共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
M. Chekerker A. F. Santos Faqir C. Khanna M. Ladrem 《International Journal of Theoretical Physics》2017,56(9):2838-2847
Parity violation implies that physics laws are not invariant under spatial coordinate reversal. Electron-positron scattering is a process that displays parity violation. Using the Thermo Field Dynamics formalism this scattering at finite temperature is analyzed. The transition amplitude is calculated as a function of temperature. The parity violation at very high temperatures tend to go to zero. 相似文献
3.
Electron-positron pair production from vacuum in an electromagnetic field created by two counterpropagating focused laser pulses interacting with each other is analyzed. The dependence of the number of produced pairs on the intensity of a laser pulse and the focusing parameter is studied with a realistic three-dimensional model of the electromagnetic field of the focused wave, which is an exact solution of the Maxwell equations. It has been shown that e+e? pair production can be experimentally observed when the intensity of each beam is I~1026 W/cm2, which is two orders of magnitude lower than that for a single pulse. 相似文献
4.
D. V. Matvienko 《Journal of Experimental and Theoretical Physics》2009,109(1):53-56
A parameterization of the amplitude of the two-photon production of 1++ and 1?+ vector resonances V in the e + e ? → e + e ? V reaction has been obtained. The differential (in momentum transfer) scattering cross section dσ/dQ 2 has been found for this reaction in the equivalent-photon approximation. The result obtained is model-independent. 相似文献
5.
A. A. Likhoded 《Physics of Particles and Nuclei》2008,39(1):37-63
The potential of experiments at e + e ? colliders to search for a signal of a new pseudoscalar Higgs boson and to study its CP properties is analyzed. A new Higgs boson coupling to the b quark and τ lepton, which is parameterized in a model-independent way as m b /v(a + iγ5 b), is chosen to be an indicator of its CP nature. We study the e + e ? → τ+τ?vv, e + e ? → b \(\bar b\)vv, and e + e ? → e + e ? b \(\bar b\) processes highly sensitive to anomalous Higgs boson couplings due to the dominant contributions from the vector boson fusion processes W*W* → H and Z*Z* → H in the central region. It is shown that the study of polarization of particles in the final state could help to separate the contributions from the scalar and pseudoscalar Higgs bosons. For instance, the consideration of the cascade decays of τ leptons in the e + e ? → τ+τ?vv process allows one to determine reliably the CP state of the Higgs boson as well as the value and the sign of the b parameter. As a result of our analysis, we develop a search strategy for a signal of a new pseudoscalar Higgs boson in future experiments at linear e + e ? colliders, which will allow one to understand the CP nature of the Higgs boson and set the bounds on its couplings to fermions. 相似文献
6.
7.
C. M. Carloni-Calame S. Moretti F. Piccinini D. A. Ross 《The European Physical Journal C - Particles and Fields》2009,62(2):453-364
We compute the full one-loop EW contributions of
entering the electron–positron into two b-quarks and one gluon cross section at the Z peak and LC energies. We include both factorisable and non-factorisable virtual corrections, photon bremsstrahlung but not
the real emission of W
± and Z bosons. Their importance for the measurement of α
S from jet rates and shape variables is explained qualitatively and illustrated quantitatively. Their impact on the forward–backward
asymmetry is also analysed.
Work supported in part by the U.K. Science and Technology Facilities Council (STFC), by the European Union (EU) under contract
MRTN-CT-2006-035505 (HEPTOOLS FP6 RTN) and by the Italian Ministero dell’Istruzione, dell’Università e della Ricerca (MIUR)
under contract 2006020509_004.
An erratum to this article can be found at 相似文献
8.
C.?M.?Carloni-Calame S.?Moretti F.?Piccinini D.?A.?Ross 《The European Physical Journal C - Particles and Fields》2009,62(2):355-364
We compute the full one-loop EW contributions of \({\mathcal{O}}(\alpha_{\mathrm{S}}\alpha_{\mathrm{EM}}^{3})\) entering the electron–positron into two b-quarks and one gluon cross section at the Z peak and LC energies. We include both factorisable and non-factorisable virtual corrections, photon bremsstrahlung but not the real emission of W ± and Z bosons. Their importance for the measurement of α S from jet rates and shape variables is explained qualitatively and illustrated quantitatively. Their impact on the forward–backward asymmetry is also analysed. 相似文献
9.
