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1.
The presence of a narrow peak in the $ \Lambda$ p invariant-mass distribution observed in the $ \bar{{p}}$ annihilation reaction at rest $\ensuremath \bar{p} {}^4\mathrm{He}\rightarrow p\pi^-p\pi^+\pi^-n X$ is discussed again through an analysis procedure which improves the ratio signal/background in comparison with the previous analysis. The peak is centred at 2223.2±3.2stat±1.2syst MeV and has a statistical significance of 4.7 $ \sigma$ , values compatible with those published previously. If interpreted as the result of the decay into $ \Lambda$ p of a $\ensuremath { }_{\bar{K}}{}^2\mathrm{H}$ bound system, the corresponding binding energy should be B = - 151.0±3.2stat±1.2syst MeV and the width $ \Gamma_{{FWHM}}^{}$ < 33.9±6.2 MeV. The production rate has a lower limit of 1.2 10-4. Data on the $ \bar{{p}}$ annihilation reaction at rest $ \bar{{p}}$ 4He $ \rightarrow$ p $ \pi^{-}_{}$ p $ \pi^{-}_{}$ p s X , analyzed for the first time, lead to a result in qualitative agreement with the previous one.  相似文献   

2.
Narrow lines were observed around 133 MeV excitation energy in the208Pb(d,3He) reaction atT d=300 MeV/u using the Fragment Separator System at GSI. They are assigned to the deeply boundπ ??207Pb states with configurations of $\left( {2p} \right)_{\pi ^ - } $ (3p1/2, 3p3/2) n ?1 .  相似文献   

3.
The general theory of inhomogeneous mean-field systems of Raggio and Werner provides a variational expression for the (almost sure) limiting free energy density of the Hopfield model $$H_{N,p}^{\{ \xi \} } (S) = - \frac{1}{{2N}}\sum\limits_{i,j = 1}^N {\sum\limits_{\mu = 1}^N {\xi _i^\mu \xi _j^\mu S_i S_j } } $$ for Ising spinsS i andp random patterns ξμ=(ξ 1 μ 2 μ ,...,ξ N μ ) under the assumption that $$\mathop {\lim }\limits_{N \to \gamma } N^{ - 1} \sum\limits_{i = 1}^N {\delta _{\xi _i } = \lambda ,} \xi _i = (\xi _i^1 ,\xi _i^2 ,...,\xi _i^p )$$ exists (almost surely) in the space of probability measures overp copies of {?1, 1}. Including an “external field” term ?ξ μ p hμμξ i=1 N ξ i μ Si, we give a number of general properties of the free-energy density and compute it for (a)p=2 in general and (b)p arbitrary when λ is uniform and at most the two componentsh μ1 andh μ2 are nonzero, obtaining the (almost sure) formula $$f(\beta ,h) = \tfrac{1}{2}f^{ew} (\beta ,h^{\mu _1 } + h^{\mu _2 } ) + \tfrac{1}{2}f^{ew} (\beta ,h^{\mu _1 } - h^{\mu _2 } )$$ for the free energy, wheref cw denotes the limiting free energy density of the Curie-Weiss model with unit interaction constant. In both cases, we obtain explicit formulas for the limiting (almost sure) values of the so-called overlap parameters $$m_N^\mu (\beta ,h) = N^{ - 1} \sum\limits_{i = 1}^N {\xi _i^\mu \left\langle {S_i } \right\rangle } $$ in terms of the Curie-Weiss magnetizations. For the general i.i.d. case with Prob {ξ i μ =±1}=(1/2)±?, we obtain the lower bound 1+4?2(p?1) for the temperatureT c separating the trivial free regime where the overlap vector is zero from the nontrivial regime where it is nonzero. This lower bound is exact forp=2, or ε=0, or ε=±1/2. Forp=2 we identify an intermediate temperature region between T*=1?4?2 and Tc=1+4?2 where the overlap vector is homogeneous (i.e., all its components are equal) and nonzero.T * marks the transition to the nonhomogeneous regime where the components of the overlap vector are distinct. We conjecture that the homogeneous nonzero regime exists forp≥3 and that T*=max{1?4?2(p?1),0}.  相似文献   

