V. Matveev

Using the ARGUS detector at the DORIS II storage ring we have searched in three different ways for B0-B0 mixing in ϒ (4S) decays. One explicitly mixed event, a decay ϒ (4S)→B0B0, has been completely reconstructed. Furthermore, we observe a 4.0 standard deviation signal of 24.8 events with like-sign lepton pairs and a 3.0 standard deviation signal of 4.1 events containing one reconstructed B0(B0) and an additional fast ℓ+(ℓ)−. This leads to the conclusion that B0-B0 mixing is substantial. For the mixing parameter we obtain r=0.21±0.08.

We present results for νμ oscillation in the KEK to Kamioka (K2K) long-baseline neutrino oscillation experiment. K2K uses an accelerator-produced νμ beam with a mean energy of 1.3 GeV directed at the Super-Kamiokande detector. We observed the energy-dependent disappearance of νμ, which we presume have oscillated to ντ. The probability that we would observe these results if there is no neutrino oscillation is 0.0050% (4.0σ).Received 9 November 2004DOI:https://doi.org/10.1103/PhysRevLett.94.081802©2005 American Physical Society

The status of our investigation of low-energy K +Xe collisions in the xenon bubble chamber DIANA is reported. In the charge-exchange reaction K +Xe → K 0 pXe′, the spectrum of K 0 p effective mass shows a resonant enhancement with M=1539±2 MeV/c 2 and Γ≤9 MeV/c 2. The statistical significance of the enhancement is near 4.4σ. The mass and width of the observed resonance are consistent with expectations for the lightest member of the antidecuplet of exotic pentaquark baryons, as predicted in the framework of the chiral soliton model.

We observe a signal for the doubly charmed baryon Xi(+)(cc) in the charged decay mode Xi(+)(cc)-->Lambda(+)(c)K-pi(+) in data from SELEX, the charm hadroproduction experiment at Fermilab. We observe an excess of 15.9 events over an expected background of 6.1+/-0.5 events, a statistical significance of 6.3sigma. The observed mass of this state is 3519+/-1 MeV/c(2). The Gaussian mass width of this state is 3 MeV/c(2), consistent with resolution; its lifetime is less than 33 fs at 90% confidence.

A search for sub-GeV dark matter production mediated by a new vector boson A^{'}, called a dark photon, is performed by the NA64 experiment in missing energy events from 100 GeV electron interactions in an active beam dump at the CERN SPS. From the analysis of the data collected in the years 2016, 2017, and 2018 with 2.84×10^{11} electrons on target no evidence of such a process has been found. The most stringent constraints on the A^{'} mixing strength with photons and the parameter space for the scalar and fermionic dark matter in the mass range ≲0.2 GeV are derived, thus demonstrating the power of the active beam dump approach for the dark matter search.

We report on the measurement of the $\gamma p \rightarrow J/\psi p$ cross section from $E_\gamma = 11.8$ GeV down to the threshold at $8.2$ GeV using a tagged photon beam with the GlueX experiment. We find the total cross section falls toward the threshold less steeply than expected from two-gluon exchange models. The differential cross section $d\sigma /dt$ has an exponential slope of $1.67 \pm 0.39$ GeV$^{-2}$ at $10.7$ GeV average energy. The LHCb pentaquark candidates $P_c^+$ can be produced in the $s$-channel of this reaction. We see no evidence for them and set model-dependent upper limits on their branching fractions $\mathcal{B}(P_c^+ \rightarrow J/\psi p)$ and cross sections $\sigma(\gamma p \to P_c^+)\times\mathcal{B}(P_c^+ \to J/\psi p) $.

We observe a signal for the doubly charmed baryon Ξcc+ in the decay mode Ξcc+→pD+K− to complement the previous reported decay Ξcc+→Λc+K−π+ in data from SELEX, the charm hadroproduction experiment at Fermilab. In this new decay mode we observe an excess of 5.62 events over a combinatoric background estimated by event mixing to be 1.38±0.13 events. The mixed background has Gaussian statistics, giving a signal significance of 4.8σ. The Poisson probability that a background fluctuation can produce the apparent signal is less than 6.4×10−4. The observed mass of this state is 3518±3MeV/c2, consistent with the published result. Averaging the two results gives a mass of 3518.7±1.7MeV/c2. The observation of this new weak decay mode confirms the previous SELEX suggestion that this state is a double charm baryon. The relative branching ratio for these two modes is 0.36±0.21.

An intense source of 37Ar was produced by the (n,α) reaction on 40Ca by irradiating 330 kg of calcium oxide in the fast neutron breeder reactor at Zarechny, Russia. The 37Ar was released from the solid target by dissolution in acid, collected from this solution, purified, sealed into a small source, and brought to the Baksan Neutrino Observatory where it was used to irradiate 13 tonnes of gallium metal in the Russian-American gallium solar neutrino experiment SAGE. Ten exposures of the gallium to the source, whose initial strength was 409±2kCi, were carried out during the period April to September 2004. The 71Ge produced by the reaction 71Ga(νe,e−)71Ge was extracted, purified, and counted. The measured production rate was 11.0+1.0−0.9(stat)±0.6(syst) atoms of 71Ge/d, which is 0.79+0.09−0.10 of the theoretically calculated production rate. When all neutrino source experiments with gallium are considered together, there is an indication the theoretical cross section has been overestimated.Received 29 December 2005DOI:https://doi.org/10.1103/PhysRevC.73.045805©2006 American Physical Society

The detector ARGUS has been designed as a universal tool to investigate final states from e+e− annihilation processes in the energy range of the ϒ resonances. ARGUS started operation in October 1982 and has since successfully taken data at the ϒ(1S), ϒ(2S) and ϒ(4S) energies, and in the nearby continuum. The detector combines excellent charged particle identification and good photon energy resolution over more than 90% of the full solid angle. A particle originating from the interaction vertex and leaving the beam tube traverses the following components: the vertex drift chamber, the main drift chamber which determines its momentum and specific ionization, the time-of-flight system through which its velocity is determined, and the electromagnetic calorimeter. Muons pass through the magnet coils and the flux return yoke and finally hit the muon chamber system which surrounds the detector. The momentum resolution of ARGUS is σ(pT)PT = (0.012 + (0.009pT[GeV/c])2)12, the photon energy resolution in the barrel shower counters is σ(E)E = (0.0722+0.0652E[GeV])12. Combining the information from all p devices, more than 80% of all charged hadrons can be recognized unambiguously. The electron-hadron and muon-hadron rejection rates are 1:200 and 1:50 respectively.

The weak nucleon axial-vector form factor for quasi-elastic interactions is determined using neutrino interaction data from the K2K Scintillating Fiber detector in the neutrino beam at KEK.More than 12,000 events are analyzed, of which half are charged-current quasi-elastic interactions νµn → µ -p occurring primarily in oxygen nuclei.We use a relativistic Fermi gas model for oxygen and assume the form factor is approximately a dipole with one parameter, the axial vector mass MA, and fit to the shape of the distribution of the square of the momentum transfer from the nucleon to the nucleus.Our best fit result for MA = 1.20 ± 0.12 GeV.Furthermore, this analysis includes updated vector form factors from recent electron scattering experiments and a discussion of the effects of the nucleon momentum on the shape of the fitted distributions.

Interaction cross sections and charged pion spectra in $p+\mathrm{C}$ interactions at 31 GeV/$c$ were measured with the large-acceptance NA61/SHINE spectrometer at the CERN SPS. These data are required to improve predictions of the neutrino flux for the T2K long-baseline neutrino oscillation experiment in Japan. A set of data collected during the first NA61/SHINE run in 2007 with an isotropic graphite target with a thickness of 4% of a nuclear interaction length was used for the analysis. The measured $p+\mathrm{C}$ inelastic and production cross sections are 257.2 $\ifmmode\pm\else\textpm\fi{}$ 1.9 $\ifmmode\pm\else\textpm\fi{}$ 8.9 and 229.3 $\ifmmode\pm\else\textpm\fi{}$ 1.9 $\ifmmode\pm\else\textpm\fi{}$ 9.0 mb, respectively. Inclusive production cross sections for negatively and positively charged pions are presented as functions of laboratory momentum in ten intervals of the laboratory polar angle covering the range from 0 up to 420 mrad. The spectra are compared with predictions of several hadron production models.

The OPERA experiment was designed to search for ν_{μ}→ν_{τ} oscillations in appearance mode, i.e., by detecting the τ leptons produced in charged current ν_{τ} interactions. The experiment took data from 2008 to 2012 in the CERN Neutrinos to Gran Sasso beam. The observation of the ν_{μ}→ν_{τ} appearance, achieved with four candidate events in a subsample of the data, was previously reported. In this Letter, a fifth ν_{τ} candidate event, found in an enlarged data sample, is described. Together with a further reduction of the expected background, the candidate events detected so far allow us to assess the discovery of ν_{μ}→ν_{τ} oscillations in appearance mode with a significance larger than 5σ.

We report on a direct search for sub-GeV dark photons (A') which might be produced in the reaction e^- Z \to e^- Z A' via kinetic mixing with photons by 100 GeV electrons incident on an active target in the NA64 experiment at the CERN SPS. The A's would decay invisibly into dark matter particles resulting in events with large missing energy. No evidence for such decays was found with 2.75\cdot 10^{9} electrons on target. We set new limits on the \gamma-A' mixing strength and exclude the invisible A' with a mass < 100 MeV as an explanation of the muon g_\mu-2 anomaly.

