120175902
A NEW SEARCH FOR A PERMANENT DIPOLE MOMENT OF THE ELECTRON IN A SOLID STATE SYSTEM
Measurements of the electric dipole moment (EDM) of the neutron and the electron put the most stringent constraints on new sources of CP violation. CP violation is essential for generating the observed baryon asymmetry of the universe (BAU). Many models which propose large CP-odd mechanisms for BAU predict EDMs that exceed the limits of the most sensitive measurements. We are conducting a high sensitivity search for the electron EDM using a solid state system. It promises orders of magnitude improvement over atomic beam experiments solely from the available electron density. We present the experimental design and report on the current status.
119507247
Storage of Ultracold Neutrons in the Magneto-Gravitational Trap of the UCN Experiment
The UCN experiment is designed to measure the lifetime n of the free neutron by trapping ultracold neutrons (UCN) in a magneto-gravitational trap. An asymmetric bowl-shaped NdFeB magnet Halbach array confines low-field-seeking UCN within the apparatus, and a set of electromagnetic coils in a toroidal geometry provides a background holding field to eliminate depolarization-induced UCN loss caused by magnetic field nodes. We present a measurement of the storage time store of the trap by storing UCN for various times and counting the survivors. The data are consistent with a single exponential decay, and we find store = 860 19 s, within 1 of current global averages for n. The storage time with the holding field deactivated is found to be store = 470 160 s; this decreased storage time is due to the loss of UCN, which undergo Majorana spin flips while being stored. We discuss plans to increase the statistical sensitivity of the measurement and investigate potential systematic effects.
118837551
New experimental limit on the electric dipole moment of the electron in a paramagnetic insulator
We report results of an experimental search for the intrinsic Electric Dipole Moment (EDM) of the electron using a solid-state technique. The experiment employs a paramagnetic, insulating gadolinium gallium garnet (GGG) that has a large magnetic response at low temperatures. The presence of the eEDM would lead to a small but non-zero magnetization as the GGG sample is subject to a strong electric field. We search for the resulting Stark-induced magnetization with a sensitive magnetometer. Recent progress on the suppression of several sources of background allows the experiment to run free of spurious signals at the level of the statistical uncertainties. We report our first limit on the eEDM of ( 5.57 ± 7.98 ± 0.12)×10 25 e·cm with 5 days of data averaging. The search for the electric dipole moment (EDM) of elementary particles is motivated to test the discrete symmetries assumed in the Standard Model (SM) of particle physics. An account of the different transformation properties of the EDM (a polar vector) and the spin (a pseudo-vector), the fundamental physical laws governing particles must violate both time-reversal (T) and parity-inversion (P) symmetries for a fermion to acquire an EDM [1]. While the phenomena of P violation is firmly established in numerous experiments, T violation has only been observed directly in the neutral kaon system [2], with more searches in the B system underway [3]. Measurements of EDMs of elementary particles use different experimental techniques, often on low energy systems at Q ≃ 0, to probe the physics of T violation (with no flavor-changing) at energy scales higher than tens of TeV, and could provide information complementary to that from high-energy collider experiments on the nature of symmetry breaking. The physics of T violation is often linked, via the CPT theorem, to the violation of the combined Charge conjugate (C) and P symmetry. The only confirmed source of CP violation in the SM is the complex phase of the CKM matrix (that describes the quark mixing in charged-current weak interactions). With it, the electron EDM (eEDM) manifests through high-order loop couplings that involve flavor-changing quark interactions with the exchange of W ± weak bosons. The resulting size of eEDM predicted within the framework of SM is no larger than 10 −38 e·cm, which is well beyond the reach of current experimental techniques. The current experimental upper bound is established using thallium atomic beams with a sensitivity of 1.6×10 −27 e·cm [4]. New sources of CP violation introduced by theories beyond
121822416
Beta decay measurements with ultracold neutrons: a review of recent measurements and the research program at Los Alamos National Laboratory
We present a review of the motivation and results of recent experiments which utilize ultracold neutrons for measurements of neutron beta decay. Because these experiments hinge critically on the available ultracold neutron source technology, we also review the status of ultracold neutron source development, emphasizing the Los Alamos ultracold neutron facility and the ongoing beta decay research program sited there.
27442116
Cold neutron energy dependent production of ultracold neutrons in solid deuterium.
A measurement of the production of ultracold neutrons from velocity-selected cold neutrons on gaseous and solid deuterium targets is reported. The expected energy dependence for two-particle collisions with well defined neutron and Maxwell-Boltzmann distributed molecular velocities is found for the gas target. The solid target data agree in shape with the phonon density-of-states curve and provide strong evidence for the phonon model including multiphonon excitations.
