Muon Measurements Research Articles

Neutrino mass, dark matter and anomalous magnetic moment of muon in a U 1 L μ − L τ $$ \mathrm{U}{(1)}_L{{}_{{}_{\mu}}}_{-}{{}_L}_{{}_{\tau }} $$ model

The observation of neutrino masses, mixing and the existence of dark matter are amongst the most important signatures of physics beyond the Standard Model (SM). In this paper, we propose to extend the SM by a local $L_\mu - L_\tau$ gauge symmetry, two additional complex scalars and three right-handed neutrinos. The $L_\mu - L_\tau$ gauge symmetry is broken spontaneously when one of the scalars acquires a vacuum expectation value. The $L_\mu - L_\tau$ gauge symmetry is known to be anomaly free and can explain the beyond SM measurement of the anomalous muon $({\rm g-2})$ through additional contribution arising from the extra $Z_{\mu\tau}$ mediated diagram. Small neutrino masses are explained naturally through the Type-I seesaw mechanism, while the mixing angles are predicted to be in their observed ranges due to the broken $L_\mu-L_\tau$ symmetry. The second complex scalar is shown to be stable and becomes the dark matter candidate in our model. We show that while the $Z_{\mu\tau}$ portal is ineffective for the parameters needed to explain the anomalous muon $({\rm g-2})$ data, the correct dark matter relic abundance can easily be obtained from annihilation through the Higgs portal. Annihilation of the scalar dark matter in our model can also explain the Galactic Centre gamma ray excess observed by Fermi-LAT. We show the predictions of our model for future direct detection experiments and neutrino oscillation experiments.

Investigating the Anisotropic Scintillation Response in Anthracene through Neutron, Gamma-Ray, and Muon Measurements

This paper reports a series of measurements that characterize the directional dependence of the scintillation response of crystalline anthracene to incident DT neutrons, DD neutrons, Cs-137 gamma rays, and, for the first time, cosmic ray muons. The neutron measurements give the amplitude and pulse shape dependence on the proton recoil direction over one hemisphere of the crystal, confirming and extending previous results in the literature. In similar measurements using incident gamma rays, no directional effect is evident, and any anisotropy with respect to the electron recoil direction is constrained to have a magnitude of less than a tenth of that present in the proton recoil events. Cosmic muons are measured at two directions, and no anisotropy is observed. This set of observations indicates that high dE/dx is necessary for an anisotropy to be present for a given type of scintillation event, which in turn could be used to discriminate among different hypotheses for the underlying causes of the anisotropy, which are not well understood.

Composite (pseudo) scalar contributions to muon g− 2

We have calculated the composite (pseudo) scalar contributions to the anomalous magnetic moment of muons in models of walking technicolor. By the axial or scale anomaly the light scalars such as techni-dilaton, techni-pions or techni-eta have anomalous couplings to two-photons, which make them natural candidates for the recent 750 GeV resonance excess, observed at LHC. Due to the anomalous couplings, their contributions to muon (g-2) are less suppressed and might explain the current deviation in muon (g-2) measurements from theory.

Measurement of cosmic-ray muons and muon-induced neutrons in the Aberdeen Tunnel Underground Laboratory

We have measured the muon flux and production rate of muon-induced neutrons at a depth of 611 m water equivalent. Our apparatus comprises three layers of crossed plastic scintillator hodoscopes for tracking the incident cosmic-ray muons and 760 L of gadolinium-doped liquid scintillator for producing and detecting neutrons. The vertical muon intensity was measured to be $I_{\mu} = (5.7 \pm 0.6) \times 10^{-6}$ cm$^{-2}$s$^{-1}$sr$^{-1}$. The yield of muon-induced neutrons in the liquid scintillator was determined to be $Y_{n} = (1.19 \pm 0.08 (stat) \pm 0.21 (syst)) \times 10^{-4}$ neutrons/($\mu\cdot$g$\cdot$cm$^{-2}$). A fit to the recently measured neutron yields at different depths gave a mean muon energy dependence of $\left\langle E_{\mu} \right\rangle^{0.76 \pm 0.03}$ for liquid-scintillator targets.

