共查询到20条相似文献,搜索用时 11 毫秒
1.
Zhi-Gang Wang 《The European Physical Journal C - Particles and Fields》2009,59(3):675-681
In this article, we assume that there exist hidden charmed tetraquark states with spin–parity J
P=1−, and we calculate their masses with the QCD sum rules. The numerical result indicates that the masses of the vector hidden
charmed tetraquark states are about M
Z
=(5.12±0.15) GeV or M
Z
=(5.16±0.16) GeV, which are inconsistent with the experimental data on the π
+
χ
c1 invariant-mass distribution. The hidden charmed mesons Z
1, Z
2 or Z may be scalar hidden charmed tetraquark states, hadro-charmonium resonances or molecular states. 相似文献
2.
A precise investigation of radiative pion decay (π+ → e+νγ) in a pion beam from the meson factory of the Paul Scherrer Institute (Switzerland) was performed by the PIBETA Collaboration with the aid of the PIBETA detector. This resulted in finding 41 601 events of radiative pion decay in three kinematical regions. The absolute values of the branching ratio for radiative pion decay were determined in each of these regions. To a precision approximately four times higher than that known previously, the ratio of the axial-vector to the vector form factor was found to be γ ≡ F A /F V = 0.443 (15), the latter being fixed at F V = 0.0259. The number of events found in the kinematical region specified by photon energies of Eγ > 55.6 MeV, positron energies of E e > 20.0 MeV, and angles of θγ, e > 40° between the momenta of the corresponding particles (B region) was 5233. In region B, the measured branching ratio for radiative pion decay, Rπ→evγ(expt) = 11.6(3) × 10?8, proved to be smaller by eight standard deviations than that which follows from the Standard Model, Rπ→evγ (theor) = 14.34(1) × 10?8. 相似文献
3.
A. I. Ahmedov G. V. Fedotovich E. A. Kuraev Z. K. Silagadze 《Physics of Atomic Nuclei》2004,67(5):985-992
We consider the π+π?π0γ final state in electron-positron annihilation at c.m.s. energies not far from the threshold. Both initial-and final-state radiations of the hard photon are considered, but without interference between them. The amplitude for the final-state radiation is obtained by using the effective Wess-Zumino-Witten Lagrangian for pion-photon interactions valid for low energies. In real experiments, energies are never so small that ρ and ω mesons would have a negligible effect. So a phenomenological Breit-Wigner factor is introduced in the final-state radiation amplitude to account for the vector mesons' influence. Using radiative 3π production amplitudes, a Monte Carlo event generator was developed which could be useful in experimental studies. 相似文献
4.
The Mellin-Barnes representation is used to improve the theoretical estimate of mass corrections to the width of a light pseudoscalar
meson decay into a lepton pair, P → l
+
l
−. The full resummation of the terms ln(m
l
2/Λ2)(m
l
2/Λ2)
n
and (m
l
2/Λ2)
n
to the decay amplitude is performed, where m
l
is the lepton mass and Λ ≈ m
ρ is the characteristic scale of the P → γ*γ* form factor. The total effect of the mass corrections for the e
+
e
− channel is negligible and, for the μ+μ−channel, its order is of a few percent.
The text was submitted by the authors in English. 相似文献
5.
V. V. Sarantsev K. N. Ermakov V. I. Medvedev O. V. Rogachevsky S. G. Sherman 《Physics of Atomic Nuclei》2007,70(11):1885-1888
The cross sections for the reaction pp → ppπ + π ? are measured at several values of the incident-proton energy. The resulting values are compared with other results, including values obtained previously for a deuteriumtarget, as well as with the predictions of a theoreticalmodel. This comparison reveals that, at energies below 850 MeV, the use of the impulse approximation in extracting the cross sections for double pion production on a free nucleon from data obtained with deuteron targets is illegitimate. 相似文献
6.
A. K. Chaudhuri 《The European Physical Journal C - Particles and Fields》2009,61(2):331-338
In a hydrodynamic model, we have studied J/ψ production in Au+Au/Cu+Cu collisions at RHIC energy,
GeV. At the initial time, J/ψ’s are randomly distributed in the fluid. As the fluid evolves in time, the free streaming J/ψ’s are dissolved if the local fluid temperature exceeds a threshold temperature T
J/ψ
. Sequential melting of charmonium states (χ
c
, ψ
′ and J/ψ), with melting temperatures
, T
J/ψ
≈2T
c
and feed-down fraction F≈0.3, explains the PHENIX data on the centrality dependence of J/ψ suppression in Au+Au collisions. J/ψ
p
T
spectra and the nuclear modification factor in Au+Au collisions are also well explained in the model. The model however overpredicts
the centrality dependence of J/ψ suppression in Cu+Cu collisions by 20–30%. The J/ψ
p
T
spectra are underpredicted by 20–30%. The model predicts that in central Pb+Pb collisions at LHC energy,
GeV, J/ψ’s are suppressed by a factor of ∼10. The model predicted a J/ψ
p
T
distribution in Pb+Pb collisions at LHC is similar to that in Au+Au collisions at RHIC. 相似文献
7.
