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Articoli di riviste sul tema "Neutron lifetime discrepancy"

Autore: Grafiati

Pubblicato: 7 dicembre 2024

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1

Wietfeldt, F. "Measurements of the Neutron Lifetime". Atoms 6, n. 4 (10 dicembre 2018): 70. http://dx.doi.org/10.3390/atoms6040070.

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Free neutron decay is a fundamental process in particle and nuclear physics. It is the prototype for nuclear beta decay and other semileptonic weak particle decays. Neutron decay played a key role in the formation of light elements in the early universe. The precise value of the neutron mean lifetime, about 15 min, has been the subject of many experiments over the past 70 years. The two main experimental methods, the beam method and the ultracold neutron storage method, give average values of the neutron lifetime that currently differ by 8.7 s (4 standard deviations), a serious discrepancy. The physics of neutron decay, implications of the neutron lifetime, previous and recent experimental measurements, and prospects for the future are reviewed.

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2

Wietfeldt, Fred E. "The Neutron Lifetime Discrepancy and Its Implications for Cosmology and Dark Matter". Symmetry 16, n. 8 (26 luglio 2024): 956. http://dx.doi.org/10.3390/sym16080956.

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Abstract (sommario):

Free neutron decay is the prototype for nuclear beta decay and other semileptonic weak particle decays. It provides important insights into the symmetries of the weak nuclear force. Neutron decay is important for understanding the formation and abundance of light elements in the early universe. The two main experimental approaches for measuring the neutron lifetime, the beam method and the ultracold neutron storage method, have produced results that currently differ by 9.8 ± 2.0 s. While this discrepancy probably has an experimental origin, a more exciting prospect is that it may be explained by new physics, with possible connections to dark matter. The experimental status of the neutron lifetime is briefly reviewed, with an emphasis on its implications for cosmology, astrophysics, and dark matter.

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3

Beck, D. H. "Neutron decay, dark matter and neutron stars". EPJ Web of Conferences 219 (2019): 05006. http://dx.doi.org/10.1051/epjconf/201921905006.

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Following up on a suggestion that decay to a dark matter fermion might explain the 4σ discrepancy in the neutron lifetime, we consider the implications of such a fermion on neutron star structure. We find that including it reduces the maximum neutron star mass to well below the observed masses. In order to recover stars with the observed masses, the (repulsive) self-interactions of the dark fermion would have to be stronger than those of the nucleon-nucleon interaction.

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4

Fornal, Bartosz. "Neutron Dark Decay". Universe 9, n. 10 (16 ottobre 2023): 449. http://dx.doi.org/10.3390/universe9100449.

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Abstract (sommario):

There exists a puzzling disagreement between the results for the neutron lifetime obtained in experiments using the beam technique versus those relying on the bottle method. A possible explanation of this discrepancy postulates the existence of a beyond-Standard-Model decay channel of the neutron involving new particles in the final state, some of which can be dark matter candidates. We review the current theoretical status of this proposal and discuss the particle physics models accommodating such a dark decay. We then elaborate on the efforts undertaken to test this hypothesis, summarizing the prospects for probing neutron dark decay channels in future experiments.

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5

Fornal, Bartosz, e Benjamín Grinstein. "Neutron’s dark secret". Modern Physics Letters A 35, n. 31 (21 agosto 2020): 2030019. http://dx.doi.org/10.1142/s0217732320300190.

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Abstract (sommario):

The existing discrepancy between neutron lifetime measurements in bottle and beam experiments has been interpreted as a sign of the neutron decaying to dark particles. We summarize the current status of this proposal, including a discussion of particle physics models involving such a portal between the Standard Model and a baryonic dark sector. We also review further theoretical developments around this idea and elaborate on the prospects for verifying the neutron dark decay hypothesis in current and upcoming experiments.

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6

Fornal, Bartosz, e Benjamín Grinstein. "Dark side of the neutron?" EPJ Web of Conferences 219 (2019): 05005. http://dx.doi.org/10.1051/epjconf/201921905005.

