Branching Ratios For Proton Decay Research Articles

First measurement of proton decay from a transfer reaction to Na21

Decay protons from excited states in $^{21}\mathrm{Na}$ populated through a previously reported $^{24}\mathrm{Mg}(p,\ensuremath{\alpha})^{21}\mathrm{Na}$ transfer reaction [Cha et al., Phys. Rev. C 96, 025810 (2017)] were analyzed to extract the proton branching ratios of the energy levels. By utilizing 31-MeV proton beams from the Holifield Radioactive Ion Beam Facility of Oak Ridge National Laboratory and isotopically enriched $^{24}\mathrm{Mg}$ solid targets, the decay protons were detected in coincidence with $\ensuremath{\alpha}$ particles from the $(p,\ensuremath{\alpha})$ reaction using a silicon strip detector array. Proton decay branching ratios of several $^{21}\mathrm{Na}$ levels were deduced for the $p0$ and $p1$ decay channels to the ground and first excited states in $^{20}\mathrm{Ne}$, respectively.

Evaluation of the K35(p,γ)Ca36 reaction rate using the Ca37(p,d)Ca36 transfer reaction

Background: A recent sensitivity study has shown that the K35(p,γ)Ca36 reaction is one of the ten (p,γ) reaction rates that could significantly impact the shape of the calculated x-ray burst light curve. Its reaction rate used up to now in type I x-ray burst calculations was estimated using an old measurement for the mass of Ca36 and theoretical predictions for the partial decay widths of the first 2+ resonance with arbitrary uncertainties. Purpose: In this work, we propose to reinvestigate the K35(p,γ)Ca36 reaction rate, as well as related uncertainties, by determining the energies and decay branching ratios of Ca36 levels, within the Gamow window of x-ray bursts, in the 0.5 to 2 GK temperature range. Method: These properties were studied by means of the one-neutron pickup transfer reaction Ca37(p,d)Ca36 in inverse kinematics using a radioactive beam of Ca37 at 48 MeV nucleon−1. The experiment was performed at the GANIL facility using the liquid hydrogen target CRYPTA, the MUST2 charged particle detector array for the detection of the light charged particles, and a zero degree detection system for the outgoing heavy recoil nuclei. Results: The atomic mass of Ca36 is confirmed and new resonances have been proposed together with their proton decay branching ratios. This spectroscopic information, used in combination with very recent theoretical predictions for the γ-decay width, were used to calculate the K35(p,γ)Ca36 reaction rate. The recommended rate of the present work was obtained within a uncertainty factor of 2 at 1σ. This is consistent with the previous estimate in the x-ray burst temperature range. A large increase of the reaction rate was found at higher temperatures due to two newly discovered resonances. Conclusions: The K35(p,γ)Ca36 thermonuclear reaction rate is now well constrained by the present work in a broad range of temperatures covering those relevant to type I x-ray bursts. Our results show that the K35(p,γ)Ca36 reaction does not affect the shape of the x-ray burst light curve, and that it can be removed from the list of the few influential proton radiative captures reactions having a strong impact on the light curve.Received 18 January 2021Accepted 12 April 2021DOI:https://doi.org/10.1103/PhysRevC.103.055809©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDirect reactionsExplosive burningNuclear astrophysicsNuclear physics of explosive environmentsNucleon induced nuclear reactionsProton emissionRadiative captureTransfer reactionsProperties20 ≤ A ≤ 38Nuclear PhysicsGravitation, Cosmology & Astrophysics

Witten’s loop in the minimal flipped SU(5) unification revisited

In the simplest potentially realistic renormalizable variants of the flipped $SU(5)$ unified model the right-handed neutrino masses are conveniently generated by means of the Witten's two-loop mechanism. As a consequence, the compactness of the underlying scalar sector provides strong correlations between the low-energy flavor observables such as neutrino masses and mixing and the flavor structure of the fermionic currents governing the baryon and lepton number violating nucleon decays. In this study, the associated two-loop Feynman integrals are fully evaluated and, subsequently, are used to draw quantitative conclusions about the central observables of interest such as the proton decay branching ratios and the absolute neutrino mass scale.