Results are reported from an improved measurement of ν_{μ}→ν_{e} transitions by the NOvA experiment. Using an exposure equivalent to 6.05×10^{20} protons on target, 33 ν_{e} candidates are observed with a background of 8.2±0.8 (syst.). Combined with the latest NOvA ν_{μ} disappearance data and external constraints from reactor experiments on sin^{2}2θ_{13}, the hypothesis of inverted mass hierarchy with θ_{23} in the lower octant is disfavored at greater than 93% C.L. for all values of δ_{CP}.

We report the first results on a direct search for a new 16.7 MeV boson (X) which could explain the anomalous excess of e^{+}e^{-} pairs observed in the excited ^{8}Be^{*} nucleus decays. Because of its coupling to electrons, the X could be produced in the bremsstrahlung reaction e^{-}Z→e^{-}ZX by a 100 GeV e^{-} beam incident on an active target in the NA64 experiment at the CERN Super Proton Synchrotron and observed through the subsequent decay into a e^{+}e^{-} pair. With 5.4×10^{10} electrons on target, no evidence for such decays was found, allowing us to set first limits on the X-e^{-} coupling in the range 1.3×10^{-4}≲ε_{e}≲4.2×10^{-4} excluding part of the allowed parameter space. We also set new bounds on the mixing strength of photons with dark photons (A^{'}) from nonobservation of the decay A^{'}→e^{+}e^{-} of the bremsstrahlung A^{'} with a mass ≲23 MeV.

A search is performed for a new sub-GeV vector boson ($A'$) mediated production of Dark Matter ($\chi$) in the fixed-target experiment, NA64, at the CERN SPS. The $A'$, called dark photon, could be generated in the reaction $ e^- Z \to e^- Z A'$ of 100 GeV electrons dumped against an active target which is followed by the prompt invisible decay $A' \to \chi \overline{\chi}$. The experimental signature of this process would be an event with an isolated electron and large missing energy in the detector. From the analysis of the data sample collected in 2016 corresponding to $4.3\times10^{10}$ electrons on target no evidence of such a process has been found. New stringent constraints on the $A'$ mixing strength with photons, $10^{-5}\lesssim \epsilon \lesssim 10^{-2}$, for the $A'$ mass range $m_{A'} \lesssim 1$ GeV are derived. For models considering scalar and fermionic thermal Dark Matter interacting with the visible sector through the vector portal the 90% C.L. limits $10^{-11}\lesssim y \lesssim 10^{-6}$ on the dark-matter parameter $y = \epsilon^2 \alpha_D (\frac{m_\chi}{m_{A'}})^4 $ are obtained for the dark coupling constant $\alpha_D = 0.5$ and dark-matter masses $0.001 \lesssim m_\chi \lesssim 0.5 $ GeV. The lower limits $\alpha_D \gtrsim 10^{-3} $ for pseudo-Dirac Dark Matter in the mass region $m_\chi \lesssim 0.05 $ GeV are more stringent than the corresponding bounds from beam dump experiments. The results are obtained by using tree level, exact calculations of the $A'$ production cross-sections, which turn out to be significantly smaller compared to the one obtained in the Weizs\"{a}cker-Williams approximation for the mass region $m_{A'} \gtrsim 0.1$ GeV.

Measurements of inclusive spectra and mean multiplicities of $$\pi ^\pm $$ , K $$^\pm $$ , p and $${\bar{\text {p}}}$$ produced in inelastic p + p interactions at incident projectile momenta of 20, 31, 40, 80 and 158 $$\text{ GeV }/c$$ ( $$\sqrt{s} = $$ 6.3, 7.7, 8.8, 12.3 and 17.3 $$\text{ GeV }$$ , respectively) were performed at the CERN Super Proton Synchrotron using the large acceptance NA61/SHINE hadron spectrometer. Spectra are presented as function of rapidity and transverse momentum and are compared to predictions of current models. The measurements serve as the baseline in the NA61/SHINE study of the properties of the onset of deconfinement and search for the critical point of strongly interacting matter.

We present experimental results on inclusive spectra and mean multiplicities of negatively charged pions produced in inelastic p+p interactions at incident projectile momenta of 20, 31, 40, 80 and 158 GeV/c ( $$\sqrt{s} = $$ 6.3, 7.7, 8.8, 12.3 and 17.3 GeV, respectively). The measurements were performed using the large acceptance NA61/SHINE hadron spectrometer at the CERN super proton synchrotron. Two-dimensional spectra are determined in terms of rapidity and transverse momentum. Their properties such as the width of rapidity distributions and the inverse slope parameter of transverse mass spectra are extracted and their collision energy dependences are presented. The results on inelastic p+p interactions are compared with the corresponding data on central Pb+Pb collisions measured by the NA49 experiment at the CERN SPS. The results presented in this paper are part of the NA61/SHINE ion program devoted to the study of the properties of the onset of deconfinement and search for the critical point of strongly interacting matter. They are required for interpretation of results on nucleus–nucleus and proton–nucleus collisions.

The $3.6\ensuremath{\sigma}$ discrepancy between the predicted and measured values of the anomalous magnetic moment of positive muons can be explained by the existence of a new dark boson ${Z}_{\ensuremath{\mu}}$ with a mass in the sub-GeV range, which is coupled predominantly to the second and third lepton generations through the ${L}_{\ensuremath{\mu}}\ensuremath{-}{L}_{\ensuremath{\tau}}$ current. After a discussion of the present phenomenological bounds on the ${Z}_{\ensuremath{\mu}}$ coupling, we show that if the ${Z}_{\ensuremath{\mu}}$ exists, it could be observed in the reaction $\ensuremath{\mu}+Z\ensuremath{\rightarrow}\ensuremath{\mu}+Z+{Z}_{\ensuremath{\mu}}$ of a muon scattering off nuclei by looking for an excess of events with large missing muon beam energy in a detector due to the prompt bremsstrahlung ${Z}_{\ensuremath{\mu}}$ decay ${Z}_{\ensuremath{\mu}}\ensuremath{\rightarrow}\ensuremath{\nu}\ensuremath{\nu}$ into a couple of neutrinos. We describe the experimental technique and the preliminary study of the feasibility for the proposed search. We show that this specific signal allows for a search for the ${Z}_{\ensuremath{\mu}}$ with a sensitivity in the coupling constant ${\ensuremath{\alpha}}_{\ensuremath{\mu}}\ensuremath{\gtrsim}1{0}^{\ensuremath{-}11}$, which is 3 orders of magnitude higher than the value required to explain the discrepancy. We point out that the availability of high-energy and -intensity muon beams at CERN SPS provides a unique opportunity to either discover or rule out the ${Z}_{\ensuremath{\mu}}$ in the proposed search in the near future. The experiment is based on the missing-energy approach developed for the searches for invisible decays of dark photons and (pseudo)scalar mesons at CERN and is complementary to these experiments.

Measurements of hadron production in p + C interactions at 31 GeV/c are performed using the NA61/SHINE spectrometer at the CERN SPS. The analysis is based on the full set of data collected in 2009 using a graphite target with a thickness of 4 % of a nuclear interaction length. Inelastic and production cross sections as well as spectra of $$\pi ^{\pm }$$ , $$K^{\pm }$$ , p, $$K^0_S$$ and $$\varLambda $$ are measured with high precision. These measurements are essential for improved calculations of the initial neutrino fluxes in the T2K long-baseline neutrino oscillation experiment in Japan. A comparison of the NA61/SHINE measurements with predictions of several hadroproduction models is presented.

This Letter reports new results on muon neutrino disappearance from NOvA, using a 14 kton detector equivalent exposure of $6.05\times10^{20}$ protons-on-target from the NuMI beam at the Fermi National Accelerator Laboratory. The measurement probes the muon-tau symmetry hypothesis that requires maximal mixing ($\theta_{23} = \pi/4$). Assuming the normal mass hierarchy, we find $\Delta m^2 = (2.67 \pm 0.11)\times 10^{-3}$ eV$^2$ and $\sin^2 \theta_{23}$ at the two statistically degenerate values $0.404^{+0.030}_{-0.022}$ and $0.624^{+0.022}_{-0.030}$, both at the 68% confidence level. Our data disfavor the maximal mixing scenario with 2.6 $\sigma$ significance.

The OPERA experiment is designed to search for ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ oscillations in appearance mode, i.e., through the direct observation of the $\ensuremath{\tau}$ lepton in ${\ensuremath{\nu}}_{\ensuremath{\tau}}$-charged current interactions. The experiment has taken data for five years, since 2008, with the CERN Neutrino to Gran Sasso beam. Previously, two ${\ensuremath{\nu}}_{\ensuremath{\tau}}$ candidates with a $\ensuremath{\tau}$ decaying into hadrons were observed in a subsample of data of the 2008--2011 runs. Here we report the observation of a third ${\ensuremath{\nu}}_{\ensuremath{\tau}}$ candidate in the ${\ensuremath{\tau}}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{\ensuremath{-}}$ decay channel coming from the analysis of a subsample of the 2012 run. Taking into account the estimated background, the absence of ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ oscillations is excluded at the $3.4\text{ }\ensuremath{\sigma}$ level.

