Antonio Garcia

New limit on the D coefficient in polarized neutron decay

We describe an experiment that has set new limits on the time reversal invariance violating D coefficient in neutron beta-decay. The emiT experiment measured the angular correlation J . p_e x p_p using an octagonal symmetry that optimizes electron-proton coincidence rates. The result is D=[-0.6+/-1.2(stat)+/-0.5(syst)]x10^(-3). This improves constraints on the phase of g_A/g_V and limits contributions to T violation due to leptoquarks. This paper presents details of the experiment, data analysis, and the investigation of systematic effects.

Performance of the Los Alamos National Laboratory spallation-driven solid-deuterium ultra-cold neutron source

In this paper, we describe the performance of the Los Alamos spallation-driven solid-deuterium ultra-cold neutron (UCN) source. Measurements of the cold neutron flux, the very low energy neutron production rate, and the UCN rates and density at the exit from the biological shield are presented and compared to Monte Carlo predictions. The cold neutron rates compare well with predictions from the Monte Carlo code MCNPX and the UCN rates agree with our custom UCN Monte Carlo code. The source is shown to perform as modeled. The maximum delivered UCN density at the exit from the biological shield is 52(9) UCN/cc with a solid deuterium volume of ~1500 cm(3).

New limit on time-reversal violation in beta decay.

We report the results of an improved determination of the triple correlation DP·(p(e)×p(v)) that can be used to limit possible time-reversal invariance in the beta decay of polarized neutrons and constrain extensions to the standard model. Our result is D=[-0.96±1.89(stat)±1.01(sys)]×10(-4). The corresponding phase between gA and gV is ϕAV=180.013°±0.028° (68% confidence level). This result represents the most sensitive measurement of D in nuclear β decay.

Search for a T-odd, P-even Triple Correlation in Neutron Decay

Search for a T-odd, P-even Triple Correlation in Neutron Decay T.E. Chupp, 1 R.L. Cooper, 1 K.P. Coulter, 1 S.J. Freedman, 2 B.K. Fujikawa, 2 A. Garc´ia, 3, 4 G.L. Jones, 5 H.P. Mumm, 6 J.S. Nico, 6 A.K. Thompson, 6 C.A. Trull, 7 F.E. Wietfeldt, 7 and J.F. Wilkerson 3, 8, 9 University of Michigan, Ann Arbor, Michigan 48104, USA Physics Department, University of California, Berkeley, and Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA CENPA and Physics Department, University of Washington, Seattle, WA 98195 USA Department of Physics, University of Notre Dame, Notre Dame, IN 46556 USA Physics Department, Hamilton College, Clinton, NY 13323, USA National Institute of Standards and Technology, Gaithersburg, MD 20899, USA Physics Department, Tulane University, New Orleans, LA 70118, USA Department of Physics and Astronomy, University of North Carolina, Chapel Hill, North Carolina 27599, USA Oak Ridge National Lab, Oak Ridge, TN, 37831 USA Background: Time-reversal-invariance violation, or equivalently CP violation, may explain the observed cosmological baryon asymmetry as well as signal physics beyond the Standard Model. In the decay of polarized neutrons, the triple correlation D J n ·(p e ×p ν ) is a parity-even, time-reversal- odd observable that is uniquely sensitive to the relative phase of the axial-vector amplitude with respect to the vector amplitude. The triple correlation is also sensitive to possible contributions from scalar and tensor amplitudes. Final-state effects also contribute to D at the level of 10 −5 and can be calculated with a precision of 1% or better. Purpose: We have improved the sensitivity to T-odd, P-even interactions in nuclear beta decay. Methods: We measured proton-electron coincidences from decays of longitudinally polarized neutrons with a highly symmetric detector array designed to cancel the time-reversal-even, parity-odd Standard-Model contributions to polarized neutron decay. Over 300 million proton-electron coincidence events were used to extract D and study systematic effects in a blind analysis. Results: We find D = [−0.94 ± 1.89(stat) ± 0.97(sys)] × 10 −4 . Conclusions: This is the most sensitive measurement of D in nuclear beta decay. Our result can be interpreted as a measurement of the phase of the ratio of the axial-vector and vector coupling constants (C A /C V = |λ|e iφ AV ) with φ AV = 180.012 ◦ ±0.028 ◦ (68% confidence level) or to constrain time-reversal violating scalar and tensor interactions that arise in certain extensions to the Standard Model such as leptoquarks. This paper presents details of the experiment, analysis, and systematic- error corrections. PACS numbers: 24.80.+y, 11.30.Er, 12.15.Ji, 13.30.Ce DISCLAIMER: This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor the Regents of the University of Cal- ifornia, nor any of their employees, makes any warranty, express or implied, or assumes any le- gal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, prod- uct, or process disclosed, or represents that its use would not infringe privately owned rights. Refer- ence herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommen- dation, or favoring by the United States Govern- ment or any agency thereof, or the Regents of the University of California. The views and opin- ions of authors expressed herein do not necessar- ily state or reflect those of the United States Gov- ernment or any agency thereof or the Regents of the University of California. I. INTRODUCTION The symmetries of physical processes under the trans- formations of charge conjugation (C), parity (P), and time reversal (T) have played a central role in the de- velopment of the Standard Model of elementary-particle interactions [1]. Time-reversal-symmetry violation (or T violation), which is equivalent to CP violation assum- ing CPT symmetry, has been of particular interest be- cause it is sensitive to many kinds of new physics. The CP-violating parameters of the Standard Model are the Cabibbo-Kobayashi-Maskawa (CKM) phase, which en- ters in the mixing of three generations of quarks, and the parameter θ QCD . The effect of the CKM phase is strongly suppressed in the permanent electric dipole mo- ments (EDMs) of the neutron [2] and heavy atoms [3, 4], and recent EDM results combine to set upper limits on θ QCD . All laboratory measurements to date are consis- tent with a single source of CP violation, i.e. the phase in the CKM matrix. An exception may be the 3.2 sigma deviation observed recently as an asymmetry in the pro- duction of pairs of like-sign muons reported by the D0

