Neutron-antineutron Oscillations Research Articles

NN interaction from chiral effective field theory and its application to neutron-antineutron oscillations

An N¯N potential is introduced which is derived within chiral effective field theory and fitted to up-to-date N¯N phase shifts and inelasticities, provided by a proper phase-shift analysis of available p¯p scattering data. As an application of this interaction neutron-antineutron oscillations in the deuteron are considered. In particular, results for the deuteron lifetime are presented, evaluated in terms of the free-space n−n¯ oscillation time, utilizing that N¯N potential together with an NN interaction likewise derived within chiral effective field theory.

Universal inverse seesaw mechanism as a source of the SM fermion mass hierarchy

We build a renormalizable theory where the inverse seesaw mechanism explains the pattern of SM fermion masses. To the best of our knowledge, our model corresponds to the first implementation of the inverse seesaw mechanism for the charged fermion sector. In our theory, the inverse seesaw mechanism is implemented at the tree and one-loop levels in order to generate the masses for the second and first families of the SM charged fermions, respectively. The third family of SM charged fermions obtain tree-level masses from the Higgs doublets phi _{1} (for the top quark) and phi _{2} (for the bottom quark and tau lepton). The masses of the active light neutrinos are generated from a two-loop level inverse seesaw mechanism. Our model successfully explains the observed SM fermion mass hierarchy, the tiny masses of the active light neutrinos, contains the necessary means for efficient leptogenesis and is in accordance with the constraints resulting from meson oscillations, as well as with the measured values of the observed dark matter relic density and of the muon and electron anomalous magnetic moments.

Baryogenesis with Observable Neutron–Antineutron Oscillation

Baryogenesis with Observable Neutron–Antineutron Oscillation

A Possible Neutron-Antineutron Oscillation Experiment at PF1B at the Institut Laue Langevin

We consider a possible neutron–antineutron (n−n¯) oscillation experiment at the PF1B instrument at Institut Laue Langevin. It can improve the best existing constraint on the transition rate and also allow the testing of the methods and instrumentation which would be needed for a later larger-scale experiment at ESS. The main gain factors over the most competitive experiment, performed earlier at PF1 instrument at ILL, are: a more intense neutron beam and a new operating mode based on coherent n and n¯ mirror reflections. The installation of such an experiment would need a temporary replacement of the existing ballistic neutron guide by a specially designed n/n¯ guide with a gradually increasing cross section and a specially selected coating as well as the development and construction of an advanced n¯ annihilation detector with a high efficiency and low background. The overall gain factor could reach up to an order of magnitude and depends on the chosen experiment configuration.

Neutron-antineutron oscillations as a probe of baryogenesis

A signal of neutron-antineutron () oscillations at experiments like the Deep Underground Neutrino Experiment or the European Spallation Source, would directly imply baryon number violation and will point towards physics beyond the Standard Model. The discovery of such a signal would have important implications for baryogenesis mechanisms in the early Universe, which can explain the observed baryon asymmetry of the Universe today. Here we discuss how an observed rate for oscillations can directly be correlated with the washout of baryon asymmetry in the early Universe and therefore, can probe high- and low-scale baryogenesis scenarios in synergy with collider searches.

An extended 3-3-1 model with two scalar triplets and linear seesaw mechanism

Low energy linear seesaw mechanism responsible for the generation of the tiny active neutrino masses, is implemented in the extended 3-3-1 model with two scalar triplets and right handed Majorana neutrinos where the gauge symmetry is supplemented by the $A_4$ flavor discrete group and other auxiliary cyclic symmetries, whose spontaneous breaking produces the observed pattern of SM charged fermion masses and fermionic mixing parameters. Our model is consistent with the low energy SM fermion flavor data as well as with the constraints arising from meson oscillations. Some phenomenological aspects such as the $Z^\prime$ production at proton proton collider and the lepton flavor violating decay of the SM-like Higgs boson are discussed. The scalar potential of the model is analyzed in detail and the SM-like Higgs boson is identified.