Measurement of cosmic-ray muons with the Distributed Electronic Cosmic-ray Observatory, a network of smartphones

Solid-state camera image sensors can be used to detect ionizing radiation in addition to optical photons. We describe the Distributed Electronic Cosmic-ray Observatory (DECO), an app and associated public database that enables a network of consumer devices to detect cosmic rays and other ionizing radiation. In addition to terrestrial background radiation, cosmic-ray muon candidate events are detected as long, straight tracks passing through multiple pixels. The distribution of track lengths can be related to the thickness of the active (depleted) region of the camera image sensor through the known angular distribution of muons at sea level. We use a sample of candidate muon events detected by DECO to measure the thickness of the depletion region of the camera image sensor in a particular consumer smartphone model, the HTC Wildfire S. The track length distribution is fit better by a cosmic-ray muon angular distribution than an isotropic distribution, demonstrating that DECO can detect and identify cosmic-ray muons despite a background of other particle detections. Using the cosmic-ray distribution, we measure the depletion thickness to be 26.3 ± 1.4 μm. With additional data, the same method can be applied to additional models of image sensor. Once measured, the thickness can be used to convert track length to incident polar angle on a per-event basis. Combined with a determination of the incident azimuthal angle directly from the track orientation in the sensor plane, this enables direction reconstruction of individual cosmic-ray events using a single consumer device. The results simultaneously validate the use of cell phone camera image sensors as cosmic-ray muon detectors and provide a measurement of a parameter of camera image sensor performance which is not otherwise publicly available.

Measurement of muon annual modulation and muon-induced phosphorescence in NaI(Tl) crystals with DM-Ice17

We report the measurement of muons and muon-induced phosphorescence in DM-Ice17, a NaI(Tl) direct detection dark matter experiment at the South Pole. Muon interactions in the crystal are identified by their observed pulse shape and large energy depositions. The measured muon rate in DM-Ice17 is 2.93 +/- 0.04 muons/crystal/day with a modulation amplitude of 12.3 +/- 1.7%, consistent with expectation. Following muon interactions, we observe long-lived phosphorescence in the NaI(Tl) crystals with a decay time of 5.5 +/- 0.5 s. The prompt energy deposited by a muon is correlated to the amount of delayed phosphorescence, the brightest of which consist of tens of millions of photons. These photons are distributed over tens of seconds with a rate and arrival timing that do not mimic a scintillation signal above 2 keVee. While the properties of phosphorescence vary among individual crystals, the annually-modulating signal observed by DAMA cannot be accounted for by phosphorescence with the characteristics observed in DM-Ice17.

Overview and outlook on muon survey tomography based on micromegas detectors for unreachable sites technology

The present document describes the functioning principles of the Muon Survey Tomography based on Micromegas detectors for Unreachable Sites Technology and its distinguishing features from other Micromegas-like detectors. Additionally, it addresses the challenges found while operating the first generation and the resulting improvements. Currently, the project Temporal Tomography of the Densitometry by the Measurement of Muons is focused on obtaining a reliable pulse from the micromesh, associated to the passing of a muon, in order to trigger the acquisition and operate in standalone mode. An outlook of the future steps of the project is provided as well.

Constraints on hadronic models in extensive air showers with the Pierre Auger Observatory

Extensive air showers initiated by ultra-high energy cosmic rays are sensitive to the details of hadronic interactions models, so we present the main results obtained using the data of the Pierre Auger Observatory. The depth at which the maximum of the electromagnetic development takes place is the most sensitive parameter to infer the nature of the cosmic rays. However, the hadronic models cannot describe consistently the maximum and the muon measurements at energies higher than those reached at the LHC.

QCD with jets and heavy flavour in pp and PbPb collisions in ATLAS

ATLAS has studied different aspects of QCD in pp and PbPb collisions. A summary of interesting recent results at centre-of-mass energies of 7 TeV, 8 TeV and 13 TeV (pp), and 2.76 TeV (PbPb) per nucleon pair is presented. Using pp collisions, measurements of Z, W, photon, quarkonia and open charm production differential cross sections in a variety of variables are presented. Jet and heavy flavour muon measurements in PbPb collisions, aimed to test the properties of the Quark Gluon Plasma, with the view of better understanding of jet quenching, are also presented.

Separating the ferromagnetic and glassy behavior within the metal-organic magnetNi(TCNQ)2