4.
A separable representation of theS-wave Paris potential and a phase-shift equivalent Yamaguchi-type potential significantly differing in their off-shell behaviours are used to calculate second-order polarization observables of elastic nucleon-deuteron scattering atE D=10 and 20MeV. Off-shell effects are found that stem from differences in the nuclear interaction in the inner regionr?1.2 fm. Adding approximate Coulomb-distortion contributions to the purely nuclear Faddeev amplitudes proton-deuteron predictions are obtained. Coulomb effects are not found to be negligible. Comparison with experimental data, in particular, the spin-correlation parameterC y,y of the reaction \({}^1\vec H(\vec d,d)^1 H\) forE D=10MeV vector-polarized deuterons and the spin-transfer coefficientsK y y′ ,K x x′ andK z x′ for \({}^2H(\vec p,\vec p)^2 H\) atE p=10MeV, prefer the interaction model that contains an intermediate-range repulsion.  相似文献   

5.
Dispersion relations in the (ν2,t) plane along hyperbolas are used in order to extrapolate the invariant isospin-even πN amplitude D+2,t) to the Cheng-Dashen point, ν=0, t=2μ. The fluctuation of the results obtained with different hyperbolas gives a realistic estimate of the errors, except for errors of the partial wave solution and of the ππ \( - N\bar N\) amplitudes assumed at t < 4μ2 —If our ππ \( - N\bar N\) partial waves are used, which are based on the ππs-wave scattering length a 0 0 =0.28 μ-1, the result for the sigma term is 64±8 MeV, in agreement with earlier determinations.—The discrepancy with the theoretical prediction σπN≈ 30 MeV is smaller by only 8 MeV, if our \( - N\bar N\) amplitudes are modified in such a way that the threshold behaviour of the ππs-wave agrees with Weinberg's prediction a 0 0 =0.16 μ-1. Further progress depends on new accurate experimental π±p scattering data in the Coulomb interference region at low energies.  相似文献   

6.
We report on the p T dependence of nuclear modification factors (R CP) for K S 0 , ??, ?? and the $\bar NK_S^0 $ ratios at mid-rapidity from Au+Au collisions at $\sqrt {s_{NN} } $ = 39, 11.5 and 7.7 GeV. At $\sqrt {s_{NN} } $ = 39 GeV, the R CP data show a baryon/meson separation at intermediate p T and a suppression for K S 0 for p T up to 4.5 GeV/c; the $\bar \Lambda K_S^0 $ shows baryon enhancement in the most central collisions. However, at $\sqrt {s_{NN} } $ = 11.5 and 7.7 GeV, R CP shows less baryon/meson separation and $\bar NK_S^0 $ shows almost no baryon enhancement. These observations indicate that the matter created in Au+Au collisions at $\sqrt {s_{NN} } $ = 11.5 or 7.7 GeV might be distinct from that created at $\sqrt {s_{NN} } $ = 39 GeV.  相似文献   

7.
The prototype of a $\bar{K}$ nuclear cluster, K ???pp, has been investigated using effective $\bar{K}N$ potentials based on chiral SU(3) dynamics. Variational calculation shows a bound state solution with shallow binding energy B(K ???pp)?=?20±3 MeV and broad mesonic decay width $\Gamma(\bar{K}NN \rightarrow \pi Y N)=40$ –70 MeV. The $\bar{K}N(I=0)$ pair in the K ???pp system exhibits a similar structure as the Λ(1405). We have also estimated the dispersive correction, p-wave $\bar{K}N$ interaction, and two-nucleon absorption width.  相似文献   

