Intense beam of metastable Muonium Janka, G.; Ohayon, B.; Burkley, Z. ...
European physical journal. C, Particles and fields,
09/2020, Volume:
80, Issue:
9
Journal Article
Peer reviewed
Open access
Precision spectroscopy of the Muonium Lamb shift and fine structure requires a robust source of 2S Muonium. To date, the beam-foil technique is the only demonstrated method for creating such a beam ...in vacuum. Previous experiments using this technique were statistics limited, and new measurements would benefit tremendously from the efficient 2S production at a low energy muon (
<
20
keV) facility. Such a source of abundant low energy
μ
+
has only become available in recent years, e.g. at the Low-Energy Muon beamline at the Paul Scherrer Institute. Using this source, we report on the successful creation of an intense, directed beam of metastable Muonium. We find that even though the theoretical Muonium fraction is maximal in the low energy range of 2–5 keV, scattering by the foil and transport characteristics of the beamline favor slightly higher
μ
+
energies of 7–10 keV. We estimate that an event detection rate of a few events per second for a future Lamb shift measurement is feasible, enabling an increase in precision by two orders of magnitude over previous determinations.
We report a case of severe tinea capitis, treated successfully with griseofulvin. In our opinion, the treatment of this severe dermatophytosis with griseofulvin is safe and effective. Other ...treatments, such as itraconazole pulsed therapy, failed, despite an initial improvement, leading to an aggressive recurrence of the lesion. We chose griseofulvin for its well-known large spectrum activity, also against uncommon species, like Microsporum Gypseum, which are responsible for the most severe cases.
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^{'}}.
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Next-generation megawatt-scale neutrino beams open the way to studying neutrino-nucleus scattering resorting, for the first time, to gaseous targets. This could lead to deeper knowledge of neutrino ...cross sections in the energy region between hundreds of MeV and a few GeV, of interest for the upcoming generation of long-baseline neutrino oscillation experiments. The challenge is, therefore, to accurately track and (especially) time the particles produced in neutrino interactions in large and seamless volumes down to few-MeV energies. We propose to accomplish this through an optically-read time projection chamber (TPC) filled with high-pressure argon and equipped with both tracking and timing functions. In this work, we present a detailed study of the time-tagging capabilities of such a device, based on end-to-end optical simulations that include the effect of photon propagation, photosensor response, dark-count rate and pulse reconstruction. We show that the neutrino interaction time could be reconstructed from the primary-scintillation signal with a precision in the range 1--2.5~ns (\(\sigma\)) for point-like deposits with energies down to 5~MeV, and well below 1~ns for minimum-ionizing particle tracks. A discussion on previous limitations towards such a detection technology, and how they can be realistically overcome in the near future thanks to recent developments in the field, is presented (particularly the strong scintillation yields recently reported for Ar/CF\(_4\) mixtures). The performance presented in our analysis seems to be well within reach of next-generation neutrino-oscillation experiments through the instrumentation of the proposed TPC with conventional reflective materials and a SiPM carpet behind a transparent cathode.
We present the first results from a proof-of-concept search for dark sectors
via invisible decays of pseudoscalar $\eta$ and $\eta'$ mesons in the NA64h
experiment at the CERN SPS. Our novel ...technique uses the charge-exchange
reaction of 50 GeV $\pi^-$ on nuclei of an active target as the source of
neutral mesons. The $\eta, \eta' \to invisible$ events would exhibit themselves
via a striking signature - the complete disappearance of the incoming beam
energy in the detector. No evidence for such events has been found with
$2.9\times10^{9}$ pions on target accumulated during one day of data taking.
This allows us to set a stringent limit on the branching ratio ${\rm Br}(\eta'
\to invisible) < 2.1 \times 10^{-4}$ improving the current bound by a factor of
$\simeq3$. We also set a limit on ${\rm Br}(\eta \to invisible) < 1.1 \times
10^{-4}$ comparable with the existing one. These results demonstrate the great
potential of our approach and provide clear guidance on how to enhance and
extend the sensitivity for dark sector physics from future searches for
invisible neutral meson decays.
