involved dynamics, we find this decay is dominated with the K*(892)- contribution and present an improved measurement of its branching fraction to be B(D0→K*(892)-e+νe)=(2.033±0.046(stat.)±0.047(syst.))%. We further access their hadronic form-factor ratios for the first time as rV=V(0)/A1(0)=1.46±0.07(stat.)±0.02(syst.) and r2=A2(0)/A1(0)=0.67±0.06(stat.)±0.01(syst.). In addition, we observe a significant K¯0π-  S-wave component accounting for (5.51±0.97(stat.)±0.62(syst.))% of the total decay rate.

Phys.Rev.Lett.

Using a 3.19  fb-1 data sample collected at an e+e- center-of-mass energy of Ecm=4.178  GeV with the BESIII detector, we measure the branching fraction of the leptonic decay Ds+→μ+νμ to be BDs+→μ+νμ=(5.49±0.16stat±0.15syst)×10-3. Combining our branching fraction with the masses of the Ds+ and μ+ and the lifetime of the Ds+, we determine fDs+|Vcs|=246.2±3.6stat±3.5syst  MeV. Using the c→s quark mixing matrix element |Vcs| determined from a global standard model fit, we evaluate the Ds+ decay constant fDs+=252.9±3.7stat±3.6syst  MeV. Alternatively, using the value of fDs+ calculated by lattice quantum chromodynamics, we find |Vcs|=0.985±0.014stat±0.014syst. These values of BDs+→μ+νμ, fDs+|Vcs|, fDs+ and |Vcs| are each the most precise results to date.

Phys. Lett. B

A search is presented for dark matter in proton-proton collisions at a center-of-mass energy of s=13 TeV using events with at least one high transverse momentum ( pT ) muon, at least one high- pT jet, and large missing transverse momentum. The data were collected with the CMS detector at the CERN LHC in 2016 and 2017, and correspond to an integrated luminosity of 77.4 fb −1 . In the examined scenario, a pair of scalar leptoquarks is assumed to be produced. One leptoquark decays to a muon and a jet while the other decays to dark matter and low- pT standard model particles. The signature for signal events would be significant missing transverse momentum from the dark matter in conjunction with a peak at the leptoquark mass in the invariant mass distribution of the highest pT muon and jet. The data are observed to be consistent with the background predicted by the standard model. For the first benchmark scenario considered, dark matter masses up to 500 GeV are excluded for leptoquark masses mLQ≈1400 GeV, and up to 300 GeV for mLQ≈1500 GeV. For the second benchmark scenario, dark matter masses up to 600 GeV are excluded for mLQ≈1400 GeV.

Eur. Phys. J. C

Measurements are presented of associated production of a $\mathrm {W}$ boson and a charm quark ( $\mathrm {W}+\mathrm {c}$ ) in proton–proton collisions at a center-of-mass energy of 13 $\,\text {Te}\text {V}$ . The data correspond to an integrated luminosity of 35.7 $\,\text {fb}^{-1}$ collected by the CMS experiment at the CERN LHC. The $\mathrm {W}$ bosons are identified by their decay into a muon and a neutrino. The charm quarks are tagged via the full reconstruction of ${\mathrm {D}^{*}(2010)^{\pm }}$ mesons that decay via ${\mathrm {D}^{*}(2010)^{\pm }}\rightarrow \mathrm {D}^0 + {\pi ^{\pm }}\rightarrow \mathrm {K}^{\mp } + {\pi ^{\pm }}+ {\pi ^{\pm }}$ . A cross section is measured in the fiducial region defined by the muon transverse momentum $p_{\mathrm {T}} ^{\mu } > 26\,\text {Ge}\text {V} $ , muon pseudorapidity $|\eta ^{\mu } | < 2.4$ , and charm quark transverse momentum $p_{\mathrm {T}} ^{\mathrm {c}} > 5\,\text {Ge}\text {V} $ . The inclusive cross section for this kinematic range is $\sigma (\mathrm {W}+\mathrm {c})=1026\pm 31\,\text {(stat)} \begin{array}{c} +76\\ -72 \end{array}\,\text {(syst)} \text { pb} $ . The cross section is also measured differentially as a function of the pseudorapidity of the muon from the $\mathrm {W}$ boson decay. These measurements are compared with theoretical predictions and are used to probe the strange quark content of the proton.

J.Contemp.Phys.

