Isospin Assignments Research Articles

Long-range structure of [formula omitted] state

Tcc is a very near-threshold state (below the D⁎+D0 threshold about 273 keV). Its long-distance structure is of the significance. In the molecular scheme, we relate the coupling constants of Tcc with D⁎+D0 and D⁎0D+ to its binding energy and mixing angle of two components with a coupled-channel effective field theory without cutoff-dependence and prior isospin assignment. We investigate the kinetically allowed strong decays Tcc→D0D0π+, Tcc→D+D0π0 and radiative decays Tcc→D+D0γ and show that the decay width of Tcc→D0D0π+ is the largest one, which is just the experimental observation channel. Our results show that the decay width obtained in the first analysis from LHCb collaboration in Breit-Wigner distribution is over-estimated. Our results were supported by the following experimental analysis from LHCb within unitarized Breit-Wigner formalism.

Formula omitted] relevant DD⁎ scattering from Nf = 2 lattice QCD

The S-wave DD⁎ scattering in the isospin I=0,1 channels is studied in Nf=2 lattice QCD at mπ≈350 MeV. It is observed that the DD⁎ interaction is repulsive in the I=1 channel when the DD⁎ energy is near the DD⁎ threshold. In contrast, the DD⁎ interaction in the I=0 channel is definitely attractive in a wide range of the DD⁎ energy. This is consistent with the isospin assignment I=0 for Tcc+(3875). By analyzing the components of the DD⁎ correlation functions, it turns out that the quark diagram responsible for the different properties of I=0,1DD⁎ interactions can be understood as the charged ρ meson exchange effect. This observation provides direct information on the internal dynamics of Tcc+(3875).

Probing the long-range structure of the Tcc+ with the strong and electromagnetic decays

Very recently, the LHCb Collaboration reported the doubly charmed tetraquark state ${T}_{cc}^{+}$ below the ${D}^{*+}{D}^{0}$ threshold about 273 keV. As a very near-threshold state, its long-distance structure is very important. In the molecular scheme, we relate the coupling constants of ${T}_{cc}^{+}$ with ${D}^{*0}{D}^{+}$ and ${D}^{*+}{D}^{0}$ to its binding energy and mixing angle of two components with a coupled-channel effective field theory. With the coupling constants, we investigate the kinetically allowed strong decays ${T}_{cc}^{+}\ensuremath{\rightarrow}{D}^{0}{D}^{0}{\ensuremath{\pi}}^{+}$, ${T}_{cc}^{+}\ensuremath{\rightarrow}{D}^{+}{D}^{0}{\ensuremath{\pi}}^{0}$ and radiative decays ${D}^{+}{D}^{0}\ensuremath{\gamma}$. Our results show that the decay width of ${T}_{cc}^{+}\ensuremath{\rightarrow}{D}^{0}{D}^{0}{\ensuremath{\pi}}^{+}$ is the largest one, which is just the experimental observation channel. Our theoretical total strong and radiative widths are in favor of the ${T}_{cc}^{+}$ as a $|{D}^{*+}{D}^{0}⟩$ dominated bound state. The total strong and radiative width in the single channel limit and isospin singlet limit are given as ${59.7}_{\ensuremath{-}4.4}^{+4.6}\text{ }\text{ }\mathrm{keV}$ and ${46.7}_{\ensuremath{-}2.9}^{+2.7}\text{ }\text{ }\mathrm{keV}$, respectively. Our calculation is cutoff-independent and without prior isospin assignment. The absolute partial widths and ratios of the different decay channels can be used to test the structure of ${T}_{cc}^{+}$ state when the updated experimental results are available.

XJ(2900) states in a hot hadronic medium

In this work we investigate the hadronic effects on the $X_{J=0,1} (2900)$ states in heavy-ion collisions. We make use of Effective Lagrangians to estimate the cross sections and their thermal averages of the processes $X_J \pi \to \bar{D}^{*} K , K^{*} \bar{D} $, as well as those of the corresponding inverse processes, considering also the possibility of different isospin assignments ($I=0,1$). We complete the analysis by solving the rate equation to follow the time evolution of the $X_J (2900)$ multiplicities and determine how they are affected by the considered reactions during the expansion of the hadronic matter. We also perform a comparison of the $X_J (2900)$ abundances considering them as hadronic molecular states ($J=0$ as a $S$-wave and $J=1$ as a $P$-wave) and tetraquark states at kinetic freeze-out.

