Mass spectra, magnetic moments and radiative decays of multi-heavy baryons in a relativistic quark model

Understanding the impact of nuclear effects on proton decay searches with the GiBUU model

Abstract We present a study of the rare baryonic decay $$\Lambda _b \rightarrow \Lambda \tau ^+ \tau ^-$$ Λ b → Λ τ + τ - as a probe of new physics (NP) coupled preferentially to third-generation fermions. Within the Standard Model, we evaluate the branching ratio and the lepton-flavour-universality (LFU) ratio $$R_{\Lambda }^{\tau /\mu },$$ R Λ τ / μ , including both perturbative and long-distance charm contributions. We show that the LFU ratio can be predicted with an uncertainty below 10%. Possible NP effects arising from lepton non-universal dynamics are analysed within an effective field theory framework motivated by the current anomalies in $$b \rightarrow c\tau \nu $$ b → c τ ν and $$b \rightarrow s\mu ^+\mu ^-$$ b → s μ + μ - transitions. In this context, $$R_{\Lambda }^{\tau /\mu }$$ R Λ τ / μ can be enhanced by several orders of magnitude, offering a clear target for upcoming searches. The implications for the related mode $$\Lambda _b \rightarrow pK\tau ^+\tau ^-$$ Λ b → p K τ + τ - are also briefly discussed.

Grand unification Higgs- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msup> <mml:mi>R</mml:mi> <mml:mn>2</mml:mn> </mml:msup> </mml:math> Inflation: Complementarity between proton decay and CMB observables

Abstract We present the first high-twist study of the proton form factors $$F_{1,2}(Q^2)$$ F 1 , 2 ( Q 2 ) in ep elastic scattering based on the perturbative QCD $$k_T$$ k T factorization, $$Q^2$$ Q 2 being momentum transfer squared. It is motivated by unexpectedly large higher-power contributions from subleading-twist light-cone distribution amplitudes (LCDAs), which are attributed to the enhancement in endpoint regions of parton momentum fractions. We highlight that the endpoint enhancement, tamed by the $$k_T$$ k T resummation effect, is crucial for accommodating the approximate scaling behavior of the $$Q^4F_1(Q^2)$$ Q 4 F 1 ( Q 2 ) data at intermediate $$Q^2\sim \mathcal{O}(10)$$ Q 2 ∼ O ( 10 ) GeV $$^2$$ 2 . The proton LCDAs up to twist 6 are then extracted, and verified by the charge-parity asymmetries observed in hadronic heavy baryon decays. Our work provides new insights into the proton three-dimensional structure and manifests the precision requirement for reliable perturbative analyses of baryonic exclusive processes.

We have reinvestigated the dynamics of excited-state proton transfer in [2,2'-bipyridyl]-3,3'-diamine, or BP(NH2)2. Femtosecond fluorescence upconversion spectroscopy for this molecule [Chem. Phys. Lett. 2005, 407, 487] identified two emission bands following photoexcitation, viz., a shorter wavelength band I identified as the emission from the (normal) diamine form and a longer wavelength band II attributed to the doubly proton transferred diimine form. Both bands were found to have low fluorescence quantum yields, and both decayed in about 250 fs. A subsequent computational investigation [ChemPhysChem 2007, 8, 1199] showed that only the formation of singly proton transferred monoimine is energetically feasible and hence would be the origin of band II. It was also suggested that, following the proton transfer, the timescale of the inter-ring twisting in the monoimine formed may correspond to that of the decay of band II. A recent study including excited-state trajectory simulations [New J. Chem. 2020, 44, 8018] showed that only the monoimine is formed and that the timescale of the proton transfer is commensurate with the experimental timescale. Revisiting BP(NH2)2 in the present work, we have used trajectory surface hopping simulations to study the proton transfer dynamics and decay rate of the experimental fluorescence signals. We find that the molecule shows both C2 and Ci types of ground-state minima, while only a Ci form is present on the lowest bright state S1. Initiating dynamics on S1 from both ground-state minima, we also find that only single proton transfer takes place, with our proton transfer times in agreement with both experiments and prior simulation studies. Our key findings are about the dynamics after the proton transfer. The nascent monoimine twists to near perpendicularity in about 200-300 fs and also loses oscillator strength for the S0 → S1 transition en route. These offer a dynamical explanation of the band II decay timescale seen in the experiments and also agree with the aforementioned computational study.