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We discuss our recently proposed interpretation of the discrepancy between the bottle and beam neutron lifetime experiments as a sign of a dark sector. The difference between the outcomes of the two types of measurements is explained by the existence of a neutron dark decay channel with a branching fraction 1%. Phenomenologically consistent particle physics models for the neutron dark decay can be constructed and they involve a strongly self-interacting dark sector. We elaborate on the theoretical developments around this idea and describe the efforts undertaken to verify it experimentally.

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7

Sun, X., E. Adamek, B. Allgeier, M. Blatnik, T. J. Bowles, L. J. Broussard, M. A. P. Brown et al. "Search for neutron dark decay: n → χ + e+e−". EPJ Web of Conferences 219 (2019): 05008. http://dx.doi.org/10.1051/epjconf/201921905008.

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Abstract (sommario):

In January, 2018, Fornal and Grinstein proposed that a previously unobserved neutron decay branch to a dark matter particle (χ) could account for the discrepancy in the neutron lifetime observed in two different types of experiments. One of the possible final states discussed includes a single χ along with an e+e− pair. We use data from the UCNA (Ultracold Neutron Asymmetry) experiment to set limits on this decay channel. Coincident electron-like events are detected with ∼ 4π acceptance using a pair of detectors that observe a volume of stored Ultracold Neutrons (UCNs). We use the timing information of coincidence events to select candidate dark sector particle decays by applying a timing calibration and selecting events within a physically-forbidden timing region for conventional n → p + e- + ν̅e decays. The summed kinetic energy (Ee+e−) from such events is reconstructed and used to set limits, as a function of the χ mass, on the branching fraction for this decay channel.

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8

Zhang, Liang, Bin Zhang, Cong Liu e Yixue Chen. "Evaluation of PWR pressure vessel fast neutron fluence benchmarks from NUREG/CR-6115 with ares transport code". Nuclear Technology and Radiation Protection 32, n. 3 (2017): 204–10. http://dx.doi.org/10.2298/ntrp1703204z.

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An accurate evaluation of PWR pressure vessel fast neutron fluence is essential to ensure pressure vessel integrity over the design lifetime. The discrete ordinates method is one of the main methods to treat such problems. In this paper, evaluations have been performed for three PWR benchmarks described in NUREG/CR-6115 using ARES transport code. The calculated results were compared to the reference values and a satisfactory agreement was obtained. In addition, the effects of SN numeric and source distribution modeling for pressure vessel fast neutron fluence calculation are investigated. Based on the fine enough grids adopted, the different spatial and angular discretization introduces derivations less than 3 %, and fix-up for negative scattering source causes no noticeable effects when calculating pressure vessel fast neutron fluence. However, the discrepancy of assembly-wise and pin-wise source modeling for peripheral assemblies reaches ~20 %, which indicates that pin-wise modeling for peripheral assemblies is essential. These results provide guidelines for pressure vessel fast neutron fluence calculation and demonstrate that the ARES transport code is capable of performing neutron transport calculations for evaluating PWR pressure vessel fast neutron fluence.

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9

Kunst, Ernst Karl. "On the common relativistic origin of the neutron lifetime discrepancy, the slight superluminality of neutrinos at Fermilab, and several astrophysical problems". Physics Essays 31, n. 2 (7 giugno 2018): 219–24. http://dx.doi.org/10.4006/0836-1398-31.2.219.

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10

Pols, Onno R., e Jasinta D. M. Dewi. "Helium-star Mass Loss and Its Implications for Black Hole Formation and Supernova Progenitors". Publications of the Astronomical Society of Australia 19, n. 2 (2002): 233–37. http://dx.doi.org/10.1071/as01121.

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AbstractRecently the observationally derived stellar-wind mass-loss rates for Wolf-Rayet stars, or massive naked helium stars, have been revised downwards by a substantial amount. We present evolutionary calculations of helium stars incorporating such revised mass-loss rates, as well as mass transfer to a close compact binary companion. Our models reach final masses well in excess of 10 M⊙, consistent with the observed masses of black holes in X-ray binaries. This resolves the discrepancy found with previously assumed high mass-loss rates between the final masses of stars which spend most of their helium-burning lifetime as Wolf-Rayet stars (˜3 M⊙) and the minimum observed black hole masses (6 M⊙). Our calculations also suggest that there are two distinct classes of progenitors for Type Ic supernovae: one with very large initial masses (35 M⊙), which are still massive when they explode and leave black hole remnants, and one with moderate initial masses (˜12–20 M⊙) undergoing binary interaction, which end up with small pre-explosion masses and leave neutron star remnants.

