共查询到20条相似文献,搜索用时 93 毫秒
1.
We discuss the possibility of a precision measurement of vacuum polarization in t-channel radiative Bhabha scattering at
a high luminosity collider. For illustration, the achievable precision is estimated for the BaBar experiment at PEP-II and
for the OPAL experiment at LEP.
Received: 6 June 2001 / Published online: 21 September 2001 相似文献
2.
The branching ratios of the
and decays have been measured using the 1991–1995 data recorded with the OPAL detector at LEP. These branching ratios are measured
simultaneously using three selection criteria and are found to be where the first error is statistical and the second is systematic.
Received: 4 December 1997 / Published online: 2 June 1998 相似文献
3.
The photon structure function has been measured using data taken by the OPAL detector at centre-of-mass energies of 91 GeV, 183 GeVand 189 \GeV, in ranges of 1.5–30.0 GeV (LEP1), and 7.0–30.0 GeV (LEP2), probing lower values of x than ever before. Since previous OPAL analyses, new Monte Carlo models and new methods, such as multi-variable unfolding,
have been introduced, reducing significantly the model dependent systematic errors in the measurement. The results do not
conclusively prove, but are completely consistent with, the presence of a rise in at low-x as expected from QCD.
Received: 9 June 2000 / Published online: 13 November 2000 相似文献
4.
Using the OPAL detector at LEP, the running of the effective QED coupling α(t) is measured for space-like momentum transfer from the angular distribution of small-angle Bhabha scattering. In an almost
ideal QED framework, with very favourable experimental conditions, we obtain:
where the first error is statistical, the second is the experimental systematic and the third is the theoretical uncertainty.
This agrees with current evaluations of α(t). The null hypothesis that α remains constant within the above interval of -t is excluded with a significance above 5σ. Similarly, our results are inconsistent at the level of 3σ with the hypothesis
that only leptonic loops contribute to the running. This is currently the most significant direct measurement where the running
α(t) is probed differentially within the measured t range.
Received: 2 March 2005, Revised: 30 August 2005, Published online: 3 November 2005 相似文献
5.
The Michel parameters of the leptonic decays are measured using the OPAL detector at LEP. The parameters , , (with ) and are extracted from the energy spectra of the charged decay leptons and from their energy–energy correlations. A new method
involving a global likelihood fit of Monte Carlo generated events with complete detector simulation and background treatment
has been applied to the data recorded at center-of-mass energies close to corresponding to an integrated luminosity of 155 pb. If e- universality is assumed and inferring the polarization from neutral current data, the measured Michel parameters are: where the value of has been constrained using the published OPAL measurements of the leptonic branching ratios and the lifetime. Limits on non-standard coupling constants and on the masses of new gauge bosons are obtained. The results are in
agreement with the V–A prediction of the Standard Model.
Received: 25 June 1998 / Published online: 1 March 1999 相似文献
6.
《The European Physical Journal C - Particles and Fields》2006,47(3):589-596
We describe the method of measuring the integrated luminosity of the e+e- collider DAΦNE, the Frascati φ-factory. The measurement is done with the KLOE detector selecting large angle Bhabha scattering
events and normalizing them to the effective cross section. The e+e-→e+e-(γ) cross section is calculated using different event generators which account for the
radiative initial and final state corrections, and the φ resonance contribution. The accuracy of the measurement is 0.6%,
where 0.3% comes from systematic errors related to the event counting and 0.5% from theoretical evaluations of the cross section. 相似文献
7.
8.
Measurements of the lepton polarization and forward-backward polarization asymmetry near the Z resonance using the OPAL detector are described. The measurements are based on analyses of and decays from a sample of 144,810 candidates corresponding to an integrated luminosity of 151 pb. Assuming that the lepton decays according to V–A theory, we measure the average polarization near to be and the polarization forward-backward asymmetry to be , where the first error is statistical and the second systematic. Taking into account the small effects of the photon propagator,
photon-Z interference and photonic radiative corrections, these results can be expressed in terms of the lepton neutral current asymmetry
parameters:
These measurements are consistent with the hypothesis of lepton universality and combine to give . Within the context of the Standard Model this combined result corresponds to . Combing these results with those from the other OPAL neutral current measurements yields a value of .
Received: 5 March 2001 / Published online: 6 July 2001 相似文献
9.