Owing to the growing interest in the low-energy nuclear physics, it becomes relevant to enhance the potential of the experimental facilities at Yerevan Physics Institute (YerPhI). The complex unit based on the linear electron accelerator LUE-75 (ARUS synchrotron injector) for applied and fundamental experiments with electron beams, the intensity and energy of which can vary in a wide range of 10$^{–18}$–10$^{–5}$ А and 10–50 MeV, has been created. In recent years, the regimes developed at LUE-75 were applied to obtain the controllable electron beams of extremely low intensity used for calibration of detectors.

Phys.Part.Nucl.Lett.

Experimental results on pion decays obtained with the PIBETA spectrometer at the Paul Scherrer Institute (PSI) are reviewed. For pion beta decay π$^{+}$ → π$^{0}$е$^{+}$ν (πβ), a precision measurement of relative probability yields Г(πβ) = [1.036 ± 0.004(stat) ± 0.004(syst) ± 0.003(π$^{+}$→е$^{+}$ν)] × 10$^{–8}$, which implies V$_{ud}$ = 0.9728(30) for the corresponding element of the Cabibbo–Kobayashi–Maskawa mixing matrix. Using a sample of 65 × 10$^{3}$ events, relative probability of the π$^{+}$→е$^{+}$νγ radiative pion decay (RPD) in the kinematic region of E$_{γ}$ > 10 MeV and θ$_{eγ}$ > 40° is measured as B$^{exp}$ = 73.86(54) × 10$^{–8}$. A statistical analysis of measured E$_{e+}$ and E$_{γ}$ distributions for this decay yield the values F$_{V}$ = 0.0258(17) and F$_{A}$ = 0.0117(17) for the pion weak formfactors. Assuming that F$_{V}$ linearly depends on the е$^{+}$ν invariant mass q$^{2}$ as F$_{V}$(q$^{2}$) = F$_{V}$(0)(1 + aq$^{2}$), the slope parameter is extracted as а = 0.10(6). The pion polarizability and neutral-pion lifetime are estimated as α$_{E}$ = 2.78(10) × 10$^{–4}$ fm$^{3}$ and τ(π$^{0}$) = (8.5 ± 1.1) × 10$^{–17}$ s, respectively. The data for decays π$^{+}$→ е$^{+}$ ν and ${\mu ^ + } \to {e^ + }v\bar v\gamma $ have been collected and are being processed. The follow-up PEN experiment aims at reducing the uncertainty on the π$^{+}$ → е$^{+}$ ν relative probability by almost an order of magnitude (to 5 × 10$^{–4}$).

Phys. Rev. Lett.

This Letter describes a search for Higgs boson pair production using the combined results from four final states: bbγγ, bbττ, bbbb, and bbVV, where V represents a W or Z boson. The search is performed using data collected in 2016 by the CMS experiment from LHC proton-proton collisions at s=13  TeV, corresponding to an integrated luminosity of 35.9  fb-1. Limits are set on the Higgs boson pair production cross section. A 95% confidence level observed (expected) upper limit on the nonresonant production cross section is set at 22.2 (12.8) times the standard model value. A search for narrow resonances decaying to Higgs boson pairs is also performed in the mass range 250–3000 GeV. No evidence for a signal is observed, and upper limits are set on the resonance production cross section.

Phys. Rev. D

A search is presented for the production of a Higgs boson in association with a single top quark, based on data collected in 2016 by the CMS experiment at the LHC at a center-of-mass energy of 13 TeV, which corresponds to an integrated luminosity of 35.9  fb-1. The production cross section for this process is highly sensitive to the absolute values of the top quark Yukawa coupling, yt; the Higgs boson coupling to vector bosons, gHVV; and, uniquely, their relative sign. Analyses using multilepton signatures, targeting H→WW, H→ττ, and H→ZZ decay modes, and signatures with a single lepton and a bb¯ pair, targeting the H→bb¯ decay, are combined with a reinterpretation of a measurement in the H→γγ channel to constrain yt. For a standard model–like value of gHVV, the data favor positive values of yt and exclude values of yt below about -0.9ytSM.