We re-evaluate the non-perturbative contribution to the thrust distribution in e
+
e
−→ hadrons, in the light of the latest experimental data and the recent NNLO perturbative calculation of this quantity. By
extending the calculation to NNLO+NLL accuracy, we perform the most detailed study to date of the effects of non-perturbative
physics on this observable. In particular, we investigate how well a model based on a low-scale QCD effective coupling can
account for such effects. We find that the difference between the improved perturbative distribution and the experimental
data is consistent with a 1/Q-dependent non-perturbative shift in the distribution, as predicted by the effective coupling model. Best fit values of α
s
(91.2 GeV)=0.1164−0.0026+0.0028 and α
0(2 GeV)=0.59±0.03 are obtained with χ
2/d.o.f.=1.09. This is consistent with NLO+NLL results but the quality of fit is improved. The agreement in α
0 is non-trivial because a part of the 1/Q-dependent contribution (the infrared renormalon) is included in the NNLO perturbative correction.
Address after 1 October 2008: Rudolf Peierls Centre for Theoretical Physics, 1 Keble Road, Oxford OX1 3NP, UK. 相似文献
8.
9.
In this paper, we calculate the branching ratio and direct CP asymmetry parameter of B
c
±→D
0
K
± in the framework of a perturbative QCD approach based on k
T
factorization. Besides the usual factorizable diagrams, both nonfactorizable and annihilation type contributions are taken
into account. We find that (a) the branching ratio is at the order of 10−5; (b) the tree annihilation diagrams and the penguin diagrams dominate the total contribution; and (c) the direct CP asymmetry
is about 7%, which can be tested in the Large Hadron Collider beauty experiments (LHC-b) at CERN. 相似文献
10.
Bastian Kubis Sebastian P. Schneider 《The European Physical Journal C - Particles and Fields》2009,62(3):511-523
Strong final-state interactions create a pronounced cusp in η′→η
π
0
π
0 decays. We adapt and generalize the non-relativistic effective field theory framework developed for the extraction of π
π scattering lengths from K→3π decays to this case. The cusp effect is predicted to have an effect of more than 8% on the decay spectrum below the π
+
π
− threshold. 相似文献
11.
The hyperfine splittings in heavy quarkonia are studied in a model-independent way using experimental data on dielectron widths.
Relativistic correlations are taken into account together with the smearing of spin-spin interaction. The radius of smearing
is fixed by known G/ψ−η
c(1S), ψ(2S)−η
c′(2S) splittings, which appears to be small, r
ss ≅ 0.06 fm. Nevertheless, even with such a small radius, substantial suppression of hyperfine splittings (∼50%) is observed
in bottomonium. For nS b
states (n = 1, 2, ..., 6), our predicted splittings (in MeV) are 28, 12, 10, 5, 6, 3. For the 3S and 4S charmonium states, the splittings 16(2) and 12(4) MeV are obtained.
The text was submitted by the authors in English. 相似文献
12.
L. I. Govor A. M. Demidov V. A. Kurkin I. V. Mikhailov 《Physics of Atomic Nuclei》2010,73(7):1101-1105
The results obtained by studying the angular distributions of gamma rays with respect to the neutron-beam axis in the reaction
178Hf(n, n′γ) involving the deexcitation of the K
π
= 0+ rotational bands of 178Hf are presented.New information about themultipole-mixing parameter δ in gamma transitions from the levels of these bands is obtained. The K
π
= 04+ band is constructed anew. The relationship between the parameter δ for the (2+0
n
−2+01) gamma transition and the energy gap Δ
n
= E
lev(2+0
n
) − E
lev(0+0
n
), on one hand, and the quasiparticle structure of the rotational band, on the other hand, is discussed for 178Hf on the basis of the quasiparticle-phonon model. 相似文献
13.
Lamia Benhabib 《The European Physical Journal C - Particles and Fields》2009,62(1):197-201
In ultra-relativistic Heavy-Ion Collisions (HIC), the properties of the quark gluon plasma (QGP) can be explored, in particular,
via measurements of neutral pions. The π
0 is an important probe for both proton and heavy ion physics. In the former case, π
0 production provides an important mean of testing pQCD as well as useful data to constrain current and future theoretical
models. In the latter case, π
0 measurements will serve as a baseline for exploring the nature of the HIC hard scattering. In the ALICE experiment, π
0 mesons are identified as they decay into two photons (π
0→γ
γ) using the high-resolution photon spectrometer (PHOS). PHOS will measure π
0 transverse momentum over a wide range, from hundreds of MeV/c to several tens of GeV/c. An estimation of π
0 production cross-section in proton–proton collisions is calculated in a next-to-leading order (NLO) approximation and first
presented. The π
0 geometrical acceptance and the identification efficiency along with the analysis on the invariant mass are the two important
correction factors for obtaining a realistic π
0 spectrum discussed in this paper. 相似文献
14.
