共查询到20条相似文献,搜索用时 15 毫秒
1.
Zhi-Gang Wang 《The European Physical Journal C - Particles and Fields》2009,61(2):299-309
We calculate the strong coupling constant g among the decuplet baryons, the octet baryons and the pseudoscalar mesons in the heavy baryon chiral perturbation theory
with the light-cone QCD sum rules, and we study the strong decays Σ
*→Λ
π,Σ
π. The numerical value of the strong coupling constant g is consistent with our previous calculation; the central values lead to small SU(3) breaking effects, less than 6%; and no definitive conclusion can be drawn due to the large uncertainties. 相似文献
2.
Junfeng Sun Dongsheng Du Yueling Yang 《The European Physical Journal C - Particles and Fields》2009,60(1):107-117
The B
c
→J/ψ
π, η
c
π decays are studied with the perturbative QCD approach. It is found that the form factors
and
for the B
c
→J/ψ, η
c
transitions and the branching ratios are sensitive to the parameters ω, v, f
J/ψ
and
, where ω and v are the parameters of the charmonium wave functions for a Coulomb potential and the harmonic-oscillator potential, respectively,
and f
J/ψ
and
are the decay constants of the J/ψ and η
c
mesons, respectively. The large branching ratios and the clear signals of the final states make the B
c
→J/ψ
π, η
c
π decays the prospective channels for measurements at the hadron colliders. 相似文献
3.
The e
+
e
− → π
+
π
−
π
+
π
− cross section is calculated for energies of 0.65 ≤ √s ≤ 1 GeV in the framework of the generalized hidden local symmetry model. The calculations are compared with the data of CMD-2
and BaBaR. It is shown that the inclusion of heavy isovector resonances ρ(1450) and ρ(1700) is necessary for reconciling calculations
with the data. It is found that, at √s ≈ 1 GeV, the contributions of the above resonances are much larger, by a factor of 30, than the ρ(770) one, and amount to
a considerable fraction ∼0.3–0.6 of the latter at √s ∼ m
ρ.
The text was submitted by the authors in English. 相似文献
4.
Dian-Yong Chen Xiang Liu Xue-Qian Li 《The European Physical Journal C - Particles and Fields》2011,71(11):1808
To solve the discrepancy between the experimental data on the partial widths and lineshapes of the dipion emission of ϒ(4S) and the theoretical predictions, we suggest that there is an additional contribution, which had not been taken into account
in previous calculations. Noticing that the mass of ϒ(4S) is above the production threshold of B[`(B)]B\bar{B}, the contribution of the sequential process
\varUpsilon(4S)? B[`(B)]? \varUpsilon(nS)+S?\varUpsilon(nS)+p+p-\varUpsilon(4S)\to B\bar{B}\to \varUpsilon(nS)+S\to\varUpsilon(nS)+\pi^{+}\pi^{-} (n=1,2) may be sizable, and its interference with that from the direct production would be important. The goal of this work
is to investigate if a sum of the two contributions with a relative phase indeed reproduces the data. Our numerical results
on the partial widths and the lineshapes
d\varGamma(\varUpsilon(4S)?\varUpsilon(2S,1S)p+p-)/d(mp+p-)d\varGamma(\varUpsilon(4S)\to\varUpsilon(2S,1S)\pi^{+}\pi^{-})/d(m_{\pi ^{+}\pi^{-}}) are satisfactorily consistent with the measurements; thus the role of this mechanism is confirmed. Moreover, with the parameters
obtained by fitting the data of the Belle and BaBar collaborations, we predict the distributions dΓ(ϒ(4S)→ϒ(2S,1S)π
+
π
−)/dcosθ, which have not been measured yet. 相似文献
5.
The decays η → 3π
0 and η → π
0
π
+
π
− are considered within the isobar model. It is shown that, in order to explain the branching ratio and the shape of the Dalitz
plot for the decay η′ → 3π
0, it is sufficient to take into account the contributions of the σ and a
0 mesons. The inclusion of the σ meson is necessary for reproducing the shape of the distribution over the Dalitz plot. The branching ratio for the decay
η′ → π
0
π
+
π
− is obtained. The predictions for the distributions over the Dalitz plot for this decay are presented. These predictions depend
strongly on model parameters. 相似文献
6.
