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.
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 shielding, and would be observed either through their \(a(s)\to\gamma \gamma\) decay in the rest of the HCAL detector or as events with large missing energy if the a(s) decays downstream of the HCAL. This method allows for the probing 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 \(2.84\times10^{11}\) electrons on target allowing to set new limits on the \(a(s)\gamma\gamma\)-coupling strength for a(s) masses below 55 MeV.
Formation of angular distributions of fission fragments for the 16O + 232Th and 12C + 235,236U reactions has been analyzed within a dynamic approach. In this approach, the component of the total ...angular momentum along the fission axis K is considered as a fluctuating quantity and the corresponding relaxation time is assumed to be the main parameter controlling the evolution of this mode. Particular attention is paid to the analysis of the effect of initial distributions over K (formed during fusion) on the angular distribution of fission fragments of nuclei having fission barriers comparable with the nuclear temperatures.
A search for sub-GeV dark matter production mediated by a new vector boson \(A'\), called 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 \(2.84\times10^{11}\) 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 \(\lesssim 0.2\) GeV are derived, thus demonstrating the power of the active beam dump approach for the dark matter search.
Liquid Argon Time Projection Chamber (LAr TPC) detectors offer charged particle imaging capability with remarkable spatial resolution. Precise event reconstruction procedures are critical in order to ...fully exploit the potential of this technology. In this paper we present a new, general approach to 3D reconstruction for the LAr TPC with a practical application to the track reconstruction. The efficiency of the method is evaluated on a sample of simulated tracks. We present also the application of the method to the analysis of stopping particle tracks collected during the ICARUS T600 detector operation with the CNGS neutrino beam.
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 Be-8 nucleus decays. Due to its coupling to ...electrons, the X could be produced in the bremsstrahlung reaction e- Z -> e- Z X by a 100 GeV e- beam incident on an active target in the NA64 experiment at the CERN SPS and observed through the subsequent decay into an e+e- pair. With 5.4\times 10^{10} electrons on target, no evidence for such decays was found, allowing to set first limits on the X-e^- coupling in the range 1.3\times 10^{-4} < \epsilon_e < 4.2\times 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 non-observation 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.
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.
We report an updated result from the ICARUS experiment on the search for ν ^sub mu^arrow rightν ^sub e^ anomalies with the CNGS beam, produced at CERN with an average energy of 20 GeV and traveling ...730 km to the Gran Sasso Laboratory. The present analysis is based on a total sample of 1995 events of CNGS neutrino interactions, which corresponds to an almost doubled sample with respect to the previously published result. Four clear ν ^sub e^ events have been visually identified over the full sample, compared with an expectation of 6.4±0.9 events from conventional sources. The result is compatible with the absence of additional anomalous contributions. At 90 % and 99 % confidence levels, the limits to possible oscillated events are 3.7 and 8.3 respectively. The corresponding limit to oscillation probability becomes consequently 3.4×10^sup -3^ and 7.6×10^sup -3^, respectively. The present result confirms, with an improved sensitivity, the early result already published by the ICARUS Collaboration.
We present the performance of multiplexed XY resistive Micromegas detectors tested in the CERN SPS 100 GeV/c electron beam at intensities up to 3.3 \(\times\) 10\(^5\) e\(^- \)/(s\(\cdot\)cm\(^2\)). ...So far, all studies with multiplexed Micromegas have only been reported for tests with radioactive sources and cosmic rays. The use of multiplexed modules in high intensity environments was not explored due to the effect of ambiguities in the reconstruction of the hit point caused by the multiplexing feature. At the beam intensities analysed in this work and with a multiplexing factor of 5, more than 50% level of ambiguity is introduced. Our results prove that by using the additional information of cluster size and integrated charge from the signal clusters induced on the XY strips, the ambiguities can be reduced to a level below 2%. The tested detectors are used in the CERN NA64 experiment for tracking the incoming particles bending in a magnetic field in order to reconstruct their momentum. The average hit detection efficiency of each module was found to be \(\sim\) 96% at the highest beam intensities. By using four modules a tracking resolution of 1.1% was obtained with \(\sim\) 85% combined tracking efficiency.
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