Decay Events Research Articles

Measurement of the [formula omitted] production cross section and limits on anomalous triple gauge couplings in proton–proton collisions at [formula omitted] with the ATLAS detector

This Letter presents a measurement of W±Z production in 1.02 fb−1 of pp collision data at s=7 TeV collected by the ATLAS experiment in 2011. Doubly leptonic decay events are selected with electrons, muons and missing transverse momentum in the final state. In total 71 candidates are observed, with a background expectation of 12.1±1.4(stat.)−2.0+4.1(syst.) events. The total cross section for W±Z production for Z/γ⁎ masses within the range 66 GeV to 116 GeV is determined to be σWZtot=20.5−2.8+3.1(stat.)−1.3+1.4(syst.)−0.8+0.9(lumi.) pb, which is consistent with the Standard Model expectation of 17.30.8+1.3 pb. Limits on anomalous triple gauge boson couplings are extracted.

Developments of Microresonators Detectors for Neutrino Physics in Milan

Superconducting microwave microresonators are low temperature detectors which are compatible with large-scale multiplexed frequency domain readout. We aim to adapt and further advance the technology of microresonator detectors to develop new devices applied to the problem of measuring the neutrino mass. More specifically, we aim to develop detector arrays for calorimetric measurement of the energy spectra of 163Ho EC decay (Q∼2–3 keV) for a direct measurement of the neutrino mass. In order to achieve these goal, we need to find the best design and materials for the detectors. A recent advance in microwave microresonator technology was the discovery that some metal nitrides, such as TiN, possess properties consistent with very high detector sensitivity. We plan to investigate nitrides of higher-Z materials, for example TaN and HfN, that are appropriate for containing the energy of keV decay events, exploring the properties relevant to our detectors, such as quality factor, penetration depth and recombination time.

Test of charge conjugation invariance in the decay of theηmeson intoπ+π−π0

In this work we present the preliminary results of the analysis of the pp->pp eta(->pp pi(+)pi(-)pi(0) reaction aiming to test the charge conjugation symmetry C in strong interactions. Based on approximately $10^5$ identified eta->pi(+)pi(-)pi(0) decay events we have extracted asymmetry parameters sensitive to C symmetry violation for different isospin values of the final state and we have established that all are consistent with zero within the obtained accuracy.

Search for τ-neutrino Interactions in the OPERA Hybrid Detector

Abstract The OPERA detector searches for neutrino oscillation in appearance mode by combining the high spatial resolution of nuclear emulsions and the features of scintillating fibers, RPC's and drift-tube spectrometers to unambiguously detect ντ CC interactions in the νμ CNGS beam. Nuclear emulsions allow the use of topology analysis to tag ντ decays. Electronic detectors allow detailed kinematical analysis to complement the topological signature and increase the signal to background ratio. The article reviews the performance of each subdetector used alone, then shows how all the subsystems interplay to locate and study each event in the modular target. The analysis of the first ντ candidate found by the OPERA Collaboration is summarized and two examples are shown of how charm production and decay events are distinguished from ντ CC.

Direct evidence of α-particle condensation for the Hoyle state

The fragmentation of quasi-projectiles from the nuclear reaction 40 Ca+ 12 C at 25 MeV/nucleon was used to produce excited states candidates to α-particle condensation. Complete kinematic characterization of individual decay events, made possible by the CHIMERA highgranularity 4π charged particle multi-detector, reveals that 7.5±4.0 % of the Hoyle state particle decays correspond to direct decays in three equal-energy α-particles. Moreover, events with increased kinetic energy dispersion in the 12 C center of mass, which amount to 9.5±4.0 %, point toward the occurrence of a second competing molecular configuration, of a linear α-chain.

