共查询到20条相似文献,搜索用时 15 毫秒
1.
A. Dzyuba V. Kleber M. Büscher V. P. Chernyshev S. Dymov P. Fedorets V. Grishina C. Hanhart M. Hartmann V. Hejny L. Kondratyuk V. Koptev P. Kulessa Y. Maeda T. Mersmann S. Mikirtychyants M. Nekipelov D. Prasuhn R. Schleichert A. Sibirtsev H. J. Stein H. Ströher I. Zychor 《The European Physical Journal A - Hadrons and Nuclei》2006,29(2):245-251
The reaction pp → dK
+ˉ has been investigated at excess energies Q = 47.4 and 104.7MeV above the K
+ˉ threshold at COSY Jülich. Coincident dK+ pairs were detected with the ANKE spectrometer, and subsequently ∼ 2000 events with a missing ˉ invariant mass were identified,
which fully populate the Dalitz plot. The joint analysis of invariant mass and angular distributions reveals s-wave dominance between the two kaons, in conjunction with a p-wave between the deuteron and the kaon pair, i.e.
Kˉ production via the a
0
+(980) channel. Integration of the differential distributions yields total cross-sections of σ(pp → dK
+ˉ) = (38±2stat±14syst)nb and (190±4stat±39syst)nb for the low and high Q value, respectively. 相似文献
2.
P. V. Fedorets M. Büscher V. P. Chernyshev S. N. Dymov V. Yu. Grishina C. Hanhart M. Hartmann V. Hejny V. Kleber H. R. Koch L. A. Kondratyuk V. P. Koptev A. E. Kudryavtsev P. Kulessa S. I. Merzliakov S. M. Mikirtychiants M. E. Nekipelov H. Ohm R. Schleichert H. Ströher V. E. Tarasov K. -H. Watzlawik I. Zychor 《Physics of Atomic Nuclei》2006,69(2):306-313
The reaction pp → dπ
+
η has been measured at a beam energy of T
p
= 2.65 GeV (p
p
= 3.46 GeV/c) using the ANKE spectrometer at COSY-Julich. The missing-mass distribution of the detected dπ
+ pairs exhibits a peak around the η mass on top of a strong background of multipion pp → dπ
+(nπ) events. The differential cross section d
4
σ/dΩd
dΩ
π
+
dp
d
dp
π
+ for the reaction pp → dπ
+
η has been determined model independently for two regions of phase space. Employing a dynamical model for the a
0
+
production allows one then to deduce a total cross section of σ(pp → da
0
+
→ dπ
+
η) = 1.1 ± 0.3stat ± 0.7syst μb for the production of π
+
η via the scalar a
0
+
(980) resonance and σ(pp → dπ
+
η) = 3.5 ± 0.3stat ± 1.0syst μb for the nonresonant production. Using the same model as for the interpretation of recent results from ANKE for the reaction
, the ratio of the total cross sections is
, which is in agreement with branching ratios in the literature.
The text was submitted by the authors in English. 相似文献
3.
S. Pacetti 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):665-671
We define a general procedure, based on analyticity and dispersion relations, to estimate low-energy amplitudes for processes
like: φ→e
+
e
-
M and φ→γM, starting from cross-section data on e
+
e
-→φM, where M is a generic light scalar or pseudoscalar meson. In particular this procedure is constructed to obtain predictions on the
radiative decay rate which are crucially linked on the assumed quark structure for the meson M under consideration. Three cases are analyzed: M = η, M = f
0(qˉ) and M = f
0(qqˉ). While in the η case the estimate of the branching fraction for the radiative decay φ→ηγ is in agreement with the data, in the case of f
0, such agreement is obtained only under the hypothesis of a tetraquark scalar meson. 相似文献
4.