The OPERA experiment was designed to study ν_{μ}→ν_{τ} oscillations in the appearance mode in the CERN to Gran Sasso Neutrino beam (CNGS). In this Letter, we report the final analysis of the full data sample collected between 2008 and 2012, corresponding to 17.97×10^{19} protons on target. Selection criteria looser than in previous analyses have produced ten ν_{τ} candidate events, thus reducing the statistical uncertainty in the measurement of the oscillation parameters and of ν_{τ} properties. A multivariate approach for event identification has been applied to the candidate events and the discovery of ν_{τ} appearance is confirmed with an improved significance level of 6.1σ. |Δm_{32}^{2}| has been measured, in appearance mode, with an accuracy of 20%. The measurement of the ν_{τ} charged-current cross section, for the first time with a negligible contamination from ν[over ¯]_{τ}, and the first direct evidence for the ν_{τ} lepton number are also reported.

The improved results on a direct search for a new $X(16.7\text{ }\text{ }\mathrm{MeV})$ boson that could explain the anomalous excess of ${e}^{+}{e}^{\ensuremath{-}}$ pairs observed in the decays of the excited $^{8}{\mathrm{Be}}^{*}$ nuclei (``Berillium or X17 anomaly'') are reported. Interestingly, new recent results in the nuclear transitions of another nucleus, $^{4}\mathrm{He}$, seems to support this anomaly spurring the need for an independent measurement. If the $X$ boson exists, it could be produced in the bremsstrahlung reaction ${e}^{\ensuremath{-}}Z\ensuremath{\rightarrow}{e}^{\ensuremath{-}}ZX$ by a high energy beam of electrons incident on the active target in the NA64 experiment at the CERN Super Proton Synchrotron and observed through its subsequent decay into ${e}^{+}{e}^{\ensuremath{-}}$ pairs. No evidence for such decays was found from the combined analysis of the data samples with total statistics corresponding to $8.4\ifmmode\times\else\texttimes\fi{}{10}^{10}$ electrons on target collected in 2017 and 2018. This allows one to set new limits on the $X\ensuremath{-}{e}^{\ensuremath{-}}$ coupling in the range $1.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\ensuremath{\lesssim}{\ensuremath{\epsilon}}_{e}\ensuremath{\lesssim}6.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$, excluding part of the parameter space favored by the X17 anomaly, and setting new bounds on the mixing strength of photons with dark photons (${A}^{\ensuremath{'}}$) with a mass $\ensuremath{\lesssim}24\text{ }\text{ }\mathrm{MeV}$. For the 2018 run, the setup was optimized to probe the region of parameter space characterized by a large coupling $\ensuremath{\epsilon}$. This allowed a significant improvement in sensitivity despite a relatively modest increase in statistics.

We carried out a model-independent search for light scalar (s) and pseudoscalar axionlike (a) particles that couple to two photons by using the high-energy CERN SPS H4 electron beam. The new particles, if they exist, could be produced through the Primakoff effect in interactions of hard bremsstrahlung photons generated by 100 GeV electrons in the NA64 active dump with virtual photons provided by the nuclei of the dump. The a(s) would penetrate the downstream HCAL module, serving as a shield, and would be observed either through their a(s)→γγ decay in the rest of the HCAL detector, or as events with a large missing energy if the a(s) decays downstream of the HCAL. This method allows for the probing of the a(s) parameter space, including those from generic axion models, inaccessible to previous experiments. No evidence of such processes has been found from the analysis of the data corresponding to 2.84×10^{11} electrons on target, allowing us to set new limits on the a(s)γγ-coupling strength for a(s) masses below 55 MeV.

Abstract Antihydrogen atoms with K or sub-K temperature are a powerful tool to precisely probe the validity of fundamental physics laws and the design of highly sensitive experiments needs antihydrogen with controllable and well defined conditions. We present here experimental results on the production of antihydrogen in a pulsed mode in which the time when 90% of the atoms are produced is known with an uncertainty of ~250 ns. The pulsed source is generated by the charge-exchange reaction between Rydberg positronium atoms—produced via the injection of a pulsed positron beam into a nanochanneled Si target, and excited by laser pulses—and antiprotons, trapped, cooled and manipulated in electromagnetic traps. The pulsed production enables the control of the antihydrogen temperature, the tunability of the Rydberg states, their de-excitation by pulsed lasers and the manipulation through electric field gradients. The production of pulsed antihydrogen is a major landmark in the AE $$\bar{g}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>ḡ</mml:mi> </mml:math> IS experiment to perform direct measurements of the validity of the Weak Equivalence Principle for antimatter.

The Baksan Experiment on Sterile Transitions (BEST) probes the gallium anomaly and its possible connections to oscillations between active and sterile neutrinos. Based on the Gallium-Germanium Neutrino Telescope (GGNT) technology of the SAGE experiment, BEST employs two zones of liquid Ga target to explore neutrino oscillations on the meter scale. Oscillations on this short scale could produce deficits in the 71Ge production rates within the two zones, as well as a possible rate difference between the zones. From July 5th to October 13th 2019, the two-zone target was exposed to a primarily monoenergetic, 3.4-MCi 51Cr neutrino source 10 times for a total of 20 independent 71Ge extractions from the two Ga targets. The 71Ge production rates from the neutrino source were measured from July 2019 to March 2020. At the end of these measurements, the counters were filled with 71Ge doped gas and calibrated during November 2020. In this paper, results from the BEST sterile neutrino oscillation experiment are presented in details. The ratio of the measured 71Ge production rates to the predicted rates for the inner and the outer target volumes are calculated from the known neutrino capture cross section. Comparable deficits in the measured ratios relative to predicted values are found for both zones, with the 4σ deviations from unity consistent with the previously reported gallium anomaly. If interpreted in the context of neutrino oscillations, the deficits give best-fit oscillation parameters of Δm2=3.3+∞−2.3eV2 and sin22θ=0.42+0.15−0.17, consistent with νe→νs oscillations governed by a surprisingly large mixing angle.7 MoreReceived 18 January 2022Accepted 12 May 2022DOI:https://doi.org/10.1103/PhysRevC.105.065502©2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasExtensions of fermion sectorHypothetical particle physics modelsNeutrino oscillationsPhysical SystemsSterile neutrinosNuclear PhysicsParticles & Fields

We report the total and differential cross sections for $J/\psi$ photoproduction with the large acceptance GlueX spectrometer for photon beam energies from the threshold at 8.2~GeV up to 11.44~GeV and over the full kinematic range of momentum transfer squared, $t$. Such coverage facilitates the extrapolation of the differential cross sections to the forward ($t = 0$) point beyond the physical region. The forward cross section is used by many theoretical models and plays an important role in understanding $J/\psi$ photoproduction and its relation to the $J/\psi-$proton interaction. These measurements of $J/\psi$ photoproduction near threshold are also crucial inputs to theoretical models that are used to study important aspects of the gluon structure of the proton, such as the gluon Generalized Parton Distribution (GPD) of the proton, the mass radius of the proton, and the trace anomaly contribution to the proton mass. We observe possible structures in the total cross section energy dependence and find evidence for contributions beyond gluon exchange in the differential cross section close to threshold, both of which are consistent with contributions from open-charm intermediate states.

We report the result from a search for charged-current coherent pion production induced by muon neutrinos with a mean energy of 1.3 GeV. The data are collected with a fully active scintillator detector in the K2K long-baseline neutrino oscillation experiment. No evidence for coherent pion production is observed, and an upper limit of is set on the cross section ratio of coherent pion production to the total charged-current interaction at 90% confidence level. This is the first experimental limit for coherent charged pion production in the energy region of a few GeV.

The AEGIS experiment, currently being set up at the Antiproton Decelerator at CERN, has the objective of studying the free fall of antimatter in the Earth's gravitational field by means of a pulsed cold atomic beam of antihydrogen atoms. Both duration of free fall and vertical displacement of the horizontally emitted atoms will be measured, allowing a first test of the WEP with antimatter.

The MultiPurpose Detector (MPD) is designed to study heavy-ion collisions at the Nuclotron-based heavy Ion Collider fAcility (NICA) at JINR, Dubna. Its main components located inside a superconducting solenoid are a tracking system composed of a silicon microstrip vertex detector followed by a large volume time-projection chamber, a time-of-flight system for particle identification and a barrel electromagnetic calorimeter. A zero degree hadron calorimeter is designed specifically to measure the energy of spectators. In this paper, all parts of the apparatus are described and their tracking and particle identification (PID) parameters are discussed in some detail.

Spectra of positively charged kaons in $p+\text{C}$ interactions at 31 GeV/$c$ were measured with the NA61/SHINE spectrometer at the CERN SPS. The analysis is based on the full set of data collected in 2007 with a graphite target with a thickness of 4$%$ of a nuclear interaction length. Interaction cross sections and charged pion spectra were already measured using the same set of data. These new measurements in combination with the published ones are required to improve predictions of the neutrino flux for the T2K long-baseline neutrino oscillation experiment in Japan. In particular, the knowledge of kaon production is crucial for precisely predicting the intrinsic electron neutrino component and the high-energy tail of the T2K beam. The results are presented as a function of laboratory momentum in two intervals of the laboratory polar angle covering the range from 20 to 240 mrad. The kaon spectra are compared with predictions of several hadron production models. Using the published pion results and the new kaon data, the ${K}^{+}$/${\ensuremath{\pi}}^{+}$ ratios are computed.