A buried glaciofluvial channel in the Anděl Col, Northern Bohemia: new evidence for the Middle Pleistocene ice sheets extent in Western Sudetes

This study presents a new finding of glaciofluvial sediments filling a buried channel in the Anděl Col (522 m a.s.l.) in the Jizera Mts., on the Czech-Polish border. At least 550 m long and 55–100 m wide channel filled by glaciofluvial sediments was determined by geophysical methods in the lowermost part of the col. The base of the channel was found at a depth of 14–19 m under the present ground surface, descending from east to west draining the ice sheet front in the same direction. The channel is incised in the bedrock representing thus a Nye channel and is filled by >13 m of glaciofluvial sand, gravel and mud, which is covered by 1–2 m thick colluvial deposits. The large part of the glaciofluvial package was deposited in subglacial environment reflecting the ice sheet decay events of higher release of the material from the ice sheet. The upper glaciofluvial part of sediments was deposited in front of the slowly decaying ice sheet front. No subglacial tills have been found in the col area, which is not unusual for such an exposed site. We reconstruct the maximum altitude limit of the ice sheet in the col as being at least at ~540 m and the ice thickness in the Anděl Col being few tens of metres. The Anděl Col is the highest known area in Northern Bohemia covered by an ice sheet and improves thus our knowledge about the maximum vertical extent of Middle Pleistocene ice sheets in Western Sudetes.

CNO and pep neutrino spectroscopy in Borexino: measurement of the cosmogenic 11C background with the Counting Test Facility

Borexino is an organic liquid scintillator detector for low energy neutrino spectroscopy at the Gran Sasso underground laboratories. Besides the main goal, the measurement of the mono-energetic 7 Be solar neutrino flux in real time, Borexino has the potential to detect pep and CNO neutrinos. For this purpose, two conditions are required: an extremely low radioactive contamination level and the efficient identification of the cosmic muon induced 11 C background. We demonstrated with the Borexino Counting Test Facility that 11 C decay events can be efficiently identified and removed event by event.

Absorbed Dose Rate Constant for 131 iodine

In this paper, Γ (absorbed dose rate constant) for 131 I is calculated theoretically and is also determined experimentally applying important correction factors. These correction factors include those factors that affect the calculations, from the radioactive source to the sensor volume detector. Particular absorbed dose rate constants were calculated for each discrete line in the photon spectrum of 131 I radionuclide with a yield per decay event>0.01% and the energy >80 keV. Estimation of dose rate for radiation source may be required for planning radiation protection measures, calibrations of radiation instruments or for estimating the absorbed dose to patients receiving brachytherapy.

Evidence for α-particle condensation in nuclei from the Hoyle state deexcitation

The fragmentation of quasi-projectiles from the nuclear reaction 40Ca + 12C at 25 MeV/nucleon was used to produce excited states candidates to α-particle condensation. Complete kinematic characterization of individual decay events, made possible by a high-granularity 4π charged particle multi-detector, reveals that 7.5±4.0% of the particle decays of the Hoyle state correspond to direct decays in three equal-energy α-particles.

Experimental Determination of theMg24I(3s3p)P23Lifetime

We present the first experimental determination of the electric-dipole forbidden $(3s3p)^{3}P_{2}\ensuremath{\rightarrow}(3{s}^{2})^{1}S_{0}$ ($M2$) transition rate in $^{24}\mathrm{Mg}$ and compare to state-of-the-art theoretical predictions. Our measurement exploits a magnetic trap isolating the sample from perturbations and a magneto-optical trap as an amplifier converting each $^{3}P_{2}\ensuremath{\rightarrow}^{1}S_{0}$ decay event into millions of photons readily detected. The transition rate is determined to be $(4.87\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\text{ }\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ corresponding to a $^{3}P_{2}$ lifetime of ${2050}_{\ensuremath{-}110}^{+140}$ sec. This value is in agreement with recent theoretical predictions, and to our knowledge the longest lifetime ever determined in a laboratory environment.

Theoretical study of neutrino scattering off the stable even Mo isotopes at low and intermediate energies

Abstract A systematic study of the cross sections of neutral-current neutrino scattering off the stable even Mo isotopes (mass number A = 92 , 94 , 96 , 98 , 100 ), at low and intermediate neutrino energies ( E ν ⩽ 130 MeV ), is presented and discussed. The required wave functions for the initial (ground state) and all accessible final nuclear states are constructed in the context of the quasi-particle random-phase approximation (QRPA) and tested against data on the low-lying energy spectra of the isotopes in question. The individual contributions coming from the polar-vector and axial-vector components of the hadronic current for the coherent and incoherent channels of each isotope are investigated. The studied Mo isotopes are contents of the detector of the MOON experiment operating at Japan with a hybrid aim to search for neutrinoless double beta decay events and to detect low- and intermediate-energy astrophysical neutrinos (solar, supernova, geo-neutrinos), and also of the NEMO neutrinoless double beta decay detector in Modane at France. For such purposes our cross section calculations are of significant importance.

