共查询到20条相似文献,搜索用时 15 毫秒
1.
About ScienceDirect 《Physics letters. [Part B]》1990,240(3-4):213-600
We report on a measurement of the mass of the Z0 boson, its total width, and its partial decay widths into hadrons and leptons. On the basis of 25 801 hadronic decays and 1999 decays into electrons, muons or taus, selected over eleven energy points between 88.28 GeV and 95.04 GeV, we obtain from a combined fit to hadrons and leptons a mass of Mz=91.154±0.021 (exp)±0.030 (LEP) GeV, and a total width of Γz=2.536±0.045 GeV. The errors on Mz have been separated into the experimental error and the uncertainty due to the LEP beam energy. The measured leptonic partial widths are Γee=81.2±2.6 MeV, Γμμ=82.6± 5.8 MeV, and Γττ=85.7±7.1 MeV, consistent with lepton universality. From a fit assuming lepton universality we obtain Γℓ+ ℓ− = 81.9±2.0 MeV. The hadronic partial width is Γhad=1838±46 MeV. From the measured total and partial widths a model independent value for the invisible width is calculated to be Γinv=453±44 MeV. The errors quoted include both the statistical and the systematic uncertainties. 相似文献
2.
《The European Physical Journal C - Particles and Fields》2007,52(4):833-847
A search for the lepton flavour violating processes ep→μX and ep→τX is performed with the H1 experiment at HERA. Final states
with a muon or tau and a hadronic jet are searched for in a data sample corresponding to an integrated luminosity of 66.5 pb-1 for e+p collisions and 13.7 pb-1 for e-p collisions at a centre-of-mass energy of 319 GeV. No evidence for lepton flavour violation is found. Limits are derived
on the mass and the couplings of leptoquarks inducing lepton flavour violation in an extension of the Buchmüller–Rückl–Wyler
effective model. Leptoquarks produced in ep collisions with a coupling strength of λ=0.3 and decaying with the same coupling
strength to a muon–quark pair or a tau–quark pair are excluded at 95% confidence level up to masses of 459 GeV and 379 GeV,
respectively. 相似文献
3.
R. Akers G. Alexander J. Allison K. J. Anderson S. Arcelli A. Astbury D. Axen G. Azuelos J. T. M. Baines A. H. Ball et al. 《Zeitschrift fur Physik C Particles and Fields》1994,61(1):19-34
We present an update with increased statistics to our published analysis of hadronic and leptonic cross sections and of the leptonic forward-backward asymmetries ine
+
e
–
collisions. The published results were based on a total 454 000 hadronic and 58 000 leptonic events. This analysis adds 733 000 hadronic and 88 000 leptonic events recorded at theZ
0 peak in 1992 by the OPAL experiment at LEP. A model independent analysis ofZ
0 parameters based on an extension of the improved Born approximation leads to tests of lepton universality and gives an interpretation of the results within the Standard Model framework. We also present a model independent test for new physics. 相似文献
4.
S. Groote J.G. Körner A.A. Pivovarov 《The European Physical Journal C - Particles and Fields》2002,24(3):393-405
We propose a simple parameterization of the two-point correlator of hadronic electromagnetic currents for the evaluation
of the hadronic contributions to the muon anomalous magnetic moment. The parameterization is explicitly done in the Euclidean
domain. The model function contains a phenomenological parameter which provides an infrared cutoff to guarantee the smooth
behavior of the correlator at the origin in accordance with experimental data in e
+e- annihilation. After fixing a numerical value for this parameter from the leading order hadronic contribution to the muon
anomalous magnetic moment, the next-to-leading order results related to the vacuum polarization function are accurately reproduced.
The properties of the four-point correlator of hadronic electromagnetic currents as for instance the so-called light-by-light
scattering amplitude relevant for the calculation of the muon anomalous magnetic moment are briefly discussed.
Received: 14 December 2001 / Published online: 7 June 2002 相似文献
5.
《Physics letters. [Part B]》2005,610(3-4):183-191
The absolute branching fraction for the decay D+→μ+ν has been directly measured based on a data sample of about 33 pb−1 collected around with the BES-II detector at the BEPC collider. A total of 5321±149±160 D− mesons are reconstructed in nine hadronic decay modes. In the system recoiling against these singly tagged D− mesons, 2.67±1.74 purely leptonic decay events of D+→μ+νμ are observed. Those yield the branching fraction of , and a corresponding value of the pseudoscalar decay constant . 相似文献
6.
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
7.
A. V. Glushkov I. T. Makarov M. I. Pravdin I. E. Sleptsov D. S. Gorbunov G. I. Rubtsov S. V. Troitsky 《JETP Letters》2008,87(4):190-194
A sample of 33 extensive air showers (EASs) with estimated primary energies above 2 × 1019 eV and high-quality muon data recorded by the Yakutsk EAS array is analyzed. The observed muon density is compared event-by-event
to that expected from CORSIKA simulations for primary protons and iron using SIBYLL and EPOS hadronic interaction models.