High precision measurements of the differential cross sections for π0 photoproduction at forward angles for two nuclei, 12C and 208Pb, have been performed for incident photon energies of 4.9-5.5 GeV to extract the π0→γγ decay width. The experiment was done at Jefferson Lab using the Hall B photon tagger and a high-resolution multichannel calorimeter. The π0→γγ decay width was extracted by fitting the measured cross sections using recently updated theoretical models for the process. The resulting value for the decay width is Γ(π0→γγ)=7.82±0.14(stat)±0.17(syst) eV. With the 2.8% total uncertainty, this result is a factor of 2.5 more precise than the current Particle Data Group average of this fundamental quantity, and it is consistent with current theoretical predictions.

The precise measurement of forces is one way to obtain deep insight into the fundamental interactions present in nature. In the context of neutral antimatter, the gravitational interaction is of high interest, potentially revealing new forces that violate the weak equivalence principle. Here we report on a successful extension of a tool from atom optics--the moiré deflectometer--for a measurement of the acceleration of slow antiprotons. The setup consists of two identical transmission gratings and a spatially resolving emulsion detector for antiproton annihilations. Absolute referencing of the observed antimatter pattern with a photon pattern experiencing no deflection allows the direct inference of forces present. The concept is also straightforwardly applicable to antihydrogen measurements as pursued by the AEgIS collaboration. The combination of these very different techniques from high energy and atomic physics opens a very promising route to the direct detection of the gravitational acceleration of neutral antimatter.

A new method of momentum measurement of charged particles through multiple Coulomb scattering (MCS) in the OPERA lead-emulsion target is presented. It is based on precise measurements of track angular deviations carried out thanks to the very high resolution of nuclear emulsions. The algorithm has been tested with Monte Carlo pions. The results are found to describe within the expected uncertainties the data obtained from test beams. We also present a comparison of muon momenta evaluated through MCS in the OPERA lead-emulsion target with those determined by the electronic detectors for neutrino-charged current interaction events. The two independent measurements agree within the experimental uncertainties, and the results validate the algorithm developed for the emulsion detector of OPERA.

We demonstrate the laser excitation of the n = 3 state of positronium (Ps) in vacuum.A combination of a specially designed pulsed slow positron beam and a high-efficiency converter target was used to produce Ps.Its annihilation was recorded by single-shot positronium annihilation lifetime spectroscopy.Pulsed laser excitation of the n = 3 level at a wavelength λ ≈ 205 nm was monitored via Ps photoionization induced by a second intense laser pulse at λ = 1064 nm.About 15% of the overall positronium emitted into vacuum was excited to n = 3 and photoionized.Saturation of both the n = 3 excitation and the following photoionization was observed and explained by a simple rate equation model.The positronium's transverse temperature was extracted by measuring 2469

We report measurements of the photon beam asymmetry $\mathrm{\ensuremath{\Sigma}}$ for the reactions $\stackrel{P\vec}{\ensuremath{\gamma}}p\ensuremath{\rightarrow}p{\ensuremath{\pi}}^{0}$ and $\stackrel{P\vec}{\ensuremath{\gamma}}p\ensuremath{\rightarrow}p\ensuremath{\eta}$ from the GlueX experiment using a 9 GeV linearly polarized, tagged photon beam incident on a liquid hydrogen target in Jefferson Lab's Hall D. The asymmetries, measured as a function of the proton momentum transfer, possess greater precision than previous ${\ensuremath{\pi}}^{0}$ measurements and are the first $\ensuremath{\eta}$ measurements in this energy regime. The results are compared with theoretical predictions based on $t$-channel, quasiparticle exchange and constrain the axial-vector component of the neutral meson production mechanism in these models.

The current most stringent constraints for the existence of sub-GeV dark matter coupling to Standard Model via a massive vector boson A′ were set by the NA64 experiment for the mass region mA′≲250 MeV, by analyzing data from the interaction of 2.84×1011 100-GeV electrons with an active thick target and searching for missing-energy events. In this work, by including A′ production via secondary positron annihilation with atomic electrons, we extend these limits in the 200–300 MeV region by almost an order of magnitude, touching for the first time the dark matter relic density constrained parameter combinations. Our new results demonstrate the power of the resonant annihilation process in missing energy dark-matter searches, paving the road to future dedicated e+ beam efforts.Received 16 August 2021Accepted 15 October 2021DOI:https://doi.org/10.1103/PhysRevD.104.L091701Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDark matterExtensions of gauge sectorParticle dark matterPhysical SystemsPositronsTechniquesElectromagnetic calorimetersParticle productionParticles & Fields

The OPERA neutrino detector at the underground Gran Sasso Laboratory (LNGS) was designed to perform the first detection of neutrino oscillations in appearance mode, through the study of nu_mu to nu_tau oscillations. The apparatus consists of a lead/emulsion-film target complemented by electronic detectors. It is placed in the high-energy, long-baseline CERN to LNGS beam (CNGS) 730 km away from the neutrino source. In August 2006 a first run with CNGS neutrinos was successfully conducted. A first sample of neutrino events was collected, statistically consistent with the integrated beam intensity. After a brief description of the beam and of the various sub-detectors, we report on the achievement of this milestone, presenting the first data and some analysis results.

We report the first observation of a charm-strange meson D(+)(sJ)(2632) at a mass of 2632.5+/-1.7 MeV/c(2) in data from SELEX, the charm hadro-production experiment E781 at Fermilab. This state is seen in two decay modes, D(+)(s)eta and D0K+. In the D(+)(s)eta decay mode we observe a peak with 101 events over a combinatoric background of 54.9 events at a mass of 2635.4+/-3.3 MeV/c(2). There is a corresponding peak of 21 events over a background of 6.9 at 2631.5+/-2.0 MeV/c(2) in the decay mode D0K+. The decay width of this state is <17 MeV/c(2) at 90% confidence level. The relative branching ratio Gamma(D0K+)/Gamma(D(+)(s)eta) is 0.14+/-0.06. The mechanism that keeps this state narrow is unclear. Its decay pattern is also unusual, being dominated by the D(+)(s)eta decay mode.

Using the ARGUS detector at the e+e− storage ring DORIS II, we have observed the decay τ−→π−π−π−π+π+ντ in tau-pair events produced at center-or-mass energies between 9.4 and 10.6 GeV. From the 5π invariant mass distribution we derive an upper limit of m(ντ)<35 MeV/c2 at the 95% confidence level. The branching ratio for this decay channel is found to be (0.064±0.023±0.01)%.

B mesons have been reconstructed in five decay channels of the type B→D∗±nπ(n=1,2,3) using data accumulated by the ARGUS experiment at the e+e− storage ring DORIS II at DESY. In total, we find 40 neutral B mesons above a background of 15±6 events with a mass of (5278.2±1.0±3.0) MeV/c2 and 32 charged B mesons above a background of 17±6 events with a mass of (5275.8±1.3±3.0) MeV/c2. The decays B0D∗+π−π0, B0D∗+π−π−π+, and B−→D∗+π−π−π0 have been observed for the first time. We find substantially smaller branching ratios for the decay modes B0→D∗+π− and B−→D∗+π−π− than previously published by the CLEO collaboration.

The reaction e+e− → ϒ′ → ϒπ+π−, with ϒ → anything, has been measured using the ARGUS detector at DORIS . We obtain a mass difference M(ϒ′) − M(ϒ) = (562 ± 3) MeV and a decay branching ratio BR(ϒ′→ϒπ+π−)=(17.9±0.9±2.1)%. The invariant mass spectrum of the π+π− system differs from phase space, but is well described by a matrix element of the form (Mππ2−λMπ2) with λ=2.6±0.5. We also report preliminary results on the exclusive decay ϒ′ → ϒπ+π−, with ϒ → e+e−, and obtain BR(ϒ → e+e−) = (2.8 ± 0.4 ± 04±0.3)%.

A bstract A first result of the search for ν μ → ν e oscillations in the OPERA experiment, located at the Gran Sasso Underground Laboratory, is presented. The experiment looked for the appearance of ν e in the CNGS neutrino beam using the data collected in 2008 and 2009. Data are compatible with the non-oscillation hypothesis in the three-flavour mixing model. A further analysis of the same data constrains the non-standard oscillation parameters θ new and $ \varDelta m_{\mathrm{new}}^2 $ suggested by the LSND and MiniBooNE experiments. For large $ \varDelta m_{\mathrm{new}}^2 $ values ( &gt; 0.1 eV 2 ), the OPERA 90% C.L. upper limit on sin 2 (2 θ new ) based on a Bayesian statistical method reaches the value 7 . 2 × 10 −3 .

A bstract The OPERA neutrino experiment is designed to perform the first observation of neutrino oscillations in direct appearance mode in the ν μ → ν τ channel, via the detection of the τ -leptons created in charged current ν τ interactions. The detector, located in the underground Gran Sasso Laboratory, consists of an emulsion/lead target with an average mass of about 1.2 kt, complemented by electronic detectors. It is exposed to the CERN Neutrinos to Gran Sasso beam, with a baseline of 730 km and a mean energy of 17 GeV. The observation of the first ν τ candidate event and the analysis of the 2008-2009 neutrino sample have been reported in previous publications. This work describes substantial improvements in the analysis and in the evaluation of the detection efficiencies and backgrounds using new simulation tools. The analysis is extended to a sub-sample of 2010 and 2011 data, resulting from an electronic detector-based pre-selection, in which an additional ν τ candidate has been observed. The significance of the two events in terms of a ν μ → ν τ oscillation signal is of 2.40 σ .