5816062
Temperature-dependent neutron scattering cross-sections for polyethylene
Abstract This note presents neutron scattering cross-sections for polyethylene at 296, 77 and 4 K derived from a new scattering kernel for neutron scattering off of hydrogen in polyethylene. The kernel was developed in ENDF-6 format as a set of S ( α , β ) tables using the LEAPR module of the NJOY94 code package. The polyethylene density of states (from 0 to sub eV) adopted to derive the new kernel is presented. We compare our calculated room temperature total scattering cross-sections and double differential cross-sections at 232 meV at various angles with the available experimental data (at room temperature), and then extrapolate the calculations to lower temperatures (77 and 4 K). The new temperature-dependent scattering kernel gives a good quantitative fit to the available room temperature data and has a temperature dependence that is qualitatively consistent with thermodynamics.
119216988
LHCb $\bigtriangleup A_{CP}$ of $D$ Meson and R-Parity Violation
LHCb collaboration has recently announced a measurement of the difference of time-integrated CP asymmetries between $D\rightarrow K^+K^-$ and $D \rightarrow \pi^+\pi^-$. This result provides the evidence of large direct CP violation in $D$ meson and reveals some important implications on underlying new physics. It is shown that the direct CP violation in $D$ meson can be enhanced by R-parity violating supersymmetry, while CP violations in $K$ and $B$ mesons are suppressed by this new physics, which is in consistence with previous experiments. Constraints on the model parameters and some consequences are also discussed.
118654249
Particle acceleration on the background of the Kerr―Taub―NUT spacetime
Abstract We study the collision of two particles with the different rest masses moving in the equatorial plane of a Kerr–Taub–NUT spacetime and get the center-of-mass (CM) energy for the particles. We find that the CM energy depends not only on the rotation parameter, a , but also on the NUT charge of the Kerr–Taub–NUT spacetime, n . Especially, for the extremal Kerr–Taub–NUT spacetime, an unlimited CM energy can be approached if the parameter a is in the range [ 1 , 2 ] , which is different from that of the Kerr and Kerr–Newman black holes.
18945028
S 1 -fixed-points in hyper-Quot-schemes and an exact mirror formula for flag manifolds from the extended mirror principle diagram
In the series of work [L-L-Y1, III: Sec. 5.4] on mirror principle, two of the current authors (K.L. and S.-T.Y.) with Bong H. Lian developed a method to compute the integral R X τ � e H·t ∩ 1d for a flag manifold X = Fl r1, ..., rI(C n ) via an extended mirror principle diagram. This integral determines the fundamental hypergeometric series HG[1] X (t) and is also related to the computation of the Gromov-Witten invariants (string world-sheet instanton numbers) on X. This method turns the required localization computation on the augmented moduli stack M0,0(CP 1 × X) of stable maps to a localization computation on a hyper-Quot-scheme HQuot(E n ) of inclusion sequences of subsheaves of a trivialized trivial bundle E n of rank n on CP 1 . In this article, the detail of this localization computation on HQuot(E n ) is carried out. The necessary ingredients in the computation, notably, the S 1 -fixed-point components and the distinguished ones E(A;0) in HQuot(E n ), the S 1 -equivariant Euler class of E(A;0) in HQuot(E n ), and a push-forward formula of cohomology classes involved in the problem from the total space of a restrictive flag manifold bundle to its base manifold are given. With these, an exact expression of R X τ � e H·t ∩ 1d is obtained. When X is a Grassmannian manifold, the same route reproduces the known exact expression for HG[1] X (t). For a general flag manifold X, our expression determines HG[1] X (t) implicitly. Remarks on what it suggests for general Hori-Vafa formula are given. Due to the technical necessity, a discussion on the general construction of restrictive flag manifold bundle, its natural embedding in a flag manifold bundle, and the Thom class of this embedding is also given. This work generalizes the result in [L-L-L-Y]. This work gives explicit formulas for mirror principle computations of Calabi-Yau manifolds in flag manifolds.
54868722
EXPERIMENTAL PROGRESS OF DC-SC PHOTOINJECTOR AT PEKING UNIVERSITY*
Beam loading experiments on DC-SC photoinjector test facility have been finished at 4.4 K. Upon the present experiments, the gradient of 6 MV/m is achieved. The maximum energy gain is 1.1 MeV at 4.4 K. With average beam current of 270 mA, the measured rms emittance is about 5 mm-mrad at the beam energy of 500 keV. Experiments on the test facility has validated that the DC-SC photoinjector is a good choice to provide moderate average current electron beams with low bunch charge and very high repetition rate.
15754800
Remarks on the Geometry of Wick Rotation in QFT and its Localization on Manifolds
The geometric aspect of Wick rotation in quantum eld theory and its localization on manifolds are explored. After the explanation of the notion and its related geometric objects, we study the topology of the set of landing W for Wick rotations and its natural stratication. These structures in two, three, and four dimensions are computed explicitly. We then focus on more details in two dimensions. In particular, we study the embedding of W in the ambient space of Wick rotations, the resolution of the generic metric singularities of a Lorentzian surface by local Wick rotations, and some related S 1 -bundles over .