04 Mar 2021-Journal of High Energy Physics (Springer Science and Business Media LLC)-Vol. 2021, Iss: 3, pp 1-17

Abstract: A search for the K+ → π+X decay, where X is a long-lived feebly interacting particle, is performed through an interpretation of the K+ → $$ {\pi}^{+}
u \overline{
u} $$
analysis of data collected in 2017 by the NA62 experiment at CERN. Two ranges of X masses, 0–110 MeV/c2 and 154–260 MeV/c2, and lifetimes above 100 ps are considered. The limits set on the branching ratio, BR(K+ → π+X), are competitive with previously reported searches in the first mass range, and improve on current limits in the second mass range by more than an order of magnitude.

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Topics: Branching fraction (55%)

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7 results found

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Abstract: With the establishment and maturation of the experimental programs searching for new physics with sizeable couplings at the LHC, there is an increasing interest in the broader particle and astrophysics community for exploring the physics of light and feebly-interacting particles as a paradigm complementary to a New Physics sector at the TeV scale and beyond. FIPs 2020 has been the first workshop fully dedicated to the physics of feebly-interacting particles and was held virtually from 31 August to 4 September 2020. The workshop has gathered together experts from collider, beam dump, fixed target experiments, as well as from astrophysics, axions/ALPs searches, current/future neutrino experiments, and dark matter direct detection communities to discuss progress in experimental searches and underlying theory models for FIPs physics, and to enhance the cross-fertilisation across different fields. FIPs 2020 has been complemented by the topical workshop "Physics Beyond Colliders meets theory", held at CERN from 7 June to 9 June 2020. This document presents the summary of the talks presented at the workshops and the outcome of the subsequent discussions held immediately after. It aims to provide a clear picture of this blooming field and proposes a few recommendations for the next round of experimental results.

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28 Citations

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Martin Bauer^{1}, Matthias Neubert^{2}, Matthias Neubert^{3}, Matthias Neubert^{4} +3 more•Institutions (6)

Abstract: We present a consistent implementation of weak decays involving an axion or axionlike particle in the context of an effective chiral Lagrangian. We argue that previous treatments of such processes have used an incorrect representation of the flavor-changing quark currents in the chiral theory. As an application, we derive model-independent results for the decays ${K}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}a$ and ${\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{\rightarrow}{e}^{\ensuremath{-}}{\overline{\ensuremath{
u}}}_{e}a$ at leading order in the chiral expansion and for arbitrary axion couplings and mass. In particular, we find that the ${K}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}a$ branching ratio is almost 40 times larger than previously estimated.

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Topics: Order (ring theory) (63%)

12 Citations

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Abstract: A light Higgs portal scalar could be abundantly produced in the earth's atmosphere and decay in large-volume neutrino detectors. We point out that the Hyper-Kamiokande detector bears a strong discovery potential of probing such particles in an uncharted section of parameter space that is actively explored by intensity frontier experiments including rare kaon decays. The signal we propose to look for is electron-positron pair creation that manifests as a double-ring appearing from the same vertex. Most of pairs originate from zenith angles above the Hyper-K detector's horizon. This search can be generalized to other new light states and is highly complementary to beam experiments.

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Topics: Higgs boson (52%), Neutrino detector (52%)

3 Citations

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Abstract: From analysis of data produced by the BABAR experiment, the first upper bounds (90% C.L.) were obtained on the branching ratios $\mathrm{Br}(\ensuremath{\tau}\ensuremath{\rightarrow}e\ensuremath{\gamma}\ensuremath{\gamma})l2.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ and $\mathrm{Br}(\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\gamma}\ensuremath{\gamma})l5.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$. In addition, improved upper bounds (95% C.L.) were found on branching ratios $\mathrm{Br}(\ensuremath{\tau}\ensuremath{\rightarrow}eX)l1.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ and $\mathrm{Br}(\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}X)l\phantom{\rule{0ex}{0ex}}2.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, where $X$ is an undetected weakly interacting boson with mass ${m}_{X}l1.6\text{ }\text{ }\mathrm{GeV}/{c}^{2}$.

