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1.
The multiple hadron production in the events induced by the heavy primary quarks in e+e- annihilation is reconsidered with account of corrected experimental data. A new value for the multiplicity in bb̄ events is presented on the basis of pQCD estimates.  相似文献   

2.
We examine distributions of leptons produced in e+e- collisions, by a family nonuniversal extra gauge boson Z, suggested by the model, and by other neutral gauge bosons occurring in left–right symmetric models and in superstring-inspired E6 models. We discuss how to distinguish the models by examining the couplings to fermions of the extra Z-boson through its leptonic production cross sections and asymmetries. We show how the universality violation inherent in the model enhances the discovery potential of Z at future planned and proposed e+e- colliders.  相似文献   

3.
Spin correlations are carefully investigated in elastic e+e- scattering in QED, for initially polarized as well as unpolarized particles, with emphasis placed on energy or speed of the underlying particles involved in the process. An explicit expression is derived for the corresponding transition probabilities in closed form to the leading order. These expressions differ from those obtained from simply combining the spins of the relevant particles, which are of kinematic nature. It is remarkable that these explicit results obtained from quantum field theory show a clear violation of Bell's inequality at all energies, in support of quantum theory in the relativistic regime. We hope that our explicit expression will lead to experiments, of the type described in the bulk of this paper, that monitor speed.  相似文献   

4.
The electromagnetic radiation emitted by colliding beams is expected to play an important role at the next generation of high energy e+e- linear colliders. Focussing on the simplest process, e+e-→μ+μ-, we show that, for suitable machine parameters and luminosity, radiative effects like initial state radiation (ISR) and beamstrahlung can be used to search for resonant graviton modes of the Randall–Sundrum model in an efficient manner.  相似文献   

5.
The littlest Higgs model is the most economical one among various little Higgs models. In the context of the littlest Higgs model, we study the process e+e-→e+e-H at the ILC and calculate the correction of the littlest Higgs model to the cross section of this process. The results show that, in the favorable parameter spaces preferred by the electroweak precision data, the value of the relative correction is in the range from a few percent to tens percent. In most cases, the correction is large enough to reach the measurement precision of the ILC. Therefore, the correction of the littlest Higgs model to the process e+e-→e+e-H might be detected at the ILC, which will give an ideal way to test the model. PACS 12.60.Nz; 14.80.Mz; 12.15.Lk; 14.65.Ha  相似文献   

6.
We consider semi-inclusive unpolarized DIS for the production of charged kaons and the different possibilities to test the conventionally used assumptions s-s̄=0 and Dd K+-K-=0. The tests considered have the advantage that they do not require any knowledge of the fragmentation functions. We also show that measurements of both charged and neutral kaons would allow for the determination of the kaon fragmentation functions Dq K++K- solely from SIDIS measurements, and we discuss the comparison of (Du-Dd)K+-K- obtained independently in SIDIS and e+e- reactions. All analyses are performed in LO and NLO in QCD. The feasibility of the tests to HERMES SIDIS data is considered. PACS 12.38.Bx; 13.85.Ni  相似文献   

7.
We reconsider QED radiative corrections (RC) to the π0→e+e- decay width. One kind of RC investigated earlier has a renormalization group origin and can be associated with the final state interaction of electron and positron. It determines the distribution of lepton pair invariant masses in the whole kinematic region. The other type of RC has a double-logarithmic character and is related to almost on-mass-shell behavior of the lepton form factors. The total effect of RC for π0→e+e- decay is estimated to be 3.2%, and for η→e+e- decay it is 4.3%. PACS  13.25.Cq; 12.38.Lg; 12.38.-t  相似文献   

8.
Understanding the mechanism of electroweak symmetry breaking and the origin of boson and fermion masses is among the most pressing questions raised in contemporary particle physics. If these issues involve one (several) Higgs boson(s), a precise measurement of all its (their) properties will be of prime importance. Among those, the Higgs coupling to matter fermions (the Yukawa coupling). At a linear collider, the process e+e-→tt̄H will allow a direct measurement of the top-Higgs Yukawa coupling. We present a realistic feasibility study of the measurement in the context of the TESLA collider. Four channels are studied and the analysis is repeated for several Higgs mass values within the range 120–200 GeV/c 2. PACS 13.66.Jn; 14.65.Ha; 14.80.Bn  相似文献   

9.
We present an estimate of the cross-section for the exclusive production of a ρL 0-meson pair in e+e- scattering, which will be studied in the future high-energy International Linear Collider. For this aim, we complete calculations of the Born order approximation of the amplitudes γ* L,T(Q1 2* L,T(Q2 2)→ρL 0ρL 0, for arbitrary polarization of virtual photons and longitudinally polarized mesons, in the kinematical region s≫-t,Q1 2,Q2 2. These processes are completely calculable in the hard region Q1 2,Q2 2≫Λ2 QCD, and we perform most of the calculations in an analytical way. The resulting cross-section turns out to be large enough for this process to be measurable with foreseen luminosity and energy, for Q1 2 and Q2 2 in the range of a few GeV2.  相似文献   

10.
The littlest Higgs model with T-parity predicts the existence of the T-odd particles, which can only be produced in pairs. We consider pair production of the T-odd leptons in a future high energy linear e+e- collider (ILC). Our numerical results show that, as long as the T-odd leptons are not too heavy, they can be copiously produced and their possible signals might be detected via the processes e+e-→L̄iLj in future ILC experiments.  相似文献   