An in-depth study of the metal-organic magnet $\mathrm{Ni}{(\mathrm{TCNQ})}_{2}$ was conducted where the deuterated form was synthesised both to attempt to alter the magnetic properties of the material and to be advantageous in techniques such as neutron scattering and muon spectroscopy. Deuteration saw a 3 K increase in ${T}_{C}$ with magnetization and heat capacity measurements demonstrating a spin wave contribution at low temperatures confirming the 3D nature of the ferromagnetic state shown by $\mathrm{Ni}{(\mathrm{TCNQ}\ensuremath{-}{\mathrm{D}}_{4})}_{2}$. AC susceptibility results suggest there is a glassy component associated with the magnetically ordered state, though muon spectroscopy measurements did not support the presence of a spin glass state. Instead muon spectroscopy at zero magnetic field indicated the presence of two magnetic transitions, one at 20 K and another below 6 K; the latter is likely due to the system entering a quasistatic regime, similar to what one might expect of a superspin or cluster glass. Neutron diffraction measurements further supported this by revealing very weak magnetic Bragg peaks suggesting that the magnetism may have a short coherence length and be confined to small grains or clusters. The separation of the ferromagnetic and glassy magnetic components of the material's properties suggest that this system may show promise as a metal-organic magnet which is easily modified to change its magnetic properties, providing larger grain sizes can be synthesized.

Mass composition measurements at the Pierre Auger Observatory

AbstractThe Pierre Auger Observatory is the largest ultra‐high energy cosmic ray experiment built so far. It is a hybrid detector, since it measures both the fluorescence light emitted while the air showers develop in the atmosphere and the particles reaching the ground. We present the results related to the mass composition of ultra‐high energy cosmic rays as obtained from both types of measurements. The depth at which the maximum of the electromagnetic development takes place and its fluctuations are the most sensitive parameters to infer the nature of the cosmic rays. In addition, we present the latest muon measurements that can be used to test and constrain models of hadronic interactions at energies larger than those reached at LHC. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Background radiation measurements at high power research reactors

Research reactors host a wide range of activities that make use of the intense neutron fluxes generated at these facilities. Recent interest in performing measurements with relatively low event rates, e.g. reactor antineutrino detection, at these facilities necessitates a detailed understanding of background radiation fields. Both reactor-correlated and naturally occurring background sources are potentially important, even at levels well below those of importance for typical activities. Here we describe a comprehensive series of background assessments at three high-power research reactors, including γ-ray, neutron, and muon measurements. For each facility we describe the characteristics and identify the sources of the background fields encountered. The general understanding gained of background production mechanisms and their relationship to facility features will prove valuable for the planning of any sensitive measurement conducted therein.

Robustness of superconductivity to structural disorder inSr0.3(NH2)y(NH3)1−yFe2Se2

The superconducting properties of a recently discovered high-${T}_{\mathrm{c}}$ superconductor, Sr/ammonia-intercalated FeSe, have been measured using pulsed magnetic fields down to 4.2 K and muon spin spectroscopy down to 1.5 K. This compound exhibits intrinsic disorder resulting from random stacking of the FeSe layers along the $c$ axis that is not present in other intercalates of the same family. This arises because the coordination requirements of the intercalated Sr and ammonia moieties imply that the interlayer stacking (along $c$) involves a translation of either $\mathbf{a}/2$ or $\mathbf{b}/2$ that locally breaks tetragonal symmetry. The result of this stacking arrangement is that the Fe ions in this compound describe a body-centered-tetragonal lattice in contrast to the primitive arrangement of Fe ions described in all other Fe-based superconductors. In pulsed magnetic fields, the upper critical field ${H}_{\text{c2}}$ was found to increase on cooling with an upward curvature that is commonly seen in type-II superconductors of a multiband nature. Fitting the data to a two-band model and extrapolation to absolute zero gave a maximum upper critical field ${\ensuremath{\mu}}_{0}{H}_{\mathrm{c}2}(0)$ of $33(2)\phantom{\rule{4pt}{0ex}}\text{T}$. A clear superconducting transition with a diamagnetic shift was also observed in transverse-field muon measurements at ${T}_{\text{c}}\ensuremath{\approx}36.3(2)\phantom{\rule{4pt}{0ex}}\text{K}$. These results demonstrate that robust superconductivity in these intercalated FeSe systems does not rely on perfect structural coherence along the $c$ axis.

NeSSiE and sterile neutrinos

The wonderful frame pinpointed for the 3 standard neutrinos, beautifully adjusted by the Θ13 measurement, left out some relevant questions such as leptonic CP violation, mass values, Dark Matter and anomalies and discrepancies in several neutrino experiment results. The NESSiE collaboration proposes to undertake conclusive experiments to clarify the muon neutrino disappearance measurements at small L/E, which will be able to put severe constraints to models with more than the three-standard neutrinos, or even to robustly measure the presence of a new kind of neutrino oscillation for the first time.

