Constraining the Surface Gravitational Redshift of Proto Neutron Stars with New Nucleon Coupling Constants

A new set of nucleon coupling constants (CZ11) is obtained for the relativistic mean field (RMF) theory based on the recent experimental information on the symmetry energy derived from the data from NSCL/MSU. The surface gravitational redshift of a proto neutron star (PNS) is examined within the RMF framework for the baryon octet system by using this set of parameters. It is found that the surface gravitational redshift for CZ11 is smaller than that for GL97. For the CZ11 parameter set, the surface gravitational redshift of a PNS at T=15 MeV is smaller than that at T=0 MeV. It is also found that the surface gravitational redshift corresponding to M _max/R for the CZ11 parameter set is smaller by about 10 percent than that for GL97, with M _max being the maximum mass and R being the corresponding radius.     

Inclusive Ξ0, Ξ(1530)- and Ξ(1530)0 production in Ξ--Be interactions at 116 GeV/c

In an experiment using the CERN SPS hyperon beam, we have measured the cross sections for inclusive production of Ξ⁰ (accompanied by a charged particle), Ξ(1530)^- and Ξ(1530)⁰ in Ξ^--beryllium collisions at 116 GeV/c. All differential cross sections are found to be well described by the from (1?x _F )ⁿ exp (?bp _T ² ) over the whole accessible kinematical region (x _F >0.3). The invariant production spectra for Ξ⁰, Ξ(1530)^- and Ξ(1530)⁰, as well as those for Ξ^-, and Ω^- (obtained previously from the same data), are compared to theoretical predictions deduced from a two-component quark-diquark cascade model.     

Strange baryon production in hadronic Z0 decays

The production of the $J^{P}={1?er 2}^{+}$ octet baryons Λ and Ξ^?, the $J^{P}={3?er 2}^{+}$ decuplet baryons Σ(1385)^±Ξ(1530)⁰, and Ω^?, and the $J^{P}={3?er 2}^{-}$ orbitally excited state Λ(1520) has been measured in a sample of approximately 3.65 million hadronic Z⁰ decays. The integrated rates and the differential cross-sections as a function of x _E, the scaled energy, are determined. The differential cross-sections of the Λ and Ξ^? baryons are found to be softer than those predicted by both the JETSET and HERWIG Monte Carlo generators. The measured baryon yields are found to disagree with the simple diquark picture where only one tuning parameter for spin 1 diquarks is allowed. The yields are further compared with a thermodynamic model of hadron production which includes the production of orbitally excited mesons and baryons. The momentum spectra of Λ, Ξ^?, Σ(1385)^±Ξ(1530)⁰, and Λ(1520) are also compared to the predictions of an analytical QCD formula.     

Charge radii of octet and decuplet baryons in chiral constituent quark model

The charge radii of the spin- $\frac{1}{2}^+$ octet and spin- $\frac{3}{2}^+$ decuplet baryons have been calculated in the framework of chiral constituent quark model (χCQM) using a general parametrization method (GPM). Our results are not only comparable with the latest experimental studies but also agree with other phenomenological models. The effects of SU(3) symmetry breaking pertaining to the strangeness contribution and GPM parameters pertaining to the one-, two- and three-quark contributions have also been investigated in detail and are found to be the key parameters in understanding the non-zero values for the neutral octet (n, Σ⁰, Ξ⁰, Λ) and decuplet (Δ⁰, Σ^*0, Ξ^*0) baryons.     

Isospin breaking mass differences from QCD

We study the contributions to the mass differences p?n, Σ⁺?Σ^?, Ξ⁰?Ξ^? proportional to the isospin breaking QCD parameters ω≡m_d/m_u?1 and $\text{δ≡〈}\text{d}\text{?}\text{d〉?1}$ within the ITEP sum rule approach. By taking into account the electromagnetic contribution as estimated with the Cottingham formula very good agreement with experiment is found for ω ≌0.8 and δ≌0.006, which are very reasonable values.     

Effects of σ* and Φ mesons on the surface redshift of a neutron star

The effects of σ and Φ mesons on the surface redshift of a neutron star have been investigated within the framework of relativistic mean field theory for the baryon octet {n,p,Λ,Σ,Σ 0,Σ +,Ξ,Ξ 0 } system.It is found that compared with those without considering the contributions of σ and Φ mesons,the surface redshift decreases and that corresponding to the maximum value of the mass also decreases from 0.2540 to 0.2236,about by 12%.Meanwhile,it is also found that including σ and Φ mesons,the M/R and that corresponding to the maximum mass decrease.     

