共查询到20条相似文献,搜索用时 31 毫秒
1.
K. Mawatari B. Oexl Y. Takaesu 《The European Physical Journal C - Particles and Fields》2011,71(11):1783
Light gravitino productions in association with a neutralino (selectron) in e
+
e
− (e
−
γ) collisions are restudied in a scenario that the lightest supersymmetric particle is a gravitino and the produced neutralino
(selectron) promptly decays into a photon (electron) and a gravitino. We explicitly give the helicity amplitudes for the production
processes by using the effective goldstino interaction Lagrangian, and present the cross sections with different collision
energies and mass spectra. We also examine selection efficiencies by kinematical cuts and beam polarizations for the signal
and background processes, and show that the energy and angular distributions of the photon (electron) can explore the mass
of the t-channel exchange particle as well as the mass of the decaying particle at a future e
+
e
− (e
−
γ) collider. 相似文献
2.
Using the CompHEP package, we provide a detailed estimate of the influence of double e
+
e
− pair production (DPP) by photons on the propagation of ultra-high-energy electromagnetic cascades. We show that in the models
where the cosmic ray photon energy reaches a few 103 EeV, a refined DPP analysis may lead to a substantial difference in the predicted photon spectrum compared to the previous
rough estimates.
The article is published in the original. 相似文献
3.
Using form factors derived from the light-cone sum rules, we investigate B
s
→φℓ
+
ℓ
− (ℓ=e,μ,τ) in a single universal extra dimension model (UED). In UED, there is only one new parameter with respect to the Standard
Model (SM), which is the inverse of the compactification radius R of the extra dimension. In this work, the branching ratios, the dilepton invariant mass spectra, the forward–backward asymmetries,
and the lepton polarization asymmetries of B
s
→φℓ
+
ℓ
− are calculated. For a lower value of 1/R, there are some considerable discrepancies between the UED and SM. However, with the increase of 1/R, the effect of UED tends to diminish; in particular for 1/R≥1000 GeV, two models have approximately the same predictions. Compared with data from CDF for B
s
→φμ
+
μ
−, we find that the 1/R tends to be larger than 350 GeV. We also find that the zero crossing point of the forward–backward asymmetry of B
s
→φμ
+
μ
− becomes smaller, which would be an important platform for probing the UED effect. These results could be tested in the Large
Hadron Collider (LHC) at CERN and the future super-B factory. 相似文献
4.
M. I. Vysotsky 《JETP Letters》2010,92(1):15-20
The photon polarization operator in superstrong magnetic fields induces the dynamical photon “mass” which leads to screening
of Coulomb potential at small distances z ≪ 1/m, m is the mass of an electron. We demonstrate that this behavior is qualitatively different from the case of D = 2 QED, where the same formula for a polarization operator leads to screening at large distances as well. Because of screening
the ground state energy of the hydrogen atom at the magnetic fields B ≫ m
2/e
3 has the finite value E
0 = −me
4/2 ln2(1/e
6). 相似文献
5.
We review high-energy scattering processes that are sensitive to the hadronic structure of the photon, describing theoretical
predictions as well as recent experimental results. These processes include deep-inelastic electron-photon scattering ate
+
e
− colliders; and the production of jets, heavy quarks and isolated photons in the collision of real photons ate
+
e
− colliders, as well as in photon-photon collisions atep colliders. We also comment on minijet based calculations of totalγp andγγ cross-sections, and discuss the possibility that future lineare
+
e
− colliders might produce very large photon fluxes due to the beamstrahlung phenomenon; in the most extreme cases, we predict
more than one hadronicγγ event to occur at every bunch crossing. 相似文献
6.
A. V. Afanasev M. I. Konchatnij N. P. Merenkov 《Journal of Experimental and Theoretical Physics》2006,102(2):220-233
The single-spin beam and target asymmetries in the hard electroproduction process e
− + p → e
− + γ + p induced by the loop radiative corrections to the vertex part of lepton interaction are considered. The physical reason for
the appearance of such asymmetries is the nonzero imaginary part of the amplitude (on the level of radiative corrections)
caused by diagrams with photon radiation from the outgoing electron. We calculate the single-spin beam and target asymmetries
at a longitudinally polarized electron beam or at arbitrary polarizations of the target proton for the CLAS and HERMES experimental
conditions.
The text was submitted by the authors in English. 相似文献
7.
The production of electron-positron pairs by a photon propagating in a thermal bath in both zero and strong (B ≫ 4.41 × 1013 G) magnetic fields has been considered. The mean free path has been calculated for the high-energy photon propagating through
a thermodynamically equilibrium photon gas along the magnetic field lines so that the γ → e
−
e
+ decay is kinematically forbidden. It has been shown that the strong magnetic field suppresses the probability of the γγ′
→ e
−
e
+ process. The analyzed process can be useful for analysis of possible mechanisms of the generation of the e
−
e
+ plasma in the regions of the polar caps of magnetars. 相似文献
8.