8.
L P Pitaevskii 《Pramana》1987,28(5):589-589
Landau’s criterion plays an important role in the theory of superfluidity. According to this criterion, superfluid motion is possible if \(\tilde \varepsilon \left( p \right) \equiv \varepsilon \left( p \right) + pV > 0\) along the curve of the spectrum?(p) of excitations. For4He it means thatv<v c,v c≈60 m/sec.v s is equal to the tangent of the slope to the roton part of the spectrum. The question of what happens to the liquid when this velocity is exceeded, as far as we know, remains unclear. We shall show that for small excesses abovev c a one-dimensional periodic structure appears in the helium. A wave vector of this structure oriented opposite to the flow and equal toρ c/h whereρ c is the momentum at the tangent point. The quantity \(\tilde \varepsilon \left( p \right)\) is the energy of excitation in the liquid moving with velocity v. Inequality of Landau ensures that \(\tilde \varepsilon \) is positive. If \(\tilde \varepsilon \) becomes negative, then the boson distribution function \(n\left( {\tilde \varepsilon } \right)\) becomes negative, indicating the impossibility of thermodynamic equilibrium of the ideal gas of rotons; therefore the interaction between them must be taken into account. The final form of the energy operator is $$\hat H = \int {\left\{ {\hat \psi + \tilde \varepsilon \left( p \right)\hat \psi + \tfrac{g}{2}\hat \psi + \hat \psi + \hat \psi \hat \psi } \right\}} d^3 x, g \sim 2 \cdot 10^{ - 38} erg.cm.$$ Then we can seek the rotonψ-operator in the formψ=ηexp(i p c r/h), determiningη from the condition that the energy is minimized. The result is (η)2=(v?v c)ρ c/g, forv>v c. The plane waveψ corresponds to a uniform distribution of rotons. It leads, however, to a spatial modulation of the density of the helium, since the density operator \(\hat n\) contains a term which is linear in the operator \(\psi :\hat n = n_0 + \left( {n_0 } \right)^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-0em} 2}} {A \mathord{\left/ {\vphantom {A {\hat \psi \to \hat \psi ^ + }}} \right. \kern-0em} {\hat \psi \to \hat \psi ^ + }}\) ), where |A|2ρ c 2 /2m?(ρ c). Finally we find that the density of helium is modulated according to the law $$\frac{{n - n_0 }}{{n_0 }} = \left[ {\frac{{\left| A \right|^2 \left( {\nu - \nu _c } \right)\rho _c }}{{n_0 g}}} \right]^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} \sin \rho _c x \approx 2,6\left[ {\frac{{\nu - \nu _c }}{{\nu _c }}} \right]^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} \sin \rho _c x$$ . This phenomenon can be observed, in principle, in the experiments on scattering ofx-rays in moving helium.  相似文献   

9.
In an experiment at the CERN-SPS charged hyperon beam, we have investigated the inclusive \(\Lambda \bar K^0 \) and \(\Sigma ^0 \bar K^0 \) final states formed in Ξ? Be interactions. In the \(\Lambda \bar K^0 \) channel, we observe a signal at 1826 MeV/c2 which can be identified with the known Ξ(1820) resonance. We determine its mass and width to be:M=1826±4 MeV/c2, Г=12±14 MeV/c2. A moment analysis is consistent with a spin of 3/2 and indicates a negative parity for this spin assignment. Also in the \(\Lambda \bar K^0 \) channel, we observe a 3.6σ signal with the following parameters:M=1963±5 MeV/c2, Г=25±15 MeV/c2. This state, which we call Ξ(1960), is not observed in the \(\Sigma ^0 \bar K^0 \) channel, leading to an upper limit on the ratio of partial widths \(\Sigma \bar K/\Lambda \bar K\) of 2.3 (90% confidence level). A moment analysis of the \(\Lambda \bar K^0 \) final state indicates a spin of 5/2 or greater in the natural spin-parity series 5/2+, 7/2?, etc.  相似文献   