Yukawa sector of minimal SO(10) unification

We show that in SO(10) models, a Yukawa sector consisting of a real 10H, a real 120H and a complex 126H of Higgs fields can provide a realistic fit to all fermion masses and mixings, including the neutrino sector. Although the group theory of SO(10) demands that the 10H and 120H be real, most constructions complexify these fields and impose symmetries exterior to SO(10) to achieve predictivity. The proposed new framework with real 10H and real 120H relies only on SO(10) gauge symmetry, and yet has a limited number of Yukawa parameters. Our analysis shows that while there are restrictions on the observables, a good fit to the entire fermion spectrum can be realized. Unification of gauge couplings is achieved with an intermediate scale Pati-Salam gauge symmetry. Proton decay branching ratios are calculable, with the leading decay modes being pto overline{nu}{pi}^{+} and p → e+π0.

New class of SO(10) models for flavor

We present a new class of unified models based on SO(10) symmetry which provides insights into the masses and mixings of quarks and leptons, including the neutrinos. The key feature of our proposal is the absence of Higgs boson 10_H belonging to the fundamental representation that is normally employed. Flavor mixing is induced via vector-like fermions in the 16 + 16-bar representation. A variety of scenarios, both supersymmetric and otherwise, are analyzed involving a 126_H along with either a 45_H or a 210_H of Higgs boson employed for symmetry breaking. It is shown that this framework, with only a limited number of parameters, provides an excellent fit to the full fermion spectrum, utilizing either type-I or type-II seesaw mechanism. These flavor models can be potentially tested and distinguished in their predictions for proton decay branching ratios, which are analyzed.

Minimal nonsupersymmetricSO(10)model: Gauge coupling unification, proton decay, and fermion masses

We present a minimal renormalizable non-supersymmetric SO(10) grand unified model with a symmetry breaking sector consisting of Higgs fields in the 54_H + 126_H + 10_H representations. This model admits a single intermediate scale associated with Pati-Salam symmetry along with a discrete parity. Spontaneous symmetry breaking, the unification of gauge couplings and proton lifetime estimates are studied in detail in this framework. Including threshold corrections self-consistently, obtained from a full analysis of the Higgs potential, we show that the model is compatible with the current experimental bound on proton lifetime. The model generally predicts an upper bound of few times 10^{35} yrs for proton lifetime, which is not too far from the present Super-Kamiokande limit of \tau_p \gtrsim 1.29 \times 10^{34} yrs. With the help of a Pecci-Quinn symmetry and the resulting axion, the model provides a suitable dark matter candidate while also solving the strong CP problem. The intermediate scale, M_I \approx (10^{13}-10^{14}) GeV which is also the B-L scale, is of the right order for the right-handed neutrino mass which enables a successful description of light neutrino masses and oscillations. The Yukawa sector of the model consists of only two matrices in family space and leads to a predictive scenario for quark and lepton masses and mixings. The branching ratios for proton decay are calculable with the leading modes being p \rightarrow e^+ \pi^0 and p \rightarrow \overline{\nu} \pi^+. Even though the model predicts no new physics within the reach of LHC, the next generation proton decay detectors and axion search experiments have the capability to pass verdict on this minimal scenario.

Proton decay and the origin of quark and lepton mixing

It was recently proposed that all flavor mixing has a single source, namely the mixing of the three quark and lepton families with "extra" vectorlike fermions in 5 + 5-bar multiplets of SU(5). This was shown to lead to several testable predictions including neutrino masses and CP-violating phases. Here it is shown that the mixing angles within grand unified fermion multiplets are also predicted. Proton decay branching ratios would thus give several independent tests of the model. Certain model parameters could be determined independently from the quark and lepton spectrum and from proton decay.

28Si(p,3He) reaction for spectroscopy of26Al

The ${}^{28}\text{Si}{(p{,}^{3}\text{He})}^{26}\text{Al}$ reaction was utilized for the first time to study the levels in ${}^{26}$Al, using a proton beam from the Holifield Radioactive Ion Beam Facility. Five previously unreported states in ${}^{26}$Al are observed and discussed, including Distorted Wave Born Approximation analysis. Proton-decay branching ratios consistent with previous studies and theoretical expectations were found by detecting decay protons from highly excited ${}^{26}$Al states in coincidence with the ${}^{3}$He particles.

