236 research outputs found
Tests of the standard electroweak model in beta decay
We review the current status of precision measurements in allowed nuclear beta decay, including neutron decay, with emphasis on their potential to look for new physics beyond the standard electroweak model. The experimental results are interpreted in the framework of phenomenological model-independent descriptions of nuclear beta decay as well as in some specific extensions of the standard model. The values of the standard couplings and the constraints on the exotic couplings of the general beta decay Hamiltonian are updated. For the ratio between the axial and the vector couplings we obtain C_A/C_V = -1.26992(69) under the standard model assumptions. Particular attention is devoted to the discussion of the sensitivity and complementarity of different precision experiments in direct beta decay. The prospects and the impact of recent developments of precision tools and of high intensity low energy beams are also addressed
Measurement of the Transverse Polarization of Electrons Emitted in Free Neutron Decay
Both components of the transverse polarization of electrons emitted in the
beta-decay of polarized, free neutrons have been measured. The T-odd, P-odd
correlation coefficient quantifying the component perpendicular to the decay
plane defined by neutron polarization and electron momentum, was found to be
R=0.008 +/- 0.015 +/-0.005. This value is consistent with time reversal
invariance, and significantly improves limits on the relative strength of
imaginary scalar couplings in the weak interaction. The value obtained for the
correlation coefficient associated with the electron polarization component
contained within the decay plane N=0.056 +/- 0.011 +/- 0.005, agrees with the
Standard Model expectation, providing an important sensitivity test of the
experimental setup.Comment: 4 pages, 4 figure
Transport and cooling of singly-charged noble gas ion beams
The transport and cooling of noble gas singly-charged ion beams by means of a
Radio Frequency Quadrupole Cooler Buncher (RFQCB) have been studied at the
LIMBE low energy beam line of the GANIL facility. Ions as light as
have been cooled and stored before their extraction in bunches using as
buffer gas. Bunches characteristics have been studied as a function of the
parameters of the device. Sizeable transmissions of up to 10 have been
obtained. A detailed study of the lifetime of ions inside the buncher has been
performed giving an estimate of the charge exchange cross-section. Results of a
microscopic Monte-Carlo transport code show reasonable agreement with
experimental data.Comment: 13 figure
Free neutron decay and time reversal violation
Both components of the transverse electron polarization have been measured in free neutron decay. The T-odd, P-odd correlation coefficient associated with polarization component perpendicular to the neutron polarization
and electron momentum, was found to be R = 0:006 0:012 0:005. This value is consistent with time reversal invariance, and significantly improves limits on the relative strength of imaginary scalar couplings in the
weak interaction. The value obtained for the T-even, P-even correlation coefficient connected with the second transversal polarization component, N = 0:065 0:012 0:004, agrees with the Standard Model expectation
providing an important sensitivity test of the experimental setup
Weak Interaction Studies with 6He
The 6He nucleus is an ideal candidate to study the weak interaction. To this
end we have built a high-intensity source of 6He delivering ~10^10 atoms/s to
experiments. Taking full advantage of that available intensity we have
performed a high-precision measurement of the 6He half-life that directly
probes the axial part of the nuclear Hamiltonian. Currently, we are preparing a
measurement of the beta-neutrino angular correlation in 6He beta decay that
will allow to search for new physics beyond the Standard Model in the form of
tensor currents.Comment: 5 pages, 4 figures, proceedings for the Eleventh Conference on the
Intersections of Particle and Nuclear Physics (CIPANP 2012
Paul trapping of radioactive 6He+ions and direct observation of their beta-decay
We demonstrate that abundant quantities of short-lived beta unstable ions can
be trapped in a novel transparent Paul trap and that their decay products can
directly be detected in coincidence. Low energy 6He+ (807 ms half-life) ions
were extracted from the SPIRAL source at GANIL, then decelerated, cooled and
bunched by means of the buffer gas cooling technique. More than 10^8 ions have
been stored over a measuring period of six days and about 10^5 decay
coincidences between the beta particles and the 6Li^{++} recoiling ions have
been recorded. The technique can be extended to other short-lived species,
opening new possibilities for trap assisted decay experiments.Comment: 4 pages, 4 figures, submitted to Phys.Rev.Let
Constraining interactions mediated by axion-like particles with ultracold neutrons
We report a new limit on a possible short range spin-dependent interaction
from the precise measurement of the ratio of Larmor precession frequencies of
stored ultracold neutrons and Hg atoms confined in the same volume. The
measurement was performed in a 1 T vertical magnetic holding field
with the apparatus searching for a permanent electric dipole moment of the
neutron at the Paul Scherrer Institute. A possible coupling between freely
precessing polarized neutron spins and unpolarized nucleons of the wall
material can be investigated by searching for a tiny change of the precession
frequencies of neutron and mercury spins. Such a frequency change can be
interpreted as a consequence of a short range spin-dependent interaction that
could possibly be mediated by axions or axion-like particles. The interaction
strength is proportional to the CP violating product of scalar and pseudoscalar
coupling constants . Our result confirms limits from complementary
experiments with spin-polarized nuclei in a model-independent way. Limits from
other neutron experiments are improved by up to two orders of magnitude in the
interaction range of m
A highly stable atomic vector magnetometer based on free spin precession
We present a magnetometer based on optically pumped Cs atoms that measures
the magnitude and direction of a 1 T magnetic field. Multiple circularly
polarized laser beams were used to probe the free spin precession of the Cs
atoms. The design was optimized for long-time stability and achieves a scalar
resolution better than 300 fT for integration times ranging from 80 ms to 1000
s. The best scalar resolution of less than 80 fT was reached with integration
times of 1.6 to 6 s. We were able to measure the magnetic field direction with
a resolution better than 10 rad for integration times from 10 s up to 2000
s
An Improved Search for the Neutron Electric Dipole Moment
A permanent electric dipole moment of fundamental spin-1/2 particles violates
both parity (P) and time re- versal (T) symmetry, and hence, also charge-parity
(CP) symmetry since there is no sign of CPT-violation. The search for a neutron
electric dipole moment (nEDM) probes CP violation within and beyond the Stan-
dard Model. The experiment, set up at the Paul Scherrer Institute (PSI), an
improved, upgraded version of the apparatus which provided the current best
experimental limit, dn < 2.9E-26 ecm (90% C.L.), by the RAL/Sussex/ILL
collaboration: Baker et al., Phys. Rev. Lett. 97, 131801 (2006). In the next
two years we aim to improve the sensitivity of the apparatus to sigma(dn) =
2.6E-27 ecm corresponding to an upper limit of dn < 5E-27 ecm (95% C.L.), in
case for a null result. In parallel the collaboration works on the design of a
new apparatus to further increase the sensitivity to sigma(dn) = 2.6E-28 ecm.Comment: APS Division for particles and fields, Conference Proceedings, Two
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