The precise value of the mean neutron lifetime, τ
, plays an important role in nuclear and particle physics and cosmology. It is used to predict the ratio of protons to helium atoms in the primordial ...universe and to search for physics beyond the Standard Model of particle physics. We eliminated loss mechanisms present in previous trap experiments by levitating polarized ultracold neutrons above the surface of an asymmetric storage trap using a repulsive magnetic field gradient so that the stored neutrons do not interact with material trap walls. As a result of this approach and the use of an in situ neutron detector, the lifetime reported here 877.7 ± 0.7 (stat) +0.4/-0.2 (sys) seconds does not require corrections larger than the quoted uncertainties.
We report on precision resonance spectroscopy measurements of quantum states of ultracold neutrons confined above the surface of a horizontal mirror by the gravity potential of Earth. Resonant ...transitions between several of the lowest quantum states are observed for the first time. These measurements demonstrate that Newton's inverse square law of gravity is understood at micron distances on an energy scale of 10-14 eV. At this level of precision, we are able to provide constraints on any possible gravitylike interaction. In particular, a dark energy chameleon field is excluded for values of the coupling constant β>5.8×108 at 95% confidence level (C.L.), and an attractive (repulsive) dark matter axionlike spin-mass coupling is excluded for the coupling strength gsgp>3.7×10-16 (5.3×10-16) at a Yukawa length of λ=20 μm (95% C.L.).
Present experimental and astrophysical limits do not exclude that the neutron (
n
) oscillation into mirror neutron (
n
′
), a sterile state exactly degenerate in mass with the neutron, can be a very ...fast process, in fact faster than the neutron decay itself, in which case it would have very interesting implications in cosmology and astrophysics. This process is sensitive to the magnetic field. Namely, if the mirror magnetic field
B
′
exists at the Earth,
n
-
n
′
oscillation probability can be suppressed or resonantly amplified by the applied magnetic field
B
, depending on its strength and on the angle
β
between
B
and
B
′
. We present the results of ultra-cold neutron storage measurements aiming to check the anomalies observed in previous experiments which could be a signal for
n
-
n
′
oscillation in the presence of mirror magnetic field
B
′
∼
0.1
G. From the analysis of the experimental data new lower limits on
n
-
n
′
oscillation time as a function of
B
′
were obtained, assuming that the mirror magnetic field is constant in time:
τ
n
n
′
>
17
s (95 % C.L.) for any
B
′
between 0.08 and 0.17 G, and
τ
n
n
′
/
cos
β
>
27
s (95 % C.L.) for any
B
′
in the interval (
0.06
÷
0.25
) G.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We present for the first time a detailed and comprehensive analysis of the experimental results that set the current world sensitivity limit on the magnitude of the electric dipole moment (EDM) of ...the neutron. We have extended and enhanced our earlier analysis to include recent developments in the understanding of the effects of gravity in depolarizing ultracold neutrons (UCN); an improved calculation of the spectrum of the neutrons; and conservative estimates of other possible systematic errors, which are also shown to be consistent with more recent measurements undertaken with the apparatus. We obtain a net result of $d_\mathrm{n} = -0.21 \pm 1.82 \times10^{-26}$ $e$cm, which may be interpreted as a slightly revised upper limit on the magnitude of the EDM of $3.0 \times10^{-26}$ $e$cm (90% CL) or $ 3.6 \times10^{-26}$ $e$cm (95% CL). This paper is dedicated by the remaining authors to the memory of Prof. J. Michael Pendlebury.
We report on a search for ultralow-mass axionlike dark matter by analyzing the ratio of the spin-precession frequencies of stored ultracold neutrons and Hg199 atoms for an axion-induced oscillating ...electric dipole moment of the neutron and an axion-wind spin-precession effect. No signal consistent with dark matter is observed for the axion mass range 10−24≤ma≤10−17eV . Our null result sets the first laboratory constraints on the coupling of axion dark matter to gluons, which improve on astrophysical limits by up to 3 orders of magnitude, and also improves on previous laboratory constraints on the axion coupling to nucleons by up to a factor of 40.
We present estimations of systematic corrections and results of their experimental studies for our neutron lifetime experiment carried out in 2008–2010 at ILL. Taking into account these systematic ...corrections, we reduce the data of three independent sets of measurements (obtained during period 2008–2010) performed with different energy spectra of ultracold neutrons (UCNs) at different trap temperatures to the mean neutron lifetime value equal to 880.2(1.2) s.
We report a measurement of the neutron lifetime using ultracold neutrons stored in a magneto-gravitational trap made of permanent magnets. Neutrons surviving in the trap after fixed storage times ...have been counted and the trap losses have continuously been monitored during storage by detecting neutrons leaking from the trap. The value of the neutron lifetime resulting from this measurement is τ
n
= (878.3 ± 1.6
stat
± 1.0
syst
) A unique feature of this experiment is the monitoring of leaking neutrons providing a robust control of the main systematic loss.
We report an improved measurement of the free neutron lifetime τn using the UCN τ apparatus at the Los Alamos Neutron Science Center. We count a total of approximately 38 × 106 surviving ultracold ...neutrons (UCNs) after storing in UCN τ's magnetogravitational trap over two data acquisition campaigns in 2017 and 2018. We extract τn from three blinded, independent analyses by both pairing long and short storage time runs to find a set of replicate τn measurements and by performing a global likelihood fit to all data while self-consistently incorporating the β -decay lifetime. Both techniques achieve consistent results and find a value τn = 877.75 ± 0.2 8stat + 0.22/−0.16syst s. With this sensitivity, neutron lifetime experiments now directly address the impact of recent refinements in our understanding of the standard model for neutron decay.
Fornal and Grinstein recently proposed that the discrepancy between two different methods of neutron lifetime measurements, the beam and bottle methods, can be explained by a previously unobserved ...dark matter decay mode, n→X+γ. We perform a search for this decay mode over the allowed range of energies of the monoenergetic γ ray for X to be dark matter. A Compton-suppressed high-purity germanium detector is used to identify γ rays from neutron decay in a nickel-phosphorous-coated stainless-steel bottle. A combination of Monte Carlo and radioactive source calibrations is used to determine the absolute efficiency for detecting γ rays arising from the dark matter decay mode. We exclude the possibility of a sufficiently strong branch to explain the lifetime discrepancy with 97% confidence.
The electrical neutrality of the neutron is linked to the electric charge quantization. It is not understood yet if the electric charge is quantized or not. Since the discovery of the neutron, many ...attempts have been made to measure its electric charge qn directly and indirectly. We present a method to search for a possible qn by means of an optical setup using ultracold neutrons. In a first run, a statistical sensitivity of δqn=2.4×10−20 e/day is achieved. Possible improvements to increase this sensitivity down to δqn≈1×10−21 e/day are found and discussed.
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