Signal modeling of high-purity Ge detectors with a small read-out electrode and application to neutrinoless double beta decay search in Ge-76

The GERDA experiment searches for the neutrinoless double beta decay of76Ge using high-purity germanium detectors enriched in76Ge. The analysis of the signal time structure provides a powerfultool to identify neutrinoless double beta decay events and to discriminate themfrom gamma-ray induced backgrounds. Enhanced pulse shape discriminationcapabilities of Broad Energy Germanium detectors with a small read-outelectrode have been recently reported. This paper describes the full simulationof the response of such a detector, including the Monte Carlo modeling ofradiation interaction and subsequent signal shape calculation. A pulse shapediscrimination method based on the ratio between the maximum current signalamplitude and the event energy applied to the simulated data shows quantitativeagreement with the experimental data acquired with calibration sources. Thesimulation has been used to study the survival probabilities of the decays whichoccur inside the detector volume and are difficult to assess experimentally.Such internal decay events are produced by the cosmogenic radio-isotopes68Ge and 60Co and the neutrinoless double beta decay of76Ge. Fixing the experimental acceptance of the double escape peakof the 2.614 MeV photon to 90%, the estimated survival probabilitiesat Qββ = 2.039 MeV are (86±3)% for 76Geneutrinoless double beta decays, (4.5±0.3)% for the 68Gedaughter 68Ga, and (0.9+0.4−0.2)% for 60Codecays.

Role of nuclear dynamics in the asymmetric molecular-frame photoelectron angular distributions for C 1sphotoejection from CO2

We report the results of semiclassical calculations of the asymmetric molecular-frame photoelectron angular distributions for C 1$s$ ionization of CO${}_{2}$ measured with respect to the CO${}^{+}$ and ${\mathrm{O}}^{+}$ ions produced by subsequent Auger decay, and show how the decay event can be used to probe ultrafast molecular dynamics of the transient cation. The fixed-nuclei photoionization amplitudes were constructed using variationally obtained electron--molecular-ion scattering wave functions. The amplitudes are then used in a semiclassical manner to investigate their dependence on the nuclear dynamics of the cation. The method introduced here can be used to study other core-level ionization events.

Exploration of Pixelated detectors for double beta decay searches within the COBRA experiment

Abstract The aim of the COBRA experiment is the search for neutrinoless double beta decay events in Cadmium Zinc Telluride (CdZnTe) room temperature semiconductor detectors. The development of pixelated detectors provides the potential for clear event identification and thus major background reduction. The tracking option of a semiconductor is a unique approach in this field. For initial studies, several possible detector systems are considered with a special regard for low background applications: the large volume system Polaris with a pixelated CdZnTe sensor, Timepix detectors with Si and enriched CdTe sensor material and a CdZnTe pixel system developed at the Washington University in St. Louis, USA. For all detector systems first experimental background measurements taken at underground laboratories (Gran Sasso Underground Laboratory in Italy, LNGS and the Niederniveau Messlabor Felsenkeller in Dresden, Germany) and additionally for the Timepix detectors simulation results are presented.

Trigger efficiencies at BESIII

Trigger efficiencies at BESIII were determined for both the J/ψ and ψ′ data taking of 2009. Both dedicated runs and physics datasets are used; efficiencies are presented for Bhabha-scattering events, generic hadronic decay events involving charged tracks, dimuon events and ψ′ → π+ π− J/ψ, J/ψ → l+l− events. The efficiencies are found to lie well above 99% for all relevant physics cases, thus fulfilling the BESIII design specifications.