Measurements ofS31energy levels and reevaluation of the thermonuclear resonantP30(p,γ)S31reaction rate

By measuring the $^{31}\mathrm{P}(^{3}\mathrm{He},t)^{31}\mathrm{S}$, $^{31}\mathrm{P}(^{3}\mathrm{He},t)^{31}\mathrm{S}{}^{*}(p)^{30}\mathrm{P}$, and $^{32}\mathrm{S}(d,t)^{31}\mathrm{S}$ reactions, the level scheme of $^{31}\mathrm{S}$ has been refined and extended up to ${E}_{x}=9.5$ MeV. A total of 17 new levels, and 5 tentative new levels, have been measured. In addition, 5 tentatively known levels have been confirmed. The uncertainties in the excitation energies of many known $^{31}\mathrm{S}$ levels have been reduced substantially. Spin constraints have been made for 8 proton-unbound levels by measuring 18 triton-proton angular correlations from the $^{31}\mathrm{P}(^{3}\mathrm{He},t)^{31}\mathrm{S}{}^{*}(p)^{30}\mathrm{P}$ reaction. Finite proton-decay branching ratios (including discrimination between decays to the ground state and first two excited states of $^{30}\mathrm{P}$) have been measured for 38 levels, and upper limits have been set for 3 additional levels. The lowest isospin $T=3/2$ level has been observed, and candidates for the second and third $T=3/2$ levels have been identified. The new experimental information on $^{30}\mathrm{P}+p$ resonance parameters has been used together with data from previous measurements to calculate the thermonuclear, resonant $^{30}\mathrm{P}(p,\ensuremath{\gamma})^{31}\mathrm{S}$ reaction rate over three orders of magnitude in temperature: $0.01<T<10$ GK. Good agreement is found with estimates based on Hauser-Feshbach statistical models over the range $0.08<T<10$ GK, but differences are found with rates previously estimated using the experimental information at hand.

Direct proton decay of the isoscalar giant dipole resonance in 208Pb

The excitation and subsequent proton decay of the isoscalar giant dipole resonance (ISGDR) in 208Pb have been investigated via the Pb208(α,α′p)Tl207 reaction at 400 MeV. Excitation of the ISGDR has been identified by the difference-of-spectra method. The enhancement of the ISGDR strength at high excitation energies observed in the multipole-decomposition-analysis of the singles Pb208(α,α′) spectra is not present in the excitation energy spectrum obtained in coincidence measurement. The partial branching ratios for direct proton decay of ISGDR to low-lying states of 207Tl have been determined and the results are compared with predictions of continuum random-phase-approximation (CRPA) calculations.

Puzzle for the existence of 3α + N structure in A=13 system

Spin-isospin excitations in 13 N have been studied by means of the (3 He ,t) and (3 He ,tp) reactions at the bombarding energy of E(3 He ) = 450 MeV . The zero-degree (3 He ,t) spectrum is found to be similar to those from the (p,n) reactions at intermediate energies, suggesting a simple direct reaction mechanism at E(3 He ) = 450 MeV . Three pairs of Gamow-Teller (GT) states with Jπ = 1/2- and 3/2- have been strongly excited at θlab. = 0°. Microscopic structures of the states in 13 N have been studied by observing decay protons in coincidence with high energy tritons measured at θlab. = 0°. The branching ratios for proton decay from the GT states in 13 N to the final low-lying T =0 states in 12 C were obtained. The wave functions of the excited states in 13 N are discussed in the view point of α cluster model.

Formula omitted] and [formula omitted] unified theories on an elongated rectangle

Maximally supersymmetric SO ( 10 ) and SU ( 6 ) unified theories are constructed on the orbifold T 2 / ( Z 2 × Z 2 ′ ) , with one length scale R 5 taken much larger than the other, R 6 . The effective theory below 1 / R 6 is found to be the highly successful SU ( 5 ) theory in 5D with natural doublet–triplet splitting, no proton decay from operators of dimension four or five, unified mass relations for heavier generations only, and a precise prediction for gauge coupling unification. A more unified gauge symmetry, and the possibility of Higgs doublets being components of the higher-dimensional gauge multiplet, are therefore compatible with a large energy interval where physics is described by SU ( 5 ) gauge symmetry in 5D. This leads to the distinctive branching ratios for proton decay from SU ( 5 ) gauge boson exchange, p → l + π 0 , l + K 0 , ν ¯ π + , ν ¯ K + ( l = e , μ ), for well-motivated locations for matter. Several phenomenological features of the higher unified gauge symmetry are discussed, including the role of an extra U ( 1 ) gauge symmetry, which survives compactification, in the generation of neutrino masses.