Role of isospin and its conservation in neutron-rich fission fragments

Following on from our earlier paper Garg and Jain (2017 Phys. Scr. 92 094001) containing some initial results, we present a detailed discussion and complete results in this paper, which provide the first direct evidence for the validity of isospin as a nearly good quantum number in neutron-rich systems. The evidence comes from the reproduction of the general features of the partition-wise relative yields of neutron-rich fission fragments produced in two heavy-ion induced fusion fission reactions, namely 208Pb (18O, f) and 238U (18O, f), by using the concept of isospin conservation. To fix the isospin values and use the isospin algebra, we invoke what we term Kelson’s conjectures. We present a consistent scheme for isospin assignments based on these considerations. Our calculated results confirm that isospin behaves as an approximately good quantum number in neutron-rich systems, in this case, the fission fragments.

Neutron decay of the pygmy and giant resonances in the13C(e,e′n)12Creaction

The cross sections and angular correlations for neutron emission to various states in the residual nucleus, following the ${}^{13}\mathrm{C}{(e,e}^{\ensuremath{'}}n)$ reaction, have been measured over the excitation energy range 8--27 MeV at the effective momentum transfer of 0.35 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$. In the pygmy resonance, neutron emission leads predominantly to the ground and first excited states of ${}^{12}\mathrm{C},$ while in the giant resonance it leads to population of two higher excited states (12.71 MeV, $T=0;$ 15.11 MeV, $T=1).$ This is the first direct observation for neutron population of these states. The isospin assignments of the resonances are made as a result of the observed decays. The branching ratio of the transition to the $T=1$ states compared to the total cross section for neutron emission is found to be $19\ifmmode\pm\else\textpm\fi{}5%,$ which is inconsistent with the theoretical predictions of about 50%. Both isospin splitting and the relative ${T}_{<}$ and ${T}_{>}$ strengths of the giant resonance are obtained for the neutron decay. The angular-correlation parameters for the decay of the giant dipole resonance are very similar for ${}^{13}\mathrm{C}$ and ${}^{12}\mathrm{C},$ which provides some support for a weak coupling model in which the giant resonance for ${}^{13}\mathrm{C}$ proceeds via core excitations in ${}^{12}\mathrm{C}.$

Width of NN resonances near threshold

We use an isobar model and first-order perturbation theory to determine the width of resonances that decay into a pion and two nucleons near the NN threshold. The perturbation is given in this case by the three-body unitarity cuts. As an application we study the case of the resonance observed in pionic double-charge-exchange reactions on nuclei. We consider the possible isospin assignments of this resonance and conclude that the isospin 2 assignment is the correct one.

Spectroscopy of the 29Si(p, gamma ) reaction for Ep=1.75-2.51 MeV.

The $^{29}\mathrm{Si}$(p,\ensuremath{\gamma}) reaction has been studied for 30 resonances in the range ${\mathit{E}}_{\mathit{p}}$=1.75--2.51 MeV. Branching ratios have been measured for 28 of these resonances. The separation energy ${\mathit{S}}_{\mathit{p}}$ for $^{30}\mathrm{P}$ has been determined to be 5594.5\ifmmode\pm\else\textpm\fi{}0.5 keV. Improved spin, parity, and isospin assignments have been made to a number of the resonant states. A new level has been identified in $^{30}\mathrm{P}$ at ${\mathit{E}}_{\mathit{x}}$=6006 keV, and its \ensuremath{\gamma}-ray branching ratios have been measured. \textcopyright{} 1996 The American Physical Society.