Performance of the prototype LANL solid deuterium ultra-cold neutron source

A prototype of a solid deuterium (SD 2 ) source of Ultra-Cold Neutrons (UCN) is currently being tested at LANSCE. The source is contained within an assembly consisting of a 4 K polyethylene moderator surrounded by a 77 K beryllium #ux trap in which is embedded a spallation target. Time-of-#ight measurements have been made of the cold neutron spectrum emerging directly from the #ux trap assembly. A comparison is presented of these measurements with results of Monte Carlo (LAHET/MCNP) calculations of the cold neutron #uxes produced in the prototype assembly by a beam of 800 MeV protons incident on the tungsten target. A UCN detector was coupled to the assembly through a guide system with a critical velocity of 8 m/s (58Ni). The rates and time-of-#ight data from this detector are compared with calculated values. Measurements of UCN production as a function of SD 2 volume (thickness) are compared with predicted values. The dependence of UCN production on SD 2 temperature and proton beam intensity are also presented. ( 2000 Elsevier Science B.V. All rights reserved.

A new limit on time-reversal violation in beta decay: Results of the emiTII experiment

We have measured the triple correlation D〈Jn〉 · (pe × pv) with a polarized cold-neutron beam at the NIST Center for Neutron Research by observing proton-electron coincidences in the decay of polarized neutrons. A non-zero value of D can arise due to parity-even-time-reversal-odd interactions that imply CP violation due to the CPT theorem. Final-state effects also contribute to D at the level of 10−5 and can be calculated with precision of 1% or better. The D coefficient is sensitive to the phase, of λ the ratio of axial-vector and vector amplitudes as well as to scalar and tensor interactions that could arise due to beyond-Standard-Model physics such as leptoquarks. Over 300 million proton-electron coincidence events were used in a blind analysis with the result D = [−0.96±1.89(stat)±1.01(sys)]×10−4.

Searching for time reversal invariance violation in polarized neutron decay

Time reversal invariance violation is tightly constrained in the Stan- dard Model, and the existence of a T-violating effect above the predicted level would be an indication of new physics. A sensitive probe of this symmetry in the weak interaction is the measurement of the D-coefficient in neutron decay. This parameter characterizes the triple-correlation of neutron spin, electron mo- mentum, and neutrino (or proton) momentum, which changes sign under time reversal. The emiT experiment, now on line, attempts to improve the measure- ment of D, whose current average is 0.3 + 1.5 x 10 -3.