In this work, we investigate the decay and production properties of the strange double-charm pentaquark P c c s + + with strangeness S = − 1 . Building upon our previous work predicting its J P = 1 / 2 − molecular configuration, we employ three-point QCD sum rules to calculate its strong decay widths and estimate its production branching ratio via Ξ b c + baryon decays. The total strong decay width to the Ξ c c K ¯ and Ω c c π final-state channels is determined as 85 ± 19 MeV . Furthermore, using a rescattering mechanism, we analyze the Ξ b c + → D s * − Ξ c c + + → D − P c c s + + process and estimate the production branching ratio to be B r ( Ξ b c + → D − P c c s + + ) = ( 4.3 − 1.5 + 2.0 ) × 10 − 6 . The relatively narrow width and detectable branching ratio suggest the possibility searching for this pentaquark state in the future.

Abstract Liquid argon time projection chambers (LArTPCs) offer millimeter-scale 3D images of particle trajectories, enabling precision studies of neutrino oscillation, detection of supernova and solar neutrinos, searches for exotic dark matter, and proton decay. Current approaches utilize supervised machine learning models, requiring extensive simulations of particle physics and detector response that can introduce bias. Self-supervised learning (SSL), a machine learning approach that learns useful representations of unlabeled data from the data itself, has significantly advanced how large datasets are utilized for representation learning; however, its potential for applications to sensory data in high precision particle physics experiments remains largely unexplored. We introduce the Point-based liquid argon masked autoencoder (PoLAr-MAE), a self-supervised framework that learns physically meaningful representations directly from unlabeled LArTPC images. PoLAr-MAE achieves remarkable data efficiency for a point-level segmentation task, outperforming fully supervised methods in low data regimes. Linear classifiers on model outputs demonstrate robust performance across multiple downstream tasks. Our results position sensor-level SSL as a practical foundation model strategy for LArTPCs.

The Deep Underground Neutrino Experiment (DUNE) is a next-generation neutrino experiment with a rich physics program that includes searches for the hypothetical phenomenon of proton decay. Utilizing liquid-argon time-projection chamber technology, DUNE is expected to achieve world-leading sensitivity in the proton decay channels that involve charged kaons in their final states. The first DUNE demonstrator, ProtoDUNE Single-Phase, was a 0.77 kt detector that operated from 2018 to 2020 at the CERN Neutrino Platform, exposed to a mixed hadron and electron test-beam with momenta ranging from 0.3 to 7 GeV / c . We present a selection of low-energy kaons among the secondary particles produced in hadronic reactions, using data from the 6 and 7 GeV / c beam runs. The selection efficiency is 1% and the sample purity 92%. The initial energies of the selected kaon candidates encompass the expected energy range of kaons originating from proton decay events in DUNE (below ∼ 200 MeV ). In addition, we demonstrate the capability of this detector technology to discriminate between kaons and other particles such as protons and muons, and provide a comprehensive description of their energy loss in liquid argon, which shows good agreement with the simulation. These results pave the way for future proton decay searches at DUNE.

A bstract Motivated by the stringent experimental bounds on proton lifetime and the need for precise low-energy predictions, there has been renewed interest in the renormalization group (RG) evolution of Wilson coefficients for baryon number violating (BNV) operators and their characteristic new-physics scales. In this work, we analyze the RG running of dimension-6 four-fermion operators in the $$ \overline{\textrm{MS}} $$ MS ¯ scheme that mediate nucleon decay channels such as p → e + π 0 , while systematically accounting for the impact of baryon number conserving (BNC) new-physics that can enter the theory at an intermediate scale as higher-dimensional effective field theory operators. These BNC operators mix with BNV ones at 1-loop and alter the RG flow. The running is performed from the electroweak scale up to representative intermediate scales of 10 4 GeV, 10 6 GeV, and 10 9 GeV, corresponding to possible thresholds for new BNC degrees of freedom. Comparing the RG evolved coefficients with current experimental bounds on nucleon decay lifetimes, we find that the inclusion of BNC-BNV mixing, dominated by top quark loops, can significantly lower the effective proton decay scale to ∼ 10 7 GeV, thus mitigating the need of a large desert. A Python package (Available at: https://github.com/rp-winter/Nucleon-Decay-SMEFT ) is provided to facilitate the RG evolution of nucleon-decay Wilson coefficients, allowing for the inclusion of generic BNC effects.

