In this study, we demonstrate the potential of the NA64 experiment at CERN SPS to search for New Physics processes involving \(e\rightarrow\mu\) transitions after the collision of 100 GeV electrons ...with target nuclei. A new Dark Sector leptonic portal in which a scalar boson \(\varphi\) could be produced in the lepton-flavor-changing bremsstrahlung-like reaction, \(eN\rightarrow \mu N\varphi\), is used as benchmark process. In this work, we develop a realistic Monte Carlo simulation of the NA64 experimental setup implementing the differential and total production cross-section computed at exact tree-level and applying the Weisz\"{a}cker-Williams phase space approximation. Using this framework, we investigate the main background sources and calculate the expected sensitivity of the experiment. The results indicate that with minor setup optimization, NA64 can probe a large fraction of the available parameter space compatible with the muon \(g-2\) anomaly and the Dark Matter relic predictions in the context of a new Dark Sector leptonic portal with \(10^{11}\) EOT. This result paves the way to the exploration of lepton-flavour-changing transitions in NA64.
We present the measurement of the intrinsic hadronic contamination at the CERN SPS H4 beamline configured to transport electrons and positrons at 100 GeV/c. The analysis, performed using data ...collected by the NA64-e experiment in 2022, is based on calorimetric measurements, exploiting the different interaction mechanisms of electrons and hadrons in the NA64 detector. We determined the contamination by comparing the results obtained using the nominal electron/positron beamline configuration with those from a dedicated setup, in which only hadrons impinged on the detector. We also obtained an estimate of the relative protons, anti-protons and pions yield by exploiting the different absorption probabilities of these particles in matter. We cross-checked our results with a dedicated Monte Carlo simulation for the hadron production at the primary T2 target, finding a good agreement with the experimental measurements.
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 π− 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 ∼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.
Al2O3 samples grown with natural well-ordered channels (having sizes of 30-90 nm in diameter) perpendicular to the surface, one side closed, were measured by means of Doppler broadening (DB) by ...variable energy positron (VEP) beam and positron annihilation lifetime (PAL) spectroscopy. The samples annealed at 300 and 560 deg C showed amorphous structure and no positronium (Ps) formation. The sample annealed at 850 deg C showed gamma-phase polycrystalline structure and Ps formation. We were not able to prove from the PAL spectroscopy results themselves whether Ps is confined to the channels. We discuss the results of decomposition of the DB annihilation peak into four Gaussians. We conclude that the greater Ps fraction is confined to the channels. From the Compton-to-peak ratio analysis, the fraction of all the injected positrons which form o-Ps and in this form escape from the sample (for a VEP experiment, we have e+ injected from the open side of the channels) has been estimated as being ~20%.
We report the first search for dark sectors performed at the NA64 experiment employing a high energy muon beam and a missing energy-momentum technique. Muons from the M2 beamline at the CERN Super ...Proton Synchrotron with a momentum of 160 GeV / c are directed to an active target. The signal signature consists of a single scattered muon with momentum < 80 GeV / c in the final state, accompanied by missing energy, i.e., no detectable activity in the downstream calorimeters. For a total dataset of ( 1.98 ± 0.02 ) × 10 10 muons on target, no event is observed in the expected signal region. This allows us to set new limits on the remaining ( m Z ′ , g Z ′ ) parameter space of a new Z ′ ( L μ − L τ ) vector boson which could explain the muon ( g − 2 ) μ anomaly. Additionally, our study excludes part of the parameter space suggested by the thermal dark matter relic abundance. Our results pave the way to explore dark sectors and light dark matter with muon beams in a unique and complementary way to other experiments. Published by the American Physical Society 2024
In this note we estimate the sensitivity of the NA64 experiment to millicharged particles (\(\chi\)). That experimental facility is dedicated to the searching for dark sector particles in missing ...energy events at the CERN SPS. We consider missing momentum signatures in the \(\simeq\) 100 GeV electron and muon beams and show that the later one allows to obtain more stringent bounds on the millicharge \(Q_{\chi}\), which for the \(\chi\) masses \(100\)~MeV \(\leq m_{\chi} \leq 500\)~MeV at the level \( Q_{\chi}/e\lesssim O(10^{-3}) - O(10^{-2})\).
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