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W. Heil

Publications and source records attributed to W. Heil.

35 records · Page 2Linked to original sources
arXiv2013

New limit on Lorentz and CPT violating neutron spin interactions using a free precession 3He-129Xe co-magnetometer

We report on the search for a CPT and Lorentz invariance violating coupling of the 3He and 129Xe nuclear spins (each largely determined by a valence neutron) to background tensor fields which permeate the universe. Our experimental approach is to measure the free precession of nuclear spin polarized 3He and 129Xe atoms in a homogeneous magnetic guiding field of about 400 nT using LTC SQUIDs as low-noise magnetic flux detectors. As the laboratory reference frame rotates with respect to distant stars, we look for a sidereal modulation of the Larmor frequencies of the co-located spin samples. As a result we obtain an upper limit on the equatorial component of the background field interacting with the spin of the bound neutron bn< 6.7*10^-34 GeV (68% C.L.). Our result improves our previous limit (data measured in 2009) by a factor of 30 and the world's best limit by a factor of 5.

gr-qc↗
arXiv2013

Measurement of the neutron electric to magnetic form factor ratio at Q2 = 1.58 GeV2 using the reaction 3He(e,e'n)pp

A measurement of beam helicity asymmetries in the reaction 3He(e,e'n)pp has been performed at the Mainz Microtron in quasielastic kinematics in order to determine the electric to magnetic form factor ratio of the neutron, GEn/GMn, at a four momentum transfer Q2 = 1.58 GeV2. Longitudinally polarized electrons were scattered on a highly polarized 3He gas target. The scattered electrons were detected with a high-resolution magnetic spectrometer, and the ejected neutrons with a dedicated neutron detector composed of scintillator bars. To reduce systematic errors data were taken for four different target polarization orientations allowing the determination of GEn/GMn from a double ratio. We find mu_n GEn/GMn = 0.250 +/- 0.058(stat.) +/- 0.017 (sys.).

nucl-ex↗
arXiv2013

Probing Physics beyond the Standard Model with He/Xe clock comparison experiments

The comparison of the free precession of co-located 3He-129Xe spins (clock comparison) enables us to search for very tiny nonmagnetic spin interactions. With our setup we could establish new limits for Lorentz invariance violating interactions of spins with a relic background field which permeates the Universe and points in a preferred direction in space.

hep-ph↗
arXiv2013

Using a rotating magnetic guiding field for the 3He-129Xe-Comagnetometer

Our search for non-magnetic spin-dependent interactions is based on the measurement of free precession of nuclear spin polarized 3He and 129Xe atoms in a homogeneous magnetic guiding field of about 400 nT. We report on our approach to perform an adiabatic rotation of the guiding field that allows us to modulate possible non-magnetic spin-dependent interactions and to find an optimization procedure for long transverse relaxation times T2* both for Helium and Xenon.

hep-ph↗
arXiv2011

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.

nucl-ex↗
arXiv2011

Limit on Lorentz and CPT violation of the bound Neutron Using a Free Precession 3He/129Xe co-magnetometer

We report on the search for Lorentz violating sidereal variations of the frequency difference of co-located spin-species while the Earth and hence the laboratory reference frame rotates with respect to a relic background field. The co-magnetometer used is based on the detection of freely precessing nuclear spins from polarized 3He and 129Xe gas samples using SQUIDs as low-noise magnetic flux detectors. As result we can determine the limit for the equatorial component of the background field interacting with the spin of the bound neutron to be bn < 3.7 x 10^{-32} GeV (95 C.L.).

gr-qc↗
arXiv2010

Impact of Neutron Decay Experiments on non-Standard Model Physics

This paper gives a brief overview of the present and expected future limits on physics beyond the Standard Model (SM) from neutron beta decay, which is described by two parameters only within the SM. Since more than two observables are accessible, the problem is over-determined. Thus, precise measurements of correlations in neutron decay can be used to study the SM as well to search for evidence of possible extensions to it. Of particular interest in this context are the search for right-handed currents or for scalar and tensor interactions. Precision measurements of neutron decay observables address important open questions of particle physics and cosmology, and are generally complementary to direct searches for new physics beyond the SM in high-energy physics. Free neutron decay is therefore a very active field, with a number of new measurements underway worldwide. We present the impact of recent developments.

nucl-ex↗
arXiv2010

Testing isotropy of the universe using the Ramsey resonance technique on ultracold neutron spins

Physics at the Planck scale could be revealed by looking for tiny violations of fundamental symmetries in low energy experiments. In 2008, a sensitive test of the isotropy of the Universe using has been performed with stored ultracold neutrons (UCN), this is the first clock-comparison experiment performed with free neutrons. During several days we monitored the Larmor frequency of neutron spins in a weak magnetic field using the Ramsey resonance technique. An non-zero cosmic axial field, violating rotational symmetry, would induce a daily variation of the precession frequency. Our null result constitutes one of the most stringent tests of Lorentz invariance to date.

physics.atom-ph↗
arXiv2010

Test of Lorentz Symmetry by using a 3He/129Xe Co-Magnetometer

To test Lorentz symmetry we used a 3He/129Xe co-magnetometer. We will give a short summary of our experimental setup and the results of our latest measurements. We obtained preliminary results for the equatorial component of the background field interacting with the spin of the bound neutron: b_n < 3.72 x 10^(-32) GeV (95 C.L.).

