Radiative Decay Modes Research Articles

Hadronization and decay of excited heavy hadrons in Herwig 7

We revisit the hadronization and decay of excited heavy mesons and heavy baryons in Herwig 7 general-purpose event-generator, following four distinct steps: (i) Passing through the polarisation of heavy hadrons at the end of parton shower through the application of heavy quark effective theory (HQET), where the emergence of a spin-flavour symmetry allows for the determination of the polarisations of the excited heavy mesons and heavy baryons from the helicity states of the light and heavy quarks. (ii) Improving the strong and radiative decay modes of the excited heavy mesons, where in the absence of conclusive experimental data on many of the decays, one needs to rely on HQET symmetries to determine the favoured decay modes, widths and branching ratios. (iii) Re-examination of the production rates of heavy hadrons using all available experimental data sources and (iv) performing a general tune for Herwig’s free parameters to reflect the implemented changes. We compare our predictions against existing experimental data in the presence/absence of the newly implemented updates. These improvements will be available with Herwig-7.3.0 public release.

Dark Matter searches with photons at the LHC

We unveil blind spot regions in dark matter (DM) direct detection (DMDD), for weakly interacting massive particles with a mass around a few hundred GeV that may reveal interesting photon signals at the LHC. We explore a scenario where the DM primarily originates from the singlet sector within the Z3-symmetric Next-to-Minimal Supersymmetric Standard Model (NMSSM). A novel DMDD spin-independent blind spot condition is revealed for singlino-dominated DM, in cases where the mass parameters of the higgsino and the singlino-dominated lightest supersymmetric particle (LSP) exhibit opposite relative signs (i.e., κ < 0), emphasizing the role of nearby bino and higgsino-like states in tempering the singlino-dominated LSP. Additionally, proximate bino and/or higgsino states can act as co-annihilation partner(s) for singlino-dominated DM, ensuring agreement with the observed relic abundance of DM. Remarkably, in scenarios involving singlino-higgsino co-annihilation, higgsino-like neutralinos can distinctly favor radiative decay modes into the singlino-dominated LSP and a photon, as opposed to decays into leptons/hadrons. In exploring this region of parameter space within the singlino-higgsino compressed scenario, we study the signal associated with at least one relatively soft photon alongside a lepton, accompanied by substantial missing transverse energy (ɆT) and a hard initial state radiation jet at the LHC. In the context of singlino-bino co-annihilation, the bino state, as the next-to-LSP, exhibits significant radiative decay into a soft photon and the LSP, enabling the possible exploration at the LHC through the triggering of this soft photon alongside large ɆT and relatively hard leptons/jets resulting from the decay of heavier higgsino-like states.

Microsphere Photonic Superlens for a Highly Emissive Flexible Upconversion-Nanoparticle-Embedded Film

Increasing upconversion luminescence (UCL) to overcome the intrinsically low conversion efficiency of upconversion nanoparticles (UCNPs) poses a fundamental challenge. Photonic nanostructures are the efficient approaches for UCL enhancement by tailoring the local electromagnetic fields. Unfortunately, such nanostructures are sensitive to environmental conditions, and the regulation strength is varied in flexible applications. Here, we report giant UCL enhancement from a flexible UCNP-embedded film coupled with a microsphere photonic superlens (MPS), by which the enhancement ratio of UCL is over 104-fold under 808 nm excitation down to 0.72 mW. The enhancement pathways of MPS-enhanced UCL are attributed to Mie-resonant nanofocusing for high excitation-photon density, optical whispering-gallery modes (WGMs) for fast radiative decay, and the directional antenna effect for far-field emission confinement. The contribution of optical resonance in the MPS to suppressing the phonon-induced nonradiative transition and thermal quenching is experimentally validated. The UCL quantum yield is therefore improved by 3-fold to 4.20% under 120 mW/cm2 near-infrared excitation, consistent with the enhancement ratio via the Purcell effect of WGMs. Furthermore, the MPS demonstrates the robust optical regulation capability toward flexible applications, opening up new opportunities for facilitating multiphoton upconversion in wearable optoelectrical devices for nanoimaging, biosensing, and energy conversion in the future.

Mass biases in exclusive radiative hadronic decays of W bosons at the LHC

The search for exclusive hadronic vector boson decays is an ongoing part of the LHC programme where, to date, no such decays have been observed. In addition to the intrinsic interest in the branching ratios, there is potential for a measurement of the W boson mass quite distinct from the usual methods. The radiative decay modes offer good potential channels for this search; however, we highlight three issues with it not previously discussed: particle misidentification, partial reconstruction and the impact of interference with QCD. These issues cause shifts in the peak position of tens or hundreds of MeV/c2.

