Unusual energy dependence of the total nuclear reaction cross section for a secondary isomeric nuclear beam (18Fm,Jπ = 5+, Ex = 1.1 MeV)

A primary ¹⁷O beam has been used to produce a 22.3 MeV/nucleon ¹⁸F^m isomeric secondary beam via a single nucleon transfer reaction on a carbon target. The total nuclear reaction cross sections for ¹⁸F^m and ¹⁸F^g.s. in silicon were measured in a stack of seven silicon solid-state detectors. The cross section for ¹⁸F^m exhibits some unusual features at low energy not seen for ¹⁸F^g.s. or other ions.     

Symmetry-restoring interactions for Kπ = 1+ isovector vibrations

The low-lying isovector 1⁺ states are studied by a symmetry-restoring RPA approach in some rare-earth nuclei. A new velocity-dependent residual interaction is proposed in order to restore the rotational invariance of the hamiltonian in the quasiparticle random-phase approximation with an axially-symmetric Woods-Saxon potential. A new quadrupole interaction is introduced with a self-consistently determined coupling strength. Calculations for six rare-earth nuclei (¹⁵⁴Sm, ^156,158Gd,¹⁶⁴Dy,¹⁶⁸Er,¹⁷⁴Yb) show a good agreement with the experimental energies and B(M1) values. The M1 transitions, corresponding to the experimental strong magnetic dipole states, have in all apart from one case a predominant orbital contribution. The largest orbital contribution (90%) is found in ¹⁵⁴Sm. About half of the low-energy (E < 5MeV, B(M1)↑>0.1μ_N²) states in each nucleus have an orbital character with a (10–40)% spin admixture. The M1 strength is concentrated in the region 2–9 MeV with a maximum around 5 MeV and corresponds to ΔN_osc = 0 transitions.     

Revisiting the Kπ puzzle in the pQCD factorization approach

In this paper,we calculated the branching ratios and direct CP violation of the four B→Kπ decays with the inclusion of all currently known next-to-leading order(NLO) contributions by employing the perturbative QCD(pQCD) factorization approach.We found that(a) Besides the 10%enhancement from the NLO vertex corrections,the quark-loops and magnetic penguins,the NLO contributions to the form factors can provide an additional~15%enhancement to the branching ratios,and lead to a very good agreement with the data;(b) The NLO pQCD predictions are A_(CP)~(dir)(B~0→K~+π~0)=(-6.5±3.1)%and A_(CP)~(dir)(B~+→K~+π~0)=(2.2±2.0)%,become well consistent with the data due to the inclusion of the NLO contributions.     

Pressure broadening of the ground vibrational state J = 31→J = 32 transition of CH3F by coincidence laser spectroscopy

We have studied self-broadening and foreign gas broadening of the ground state J = 31→J = 32 transition of CH₃F using a coincidence with the 184.3 μm emission from an optically pumped CH₂F₂ laser. Experiments have been carried out with polar and non-polar species as well as the noble gases.This transition is in the region where the classical rotation period is of the same order as the duration of a collision. The measurements indicate an anomalously low value of 7.0 MHz/Torr for the self-broadening coefficient of CH₃F and an unusually large value for the CH₃OH broadening coefficient. The latter is believed to be due to the presence of a low energy OH torsional model in CH₃OH.     

J/ψ pair production at the Tevatron with s=1.96 TeV

We study the m J/ψ pair production issue at the Fermilab Tevatron Run II with a center-of-mass energy of √s=1.96 TeV. Both the color-singlet and color-octet production mechanisms are considered. Our results show that the transverse momentum (p_T) scaling behaviors of the double m J/ψ differential cross-sections in the color-singlets and color-octets deviate distinctively from each other while p_T is larger than 8 GeV, and with a luminosity of 5 fb^-1, the m J/ψ pair events from the color-singlet scheme are substantially measurable in the Tevatron experiments, even with a certain lower transverse momentum cut. Hence the Tevatron is still a possible platform to check the heavy quarkonium production mechanism.     