Abstract Proton radioactivity is a rare form of nuclear decay near the proton drip line, where proton-rich nuclei emit a proton to become more stable. The process provides useful information on the nuclear structure and shell effects in exotic regions of the nuclear chart. In this work, we obtain compact and robust empirical models with few parameters for the prediction of logarithmic half-lives of oneproton radioactivity through symbolic regression. A set of 44 experimentally determined one-proton emitters with decay energy (Q), orbital angular momentum (ℓ), and charge number (Z) are used to train an interpretable symbolic regression model (PySR). The model uses evolutionary algorithms to search a vast space of mathematical expressions and identify brief, physically insightful formulas for the logarithmic half-lives of proton decay. Among the expressions generated, the best-performing model achieves a root mean square error (RMSE) of 0.394 and a mean absolute error (MAE) of 0.322, highlighting high predictive accuracy. The model further precisely predicts the logarithmic half-life of recently observed heaviest proton-emitting isotope, 188 At, which was excluded from the training set. The prediction exhibited an absolute error of 0.407 (on the logarithmic scale) compared to the experimental value, demonstrating strong generalization capability. These results confirm that physics-informed symbolic regression is an effective and interpretable tool for modeling proton radioactivity and can be useful to explore the uncharted regions of the nuclear landscape.

A search is presented for the two-body charmed baryonic decays, B[over ¯]_{(s)}^{0}→Λ_{c}^{+}Λ[over ¯]_{c}^{-}, using a data sample collected by the LHCb experiment during 2011-2012 and 2015-2018, corresponding to an integrated luminosity of 9 fb^{-1}. The first observation of the B[over ¯]_{s}^{0}→Λ_{c}^{+}Λ[over ¯]_{c}^{-} decay is reported with 6.2σ significance along with 4.3σ evidence for the B[over ¯]^{0}→Λ_{c}^{+}Λ[over ¯]_{c}^{-} decay. The branching fractions are measured to be B(B[over ¯]^{0}→Λ_{c}^{+}Λ[over ¯]_{c}^{-})=(1.01_{-0.28}^{+0.27}±0.08±0.15)×10^{-5} and B(B[over ¯]_{s}^{0}→Λ_{c}^{+}Λ[over ¯]_{c}^{-})=(5.0±1.3±0.5±0.8)×10^{-5}, where the first uncertainty is statistical, the second systematic, and the third due to external inputs. These results provide novel experimental inputs for the theoretical framework describing two-body baryonic decays of B mesons via W-emission and W-exchange mechanisms.

In the Standard Model, baryon number is an accidental symmetry, whose violation would constitute unambiguous evidence of new physics, with proton decay providing its most prominent experimental signature. At the same time, the peculiar structure of flavor can serve as a guiding principle for exploring possible new-physics effects. In this work, we present a systematic classification of dimension-six baryon-number-violating (BNV) standard model effective field theory (SMEFT) operators across several flavor-symmetry assumptions and analyze the resulting phenomenology. Interestingly, in certain flavor scenarios the nontrivial interplay with tiny neutrino masses leads to proton-decay constraints compatible with BNV scales in the multi-TeV range. Finally, we complement the EFT analysis by identifying one-particle UV completions of the BNV operators, revealing scenarios in which the leading-order EFT description may not fully account for their underlying dynamics.