A Jπ = 0 − resonance for πNN → πNN in the Skyrme model

The scattering of pions on a dibaryon configuration is analyzed within the SU(2) Skyrme model. It is shown that this model leads to a low-lying ( J p , I) = (0 −, 2) resonance. The possibility that this resonance corresponds to one proposed recently in the context of double charge exchange pion scattering on nuclei is discussed. Given the setup used in those experiments we also show that a resonance with isospin assignment I = 0 cannot be excited according to the description presented here.

Isospin splitting in analog giant resonances excited by single pion charge exchange reactions

Giant isovector analog E1 resonances have been observed by means of the pion single-charge-exchange reactions ( π ±, π 0). The giant T = 1 analog E1 resonances in 12B and 12N, built on the ground state of 12C, were observed in the 12C( π ±, π 0) reactions. The giant T = 3 2 resonances in 13B and 9Li, built on the ground states of 13C and 9Be, were studied with the 13C, 9Be( π −, π 0) reactions, respectively. Analogs of these resonances were found in the 13C, 9Be( π +, π 0) reactions along with lower lying T = 1 2 resonances. These resonances together with the higher T = 3 2 resonances constitute isospin-splitting in the nuclei, 13N and 9B. These isospin assignments were made by comparing results from the ( π ±, π 0) reactions and their measured angular distributions. The assignments were confirmed by determining the decay properties of the resonances with coincident ( π 0p) measurements in the ( π +, π 0p) reactions. The proton angular distributions measured relative to the momentum transfer direction were consistent with a dipole process.

Identification of 4(-) states in the 14C(p,n)14N reaction at 135 MeV.

Neutron time-of-flight spectra were measured for the $^{14}\mathrm{C}$(p,n${)}^{14}$N reaction at 135 MeV with the beam-swinger system at the Indiana University Cyclotron Facility. Excitation-energy spectra and differential cross sections for the observed excitations in this reaction were extracted over the momentum transfer range from 0 to 2.5 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$. The goal of this work is to identify the ${4}^{\mathrm{\ensuremath{-}}}$ states in $^{14}\mathrm{N}$ and to determine the isovector transition strengths. The identification of the ${4}^{\mathrm{\ensuremath{-}}}$ states is based on comparisons of the theoretical differential cross sections, performed in a DWIA formalism, with the experimental cross sections and with information from the $^{14}\mathrm{C}$(e,e') reaction. Isospin assignments are based primarily on comparisons of the measured (p,n) and (e,e') isovector strengths. Candidate ${4}^{\mathrm{\ensuremath{-}}}$ states are identified at excitation energies of 8.49 MeV (T=0), 13.76 MeV and 19.49 MeV (T=1), and 26.61 MeV (T=2) in the $^{14}\mathrm{C}$(p,n${)}^{14}$N reaction, and the isovector strengths for the transitions leading to these states re extracted. The observed excitation energies and isovector strengths are in good agreement with the analog T=1 and T=2 ${4}^{\mathrm{\ensuremath{-}}}$ states observed in the (e,e') reaction. The experimental results are compared with results from shell-model calculations.

Spectroscopic study of oxygen and fluorine isotopes with the ( alpha,3He) and ( alpha,t) reactions on 16,17,18O.

The (\ensuremath{\alpha}${,}^{3}$He) and (\ensuremath{\alpha},t) reactions on $^{16,17,18}\mathrm{O}$ were studied at ${\mathit{E}}_{\mathrm{\ensuremath{\alpha}}}$=65 MeV. Measured cross sections for the states up to 15 MeV in the residual nuclei were analyzed with the distorted wave Born approximation theory. Many spin-parity and isospin assignments were proposed based on the strengths, angular distributions, and excitation energies. Nearly equal spectroscopic factors were obtained for bound and unbound analog pairs except for the ${2}_{1}^{+}$, T=1 states in $^{18}\mathrm{O}$ and $^{18}\mathrm{F}$. Almost full strengths were observed for the 0${\mathit{d}}_{5/2}$, 1${\mathit{s}}_{1/2}$, and 0${\mathit{d}}_{3/2}$ transfers. The obtained spectroscopic factors for the 0${\mathit{d}}_{5/2}$ and 1${\mathit{s}}_{1/2}$ transfers were in good agreement with shell-model calculations, while the agreement was unsatisfactory for the 0${\mathit{d}}_{3/2}$ transfer in many respects. The ${\mathit{d}}_{3/2}$ strengths in $^{17}\mathrm{O}$ and $^{17}\mathrm{F}$ were more fragmented than the shell-model prediction, while only half of the expected 0${\mathit{d}}_{3/2}$ strength was found in $^{18}\mathrm{O}$ and $^{19}\mathrm{O}$. The strength to the first excited 3/${2}^{+}$, T=1/2 state in $^{19}\mathrm{F}$ was twice that predicted. Spectroscopic factors for many 0${\mathit{f}}_{7/2}$ transitions were also deduced. The 14.1 and 14.3 MeV states in $^{18}\mathrm{O}$, in particular, proposed to be the stretched ${6}^{\mathrm{\ensuremath{-}}}$ states in a recent (e,e') experiment, were found to be excited by pure l=3 transfer with spectroscopic factors 0.16 and 0.05, respectively.