It is shown that the list of unusual mesons that are planned to be studied in photoproduction reactions can be supplemented
with I
G (J
PC)=2+ (2++) exotic states X
±(1600), which are natural to seek as manifestations of the ρ±ρ0 decay channels in the reactions γN → ρ±ρ0
N and γN → ρ±ρ0Δ. A classification of the ρ±ρ0 states according to their quantum numbers is presented. A model for the spin structure of the amplitudes for the reactions
γp → f
2(1270)p, γp → a
2
0
(1320)p, and γN → X
±(N, Δ) is proposed, and estimates are obtained for the corresponding cross sections. At E
γ≈6 GeV, it is found that σ(γP → f
2(1270)p)≈0.12 μb, σ(γp → a
2
0
(1320)p)≈0.25 μb, σ(γN → X
±
N → ρ±ρ0
N) ≈ 0.018 μb, and σ(γp → X
−Δ++ → ρ−ρ0Δ++≈0.031 μb. The problem of isolating signals from X
± states against the natural background that is associated with other channels of π±π0π+π− production is discussed. It is deduced that searches for exotic states X
±(2+ (2++)) in experiments at JLAB will be quite efficient—for example, the yield of about 2.8×106 events per month is expected to correspond to the estimated cross sections for the reactions γN → X
±
N → ρ±ρ0
N.
__________
Translated from Yadernaya Fizika, Vol. 63, No. 10, 2000, pp. 1904–1912.
Original Russian Text Copyright ? 2000 by Achasov, Shestakov. 相似文献
5.
The mechanism of 1:1 dipolar complexation of some long-chain aliphatic alcohols with chlorobenzene and acetic acids in a non-polar
medium is studied. The interaction dipole moment △→μ, the excess molar polarization ΔP and apparent complex formation constantK
app are evaluated following two independent methods. It is observed from the value of △→μ that the complex formation is mostly due to polarization interaction and is of the same type as involving lower alcohols.
ΔP andK
app are, however, of different nature compared to those in lower alcohols suggesting that the unlike molecules form relatively
stable linear linkage resulting in antiparallel orientation prior to forming complexes. 相似文献
6.
Antiproton proton annihilation reactions allow unique access to the moduli and phases of nucleon electromagnetic form factors
in the time-like region. We present the helicity amplitudes for the unequal-mass single-photon reaction pˉ → l
+
l
- in the s channel including the lepton mass. The relative signs of these amplitudes are determined using simple invariance properties.
Helicity amplitudes for one-photon exchange annihilation reaction pˉ → Bˉ are also given, where B is any spin-one-half particle with structure. Crossing relations between the ep → ep scattering and the pˉ → l
+
l
- annihilation channels are discussed and the crossing matrix for the helicity amplitudes is given. This matrix may be used
to verify known expressions for the space-like helicity amplitudes due to one-photon exchange. 相似文献
7.
On the basis of the experimental data on diffractive processes in πp, pp and pˉp collisions at intermediate, moderately high and high energies, we restore the scattering amplitude related to the t-channel exchange by vacuum quantum numbers by taking account of the diffractive s-channel rescatterings. At intermediate and moderately high energies, the t-channel exchange amplitude turns, with a good accuracy, into an effective pomeron which renders the results of the additive
quark model. At superhigh energies the scattering amplitude provides a Froissart-type behaviour, with an asymptotic universality
of cross sections such as σtot
πp/σtot
pp→ 1 at s→∞. The quark structure of hadrons being taken into account at the level of constituent quarks, the cross sections of pion
and proton (antiproton) in the impact parameter space of quarks, σπ(r
1⊥, r
2⊥; s) and σp(r
1⊥, r
2⊥, r
3⊥; s), are found as functions of s. These cross sections implicate the phenomenon of colour screening: they tend to zero at |r
i⊥−r
k⊥|→ 0. The effective colour screening radius for pion (proton) is found for different s. The predictions for the diffractive cross sections at superhigh energies are presented.
Received: 15 December 1998 相似文献
8.
M. Schumacher 《The European Physical Journal A - Hadrons and Nuclei》2006,30(2):413-422
The t-channel contribution to the difference of electromagnetic polarizabilities of the nucleon, (α - β)t, can be quantitatively understood in terms of a σ-meson pole in the complex t-plane of the invariant scattering amplitude A
1(s, t) with properties of the σ-meson as given by the quark-level Nambu-Jona-Lasinio model (NJL). Equivalently, this quantity may
be understood in terms of a cut in the complex t-plane where the properties of the σ-meson are taken from the ππ → σ → ππ, γγ → σ → ππ and Nˉ → σ → ππ reactions. This equivalence may be understood as a sum rule where the properties of the σ-meson as predicted by
the NJL model are related to the f
0(600) particle observed in the three reactions. In the following, we describe details of the derivation of (α - β)t making use of predictions of the quark-level NJL model for the σ-meson mass.