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11

Shin, Michael, e Dennis Silverman. "A heavy unstable fourth family neutrino and the τ-lifetime discrepancy". Physics Letters B 213, n. 3 (ottobre 1988): 379–85. http://dx.doi.org/10.1016/0370-2693(88)91780-7.

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12

SAMUEL, MARK A. "IS THERE A NEW PSEUDOSCALAR PARTICLE?" Modern Physics Letters A 03, n. 11 (settembre 1988): 1117–23. http://dx.doi.org/10.1142/s0217732388001331.

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The decay rate of orthopositronium has recently been measured in a new high precision experiment. The result is 10 standard deviations above the theoretical value. It is shown that a light neutral pseudoscalar R may resolve this discrepancy and still be consistent with the anomalous magnetic moments of the electron and the muon. If the mass mR≤5.7 keV , then the existence of this proposed particle R is consistent with the beam-dump experiments. The lifetime of R is large, τ≥0.14 s.

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13

Weiss, A. W. "The calculation of atomic oscillator strengths: the lithium atom revisited". Canadian Journal of Chemistry 70, n. 2 (1 febbraio 1992): 456–63. http://dx.doi.org/10.1139/v92-066.

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Extensive configuration interaction calculations have been done for the ground and first excited states of neutral lithium and singly ionized beryllium. While the calculations reproduce the ionization and excitation energies to within 3 cm−1 for Li and 10 cm−1 for Be+, the main purpose of this work is the accurate evaluation of the 2s–2p resonance line oscillator strength. The calculated value of 0.7478 agrees to within less than 1% with the very accurate laser excitation lifetime measurement of 0.7416 ± 0.0012. However, internal consistency checks of the accuracy of these calculations suggest that more precise calculations are unlikely to reduce this discrepancy significantly. Furthermore, when placed together with other independent calculations that should be of comparable, if not better, accuracy, all theoretical predictions strongly indicate an f-value of 0.7475 ± 0.0010, which differs from the experiment by 4 experimental standard deviations. Keywords: configuration interaction, correlation, oscillator strength.

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14

Zlatar, Matej, Daniel Escalera López, Kevin Stojanovski, Valentin Briega Martos e Serhiy Cherevko. "Effect of pH on Electrochemical Dissolution of Iridium". ECS Meeting Abstracts MA2022-02, n. 54 (9 ottobre 2022): 2050. http://dx.doi.org/10.1149/ma2022-02542050mtgabs.