Eur. Phys. J. C

A search is presented for resonant production of second-generation sleptons ( $\widetilde{\mu } _{\mathrm {L}}$ , $\widetilde{\nu }_{\mu }$ ) via the R-parity-violating coupling ${\lambda ^{\prime 211}}$ to quarks, in events with two same-sign muons and at least two jets in the final state. The smuon (muon sneutrino) is expected to decay into a muon and a neutralino (chargino), which will then decay into a second muon and at least two jets. The analysis is based on the 2016 data set of proton-proton collisions at $\sqrt{s}=13\,\text {TeV} $ recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9 $\,\text {fb}^{-1}$ . No significant deviation is observed with respect to standard model expectations. Upper limits on cross sections, ranging from 0.24 to 730 $\,\text {fb}$ , are derived in the context of two simplified models representing the dominant signal contributions leading to a same-sign muon pair. The cross section limits are translated into coupling limits for a modified constrained minimal supersymmetric model with ${\lambda ^{\prime 211}}$ as the only nonzero R-parity violating coupling. The results significantly extend restrictions of the parameter space compared with previous searches for similar models.

Phys. Rev. D

A measurement of production cross sections of the Higgs boson in proton-proton collisions is presented in the $H\rightarrow\tau\tau$ decay channel. The analysis is performed using $36.1\mathrm{fb}^{-1}$ of data recorded by the ATLAS experiment at the Large Hadron Collider at a center-of-mass energy of $\sqrt{s}=13$ TeV. All combinations of leptonic ($\tau \rightarrow l \nu \bar{\nu}$ with $l = e$, $\mu$) and hadronic ($\tau \to$ hadrons $\nu$) $\tau$ decays are considered. The $H\rightarrow\tau\tau$ signal over the expected background from other Standard Model processes is established with an observed (expected) significance of 4.4 (4.1) standard deviations. Combined with results obtained using data taken at 7 and 8 TeV center-of-mass energies, the observed (expected) significance amounts to 6.4 (5.4) standard deviations and constitutes an observation of $H\rightarrow\tau\tau$ decays. Using the data taken at $\sqrt{s}=13$ TeV, the total cross section in the $H\rightarrow\tau\tau$ decay channel is measured to be $3.77^{+0.60}_{-0.59}\mathrm{(stat.)}^{+0.87}_{-0.74}\mathrm{(syst.)}\mathrm{pb}$, for a Higgs boson of mass 125 GeV assuming the relative contributions of its production modes as predicted by the Standard Model. Total cross sections in the $H\rightarrow\tau\tau$ decay channel are determined separately for vector-boson-fusion production and gluon-gluon-fusion production to be $\sigma ^{\mathrm{VBF}}_{H \to \tau \tau} = 0.28 \pm 0.09\mathrm{(stat.)}^{+0.11}_{-0.09}\mathrm{(syst.)}\mathrm{pb}$ and $\sigma ^{gg \mathrm{F}}_{H \to \tau \tau} = 3.1 \pm 1.0\mathrm{(stat.)}^{+1.6}_{-1.3}\mathrm{(syst.)}\mathrm{pb}$, respectively. Similarly, results of a fit are reported in the framework of simplified template cross sections. All measurements are in agreement with Standard Model expectations.

Phys. Rev. D

The cross section of the process e+e-→K+K- is measured at a number of center-of-mass energies s from 2.00 to 3.08 GeV with the BESIII detector at the Beijing Electron Positron Collider (BEPCII). The results provide the best precision achieved so far. A resonant structure around 2.2 GeV is observed in the cross section line shape. A Breit-Wigner fit yields a mass of M=2239.2±7.1±11.3  MeV/c2 and a width of Γ=139.8±12.3±20.6  MeV, where the first uncertainties are statistical and the second ones are systematic. In addition, the timelike electromagnetic form factor of the kaon is determined at the individual center-of-mass energy points.

Phys. Rev. Lett.

The adapted DIRAC experiment at the CERN PS accelerator observed for the first time long-lived hydrogenlike π+π- atoms, produced by protons hitting a beryllium target. A part of these atoms crossed the gap of 96 mm between the target and a 2.1  μm thick platinum foil, in which most of them dissociated. Analyzing the observed number of atomic pairs, nAL=436-61+157|tot, the lifetime of the 2p state is found to be τ2p=(0.45-0.30+1.08|tot)×10-11  s, not contradicting the corresponding QED 2p state lifetime τ2pQED=1.17×10-11  s. This lifetime value is three orders of magnitude larger than our previously measured value of the π+π- atom ground state lifetime τ=(3.15-0.26+0.28|tot)×10-15  s. Further studies of long-lived π+π- atoms will allow us to measure energy differences between p and s atomic states and so to discriminate between the isoscalar and isotensor ππ scattering lengths with the aim to check QCD predictions.