An erratum to this article is available at . 相似文献
9.
L. Roca C. Hanhart E. Oset U. -G. Meißner 《The European Physical Journal A - Hadrons and Nuclei》2006,27(3):373-380
The Λ(1520)-resonance has been recently studied in a unitarized coupled-channel formalism with πΣ(1385), KΞ(1530), ˉN and πΣ as constituents blocks. We provide a theoretical study of the predictions of this model in physical observables of
the pp → pK+K-p and pp → pK+π0π0Λ reactions. In particular, we show that the ratio between the π0π0Λ and K-p mass distributions can provide valuable information on the ratio of the couplings of the Λ(1520)-resonance to πΣ(1385) and
ˉN than the theory predicts. Calculations are done for energies which are accessible in an experimental facility like COSY at
Jülich or the developing CSR facility at Lanzhou. 相似文献
10.
W. Deconinck 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):653-655
An experimental search for the Θ(1540)- and Λ(1520)-resonance was performed in quasi-real photoproduction on deuterium at the HERMES experiment. While evidence for Θ(1540) was found in the decay channel pK
0
S→pπ
+
π
-, no evidence for the corresponding anti-particle was found. In some models it is expected that the Θ(1540) and the Λ(1520) have similar production mechanisms. The photoproduction cross-sections for the Λ(1520) in the decay channel Λ(1520)→pK
- and the corresponding anti-particle are determined. The partial photoproduction cross-sections for Λ(1520) and ˉ(1520) are obtained as σ
Λ(1520) = 65.3±8.8(stat)±6.9(syst)nb and σ
ˉ(1520) = 9.8±2.6(stat)±0.9(syst)nb, corresponding to a ratio R
Λ(1520) = σ
ˉ(1520)/σ
Λ(1520) = 0.15±0.05(stat)±0.02(syst). 相似文献
11.
S.V. Golovkin A.P. Kozhevnikov V.P. Kubarovsky V.F. Kurshetsov L.G. Landsberg V.V. Molchanov V.A. Mukhin S.V. Petrenko V.A. Senko D.V. Vavilov V.A. Victorov V.Z. Kolganov G.S. Lomkatsi A.F. Nilov V.T. Smolyankin 《The European Physical Journal A - Hadrons and Nuclei》1999,5(4):409-416
New data for the diffractive reaction p+N→ [Σ0
K
+] +N at E
p= 70 GeV were obtained with partially upgraded SPHINX setup. The data are in a good agreement with the results of our previous
study of this reaction. In the mass spectrum M(Σ0
K
+) a structure at the threshold region with a mass ∼1810 MeV and a distinct X(2000) peak with M= 1989 ± 6 MeV and γ= 91 ± 20 MeV are observed. Unusual features of the massive X(2000) state (narrow decay width, anomalously
large branching ratio for the decay channel with strange particle emission) make it a serious candidate for cryptoexotic pentaquark
baryon with hidden strangeness |qqqsˉs>. We also present new results on the narrow threshold structure X(1810) with M= 1807 ± 7 MeV and γ= 62 ± 19 MeV which is produced in the region of very small P
2
T < 0.01 GeV2. The possibility of the Coulomb production mechanism for X(1810) is discussed.
Received: 28 April 1999 相似文献
12.
The photoinduced optical absorption α of doped yttrium iron garnets (YIG) is investigated. It is found that the optical absorption
α at a wavelength of 1.1 μm depends on the wavelength of irradiating light in the range 0.6–1.9 μm. It is demonstrated that,
in the Y3Fe5O12 crystal with an acceptor Ba impurity, the photoinduced increase in α is due to the formation of Fe4+ ions in octahedral sites. The charge transfer occurs through photoexcitation of the 6
A
1g
(6
S) → 4
T
1g
(4
G) and 6
A
1g
(6
S) → 4
T
2g
(4
G) transitions of octahedral Fe3+ ions. In the crystal with a donor Si impurity, the increase in α is caused by the formation of Fe2+ ions upon photoionization of silicon.
__________
Translated from Fizika Tverdogo Tela, Vol. 43, No. 7, 2001, pp. 1233–1235.
Original Russian Text Copyright ? 2001 by Doroshenko, Nadezhdin. 相似文献
13.