Energy levels of A = 21–44 nuclei (VII)

The experimentally determined properties of A = 21–44 nuclides are complied and evaluated with special emphasis on nuclear spectroscopy. Separate tables for each of the nuclides reviewed present the available information about the following properties (in this order): • - excitation energies E x, • - γ-ray branching ratios b( γ), • - γ-ray mixing ratios σ, • - lifetimes γ m or widths Λ, • - neutron, proton, or α-particle resonances, • - partial widths, • - single-nucleon transfer reactions, • - beta-decay, • - arguments for spin and parity ( J π ) and isospin ( T) assignments. For each nuclide a master table summarizing the “best” or adopted values for E x, J π ; T and τ m or Λ precedes the auxiliary tables listed above. The review of each A-chain concludes with a discussion of isospin multiplets. Figures are presented of the level schemes of all nuclei and, for each A-chain, an overview of the relative energies of the ground states and lowest analogue states of all nuclei in the chain.

Isospin in 17O( gamma,n0) reactions.

This Brief Report presents a reanalysis of the energy scale of published measurements by Johnson {ital et} {ital al}. and Jury {ital et} {ital al}. of the {sup 17}O({gamma},{ital n}{sub 0}) cross section which brings the two sets into good agreement. This leads directly to new ({ital T}{sub {lt}}) isospin assignments for levels previously reported by Ajzenberg-Selove at energies of 14.4, 15.2, and 15.6 MeV.

30Si(3He,d)31P reaction at 25 MeV.

The $^{30}\mathrm{Si}$${(}^{3}$He,d${)}^{31}$P reaction has been investigated at 25 MeV incident energy. About 80 levels were observed up to an excitation energy of 10 MeV by using a split-pole magnetic spectrograph. Most of the proton-unbound states were identified with resonance levels observed in proton capture reactions on $^{30}\mathrm{Si}$. Four levels were observed for the first time in a reaction which couples a proton to a $^{30}\mathrm{Si}$ core. Spectroscopic information has been obtained for about 60 levels through angular distribution measurements and distorted wave Born approximation analyses, with special treatment applied in the cases of the proton-unbound states. The spectroscopic factors of the proton-unbound states are in overall agreement with the spectroscopic factors which are deduced from the proton partial widths measured in resonant proton scattering experiments, but the proton partial width which is obtained in this work for the 7897 keV level is in disagreement with previous values from \ensuremath{\gamma}-ray resonant absorption measurements. The strengths of the l=0, 2, and 3 transfers are essentially concentrated into one level, each of isospin T=1/2 and T=3/2. In contrast the l=1,T=1/2, strength is distributed over many levels, especially in a cluster of six levels between 9.0 and 9.8 MeV. The sum rule for the 2${\mathit{p}}_{3/2}$,T=1/2, proton single-particle strength is exhausted, leading to a centroid energy of about 7.9 MeV for this configuration. Isospin assignments are discussed for some levels. The excitation energies and spectroscopic factors for even-parity states are compared with the results of a recent, complete sd-shell space, shell-model calculation.

