Performance of the upgraded ultracold neutron source at Los Alamos National Laboratory and its implication for a possible neutron electric dipole moment experiment

Ito, T. M.; Adamek, Evan; Callahan, Nathan; Choi, J.; Clayton, S. M.; Cude-Woods, C.; Currie, Scott; Ding, X.; Fellers, Deion Elgin; Geltenbort, P.; Lamoreaux, S. K.; Liu, C. Y.; MacDonald, Stephen; Makela, M.; Morris, C. L.; Pattie, R. W.; Ramsey, J.; Salvat, Daniel; Saunders, A.; Sharapov, E.I.; Sjue, Sky; Sprow, Aaron; Tang, Z.; Weaver, H.; Wei, Wanchun; Young, A. R.

doi:10.1103/physrevc.97.012501

Cited by 71 publications

(52 citation statements)

References 43 publications

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“…LQCD computations of the contributions of the CEDMs and the leading Weinberg operator have gained significant momentum in recent years [41][42][43][44][45][46][47][48], and considering the ongoing efforts by several LQCD groups, calculations with uncertainties similar to those of the sum-rule estimates may be achievable within the next five years [49,50]. To fully exploit the expected increase in sensitivity of future EDM searches (see for instance [51][52][53] for discussions), improved calculations of the hadronic matrix elements of CEDMs and Weinberg-type operators are direly needed.…”

Section: Introductionmentioning

confidence: 99%

Sum rules for CP-violating operators of Weinberg type

Haisch

Hala

2019

J. High Energ. Phys.

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We estimate the size of the hadronic matrix elements of CP-violating three-gluon and four-gluon Weinberg operators using sum-rule techniques. In the three-gluon case, we are able to reproduce the expressions given in earlier works, while the four-gluon results obtained in this article are new. Our paper therefore represents the first systematic study of contributions to the electric dipole moment of the neutron due to CP-violating dimension-six and dimension-eight operators. We provide many details on both the derivation of the sum rules as well as the analysis of the uncertainties that plague our final predictions.Here G A µν is the QCD field strength tensor,G A µν = 1/2 µνρλ G A ρλ with 0123 = +1 denotes its dual, f ABC are the fully anti-symmetric structure constants of SU(3) and c ABCD denote the colour structures defined in (5.20). Lacking the expertise in LQCD as well as the needed computer resources, we will present estimates of the hadronic matrix elements of the operators in (1.1) using QCD sum-rule techniques. In the case of the dimension-six contribution O 6 such a calculation has already been performed in [40], but the latter publication does not provide details on the actual computation making an independent reevaluation worthwhile. Our determination of the hadronic matrix elements of the dimension-eight term O 8 is instead new. Both results will be used in a companion paper [59], where we derive model-independent bounds on CP-violating Higgs-gluon interactions in BSM scenarios with vanishing or highly suppressed light-quark Yukawa couplings.Our work is organised as follows. After briefly reviewing the basic idea behind the sum-rule determinations of the hadronic matrix elements of O 6 and O 8 , we discuss in Section 3 the phenomenological side of the sum rules. The operator product expansion (OPE) computation of the dimension-six and dimension-eight contributions is described in Section 4 and Section 5, respectively. The matching and the numerical analysis of the sum rules are performed in Section 6. We conclude in Section 7. Technical details are relegated to several appendices. General idea behind the sum rulesThe central object for the derivation of the sum-rule estimates for the hadronic matrix elements of operators of the type (1.1) is the following correlation function Π(q 2 ) = i d 4 x e iqx Ω T η(x)η(0) Ω EM,O k , (2.1)

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Section: Introductionmentioning

confidence: 99%

Sum rules for CP-violating operators of Weinberg type

Haisch

Hala

2019

J. High Energ. Phys.

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“…However, the precision of such experiments is limited by the low UCN densities that can be delivered by current sources. Typically, less than two dozen UCNs per cm 3 are detected after filling an experiment [8,9]. The UCN source that has been operating the longest, but still is one of the most intense ones, is installed at Institute Laue- * wschreyer@triumf.ca Langevin, Grenoble, France.…”

Section: Introductionmentioning

confidence: 99%

“…Laboratory [9], Paul Scherrer Institut [13] (both using spallation neutron sources), and at University of Mainz [14] (using a reactor neutron source).…”