Nuclear structure of the spin-isospin excited states inN13studied via the(He3,t)and(He3,tp)reactions at450MeV

Spin-isospin excitations in $^{13}\mathrm{N}$ have been studied by means of the $(^{3}\mathrm{He},t)$ and $(^{3}\mathrm{He},tp)$ reactions at a bombarding energy of $E(^{3}\mathrm{He})=450\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$. The zero-degree $(^{3}\mathrm{He},t)$ spectrum is found to be similar to those from the $(p,n)$ reactions at intermediate energies, suggesting a simple direct reaction mechanism at $E(^{3}\mathrm{He})=450\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$. The Gamow-Teller $(\mathrm{GT})$ states with ${J}^{\ensuremath{\pi}}=1∕{2}^{\ensuremath{-}}$ and $3∕{2}^{\ensuremath{-}}$ have been strongly excited at ${\ensuremath{\theta}}_{\mathrm{lab}}=0\ifmmode^\circ\else\textdegree\fi{}$. The angular distribution of cross sections for the $^{13}\mathrm{C}(^{3}\mathrm{He},t)^{13}\mathrm{N}$ reaction and the elastic $^{3}\mathrm{He}$ scattering off $^{13}\mathrm{C}$ were obtained at ${\ensuremath{\theta}}_{\mathrm{lab}}=0\ifmmode^\circ\else\textdegree\fi{}--17\ifmmode^\circ\else\textdegree\fi{}$ and at ${\ensuremath{\theta}}_{\mathrm{lab}}=2\ifmmode^\circ\else\textdegree\fi{}--22\ifmmode^\circ\else\textdegree\fi{}$, respectively. The obtained experimental results were compared with calculations performed in distorted-wave Born approximation. Microscopic structures of the states in $^{13}\mathrm{N}$ have further been studied by observing decay protons in coincidence with high-energy tritons measured at ${\ensuremath{\theta}}_{\mathrm{lab}}=0\ifmmode^\circ\else\textdegree\fi{}$. The branching ratios for proton decay from the $\mathrm{GT}$ states in $^{13}\mathrm{N}$ to the final low-lying $T=0$ states in $^{12}\mathrm{C}$ were obtained. The wave functions of the excited states in $^{13}\mathrm{N}$ are discussed on the basis of obtained experimental data and relevant theoretical calculations.

Direct-decay properties of charge-exchange spin giant resonances

An extended continuum-RPA approach is applied to describe direct-decay properties of spin giant resonances in $^{208}$Bi and $^{90}$Nb. Partial branching ratios for direct proton decay from these resonances are evaluated. The branching ratio for $\gamma$-decay from the spin-dipole resonance to the Gamow-Teller resonance (main peak) is estimated. The saturation-like behaviour of the mean doorway-state spreading width in $^{208}$Pb is discussed in connection with the branching ratio for direct proton decay from the spin-monopole resonance and the Gamow-Teller strength distribution.

Fine structure in the decay of deformed proton emitters: nonadiabatic approach

The coupled-channel Schrodinger equation with outgoing wave boundary conditions is employed to study the fine structure seen in the proton decay of deformed even- N, odd- Z rare earth nuclei 131Eu and 141Ho. Experimental lifetimes and proton-decay branching ratios are reproduced. Variations with the standard adiabatic theory are discussed.

Direct proton decay and microscopic structure of the spin-dipole resonance in208Bi

The microscopic structure of the spin-dipole resonance (SDR) at ${E}_{x}=21.1 \mathrm{MeV}$ in ${}^{208}\mathrm{Bi}$ has been investigated in the ${}^{208}\mathrm{Pb}{(}^{3}\mathrm{He}{,t)}^{208}\mathrm{Bi}$ reaction at ${E(}^{3}\mathrm{He})=450 \mathrm{MeV}$ and very forward scattering angles. Protons emitted due to the decay of the SDR were measured in solid-state detectors in coincidence with tritons detected with the high resolution magnetic spectrometer Grand Raiden. The total and partial branching ratios for proton decay from the SDR to the residual neutron-hole states in ${}^{207}\mathrm{Pb}$ have been measured. The deduced escape widths are found to be in good agreement with recent theoretical estimates.