Probing baryogenesis with neutron-antineutron oscillations

In the near future, the Deep Underground Neutrino Experiment and the European Spallation Source aim to reach unprecedented sensitivity in the search for neutron-antineutron (n- overline{n} ) oscillations, whose observation would directly imply |∆B| = 2 violation and hence might hint towards a close link to the mechanism behind the observed baryon asymmetry of the Universe. In this work, we explore the consequences of such a discovery for baryogenesis first within a model-independent effective field theory approach. We then refine our analysis by including a source of CP violation and different hierarchies between the scales of new physics using a simplified model. We analyse the implication for baryogenesis in different scenarios and confront our results with complementary experimental constraints from dinucleon decay, LHC, and meson oscillations. We find that for a small mass hierarchy between the new degrees of freedom, an observable rate for n- overline{n} oscillation would imply that the washout processes are too strong to generate any sizeable baryon asymmetry, even if the CP violation is maximal. On the other hand, for a large hierarchy between the new degrees of freedom, our analysis shows that successful baryogenesis can occur over a large part of the parameter space, opening the window to be probed by current and future colliders and upcoming n- overline{n} oscillation searches.

The charm of 331

We perform a detailed analysis of flavour changing neutral current processes in the charm sector in the context of 331 models. As pointed out recently, in the case of Z′ contributions in these models there are no new free parameters beyond those already present in the Bd,s and K meson systems analyzed in the past. As a result, definite ranges for new Physics (NP) effects in various charm observables could be obtained. While generally NP effects turn out to be small, in a number of observables they are much larger than the tiny effects predicted within the Standard Model. In particular we find that the branching ratio of the mode D0→ μ+μ−, despite remaining tiny, can be enhanced by 6 orders of magnitude with respect to the SM. We work out correlations between this mode and rare Bd,s and K decays. We also discuss neutral charm meson oscillations and CP violation in the charm system. In particular, we point out that 331 models provide new weak phases that are a necessary condition to have non-vanishing CP asymmetries. In the case of ∆ACP, the difference between the CP asymmetries in D0→ K+K− and D0→ π+π−, we find that agreement with experiment can be obtained provided that two conditions are verified: the phases in the ranges predicted in 331 models and large hadronic matrix elements.

Investigation of the FCNC Processes in the 3-4-1-1 Model

We study the FCNC problems in 3-4-1-1 model in a way different from the previous work. The sources of FCNC at the tree-level in the 3-4-1-1 model come from both the gauge and scalar sectors. We show that the most stringently bound on the tree-level FCNC interactions comes from the meson oscillations. The lower bound on the new physics scale is imposed more tightly than in the previous work, \(M_{new} > 22\) TeV. On the allowed value domain of the new physical scale, we show that the contribution of the tree-level FCNC interactions to the BrB\(_s \rightarrow \mu^+ \mu^-)\) is negligible.

Parity of the neutron consistent with neutron-antineutron oscillations

In the analysis of neutron-antineutron oscillations, it has been recently argued in the literature that the use of the $i\gamma^{0}$ parity $n^{p}(t,-\vec{x})=i\gamma^{0}n(t,-\vec{x})$ which is consistent with the Majorana condition is mandatory and that the ordinary parity transformation of the neutron field $n^{p}(t,-\vec{x}) = \gamma^{0}n(t,-\vec{x})$ has a difficulty. We show that a careful treatment of the ordinary parity transformation of the neutron works in the analysis of neutron-antineutron oscillations. Technically, the CP symmetry in the mass diagonalization procedure is important and the two parity transformations, $i\gamma^{0}$ parity and $\gamma^{0}$ parity, are compensated for by the Pauli-G\"ursey transformation. Our analysis shows that either choice of the parity gives the correct results of neutron-antineutron oscillations if carefully treated.

Neutron-antineutron oscillation search using a 0.37 megaton-years exposure of Super-Kamiokande

As a baryon number violating process with ΔB=2, neutron-antineutron oscillation (n→n¯) provides a unique test of baryon number conservation. We have performed a search for n→n¯ oscillation with bound neutrons in Super-Kamiokande, with the full dataset from its first four run periods, representing an exposure of 0.37 Mton−years. The search used a multivariate analysis trained on simulated n→n¯ events and atmospheric neutrino backgrounds and resulted in 11 candidate events with an expected background of 9.3 events. In the absence of statistically significant excess, we derived a lower limit on n¯ appearance lifetime in O16 nuclei of 3.6×1032 years and on the neutron-antineutron oscillation time of τn→n¯>4.7×108 s at 90% C.L.1 MoreReceived 6 December 2020Accepted 24 December 2020DOI:https://doi.org/10.1103/PhysRevD.103.012008Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBaryogenesis & leptogenesisHadron mixingPhysical SystemsNeutronsPropertiesC-symmetryTechniquesArtificial neural networksCherenkov detectorsParticles & Fields

