New measurement of the neutron lifetime with a large gravitational trap

The lifetime of the neutron is one of the key physical quantities used to determine the weak interaction parameters and to test predictions of the theory of primary nucleosynthesis. The lifetime of the neutron has been measured in the reported experiment by the method of storing neutrons in a material trap with a gravitational valve. Fomblin grease UT-18 hydrogen-free fluorine polymer has been used as coating. The resistance of the coating to repeated cooling down to 80 K combined with heating up to 300 K has been studied. The probability of losses in the trap is as small as 1.5% of the neutron decay probability. The lifetime of the neutron τ_n = (881.5 ± 0.7_stat ± 0.6_syst)s obtained at the new step is in good agreement with a commonly accepted value of (880.2 ± 1.0) s presented by the Particle Data Group.     

Neutron lifetime and the background structure in a neutron magnetic trap

A new cycle of processing the 1985–1986 experimental data concerning the storage of neutrons in a magnetic gravitational trap was carried out. It was shown that the count rates determined for the background are multiples of the neutron decay constant. This is explained by the fact that the background in the experiment on the storage of ultracold neutrons was caused by the electron count from background neutrons penetrating through trap walls. Numerous measurements for a small and varying number of background neutrons in the trap make it possible to extract and use data for determining the mean neutron lifetime. This lifetime turns out to be τtn=900.01±0.15 s in a nonuniform magnetic field.     

Measurement of the neutron lifetime in a magnetic storage ring

In previous papers a storage ring for neutrons was reported, which enables the confinement of very slow neutrons by means of their magnetic moment in a magnetic multipole torus. Improved experimental conditions permitted to determine the life-time of the stored neutrons by measuring their number with good accuracy up to one hour. After an initial phase the decrease with time follows very well a single exponential function with a time constant τ=877±10s. As explained in the paper this number represents the lifetime of the free neutron within the given errors.     

New installation for measuring a neutron lifetime with a big gravitational trap of ultra cold neutrons

At present the highest precision of neutron lifetime measurements has been achieved by the experiment made in Petersburg Nuclear Physics Institute (PNPI) with a gravitational trap of ultracold neutrons (UCN). A new installation with a big gravitational trap is an advanced development of methods and approaches applied in the previous experiment. We are planning to attain the measurement precision of 0.2 s which is four times better than the existing level of precision. A model of the experiemnt has been made for simulation by the Monte Carlo method. This model allows one to imply the concrete value of the neutron lifetime, then to reproduce an experiemental procedure and to see if there is any difference between the implied value and the measured one. As a result of modelling one has determined systematic uncertainty related to the procedure of calculating the efficient frequency of collisions of UCNs. It is equal to 0.1 s. We have also carried on modeling of different construction units of the installation.     

Measurement of the proton asymmetry parameter in neutron beta decay

The proton asymmetry parameter C in neutron decay describes the angular correlation between neutron spin and proton momentum. In this Letter, the first measurement of this quantity is presented. The result C= -0.2377(26) agrees with the standard model expectation. The coefficient C provides an additional parameter for new and improved standard model tests.     

Ultracold neutron detector for the spectrometer of a neutron lifetime measuring

The gas-discharge detector is designed for the neutron lifetime spectrometer. The detector is intended for ultracold neutron flux monitoring in measurement cycles at the specrtometer (ILL, Grenoble, France). The detector has been successively tested with a Pu–Be neutron source under laboratory conditions and as a part of the spectrometer.     

Uncertainties in the proton lifetime

We discuss the masses of the leptoquark bosons m_x and the proton lifetime in grand unified theories based principally on SU(5). It is emphasized that estimates of m_x based on the QCD coupling and the fine structure constant are probably more reliable than those using the experimental value of sin²θ_w. Uncertainties in the QCD Λ parameter and the correct value of α are discussed. We estimate higher-order effects on the evolution of coupling constants in a momentum-space renormalization scheme. It is shown that increasing the number of generations of fermions beyond the minimal three increases m_x by almost a factor of 2 per generation. Additional uncertainties exist for each generation of technifermions that may exist. We discuss and discount the possibility that proton decay could be “Cabibbo rotated” away, and a speculation that Lorentz invariance may be violated in proton decay at a detectable level. We estimate that in the absence of any substantial new physics beyond that in the minimal SU(5) model the proton lifetime is 8 × 10^30±2 years.     

Measurement of antiproton lifetime using the ice storage ring

Antiprotons have been stored in the ICE Storage Ring and held for 85h with the help of stochastic cooling. We set a limit of at least 32 h for the antiproton lifetime (in its rest frame).     

Problem of the neutron lifetime measurements

The current status of the measurements of the neutron lifetime has been analyzed. The problem of experimental data discrepancy has been analyzed and systematic errors of some experiments have been found out. The corrected table of measurements is given and a new world average value of neutron lifetime 879.9 ± 0.9 s is presented.     