E. M. Baldin 《Physics of Atomic Nuclei》2009,72(3):495-500
The product of the electron width of the J/ψ meson and the probability for its decay to an electron-positron pair was measured by using data from the KEDR experiment at the VEPP-4M electron-positron collider. The result was Γ ee × Γ ee /Γ = 0.3392 ± 0.0068(stat.) ± 0.0063(syst.) keV. 相似文献
15.
Sergey V. Donskov Anatoly K. Likhoded Alexey V. Luchinsky Vladimir D. Samoylenko 《Central European Journal of Physics》2010,8(3):393-399
The decay η′ → ηπ
0
π
0 is studied in the framework of isobar model. It is shown, that good agreement with the experiment is achieved if α
0- and σ-meson contributions are taken into account. The contribution of α
0-meson is dominant, but σ-meson is necessary to reproduce the form of the Dalitz plot. Instead of the usual Breit-Wigner form of σ-meson propagator we use parametrization of the ππ-amplitude, which satisfies analyticity, crossing, unitarity and chirality constraints. This amplitude has a pole in the complex
plane, which corresponds to σ-meson and describe experimental data on ππ-scattering in K
e4 decay. 相似文献
16.
A. Aprahamian 《Physics of Atomic Nuclei》2004,67(9):1750-1755
Low-lying K π = 0+ bands are one of the most fundamental excitation modes in the spectra of deformed nuclei; however, very little is known about the nature of these excitations. We report on some new lifetime measurements using the GRID technique at ILL, and high-precision (p, t) reactions to elucidate the character of low-lying K π = 0+ bands in deformed nuclei. We also present results from a recent calculation on the nature of 0+ states using the projected shell model. 相似文献
17.
N. Mironova-Ulmane U. Ulmanis A. Kuzmin I. Sildos M. Pärs M. Cestelli Guidi M. Piccinini A. Marcelli 《Physics of the Solid State》2008,50(9):1723-1726
The influence of dilution by diamagnetic ions on the magnetic ordering in single-crystal Co
c
Mg1−c
O solid solutions was studied by Raman spectroscopy and magneto-optical microscopy in a wide range of temperatures (6 < T < 200 K). Far infrared absorption measurements of antiferromagnetic resonance (AFMR) were also performed for pure CoO. It
was found that the domain structure and the contribution from Brillouin zone center magnons to Raman scattering and AFMR disappear
well below the Néel temperature, whose value was determined from neutron diffraction and magnetic susceptibility measurements.
The text was submitted by the authors in English. 相似文献
18.
A. I. Golokhvastov 《Physics of Atomic Nuclei》2004,67(12):2227-2244
It is shown that experimental data on the multiparticle production of negatively charged pions in proton-proton interactions at \(\sqrt s \leqslant 30 GeV\) do not involve significant indications of the existence of anycorrela tions between negatively charged pions, apart from those that are associated with momentum conservation and with interference. The multiplicity distributions in rapidity intervals, forward-backward correlations, and two-particle rapidity and transverse-momentum correlations do not contradict the independent production of negatively charged pions. No constraints on the multiplicity distributions of product particles follow from their independent production. 相似文献
19.
S. P. Baranov A. V. Lipatov N. P. Zotov 《The European Physical Journal C - Particles and Fields》2011,71(4):1631
We investigate the inclusive photoproduction of J/ψ mesons at HERA within the framework of the k
T
-factorization QCD approach. Our study is based on the color singlet model supplemented with the relevant off-shell matrix
elements and the CCFM and KMR unintegrated gluon densities in a proton and in a photon. Both the direct and resolved photon
contributions are taken into account. Our predictions are compared with the recent experimental data taken by the H1 and ZEUS
collaborations. Special attention is put on the J/ψ polarization parameters λ and ν, which are sensitive to the production dynamics. 相似文献
20.
K. G. Akhobadze T. S. Grigalashvili E. Sh. Ioramashvili E. S. Mailian M. I. Nikoladze L. V. Shalamberidze 《Physics of Atomic Nuclei》2003,66(2):362-367
Maximum fluctuations of charged-particle multiplicities over narrow rapidity intervals are investigated for high-P⊥ processes in π?A collisions (where A=H, D, C, Cu, Pb) at 40 GeV/c. The observed fluctuations are studied by the method of factorial moments. The results show that the factorial moments 〈F i 〉 vary in proportion to a power of the rapidity gap δy. This suggests that there are dynamical fluctuations in the processes under study. The experimental data are compared with theoretical results obtained on the basis of the model of quark-gluon strings by using the FRITIOF-7.02 package. 相似文献