We report results from the first search for sterile neutrinos mixing with active neutrinos through a reduction in the rate of neutral-current interactions over a baseline of 810\,km between the NOvA detectors. Analyzing a 14-kton detector equivalent exposure of 6.05$\times$10$^{20}$ protons-on-target in the NuMI beam at Fermilab, we observe 95 neutral-current candidates at the Far Detector compared with $83.5 \pm 9.7 \mbox{(stat.)} \pm 9.4 \mbox{(syst.)}$ events predicted assuming mixing only occurs between active neutrino species. No evidence for $\nu_{\mu} \rightarrow \nu_{s}$ transitions is found. Interpreting these results within a 3+1 model, we place constraints on the mixing angles $\theta_{24}<20.8^{\circ}$ and $\theta_{34}<31.2^{\circ}$ at the 90% C.L. for $0.05~eV^2\leq \Delta m^2_{41}\leq 0.5~eV^2$, the range of mass splittings that produce no significant oscillations over the Near Detector baseline.

The NICA (Nuclotron-based Ion Collider fAcility) project is under realization at the Joint Institute for Nuclear Research (JINR, Dubna). The main goal of the project is a study of hot and dense strongly interacting matter in heavy ion collisions (up to Au) in the energy range up to sNN=11 GeV. Two modes of operation are foreseen, collider and extracted beam operations, with two detectors: MPD and [email protected] In the Au + Au collider mode the expected average luminosity is L=1027cm−2s−1. The proposed experimental program allows one to search for possible manifestations of the phase transitions and critical phenomena.

We performed a search for a new generic $X$ boson, which could be a scalar ($S$), pseudoscalar ($P$), vector ($V$) or an axial vector ($A$) particle produced in the 100 GeV electron scattering off nuclei, $e^- Z \to e^- Z X$, followed by its invisible decay in the NA64 experiment at CERN. No evidence for such process was found in the full NA64 data set of $2.84\times 10^{11}$ electrons on target. We place new bounds on the $S, P, V, A$ coupling strengths to electrons, and set constraints on their contributions to the electron anomalous magnetic moment $a_e$, $|\Delta a_{X}| \lesssim 10^{-15} - 10^{-13}$ for the $X$ mass region $m_X\lesssim 1$ GeV. These results are an order of magnitude more sensitive compared to the current accuracy on $a_e$ from the electron $g-2$ experiments and recent high-precision determination of the fine structure constant.

A search for a new Z^{'} gauge boson associated with (un)broken B-L symmetry in the keV-GeV mass range is carried out for the first time using the missing-energy technique in the NA64 experiment at the CERN SPS. From the analysis of the data with 3.22×10^{11} electrons on target collected during 2016-2021 runs, no signal events were found. This allows us to derive new constraints on the Z^{'}-e coupling strength, which, for the mass range 0.3≲m_{Z^{'}}≲100 MeV, are more stringent compared to those obtained from the neutrino-electron scattering data.

Using the ARGUS detector at the e+e− storage ring DORIS II at DESY we have investigated the decays B0→D∗−e+v and B0→D∗−μ+ν. The B0 mesons were produced in 39600 ϒ(4S)→B0B0 decays. Assuming electron-muon universality we obtain a branching ratio BR(B0→D∗−e+v)=BR(B0→D∗−γm+ν)=(7.0±1.2±1.9)%.

Using the ARGUS detector at the e+e− storage ring DORIS II, we have observed charmless decays of B mesons into the final states pp̄π± and pp̄π+π−. The significance of the signal corresponds to more than five standard deviations. The branching ratios are (5.2±1.4±1.9)×10−4 for the three-body and (6.0±2.0±2.2)×10−4 for the four-body final state. These decays cannot proceed via the dominant b→c transitions, and we show that they are not the result of penguin-type processes. Thus, the observed decays must represent b→u quark transitions. Consequently, the Kobayashi-Maskawa matrix element Vub is non-zero.

Using the ARGUS detector at DORIS II, we have analyzed tau decays into π−π−π+π0ντ. The branching ratio was determined to be (4.2±0.5±0.9)%. From a study of the three pion sub-system, we find evidence for the decay τ−→ωπ−ντ with a branching ratio of (1.5±0.3±0.3)%. The ωπ− system is found to be predominantly in a JP=1− state. There is no evidence for second-class axial-vector currents. The spectral function for the ωπ− final state is in agreement with a prediction based on CVC and σe+e−→ωπ0.

The SU c (3) ⊗ SU L (2) ⊗ SU R (2) ⊗ U(1) left-right (LR) symmetric model explains the origin of the parity violation in weak interactions and predicts the existence of additional gauge bosons W R and Z′. In addition, heavy right-handed Majorana neutrino states N arise naturally within the LR symmetric model. The states N could be partners of light neutrino states, related to their nonzero masses through the seesaw mechanism. This makes the searches for W R , Z′, and N interesting and important. In the framework of the minimal LR model, we study the possibility to observe signals from N and W R production in pp collisions after three years of running at low LHC luminosity. We show that their decay signals can be identified with a small background, especially in the case of same-sign leptons in the final state. For the integral LHC luminosity of L t = 30 fb−1, the 5σ discovery of W R boson and heavy Majorana neutrinos N e with masses $$M_{W_R } $$ up to 4 TeV and $$M_{N_e } $$ up to 2.4 TeV, respectively, is found to be possible.

This chapter of the "Flavor in the era of LHC" workshop report discusses flavor-related issues in the production and decays of heavy states at the LHC at high momentum transfer Q, both from the experimental and the theoretical perspective. We review top quark physics, and discuss the flavor aspects of several extensions of the standard model, such as supersymmetry, little Higgs models or models with extra dimensions. This includes discovery aspects, as well as the measurement of several properties of these heavy states. We also present publicly available computational tools related to this topic.

The OPERA experiment is based on a hybrid technology combining electronic detectors and nuclear emulsions. OPERA collected muon-neutrino interactions during the 2008 and 2009 physics runs of the CNGS neutrino beam, produced at CERN with an energy range of about 5-35 GeV. A total of $5.3 \times 10^{19}$ protons on target equivalent luminosity has been analysed with the OPERA electronic detectors: scintillator strips target trackers and magnetic muon spectrometers equipped with resistive plate gas chambers and drift tubes, allowing a detailed reconstruction of muon-neutrino interactions. Charged Current (CC) and Neutral Current (NC) interactions are identified, using the measurements in the electronic detectors, and the NC/CC ratio is computed. The momentum distribution and the charge of the muon tracks produced in CC interactions are analysed. Calorimetric measurements of the visible energy are performed for both the CC and NC samples. For CC events the Bjorken-$y$ distribution and the hadronic shower profile are computed. The results are compared to a detailed Monte Carlo simulation of the electronic detectors' response.

The main goal of the AEgIS experiment at CERN is to test the weak equivalence principle for antimatter. We will measure the Earth's gravitational acceleration g¯ with antihydrogen atoms being launched in a horizontal vacuum tube and traversing a moiré deflectometer. We intend to use a position sensitive device made of nuclear emulsions (combined with a time-of-flight detector such as silicon μ-strips) to measure precisely their annihilation points at the end of the tube. The goal is to determine g¯ with a 1% relative accuracy. In 2012 we tested emulsion films in vacuum and at room temperature with low energy antiprotons from the CERN antiproton decelerator. First results on the expected performance for AEgIS are presented.

Measurements of multiplicity and transverse momentum fluctuations of charged particles were performed in inelastic p+p interactions at 20, 31, 40, 80, and 158 $$\text{ GeV }\!/\!c$$ beam momentum. Results for the scaled variance of the multiplicity distribution and for three strongly intensive measures of multiplicity and transverse momentum fluctuations $$\varDelta [P_{T},N]$$ , $$\varSigma [P_{T},N]$$ and $$\varPhi _{p_T}$$ are presented. For the first time the results on fluctuations are fully corrected for experimental biases. The results on multiplicity and transverse momentum fluctuations significantly deviate from expectations for the independent particle production. They also depend on charges of selected hadrons. The string-resonance Monte Carlo models Epos and Urqmd do not describe the data. The scaled variance of multiplicity fluctuations is significantly higher in inelastic p+p interactions than in central Pb+Pb collisions measured by NA49 at the same energy per nucleon. This is in qualitative disagreement with the predictions of the Wounded Nucleon Model. Within the statistical framework the enhanced multiplicity fluctuations in inelastic p+p interactions can be interpreted as due to event-by-event fluctuations of the fireball energy and/or volume.