The description of the Kπ = 1+ isovector M1 state within a boson expansion formalism

A nuclear system of Z protons and N neutrons moving in an anisotropic potential well and interacting among themselves through an isoscalar plus an isovector quadrupole-quadrupole interaction is treated within a boson expansion formalism. The expansion is performed in terms of the particle-hole RPA bosons. Application refers to ¹⁵⁶Gd. Appreciable corrections to the RPA results concerning both the energies and the B(M1↑) values are obtained. The higher RPA corrections destroy the fragmentation of the RPA-M1 strength and most of the collectivity is concentrated in one state.     

Measuring dynamical K/π and p/π fluctuations in AuAu collisions from the STAR experiment

Results from new measurements of dynamical K/?? and p/?? ratio fluctuations are presented. Dynamical fluctuations in global conserved quantities such as baryon number, strangeness, or charge may be observed near a QCD critical point. The STAR experiment has previously acquired data in AuAu collisions at the energies $\sqrt {s_{NN} }$ = 200, 130, 62.4, and 19.6 GeV and CuCu collisions at $\sqrt {s_{NN} }$ = 200, 62.4, and 22.4 GeV. The commencing of a QCD critical point search at RHIC has extended the reach of possible measurements of dynamical K/?? and p/?? ratio fluctuations from AuAu collisions to lower energies. New results are compared to previous measurements and to theoretical predictions from the UrQMD model.     

Geometric localization of the threshold in two-dimensional Ising ±J spin glasses forT=0

Following an approach of Toulouse, ground states in random 2D Ising ±J spin glasses (without external magnetic field), on square lattices, and with concentrations 0p0.5 of antiferromagnetic bonds are studied by means of minimal matchings of frustrated plaquettes. Lete(p) be the ground-state energy per spin in the thermodynamic limit. Then the well-known equatione(p)=–2+(p)f(p) holds, wheref(p) is the concentration of frustrated plaquettes and(p) is the average connection length between paired frustrated plaquettes in minimal matchings. Introducing (p) as the probability that a frustrated plaquette is matched to another frustrated plaquette by a connection of length (in a minimal matching), the average length(p) can be rewritten asgl(p)=(p). The study of(p) and its components (p) leads to an intervalp ^*pp ₂ (p ^*0.121±0.008,p ₂0.161±0.008) where the threshold between ferromagnet and paramagnet forT=0 lies. Analyzing a similar so-called adjoined average lengthl(p) admits further insight.     

Re-study of Nucleon Pole Contribution in J/ψ → NN^-π Decay

We re-study nucleon pole contribution in J/ψ → NN^-π decays by including the imaginary part for the propagator of the off-shell nucleon with energy above π N threshold. It is found that when including the imaginary part in the propagator, the branching ratio of the decay width will descend about 11% compared with the result without including the imaginary part, no matter whether including the off-shell form factors or not. It also leads to a phase of up to 25° for the off-shell nucleon propagator at invariant mass around 1400 MeV. This effect needs to be considered for detailed partial wave analysis of N^＊ resonances around this mass region.     

Study of the B_c→B_sπ decay with the perturbative QCD approach

The Bc→Bsπ decay is studied with the perturbative QCD approach. Three types of wave functions for Bsmeson are considered.The transition form factor FBc→Bs0(0) and the branching ratio Br(Bc→Bsπ)aresensitivetothemodelofthe Bsmeson wave functions.With appropriate inputs, our estimate on Br(Bc→Bsπ) is comparable with the recent LHCb measurement. A clear signal of Bc→Bsπ decay should be easily observed at the Large Hadron Collider.     

Variability of the atmospheric N2O line (J=3→4)

We analyze the results of observations of the radio emission of atmospheric N₂O in the line J=3→4 at frequency near 100.5 GHz. Observations aimed at monitoring the nitrous oxide content at altitudes h>20 km were performed in Nizhny Novgorod from March to May, 1997. We discover variations of the optical-depth decrement in the line, which can be explained by the redistribution of nitrous oxide over the altitude range h=20–55 km. This assumption does not contradict published data on in-situ measurements of N₂O density at h=5–35 km. Using the obtained data we calculate the rotational-line spectra of atmospheric N₂O. We point out that the measured decrements of the optical depths are greater than the calculated ones. We discuss observations of the N₂O lines in the mm-wave band as a promising method for monitoring the vertical mixing in the atmosphere. N. I. Lobachevsky State University, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 10, pp. 933–939, October 1999.     