Simultaneous Reconstruction of Activity and Attenuation for PET/MR

Medical investigations targeting a quantitative analysis of the position emission tomography (PET) images require the incorporation of additional knowledge about the photon attenuation distribution in the patient. Today, energy range adapted attenuation maps derived from computer tomography (CT) scans are used to effectively compensate for image quality degrading effects, such as attenuation and scatter. Replacing CT by magnetic resonance (MR) is considered as the next evolutionary step in the field of hybrid imaging systems. However, unlike CT, MR does not measure the photon attenuation and thus does not provide an easy access to this valuable information. Hence, many research groups currently investigate different technologies for MR-based attenuation correction (MR-AC). Typically, these approaches are based on techniques such as special acquisition sequences (alone or in combination with subsequent image processing), anatomical atlas registration, or pattern recognition techniques using a data base of MR and corresponding CT images. We propose a generic iterative reconstruction approach to simultaneously estimate the local tracer concentration and the attenuation distribution using the segmented MR image as anatomical reference. Instead of applying predefined attenuation values to specific anatomical regions or tissue types, the gamma attenuation at 511 keV is determined from the PET emission data. In particular, our approach uses a maximum-likelihood estimation for the activity and a gradient-ascent based algorithm for the attenuation distribution. The adverse effects of scattered and accidental gamma coincidences on the quantitative accuracy of PET, as well as artifacts caused by the inherent crosstalk between activity and attenuation estimation are efficiently reduced using enhanced decay event localization provided by time-of-flight PET, accurate correction for accidental coincidences, and a reduced number of unknown attenuation coefficients. First results achieved with measured whole body PET data and reference segmentation from CT showed an absolute mean difference of 0.005 cm⁻¹ (< 20%) in the lungs, 0.0009 cm⁻¹ (< 2%) in case of fat, and 0.0015 cm⁻¹ (< 2%) for muscles and blood. The proposed method indicates a robust and reliable alternative to other MR-AC approaches targeting patient specific quantitative analysis in time-of-flight PET/MR.

A CMOS compatible Microbulk Micromegas-like detector using silicon oxide as spacer material

We present a new Micro Pattern Gaseous Detector (MPGD) fabricated with nonpolymeric materials. The device structure is similar to a Microbulk Micromegas design, consisting of a punctured metal grid supported by a continuous perforated insulating structure. In this detector, the supporting structure is made out of silicon oxide. Devices were tested in He/ iC 4H 10 (80/20) and Ar/ iC 4H 10 (80/20) gas mixtures under 55Fe irradiation. Gas gain of 20,000 and energy resolution below 13% FWHM were achieved. The CMOS compatibility of the fabrication process has been studied in Timepix chips as well as individual 0.13-μm technology CMOS transistors. Complete detectors have been fabricated on top of Timepix chips. In an Ar/ iC 4H 10 (80/20) gas mixture 55Fe decay events were recorded operating the Timepix chip in 2D readout mode.

Collinear cluster tripartition channel in the reaction 235U(n th, f)

Investigation of the 235U(n th, f) reaction using the miniFOBOS double-arm time-of-flight spectrometer of fission fragments confirmed manifestations of the earlier unknown many-body, at least ternary, decay involving almost collinear decay-product escape, which were first observed in the spontaneous fission of 252Cf(sf). The use of variables sensitive to the nuclear charge of fission fragments allowed the reliability of identification of decay events to be increased and new decay modes to be revealed.

Decoherence suppression by quantum measurement reversal

We show that qubit decoherence due to zero-temperature energy relaxation can be almost completely suppressed by using the quantum uncollapsing (measurement reversal) procedure. To protect a qubit state, a partial quantum measurement moves it toward the ground state, where it is kept during the storage period, while the second partial measurement restores the initial state. This procedure preferentially selects the cases without energy decay events. Stronger decoherence suppression requires smaller selection probability; a desired point in this trade-off can be chosen by varying the measurement strength. The experiment can be realized in a straightforward way using the superconducting phase qubit.

Proton decay and nuclear dynamics

The kinematics of the decay of a bound proton is governed by the proton spectral function. We evaluate this quantity in 16O using the information from nuclear physics experiments. It also includes a correlated part. The reliability of this evaluation is sufficient to open the possibility of correlated cuts in the missing mass and momentum variables in order to identify the decay events from the bound protons with a possible increase of the signal to noise ratio.