The results of recent experiments performed at KEK, Brookhaven National Laboratory, the Institute for High-Energy Physics
(Protvino), and CERN to study the reaction π
−
p → π
0
π
0
n are analyzed in detail. For S-wave pion-pion scattering in the channel of isospin I=0, new data are obtained for the phase shift δ
0
0
and the inelasticity parameter η
0
0
. Difficulties that arise in using, for the amplitudes of the S and D waves of the final π
0
π
0 system, physical solutions selected on the basis of partial-wave analyses are discussed. It is noteworthy that other solutions
are preferable in principle in the region of the invariant mass m of the π
0
π
0 system above 1 GeV. With the aim of clarifying the situation and further studying the properties of the f
0(980) resonance, it is proposed to perform, in the reaction π
−
p → π
0
π
0
n, an especially careful examination of the m region in the vicinity of the
threshold.
__________
Translated from Yadernaya Fizika, Vol. 67, No. 7, 2004, pp. 1380–1391.
Original Russian Text Copyright ? 2004 by Achasov, Shestakov. 相似文献
7.
The branching ratios and photon spectra of the rare processes ρ(ω) → π
0
π
0
γ, ρ(ω) → ηπ
0
γ are calculated in the framework of the standard local quark Nambu-Jona-Lasinio model. Three types of diagrams are considered:
the quark box and the pole diagrams with scalar (σ, α
0(980)) and vector (ρ, ω) mesons. The obtained estimates for the widths of the processes ρ(ω) → π
0
π
0
γ are in satisfactory agreement with existing experimental data. Predictions are made for the widths of the processes ρ(ω) → ηπ
0
γ.
The text was submitted by the authors in English. 相似文献
8.
Current and upcoming experiments should improve the sensitivity to e
α
→e
β
γ decays by an order of magnitude. This paper assumes that one of the τ→e
β
γ decays is observed, and explores the structure and consequences of the required new flavoured couplings. In simple models
(a low-scale seesaw, leptoquarks) it is shown that the dipole vertex function is proportional to a product of flavoured matrices
from the Lagrangian (a “Jarlskog-like” invariant), provided that the loop particles are weakly coupled to the Higgs. Secondly,
if the dipole vertex function has a hierarchical structure, this might imply that only some of the τ→e
β
γ modes can be observed, due to the “approximate zero” implied by the bound on μ→eγ. The assumptions underlying this potential test of a hierarchical structure are discussed. 相似文献
9.
Swapan Das 《Pramana》2010,75(4):665-674
The cross-section for the π
+
π
−
π
0 invariant mass distribution in the γp reaction in the GeV region is calculated. This reaction is assumed to proceed through the formation of the ω-meson in the intermediate state, because the production cross-section for this meson in the γp reaction in the GeV region is significant and it has a large branching ratio (88.8%) in the π
+
π
−
π
0 channel. The cross-sections for this reaction are calculated using the energy-dependent reaction amplitude, f
γp→ωp(0), extracted from the latest ω-meson photoproduction data. We use established procedure to calculate other factors, like width and propagator of the ω-meson, so that our calculation can provide reliable cross-section. The calculated results reproduce the measured π
+
π
−
π
0 invariant mass distribution spectra in the γp reaction. 相似文献
10.
11.
Yu-Ming Wang M. Jamil Aslam Cai-Dian Lü 《The European Physical Journal C - Particles and Fields》2009,59(4):847-860
The exclusive weak decay of Λ
b
→Λ
γ and Λ
b
→Λ
l
+
l
− are investigated in the Appelquist–Cheng–Dobrescu model, which is an extension of the standard model in the presence of universal
extra dimensions. Employing the transition form factors obtained in the light-cone sum rules, we analyze how the invariant-mass
distribution, the forward–backward asymmetry and the polarization asymmetry of the Λ baryon of these decay modes can be used to constrain the only additional free parameter with respect to the standard model,
namely, the radius, R, of the extra dimension. Our results indicate that the Kaluza–Klein modes can lead to approximately 25% suppression of the
branching ratio of Λ
b
→Λ
γ; however, their contributions can bring about 10% enhancement to the decay rate of Λ
b
→Λ
l
+
l
−. It is shown that in the present scenario the zero position of the forward–backward asymmetry of Λ
b
→Λ
μ
+
μ
− is sensitive to the compactification parameter R, while the measurement of polarizations of Λ baryon in the Λ
b
decays are not a useful tool to provide any valuable information for the universal extra-dimension model. 相似文献
12.