10.
A powerful dynamical neutrino source with a hard spectrum obtained via the (n, γ) activation of 7Li and a subsequent β? decay (T 1/2=0.84 s) of 8Li with the emission of high-energy $\tilde \nu _e$ (up to 13 MeV) is discussed. In the dynamical system, lithium is pumped over in a closed cycle through a converter near the reactor core and further to a remote $\tilde \nu _e$ detector. It is shown that, owing to a large growth of the hardness of the total $\tilde \nu _e$ spectrum, the cross section for the interaction with a deuteron can strongly increase both in the neutral ( $\tilde \nu _e + d \uparrow n + p + \tilde \nu _e$ ) and in the charged ( $\tilde \nu _e + d \uparrow n + n + e^ +$ ) channel in relation to the analogous cross sections in the reactor $\tilde \nu _e$ spectrum.  相似文献   

11.
A parametrization of theJ p =0? hadronic continuum, in the framework of Extended PCAC, is discussed with emphasis on finite-width effects and on the constraints imposed by the correct threshold behavior of the pion spectral function. As an application light quark masses are calculated using both Hilbert and Laplace transform QCD sum rules. The results for the runing quark masses are: \((\bar m_u + \bar m_d )|_{1 Gev} = 16 \pm 2 MeV,(\bar m_u + \bar m_s )|_{1 Gev} = 199 \pm 27 MeV\) , and a ratio \(R \equiv 2(\bar m_u + \bar m_s )/(\bar m_u + \bar m_d )_{1 Gev} = 25 \pm 4\) .  相似文献   

12.
The photo-fission yields and photo-neutron cross-sections of ( $ \gamma$ , 3n) and ( $ \gamma$ , 4n) on 209Bi induced by 50 and 65MeV bremsstrahlung have been measured by using a recoil catcher and an off-line $ \gamma$ -ray spectrometric technique. The mass-yield distribution of fission products in 209Bi induced by bremsstrahlung photons from the present work and literature data in the energy range 28-85MeV is symmetric around 103 mass units. However, the full width at half maximum of the yields distribution increases from 19 mass units at 28-40MeV to 23 mass units at 85MeV. The ( $ \gamma$ , 3n) reaction cross-section in the 50MeV and the ( $ \gamma$ , 4n) reaction cross-section in the 50 and 65MeV bremsstrahlung-induced reaction of 209Bi were determined for the first time.  相似文献   

13.
The rapidity distributions of inclusive \(e^ + e^ - \to h\bar h + \cdot \cdot \cdot\) of PEP and DESY experiments are analyzed in terms of the covariant partition temperatureT p model. The estimates ofT p * in the fireball system are comparable to the conventional temperature, the energy dependence follows approximately Stefan's law, the radius of the specific volume ralative to the energy density being ~1.18 fm. In the c.m.s. of collision, \(T_p = AW^a (W = \sqrt s in GeV)\) witha=0.60±0.05 andA=0.256±0.006, it is found \(T_p \cong {W \mathord{\left/ {\vphantom {W {\tfrac{3}{2}\left\langle {n_ \pm } \right\rangle }}} \right. \kern-0em} {\tfrac{3}{2}\left\langle {n_ \pm } \right\rangle }}\) . These properties hold also for \(\bar pp\) collision, but not forpp→π?+...  相似文献   

14.
We consider an anisotropic bond percolation model on $\mathbb{Z}^{2}$ , with p=(p h ,p v )∈[0,1]2, p v >p h , and declare each horizontal (respectively vertical) edge of $\mathbb{Z}^{2}$ to be open with probability p h (respectively p v ), and otherwise closed, independently of all other edges. Let $x=(x_{1},x_{2}) \in\mathbb{Z}^{2}$ with 0<x 1<x 2, and $x'=(x_{2},x_{1})\in\mathbb{Z}^{2}$ . It is natural to ask how the two point connectivity function $\mathbb{P}_{\mathbf{p}}(\{0\leftrightarrow x\})$ behaves, and whether anisotropy in percolation probabilities implies the strict inequality $\mathbb{P}_{\mathbf{p}}(\{0\leftrightarrow x\})>\mathbb{P}_{\mathbf {p}}(\{0\leftrightarrow x'\})$ . In this note we give an affirmative answer in the highly supercritical regime.  相似文献   