Angular Dependence of Electronic Excitation Energy Transfer Efficiency Between Dye Molecules in a Photonic Crystal

Spectral and luminescent characteristics of a mixture of coumarin 7 and rhodamine B dyes infiltrated into a onedimensional photonic crystal of mesoporous silicon are studied. Electronic excitation energy transfer between molecules that is associated with fluorescence quenching of the donor (coumarin 7) and enhancement of acceptor emission (rhodamine B) is detected. The angular dependence of excitation energy transfer efficiency in the donor–acceptor pair is due to depletion of available photon modes for donor radiative decay in a photonic crystal as compared with a homogeneous medium and depends on the spectral position of the photonic stop zone of a photonic crystal.

The radiative decay with vector meson dominance**J. M. Dias would like to thank the Brazilian funding agency FAPESP for the financial support (2016/22561-2), V. R. Debastiani wishes to acknowledge the support from the Programa Santiago Grisolia of Generalitat Valenciana (Exp. GRISOLIA/2015/005). This work is also partly supported by the Spanish Ministerio de Economia y Competitividad and European FEDER funds (FIS2014-57026-

Motivated by the experimental measurements of D0 radiative decay modes, we have proposed a model to study the decay, by establishing a link with (V=ρ0, ω) decays through the vector meson dominance hypothesis. In order to do this properly, we have used the Lagrangians from the local hidden gauge symmetry approach to account for Vγ conversion. As a result, we have found the branching ratio , which is in fair agreement with the experimental values reported by the Belle and BaBar collaborations.

Strong and radiative decays of the low-lying S - and P -wave singly heavy baryons

The strong and radiative decays of the low-lying $S$- and $P$-wave $\Lambda_{c(b)}$, $\Sigma_{c(b)}$, $\Xi_{c(b)}$, $\Xi_{c(b)}'$ and $\Omega_{c(b)}$ baryons are systematically studied in a constituent quark model. We find that the radiative decay mode $\Lambda_b^0\gamma$ could be very useful for us to establish the missing neutral states $\Sigma_b^{0}$ and $\Sigma_b^{*0}$. Our calculation shows that most of those missing $\lambda$-mode $P$-wave singly heavy baryons have relatively narrow decay width of less than 30 MeV. Their dominant strong and radiative decay channels can be ideal for searching for their signals in future experiment. Configuration mixings between the $J^P=1/2^-$ states $|^2P_{\lambda} \frac{1}{2}^- \rangle$ and $|^4P_{\lambda} \frac{1}{2}^- \rangle$ of the $\mathbf{6}_F$ multiplet are discussed. The $\Xi_c(2930)^0$ state seems to favor the mixed state $|\Xi_c'~ P_{\lambda}\frac{1}{2}^-\rangle_2$ with $J^P=1/2^-$. The $\Sigma_c(2800)$ resonance may be assigned to $|\Sigma_c~ ^2P_{\lambda} \frac{3}{2}^- \rangle$ with $J^P=3/2^-$ or $|\Sigma_c~ ^4P_{\lambda} \frac{5}{2}^- \rangle$ with $J^P=5/2^-$. In general, the excitations of $|^2P_{\lambda} \frac{3}{2}^- \rangle$ and $|^4P_{\lambda} \frac{5}{2}^- \rangle$ of the $\mathbf{6}_F$ multiplet have similar strong decay properties. In order to to identify them, angular distributions of their decays in either strong decay modes or radiative transitions should be needed.

Constraints on new physics from radiative B decays

A new phase for the measurements of radiative decay modes in b → s transitions has started with new measurements of exclusive modes by LHCb and with Belle-II showing distinctive promises in both inclusive and exclusive channels. After critically reviewing the hadronic uncertainties in exclusive radiative decays, we analyze the impact of recent measurements of the branching ratio and mass-eigenstate rate asymmetry in Bs → ϕγ and of the angular distribution of B → K∗e+e− at low q2 on new physics in the b→sγ transition.

Cyclometalated Iridium(III) Complexes Containing 4,4'-π-Conjugated 2,2'-Bipyridine Derivatives as the Ancillary Ligands: Synthesis, Photophysics, and Computational Studies.