Pressure and temperature effect corrections of atmospheric muon data in the Belgrade cosmic-ray station

We present results of continuous monitoring of the cosmic-ray muon intensity at the ground and shallow underground level at the Belgrade cosmic-ray station. The cosmic-ray muon measurements have been performed since 2002, by means of plastic scintillation detectors. The scintillator counts are corrected for atmospheric pressure for the whole period of measurements and, as well, for vertical temperature profile for the period of the last six years. The results are compared with other correction methods available. One-hour time series of the cosmic-ray muon intensity at the ground level are checked for correlation with European neutron monitors, with emphasis on occasional extreme solar events, e.g. Forbush decreases.

Measurements of heavy-flavour decay leptons with ALICE

We present measurements of electrons and muons from heavy-flavour hadron decays at central and forward rapidity performed by the ALICE Collaboration in p–Pb (√s NN = 5.02 TeV) and Pb–Pb collisions (√s NN = 2.76 TeV). Electrons are reconstructed using several detectors of the ALICE central barrel. Muons are reconstructed using the muon spectrometer at forward rapidity (2.5 AA ) and in p–Pb (R pPb ) collisions, and the azimuthal anisotropy (v 2 ) in Pb– Pb collisions will be discussed. Theoretical predictions are compared with the data. In addition, the measurement of the azimuthal correlation between electrons from heavyflavour hadron decays and charged hadrons in p–Pb collisions will be shown.

Simulation of a small muon tomography station system based on RPCs

In this work, Monte Carlo simulations were used to study the performance of a small muon Tomography Station based on four glass resistive plate chambers(RPCs) with a spatial resolution of approximately 1.0mm (FWHM). We developed a simulation code to generate cosmic ray muons with the appropriate distribution of energies and angles. PoCA and EM algorithm were used to rebuild the objects for comparison. We compared Z discrimination time with and without muon momentum measurement. The relation between Z discrimination time and spatial resolution was also studied. Simulation results suggest that mean scattering angle is a better Z indicator and upgrading to larger RPCs will improve reconstruction image quality.

Measurements of heavy-flavour decay leptons in pp, p-Pb, and Pb-Pb collisions with ALICE

We present measurements of electrons and muons originating from the semi-leptonic decays of heavy-flavour hadrons at central and forward rapidities with ALICE in pp ( = 2.76 and 7 TeV), p-Pb ( = 5.02 TeV), and Pb-Pb ( = 2.76 TeV) collisions. The measured pT-differential production cross sections in pp collisions, the nuclear modification factors in p-Pb and Pb-Pb, and the v2 measurements in Pb-Pb collision are disgusted. In addition, the angular correlation distribution between heavy-flavour decay electrons and charged particles, measured in p-Pb collisions, is shown. The results are compared to their corresponding theoretical predictions.

Study of diphoton decays of the lightest scalar Higgs boson in the Next-to-Minimal Supersymmetric Standard Model

The CMS and ATLAS experiments at the LHC have announced the discovery of a Higgs boson with mass at approximately 125 GeV/c2 in the search for the Standard Model Higgs boson via, notably, the γγ and ZZ to four leptons final states. Considering the recent results of the Higgs boson searches from the LHC, we study the lightest scalar Higgs boson h1 in the Next-to-Minimal Supersymmetric Standard Model by restricting the next-to-lightest scalar Higgs boson h2 to be the observed to the 125 GeV/c2 state. We perform a scan over the relevant NMSSM parameter space that is favoured by low fine-tuning considerations. Moreover, we also take the experimental constraints from direct searches, B-physics observables, relic density, and anomalous magnetic moment of the muon measurements, as well as the theoretical considerations, into account in our specific scan. We find that the signal rate in the two-photon final state for the NMSSM Higgs boson h1 with the mass range from about 80 GeV/c2 to about 122 GeV/c2 can be enhanced by a factor of up to 3.5 when the Higgs boson h2 is required to be compatible with the excess from latest LHC results. This motivates the extension of the search at the LHC for the Higgs boson h1 in the diphoton final state down to masses of 80 GeV/c2, particularly with the upcoming proton-proton collision data to be taken at center-of-mass energies of 13–14 TeV.

Heavy-flavour decay lepton measurements in pp, p–Pb, and Pb–Pb collisions with ALICE at the LHC

We present the measurements of electrons and muons from the semi-leptonic decays of heavy-flavour hadrons measured in the central and forward rapidity regions with ALICE in pp ( s = 2.76 TeV and 7 TeV), Pb–Pb ( s NN = 2.76 TeV ), and p–Pb ( s NN = 5.02 TeV ) collisions at the LHC. The p T -differential production cross section in pp collisions, the elliptic flow in Pb–Pb collisions, and the nuclear modification factor in Pb–Pb and p–Pb collisions are shown. The results are compared to theoretical predictions.