Production of bb¯ at forward rapidity in p+p collisions at s=510 GeV

The cross section of bottom quark-antiquark ($b\bar{b}$) production in $p$+$p$ collisions at $\sqrt{s}=510$ GeV is measured with the PHENIX detector at the Relativistic Heavy Ion Collider. The results are based on the yield of high mass, like-sign muon pairs measured within the PHENIX muon arm acceptance ($1.2<|y|<2.2$). The $b\bar{b}$ signal is extracted from like-sign dimuons by utilizing the unique properties of neutral $B$ meson oscillation. We report a differential cross section of $d\sigma_{b\bar{b}\rightarrow \mu^\pm\mu^\pm}/dy = 0.16 \pm 0.01~(\mbox{stat}) \pm 0.02~(\mbox{syst}) \pm 0.02~(\mbox{global})$ nb for like-sign muons in the rapidity and $p_T$ ranges $1.2<|y|<2.2$ and $p_T>1$ GeV/$c$, and dimuon mass of 5--10 GeV/$c^2$. The extrapolated total cross section at this energy for $b\bar{b}$ production is $13.1 \pm 0.6~(\mbox{stat}) \pm 1.5~(\mbox{syst}) \pm 2.7~(\mbox{global})~\mu$b. The total cross section is compared to a perturbative quantum chromodynamics calculation and is consistent within uncertainties. The azimuthal opening angle between muon pairs from $b\bar{b}$ decays and their $p_T$ distributions are compared to distributions generated using {\sc ps pythia 6}, which includes next-to-leading order processes. The azimuthal correlations and pair $p_T$ distribution are not very well described by {\sc pythia} calculations, but are still consistent within uncertainties. Flavor creation and flavor excitation subprocesses are favored over gluon splitting.

Theoretical analysis of antineutron-nucleus data needed for antineutron mirrors in neutron-antineutron oscillation experiments

The values of the antineutron-nucleus scattering lengths, and in particular their imaginary parts, are needed to evaluate the feasibility of using neutron mirrors in laboratory experiments to search for neutron-antineutron oscillations. We analyze existing experimental and theoretical constraints on these values with emphasis on low $A$ nuclei and use the results to suggest materials for the neutron/antineutron guide and to evaluate the systematic uncertainties in estimating the neutron-antineutron oscillation time. As an example we discuss a scenario for a future neutron-antineutron oscillation experiment proposed for the European Spallation Source. We also suggest future experiments which can provide a better determination of the values of antineutron-nuclei scattering lengths.

Fuzzy dark matter and neutron Majorana mass from gravitational instantons

We explore the possibility that a super-light candidate for fuzzy (or wave) Dark Matter (fDM) may be a new composite boson state of fermions, rather than an axion-like Bose-Einstein condensate. We start from string-inspired massless Majorana fermions χ thought as super-modulini fields from string compactifications. We show that massless (or nearly massless) fermions can form a Bose-Einstein condensate and they can acquire a tiny mass term from quantum-gravitational non-perturbative effects such as gravitational instantons. For having a successful candidate for fDM, the so generated Majorana mass is , or so; otherwise decoherence would suppress quantum-mechanical effects in the macroscopic limit. Gravity is democratically coupled with every standard model particles; any neutral fermions acquire a Majorana mass equal to . While for neutrinos, such a mass would be completely out of any testability, a neutron Majorana mass can also be envisaged. A gravitational Majorana mass for the neutron generates baryon violating neutron-antineutron oscillations. Contrary to other competitive models, here the transition is generated without adding any new particles or interactions to the standard model: it is a genuine quantum gravity effect. Current limits on imply a Majorana mass bound and, therefore, the very same limit on the Gravi-fuzzy DM (GfDM) candidate. The next generation of experiments searching for can probe up to the , potentially excluding Gravi-fuzzy DM up to it.