The first observation of the decay B^{+}→pΛ[over ¯] is presented using proton-proton collision data collected by the LHCb experiment between 2016 and 2018 at a center-of-mass energy of 13TeV, corresponding to an integrated luminosity of 5.4 fb^{-1}. The signal significance exceeds seven standard deviations. Using the B^{+}→K_{S}^{0}π^{+} decay as a normalization channel, the branching fraction is measured and combined with previous LHCb results based on data collected at 7 and 8TeV in 2011 and 2012, yielding B(B^{+}→pΛ[over ¯])=(1.24±0.17±0.05±0.03)×10^{-7}, where the first uncertainty is statistical, the second is systematic, and the third comes from the uncertainty on the branching fraction of the normalization channel. The B^{+}→pΛ[over ¯] weak decay parameter is measured to be α_{B}=0.87_{-0.29}^{+0.26}±0.09, indicating the presence of comparable S-wave and P-wave decay amplitudes.

The presence of a topological susceptibility in the electroweak sector of the Standard Model motivates the existence of a weak axion <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:msub> <a:mi>a</a:mi> <a:mi>W</a:mi> </a:msub> </a:math> , associated with the spontaneous breaking of <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:mi>B</c:mi> <c:mo>+</c:mo> <c:mi>L</c:mi> </c:math> . Its anomalous couplings and tiny mass, generated from electroweak instantons, render <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:msub> <e:mi>a</e:mi> <e:mi>W</e:mi> </e:msub> </e:math> photophobic. We find that the strongest bound on the associated decay constant <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:msub> <g:mi>f</g:mi> <g:mi>W</g:mi> </g:msub> </g:math> stems from a loop-induced coupling to electrons, leading to <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"> <i:msub> <i:mi>f</i:mi> <i:mi>W</i:mi> </i:msub> <i:mo>≳</i:mo> <i:mn>1000</i:mn> <i:mtext> </i:mtext> <i:mtext> </i:mtext> <i:mi>TeV</i:mi> </i:math> from stellar cooling. Spontaneous breaking of the Abelian <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:mi>B</k:mi> <k:mo>+</k:mo> <k:mi>L</k:mi> </k:math> symmetry induces proton decay via higher-dimensional operators controlled by a new physics scale <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"> <m:mi mathvariant="normal">Λ</m:mi> </m:math> . Existing Super-Kamiokande limits on these decay channels constrain the new physics scale to be <p:math xmlns:p="http://www.w3.org/1998/Math/MathML" display="inline"> <p:mi mathvariant="normal">Λ</p:mi> <p:mo>≳</p:mo> <p:msup> <p:mn>10</p:mn> <p:mn>12</p:mn> </p:msup> <p:mtext> </p:mtext> <p:mtext> </p:mtext> <p:mi>GeV</p:mi> </p:math> . The characteristic channel <s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline"> <s:mi>p</s:mi> <s:mo stretchy="false">→</s:mo> <s:msup> <s:mi>e</s:mi> <s:mo>+</s:mo> </s:msup> <s:msub> <s:mi>a</s:mi> <s:mi>W</s:mi> </s:msub> </s:math> and other possible operators mediating interactions with the Standard Model fields yield signals which are not detectable within the allowed parameter space. Future proton decay searches at the next generation of neutrino experiments offer the most promising avenues to test the good qualities of the weak axion paradigm.

We study heavy-hadron semileptonic decays proceeding via b → c transition, such as B → D ( * ) τ ν ¯ τ and Λ b → Λ c τ ν ¯ τ . In the heavy-quark limit, where the heavy-quark symmetry holds, we provide a fundamental framework for heavy-quark sum rules among these decays based on the spin decomposition picture. The relation holds directly for the squared amplitudes without requiring phase-space integration. We then apply this relation to reproduce the sum rule among B → D ( * ) τ ν ¯ τ and Λ b → Λ c τ ν ¯ τ . Furthermore, we derive new sum rules for Ω b → Ω c ( * ) transitions and those involving excited states, such as B → { D 0 * , D 1 * } and B → { D 1 , D 2 * } .