JHEP

A search for CP violation in the Cabibbo-suppressed D$^{0}$ → K$^{+}$K$^{−}$π$^{+}$π$^{−}$ decay mode is performed using an amplitude analysis. The measurement uses a sample of pp collisions recorded by the LHCb experiment during 2011 and 2012, corresponding to an integrated luminosity of 3.0 fb$^{−1}$. The D$^{0}$ mesons are reconstructed from semileptonic b-hadron decays into D$^{0}$μ$^{−}$X final states. The selected sample contains more than 160 000 signal decays, allowing the most precise amplitude modelling of this D$^{0}$ decay to date. The obtained amplitude model is used to perform the search for CP violation. The result is compatible with CP symmetry, with a sensitivity ranging from 1% to 15% depending on the amplitude considered.

Phys. Lett. B

The results of a search for a standard model-like Higgs boson in the mass range between 70 and 110 GeV decaying into two photons are presented. The analysis uses the data set collected with the CMS experiment in proton-proton collisions during the 2012 and 2016 LHC running periods. The data sample corresponds to an integrated luminosity of 19.7 (35.9)fb−1 at s=8 (13) TeV. The expected and observed 95% confidence level upper limits on the product of the cross section and branching fraction into two photons are presented. The observed upper limit for the 2012 (2016) data set ranges from 129 (161) fb to 31 (26) fb. The statistical combination of the results from the analyses of the two data sets in the common mass range between 80 and 110 GeV yields an upper limit on the product of the cross section and branching fraction, normalized to that for a standard model-like Higgs boson, ranging from 0.7 to 0.2, with two notable exceptions: one in the region around the Z boson peak, where the limit rises to 1.1, which may be due to the presence of Drell–Yan dielectron production where electrons could be misidentified as isolated photons, and a second due to an observed excess with respect to the standard model prediction, which is maximal for a mass hypothesis of 95.3 GeV with a local (global) significance of 2.8 (1.3) standard deviations.

Chin. Phys. C

We study the hadronic decays of to the final states and , using an annihilation data sample of 567 pb-1 taken at a center-of-mass energy of 4.6 GeV with the BESIII detector at the BEPCII collider. We find evidence for the decays and with statistical significance of and , respectively. Normalizing to the reference decays and , we obtain the ratios of the branching fractions and to be and , respectively. The upper limits at the 90% confidence level are set to be and . Using BESIII measurements of the branching fractions of the reference decays, we determine % (<0.68%) and % (<1.9%). Here, the first uncertainties are statistical and the second systematic. The obtained branching fraction of is consistent with the previous measurement, and the branching fraction of is measured for the first time.

Phys.Rev.D

A search for long-lived particles decaying into jets is presented. Data were collected with the CMS detector at the LHC from proton-proton collisions at a center-of-mass energy of 13 TeV in 2016, corresponding to an integrated luminosity of 35.9  fb-1. The search examines the distinctive topology of displaced tracks and secondary vertices. The selected events are found to be consistent with standard model predictions. For a simplified model in which long-lived neutral particles are pair produced and decay to two jets, pair production cross sections larger than 0.2 fb are excluded at 95% confidence level for a long-lived particle mass larger than 1000 GeV and proper decay lengths between 3 and 130 mm. Several supersymmetry models with gauge-mediated supersymmetry breaking or R-parity violation, where pair-produced long-lived gluinos or top squarks decay to several final-state topologies containing displaced jets, are also tested. For these models, in the mass ranges above 200 GeV, gluino masses up to 2300–2400 GeV and top squark masses up to 1350–1600 GeV are excluded for proper decay lengths approximately between 10 and 100 mm. These are the most restrictive limits to date on these models.

Phys. Rev. D

A search for the decay of neutral, weakly interacting, long-lived particles using data collected by the ATLAS detector at the LHC is presented. The analysis in this paper uses 36.1  fb-1 of proton-proton collision data at s=13  TeV recorded in 2015–2016. The search employs techniques for reconstructing vertices of long-lived particles decaying into jets in the muon spectrometer exploiting a two-vertex strategy and a novel technique that requires only one vertex in association with additional activity in the detector that improves the sensitivity for longer lifetimes. The observed numbers of events are consistent with the expected background and limits for several benchmark signals are determined.