Structure and decay properties of spin-dipole giant resonances within a semimicroscopical approach

A semimicroscopical approach is applied to calculate: (i) strength functions for the charge-exchange spin-dipole giant resonances in the 208Pb parent nucleus; (ii) partial and total branching ratios for the direct proton decay of the resonance in 208Bi. The approach is based on continuum-RPA calculations of corresponding reaction-amplitudes and phenomenological description of the doorway-state coupling to many-quasiparticle configurations. The only adjustable parameter needed for the description is found by comparison of the calculated and experimental total widths of the resonance. Other model parameters used in calculations are taken from independent data. The calculated total branching ratio is found to be in reasonable agreement with the experimental value.

Realistic quark and lepton masses through SO(10) symmetry

In a recent paper a model of quark and lepton masses was proposed. Without any family symmetries almost all the qualitative and quantitative features of the quark and lepton masses and Kobayashi-Maskawa mixing angles are explained, primarily as consequences of various aspects of $SO(10)$ symmetry. Here the model is discussed in much greater detail. The threefold mass hierarchy as well as the relations $m_\tau^0 \simeq m_b^0, ~m_\mu^0 \simeq 3m_s^0,~ m_e^0 \simeq {1 \over 3} m_d^0, ~m_u^0/m_t^0 \ll m_d^0/m_b^0, ~{\rm tan}\theta_C \simeq \sqrt{m_d^0/m_s^0},~ V_{cb} \ll \sqrt{m_s^0/m_b^0}$ and $V_{ub} \sim V_{us}V_{cb}$ follow from a simple Yukawa structure at the unification scale. The model also gives definite predictions for $\tan \beta$, the neutrino mixing angles, and proton decay branching ratios. The $(\nu_\mu-\nu_\tau)$ mixing angle is typically large, tan$\beta$ is close to either $m_t^0/m_b^0$ or $m_c^0/m_s^0$, and proton decay is in the observable range, but there is a group theoretical suppression factor in the rate.

Investigation of the 12C(α, γ) 16O reaction via the β-delayed proton decay of 17Ne

We have determined the branching ratios for the β-delayed proton decay of excited states in 17F to excited states in 16O by measuring proton-γ-ray coincidences. We have observed transitions to the 2 + state at 6.917 MeV in 16O from 17F states at 11.193, 10.0, 9.45, 8.83 and 8.44 MeV. In particular, the transition from the 9.45 MeV state is an order of magnitude stronger than the accompanying transitions to the 1 − state at 7.117 MeV and the 3 − state at 6.130 MeV, and seems a favourable case for the observation of 16O break-up into α + 12 C .

Nucleon decay in a realistic SO(10) SUSY GUT

In this paper, we calculate neutron and proton decay rates and branching ratios in a predictive SO(10) SUSY GUT which agrees well with low energy data. We show that the nucleon lifetimes are consistent with the experimental bounds. The nucleon decay rates are calculated using all one-loop chargino and gluino dressed diagrams regardless of their chiral structure. We show that the four-fermion operator $C_{jk} (u_R {d_j}_R)({d_k}_L {\nu_\tau}_L)$, commonly neglected in previous nucleon decay calculations, not only contributes significantly to nucleon decay, but, for many values of the initial GUT parameters and for large $\tan\beta$, actually dominates the decay rate. As a consequence, we find that $\tau_p/\tau_n$ is often substantially larger than the prediction obtained in small $\tan\beta$ models. We also find that gluino-dressed diagrams, often neglected in nucleon decay calculations, contribute significantly to nucleon decay. In addition we find that the branching ratios obtained from this realistic SO(10) SUSY GUT differ significantly from the predictions obtained from ``generic" SU(5) SUSY GUTS. Thus nucleon decay branching ratios, when observed, can be used to test theories of fermion masses.