The T2K off-axis near detector, ND280, is used to make the first differential cross section measurements of muon neutrino charged current single positive pion production on a water target at energies $\ensuremath{\sim}0.8\text{ }\text{ }\mathrm{GeV}$. The differential measurements are presented as a function of the muon and pion kinematics, in the restricted phase space defined by ${p}_{{\ensuremath{\pi}}^{+}}&gt;200\text{ }\text{ }\mathrm{MeV}/c$, ${p}_{\ensuremath{\mu}}&gt;200\text{ }\text{ }\mathrm{MeV}/c$, $\mathrm{cos}({\ensuremath{\theta}}_{{\ensuremath{\pi}}^{+}})&gt;0.3$ and $\mathrm{cos}({\ensuremath{\theta}}_{\ensuremath{\mu}})&gt;0.3$. The total flux integrated ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ charged current single positive pion production cross section on water in the restricted phase space is measured to be $⟨\ensuremath{\sigma}{⟩}_{\ensuremath{\phi}}=4.25\ifmmode\pm\else\textpm\fi{}0.48(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}1.56(\mathrm{syst})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}40}\text{ }\text{ }{\mathrm{cm}}^{2}/\text{nucleon}$. The total cross section is consistent with the NEUT prediction ($5.03\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}40}\text{ }\text{ }{\mathrm{cm}}^{2}/\text{nucleon}$) and $2\ensuremath{\sigma}$ lower than the GENIE prediction ($7.68\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}40}\text{ }\text{ }{\mathrm{cm}}^{2}/\text{nucleon}$). The differential cross sections are in good agreement with the NEUT generator. The GENIE simulation reproduces well the shapes of the distributions, but overestimates the overall cross section normalization.

We describe a system designed to re-bunch positron pulses delivered by an accumulator supplied by a positron source and a Surko-trap. Positron pulses from the accumulator are magnetically guided in a 0.085 T field and are injected into a region free of magnetic fields through a μ-metal field terminator. Here positrons are temporally compressed, electrostatically guided and accelerated towards a porous silicon target for the production and emission of positronium into vacuum. Positrons are focused in a spot of less than 4 mm FWTM in bunches of ∼8 ns FWHM. Emission of positronium into the vacuum is shown by single shot positron annihilation lifetime spectroscopy.

The project NICA (Nuclotron-based Ion Collider fAcility) is aimed to study hot and baryon rich QCD matter in heavy ion collisions in the energy range up to sNN=11GeV. The heavy ion program includes a study of collective phenomena, dilepton, hyperon and hypernuclei production under extreme conditions of highest baryonic density. This program will be performed at a fixed target experiment [email protected] and with MPD detector at the NICA collider.

Thermal dark matter models with particle χ masses below the electroweak scale can provide an explanation for the observed relic dark matter density. This would imply the existence of a new feeble interaction between the dark and ordinary matter. We report on a new search for the sub-GeV χ production through the interaction mediated by a new vector boson, called the dark photon A^{'}, in collisions of 100 GeV electrons with the active target of the NA64 experiment at the CERN SPS. With 9.37×10^{11} electrons on target collected during 2016-2022 runs NA64 probes for the first time the well-motivated region of parameter space of benchmark thermal scalar and fermionic dark matter models. No evidence for dark matter production has been found. This allows us to set the most sensitive limits on the A^{'} couplings to photons for masses m_{A^{'}}≲0.35 GeV, and to exclude scalar and Majorana dark matter with the χ-A^{'} coupling α_{D}≤0.1 for masses 0.001≲m_{χ}≲0.1 GeV and 3m_{χ}≤m_{A^{'}}.

Using the ARGUS detector at the e +e− storage ring DORIS II, we have studied the colour-suppressed decays B→Jψ X and B→ψ′ X. We find the inclusive branching ratios for these two channels to be (1.07±0.16±0.19) % and (0.46±0.17±0.11) %, respectively. From a sample of reconstructed exclusive events the masses of the B0 and B+ mesons are determined to be (5279.5±1.6±3.0) MeVc2 and (5278.5±1.8±3.0) MeVc2, respectively. Branching ratios are determined from five events of the type B0→Jψ K∗0 and three of B+→J/ψ K+. In the same data sample a search for B0→e+e−, μ+μ− and μ±e∓ leads to upper limits for such decays.

Using the ARGUS detector at DORIS we have observed the prediction of the charged D∗ meson in e+e− annihilation at a center of mass energy of 10 GeV. The D∗ fragmentation function has been measured using the decay channels D∗+ → D0π+ and D0 → K−π+ and K−π+π+π−. We find σ·Br for the channels D0 → K−π+ and D0 → K−π+π+π− to be (23.6 ± 2.2 ± 4.7) pb and (51.0 ± 4.6 ± 15.5) pb respectively, and the ratio of branching ratios Br(D0 → K−π+π+π−)/Br(D0 → K−π+) = 2.17 ± 0.28 ± 0.23. In addition we measure the mass difference M(D∗+) − M(D0) to be (145.46 ± 0.07 ± 0.03) MeV, and set an upper limit for D0 − D̄0 mixing of 0.11.

Using the ARGUS detector at DORIS II, we have observed a signal of 36.7±8.0 events in the decay channel D0→Ks0φ. In the same data sample, we have observed the well established decay D0→Ks0π+π−, and find the ratio, Br(D)0→Ks0φ)Br(D)0→Ks0π+π−), to be 0.186±0.052. The substantial value of (0.99±0.32±0.17)% then derived for the branching ratio for D0→K0φ gives direct evidence that W exchange contributes D0 decay.

The main goal of the AEgIS experiment at CERN is to test the weak equivalence principle for antimatter. AEgIS will measure the free-fall of an antihydrogen beam traversing a moir&apos;e deflectometer. The goal is to determine the gravitational acceleration with an initial relative accuracy of 1% by using an emulsion detector combined with a silicon μ-strip detector to measure the time of flight. Nuclear emulsions can measure the annihilation vertex of antihydrogen atoms with a precision of ∼ 1–2 μm r.m.s. We present here results for emulsion detectors operated in vacuum using low energy antiprotons from the CERN antiproton decelerator. We compare with Monte Carlo simulations, and discuss the impact on the AEgIS project.

The OPERA experiment, designed to perform the first observation of $$\nu _\mu \rightarrow \nu _\tau $$ oscillations in appearance mode through the detection of the $$\tau $$ leptons produced in $$\nu _\tau $$ charged current interactions, has collected data from 2008 to 2012. In the present paper, the procedure developed to detect $$\tau $$ particle decays, occurring over distances of the order of $$1~\mathrm{mm}$$ from the neutrino interaction point, is described in detail and applied to the search for charmed hadrons, showing similar decay topologies as the $$\tau $$ lepton. In the analysed sample, 50 charm decay candidate events are observed while $$54\pm 4$$ are expected, proving that the detector performance and the analysis chain applied to neutrino events are well reproduced by the OPERA simulation and thus validating the methods for $$\nu _\tau $$ appearance detection.

The problem of the asymptotic behaviour of high-energy elastic and inelastic amplitudes is studied by means of the functional methods of quantum field theory. The straight-line paths approximation (SLPA), making it possible to effectively calculate the functional integrals which arise, is formulated.

Measurements of the $$\pi ^\pm $$ , $$K^\pm $$ , and proton double differential yields emitted from the surface of the 90- $$\hbox {cm}$$ -long carbon target (T2K replica) were performed for the incoming $$31\,$$ $$\hbox {GeV}\!/\!c$$ protons with the NA61/SHINE spectrometer at the CERN SPS using data collected during 2010 run. The double differential $$\pi ^\pm $$ yields were measured with increased precision compared to the previously published NA61/SHINE results, while the $$K^\pm $$ and proton yields were obtained for the first time. A strategy for dealing with the dependence of the results on the incoming proton beam profile is proposed. The purpose of these measurements is to reduce significantly the (anti)neutrino flux uncertainty in the T2K long-baseline neutrino experiment by constraining the production of (anti)neutrino ancestors coming from the T2K target.

Measurements of particle emission from a replica of the T2K 90 cm-long carbon target were performed in the NA61/SHINE experiment at CERN SPS, using data collected during a high-statistics run in 2009. An efficient use of the long-target measurements for neutrino flux predictions in T2K requires dedicated reconstruction and analysis techniques. Fully-corrected differential yields of $$\pi ^\pm $$ -mesons from the surface of the T2K replica target for incoming 31 GeV/c protons are presented. A possible strategy to implement these results into the T2K neutrino beam predictions is discussed and the propagation of the uncertainties of these results to the final neutrino flux is performed.

The NA64 experiment consists of two detectors which are planned to be located at the electron (NA64e) and muon (NA64μ) beams of the CERN SPS and start operation after the LHC long-stop 2 in 2021. Its main goals include searches for dark sector physics—particularly light dark matter (LDM), visible and invisible decays of dark photons ( $$A{\kern 1pt} '$$ ), and new light particles that could explain the 8Be and $${{g}_{\mu }} - 2$$ anomalies. Here we review these physics goals, the current status of NA64 including recent results and perspectives of further searches, as well as other ongoing or planned experiments in this field. The main theoretical results on LDM, the problem of the origin of the $$\gamma {\text{ - }}A{\kern 1pt} '$$ mixing term and its connection to loop corrections, possible existence of a new light $$Z{\kern 1pt} '$$ coupled to $${{L}_{\mu }} - {{L}_{\tau }}$$ current are also discussed.