Mod. Phys. Lett. A

We study associated production of prompt photon and two jets at high energies in the framework of the parton Reggeization approach (PRA), which is based on multi-Regge factorization of hard processes and Lipatov’s effective theory of Reggeized gluons and quarks. In this approach, initial-state off-shell effects and transverse momenta of initial partons are included in a gauge-invariant way. We compute azimuthal angle difference spectra in γ + 2jets events and compare results with data from D0 Collaboration at the Tevatron. It was found that agreement between predictions and data can be achieved only under assumption on strong violation in transverse momentum ordering during initial-state quantum chromodynamics (QCD) evolution which corresponds multi-Regge kinematical regime instead of DGLAP picture.

Phys.Part.Nucl.Lett.

We study angular correlations in associated hadroproduction of $\Upsilon (1S)$ with the ${{D}^{ \pm }}$ and ${{D}^{0}}$ -mesons at the LHC in the Leading Order of the parton Reggeization approach. Hadronization of $b\bar {b}$ -pair to $\Upsilon (1S)$ is described within the NRQCD-factorization framework. Production of $D$ -mesons is described in the fragmentation model with scale-dependent fragmentaion functions. We have found good agreement with LHCb data for various differential distributions, except for the case of spectra on azimuthal angle differences at the small $\Delta \phi $ values. The total cross-section in our Single Parton Scattering model, calculated under conservative assumptions, accounts for almost one half of observed cross-section, thus dramatically shrinking the room for Double Parton Scattering mechanism.

JHEP

A search for a heavy W′ resonance decaying to one B or T vector-like quark and a top or bottom quark, respectively, is presented. The search uses proton-proton collision data collected in 2016 with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9 fb$^{−1}$ at $ \sqrt{s}=13 $ TeV. Both decay channels result in a final state with a top quark, a Higgs boson, and a b quark, each produced with significant energy. The all-hadronic decays of both the Higgs boson and the top quark are considered. The final-state jets, some of which correspond to merged decay products of a boosted top quark and a Higgs boson, are selected using jet substructure techniques, which help to suppress standard model backgrounds. A W′ boson signal would appear as a narrow peak in the invariant mass distribution of these jets. No significant deviation in data with respect to the standard model background predictions is observed. Cross section upper limits on W′ boson production in the top quark, Higgs boson, and b quark decay mode are set as a function of the W′ mass, for several vector-like quark mass hypotheses. These are the first limits for W′ boson production in this decay channel, and cover a range of 0.01 to 0.43 pb in the W′ mass range between 1.5 and 4.0 TeV.

Eur. Phys. J. C

A search for dark matter produced in association with a Higgs boson decaying to a pair of bottom quarks is performed in proton–proton collisions at a center-of-mass energy of 13 $\,\text {Te}\text {V}$ collected with the CMS detector at the LHC. The analyzed data sample corresponds to an integrated luminosity of 35.9 $\,\text {fb}^{-1}$ . The signal is characterized by a large missing transverse momentum recoiling against a bottom quark–antiquark system that has a large Lorentz boost. The number of events observed in the data is consistent with the standard model background prediction. Results are interpreted in terms of limits both on parameters of the type-2 two-Higgs doublet model extended by an additional light pseudoscalar boson $\mathrm {a}$ (2HDM+ $\mathrm {a}$ ) and on parameters of a baryonic $\mathrm {Z}'$ simplified model. The 2HDM+ $\mathrm {a}$ model is tested experimentally for the first time. For the baryonic $\mathrm {Z}'$ model, the presented results constitute the most stringent constraints to date.

JHEP

Measurements of differential top quark pair $ \mathrm{t}\overline{\mathrm{t}} $ cross sections using events produced in proton-proton collisions at a centre-of-mass energy of 13 TeV containing two oppositely charged leptons are presented. The data were recorded by the CMS experiment at the CERN LHC in 2016 and correspond to an integrated luminosity of 35.9 fb$^{−1}$. The differential cross sections are presented as functions of kinematic observables of the top quarks and their decay products, the $ \mathrm{t}\overline{\mathrm{t}} $ system, and the total number of jets in the event. The differential cross sections are defined both with particle-level objects in a fiducial phase space close to that of the detector acceptance and with parton-level top quarks in the full phase space. All results are compared with standard model predictions from Monte Carlo simulations with next-to-leading-order (NLO) accuracy in quantum chromodynamics (QCD) at matrix-element level interfaced to parton-shower simulations. Where possible, parton-level results are compared to calculations with beyond-NLO precision in QCD. Significant disagreement is observed between data and all predictions for several observables. The measurements are used to constrain the top quark chromomagnetic dipole moment in an effective field theory framework at NLO in QCD and to extract $ \mathrm{t}\overline{\mathrm{t}} $ and leptonic charge asymmetries.