In this article, we study the decays ψ′ → J/ψπ
+
π
− and η′c → η
c
π
+
π
− by taking into account the chiral symmetry breaking effects, the final-state interactions and the heavy-quark symmetry. We
can confront the predictions of the η′c → η
c
π
+
π
− decay width and differential decay width with the experimental data in the future, and obtain powerful constraints on the
chiral breaking effects and the final-state interactions, and test the heavy-quark symmetry. 相似文献
13.
Murugesh Duraisamy Alexander L. Kagan 《The European Physical Journal C - Particles and Fields》2010,70(4):921-925
CLEO-c measurements of the timelike form factors F
π
, F
K
at ?s=3.671\sqrt{s}=3.671 GeV provide a direct probe of power corrections (PC’s) at energies near m
B
. PC’s in F
π,K
and B→Kπ,ππ are separated into perturbative and soft parts. In F
π,K
the latter are ≥O(10) larger. A PC fit to the B→Kπ,ππ data also yields a ≥O(10) soft-to-perturbative hierarchy for the QCD penguin PC’s. Hence, both can be attributed to dominance of the soft-overlap
between energetic (approximately) back-to-back collinear partons, and consistency of the B→Kπ,ππ fit with the Standard Model appears to be naturally realized. The CP asymmetries SKs p0S_{K_{s} \pi^{0}}, CKs p0C_{K_{s} \pi^{0}} are well determined, providing a clean test for new physics. 相似文献
14.
15.
S. Rai Choudhury A. S. Cornell Naveen Gaur 《The European Physical Journal C - Particles and Fields》2008,58(2):251-259
Flavor changing neutral current (FCNC) decays of the B-meson are a very useful tool for studying possible physics scenarios beyond the standard model (SM), where of the many FCNC
modes radiative, purely leptonic and semi-leptonic decays of the B-meson are relatively clean tests. Within this context, the BELLE collaboration has measured the process B→K
*
γ and also searched for the B→K
1(1270)γ process. Theoretical analyses of these processes are yielding similar values of the relevant form factors. In this work we
have used this upper bound in studying the angular correlations for the related semi-leptonic decay mode B
−→K
1−(1270)(→ρ
0
K
−)ℓ
+
ℓ
−, where we have used the form factors that have already been estimated for the B→K
1(1270)γ mode. Note that the additional form factors that are required were calculated using large energy effective theory (LEET). 相似文献
16.
Jianhua Wang Kang Li Sayipjamal Dulat Yi Yuan Kai Ma 《International Journal of Theoretical Physics》2012,51(8):2639-2647
By studying the scattering process of scalar particle pion on the noncommutative scalar quantum electrodynamics, the non-commutative amendment of differential scattering cross-section is found, which is dependent of polar-angle and the results are significantly different from that in the commutative scalar quantum electrodynamics, particularly when cosθ∼±1. The non-commutativity of space is expected to be explored at around ΛNC∼TeV. 相似文献
17.
D. Babusci H. Czy? F. Gonnella S. Ivashyn M. Mascolo R. Messi D. Moricciani A. Nyffeler G. Venanzoni KLOE-?Collaboration 《The European Physical Journal C - Particles and Fields》2012,72(3):1917
A possibility of KLOE-2 experiment to measure the width
\varGammap0 ?gg\varGamma_{\pi^{0} \to\gamma\gamma} and the π
0
γγ
∗ form factor F(Q
2) at low invariant masses of the virtual photon in the space-like region is considered. This measurement is an important test
of the strong interaction dynamics at low energies. The feasibility is estimated on the basis of a Monte-Carlo simulation.