hep-ph↗
arXiv2009

Test of Lorentz invariance with spin precession of ultracold neutrons

A clock comparison experiment, analyzing the ratio of spin precession frequencies of stored ultracold neutrons and $^{199}$Hg atoms is reported. %57 No daily variation of this ratio could be found, from which is set an upper limit on the Lorentz invariance violating cosmic anisotropy field $b_{\bot} < 2 \times 10^{-20} {\rm eV}$ (95% C.L.). This is the first limit for the free neutron. This result is also interpreted as a direct limit on the gravitational dipole moment of the neutron $|g_n| < 0.3 $eV/$c^2$ m from a spin-dependent interaction with the Sun. Analyzing the gravitational interaction with the Earth, based on previous data, yields a more stringent limit $|g_n| < 3 \times 10^{-4} $eV/$c^2 $m.

nucl-ex↗
arXiv2009

Ultra-sensitive magnetometry based on free precession of nuclear spins

We discuss the design and performance of a very sensitive low-field magnetometer based on the detection of free spin precession of gaseous, nuclear polarized 3He or 129Xe samples with a SQUID as magnetic flux detector. The device will be employed to control fluctuating magnetic fields and gradients in a new experiment searching for a permanent electric dipole moment of the neutron as well as in a new type of 3He/129Xe clock comparison experiment which should be sensitive to a sidereal variation of the relative spin precession frequency. Characteristic spin precession times T_2 of up to 60h could be measured. In combination with a signal-to-noise ratio of > 5000:1, this leads to a sensitivity level of deltaB= 1fT after an integration time of 220s and to deltaB= 10^(-4)fT after one day. Even in that sensitivity range, the magnetometer performance is statistically limited, and noise sources inherent to the magnetometer are not limiting. The reason is that free precessing 3He (129Xe) nuclear spins are almost completely decoupled from the environment. That makes this type of magnetometer in particular attractive for precision field measurements where a long-term stability is required.

physics.ins-det↗
arXiv2009

Cubic boron nitride: a new prospective material for ultracold neutron application

For the first time, the neutron optical wall-potential of natural cubic boron nitride (cBN) was measured at the ultracold neutron (UCN) source of the research reactor TRIGA Mainz using the time-of-flight method (TOF). The samples investigated had a wall-potential of (305 +/- 15) neV. This value is in good agreement with the result extracted from neutron reflectometry data and theoretical expectations. Because of its high critical velocity for UCN and its good dielectric characteristics, cubic boron nitride coatings (isotopically enriched) will be useful for a number of applications in UCN experiments.

nucl-ex↗
arXiv2008

Measuring the proton spectrum in neutron decay - latest results with aSPECT

The retardation spectrometer aSPECT was built to measure the shape of the proton spectrum in free neutron decay with high precision. This allows us to determine the antineutrino electron angular correlation coefficient a. We aim for a precision more than one order of magnitude better than the present best value, which is Delta_a /a = 5%. In a recent beam time performed at the Institut Laue-Langevin during April / May 2008 we reached a statistical accuracy of about 2% per 24 hours measurement time. Several systematic effects were investigated experimentally. We expect the total relative uncertainty to be well below 5%.

nucl-ex↗
arXiv2008

An Improved Neutron Electric Dipole Moment Experiment

A new measurement of the neutron EDM, using Ramsey's method of separated oscillatory fields, is in preparation at the new high intensity source of ultra-cold neutrons (UCN) at the Paul Scherrer Institute, Villigen, Switzerland (PSI). The existence of a non-zero nEDM would violate both parity and time reversal symmetry and, given the CPT theorem, might lead to a discovery of new CP violating mechanisms. Already the current upper limit for the nEDM (|d_n|<2.9E-26 e.cm) constrains some extensions of the Standard Model. The new experiment aims at a two orders of magnitude reduction of the experimental uncertainty, to be achieved mainly by (1) the higher UCN flux provided by the new PSI source, (2) better magnetic field control with improved magnetometry and (3) a double chamber configuration with opposite electric field directions. The first stage of the experiment will use an upgrade of the RAL/Sussex/ILL group's apparatus (which has produced the current best result) moved from Institut Laue-Langevin to PSI. The final accuracy will be achieved in a further step with a new spectrometer, presently in the design phase.

nucl-ex↗
arXiv2005

Measurement of the asymmetries in 3He(e,e'p)d and 3He(e,e'p)np

The electron-target-asymmetries A_parallel and A_perpendicular with target spin parallel and perpendicular to the momentum transfer q were measured for both the two-- and three-body breakup of 3He in the 3He(e,e'p)-reaction. Polarized electrons were scattered off polarized 3He in the quasielastic regime in parallel kinematics with the scattered electron and the knocked-out proton detected using the Three-Spectrometer-Facility at MAMI. The results are compared to Faddeev calculations which take into account Final State Interactions as well as Meson Exchange Currents. The experiment confirms the prediction of a large effect of Final State Interactions in the asymmetry of the three-body breakup and of an almost negligible one for the two-body breakup.

nucl-ex↗
arXiv2003

Final State Interaction Effects in pol 3He(pol e,e'p)

Asymmetries in quasi-elastic pol 3He(pol e,e'p) have been measured at a momentum transfer of 0.67 (GeV/c)^2 and are compared to a calculation which takes into account relativistic kinematics in the final state and a relativistic one-body current operator. With an exact solution of the Faddeev equation for the 3He-ground state and an approximate treatment of final state interactions in the continuum good agreement is found with the experimental data.

nucl-ex↗