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Horizontal cut of the Trine detector. The longitudinally polarised neutron beam enters the chamber from the left side through diaphragms. From outside to inside are shown the detector chamber, the scintillators with light guides and photomultipliers, the MWPC, the Mylar foil supported by bars, the electrode, and the two rows of PIN diodes. For symmetrisation, only events with the electron passing a range symmetric to the PIN diode plane hit by the proton are accepted in the analysis (as indicated for plane 5 from the left), instead of the full scintillator (dashed lines).
Source publication
We have measured the triple correlation D of the neutron polarisation and the momenta of electron and antineutrino, , in neutron beta decay. Our result is D=[−2.8±6.4(stat)±3.0(syst)]×10−4. The corresponding phase between gA and gV in V–A-theory follows as φAV=180.04°±0.09°. This result improves the limit on a possible T violation in neutron beta d...
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Citations
... [277,276,315]. Spatial resolution, in some cases including electron tracking, yields complementary systematics and is required in measurements of triple correlations [316,299,317] or of correlations involving the transverse electron polarisation [299], see Section 5.2.3. All experiments may profit from time localisation of the neutron pulse for background suppression or, in case of CRES, to reduce the data volume (Section 5.2.4). ...
Presently under construction in Lund, Sweden, the European Spallation Source (ESS) will
be the world’s brightest neutron source. As such, it has the potential for a particle physics
program with a unique reach and which is complementary to that available at other
facilities. This paper describes proposed particle physics activities for the ESS. These
encompass the exploitation of both the neutrons and neutrinos produced at the ESS for
high precision (sensitivity) measurements (searches).
... Given the exceedingly small interaction cross section for antineutrinos, this correlation is typically measured by detecting the outgoing proton, possibly in coincidence with the outgoing electron. Because the proton emerges with a maximal kinetic energy of 751 eV, these are detected after post-acceleration using a variety of detector technologies [54][55][56][57][58][59][60]. The Nab experiment uses high-purity, thick silicon detectors [61,62] which display excellent linearity over the full range of energies for electrons emerging from neutron β decay. ...
The Nab experiment at Oak Ridge National Laboratory, USA, aims to measure the beta-antineutrino angular correlation following neutron $\beta$ decay to an anticipated precision of approximately 0.1\%. The proton momentum is reconstructed through proton time-of-flight measurements, and potential systematic biases in the timing reconstruction due to detector effects must be controlled at the nanosecond level. We present a thorough and detailed semiconductor and quasiparticle transport simulation effort to provide precise pulse shapes, and report on relevant systematic effects and potential measurement schemes.
... [277,276,315]. Spatial resolution, in some cases including electron tracking, yields complementary systematics and is required in measurements of triple correlations [316,299,317] or of correlations involving the transverse electron polarisation [299], see Section 5.2.3. All experiments may profit from time localisation of the neutron pulse for background suppression or, in case of CRES, to reduce the data volume (Section 5.2.4). ...
Presently under construction in Lund, Sweden, the European Spallation Source (ESS) will be the world's brightest neutron source. As such, it has the potential for a particle physics program with a unique reach and which is complementary to that available at other facilities. This paper describes proposed particle physics activities for the ESS. These encompass the exploitation of both the neutrons and neutrinos produced at the ESS for high precision (sensitivity) measurements (searches).
... Optical Potential ∼100 neV Material dependencies Gravity Potential 100 neV/m V = m × g × z Magnetic Field 60 neV/T Zeeman Splitting of its magnetic moment, quantum mechanical [31,32] or neutron optical [33,34] properties, and searches for a charge of the neutron [35]. The β-decay measurements are complemented by experiments with cold neutrons for the lifetime [36][37][38][39], see also the review [40], and measurements of correlation coefficients [41][42][43][44][45][46][47][48][49][50][51][52][53][54][55]. Other searches include a conversion of a neutron into an anti-neutron [56] or mirror-neutron [57,58] or a decay into a hypothetical dark matter particle [59]. ...
What is driving the accelerated expansion of the universe and do we have an alternative for Einstein's cosmological constant? What is dark matter made of? Do extra dimensions of space and time exist? Is there a preferred frame in the universe? To which extent is left-handedness a preferred symmetry in nature? What's the origin of the baryon asymmetry in the universe? These fundamental and open questions are addressed by precision experiments using ultra-cold neutrons. This year, we celebrate the 50th anniversary of their first production, followed by first pioneering experiments. Actually, ultra-cold neutrons were discovered twice in the same year, once in the eastern and once in the western world. For five decades now research projects with ultra-cold neutrons have contributed to the determination of the force constants of nature's fundamental interactions, and several technological breakthroughs in precision allow to address the open questions by putting them to experimental test. To mark the event and tribute to this fabulous object, we present a birthday song for ultra-cold neutrons with acoustic resonant transitions, which are based solely on properties of ultra-cold neutrons, the inertial and gravitational mass of the neutron, Planck's constant, and the local gravity. We make use of a musical intonation system that bears no relation to basic notation and basic musical theory as applied and used elsewhere but addresses two fundamental problems of music theory, the problem of reference for the concert pitch and the problem of intonation.