V. N. Baier A. I. Mil’shtein R. Zh. Shaisultanov 《Journal of Experimental and Theoretical Physics》1997,84(1):29-34
We analyze the splitting of a photon with energy ω below the e
+
e
− pair-production threshold in an ultrastrong magnetic field. We use the amplitudes found by employing the operator diagrammatic
technique. In a field considerably above the critical values the process amplitudes become independent of the field strength.
A study of the polarization operator of a photon in an external field of arbitrary strength in the energy range considered
in the present investigation shows that there is only one set of polarizations of the initial and final photons for which
the splitting amplitude is nonzero.
Zh. éksp. Teor. Fiz. 111, 52–62 (January 1997) 相似文献
9.
The process pe
±→pe
±
γ with the photon emitted along the electron beam axis is used for luminosity measurement at HERA. In this paper the process
is calculated including one-loop QED radiative corrections. In the ZEUS experiment, both the electron and the photon can be
detected. Therefore both photon and electron spectra with and without the γ–e coincidence are analyzed. We also calculate the process pe
±→pe
±
l
−
l
+ which contributes to the background in the electron tagger. 相似文献
10.
The polarization of a bremsstrahlung photon during the processes ee
± → (eγ)e
± and ep → (eγ)p is calculated for peripheral kinematics in the high-energy limit, where the cross section does not decrease with the incident
energy. When the initial electron is unpolarized (longitudinally polarized), the final photon can be linearly (circularly)
polarized. The Stokes parameters of the photon polarization are calculated as a function of the kinematical variables of the
process: the energy of the recoil particle, the energy fraction of the scattered electron, and the polar and azimuthal angles
of the photon. The numerical results are given in the form of tables for typical values of the relevant kinematic variables.
The text was submitted by the authors in English. 相似文献
11.
E.O. Iltan 《The European Physical Journal C - Particles and Fields》2008,54(4):583-590
We study the charged lepton electric dipole moments in the Randall–Sundrum model where the leptons and the gauge fields are
accessible to the extra dimension. We observe that the electric dipole moment of the electron (muon; tau) reaches a value
of the order of 10-26 e cm (10-20 e cm; 10-20 e cm) with the inclusion of the lepton KK modes. 相似文献
12.
Summary A microwave coherent backscattering experiment has been carried out on Mirabelle, a weakly ionised plasma device, with the
objective of measuring the electron density fluctuation level. The experiment is a preliminary step in order to prepare the
detection system for a microwave stimulated backscattering experiment. The incident electromagnetic wave is focused in front
of a plane grid which excites ion acoustic or electron Bernstein waves inducing fluctuations in the plasma. The backscattering
signal is collected by the launching circuit and detected by homodyne mixing. The typical ratio of the scattered power to
the incident power is about 10−12 and the relative density fluctuations are of the order of δn
e/n
e=10−3 against a background electron density ofn
e=1–5·109 cm−3. The backscattering measurement is compared with Langmuir probe measurements. The spectral width of the backscattered signal
has also been studied, by taking into account effects due to the incident wave focusing and plasma wave damping.
The authors of this paper have agreed to not receive the proofs for correction 相似文献
13.
Simultaneous ionization and excitation of helium by electron impact is considered in an improved second Born approximation.
The wave function of the low energy ejected electron is obtained in the field of residual He+ ion in 2s-state. The calculation has been done for the processe
−+He→e
−+He+(2s)+e
− in the coplanar asymmetric geometry with Hartree-Fock wave function of Byron and Joachain for the helium ground state and
the results are compared with the absolute experimental data of Dupreet al [J. Phys.
B25, 259 (1992)] at ∼ 5.5 keV incident energy. Our results are found to increase the ratio of the recoil peak to binary peak
intensity by about 30% over the first Born results and thus to bring it closer to the experimental data. 相似文献
14.
V. I. Telnov 《Pramana》2007,69(6):957-961
At linear colliders, the e
+
e
− luminosity is limited by beam-collision effects, which determine the required emittances of beams in damping rings (DRs).
In γγ collisions at the photon collider, these effects are absent, and so smaller emittances are desirable. In the present damping
ring designs, nominal DR parameters correspond to those required for e
+
e
− collisions. In this note, I would like to stress once again that as soon as we plan the photon collider mode of ILC operation,
the damping ring emittances are dictated by the photon collider requirements — namely, they should be as small as possible.
This can be achieved by adding more wigglers to the DRs; the incremental cost is easily justified by a considerable potential
improvement of the γγ luminosity. No expert analysis exists as of now, but it seems realistic to obtain a factor five increase of the γγ luminosity compared to the ‘nominal’ DR design.
相似文献
15.