Section: Introductionmentioning

confidence: 99%

First ultracold neutrons produced at TRIUMF

Ahmed¹,

Altiere²,

Andalib³

et al. 2019

Phys. Rev. C

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We installed a source for ultracold neutrons at a new, dedicated spallation target at TRIUMF. The source was originally developed in Japan and uses a superfluid-helium converter cooled to 0.9 K. During an extensive test campaign in November 2017, we extracted up to 325 000 ultracold neutrons after a one-minute irradiation of the target, over three times more than previously achieved with this source. The corresponding ultracold-neutron density in the whole production and guide volume is 5.3 cm −3 . The storage lifetime of ultracold neutrons in the source was initially 37 s and dropped to 24 s during the eighteen days of operation. During continuous irradiation of the spallation target, we were able to detect a sustained ultracold-neutron rate of up to 1500 s −1 .Simulations of UCN production, UCN transport, temperature-dependent UCN yield, and temperature-dependent storage lifetime show excellent agreement with the experimental data and confirm that the ultracold-neutron-upscattering rate in superfluid helium is proportional to T 7 .

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“…In summary, we have used the Los Alamos UCN source [13] to search for monoenergetic γ rays from neutron decay to dark matter, a solution recently proposed to explain the difference between beam and bottle neutron lifetime results [11]. Our measurements exclude this possible explanation [11] with 97% confidence.…”

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confidence: 52%

“…The bottle is filled with UCNs from the Los Alamos UCN facility [13] parasitically during the running of the UCN τ experiment [7], with the source operated in production mode. The γ rays are detected in a lead shielded, Compton-scatteringsuppressed 140% high-purity germanium (HPGe) detector (Fig.…”

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confidence: 99%

Search for the Neutron Decay n→X+γ , Where X is a Dark Matter Particle

et al. 2018

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Fornal and Grinstein recently proposed that the discrepancy between two different methods of neutron lifetime measurements, the beam and bottle methods, can be explained by a previously unobserved dark matter decay mode, n → X þ γ. We perform a search for this decay mode over the allowed range of energies of the monoenergetic γ ray for X to be dark matter. A Compton-suppressed high-purity germanium detector is used to identify γ rays from neutron decay in a nickel-phosphorous-coated stainless-steel bottle. A combination of Monte Carlo and radioactive source calibrations is used to determine the absolute efficiency for detecting γ rays arising from the dark matter decay mode. We exclude the possibility of a sufficiently strong branch to explain the lifetime discrepancy with 97% confidence. DOI: 10.1103/PhysRevLett.121.022505 There is nearly a five-standard-deviation disagreement [1,2] between measurements of the rate of neutron decay producing protons measured in cold neutron beam experiments [3-5] (888.0 AE 2.0 s) and free neutron lifetime in bottle experiments [6-8] (878.1 AE 0.5 s). The cold neutron beam method consists of counting the number of protons emitted from neutron β decay in a well-characterized neutron beam, and the bottle experiments measure the number of ultracold neutrons (UCNs) that remain inside a trap after a certain storage time. A longer lifetime from the beam measurements could point to the existence of possible other decay modes of the neutron where a proton is not produced. Serebrov has suggested that the discrepancy could be due to neutrons oscillating into mirror neutrons [9,10]. Recently, Fornal and Grinstein suggested in Ref.[11] that the neutron lifetime discrepancy can be explained if the neutron were to decay into a γ ray and a dark matter particle, X. The γ ray has an allowable energy range of 782 to 1664 keV, where it is bounded from above by the stability of 9 Be and bounded from below by requiring X to be stable.Here, we report the results of a search for γ rays arising from UCNs decaying inside a nickel-phosphorouscoated [12], 560 l stainless-steel bottle. The bottle is filled with UCNs from the Los Alamos UCN facility [13] parasitically during the running of the UCN τ experiment [7], with the source operated in production mode. The γ rays are detected in a lead shielded, Compton-scatteringsuppressed 140% high-purity germanium (HPGe) detector (Fig. 1). The Compton-scattering suppression is achieved by an anticoincidence with an annular bismuth germinate (BGO) detector surrounding the HPGe detector. The Compton suppression reduced the background in the low energy part of the spectrum by a factor of 1.7. A gate valve placed upstream controlled the loading of UCNs into the bottle. The background γ rates were measured with the UCNs in production mode and the gate valve closed. This resulted in a factor of 4 reduction in the continuum background in the region of interest (ROI).The energy calibration of the HPGe spectrum was obtained from a linear fit to 13γ-ray lines from source...

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Performance of the upgraded ultracold neutron source at Los Alamos National Laboratory and its implication for a possible neutron electric dipole moment experiment

Cited by 71 publications

References 43 publications

Sum rules for CP-violating operators of Weinberg type

Sum rules for CP-violating operators of Weinberg type

First ultracold neutrons produced at TRIUMF

Search for the Neutron Decay n→X+γ , Where X is a Dark Matter Particle

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