A bstract We discuss the role of heavy scalar fields in mediating neutrinoless double beta decay (0 νββ ) within the SU(5) Grand Unified Theory framework, extended suitably to include neutrino mass. In such a minimal realistic SU(5) setup for fermion masses, the scalar contributions to 0 νββ are extremely suppressed as a consequence of the proton decay bound. We circumvent this problem by imposing a discrete $${\mathcal{Z}}_{3}$$ symmetry. However, the scalar contributions to 0 νββ remain suppressed in this $$\text{SU}(5)\times {\mathcal{Z}}_{3}$$ model due to the neutrino mass constraint. We find that the 0 νββ contribution can be enhanced by extending the scalar sector with an additional 15 -dimensional scalar representation with suitable $${\mathcal{Z}}_{3}$$ charge. Such an extension not only yields realistic fermion mass spectra but also leads to experimentally testable predictions in upcoming ton-scale 0 νββ searches, which can be used as a sensitive probe of the new scalars across a broad range, from LHC-accessible scales up to ∼ 10 10 GeV.

We investigate proton emission from the highly deformed nucleus 131 Eu within the angular-momentum-conserving core-quasiparticle coupling (CQPC) model. The calculations reproduce well the observed energy spectra and decay properties, and demonstrate that the dominant emitting configuration originates from the d 3/2 spherical component of a deformed configuration, consistent with experimental assignments. Complementary calculations for the triaxially deformed nucleus 145 Tm and the weakly deformed nucleus 151 Lu further confirm that the CQPC framework provides a unified and reliable description of proton emission across a wide deformation range. The results highlight the importance of coherent single-particle-collective coupling in shaping proton decay from deformed nuclei beyond the drip line and provide a fresh perspective on the interpretation of decays traditionally assigned to deformed Nilsson orbitals.

Understanding strangeness enhancement in proton-proton (pp) collisions at the LHC is a challenge for hadronization models. Recent observations indicate that a substantial fraction of the detected Ω − baryons may originate from the decay of charm baryons, e.g. from Ω c 0 → Ω − + π + . However, the Ω c 0 production cross section, as well as branching ratios in different Ω c 0 decay channels, are unknown, preventing an exact estimation of the contribution of baryons coming from charm-hadron decays. In this work, the first measurement of the fraction of Ω − baryons originating from heavy hadron decays in pp collisions at √ s = 13.6 TeV, performed by the ALICE collaboration, is presented. This result is enabled by the new ALICE Inner Tracking System, which allows for the tracking of the Ω − baryon prior to its decay. By studying the evolution of the fraction of Ω − coming from heavy hadron decays and by comparing it with the existing models, the role of heavy hadron production as a driver of strangeness enhancement is explored.

Abstract This study explores the realization of nonminimally coupled Higgs inflation in the context of no-scale supergravity, investigates the formation of primordial black holes, and examines the potential for observable proton decay within the framework of the R-symmetric SU (5) model. For inflation, both single and multifield scenarios are investigated. The prediction of the single-field model for the tensor-to-scalar ratio, r , is approximately $$10^{-3}$$ 10 - 3 , and the scalar spectral index falls within Planck’s 1 $$\sigma $$ σ range. The running of the scalar spectral index, $$-{dn_{s}}/{d\ln {k}}$$ - d n s / d ln k , is approximately $$10^{-4}$$ 10 - 4 . A realistic scenario of reheating and non-thermal leptogenesis is employed with reheat temperature $$T_r\sim 10^9$$ T r ∼ 10 9 GeV. In the multifield case, we mainly focus on Primordial Black Holes (PBHs) and Gravitational Waves (GWs). In this inflationary framework, we demonstrate how a suitable choice of parameters can result in an enhanced scalar power spectrum, leading to the production of primordial black holes (PBHs) capable of fully accounting for dark matter. We also show that this scenario leads to Scalar Induced Gravitational Waves (SIGW) which can be detected in current and future GW detectors. We explore different proton decay channels to look for observable predictions for the next-generation proton decay experiments Hyper-K and DUNE consistent with gauge coupling unification and cosmological bounds.