... Examples include the neutron lifetime [20][21][22][23][24][25][26][27] and other decay parameters like β-decay correlation coefficients [28][29][30], measurements of its magnetic moment, quantum mechanical [31,32] or neutron optical [33,34] properties, and searches for a charge of the neutron [35]. The β-decay measurements are complemented by experiments with cold neutrons for the lifetime [36][37][38][39], see also the review [40], and measurements of correlation coefficients [41][42][43][44][45][46][47][48][49][50][51][52][53][54][55]. Other searches include a conversion of a neutron into an antineutron [56] or mirror-neutron [57,58] or a decay into a hypothetical dark matter particle [59]. ...
What is driving the accelerated expansion of the universe and do we have an alternative for Einstein's cosmological constant? What is dark matter made of? Do extra dimensions of space and time exist? Is there a preferred frame in the universe? To which extent is left-handedness a preferred symmetry in nature? What's the origin of the baryon asymmetry in the universe? These fundamental and open questions are addressed by precision experiments using ultra-cold neutrons. This year, we celebrate the 50th anniversary of their first production, followed by first pioneering experiments. Actually, ultra-cold neutrons were discovered twice in the same year – once in the eastern and once in the western world [1, 2]. For five decades now research projects with ultra-cold neutrons have contributed to the determination of the force constants of nature's fundamental interactions, and several technological breakthroughs in precision allow to address the open questions by putting them to experimental test. To mark the event and tribute to this fabulous object, we present a birthday song for ultra-cold neutrons with acoustic resonant transitions [3], which are based solely on properties of ultra-cold neutrons, the inertial and gravitational mass of the neutron m , Planck's constant h , and the local gravity g . We make use of a musical intonation system that bears no relation to basic notation and basic musical theory as applied and used elsewhere [4] but addresses two fundamental problems of music theory, the problem of reference for the concert pitch and the problem of intonation.
... The TRINE experiment at the ILL yielded D n = −0.00028(64) stat (30) syst [406], whereas the emiT experiment at NIST [407] yielded a final result of D n = −0.000094(189) stat (97) syst [408,409]. ...
The status of tests of the standard electroweak model and of searches for new physics in allowed nuclear $\beta$ decay and neutron decay is reviewed including both theoretical and experimental developments. The sensitivity and complementarity of recent and ongoing experiments are discussed with emphasis on their potential to look for new physics. Measurements are interpreted using a model-independent effective field theory approach enabling to recast the outcome of the analysis in many specific new physics models. Special attention is given to the connection that this approach establishes with high-energy physics. A new global fit of available $\beta$-decay data is performed incorporating, for the first time in a consistent way, superallowed $0^+\to 0^+$ transitions, neutron decay and nuclear decays. The constraints on exotic scalar and tensor couplings involving left- or right-handed neutrinos are determined while a constraint on the pseudoscalar coupling from neutron decay data is obtained for the first time as well. The values of the vector and axial-vector couplings, which are associated within the standard model to $V_{ud}$ and $g_A$ respectively, are also updated. The ratio between the axial and vector couplings obtained from the fit under standard model assumptions is $C_A/C_V = -1.27510(66)$. The relevance of the various experimental inputs and error sources is critically discussed and the impact of ongoing measurements is studied. The complementarity of the obtained bounds with other low- and high-energy probes is presented including ongoing searches at the Large Hadron Collider.
... Recoil protons have a maximum initial energy of 751 eV and therefore require an accelerating potential to be detected. Previous experiments in neutron beta decay have used a variety of instruments to detect the accelerated protons including CH 4 -filled proportional counters [33], photomultipliers with thin scintillating layers of CsI(TI) [34] or NaI(TI) [35], microchannel plates [23,36,37], silicon PIN diodes [38], conversion foils which eject secondary electrons [25,[39][40][41], Avalanche Photodiodes [42], silicon drift detectors [21], and silicon surface barrier detectors [20,[43][44][45][46][47]. Multipixel silicon PIN diodes have been used for precision β spectroscopy in tritium decay in the KATRIN experiment [48]. ...