S. S. Bulanov 《Physics of Atomic Nuclei》2004,67(2):314-327
The dependence of K
S, L
→ π
+
π
−
γ decay probabilities on photon polarization is calculated. The phases of the terms of the amplitude that arise from the pion-pion
interaction are obtained by using a simple realistic model of pion-pion interaction via virtual ρ meson, instead of chiral perturbation theory (ChPT). The results are compared with those of other authors and the origin
of the discrepancies is explained. It is shown that the standard ChPT approach for K
S, L
→ π
+
π
−
γ decays cannot reproduce the contribution of the ρ meson to the P-wave ππ interaction. The departure of the photon spectrum from pure bremsstrahlung due to the pion-loop contribution to the electric
direct emission amplitude is calculated. It is shown that the interference between the terms of amplitude with different CP parity appears only when the photon is polarized (linearly or circularly). Instead of measuring the linear polarization,
the angular correlation between the π
+
π
− and e
+
e
− planes in K
S, L
→ π
+
π
−
e
+
e
− decay can be studied.
From Yadernaya Fizika, Vol. 67, No. 2, 2004, pp. 332–345.
Original English Text Copyright ? 2004 by Bulanov.
This article was submitted by the author in English. 相似文献
16.
Doubly-charged scalars, predicted in many models having exotic Higgs rep-resentations, can in general have lepton-number violating
(LFV) couplings. We show that by using an associated monoenergetic final state photon seen at a future linear e
−
e
− collider, we can have a clear and distinct signature for a doubly-charged resonance. The strength of the ΔL = 2 coupling can also be probed quite effectively as a function of the recoil mass of the doubly-charged scalar.
相似文献
17.
Saurabh D Rindani 《Pramana》2000,54(6):791-812
We obtain analytic expressions for the energy and polar-angle double differential distributions of a secondary lepton l
+ (l
−) arising from the decay of t(t) in e
+
e
− → tt with an anomalous tbW decay vertex. We also obtain analytic expressions for the various differential cross-sections with the lepton energy integrated
over. In this case, we find that the angular distributions of the secondary lepton do not depend on the anomalous coupling
in the decay, regardless of possible anomalous couplings occurring in the production amplitude for e
+
e
− → tt. Our study includes the effect of longitudinal e
− and e
+ beam polarization. We also study the lepton energy and beam polarization dependence of certain CP-violating lepton angular
asymmetries arising from an anomalous tbW decay vertex and compare them with the asymmetries arising due to CP-violation in the production process due to the top electric
or weak dipole moment. 相似文献
18.
We determined and tried to understand the spectroscopic and structural properties of small LiAr and LiAr2 molecules within a simple model considering LiAr as a result of interaction between a valence electron and a LiAr+ molecular ion. Potential energy curves, spectroscopic constants, and vibrational levels corresponding to the Li(2s, 2p, 3s, and 3p)+Ar dissociation are reported for the LiAr molecule. The depth of the potential well for the X
2Σ+ ground state is found to be 50 cm−1 (the corresponding experimental value is (42.5±1.2) cm−1 [1]). R
e is determined to be 9.36 a.u. (the experimental value is 9.24 a.u.). For the first excited state A, R
e = 4.97 a.u. and D
e = 993cm −1 (the corresponding experimental values are 4.68 a.u. and (925−40) cm−1, respectively [1]). The spacing between the vibrational levels for the ground and first excited states is in very good agreement
with the experiment. For the ground state, the difference between our results and the data of the most recent experiment is
about 1 cm−1. The model has been extended to study the LiAr2 molecule in two forms (linear and triangular). We have determined the potential energy surfaces of the states dissociating
to Li(2s, 2p)+Ar2 and thus found the triangular form to be more stable as compared to the linear one. We have also calculated the transition
energy between the ground state and first excited states of this molecule. The emission spectrum of the Li(2s)+Ar2→Li(2p)+Ar2 transition in both forms redshifts as compared to the Li(2s)→Li(2p) atomic transition. 相似文献
19.
We examine the sensitivity of eγ colliders (based on e
+
e
− linear colliders of c.m. energy 500 GeV) to the anomalous couplings of the Higgs to W-boson via the process e
−
γ → νWH. This has the advantage over e
+
e
− collider in being able to dissociate WWH vertex from ZZH. We are able to construct several dynamical variables which may be used to constrain the various couplings in the WWH vertex.
相似文献
20.
It is shown that the expected dip in the diffuse photon spectrum above the threshold of e
+
e
− pair production, i.e., at energies 1015–1017 eV, may be absent due to the synchrotron radiation by the electron component of the extragalactic ultrahigh-energy cosmic
rays (UHE CRs) in the Galactic magnetic field. The mechanism we propose requires small (<2×10−12 G) extragalactic magnetic fields and a large photon fraction in the UHE CRs. For a typical photon flux expected in top-down
scenarios of UHE CRs, the predicted flux in the region of the dip is close to the existing experimental limit. The sensitivity
of our mechanism to the extragalactic magnetic field may be used to improve existing bounds on the latter by two orders of
magnitude.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 8, 487–492 (25 October 1999)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献