This article demonstrates a series of cyclometalated Ir(III) complexes of the type [Ir(III)(C^N)2(N^N)](PF6), where C^N is 2-phenylpyridine, and N^N corresponds to the 4,4'-π-conjugated 2,2'-bipyridine ancillary ligands. All these compounds were synthesized through splitting of the binuclear dichloro-bridged complex precursor, [Ir(C^N)2(μ-Cl)]2, with the appropriate bipyridine ligands followed by the anion exchange reaction. The linear and nonlinear absorption properties of the synthesized complexes were investigated. The absorption spectra of all the title complexes exhibit a broad structureless feature in the spectral region of 350-700 nm with two bands being well-resolved in most of the cases. The structures of all the compounds were modeled in dichloromethane using the density functional theory (DFT) algorithm. The nature of electronic transitions was further comprehended on the basis of time-dependent DFT analysis, which indicates that the origins of various bands are primarily due to intraligand charge transfer transitions along with mixed-metal and ligand-centered transitions. The synthesized compounds are found to be nonemissive at room temperature because of probable nonradiative deactivation pathways of the T1 state that compete with the radiative (phosphorescence) decay modes. However, the frozen solutions of compounds Ir(MS 3) and Ir(MS 5) phosphoresce at the near-IR region, the other complexes remaining nonemissive up to 800 nm wavelength window. The two-photon absorption studies on the synthesized complexes reveal that values of the absorption cross-section are quite notable and lie in the range of 300-1000 GM in the picosecond case and 45-186 GM in the femtosecond case.

Production of quarkonium states at the ATLAS experiment

An overview is given of recent measurements of the production of various heavy quarkonium states in pp collisions at = 7 TeV, using the ATLAS detector at the LHC. These include the production cross sections of the C-even states χc1 and χc2 in their radiative decay modes into J/ψγ, and of the radially excited vector state ψ(2S) in its decay mode into J/ψπ+π−. Differential spectra in transverse momentum are measured separately for promptly produced charmonium states, originating from QCD sources, and for non-prompt states from the decays of B-hadrons. Results are compared to other existing measurements and various theoretical models.

Nonproportionality in the scintillation light yield of bismuth germanate

We present measurements of nonproportionality in the scintillation light yield of bismuth germanate (BGO) for gamma-rays with energies between 6keV and 662keV. The scintillation light was read out by avalanche photodiodes (APDs) with both the BGO crystals and APDs operated at a temperature of ≈90K. Data were obtained using radioisotope sources to illuminate both a single BGO crystal in a small test cryostat and a 12-element detector in a neutron radiative beta-decay experiment. In addition one datum was obtained in a 4.6T magnetic field based on the bismuth K x-ray escape peak produced by a continuum of background gamma rays in this apparatus. These measurements and comparison to prior results were motivated by an experiment to study the radiative decay mode of the free neutron. The combination of data taken under different conditions yields a reasonably consistent picture for BGO nonproportionality that should be useful for researchers employing BGO detectors at low gamma ray energies.

End of the cosmic neutrino energy spectrum

There may be a high-energy cutoff of neutrino events in IceCube data. In particular, IceCube does not observe either continuum events above 2 PeV, or the Standard Model Glashow-resonance events expected at 6.3 PeV. There are also no higher energy neutrino signatures in the ANITA and Auger experiments. This absence of high-energy neutrino events motivates a fundamental restriction on neutrino energies above a few PeV. We postulate a simple scenario to terminate the neutrino spectrum that is Lorentz-invariance violating, but with a limiting neutrino velocity that is always smaller than the speed of light. If the limiting velocity of the neutrino applies also to its associated charged lepton, then a significant consequence is that the two-body decay modes of the charged pion are forbidden above two times the maximum neutrino energy, while the radiative decay modes are suppressed at higher energies. Such stabilized pions may serve as cosmic ray primaries.

Hunting for the Xb via radiative decays

In this paper, we study radiative decays of Xb, the counterpart of the famous X(3872) in the bottomonium-sector as a candidate for meson–meson molecule, into the γϒ(nS) (n=1,2,3). Since it is likely that the Xb is below the BB¯⁎ threshold and the mass difference between the neutral and charged bottom meson is small compared to the binding energy of the Xb, the isospin violating decay mode Xb→ϒ(nS)π+π− would be greatly suppressed. This will promote the importance of the radiative decays. We use the effective Lagrangian based on the heavy quark symmetry to explore the rescattering mechanism and calculate the partial widths. Our results show that the partial widths into γϒ(nS) are about 1 keV, and thus the branching fractions may be sizeable, considering the fact the total width may also be smaller than a few MeV like the X(3872). These radiative decay modes are of great importance in the experimental search for the Xb particularly at hadron collider. An observation of the Xb will provide a deeper insight into the exotic hadron spectroscopy and is helpful to unravel the nature of the states connected by the heavy quark symmetry.