G. Abbiendi et al. 《The European Physical Journal C - Particles and Fields》2003,26(3):321-330
A novel method of determining the mass of the W boson in the channel is presented and applied to 667 pb-1 of data recorded at center-of-mass energies in the range 183-207 GeV with the OPAL detector at LEP. The measured energies
of charged leptons and the results of a new procedure based on an approximate kinematic reconstruction of the events are combined
to give: where the first error is statistical and the second is systematic. The systematic error is dominated by the uncertainty on
the lepton energy, which is calibrated using data, and the parameterization of the variables used in the fitting, which is
obtained using Monte Carlo events. Both of these are limited by statistics.
Received: 13 March 2002 / Published online: 31 October 2002 相似文献
10.
G. Abbiendi et al. 《The European Physical Journal C - Particles and Fields》2000,14(2):199-212
The total hadronic cross-section for the interaction of real photons, hadrons, is measured for centre-of-mass energies GeV. The cross-section is extracted from a measurement of the process hadrons, using a luminosity function for the photon flux together with form factors for extrapolating to real photons ( GeV). The data were taken with the OPAL detector at LEP at centre-of-mass energies , 172$ and 183 GeV. The cross-section is compared with Regge factorisation and with the energy dependence observed in p and pp interactions. The data are also compared to models which predict a faster rise of compared to p and pp interactions due to additional hard interactions not present in hadronic collisions.
Received: 3 June 1999 / Published online: 6 April 2000 相似文献
11.
The branching ratios of the decay of the lepton to five charged hadrons have been measured with the OPAL detector at LEP using data collected between 1991 and 1995
at centre-of-mass energies close to the resonance. The branching ratios are measured to be
where the first error is statistical and the second systematic.
Received: 4 June 1998 / Published online: 11 March 1999 相似文献
12.
《Physics letters. [Part B]》1991,260(3-4):438-446
We calculate the QED bremmstrahlung corrections beyond O() for small-angle scattering. These corrections are of vital importance for measuring the luminosity and consequently the total cross sections in LEP experiments. They are dominated by the second order leading-logarithmic contributions. We calculate them with the high technical precision 0.02% and we show that they depend strongly of the details of experiment cut-off. We propose a practical method of introducing the O(2) correction calculated in this paper into current procedures of the luminosity measurement at LEP. The remaining overall QED uncertainty is estimated to be 0.3%. This estimate includes 0.2% due to pure bremsstrahlung and 0.1% due to light pair production but does not include hadronic uncertainty in the photon vaccum polarization. 相似文献
13.
N.N. Nikolaev J. Speth V.R. Zoller 《The European Physical Journal C - Particles and Fields》2002,22(4):637-646
High-energy virtual photon–virtual photon scattering can be viewed as an interaction of small size color dipoles from the
beam and target photons, which makes scattering at high energies (LEP, LEP200 and NLC) an indispensable probe of the short distance properties of the QCD pomeron
exchange. Based on the color dipole representation, we investigate the consequences for the scattering of the incorporation of asymptotic freedom into the BFKL equation which makes the QCD pomeron a series of isolated
poles in the angular momentum plane. The emerging color dipole BFKL–Regge factorization allows us to relate in a model-independent
way the contributions of each BFKL pole to scattering and DIS off protons. Numerical predictions based on our early works on the color dipole BFKL phenomenology of
DIS on protons are in good agreement with the experimental data on the photon structure function and the most recent data on the cross section from the OPAL and L3 experiments at LEP200. We discuss the role of non-perturbative dynamics and predict a pronounced effect
of the Regge-factorization breaking due to large unfactorizable non-perturbative corrections to the perturbative vacuum exchange.
We comment on the salient features of the BFKL–Regge expansion for scattering including the issue of the decoupling of subleading BFKL poles and the soft plus rightmost hard BFKL pole dominance.
Received: 9 January 2001 / Revised version: 25 September 2001 / Published online: 7 December 2001 相似文献
14.
《Physics letters. [Part B]》1986,177(1):97-105
A complete analysis of EM radiative corrections to Bhabha scattering near the Z0 is presented Compact analytic formulae are given which include exact one-loop results and soft-and-collinear photon effects resummed to all orders. Detection of back-to-back e+e− pairs can be therefore used as a high precision monitor of luminosity at LEP/SLC energies. 相似文献
15.
The LEP2 data set on the Bhabha process is analyzed with the aim to detect the signals of the heavy virtual Z′ gauge boson. The state interacting with the left-handed Standard Model doublets and called the chiral Z′ is investigated. This particle was introduced already as the low-energy state allowed by the renormalizability. The contribution
of the chiral-Z′ state to the Bhabha process is described by two parameters: the coupling to electrons and the Z–Z′ mixing angle. The sign-definite one-parameter observable is proposed to measure the Z′ coupling to the electron current. The one-parameter fit of the data shows no signals of the particle. The alternative two-parameter
fit of the differential cross sections is also performed. It also shows no chiral-Z′ signals. The comparisons with other fits are discussed.