Analytic expressions are obtained for vibrational transition moments of the first, second, and third orders using the eigenfunctions
in the second-order perturbation theory. These expressions can be used to solve the inverse electrooptical problem for the
12C16O2 molecule. The resonance interactions were taken into account by solving secular equations. The mixing coefficients for the
eigenfunctions were calculated with an accuracy of 0.1%. The experimental data on purely vibrational transition moments 〈μ〉2 used in the solution were obtained by averaging the data available in the literature with the weights that are inversely
proportional to the error, resulting in mean-square deviations of (0.1–10)%. Five parameters of the dipole moment of the Σ
u
symmetry were calculated using 29 values of the transition moments; five parameters of the πu symmetry were calculated using 27 values of the transition moments. The accuracy of the solution of the inverse problem is
characterized by the quantity Q=[Σ(δμ
i
(theor)
/δμ
i
(exp)
)2/(n-m)]1/2, where δμ
i
(theor)
is the deviation of calculations from the experiment, δμ
(exp)
i
is the experimental error, n is the number of the experimental data used, and m is the number of parameters smaller than unity.
__________
Translated from Optika i Spektroskopiya, Vol. 88, No. 5, 2000, pp. pp719–732.
Original Russian Text Copyright ? 2000 by Kolomiĭtsova, Lyaptsev, Shchepkin. 相似文献
14.
A. M. Tkachuk I. K. Razumova A. A. Mirzaeva A. V. Malyshev V. P. Gapontsev 《Optics and Spectroscopy》2002,92(1):67-82
Formation of the inverse population of working levels of 3-μm laser transition in LiY1−x
ErxF4 (x=0.003–1) crystals under CW InGaAs laser-diode pumping (0.967–0.982 μm) was investigated. Dependences of population of the
4
I
11/2 and 4
I
13/2 levels on the dopant concentration and pump power were studied theoretically and experimentally. Relative changes in populations
of the studied levels were experimentally monitored by measuring the steady-state spectra of IR crystal luminescence in the
wavelength range corresponding to 4
I
11/2→4
I
13/2 (2.7–2.8 μm), 4
I
11/2→4
I
15/2 (0.96–1.04 μm), and 4
I
13/2→4
I
15/2 (1.45–1.65 μm) transitions. Theoretical and experimental estimates of the rates of intracenter and intercenter relaxation
processes (migration, self-quenching, and up-conversion) with allowance for statistics of coupling of impurity centers in
the system were used to determine the energy-transfer mechanisms, elucidate the predominant mechanisms, and obtain microparameters
and concentration dependences of the energy-transfer rates and nonlinear coupling. Dependences of the steady-state population
of the levels of laser transition 4
I
11/2→4
I
13/2 on the dopant concentration and pumping power density were calculated within the context of rate balance equations for the
scheme with the five lowest excited states of erbium. Good agreement between theory and experiment was obtained.
__________
Translated from Optika i Spektroskopiya, Vol. 92, No. 1, 2002, pp. 73–88.
Original Russian Text Copyright ? 2002 by Tkachuk, Razumova, Mirzaeva, Malyshev, Gapontsev. 相似文献
15.
M.H. Thoma S. Leupold U. Mosel 《The European Physical Journal A - Hadrons and Nuclei》2000,7(2):219-223
Assuming that ρ-mesons exist in a quark-gluon plasma at temperatures close to the QCD phase transition, we calculate the
dilepton production rate from q-ˉq annihilation via a ρ-meson state using Vector Meson Dominance. The result is compared to the rates from direct q-ˉq annihilation and from π+-π− annihilation. Furthermore we discuss the suppression of low mass dileptons if the quarks assume an effective mass in the
quark-gluon plasma.
Received: 8 September 1999 / Revised version: 22 October 1999 相似文献
16.
A ππ, ˉKK, and ρρ(ωω) fully coupled channel model is used to predict the lowest isospin S, P, D, F-wave phase shifts and inelasticities
for elastic ππ scattering from threshold to 2.0 GeV. As input the S-matrix is required to exhibit poles corresponding to the
meson resonance table of the Particle Data Group. As expected, the ππ inelasticity is very strongly related to the opening
of the ˉK channel near 1 GeV, and the opening of ρρ(4π) and ωω(6π) channels in the 1.5 GeV region. The predictions of this model are
compared to the various elastic ππ→ππ amplitudes, that were obtained from analyses of π− p →π−π+n data. The role of the various resonances, in particular the glueball candidate f
0(1500) and the f
J(1710) is investigated.
