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Register a new userEvidence for $Delta(2200)7/2^-$ from photoproduction and consequence for chiral-symmetry restoration at high mass
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We report a partial-wave analysis of new data on the double-polarization variable $E$ for the reactions $gamma pto pi^+ n$ and $gamma pto pi^0 p$ and of further data published earlier. The analysis within the Bonn-Gatchina (BnGa) formalism reveals evidence for a poorly known baryon resonance, the one-star $Delta(2200)7/2^-$. This is the lowest-mass $Delta^*$ resonance with spin-parity $J^P=7/2^-$. Its mass is significantly higher than the mass of its parity partner $Delta(1950)7/2^+$ which is the lowest-mass $Delta^*$ resonance with spin-parity $J^P=7/2^+$. It has been suggested that chiral symmetry might be restored in the high-mass region of hadron excitations, and that these two resonances should be degenerate in mass. Our findings are in conflict with this prediction.
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We report a measurement of a new high spin Jp = 5- state at 22.4(0.2) MeV in 12C which fits very well to the predicted (ground state) rotational band of an oblate equilateral triangular spinning top with a D_3h symmetry characterized by the sequence 0+, 2+, 3-, 4+/-, 5- with almost degenerate 4+ and 4- (parity doublet) states. Such a D_3h symmetry was observed in triatomic molecules and it is observed here for the first time in nuclear physics. We discuss a classification of other rotation-vibration bands in 12C such as the (0+) Hoyle band and the (1-) bending mode band and suggest measurements in search of the predicted (missing) states that may shed new light on clustering in 12C and light nuclei. In particular the observation (or non-observation) of the predicted (missing) states in the Hoyle band will allow us to conclude the geometrical arrangement of the three alpha-particle composing the Hoyle state at 7.654 MeV in 12C.
We study the phase structure of dense hadronic matter including $Delta(1232)$ as well as N(939) based on the parity partner structure, where the baryons have their chiral partners with a certain amount of chiral invariant masses. We show that, in symmetric matter, $Delta$ enters into matter in the density region of about one to four times of normal nuclear matter density, $rho_B sim 1 - 4rho_0$. The onset density of $Delta$ matter depends on the chiral invariant mass of $Delta$, $m_{Delta0}$: The lager $m_{Delta0}$, the bigger the onset density. The $Delta$ matter of $rho_B sim 1 - 4rho_0$ is unstable due to the existence of $Delta$, and the stable $Delta$-nucleon matter is realized at about $rho_B sim 4rho_0$, i.e., the phase transition from nuclear matter to $Delta$-nucleon matter is of first order for small $m_{Delta0}$, and it is of second order for large $m_{Delta0}$. We find that, associated with the phase transition, the chiral condensate changes very rapidly, i.e., the chiral symmetry restoration is accelerated by Delta matter. As a result of the accelerations, there appear $N^*$(1535) and $Delta$(1700), which are the chiral partners to N(939) and ${Delta}$(1232), in high density matter, signaling the partial chiral symmetry restoration. Furthermore, we find that complete chiral symmetry restoration itself is delayed by $Delta$ matter. We also calculate the effective masses, pressure and symmetry energy to study how the transition to $Delta$ matter affects such physical quantities. We observe that the physical quantities change drastically at the transition density.
We study chiral symmetry restoration by analyzing thermal properties of QCDs (pseudo-)Goldstone bosons, especially the pion. The meson properties are obtained from the spectral densities of mesonic imaginary-time correlation functions. To obtain the correlation functions, we solve the Dyson-Schwinger equations and the inhomogeneous Bethe-Salpeter equations in the leading symmetry-preserving rainbow-ladder approximation. In the chiral limit, the pion and its partner sigma degenerate at the critical temperature $T_c$. At $T gtrsim T_c$, it is found that the pion rapidly dissociates, which signals deconfinement phase transition. Beyond the chiral limit, the pion dissociation temperature can be used to define the pseudo-critical temperature of chiral phase crossover, which is consistent with that obtained by the maximum point of the chiral susceptibility. The parallel analysis for kaon and pseudoscalar $sbar{s}$ suggests that heavy mesons may survive above $T_c$.
Properties of cold nuclear matter are studied within a generalized Nambu-Jona-Lasinio model formulated on the level of constituent nucleons. The model parameters are chosen to reproduce simultaneously the observed nucleon and pion masses in vacuum as well as saturation properties of nuclear matter. The strongest constraints on these parameters are given by the empirical values of the nucleon effective mass and compression modulus at nuclear saturation density. A preferable value of the cut-off momentum, determining density of active quasinucleon states in the Dirac sea, is estimated to about 400 MeV/c. With the most reasonable choice of model parameters we have found a first order phase transition of the liquid-gas type at subsaturation densities and the gradual restoration of chiral symmetry at about 3 times the saturation density. Fluctuations of the scalar condensate around its mean-field value are estimated and shown to be large in the vicinity of chiral transition.
One new pair of positive-parity chiral doublet bands have been identified in the odd-$A$ nucleus $^{135}$Nd which together with the previously reported negative-parity chiral doublet bands constitute a third case of multiple chiral doublet (M$chi$D) bands in the $Aapprox130$ mass region. The properties of the M$chi$D bands are well reproduced by constrained covariant density functional theory and particle rotor model calculations. The newly observed M$chi$D bands in $^{135}$Nd represents an important milestone in supporting the existence of M$chi$D in nuclei.
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