Study of Ξ− and Ω− production from K−n and K−p interactions at 4.93 GeV/c

Cross sections, mass spectra, angular distributions and several other features of Ξ^? and Ω^? production from photons and neutrons in K^?d interactions at 4.93 GeV/c are presented. A five standard deviation peak is observed in ΞKπ mass spectra near 2.6 GeV/c². A sharp rise in the Ξ^? three- and four-body cross sections from K^?n interactions suggests direct-channel Σ¹ (3.0–3.5) formation.     

A search for the exotic Ξ<Superscript>−−</Superscript> (1860) in the hyperon beam experiment WA89(1860) in the hyperon beam experiment WA89

We report on a high statistics search for the Ξ^??(1860) resonance in Σ^?-nucleus collisions at 340 GeV/c. No evidence for this resonance is found in our data sample which contains 676000 Ξ^? candidates above bakground. For the decay channel Ξ^??(1860)→Ξ^? π ^? and the kinematic range 0.15<xF<0.9 we find a 3σ upper limit for the production cross section of 3.1 and 3.5 μb per nucleon, for reactions with carbon and copper, respectively.     

Radiative decays as a test for right-handed currents

It is shown that the purity violating amplitude for the decays Σ⁺ → pγ and Ξ^? → Σ^?γ vanish in the SU(3) symmetry limit if the charged weak currents possess a U spin symmetry for strangeness changing processes. This applies to Cabibbo currents and their SU (4) generalization. Assuming an asymptotically free model for the strong interactions this result applies to all models with only left-handed charged currents. Observation of a large parity violating amplitude would indicate right-handed charged weak currents. Tests involving other radiative decays are also considered.     

Effect of the mesons σ* and Φ and the variety of U(N)Σ on the transition density of hyperon stars

The effect of the mesons σ* and φ and the variety of U(N)Σ on the transition density of hyperon stars is examined within the framework of relativistic mean field theory for the baryon octet {n,p,∧,∑-,∑0,∑+,Ξ- and Ξ0} system.It is found that,compared with that without considering the mesons δ* and φ,the transition density of hyperon stars decreases,the critical baryon density that hyperons Σ-,Σ0,Ξ+,Ξ- and Ξ0 appears to decrease too,but for A the effect is not obvious.As U(N)Σ goes up,the critical baryon density of Σ+,Σ0 and Σ- increases,that of Ξ0 decreases and that of A and Ξ- is fixed.In addition,it is found that the variety of U(N)Σ almost does not influence the transition density.     

Hyperon production in pp interactions at √s = 53 and 62 GeV

Inclusive measurements of Λ⁰, $\text{Λ}$⁰, Ξ^?, Σ(1385)^±) production in the forward direction at the CERN intersecting storage rings are presented. A signal for simulataneous Λ⁰$\text{Λ}$⁰ production is also observed with total $\text{x > 0.6, 2.3 < M}{}_{\mathrm{<mtext>\Lambda </mtext><mtext>\Lambda </mtext>}}\text{< 2.5}\text{GeV}$ and with a cross section of (1.7 ± 0.2) μb.     

Searches for the pentaquark states Ξ(1860)0 and Ξ(1860)−− in neutron-carbon interactions via the EXCHARM experiment

Results of searches for the pentaquark states Ξ(1860)⁰ and Ξ(1860)^?? in neutron-carbon interactions at an average neutron energy of about 51 GeV via the EXCHARM experiment are presented. No such states are found in the Ξ^? π ⁺ and Ξ^? π ^? effective-mass spectra examined in this study. Upper limits on the cross sections for Ξ(1860)⁰ and Ξ(1860)^?? production are estimated.     

Radiative K- capture in hydrogen

The branching ratios for the decays K^-p → Λγ and K^-p → Σ⁰γ are investigated in a chiral SU(3) version of the cloudy-bag model. The calculated branching ratio for Λγ agrees with the existing experimental data, while the prediction for Σ⁰γ (being only slightly smaller) is well within the range accessible to an experiment currently under way at Brookhaven.     

Effect of σ*,φ Mesons on the Neutron Star Matter at Finite Temperature

Within the RMF approach, considering the contribution of σ*,φ mesons and baryon octet {n,p,Λ,Σ^－,Σ⁰,Σ⁺,Ξ^－,Ξ⁰}, some properties of neutron star matter have been investigated in the temperature region between 5—15MeV. It is found that when the contributions of σ*,φ mesons are included, (1) the critical baryon density decreases (but for the Λ hyperon, the effect is not obvious), but the number of hyperons increases; (2) the equation of state becomes soft at higher energy density; (3) the maximum mass decreases while the corresponding radius increases; (4) the central density, the central energy density, and the central pressure all become smaller. At T=5MeV and 10MeV and for Σ⁰,Ξ⁰,Σ⁺, the σ*,φ mesons make critical baryon density greatly decrease; but at T=15MeV, 20MeV, and 25MeV, the effect is not obvious. However, for Λ,Σ^－,Ξ^－ hyperons, at all the above temperatures, the effect is not obvious.     