Received: 19 November 1997 相似文献
17.
E. M. Drobyshevski 《Physics of Atomic Nuclei》2000,63(6):1037-1041
A possibility is considered of detecting Planckian particles carrying an electric charge Z≈10 and supposedly forming the dark matter of the Galactic disk, whence they are captured by combined action of the Sun and
the Earth into strongly elongated Earth-crossing orbits. The flux of such dark electric matter objects, daemons, at the Earth’s
orbit may reach f
⊕≈3×10−7cm−2s−1 at a velocity about 52 km/s. Negatively charged daemons are capable of catalyzing the fusion of light (Z
n<10) nuclei. The rate of capture (and fusion) of nuclei should be particularly high in a metallic phase. A detection system
is described that consists of beryllium plates 45 mm thick and 1200 cm2 in area coated with a ZnS(Ag) scintillator. It is assumed that the products of the fusion reaction 29Be → 18O that are ejected in amounts of up to about 104 from the points of daemon entrance and exit would give rise to scintillations with a delay of about 1μs. An exposure of the
system for 300 h revealed no event. The reason for the negative result can be (1) too optimistic an estimate of the flux (the
inclusion of some factors could lower it by 1.5–3 orders of magnitude) and (2) the poisoning of the catalyst by capture of
nuclei with Z
n≥10. The time required for the recovery of the daemon catalytic properties is estimated from the analysis of the energy release
in the Sun at no less than 3×10−7 s. The analysis of the total available data suggests that the daemon flux at the Earth is about 3×10−8 cm−2 s−1. The experiments will be continued.
From Yadernaya Fizika, Vol. 63, No. 6, 2000, pp. 1112–1117.
Original English Text Copyright ? 2000 by Drobyshevski.
This article was submitted by the author in English. 相似文献
18.
E.G. Drukarev M.G. Ryskin V.A. Sadovnikova 《The European Physical Journal A - Hadrons and Nuclei》1999,4(2):171-186
We calculate the contribution of pions to the $\bar qq$-expectation value κ(ρ) =<M|ˉq
q|M> in symmetric nuclear matter. We employ exact pion propagator renormalized by nucleon-hole and isobar-hole excitations. Conventional
straightforward calculation leads to the “pion condensation” at unrealistically small values of densities, causing even earlier
restoration of chiral symmetry. This requires a self-consistent approach, consisting in using the models, which include direct
dependence of in-medium mass values on κ(ρ), e.g. the Nambu–Jona-Lasinio–model. We show, that in the self-consistent approach
the ρ-dependence of the condensate is described by a smooth curve. The “pion condensate” point is removed to much higher values
of density. The chiral restoration does not take place at least while ρ < 2.8ρ0 with ρ0 being the saturation value. Validity of our approach is limited by possible accumulation of heavier baryons (delta isobars)
in the ground state of nuclear matter. For the value of effective nucleon mass at the saturation density we found m
*(ρ0) = 0.6m, consistent with nowadays results of other authors.
Received: 8 October 1998 相似文献
19.
E.L. Bratkovskaya W. Cassing L.A. Kondratyuk A. Sibirtsev 《The European Physical Journal A - Hadrons and Nuclei》1999,4(2):165-170
Within the meson-exchange model we calculate f
0-meson production cross section in πN and NN reactions and investigate the possibility for f
0 observation via the KˉK decay mode in pp collisions. Our studies indicate that an extraction of the f
0 signal is unlikely due to the large background from other reaction channels.
Received: 14 October 1998 / Revised version: 17 November 1998 相似文献
20.
S. Heinemeyer 《Pramana》2007,69(5):947-951
Electroweak precision measurements can provide indirect information about the possible scale of supersymmetry already at the
present level of accuracy. We review present day sensitivities of precision data in mSUGRA-type models with the gravitino
as the lightest supersymmetric particle (LSP). The χ
2 fit is based on M
W
, sin2
θ
eff, (g−2)
μ
, BR(b → sγ) and the lightest MSSM Higgs boson mass, M
h
. We find indications for relatively light soft supersymmetry-breaking masses, offering good prospects for the LHC and the
ILC, and in some cases also for the Tevatron.
相似文献