The study suggests the presence of two distinct hadronic components, “light” and “heavy.” Simulations with EPOS are in good
agreement with the expected composition in which the light component corresponds to protons and the heavy component to iron-like
nuclei. With SIBYLL, simulated muon densities for iron primaries are a factor of ∼ 1.5 less than those observed for the heavy
component for the same electromagnetic signal. Assuming a two-component proton-iron composition and the EPOS model, the fraction
of protons with energies E > 1019 eV is 0.52−0.20+0.19 at the 95% C.L.
The text was submitted by the authors in English. 相似文献
8.
We study the production of scalar and vector leptoquarks in e−e− scattering. We use the most general couplings to the known fermions which are dimensionless, baryon and lepton number conserving, and SU(3)c SU (2)L U(1)Y invariant. Expressions are presented for production cross sections and predictions are given for future linear colliders. 相似文献
9.
《Physics letters. [Part B]》1996,380(3-4)
In a data sample of four million hadronic Z decays collected with the ALEPH detector at LEP, four Λb baryon candidates are exclusively reconstructed in the Λb → Λc+π− channel, with the Λc+ decaying into pK−π+,
, or Λπ+π+π−. The probability of the observed signal to be due to a background fluctuation is estimated to be 4.2 × 10−4. The mass of the Λb is measured to be 5614±21 (stat.) ± 4 (syst.) MeV/c2. 相似文献
10.
Yu. M. Bystritskiy É. A. Kuraev A. V. Bogdan F. V. Ignatov G. V. Fedotovich 《JETP Letters》2006,83(2):51-53
A new definition is proposed for the hadronic contribution to the muon anomalous magnetic moment that is based on the inclusion of the effects of vacuum polarization by leptons into the cross section for one-photon annihilation of a lepton pair into hadrons. The formula for the hadronic contribution includes the convolution of the measured cross section for annihilation into hadrons with a certain standard function. This remark concerns radiative correction to this function. A particular form has been proposed for this correction. It has been shown that the use of the new function makes it possible to reduce the uncertainty in such contributions due to radiative correctioins to δa h/a h ~ 10?4. 相似文献
11.
C. W. Darden H. Hasemann A. Krolzig W. Schmidt-Parzefall H. Schrder H. D. Schulz F. Selonke E. Steinmann R. Wurth 《Physics letters. [Part B]》1979,80(4-5)
New data for the reaction e+e−→(9.46) have been obtained using the DASP detector at the DORIS storage ring. The electronic width Γee is (1.5±0.4) keV. The branching ratio for the decay into muon pairs is (2.5 ± 2.1)%. Energy spectra for inclusive production of hadrons are given. 相似文献
12.
V. M. Belyaev 《Physics letters. [Part B]》1992,280(3-4)
We study a possible explanation of the tensor currents in the weak radiative
decay which was suggested recently by Bolotov et al. [Phys. Lett. B 243 (1990) 308] and Poblaguev [Phys. Lett. B 238 (1990) 108]. It can be shown that the supersymmetric particles can produce a tensor coupling at order (10−4−10−5)GF which is 2–3 orders of magnitude smaller than the estimates extracted from the experimental data. A reliable calculation of the hadronic matrix element
is done. The importance of a precision measurement of the tensor coupling in this decay is discussed as well as the possible relevance of the technicolour models. 相似文献
13.
George M. Fuller Alexander Kusenko Kalliopi Petraki 《Physics letters. [Part B]》2009,670(4-5):281-284
We consider sterile neutrinos with rest masses 0.2 GeV and with vacuum flavor mixing angles θ2>10−8 for mixing with τ-neutrinos, or 10−8<θ2<10−7 for mixing with muon neutrinos. Such sterile neutrinos could augment core collapse supernova shock energies by enhancing energy transport from the core to the vicinity of the shock front. The decay of these neutrinos could produce a flux of very energetic active neutrinos, detectable by future neutrino observations from galactic supernova. The relevant range of sterile neutrino masses and mixing angles can be probed in future laboratory experiments. 相似文献
14.
We have performed a holographic calculation of the hadronic contributions to the anomalous magnetic moment of the muon, using the gauge/gravity duality. As a gravity dual model of QCD with three light flavors, we study a U(3)L×U(3)R flavor gauge theory in the five-dimensional AdS background with a hard-wall cutoff. The anomalous (electromagnetic) form factors for the pseudo scalars, π0, η and η′, are obtained from the 5D Chern–Simons term of the gravity dual, which correctly reproduce the asymptotic behavior of the form factor, dictated by QCD. We find the total light-by-light contributions of pseudo scalars to the muon anomalous magnetic moment, , which is consistent with previous estimates, based on other approaches. 相似文献
15.