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Replacing fossil fuels with renewable energy sources is one of the most challenging tasks in today's society. As renewable sources are intermittent in nature, a promising solution is to store the produced energy in the form of hydrogen, which can be produced electrochemically by using proton exchange membrane water electrolyzers (PEMWEs). A limiting factor of PEMWEs is that the harsh conditions and sluggish kinetics of oxygen evolution reaction (OER) at the PEMWE anode require that the state-of-the-art catalysts employed are based mostly on Iridium (Ir). (1) Given its scarcity, the use of Ir in OER electrocatalysis is under increasing scrutiny, where current efforts have focused on maximizing activity while decreasing its loading. This is crucial in order to implement PEMWEs in the giga-to-terawatt scale, one of the goals set by the U.S. DoE "Hydrogen Shot". (2) The benchmarking of Ir catalysts for OER electrocatalysis is mostly performed in aqueous model systems (AMS) using acidic electrolytes, but recent works directly comparing AMS and PEMWE showed a clear discrepancy in the catalyst lifetimes. (3) Indeed, a higher pH value under PEMWE operation (ca. 3) was proposed as the main factor responsible for the extended lifetimes. (4) Consequently, both activity and stability of Ir need to be carefully reassessed in a wider pH window. Several works have already evaluated the influence of pH on Ir OER activity over the entire pH scale with buffered (5) and unbuffered electrolytes, (6) but so far, very few works have looked into its stability. Ir stabilities have been reported either in highly acidic (1) or alkaline conditions, (7) where Ir stability significantly changed between such pHs. In this context, studying the Iridium stability over the entire pH scale is essential for understanding and designing more stable and active catalysts. The presented work aims to fill the gap in the current literature regarding Ir activity-stability relationships at different pHs. To do so, we tested a polycrystalline iridium electrode with scanning flow cell coupled to an inductively coupled plasma mass spectrometer setup (SFC-ICP-MS) in pH range from 1 to 12.7. For pH 1 and 12.7, 0.1 M HClO4 and 0.05 M KOH were used, respectively, while pH range of 3-11 was achieved by the addition of phosphate buffer. Using this approach, we distinguished the clear influence of pH on the stability of Iridium, which decreased by shifting the pH value from 1 to 12.7. Lastly, the lower stability of Ir in near-neutral pH compared to acidic, raises questions about the applicability of OER at near-neutral pHs in buffered conditions, which recently gained increased attention. References: S. Cherevko, A. R. Zeradjanin, A. A. Topalov, N. Kulyk, I. Katsounaros and K. J. J. Mayrhofer, ChemCatChem, 6, 2219 (2014). Hydrogen and Fuel Cell Technologies Office - Hydrogen Shot, in, https://www.energy.gov/eere/fuelcells/hydrogen-shot. S. Geiger, O. Kasian, M. Ledendecker, E. Pizzutilo, A. M. Mingers, W. T. Fu, O. Diaz-Morales, Z. Li, T. Oellers, L. Fruchter, A. Ludwig, K. J. J. Mayrhofer, M. T. M. Koper and S. Cherevko, Nature Catalysis, 1, 508 (2018). J. Knöppel, M. Möckl, D. Escalera-López, K. Stojanovski, M. Bierling, T. Böhm, S. Thiele, M. Rzepka and S. Cherevko, Nature Communications, 12, 2231 (2021). D.-Y. Kuo, J. K. Kawasaki, J. N. Nelson, J. Kloppenburg, G. Hautier, K. M. Shen, D. G. Schlom and J. Suntivich, Journal of the American Chemical Society, 139, 3473 (2017). T. Nishimoto, T. Shinagawa, T. Naito and K. Takanabe, Journal of Catalysis, 391, 435 (2020). M. Schalenbach, O. Kasian, M. Ledendecker, F. D. Speck, A. M. Mingers, K. J. J. Mayrhofer and S. Cherevko, Electrocatalysis, 9, 153 (2018).

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15

"Using Pulsed Cold Neutrons to Measure Neutron Lifetime". JPS Hot Topics 1 (2021). http://dx.doi.org/10.7566/jpsht.1.043.

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16

Anonymous. "Discrepancy in Neutron Lifetime Still Unresolved". Physics 6 (27 novembre 2013). http://dx.doi.org/10.1103/physics.6.s150.

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17

Koch, Benjamin, e Felix Hummel. "Exciting hint toward the solution of the neutron lifetime puzzle". Physical Review D 110, n. 7 (10 ottobre 2024). http://dx.doi.org/10.1103/physrevd.110.073004.

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Abstract (sommario):

We revisit the neutron lifetime puzzle, a discrepancy between beam and bottle measurements of the weak neutron decay. Since both types of measurements are realized at different times after the nuclear production of free neutrons, we argue that the existence of excited states could be responsible for the different lifetimes. We elaborate on the required properties of such states and under what circumstances it is possible that these states have not been experimentally identified yet. Published by the American Physical Society 2024

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18

Rajan, Ashwani, e Shantanu Desai. "A meta-analysis of neutron lifetime measurements". Progress of Theoretical and Experimental Physics 2020, n. 1 (1 gennaio 2020). http://dx.doi.org/10.1093/ptep/ptz153.