15.
A search for narrow Θ+(1540), a candidate for a pentaquark baryon with positive strangeness, has been performed in an exclusive proton-induced reaction $p + C(N) \to \Theta ^ + \bar \kappa ^0 + C(N)$ on carbon nuclei or quasifree nucleons at $E_{beam} = 70GeV(\sqrt s = 11.5GeV)$ studying nK +, pK S 0 , and pK L 0 decay channels of Θ+(1540) in four different final states of the $\Theta ^ + \bar K^0 $ system. In order to assess the quality of the identification of the final states with neutron or K L 0 , we reconstructed Λ(1520) → nK S 0 and ?K L 0 K S 0 decays in the calibration reactions p + C(N) → Λ (1520)K ++C(N) and p+C(N) → p?+C(N). We found no evidence for a narrow pentaquark peak in any of the studied final states and decay channels. Assuming that the production characteristics of the $\Theta ^ + \bar K^0 $ system are not drastically different from those of the Λ(1520)K + and p? systems, we established upper limits on the cross-section ratios $\sigma (\Theta ^ + \bar K^0 )/\sigma (\Lambda (1520)K^ + ) < 0.02$ and $\sigma (\Theta ^ + \bar K^0 )/\sigma (p\phi ) < 0.15$ at 90% C.L. and a preliminary upper limit for the forward-hemisphere cross section $\sigma (\Theta ^ + \bar K^0 )$ nb/nucleon.  相似文献   

16.
In this paper, we consider the spread-out oriented bond percolation models inZ d ×Z withd>4 and the nearest-neighbor oriented bond percolation model in sufficiently high dimensions. Let η n ,n=1, 2, ..., be the random measures defined onR d by $$\eta _n (A) = \sum\limits_{x \in Z^d } {1_A (x/\sqrt n )1_{\{ (0,0) \to (x,n)\} } } $$ The mean of η n , denoted by $\bar \eta _n $ , is the measure defined by $$\bar \eta _n (A) = E_p [\eta _n (A)]$$ We use the lace expansion method to show that the sequence of probability measures $[\bar \eta _n (R^d )]^{ - 1} \bar \eta _n $ converges weakly to a Gaussian limit asn→∞ for everyp in the subcritical regime as well as the critical regime of these percolation models. Also we show that for these models the parallel correlation length $\xi (p)~|p_c - p|^{ - 1} $ asp?pc  相似文献   

17.
We investigate hadronic molecule states of $K \bar K N$ and $\bar K \bar K N$ systems with I?=?1/2 and J P ?=?1/2?+?, assuming that Λ(1405) and the scalar mesons, f 0(980), a 0(980), are reproduced as quasi-bound states of $\bar KN$ and $K \bar K$ . Performing non-relativistic three-body calculations for these systems, we find weakly bound states for $K \bar K N$ and $\bar K \bar K N$ around 1900 MeV, which correspond to new baryon resonances of N * and Ξ * with J P ?=?1/2?+?. We find that these resonances have cluster structure of the two-body bound state keeping its properties as in the isolated two-particle system.  相似文献   