The lepton pair production via the quark-antiquark annihilation subprocess in collisions of beam antiproton with the proton
target at E
beam = 14 GeV is studied on the basis of the event sample simulated by PYTHIA6 generator. Different kinematical variables which
may be useful for the design of the muon system and the electromagnetic calorimeter of the detector of PANDA experiment at
FAIR, as well as for the study of proton structure functions in the available x-Q
2 kinematical region, are considered. It is also argued that the measurement of the total transverse momentum of a lepton-antilepton
system may provide important information about the intrinsic transverse momentum 〈k
T
〉 that appears due to the Fermi motion of quarks inside the nucleon. Another interesting possibility is the measurement of
the production rate of two or three lepton pairs in one event that can give the information about the rate of multiple quarks
interactions and the proton space structure. The problems due to the presence of fake leptons that appear from meson decays,
as well as due to the contribution of background QCD processes and minimum bias events, are also discussed. The set of cuts
which allows one to separate the events with the signal lepton pairs from different kind of background events is proposed.
The article is published in the original. 相似文献
16.
Harald Fritzsch 《Physics letters. [Part B]》1977,67(4):451-454
Introducing a new weak doublet of heavy leptons, one is led to a mixing of the various lepton states with respect to the weak interaction and subsequently to the violation of electron and muon number conservation (e.g., the decay μ→eγ). The new charged lepton can only decay via such a mixing and is therefore relatively long-lived (τ>10?11 sec). It can be produced singly in νμ nucleus scattering at high energies. Various other phenomenological consequences are discussed. 相似文献
17.
M. Davier S. Eidelman A. Höcker Z. Zhang 《The European Physical Journal C - Particles and Fields》2003,27(4):497-521
Vacuum polarization integrals involve the vector spectral functions which can be experimentally determined from two sources:
(i) e
+
e
-
annihilation cross sections and (ii) hadronic decays. Recently results with comparable precision have become available from CMD-2 on one side, and ALEPH, CLEO and OPAL
on the other. The comparison of the respective spectral functions involves a correction from isospin-breaking effects, which
is evaluated. After the correction it is found that the dominant spectral functions do not agree within experimental and theoretical uncertainties. Some disagreement is also found for the
spectral functions. The consequences of these discrepancies for vacuum polarization calculations are presented, with the
emphasis on the muon anomalous magnetic moment. The work includes a complete re-evaluation of all exclusive cross sections,
taking into account the most recent data that became available in particular from the Novosibirsk experiments and applying
corrections for the missing radiative corrections. 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 Standard Model predictions for the muon magnetic anomaly read where the errors account for the hadronic, light-by-light scattering and electroweak contributions. We observe deviations
with the recent BNL measurement at the 3.0 (e
+
e
-
) and 0.9 () level, when adding experimental and theoretical errors in quadrature.
Received: 27 August 2002 / Revised version: 10 January 2003 / Published online: 26 February 2003
RID="a"
ID="a" e-mail: davier@lal.in2p3.fr
RID="b"
ID="b" e-mail: simon.eidelman@cern.ch
RID="c"
ID="c" e-mail: hoecker@lal.in2p3.fr
RID="d"
ID="d" e-mail: zhangzq@lal.in2p3.fr 相似文献
18.
The dependence of the strangeness production on the number of nucleons involved in the annihilation process is investigated experimentally in and 4He annihilation at rest. In He, annihilations with the involvement of one and several nucleons (B=0 and B1 baryonic number, respectively) are identified. Strangeness enhancement factors, i.e., ratios of K±, , K0* and ϕ meson yields in 4He to the same yields in H, are derived for final states containing 4 charged mesons (2π+2π−, π+π−πK±, π+π−K+K−). This work completes a previous investigation concerning charged kaon production in meson final states without neutral mesons. The results are compared with our previous ones and with results found in experiments on heavy-ion collisions. It is put in evidence that the strangeness content in the energy blob created by the annihilation has a lower or higher intensity depending on the reaction channel: for instance, π+π−πK± production increases with B and π+π−K+K− production decreases. The maximum enhancement factor (about 22) is found for π+π−π−K+ without neutral mesons. This value (as well as that concerning π+π+π−K−) is definitely higher than the values predicted by theoretical investigations based on the formation of a highly excited hadronic gas in the annihilation on few nucleons and values found in heavy-ion collisions. Is it the signature of the formation of quark–gluon plasma? 相似文献
19.
《Physics letters. [Part B]》1996,380(3-4)
During the last 1995 data acquisition period at LEP, the DELPHI experiment collected an integrated luminosity of 5.9 pb−1 at centre-of-mass energies of 130 GeV and 136 GeV. Radiative leptonic events (e, μ, τ) with high energy photons were studied and compared to Standard Model predictions. The data were used to search for charged excited leptons decaying through an electromagnetic transition. No significant signal was found. From the search for pair produced excited leptons, the limits me* > 62.5 GeV/c2, mμ* > 62.6 GeV/c2 and mτ* > 62.2 GeV/c2 at 95% confidence level were established. For single excited lepton production, upper limits on the ratio λ/ml* of the coupling of the excited charged lepton to its mass were derived. 相似文献
20.
We report on the observation of 1 3PJ (χb) production in the reaction ′→γχb→γγ→γγ(e+e− or μ+μ−). The data were recorded with the nonmagnetic CUSB detector at the Cornell Electron Storage Ring, CESR. We observe 124 γγ events with either an electron or muon pair in the final state. In the γγ correlation plot about 40% of the events cluster around (120, 430) MeV. 相似文献