The expected accuracy for
\varGammap0 ?gg\varGamma_{\pi^{0} \to\gamma\gamma} is at a per cent level, which is better than the current experimental world average and theory. The form factor will be measured
for the first time at Q
2≤0.1 GeV2 in the space-like region. The impact of these measurements on the accuracy of the pion-exchange contribution to the hadronic
light-by-light scattering part of the anomalous magnetic moment of the muon is also discussed. 相似文献
18.
We study the deep inelastic process ν
τ
+ N → τ
− + X (with N ≡ (n + p)/2 an isoscalar nucleon), in the context of the two-Higgs doublet model Type II (2HDM(II)). We discuss the contribution to
the total cross-section of diagrams, in which a charged Higgs boson is exchanged. We present results which show strong dependence
of such contributions on tan β and M
H
±. We show that for tan β ≈ 150 and M
H
± ≈ 300 GeV, the contribution of the charged Higgs boson exchange diagrams to the cross-section of the charged current inclusive
ν
τ
N collision can become important. We find that this contribution for an inclusive dispersion generated through the collision
of an ultra-high-energy tau-neutrino with E
ν
≈ 1021 eV on a target nucleon can be as large as 40% of the value of the contribution of the W
± exchange diagrams, provided M
H
± ≈ 300 GeV and tan β ≈ 150. Such enhancement and the induced variation on the mean inelasticity 〈y〉CC could lead to sizeable effects in the acceptance of cosmic tau-neutrino detectors at experiments such as HiRes, PAO, and
the CRTNT, which are anchored to the ground, and at experiments such as EUSO and OWL, which are proposed to orbit around the
Earth. We also compare the contribution to σ
H+tot from the different allowed initial quarks and we show that the contribution from the bottom quark dominates by far. This
means that the H
± contribution practically always gives a top quark in the final state. Such a large component of the cross-section having
a top quark event in the final state could have recognizable features in the EAS experiments.
相似文献
19.
Ahmed Ali Fernando Barreiro Javier Llorente 《The European Physical Journal C - Particles and Fields》2011,71(9):1737
We present an analysis with improved sensitivity to the light charged Higgs (mH+ < mt-mbm_{H^{+}} < m_{t}-m_{b}) searches in the top quark decays t→bH
+→b(τ
+
ν
τ
)+c.c. in the t[`(t)]t\bar{t} and single t/[`(t)]t/\bar{t} production processes at the LHC. In the Minimal Supersymmetric Standard Model (MSSM), one anticipates the branching ratio
B (H+ ?t+nt) @ 1{\mathcal{B}} (H^{+} \to\tau^{+}\nu_{\tau})\simeq1 over almost the entire allowed tanb\tan\beta range. Noting that the τ
+ arising from the decay H
+→τ
+
ν
τ
are predominantly right-polarized, as opposed to the τ
+ from the dominant background W
+→τ
+
ν
τ
, which are left-polarized, a number of H
+/W
+→τ
+
ν
τ
discriminators have been proposed and studied in the literature. We consider hadronic decays of the τ
±, concentrating on the dominant one-prong decay channel τ
±→ρ
±
ν
τ
. The energy and p
T
of the charged prongs normalised to the corresponding quantities of the ρ
± are convenient variables which serve as τ
± polariser. We use the distributions in these variables and several other kinematic quantities to train a boosted decision
tree (BDT). Using the BDT classifier, and a variant of it called BDTD, which makes use of decorrelated variables, we have
calculated the BDT(D)-response functions to estimate the signal efficiency vs. the rejection of the background. We argue that
this chain of analysis has a high sensitivity to light charged Higgs searches up to a mass of 150 GeV in the decays t→bH
+ (and charge conjugate) at the LHC. For the case of single top production, we also study the transverse mass of the system
determined using Lagrange multipliers. 相似文献
20.
R. A. Ryutin V. A. Petrov A. E. Sobol 《The European Physical Journal C - Particles and Fields》2011,71(5):1667
We study the possibilities to analyse the data on leading neutrons production at first LHC runs. These data could be used
to extract from it π
+
p and π
+
π
+ cross-sections. In this note we estimate relative contributions of π, ρ and a
2 reggeons to charge exchanges and discuss related problems of measurements. 相似文献