We describe a detection system designed for precise measurements of angular correlations in neutron $\beta$ decay. The system is based on thick, large area, highly segmented silicon detectors developed in collaboration with Micron Semiconductor, Ltd. The prototype system meets specifications for $\beta$ electron detection with energy thresholds below 10 keV, energy resolution of $\sim$3 keV FWHM, and rise time of $\sim$50 ns with 19 of the 127 detector pixels instrumented. Using ultracold neutrons at the Los Alamos Neutron Science Center, we have demonstrated the coincident detection of $\beta$ particles and recoil protons from neutron $\beta$ decay. The fully instrumented detection system will be implemented in the UCNB and Nab experiments, to determine the neutron $\beta$ decay parameters $B$, $a$, and $b$.
... Observables in free neutron decay are abundant: besides the lifetime τ n , angular correlations involving the neutron spin as well as momenta and spins of the emitted particles are characterized by individual coefficients, which can be related to the underlying coupling strengths of the weak interaction. Examples are the electron-antineutrino correlation coefficient a [2][3][4], the beta asymmetry parameter A [5][6][7][8][9], the neutrino asymmetry parameter B [10,11] (reconstructed from proton and electron momenta), the proton asymmetry parameter C [12], the triple correlation coefficient D [13,14], the Fierz interference term b, and various correlation coefficients involving the electron spin [15,16]. Each coefficient in turn relates to an underlying broken symmetry. ...
This work presents selected results from the first round of the DFG Priority
Programme SPP 1491 "precision experiments in particle and astroparticle physics
with cold and ultra-cold neutrons".
... Neutron decay offers a number of independent observables, considerably larger than the small number of parameters describing this decay in the Standard Model. Examples are the electron-antineutrino correlation coefficient a [3][4][5][6], the beta asymmetry parameter A [7][8][9][10][11], the neutrino asymmetry parameter B [12,13] (reconstructed from proton and electron momenta), the proton asymmetry parameter C [14], the triple correlation coefficient D [15,16], the Fierz interference term b, and various correlation coefficients involving the electron spin [17,18]. Each coefficient in turn relates to an underlying broken symmetry. ...
We present two new types of spectroscopy methods for cold and ultra-cold
neutrons. The first method, which uses the \RB drift effect to disperse charged
particles in a uniformly curved magnetic field, allows to study neutron
$\beta$-decay. We aim for a precision on the 10$^{-4}$ level. The second method
that we refer to as gravity resonance spectroscopy (GRS) allows to test
Newton's gravity law at short distances. At the level of precision we are able
to provide constraints on any possible gravity-like interaction. In particular,
limits on dark energy chameleon fields are improved by several orders of
magnitude.
... Values up to about 10 have readily been obtained [79]. Measurements of this type with the isotopes 107 In [79][80][81][82] and 12 N [20,83] yielded a combined value of (δ + ζ ) 2 = −0.0004(26) corresponding to the lower limit m 2 > 310 GeV/c 2 (90% C.L.) for the mass of a right-handed W boson [20]. ...
... A nuclear polarization of about 81% was thus obtained. A spectrometer consisting of the magnet in the refrigerator and a room temperature 0.06 T iron-free solenoid selected positrons with a mean kinetic energy of 1.14 MeV (momentum resolution p/p 27%) from the decay of the polarized 107 In nuclei, which were subsequently focused into the positron polarimeter magnet. The axis of the spectrometer and polarimeter magnetic fields was at 35 • with respect to the plane of the implantation foil (which also contained the nuclear polarization axis) so as to be able to implant the nuclei into the foil and at the same time minimize effects of scattering of the outgoing β-particles (figure 1). ...
... [95]. A second measurement with 107 In, this time determining the ratio P − /P 0 with P 0 the positron polarization observed with unpolarized nuclei, yielded a preliminary value of (δ + ζ ) 2 = 0.0004 (26) [81,82] but was never officially published as it turned out to be difficult to estimate a possible correction for the precession of the positron spin in the magnetic field that was guiding the positrons toward the polarimeter. A further attempt with 118 Sb [96] was hampered by similar problems as well as by the then still limited reliability of the Geant code for β-particles with keV to MeV energies. ...
The beta-decay process offers unique possibilities for testing the fundamental symmetries of the standard model and searching for non-standard model components in the weak interaction. Here a non-exhaustive review of this field is given highlighting a number of key experiments or recently performed experiments. Also included are new and ongoing developments providing new opportunities for further significant progress in this research field in the era of the large hadron collider.