The explicit breaking of the axial symmetry by quantum fluctuations gives rise to the so-called axial anomaly. This phenomenon is solely responsible for the decay of the neutral pion π0 into two photons (γγ), leading to its unusually short lifetime. We precisely measured the decay width Γ of the [Formula: see text] process. The differential cross sections for π0 photoproduction at forward angles were measured on two targets, carbon-12 and silicon-28, yielding [Formula: see text], where stat. denotes the statistical uncertainty and syst. the systematic uncertainty. We combined the results of this and an earlier experiment to generate a weighted average of [Formula: see text] Our final result has a total uncertainty of 1.50% and confirms the prediction based on the chiral anomaly in quantum chromodynamics.

We present a search for axionlike particles, $a$, produced in photon-proton collisions at a center-of-mass energy of approximately 4 GeV, focusing on the scenario where the $a$-gluon coupling is dominant. The search uses $a\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$ and $a\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ decays, and a data sample corresponding to an integrated luminosity of $168\text{ }\text{ }{\mathrm{pb}}^{\ensuremath{-}1}$ collected with the GlueX detector. The search for $a\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$ decays is performed in the mass range of $180&lt;{m}_{a}&lt;480\text{ }\text{ }\mathrm{MeV}$, while the search for $a\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ decays explores the $600&lt;{m}_{a}&lt;720\text{ }\text{ }\mathrm{MeV}$ region. No evidence for a signal is found, and 90% confidence-level exclusion limits are placed on the $a$-gluon coupling strength. These constraints are the most stringent to date over much of the mass ranges considered.

The Sigma^- mean squared charge radius has been measured in the space-like Q^2 range 0.035-0.105 GeV^2/c^2 by elastic scattering of a Sigma^- beam off atomic electrons. The measurement was performed with the SELEX (E781) spectrometer using the Fermilab hyperon beam at a mean energy of 610 GeV/c. We obtain <r^2> = (0.61 +/- 0.12 (stat.) +/- 0.09 (syst.)) fm^2. The proton and pi^- charge radii were measured as well and are consistent with results of other experiments. Our result agrees with the recently measured strong interaction radius of the Sigma^-.

Using the ARGUS detector at DORIS II, we have studied the production of the charmed baryon Λc in e+e− annihilation at centre-of-mass energies near 10 GeV. The Λc+ was seen in the three decay modes pK−π+, Λπ+π−π+ and K̄0p, with products of normalized cross section times branching ratio [R·Br] of (10.8±1.4±1.2)×10−3, 6.6±1.5±0.9)×10−3 and (6.7±1.4±0.8)×10−3 respectively. The measured mass for the Λc was (2283.1±1.7±2.0) MeV/c2. A limit on the decay rates to Λπ+ is reported. The fragmentation function of the Λc was measured.

We performed an improved search for ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{e}$ oscillation with the KEK to Kamioka (K2K) long-baseline neutrino oscillation experiment, using the full data sample of $9.2\ifmmode\times\else\texttimes\fi{}{10}^{19}$ protons on target. No evidence for a ${\ensuremath{\nu}}_{e}$ appearance signal was found, and we set bounds on the ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{e}$ oscillation parameters. At $\ensuremath{\Delta}{m}^{2}=2.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\text{ }\text{ }{\mathrm{eV}}^{2}$, the best-fit value of the K2K ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ disappearance analysis, we set an upper limit of ${sin}^{2}2{\ensuremath{\theta}}_{\ensuremath{\mu}e}&lt;0.13$ at a 90% confidence level.

Using the ARGUS detector at the e+e− storage ring DORIS II, we have measured the vτ energy spectrum in the decay π+π−π±vτ of τ leptons produced near s=10 GeV. From this energy spectrum, we derive an upper limit of m(vτ)<70MeVc2 at the 95% confidence level.

Single charged pion production in charged-current muon neutrino interactions with carbon is studied using data collected in the K2K long-baseline neutrino experiment. The mean energy of the incident muon neutrinos is 1.3 GeV. The data used in this analysis are mainly from a fully active scintillator detector, SciBar. The cross section for single π+ production in the resonance region (W<2 GeV/c2) relative to the charged-current quasielastic cross section is found to be 0.734−0.153+0.140. The energy-dependent cross section ratio is also measured. The results are consistent with a previous experiment and the prediction of our model.5 MoreReceived 5 May 2008DOI:https://doi.org/10.1103/PhysRevD.78.032003©2008 American Physical Society

We have continued our investigation of the charge-exchange reaction K^+ Xe --> K^0 p Xe' in the bubble chamber DIANA. In agreement with our previous results based on part of the present statistics, formation of a narrow p K^0 resonance with mass of 1537+-2 MeV/c^2 is observed in the elementary transition K^+ n --> K^0 p on a neutron bound in the Xenon nucleus. Visible width of the peak is consistent with being entirely due to instrumental resolution and allows to place an upper limit on its intrinsic width: \Gamma < 9 MeV/c^2. A more precise estimate of the resonance intrinsic width, \Gamma = 0.36+-0.11 MeV/c^2, is obtained from the ratio between the numbers of resonant and non-resonant charge-exchange events. The signal is observed in a restricted interval of incident K^+ momentum, that is consistent with smearing of a narrow p K^0 resonance by Fermi motion of the target neutron. Statistical significance of the signal is some 7.3, 5.3, and 4.3 standard deviations for the estimators S/sqrt{B}, S/sqrt{S+B}, and S/sqrt{S+2B}, respectively. This observation confirms and reinforces our earlier results, and offers strong evidence for formation of a pentaquark baryon with positive strangeness in the charge-exchange reaction K^+ n --> K^0 p on a bound neutron.

In spring 2012 CERN provided two weeks of a short bunch proton beam dedicated to the neutrino velocity measurement over a distance of 730 km. The OPERA neutrino experiment at the underground Gran Sasso Laboratory used an upgraded setup compared to the 2011 measurements, improving the measurement time accuracy. An independent timing system based on the Resistive Plate Chambers was exploited providing a time accuracy of $\sim$1 ns. Neutrino and anti-neutrino contributions were separated using the information provided by the OPERA magnetic spectrometers. The new analysis profited from the precision geodesy measurements of the neutrino baseline and of the CNGS/LNGS clock synchronization. The neutrino arrival time with respect to the one computed assuming the speed of light in vacuum is found to be $\delta t_\nu \equiv TOF_c - TOF_\nu= (0.6 \pm 0.4\ (stat.) \pm 3.0\ (syst.))$ ns and $\delta t_{\bar{\nu}} \equiv TOF_c - TOF_{\bar{\nu}} = (1.7 \pm 1.4\ (stat.) \pm 3.1\ (syst.))$ ns for $\nu_{\mu}$ and $\bar{\nu}_{\mu}$, respectively. This corresponds to a limit on the muon neutrino velocity with respect to the speed of light of $-1.8 \times 10^{-6} < (v_{\nu}-c)/c < 2.3 \times 10^{-6}$ at 90% C.L. This new measurement confirms with higher accuracy the revised OPERA result.

A relativistic model of high-energy elastic scattering is considered on thebasis of the quasipotential equation in quantum field theory. The behaviour of the scattering amplitude for small and large momentum transfers is investigated.

Inclusive production of $\Lambda$-hyperons was measured with the large acceptance NA61/SHINE spectrometer at the CERN SPS in inelastic p+p interactions at beam momentum of 158~\GeVc. Spectra of transverse momentum and transverse mass as well as distributions of rapidity and x$_{_F}$ are presented. The mean multiplicity was estimated to be $0.120\,\pm0.006\;(stat.)\,\pm 0.010\;(sys.)$. The results are compared with previous measurements and predictions of the EPOS, UrQMD and FRITIOF models.

In high energy experiments such as active beam dump searches for rare decays and missing energy events, the beam purity is a crucial parameter. In this paper we present a technique to reject heavy charged particle contamination in the 100 GeV electron beam of the H4 beam line at CERN SPS. The method is based on the detection with BGO scintillators of the synchrotron radiation emitted by the electrons passing through a bending dipole magnet. A 100 GeV $\pi^-$ beam is used to test the method in the NA64 experiment resulting in a suppression factor of $10^{-5}$ while the efficiency for electron detection is $\sim$95%. The spectra and the rejection factors are in very good agreement with the Monte Carlo simulation. The reported suppression factors are significantly better than previously achieved.

The extension of Standard Model made by inclusion of additional $U(1)$ gauge ${L}_{\ensuremath{\mu}}\ensuremath{-}{L}_{\ensuremath{\tau}}$ symmetry can explain the difference between the measured and the predicted value of the muon magnetic moment and solve the tension in $B$ meson decays. This model predicts the existence of a new, light ${Z}^{\ensuremath{'}}$ vector boson, predominantly coupled to second and third generation leptons, whose interaction with electrons is due to a loop mechanism involving muons and taus. In this work, we present a rigorous evaluation of the upper limits in the ${Z}^{\ensuremath{'}}$ parameter space, obtained from the analysis of the data collected by the NA64-$e$ experiment at CERN SPS, that performed a search for light dark matter with $2.84\ifmmode\times\else\texttimes\fi{}{10}^{11}$ electrons impinging with 100 GeV on an active thick target. The resulting limits touch the muon $g\ensuremath{-}2$ preferred band for values of the ${Z}^{\ensuremath{'}}$ mass of order of 1 MeV, while the sensitivity projections for the future high-statistics NA64-$e$ runs demonstrate the power of the electrons/positron beam approach in this theoretical scenario.