The text was submitted by the authors in English. 相似文献
16.
G. Abbiendi et al. 《The European Physical Journal C - Particles and Fields》2003,26(3):331-344
The process is studied using data collected by the OPAL detector at LEP between the years 1997 and 2000. The data set corresponds to
an integrated luminosity of 672.3 pb-1 at centre-of-mass energies lying between 181 GeV and 209 GeV. Total and differential cross-sections are determined and found
to be in good agreement with the predictions of QED. Fits to the observed angular distributions are used to set limits on
parameters from several models of physics beyond the Standard Model such as cut-off parameters, contact interactions of the
type , gravity in extra spatial dimensions and excited electrons. In events with three photons in the final state the mass spectrum
of photon pairs is investigated. No narrow resonance is found and limits are placed on the product of the production cross-section and branching ratio.
Received: 22 July 2002 / Published online: 8 November 2002 相似文献
17.
G. Abbiendi et al. The OPAL Collaboration 《The European Physical Journal C - Particles and Fields》2001,20(3):445-454
A sample of 3.73 million hadronic Z decays, recorded with the OPAL detector at LEP in the years 1991–95, has been used to
search for a narrow resonance corresponding to the decay of the meson into . The mesons are reconstructed in the decay channel with . No evidence for a narrow resonance is found. A limit on the production of narrow in hadronic Z decays is derived:
Received: 16 January 2001 / Published online: 28 May 2001 相似文献
18.
A. V. Kopylov I. V. Orekhov V. V. Petukhov A. E. Solomatin 《Physics of Atomic Nuclei》2006,69(11):1829-1832
Experiments sensitive to pp neutrinos from the Sun are very promising for precise measurement of the mixing angle ϑ
12. A νe
− scattering experiment (XMASS) and/or a charged-current experiment (indium detector) can measure the flux of electron pp neutrinos. One can find the total flux of pp neutrinos from a luminosity constraint after the contributions of 7Be and CNO neutrinos to the total luminosity of the Sun are measured. A radiochemical experiment utilizing a lithium target
has high sensitivity to the CNO neutrinos; thus, it has a good promise for precise measurement of the mixing angle and for
a test of the current theory of evolution of the stars.
The text was submitted by the authors in English. 相似文献
19.
R. Göbel W. Arnold Th. Frommhold R. Stock Th. Weber U. Kneissl F. Steiper C. Kozhuharov P. Kienle 《Zeitschrift für Physik A Hadrons and Nuclei》1993,345(1):79-88
The cross sections for Bhabha and Møller scattering have been investigated in the energy range 2.1–2.4 MeV using monoenergetic positrons and electrons to search for hypothetical resonances superimposed to the continuum predicted by quantum electro dynamics. Bhabba-to-Mott, Møller-to-Mott and Møller-to-Bhabha cross section ratios were measured. The Bhabha-to-Mott ratios could be determined with statistical errors of typically 1% and remaining systematic errors not exceeding the statistical ones. No resonances in Bhabha scattering were observed. Limits for the intrinsic widths of hypothetical resonances are given. For the first time upper limits are deduced from our data for hypothetical resonances in the Møller scattering cross section in the MeV range. Additionally, Møller-to-Bhabha cross section ratios could be determined with good precision. A good agreement between the experimental and theoretical Møller-to-Bhabha ratios can be stated calling in question the recently predicted existence of series of narrow, unresolvable resonances in the Bhabha scattering cross section. 相似文献
20.
A good knowledge of the luminosity spectrum is mandatory for many measurements at future $\mathrm {e}^{+}\mathrm {e}^{-}$ colliders. As the beam-parameters determining the luminosity spectrum cannot be measured precisely, the luminosity spectrum has to be measured through a gauge process with the detector. The measured distributions, used to reconstruct the spectrum, depend on Initial State Radiation, cross-section, and Final State Radiation. To extract the basic luminosity spectrum, a parametric model of the luminosity spectrum is created, in this case the spectrum at the 3 TeV compact linear collider. The model is used within a reweighting technique to extract the luminosity spectrum from measured Bhabha event observables, taking all relevant effects into account. The centre-of-mass energy spectrum is reconstructed within 5 % over the full validity range of the model. The reconstructed spectrum does not result in a significant bias or systematic uncertainty in the exemplary physics benchmark process of smuon pair production. 相似文献