Although the standard model (SM) is extremely successful, there are various motivations for considering the physics beyond the SM. For example, the SM includes neither dark energy nor dark matter, which has been confirmed through astrophysical observations. Examination of the dark sector, which contains new, light, weakly-coupled particles at the GeV scale or lower, is well motivated by both theory and dark-matter detection experiments. In this mini-review, we focus on one particular case in which these new particles can interact with SM particles through a kinematic mixing term between U(1) gauge bosons. The magnitude of the mixing can be parameterized by a parameter ?. Following a brief overview of the relevant motivations and the constraints determined from numerous experiments, we focus on the light dark sector phenomenology at low-energy high-luminosity e + e ? colliders. These colliders are ideal for probing the new light particles, because of their large production rates and capacity for precise resonance reconstruction. Depending on the details of a given model, the typical observed signatures may also contain multi lepton pairs, displaced vertices, and/or missing energy. Through the use of extremely large data samples from existing experiments, such as KLOE, CLEO, BABAR, Belle, and BESIII, the magnitude of the mixing can be parameterized by a parameter ? < 10?4–10?3 constraint can be obtained. Obviously, future experiments with larger datasets will provide opportunities for the discovery of new particles in the dark sector, or for stricter upper limits on ?. Once the light dark sector is confirmed, the particle physics landscape will be changed significantly. 相似文献
10.
A. V. Luchinsky 《Physics of Atomic Nuclei》2005,68(8):1400-1404
One of the processes involving the inclusive production of the vector-charmonium states J/ψ. and ψ(2S) in two-photon electron-positron annihilation at \(\sqrt s = 10.6 GeV\) is studied on the basis of the singlet model. Analytic expressions are derived for respective differential cross sections, and numerical values of the total cross sections are given, along with graphs that represent the distributions of cross sections in the scattering angle and in the vector-meson energy. It is shown that these distributions differ substantially from the analogous distributions for charmonium production in one-photon electron-positron annihilation. For this reason, the process under consideration can readily be isolated despite the smallness caused by an extra power of α. 相似文献
11.
Sa Thi Lan Anh Phan Thi Ha Trang Trieu Quynh Trang Ha Huy Bang 《International Journal of Theoretical Physics》2018,57(7):2015-2021
In this work, we study the effects of the vector unparticle on e+e?→ γa processes. From the numerical results, we show that the cross-section with unparticle effects should be about 1014 ??1023 times larger than the one without unparticle effects. This could have important implication for axion like particle searches in near future experiments. 相似文献
12.
Some aspects of supersymmetric particles pair production in e + e ?-annihilation in processes \(e^ + + e^ - \to \tilde l^ + + \tilde l^ -\), \(e^ + + e^ - \to \tilde \chi ^ + + \tilde \chi ^ -\) are studied. Aparatus, in which long-lived charged particles deceleraition and accumulation take place, is considered. Binding energy of a negatively charged particle with nucleus is obtained. Probability of β-decay of a nucleus bounded with a long-lived negatively charged particle is considered. 相似文献
13.
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
14.
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
15.
16.
A. I. Akhmedov 《Russian Physics Journal》2005,48(6):605-617
The production of the lightest stable neutralino in the reaction
with general mixing of the higgsino and gaugino is studied. General formulas for differential cross sections are presented.
The dependence of the effective differential cross section on the photon energy spectrum and electron mass is illustrated
together with the dependence of the effective total cross section on the beam energy for three different scenarios.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 48–57, June, 2005. 相似文献
17.
L. Barzè G. Balossini C. Bignamini C. M. Carloni Calame G. Montagna O. Nicrosini F. Piccinini 《The European Physical Journal C - Particles and Fields》2011,71(6):1680
High-luminosity e
+
e
− colliders at the GeV scale (flavor factories) have been recently recognized to be an ideal environment to search for a light
weakly coupled vector boson U (dark photon) emerging in several new physics models. At flavor factories a particularly clean channel is the production
of the U boson in association with a photon, followed by the decay of the U boson into lepton pairs. Beyond the approximations addressed in previous works, we perform an exact lowest order calculation
of the signal and background processes of this channel. We also include the effect of initial- and final-state QED corrections
neglected so far, to show how they affect the distributions of experimental interest. We present new results for the expected
statistical significance to a dark photon signal at KLOE/KLOE-2 and future super-B factories. The calculation is implemented in a new release of the event generator BabaYaga@NLO, which is available for full
event simulations and data analysis. 相似文献
18.
19.
A. E. Dorokhov 《Physics of Particles and Nuclei Letters》2010,7(4):229-234
Experimental and theoretical progress concerning the rare decay π0 → e
+
e
− is briefly reviewed. It includes the latest data from KTeV and a new model-independent estimate of the decay branching which
show the deviation between experiment and theory at the level of 3.3σ. The predictions for η and η′ decays into lepton pair
are presented. We also comment on the impact on the pion rare decay estimate of the data of BABAR collaboration on the pion
transition form factor at large momentum transfer. 相似文献
20.
The total and differential cross sections for the production of triply charmed Ωccc baryons in e+e? annihilation are calculated at the Z-boson pole. 相似文献