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 2.84×1011 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 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.
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.
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 → e− ZX, followed by its invisible decay in the NA64 experiment at CERN. No evidence for such a process was found in the full NA64 dataset of 2.84 × 1011 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 ae,|ΔaX|≲ 10−15 –10−13 for the X mass region 1 MeV ≲ mX ≲ 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 present the results of a missing-energy search for Light Dark Matter which has a new interaction with ordinary matter transmitted by a vector boson, called dark photon \(A^\prime\). For the first ...time, this search is performed with a positron beam by using the significantly enhanced production of \(A^\prime\) in the resonant annihilation of positrons with atomic electrons of the target nuclei, followed by the invisible decay of \(A^\prime\) into dark matter. No events were found in the signal region with \((10.1 \pm 0.1)~\times~10^{9}\) positrons on target with 100 GeV energy. This allowed us to set new exclusion limits that, relative to the collected statistics, prove the power of this experimental technique. This measurement is a crucial first step toward a future exploration program with positron beams, whose estimated sensitivity is here presented.
The measurements of the Collins and Sivers asymmetries of identified hadrons produced in deep-inelastic scattering of 160 GeV/c muons on a transversely polarised 6LiD target at COMPASS are presented. ...The results for charged pions and charged and neutral kaons correspond to all data available, which were collected from 2002 to 2004. For all final state particles both, the Collins and Sivers asymmetries turn out to be small, compatible with zero within the statistical errors, in line with the previously published results for not identified charged hadrons, and with the expected cancellation between the u- and d-quark contributions.
Present status of silicon detectors in Compass Angerer, H.; De Masi, R.; Esposito, A. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2003, Letnik:
512, Številka:
1-2
Journal Article
We report the results of a search for a new vector boson (\(A'\)) decaying into two dark matter particles \(\chi_1 \chi_2\) of different mass. The heavier \(\chi_2\) particle subsequently decays to ...\(\chi_1\) and \(A' \to e^- e^+\). 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 \(A'\to \chi \overline{\chi}\) and axion-like or pseudo-scalar particles \(a \to \gamma \gamma\). 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\(m_e\) up to 390 MeV and mixing parameter \(\epsilon\) between \(3\times10^{-5}\) and \(2\times10^{-2}\).
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