11.
The littlest Higgs (LH) model predicts the existence of the doubly charged scalars , which generally have large flavor changing couplings to leptons. We calculate the contributions of Φ±± to the lepton flavor violating (LFV) processes li→ljγ and li→ljlklk, and we compare our numerical results with the current experimental upper limits on these processes. We find that some of these processes can give severe constraints on the coupling constant Yij and the mass parameter MΦ. Taking into account the constraints on these free parameters, we further discuss the possible lepton flavor violating signals of at high energy linear e+e- collider (ILC) experiments. Our numerical results show that the possible signals of might be detected via the subprocesses e±e±→l±l± in future ILC experiments.  相似文献   

12.
We present the combined results on electron-pair production in 158 GeV/n Pb-Au ( = 17.2 GeV) collisions taken at the CERN SPS in 1995 and 1996, and give a detailed account of the data analysis. The enhancement over the reference of neutral meson decays amounts to a factor of 2.31 for semi-central collisions (28 ) when yields are integrated over m > 200 MeV/c2 in invariant mass. The measured yield, its stronger-than-linear scaling with , and the dominance of low pair pt strongly suggest an interpretation as thermal radiation from pion annihilation in the hadronic fireball. The shape of the excess centring at 500 MeV/c2, however, cannot be described without strong medium modifications of the meson. The results are put into perspective by comparison to predictions from Brown-Rho scaling governed by chiral symmetry restoration, and from the spectral-function many-body treatment in which the approach to the phase boundary is less explicit.Received: 2 March 2005, Published online: 8 June 2005  相似文献   

13.
Electron-hydrogen scattering has been investigated in Debye plasma environment employing the close-coupling approximation. Two models, viz., 6-state CCA and 9-state CCA have been used. Plasma screening has been taken into account via Debye-Hückel model potential. The lowest lying 1De^1{\rm D}^{{\rm e}} auto-detaching resonance of the hydrogen negative ion has been successfully predicted for various plasma conditions. The resonant state changes to shape resonance for Debye scattering lengths less than a critical value.  相似文献   

14.
Standard model (SM) CP asymmetries in B→Kℓ+- are expected to be very small. This feature could help in the understanding of new physics scenarios which predict the existence of CP odd phases in various Wilson coefficients. In this paper we have analyzed the B→Kℓ+- decay in scenarios beyond the SM where the Wilson coefficients have new CP odd phases. The sensitivity of the CP asymmetries on these new weak phases is discussed. PACS 13.20.He; 12.60.-i; 13.88.+e  相似文献   

15.
A new evaluation of the hadronic vacuum polarization contribution to the muon magnetic moment is presented. We take into account the reanalysis of the low-energy e + e -annihilation cross section into hadrons by the CMD-2 Collaboration. The agreement between e + e -and spectral functions in the channel is found to be much improved. Nevertheless, significant discrepancies remain in the center-of-mass energy range between 0.85 and , so that we refrain from averaging the two data sets. The values found for the lowest-order hadronic vacuum polarization contributions are where the errors have been separated according to their sources: experimental, missing radiative corrections in e + e -data, and isospin breaking. The corresponding Standard Model predictions for the muon magnetic anomaly read where the errors account for the hadronic, light-by-light (LBL) scattering and electroweak contributions. The deviations from the measurement at BNL are found to be (1.9 ) and (0.7 ) for the e + e -- and -based estimates, respectively, where the second error is from the LBL contribution and the third one from the BNL measurement.Received: 7 September 2003, Published online: 30 October 2003  相似文献   

16.
The W + W- production cross section is measured from a data sample corresponding to a total integrated luminosity of 683 pb-1, collected by the ALEPH experiment at LEP at centre-of-mass energies from 183 to 209 GeV. Individual cross sections for the different topologies arising from W decays into leptons or hadrons, as well as the total W-pair cross section are given at eight centre-of-mass energies. The results are found to be in agreement with recently developed Standard Model calculations at the one percent level. The hadronic branching fraction of the W boson is measured to be = 67.13 0.37(stat.) 0.15(syst.)%, from which the CKM matrix element is determined to be 0.958 0.017(stat.) 0.008(syst.)Received: 1 October 2004, Published online: 15 November 2004  相似文献   

17.
Born differential cross sections and the lowest-order radiative correction to them are obtained in the kinematics of large-angle final photon emissions in high-energy electron-positron annihilation processes. Taking into account the possible emission of real soft and hard photons in collinear kinematics, we show the validity of the Drell-Yan form of the differential cross section with the nonsinglet structure functions of the initial leptons. The leading and next-to-leading contribution to the cross sections is obtained. The relevant numerical estimations are presented. The text was submitted by the authors in English.  相似文献   

18.
19.
The observation of three events for the decay Σ+→pμ+μ- with a dimuon invariant mass of 214.3 ± 0.5 MeV by the HyperCP Collaboration implies that a new particle X may be needed to explain the observed dimuon invariant mass distribution. We show that there are regions in the SUSY-FCNC parameter space where the A0 1 in the NMSSM can be used to explain the HyperCP events without contradicting all the existing constraints from the measurements of the kaon decays, and the constraints from K0–K̄0 mixing are automatically satisfied once the constraints from kaon decays are satisfied. PACS  14.80.Cp; 12.60.Jv; 14.20.Jn  相似文献   

20.
We present predictions for the K-α scattering length obtained within the framework of the multiple-scattering approach. Evaluating the pole position of the K-α scattering amplitude within the zero-range approximation, we find a loosely bound K-α state with a binding energy of ER = - 2,..., - 7 MeV and a width ΓR = 11,..., 18 MeV. We propose to measure the K-α scattering length through the final-state interaction between the α and K--meson produced in the reaction dd↦αK+K-. It is found that the K-α invariant-mass distribution from this reaction at energies near the threshold provides a new tool to determine the s-wave K-α scattering length.  相似文献   

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