18.
The two ? reactions at rest ? pΛ 0 n and ? pΛ 0 n have been studied in order to determine the capture ratio $$r_c = \frac{{\sum ^ - p \to \sum ^0 n}}{{(\sum ^ - p \to \sum ^0 n) + (\sum ^ - p \to \Lambda ^0 n)}}$$ , theΛ 0-lifetime and the ?-Λ 0 mass difference. The following results were obtained: $$\begin{gathered} rc = 0.474 \pm 0.016 \hfill \\ \tau _{\Lambda ^0 } = (2.47 \pm 0.08) \times 10^{ - 10} \sec \hfill \\ M_{\sum ^ - } - M_{\sum ^0 } = 81.64 \pm 0.09{{MeV} \mathord{\left/ {\vphantom {{MeV} {c^2 }}} \right. \kern-\nulldelimiterspace} {c^2 }} \hfill \\ \end{gathered} $$ The ?-mass was determined from the range of the stopping ?-hyperons,M ∑} =1197.19±0.32 MeV/c 2.  相似文献   

19.
Thep th Gel'fand-Dickey equation and the string equation [L, P]=1 have a common solution τ expressible in terms of an integral overn×n Hermitean matrices (for largen), the integrand being a perturbation of a Gaussian, generalizing Kontsevich's integral beyond the KdV-case; it is equivalent to showing that τ is a vacuum vector for aW ?p + , generated from the coefficients of the vertex operator. This connection is established via a quadratic identity involving the wave function and the vertex operator, which is a disguised differential version of the Fay identity. The latter is also the key to the spectral theory for the two compatible symplectic structures of KdV in terms of the stress-energy tensor associated with the Virasoro algebra. Given a differential operator $$L = D^p + q_2 (t) D^{p - 2} + \cdots + q_p (t), with D = \frac{\partial }{{dx}},t = (t_1 ,t_2 ,t_3 ,...),x \equiv t_1 ,$$ consider the deformation equations1 (0.1) $$\begin{gathered} \frac{{\partial L}}{{\partial t_n }} = [(L^{n/p} )_ + ,L] n = 1,2,...,n + - 0(mod p) \hfill \\ (p - reduced KP - equation) \hfill \\ \end{gathered} $$ ofL, for which there exists a differential operatorP (possibly of infinite order) such that (0.2) $$[L,P] = 1 (string equation).$$ In this note, we give a complete solution to this problem. In section 1 we give a brief survey of useful facts about theI-function τ(t), the wave function Ψ(t,z), solution of ?Ψ/?t n=(L n/p) x Ψ andL 1/pΨ=zΨ, and the corresponding infinitedimensional planeV 0 of formal power series inz (for largez) $$V^0 = span \{ \Psi (t,z) for all t \in \mathbb{C}^\infty \} $$ in Sato's Grassmannian. The three theorems below form the core of the paper; their proof will be given in subseuqent sections, each of which lives on its own right.  相似文献   

20.
An investigation of inclusivepp→π?+? in terms of the covariant Boltzmann factor (BF) including the chemical potential μ indicates a) that the temperatureT increases less rapidly than expected from Stefan's law, b) that a scaling property holds for the fibreball velocity of π? secondaries, leading to a multiplicity law like ~E cm 1/2 at high energy, and c) that μπ is related to the quark mass: μπ=2m q ?m π the quark massm q determined by \(T_{\pi ^ - } \) at \(\bar pp\) threshold beingm q =3Tπ?330 MeV. Because ofthreshold effects \(T_{\bar p}< T_{\pi ^ - } \) , whereas \({{\mu _p } \mathord{\left/ {\vphantom {{\mu _p } {\mu _{\pi ^ - } }}} \right. \kern-0em} {\mu _{\pi ^ - } }} \simeq {3 \mathord{\left/ {\vphantom {3 2}} \right. \kern-0em} 2}\) as expected from the quark contents of \(\bar p\) and π. The antinuclei \(\bar d\) and \({{\bar t} \mathord{\left/ {\vphantom {{\bar t} {\overline {He^3 } }}} \right. \kern-0em} {\overline {He^3 } }}\) observed inpp events are formed by coalescence of \(\bar p\) and \(\bar n\) produced in thepp collision. Semi-empirical formulae are proposed to estimate multiplicities of π?, \(\bar p\) and antinuclei.  相似文献   

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