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Abstract We calculate the median as well as weighted mean central estimates for the neutron lifetime from a subset of measurements compiled in the 2019 update of the Particle Data Group (PDG). We then reconstruct the error distributions for the residuals using three different central estimates and then check for consistency with a Gaussian distribution. We find that although the error distributions using the weighted mean as well as median estimate are consistent with a Gaussian distribution, the Student’s $t$ and Cauchy distribution provide a better fit. This median statistic estimate of the neutron lifetime from these measurements is given by $881.5 \pm 0.47$ seconds. This can be used as an alternate estimate of the neutron lifetime. We also note that the discrepancy between beam and bottle-based measurements using median statistics of the neutron lifetime persists with a significance between 4 $\sigma$ and 8 $\sigma$, depending on which combination of measurements is used.

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19

Belfatto, Benedetta, Revaz Beradze e Zurab Berezhiani. "The CKM unitarity problem: a trace of new physics at the TeV scale?" European Physical Journal C 80, n. 2 (febbraio 2020). http://dx.doi.org/10.1140/epjc/s10052-020-7691-6.

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Abstract After the recent high precision determinations of $$V_{us}$$Vus and $$V_{ud}$$Vud, the first row of the CKM matrix shows more than $$4\sigma $$4σ deviation from unitarity. Two possible scenarios beyond the Standard Model can be investigated in order to fill the gap. If a 4th non-sequential quark $$b'$$b′ (a vector-like weak isosinglet) participates in the mixing, with $$\vert V_{ub'} \vert \sim 0.04$$|Vub′|∼0.04, then its mass should be no more than 6 TeV or so. A different solution can come from the introduction of the gauge horizontal family symmetry $$SU(3)_\ell $$SU(3)ℓ acting between the lepton families and spontaneously broken at the scale of about 6 TeV. Since the gauge bosons of this symmetry contribute to muon decay in interference with Standard Model, the Fermi constant is slightly smaller than the muon decay constant so that unitarity is recovered. Also the neutron lifetime problem, that is about $$4\sigma $$4σ discrepancy between the neutron lifetimes measured in beam and trap experiments, is discussed in the light of the these determinations of the CKM matrix elements.

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20

Mahony, J., e P. Mascher. "Defect Characterization Of InAs Wafers Using Positron Lifetime Spectroscopy". MRS Proceedings 442 (1996). http://dx.doi.org/10.1557/proc-442-547.

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AbstractPositron lifetime measurements on InAs wafers have shown that the positron bulk lifetime in InAs is 246±2 ps. Most samples exhibit a defect lifetime of 287±6 ps, which is attributable to monovacancy-impurity complexes with a concentration of 7±2×10 16 cm-3. Very heavily doped n-type samples exhibit a defect lifetime of 332–340 ps, characteristic of divacancies. The concentration of these defects is also close to 1017 cm−3. Both types of defects are stable for rapid thermal annealing up to 850 °C, and both defects are neutral. The formation of the divacancytype defects may be correlated with a discrepancy between the carrier concentration and the total

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21

Ema, Yohei, Zhen Liu, Kun-Feng Lyu e Maxim Pospelov. "Flavor-changing light bosons with accidental longevity". Journal of High Energy Physics 2023, n. 2 (14 febbraio 2023). http://dx.doi.org/10.1007/jhep02(2023)135.

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Abstract We consider a model with a complex scalar field that couples to (e, μ) or (μ, τ) within the “longevity” window: $$ \left[|{m}_{l_1}-{m}_{l_2}|,{m}_{l_1}+{m}_{l_2}\right] $$ m l 1 − m l 2 m l 1 + m l 2 in which l1 and l2 are the two different charged leptons. Within such a mass window, even a relatively large coupling (e.g. of the size commensurate with the current accuracy/discrepancy in the muon g − 2 experiment) leads to long lifetimes and macroscopic propagation distance between production and decay points. We propose to exploit several existing neutrino experiments and one future experiment to probe the parameter space of this model. For the μ − e sector, we exploit the muonium decay branching ratio and the production and decay sequence at the LSND experiment, excluding the parametric region suggested by gμ − 2 anomaly. For the τ − μ sector, we analyze three main production mechanisms of scalars at beam dump experiments: the Drell-Yan process, the heavy meson decay, and the muon scattering. We explore the constraints from the past CHARM and NuTeV experiments, and evaluate sensitivity for the proposed beam dump experiment, SHiP. The latter can thoroughly probe the parameter space relevant for the gμ− 2 anomaly.

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