A new approach to search for free neutron-antineutron oscillations using coherent neutron propagation in gas

Coherent forward neutron propagation in gas is discussed as a new approach to search for neutron-antineutron oscillations (n−n¯), which violate both B and B−L conservation. We show that one can increase the probability of neutron - antineutron transitions in the presence of a nonzero external magnetic field to essentially free neutron oscillation probability by tuning the density of an appropriate mixture of gases so that the neutron optical potential of the gas cancels that from the magnetic field.

Direct baryogenesis in the broken phase

We show a new mechanism for baryogenesis where the reheating temperature can be smaller than the electroweak scale. The baryon number symmetry is violated by a dimension nine operator which conserves a baryon parity. A high energy quark from the decay of a heavy particle, e.g. inflaton, modulus or gravitino, undergoes flavor oscillation, and is thermalized due to the scatterings with the ambient thermal plasma. We point out that the baryon asymmetry of our universe can be generated due to the scatterings via the baryon number violating operator. Our scenario can be tested in neutron-antineutron oscillation experiments as well as other terrestrial experiments.

Collider phenomenology of a unified leptoquark model

We demonstrate that in a recently proposed unified leptoquark model based on the gauge group $SU(4)_C\times SU(2)_L \times U(1)_R$ significant deviations from the Standard Model values of $R_K$ and $R_{K^*}$ can be accommodated without any need of extra heavy fermions. Low energy data, in particular lepton flavour violating $\mu$ decays and $K_L\to e \mu$, severely constrain the available parameter space. We show that in the allowed part of the parameter space (i) some of the lepton-flavour-violating tau decay branching ratios are predicted to be close to their current experimental limits. (ii) The underlying scalar leptoquarks can be probed at the LHC via their dominant decay modes into tau-leptons and electrons and the third generation quarks. (iii) The constraints from meson oscillations imply that the masses of scalar gluons, another pair of coloured multiplets around, have to be bigger than around 15 TeV and, thus, they can be probed only at a future 100 TeV collider. In both neutral and charged variants, these scalars decay predominantly into third generation quarks, with up to $O$(10\%) branching ratios into family-mixed final states. Besides that, we comment on the phenomenology of the scalar gluons in the current scenarios in the case that the $B$-decay anomalies eventually disappear.

Neutron-antineutron oscillations in the deuteron studied with NN and N̄N interactions based on chiral effective field theory * * This work is supported in part by the DFG and the NSFC through funds provided to the Sino-German CRC 110 "Symmetries and the Emergence of Structure in QCD" (DFG grant. no. TRR 110) and the VolkswagenStiftung (93562). The work of UGM

Neutron-antineutron ( ) oscillations in the deuteron are considered. Specifically, the deuteron lifetime is calculated in terms of the free-space oscillation time based on and interactions derived within chiral effective field theory (EFT). This results in s, which is close to the value obtained by Dover and collaborators more than three decades ago, but disagrees with recent EFT calculations that were performed within the perturbative scheme proposed by Kaplan, Savage, and Wise. Possible reasons for the difference are discussed.

Project on searching for neutron-antineutron oscillation at the WWR-M reactor

Supersource of ultracold neutrons on the basis of superfluid helium is under construction in PNPI NRC KI. It must provide UCN density 2-3 orders of magnitude higher than existing sources. For the new source we propose an experiment on search for neutron–antineutron oscillations based on the storage of ultracold neutrons in a material trap. The sensitivity of the experiment mostly depends on the trap size and the amount of UCN in it. The geometric configuration of the experimental setup was developed based on the MC simulations of neutrons trajectories into the trap. To calculate detector efficiency the GEANT4 model of the detector was created.

Status of UCN supersource at WWR-M reactor

The WWR-M reactor at NRC «Kurchatov Institute» - PNPI is going to be equipped with high-density ultracold neutron source. Method of UCN production is based on their accumulation in the superfluid helium at 1.2 K temperature. Thus, the source will provide the UCN density at EDM spectrometer equals to ρ = 1.3⋅104 cm−3 which is 2 order magnitude greater than the output density of existing UCN source in the world. An extensive program of fundamental researches such as measuring of neutron lifetime and searching of neutron-antineutron oscillation is planned. In addition, CN and VCN beams are going to be equipped with condensed matter physics experimental setups. The design of the UCN source has been completed, complex tests at full-scale model showed that is possible to maintain superfluid helium under reactor heat load; calculations of an UCN source passive shielding, which ensures source safe operation, is completed. At the moment the process of UCN source manufacturing is taking place.