Measurement of the Lambdab0 lifetime using semileptonic decays

We report a measurement of the Lambda(b)(0) lifetime using a sample corresponding to 1.3 fb(-1) of data collected by the D0 experiment in 2002-2006 during run II of the Fermilab Tevatron collider. The Lambda(b)(0) baryon is reconstructed via the decay Lambda(b)(0)-->micronuLambda(c)(+)X. Using 4437+/-329 signal candidates, we measure the Lambda(b)(0) lifetime to be tau(Lambda(b)(0))=1.290(-0.110)(+0.119)(stat)(-0.091)(+0.087)(syst) ps, which is among the most precise measurements in semileptonic Lambda(b)(0) decays. This result is in good agreement with the world average value.     

Precision mass measurements of neutron halo nuclei using the TITAN Penning trap

Precise atomic mass determinations play a key role in various fields of physics, including nuclear physics, testing of fundamental symmetries and constants and atomic physics. Recently, the TITAN Penning trap measured the masses of several neutron halos. These exotic systems have an extended, diluted, matter distribution that can be modelled by considering a nuclear core surrounded by a halo formed by one or more of loosely bound neutrons. Combined with laser spectroscopy measurements of isotopic shifts precise masses can be used to obtain reliable charge radii and two-neutron-seperation energies for these halo nuclei. It is shown that these results can be used as stringent tests of nuclear models and potentials providing an important metric for our understanding of the interactions in all nuclei.     

A new estimate of the proton lifetime

We find a theoretical upper limit of 10³² years for the proton decay lifetime in the SU(5) grand unified theory of Georgi and Glashow based on a calculation at the two-loop level.     

Measurement of neutron fluence with CR-39 using a UV spectrophotometer

Measurement of the correct neutron fluence in various energy intervals in and around the neutron sources is important for the purpose of personnel and environmental neutron dosimetry. In the present paper we present a method for the measurement of neutron fluence using a CR-39 plastic track detector. The samples exposed to fission neutrons from a reactor with 10¹²– fluence and to fast neutrons from a ²⁴¹Am–Be source with a fluence of were etched for 14 time intervals starting from 10 to 570 min in 6 N NaOH at . The etched samples were exposed to the monochromatic light signal from an iodine–tungsten lamp and the transmittance was measured after each etching time interval using a UV Spectrophotometer. An exponential decay of the transmittance has been observed with increasing etching time. The behaviour of the fission neutrons having four different values of fluence has been observed to be distinctly different from that of the fast neutrons. It has also been observed that there is a linear relationship between the transmittance decay constant and fission neutron fluence.     

Measurement of the τ lifetime

Using the 3-prong decays of τ leptons observed at the CELLO detector at PETRA, the τ lifetime is determined to be 4.7(_?2.9^+3.9)×10^?13s.     

Measurement of the Bs(0) lifetime using semileptonic decays

We report a measurement of the Bs(0) lifetime in the semileptonic decay channel Bs(0) --> Ds- mu+ nuX (and its charge conjugate), using approximately 0.4 fb(-1) of data collected with the D0 detector during 2002-2004. Using 5176 reconstructed Ds- mu+ signal events, we have measured the Bs(0) lifetime to be tau(Bs(0))=1.398+/-0.044(stat)(-0.025)(+0.028)(syst) ps. This is the most precise measurement of the Bs(0) lifetime to date.     

Characterisation of proton irradiated CR-39 detector using positron annihilation lifetime spectroscopy

The damaged produced by proton beam slowed down in CR-39 polymer results in highest degree of disorder with change of free volume proprieties. Positron annihilation lifetime spectroscopy (PALS) is nowadays well recognized as powerful tool of microstructure investigations. PALS is used in order to get more information at an atomic scale of modifications induced by irradiation of polymers particularly the variation of free volume in the irradiated region. In this paper, the mean free volume hole radii and average free volume of the micro-voids in CR-39 polymer irradiated with 200 MeV therapy proton beam at different positions in spread out Bragg Peak region (SOBP) at Ithemba proton therapy facility have been determined using PALS. © 2006 Elsevier Ltd. All rights reserved.     

Measurement of the excited-state lifetime of a microelectronic circuit

We demonstrate that a continuously measured microelectronic circuit, the Cooper-pair box measured by a radio-frequency single-electron transistor, approximates a quantum two-level system. We extract the Hamiltonian of the circuit through resonant spectroscopy and measure the excited-state lifetime. The lifetime is more than 10(5) times longer than the inverse transition frequency of the two-level system, even though the measurement is active. This lifetime is also comparable to an estimate of the known upper limit, set by spontaneous emission, for this circuit.