Abstract This paper reports measurements of two-pion femtoscopic correlations in Be+Be collisions at a beam momentum of 150 $$A\,\hbox {GeV}\!/\!c$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>A</mml:mi> <mml:mspace /> <mml:mtext>GeV</mml:mtext> <mml:mspace /> <mml:mo>/</mml:mo> <mml:mspace /> <mml:mi>c</mml:mi> </mml:mrow> </mml:math> (energy available in the center-of-mass system for nucleon pair $$\sqrt{s_{\text {NN}}} = 16.84$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msqrt> <mml:msub> <mml:mi>s</mml:mi> <mml:mtext>NN</mml:mtext> </mml:msub> </mml:msqrt> <mml:mo>=</mml:mo> <mml:mn>16.84</mml:mn> </mml:mrow> </mml:math> GeV) by the NA61/SHINE experiment at the CERN SPS accelerator. The obtained momentum space correlation functions can be well described by a Lévy distributed source model. The transverse mass dependence of the Lévy source parameters is presented, and their possible theoretical interpretations are discussed. The results show that the Lévy exponent $$\alpha $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>α</mml:mi> </mml:math> is approximately constant as a function of $$m_{\text {T}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>m</mml:mi> <mml:mtext>T</mml:mtext> </mml:msub> </mml:math> , and far from both the Gaussian case of $$\alpha = 2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>α</mml:mi> <mml:mo>=</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:math> or the conjectured value at the critical endpoint, $$\alpha = 0.5$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>α</mml:mi> <mml:mo>=</mml:mo> <mml:mn>0.5</mml:mn> </mml:mrow> </mml:math> . The radius scale parameter R shows a slight decrease in $$m_{\text {T}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>m</mml:mi> <mml:mtext>T</mml:mtext> </mml:msub> </mml:math> , which can be explained as a signature of transverse flow. Finally, an approximately constant trend of the intercept parameter $$\lambda $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>λ</mml:mi> </mml:math> as a function of $$m_{\text {T}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>m</mml:mi> <mml:mtext>T</mml:mtext> </mml:msub> </mml:math> was observed, similar to previous NA44 S + Pb results (obtained with a Gaussian approximation, but unlike RHIC results).

We present data from Fermilab experiment E781 (SELEX) on the hadroproduction asymmetry for Λ̄c− compared to Λc+ as a function of xF, and on pt2 distributions for Λc+. These data were measured in the same apparatus using incident π−, Σ− beams at 600 GeV/c and proton beam at 540 GeV/c. The asymmetry is studied as a function of xF. In the forward hemisphere with xF⩾0.2 both baryon beams exhibit very strong preference for producing charm baryons rather than charm antibaryons, while the pion beam asymmetry is much smaller. In this energy regime the results show that beam fragments play a major role in the kinematics of Λc formation, as suggested by the leading quark picture.

It is shown that in four-dimensional abelian (V - A) theories, the ground state of cold neutral fermionic matter is an anomalous state containing domains of abnormal phase surrounded by the normal vacuum. Inside these domains, there exists a gauge field condensate which makes real fermions disappear both inside and outside the domains. In non-abelian theories, the abnormal matter is unstable in its turn, and the system rolls back down into the normal state with a small number of fermions above the topologically non-trivial vacuum. Thus, in several non-abelian gauge theories, the fermion number density of cold neutral matter cannot exceed some critical value.

Using the ARGUS detector at DORIS, we have observed the production of F± mesons in e+e− annihilation at a centre of mass energy of 10 GeV through their subsequent decays into φπ± and φπ+π−π±. The values obtained for [R(e+e−→FX). Branching Ratio] are (1.47 ± 0.32 ± 0.20)% and (1.63 ± 0.42 ± 0.41)% respectively. The observed mass is (1973.6 ± 2.6 ± 3.0)MeVc2. The F momentum spectrum is as expected for the fragmentation of c quarks into charmed mesons, but is somewhat softer than for fragmentation into D∗ mesons. The relevant angular distributions are consistent with a spin-zero assignment of the F meson.

The OPERA detector at the Gran Sasso underground laboratory (LNGS) was used to measure the atmospheric muon charge ratio $R_{\mu}=N_{\mu^{+}}/N_{\mu^{-}}$ in the TeV energy region. We analyzed 403069 atmospheric muons corresponding to 113.4 days of livetime during the 2008 CNGS run. We computed separately the muon charge ratio for single and for multiple muon events in order to select different energy regions of the primary cosmic ray spectrum and to test the R μ dependence on the primary composition. The measured R μ values were corrected taking into account the charge-misidentification errors. Data have also been grouped in five bins of the "vertical surface energy" ℰ μ cos θ. A fit to a simplified model of muon production in the atmosphere allowed the determination of the pion and kaon charge ratios weighted by the cosmic ray energy spectrum.

The OPERA detector, designed to search for $$\nu _{\mu } \rightarrow \nu _{\tau }$$ oscillations in the CNGS beam, is located in the underground Gran Sasso laboratory, a privileged location to study TeV-scale cosmic rays. For the analysis here presented, the detector was used to measure the atmospheric muon charge ratio in the TeV region. OPERA collected charge-separated cosmic ray data between 2008 and 2012. More than 3 million atmospheric muon events were detected and reconstructed, among which about 110000 multiple muon bundles. The charge ratio $$R_{\mu } \equiv N_{\mu ^+}/N_{\mu ^-}$$ was measured separately for single and for multiple muon events. The analysis exploited the inversion of the magnet polarity which was performed on purpose during the 2012 Run. The combination of the two data sets with opposite magnet polarities allowed minimizing systematic uncertainties and reaching an accurate determination of the muon charge ratio. Data were fitted to obtain relevant parameters on the composition of primary cosmic rays and the associated kaon production in the forward fragmentation region. In the surface energy range 1–20 TeV investigated by OPERA, $$R_{\mu }$$ is well described by a parametric model including only pion and kaon contributions to the muon flux, showing no significant contribution of the prompt component. The energy independence supports the validity of Feynman scaling in the fragmentation region up to $$200$$ TeV/nucleon primary energy.

Producing positronium (Ps) in the metastable 2 3 S state is of interest for various applications in fundamental physics.We report here on an experiment in which Ps atoms are produced in this long-lived state by spontaneous radiative decay of Ps excited to the 3 3 P level manifold.The Ps cloud excitation is obtained with a UV laser pulse in an experimental vacuum chamber in presence of guiding magnetic field of 25 mT and an average electric field of 300 V cm -1 .The evidence of the 2 3 S state production is obtained to the 3.6σ level of statistical significance using a novel analysis technique of the single-shot positronium annihilation lifetime spectra.The dynamic of the Ps population on the involved levels has been studied with a rate equation model.

We report the results of a search for a new vector boson ( A' ) decaying into two dark matter particles χ1χ2 of different mass. The heavier χ2 particle subsequently decays to χ1 and an off-shell Dark Photon A'∗→e+e- . For a sufficiently large mass splitting, this model can explain in terms of new physics the recently confirmed discrepancy observed in the muon anomalous magnetic moment at Fermilab. Remarkably, it also predicts the observed yield of thermal dark matter relic abundance. A detailed Monte-Carlo simulation was used to determine the signal yield and detection efficiency for this channel in the NA64 setup. The results were obtained re-analyzing the previous NA64 searches for an invisible decay A'→χχ¯ and axion-like or pseudo-scalar particles a→γγ . With this method, we exclude a significant portion of the parameter space justifying the muon g-2 anomaly and being compatible with the observed dark matter relic density for A' masses from 2 me up to 390 MeV and mixing parameter ε between 3×10-5 and 2×10-2 .

We report the results of a search for a light pseudoscalar particle $a$ that couples to electrons and decays to $e^+e^-$ performed using the high-energy CERN SPS H4 electron beam. If such pseudoscalar with a mass $\simeq 17$ MeV exists, it could explain the ATOMKI anomaly. We used the NA64 data samples collected in the "visible mode" configuration with total statistics corresponding to $8.4\times 10^{10}$ electrons on target (EOT) in 2017 and 2018. In order to increase sensitivity to small coupling parameter $\epsilon$ we used also the data collected in 2016-2018 in the "invisible mode" configuration of NA64 with a total statistics corresponding to $2.84\times 10^{11}$ EOT. A thorough analysis of both these data samples in the sense of background and efficiency estimations was already performed and reported in our previous papers devoted to the search for light vector particles and axion-like particles (ALP). In this work we recalculate the signal yields, which are different due to different cross section and life time of a pseudoscalar particle $a$, and perform a new statistical analysis. As a result, the region of the two dimensional parameter space $m_a - \epsilon$ in the mass range from 1 to 17.1 MeV is excluded. At the mass of the ATOMKI anomaly the values of $\epsilon$ in the range $2.1 \times 10^{-4} < \epsilon < 3.2 \times 10^{-4}$ are excluded.

Total cross sections for Σ− and π− on beryllium, carbon, polyethylene and copper as well as total cross sections for protons on beryllium and carbon have been measured in a broad momentum range around 600GeV/c . These measurements were performed with a transmission technique in the SELEX hyperon-beam experiment at Fermilab. We report on results obtained for hadron–nucleus cross sections and on results for σtot(Σ−N) and σtot(π−N) , which were deduced from nuclear cross sections.