Towards more exoticness—X-ray spectroscopy of Ξ− atoms at J-PARC

Atoms with a doubly-strange hadron, namely Ξ^?, are really exotic and interesting objects. We are planning to measure X rays from Ξ^? atoms for the first time at J-PARC, where a high intensity and high quality kaon beam is available. Our purpose is to obtain the strength of the optical potential, and hence to provide information on the Ξ-N interaction which is currently very poorly known. We can accumulate several thousand counts of X rays and determine the level energy shift down to ~0.05 keV. This is sensitive enough to observe the expected level shift (~1 keV) with reasonable accuracy, while the sensitivities for the level width is somewhat weaker (measurable down to ~1 keV).     

Baryon mass splitting by the strong hyperfine interaction and SU(3) breaking

We calculate mass splittings of strange and non-strange baryons in the [56, 0⁺] and the [70, 1^?]. As the most important spin-dependent force we only analyse the hyperfine interaction. The exact treatment of the quark mass breaking shows contributions which have not been considered in similar investigations up to now. Taking $\text{mλ}\text{m}{}_{\mathrm{<mtext>p</mtext>}}\text{? 2}$ and popular values for the slope of the linear potential a, the strong coupling constant α_s and the p-quark mass, we get excellent results for the four mass splittings 〈Σ-Λ〉, $\text{〈Σ}{}^1\text{? Σ〉}$, 〈Δ-N〉 and $\text{〈Ξ}{}^1\text{? Ξ〉}$ in the [56, 0⁺]. The structure of mass spectrum in the [70, 1^?] is well described, too; the strong SU(3) mixing of Σ and Λ states is seen to be due to the quark mass breaking. Predictions for missing Σ states in the [70, 1^?] as as for splittings between charmed baryons can be made.     

Observation of a narrow hyperon state of mass 3.17 GeV

We present evidence for a narrow Y¹ with a mass of 3.17 GeV and a width ? 20 MeV decaying to ΣKK? + pions, ΛKK? + pions and ΞK + pions. The data come from two high statistics K^?p bubble chamber experiments with a sensitivity of ≈100 eV/μbat 8.25 GeV/c and ≈ 45 eV/μbat 6.5 GeV/c.     

Optimization of LEPTO/JETSET generator parameters for deep inelastic scattering of charged leptons

Results of measurements of heavy hyperon and antihyperon yields in deep inelastic muon scattering obtained in the COMPASS experiment and their matching with Monte Carlo predictions are presented. Those of relative yields of heavy hyperons Σ(1385)⁺, Σ(1385)^?, \(\bar \Sigma (1385)^ -\) , \(\bar \Sigma (1385)^ +\) , Ξ(1321)^?, \(\bar \Xi (1321)^ +\) with respect to Λ and \(\bar \Lambda\) baryons were used to optimize the LEPTO/JETSET generator, which is heavily exploited for event simulation in a deep inelastic scattering region.     

A study of inclusive Ξ− production from K−p interactions at 4.2 GeV/c

A study of inclusive Ξ^? production from a high statistics K^?p experiment at 4.2 GeV/c has been made. The total Ξ^? production cross section is 157 ± 8 μb. Approximately 15% of the Ξ^? arise from decay of the Ξ¹⁰(1530) resonance. The polarization of the Ξ^? is found to be negative and is nearly equal in value to that of the Λ⁰ from the inclusive reaction K^? + p → Λ⁰ + anything. An analysis of the inclusive production of Ξ^? has been made in the framework of the triple-Reege formalism.     

Vacuum alignment by broken gauge interactions

We study the problem of vacuum alignment by the extended technicolour (ETC)forces which have been invoked to give mass to ordinary fermions (quarks and leptons) in technicolour theories. We find that the ETC interactions prefer to align the vacuum in such a way as to give the maximum possible mass to the ordinary fermions. We show that the P⁰, P³, P^+-, P₈⁰, P₈³, and P₈^+- pseudo-Goldstone bosons in one technifamily ETC models cannot acquire any mass from ETC interactions alone. Finally, we point out that the Pati-Salam unification which has been invoked to give mass to the P⁰ and P³ implies a remaining discrete degeneracy of the vacuum.