Search results for "Isospin"
showing 10 items of 264 documents
B* production in Z decays
1995
The decay B*→Bγ has been observed with the DELPHI detector at LEP, where the B* meson is produced in Z boson decays. The combination of inclusively reconstructed B mesons with well-measured converted photons yields a measurement of the flavour-averaged B*-B mass difference of 45.5±0.3 (stat.) ±0.8 (syst.) MeV/c2. 95% confidence level upper limits at 6 MeV/c2 are placed on both the isospin (i.e. B+-B0) and the Bs-Bud splitting of the mass difference. The production ratio of B* to B mesons in Z decays is measured to be 0.72±0.03 (stat.) ±0.06 (syst.). Limits on the production cross-section of other hypothetical excited B hadron states decaying radiatively are established. The differential B* …
Isospin breaking in the nucleon mass and the sensitivity of β decays to new physics.
2013
We discuss the consequences of the approximate conservation of the vector and axial currents for the hadronic matrix elements appearing in beta decay if non-standard interactions are present. In particular the isovector (pseudo)scalar charge g_S(P) of the nucleon can be related to the difference (sum) of the nucleon masses in the absence of electromagnetic effects. Using recent determinations of these quantities from phenomenological and lattice QCD studies we obtain the accurate values g_S=1.02(11) and g_P=349(9) in the MS-bar scheme at mu=2 GeV. The consequences for searches of non-standard scalar interactions in nuclear beta decays are studied, finding epsilon_S=0.0012(24) at 90%CL, whic…
Lattice QCD study of the $H$ dibaryon using hexaquark and two-baryon interpolators
2019
Physical review / D 99(7), 074505 (2019). doi:10.1103/PhysRevD.99.074505
Observation ofe+e−→γX(3872)at BESIII
2014
Using data collected with the BESIII detector operating at the Beijing Electron Positron Collider at center-of-mass energies of root s = 4.23, 4.26, and 4.36 GeV, we observe e(+)e(-) -> pi(0)pi(0)h(c) for the first time. The Born cross sections are measured and found to be about half of those of e(+)e(-) -> pi(+)pi(-)h(c) within less than 2 sigma. In the pi(0)h(c) mass spectrum, a structure at 4.02 GeV/c(2) is found. It is most likely to be the neutral isospin partner of the Z(c)(4020)(+/-) observed in the process of e(+)e(-) -> pi(+)pi(-)h(c) being found. A fit to the pi(0)h(c) invariant mass spectrum, with the width of the Z(c)(4020)(0) fixed to that of its charged isospin partner and pos…
The $T_{z} = \pm 1 \to 0$ and $\pm 2 \to \pm 1$ Mirror Gamow--Teller Transitions in $pf$-shell Nuclei
2016
Gamow–Teller (GT) transitions are the most common weak-interaction processes in the Universe. They play important roles in various processes of nucleosynthesis, for example, in the rapid proton-capture process (rp-process). In the pf-shell region, the rp-process runs through neutron-deficient nuclei with Tz = −2, −1, and 0 mainly by means of GT and Fermi transitions, where Tz is the z component of isospin T defined by Tz = (N − Z)∕2. Under the assumption of isospin symmetry, mirror nuclei with reversed Z and N numbers, and thus with opposite signs of Tz, have the same structure. Therefore, symmetry is also expected for the GT transitions starting from and ending up in mirror nuclei. We have…
Anomalous enhancement of the isospin-violating Λ(1405) production by a triangle singularity in Λc→π+π0π0Σ0
2018
The decay of ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}$ into ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{0}\mathrm{\ensuremath{\Lambda}}(1405)$ with the $\mathrm{\ensuremath{\Lambda}}(1405)$ decay into ${\ensuremath{\pi}}^{0}{\mathrm{\ensuremath{\Sigma}}}^{0}$ through a triangle diagram is studied. This process is initiated by ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\overline{K}}^{*}N$, and then the ${\overline{K}}^{*}$ decays into $\overline{K}\ensuremath{\pi}$ and $\overline{K}N$ produce the $\mathrm{\ensuremath{\Lambda}}(1405)$ through a triangle loop containing ${\overline{K}}^{*}N\overline{K}$ which develops a singularity around 1890 MeV. Th…
P -wave nucleon-pion scattering amplitude in the Δ(1232) channel from lattice QCD
2021
We determine the $\mathrm{\ensuremath{\Delta}}(1232)$ resonance parameters using lattice QCD and the L\"uscher method. The resonance occurs in elastic pion-nucleon scattering with ${J}^{P}=3/{2}^{+}$ in the isospin $I=3/2$, $P$-wave channel. Our calculation is performed with ${N}_{f}=2+1$ flavors of clover fermions on a lattice with $L\ensuremath{\approx}2.8\text{ }\text{ }\mathrm{fm}$. The pion and nucleon masses are ${m}_{\ensuremath{\pi}}=255.4(1.6)\text{ }\text{ }\mathrm{MeV}$ and ${m}_{N}=1073(5)\text{ }\text{ }\mathrm{MeV}$, respectively, and the strong decay channel $\mathrm{\ensuremath{\Delta}}\ensuremath{\rightarrow}\ensuremath{\pi}N$ is found to be above the threshold. To thorough…
Isospin symmetry in B(E2) values: Coulomb excitation study of Mg21
2019
The Tz=−32 nucleus 21Mg has been studied by Coulomb excitation on 196Pt and 110Pd targets. A 205.6(1)-keV γ-ray transition resulting from the Coulomb excitation of the 52+ ground state to the first excited 12+ state in 21Mg was observed for the first time. Coulomb excitation cross-section measurements with both targets and a measurement of the half-life of the 12+ state yield an adopted value of B(E2;52+→12+)=13.3(4) W.u. A new excited state at 1672(1) keV with tentative 92+ assignment was also identified in 21Mg. This work demonstrates a large difference in the B(E2;52+→12+) value between T=32, A=21 mirror nuclei. The difference is investigated in the shell-model framework employing both i…
Spectroscopy of Kr70 and isospin symmetry in the T=1 fpg shell nuclei
2016
The recoil-β tagging technique has been used in conjunction with the 40 Ca(32 S ,2n) reaction at a beam energy of 88 MeV to identify transitions associated with the decay of the 2 + and, tentatively, 4 + states in the nucleus 70 Kr. These data are used, along with previously published data, to examine the triplet energy differences (TED) for the mass 70 isobars. The experimental TED values are compared with shell model calculations, performed with the JUN45 interaction in the fpg model space, that include a J = 0 isospin nonconserving (INC) interaction with an isotensor strength of 100 keV. The agreement is found to be very good up to spin 4 and supports the expectation for analog states th…
Analysis of the γγ→DD¯ reaction and the DD¯ bound state
2021
In this work, we investigate the reaction of $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}D\overline{D}$, taking into account the $S$-wave $D\overline{D}$ final state interaction. By fitting to the $D\overline{D}$ invariant mass distributions measured by the Belle and BABAR Collaborations, we obtain a good reproduction of the data by means of a $D\overline{D}$ amplitude that produces a bound $D\overline{D}$ state with isospin $I=0$ close to threshold. The error bands of the fits indicate, however, that more precise data on this reaction are needed to be more assertive about the position and width of such a state.