The inclusion of an additional $U(1)$ gauge $L_\mu-L_\tau$ symmetry would
release the tension between the measured and the predicted value of the
anomalous muon magnetic moment: this paradigm assumes ...the existence of a new,
light $Z^\prime$ vector boson, with dominant coupling to $\mu$ and $\tau$
leptons and interacting with electrons via a loop mechanism. The $L_\mu-L_\tau$
model can also explain the Dark Matter relic abundance, by assuming that the
$Z'$ boson acts as a "portal" to a new Dark Sector of particles in Nature, not
charged under known interactions. In this work we present the results of the
$Z'$ search performed by the NA64-$e$ experiment at CERN SPS, that collected
$\sim 9\times10^{11}$ 100 GeV electrons impinging on an active thick target.
Despite the suppressed $Z'$ production yield with an electron beam, NA64-$e$
provides the first accelerator-based results excluding the $g-2$ preferred band
of the $Z'$ parameter space in the 1 keV $ < m_{Z'} \lesssim 2$ MeV range, in
complementarity with the limits recently obtained by the NA64-$\mu$ experiment
with a muon beam.
We report on a search for a new $Z'$ ($L_\mu-L_\tau$) vector boson 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. A
signal event is 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 statistic of $(1.98\pm0.02)\times10^{10}$
muons on target, no event is observed in the expected signal region. This
allows us to set new limits on part of the remaining $(m_{Z'},\ g_{Z'})$
parameter space which could provide an explanation for the muon $(g-2)_\mu$
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.
Precision spectroscopy of the Muonium Lamb shift and fine structure requires a robust source of 2S Muonium. To date, the beam-foil technique is the only demonstrated method for creating such a beam ...in vacuum. Previous experiments using this technique were statistics limited, and new measurements would benefit tremendously from the efficient 2S production at a low energy muon (\(<20\) keV) facility. Such a source of abundant low energy \(\mathrm{\mu^+}\) has only become available in recent years, e.g. at the Low-Energy Muon beamline at the Paul Scherrer Institute. Using this source, we report on the successful creation of an intense, directed beam of metastable Muonium. We find that even though the theoretical Muonium fraction is maximal in the low energy range of \(2-5\) keV, scattering by the foil and transport characteristics of the beamline favor slightly higher \(\mathrm{\mu^+}\) energies of \(7-10\) keV. We estimate that an event detection rate of a few events per second for a future Lamb shift measurement is feasible, enabling an increase in precision by two orders of magnitude over previous determinations.
In this study, 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 momentum. The analysis was ...performed using data
collected by the NA64-$e$ experiment in 2022. Our study is based on
calorimetric measurements, exploiting the different interaction mechanisms of
electrons and hadrons in the NA64-ECAL and NA64-HCAL detectors. We determined
the intrinsic hadronic contamination by comparing the results obtained using
the nominal electron/positron beamline configuration with those obtained in a
dedicated setup, in which only hadrons impinged on the detector. The
significant differences in the experimental signatures of electrons and hadrons
motivated our approach, resulting in a small and well-controlled systematic
uncertainty for the measurement. Our study allowed us to precisely determine
the intrinsic hadronic contamination, which represents a crucial parameter for
the NA64 experiment in which the hadron contaminants may result in non-trivial
backgrounds. Moreover, we performed dedicated Monte Carlo simulations for the
hadron production induced by the primary T2 target. We found a good agreement
between measurements and simulation results, confirming the validity of the
applied methodology and our evaluation of the intrinsic hadronic contamination.
The inclusion of an additional \(U(1)\) gauge \(L_\mu-L_\tau\) symmetry would release the tension between the measured and the predicted value of the anomalous muon magnetic moment: this paradigm ...assumes the existence of a new, light \(Z^\prime\) vector boson, with dominant coupling to \(\mu\) and \(\tau\) leptons and interacting with electrons via a loop mechanism. The \(L_\mu-L_\tau\) model can also explain the Dark Matter relic abundance, by assuming that the \(Z'\) boson acts as a "portal" to a new Dark Sector of particles in Nature, not charged under known interactions. In this work we present the results of the \(Z'\) search performed by the NA64-\(e\) experiment at CERN SPS, that collected \(\sim 9\times10^{11}\) 100 GeV electrons impinging on an active thick target. Despite the suppressed \(Z'\) production yield with an electron beam, NA64-\(e\) provides the first accelerator-based results excluding the \(g-2\) preferred band of the \(Z'\) parameter space in the 1 keV \( < m_{Z'} \lesssim 2\) MeV range, in complementarity with the limits recently obtained by the NA64-\(\mu\) experiment with a muon beam.
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