Threshold enhancement phenomena in Y(4260) decays

We investigate several strong and radiative decay modes of Y(4260), by assuming that Y(4260) either is a [Formula: see text] molecular state, or has sizeable couplings with [Formula: see text] and [Formula: see text]. In such ansatzes, obvious threshold enhancements or narrow cusp structures appear quite naturally without introducing a genuine resonance. And we emphasize that the radiative decay modes may be useful for studying [Formula: see text]S-wave scattering.

Exploring the threshold behavior and implications on the nature ofY(4260)andZc(3900)

By assuming that $Y(4260)$ either is a ${D}_{1}\overline{D}$ molecular state or has sizeable couplings with ${D}_{0}{\overline{D}}^{*}$ and ${D}_{1}^{\ensuremath{'}}\overline{D}$, we investigate several decay modes of $Y(4260)$. Under the special kinematic configurations, triangle singularity may occur in the rescattering amplitude, which will significantly change the threshold behavior. Obvious threshold enhancements or narrow cusp structures appear quite naturally without introducing a genuine resonance. We emphasize that the radiative decay modes may be useful for studying ${D}^{(*)}\overline{D}$ $S$-wave scattering.

Predictions of selected flavor observables within the standard model

This paper gathers a selection of standard model predictions issued from the metrology of the Cabibbo-Kobayashi-Maskawa parameters performed by the CKMfitter group. The selection includes purely leptonic decays of neutral and charged $B$, $D$, and $K$ mesons. In the light of the expected measurements from the LHCb experiment, special attention is given to the radiative decay modes of $B$ mesons as well as to the $B$-meson mixing observables, in particular the semileptonic charge asymmetries ${a}_{\mathrm{SL}}^{d,s}$ which have been recently investigated by the D0 experiment at Tevatron. Constraints arising from rare kaon decays are addressed, in light of both current results and expected performances of future rare kaon experiments. All results have been obtained with the CKMfitter analysis package, featuring the frequentist statistical approach and using Rfit to handle theoretical uncertainties.

QCD sum rules for the production of the [formula omitted] as a mixed molecule-charmonium state in B meson decay

We use QCD sum rules to calculate the branching ratio for the production of the meson X(3872) in the decay B→X(3872)K, assumed to be a mixture between charmonium and exotic molecular [cq¯][qc¯] states with JPC=1++. We find that in a small range for the values of the mixing angle, 5°⩽θ⩽13°, we get the branching ratio B(B→XK)=(1.00±0.68)×10−5, which is in agreement with the experimental upper limit. This result is compatible with the analysis of the mass and decay width of the mode J/ψ(nπ) and the radiative decay mode J/ψγ performed in the same approach.

Measurement of ω mesons via radiative decay mode in $\surd s$ = 200 GeV Au+Au collisions at RHIC-PHENIX

We report on ω mesons’ production via radiative decay mode (ω → π0γ, π0 → 2γ) in \(\sqrt s \) = 200 GeV Au+Au collisions at RHIC-PHENIX. The main difficulty of this analysis is the huge combinatorial background inevitable for reconstructing particles from the three- body decay mode. The emphasis is on the feasibility study using both simulation and real data to search the best parameters that improve \(S/\sqrt B \). For this purpose, we examine several sets of energy and momentum cuts for selecting π0 and γ. To evaluate the remaining background, we consider three background sources; correlated/uncorrelated background and Ks0 contribution, then we subtract them. The amount of these contributions is determined by a fit on a mass spectrum. The result suggests that ω meson production is suppressed in central Au+Au collisions at high pT region.

Exclusive rare decayb→sγof heavybbaryons

We present an analysis on the exclusive rare radiative decay modes Sigma_b->Sigma gamma and Xi_b->Xi gamma. The transition form factors which parameterize these processes are calculated using QCD light-cone sum rules. The decay widths we predict are Gamma(Sigma_b->Sigma gamma)=(7.21\pm0.04)\times10^{-18}GeV} and Gamma(Xi_b->Xi gamma)=(1.34\pm0.07)\times10^{-16}GeV. The Branching ratio of Xi_b->Xi gamma is predicted to be Br(\Xi_b->Xi gamma)=(3.03\pm0.10)\times10^{-4}.

Study of the f2(1270) , f2′(1525) , f0(1370) and f0(1710) in the J/ψ radiative decays

In this paper we present an approach to study the radiative decay modes of the $J/\psi$ into a photon and one of the tensor mesons $f_2(1270)$, $f'_2(1525)$, as well as the scalar ones $f_0(1370)$ and $f_0(1710)$. Especially we compare predictions that emerge from a scheme where the states appear dynamically in the solution of vector meson--vector meson scattering amplitudes to those from a (admittedly naive) quark model. We provide evidence that it might be possible to distinguish amongst the two scenarios, once improved data are available.