What do we learn from the ρ-π puzzle

The experimental observation indicates that the branching ratio of ψ＇→ρπ is very small while the ρ-π channel is a main one in J/ψ decays. To understand the puzzle, various interpretations have been proposed. Meanwhile according to the hadronic helicity selection rule, this decay mode should be suppressed. Numerical calculations are needed to determine how it is suppressed. We calculate the branching ratios of J/ψ→ρπ and ππ in the framework of QCD. The results show that the branching ratios are proportional to （mu＋md/MJ/ψ）^2 for the ρπ mode and （mu-md/MJ/ψ）^2 for the ππ mode which is isospin violated. The theoretical prediction of the ratio of J/ ψ→ρπ is smaller than data, but not too small to invoke a completely new mechanism. Thus the puzzle is still standing even though we learn much knowledge towards the puzzle and this will help to finally interpret the puzzle and then gain a deeper insight to the heavy quarkonia.     

What do we learn from the ρ-π puzzle

The experimental observation indicates that the branching ratio of ψ→ρπ is very small while the ρ-π channel is a main one in J/ψ decays.To understand the puzzle,various interpretations have been proposed.Meanwhile according to the hadronic helicity selection rule,this decay mode should be suppressed.Numerical calculations are needed to determine how it is suppressed.We calculate the branching ratios of J/ψ→ρπ and ππ in the framework of QCD.The results show that the branching ratios are proportional to [(Mu+md)/(mJ/ψ)]2 for the ρπ mode and [(Mu-md)/(mJ/ψ)]2 for the ππ mode which is isospin violated.The theoretical prediction of the ratio of J/ψ→ρπ is smaller than data,but not too small to invoke a completely new mechanism.Thus the puzzle is still standing even though we learn much knowledge towards the puzzle and this will help to finally interpret the puzzle and then gain a deeper insight to the heavy quarkonia.     

j—j耦合中J（J=1）校正项

此文以第四族元素第一激发（ｎｐ）＾１［（ｎ＋１）ｓ］＾１为例，在（ＪＭＪ）表象中，建立新的单组态谱项能量表达式，添加α（Ｊ＋１）校正项后，显著地改善谱项理论值与实验值拟合程度。     

On the e/π identification applying the CBM TRD: Comparison of measurements with the TRD prototype and GEANT3 simulation at p = 1.5 GeV/c

The comparison of the distributions of the e/π energy losses in the TRD prototype and GEANT3 simulation of the n-layered TRD realized in frames of the CBM ROOT at p = 1.5 GeV/c has shown that the GEANT3 simulation reproduces real data quite well. However, contrary to the real measurements, this does not permit one to obtain a comparable level of pion’s suppression for GEANT3 data using the most powerful method based on a likelihood functions ratio test. It is shown that the procedure of preparation of data sets corresponding to the n-layered TRD based on prototype measurements is a reason of reaching an erroneous and highly overestimated level of pion’s suppression. It is also demonstrated that the needed level of pion’s suppression could be achieved using a combined method, which is more simple for practical application. The article is published in the original.     

The relationship between four-dimensional θ=π Yang－Mills theory and the two-dimensional Wess－Zumino－Novikov－Witten model

Used the dimensional reduction in the sense of Parisi and Sourlas, the gauge fixing term of the four-dimensional Yang－Mills field without the theta term is reduced to a two-dimensional principal chiral model. By adding the θ term (θ=π), the two-dimensional principal chiral model changes into the two-dimensional level 1 Wess－Zumino－Novikov－Witten model. The non-trivial fixed point indicates that Yang－Mills theory at θ=π is a critical theory without mass gap and confinement.     

Implications of unitarity and analyticity for the Dπ form factors

We consider the vector and scalar form factors of the charm-changing current responsible for the semileptonic decay D → πlν. Using as input dispersion relations and unitarity for the moments of suitable heavy-light correlators evaluated with Operator Product Expansions, including O(α _s ²) terms in perturbative QCD, we constrain the shape parameters of the form factors and find exclusion regions for zeros on the real axis and in the complex plane. For the scalar form factor, a low-energy theorem and phase information on the unitarity cut are also implemented to further constrain the shape parameters. We finally propose new analytic expressions for the Dπ form factors, derive constraints on the relevant coefficients from unitarity and analyticity, and briefly discuss the usefulness of the new parametrizations for describing semileptonic data.