Hole-strength distributions from the 34S(, 3He)33P and 34S(, t)33S reactions

Abstract A vector-polarized deuteron beam of 52 MeV was used to excite proton and neutron hole states via the 34S( d , 3He)33P and the 34S( d , t)33S reactions. From the measured angular distributions of differential cross sections σ(θ) and analyzing powers T11(θ) we determined the spins of 9 states in 33P and of 13 states in 33S. The comparison of proton and neutron pick-up spectra yields isospin assignments for 33S states (T = 1 2 , 3 2 ). Spectroscopic factors deduced from a DWBA analysis were used to determine the lowest moments of the strengths distributions in 33P and 33S. Combined with proton and neutron stripping data we calculate ground state occupancies and single-particle energies for 34S and determine the Fermi surfaces for protons and neutrons. This information allows the application of a recently published sum rule to predict Gamow-Teller strengths S+ and S−. Combined with previous data the extracted single-particle energies exhibit systematic features which we parametrise as linear functions of mass number A and isospin To for target nuclei with 28 ⩽ A ⩽ 52. The parameters are closely related to effective particle-hole interactions.

Continuum shell model calculations and the resonances below the GDR in12C

The excitation functions in the11B(p, n0),11B(p, p1) and11B(p, γ) reaction channels predicted by a continuum shell model calculation are compared to facilitate isospin assignments forJ− resonances in the (19÷22) MeV region of excitation in12C. Model predictions are also tested against differential cross-section data in the particle channels. It is shown that definitive spin, isospin and parity assignments can be made for several dominant resonances reported in the literature. Comparison with recent (e, e′) data analysis not only confirms our model predictions but also demonstrates that level energies are well reproduced within the multiconfiguration shell model only if continuum effects are included.

Weak isospin spectroscopy of excited quarks and leptons

We investigate new excited states of quarks and leptons in the light of weak isospin invariance. We find to first order that while quark states with isospin assignment I W = 0, 1 2 are dominantly decaying strongly, I W = 1, 3 2 quark s can only decay electroweakly. Decay of higher isospin assignments are permitted only in higher orders. Experimental signatures are considered. Production cross section and decay branching ratios are given. It is also found that I W ⩾ 1 quarks, will give rise to “exotic” hadrons, namely mesons of charges ±2 e and baryons with charge 3 e.

Anomalous Z decays: excited leptons?

We study the possibility that the recently observed ℓ +ℓ − γ decays of the Z are due to the existence of an excited electron (muon) with approximately 75 GeV (60 GeV) mass. We point out that in a composite picture of leptons such states should fall in vectorlike SU(2) ⊗ U(1) multiplets, with weak isospin I ⩽ 3/2, and be coupled with a magnetic moment type transition to the light leptons. We study the relative rates of the Z→ ℓ +ℓ − γ or νν¯γ and W + → ℓ +νγ, ℓ +νγ, ℓ +ℓ −(ff¯) +, νν¯(ff¯) + channels, as means of determining the weak isospin assignment of the excited leptons. All present information is seen to be compatible with the existence of the required excited leptons, including the absence of observed anomalies in the e +e − → γγ cross sections and in the muon ( g − 2). For spin 1/2, the distribution of the invariant mass for the direct lepton photon pair in ℓ +ℓ − γ events is expected to be flat, leaving unexplained why, in the observed three events, this mass is found to be less than about 10 GeV.

Spin-flip strength in the 20-28 MeV region of excitation inC12and the extended coupled-channels model predictions

The spin-flip strength distribution in the 20 to 28 MeV excitation in $^{12}\mathrm{C}$ deduced from a recent study of the $^{12}\mathrm{C}({\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}, {{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}}^{\ensuremath{'}})$ reaction is discussed in the context of an earlier coupled-channel analysis of the $^{11}\mathrm{B}(\mathrm{p}, {\ensuremath{\gamma}}_{1})$ reaction data. It is shown that a good correspondence can be established between certain broad resonances observed in the two types of reactions not only with regard to the energy but also the width. Definitive spin, isospin, and parity assignments can be made on the basis of this comparison.