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1 Citations

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Gonzalo Alonso-Álvarez^{1}, Fatih Ertas^{2}, Joerg Jaeckel^{3}, Felix Kahlhoefer^{2} +1 more•Institutions (3)

Abstract: The axion is much lighter than all other degrees of freedom introduced by the Peccei-Quinn mechanism to solve the strong CP problem. It is therefore natural to use an effective field theory (EFT) to describe its interactions. Loop processes calculated in the EFT may, however, explicitly depend on the ultraviolet cutoff. In general the UV cutoff is not uniquely defined, but the dimensionful couplings suggest to identify it with the Peccei-Quinn symmetry-breaking scale. An example are $K \rightarrow \pi + a$ decays that will soon be tested to improved precision in NA62 and KOTO and whose amplitude is dominated by the term logarithmically dependent on the cutoff. In this paper, we critically examine the adequacy of using such a naive EFT approach to study loop processes by comparing EFT calculations with ones performed in complete QCD axion models. In DFSZ models, for example, the cutoff is found to be set by additional Higgs degrees of freedom and to therefore be much closer to the electroweak scale than to the Peccei-Quinn scale. In fact, there are non-trivial requirements on axion models where the cutoff scale of loop processes is close to the Peccei-Quinn scale, such that the naive EFT result is reproduced. This suggests that the existence of a suitable UV embedding may impose restrictions on axion EFTs. We provide an explicit construction of a model with suitable fermion couplings and find promising prospects for NA62 and IAXO.

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Topics: Electroweak scale (56%), Effective field theory (55%), Axion (54%) ... show more

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23 results found

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Abstract: The complete Review(both volumes) is published online on the website of the Particle Data Group(http://pdg.lbl.gov) and in a journal. Volume 1 is available in print as thePDG Book. AParticle Physics Bookletwith the Summary Tables and essential tables, figures, and equations from selected review articles is also available.

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Topics: Particle Data Group (59%), Anomalous magnetic dipole moment (53%), Deep inelastic scattering (52%)

5,916 Citations

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Abstract: We give an explanation of the $\mathrm{CP}$ conservation of strong interactions which includes the effects of pseudoparticles. We find it is a natural result for any theory where at least one flavor of fermion acquires its mass through a Yukawa coupling to a scalar field which has nonvanishing vacuum expectation value.

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Topics: Vacuum expectation value (57%), Strong CP problem (56%), Yukawa potential (55%) ... show more

4,799 Citations

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Abstract: It is pointed out that a global U(1) symmetry, that has been introduced in order to preserve the parity and time-reversal invariance of strong interactions despite the effects of instantons, would lead to a neutral pseudoscalar boson, the "axion," with mass roughly of order 100 keV to 1 MeV. Experimental implications are discussed.

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Topics: Scalar boson (64%), Boson (56%), Pseudoscalar (55%) ... show more

3,357 Citations

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Abstract: We elaborate on an earlier discussion of CP conservation of strong interactions which includes the effect of pseudoparticles. We discuss what happens in theories of the quantum-chromodynamics type when we include weak and electromagnetic interactions. We find that strong CP conservation remains a natural symmetry if the full Lagrangian possesses a chiral U(1) invariance. We illustrate our results by considering in detail a recent model of (weak) CP nonconservation.

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Topics: Strong CP problem (59%), Axion (50%)

2,085 Citations

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Abstract: I describe a framework for the presentation of search results which is motivated by frequentist statistics. The most well-known use of this framework is for the combined search for the Higgs boson at LEP. A toy neutrino oscillations experiment is used to illustrate the rich information available in the framework for exclusion and discovery. I argue that the so-called CLs technique for setting limits is appropriate for determining exclusion intervals while the determination of confidence intervals advocated by Feldman and Cousins' method is more appropriate for treating established signals, i.e. going beyond discovery to measurement. (From the workshop 'Advanced Statistical Techniques in Particle Physics', 18–22 March 2002)

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Topics: Search for the Higgs boson (62%), Neutrino oscillation (55%), Frequentist inference (54%)

1,917 Citations