共查询到20条相似文献,搜索用时 250 毫秒
1.
The ALEPH Collaboration A. Heister et al. 《The European Physical Journal C - Particles and Fields》2002,25(1):1-12
A search for single sneutrino production under the assumption that R-parity is violated via a single dominant coupling is presented. This search considers the process and is performed using the data collected by the ALEPH detector at centre-of-mass energies from 189 GeV up to 209 GeV corresponding
to an integrated luminosity of 637.1 pb-1. The numbers of observed candidate events are in agreement with Standard Model expectations and 95% confidence level upper
limits on five of the couplings are given as a function of the assumed sneutrino mass.
Received: 19 December 2001 / Published online: 26 July 2002 相似文献
2.
In total 1317 di-lepton events with significant missing transverse momentum were identified in a total data sample of 680 pb-1 collected at e + e- centre-of-mass energies ranging from 183 GeV to 209 GeV. The number of di-lepton events, the dependence on centre-of-mass energy, and the event properties are consistent with expectations from Standard Model processes, predominantly W + W- production with both W bosons decaying leptonically. This topology is also an experimental signature for the pair production of new particles that decay to a charged lepton accompanied by one or more invisible particles. No evidence for new phenomena is apparent. Upper limits are presented on the production cross-section multiplied by the relevant branching ratio squared for sleptons, leptonically decaying charginos and charged Higgs bosons. Mass limits are also given.Received: 14 July 2003, Published online: 9 January 2004 相似文献
3.
Search for pair-produced leptoquarks in e + e- interactions at $\sqrt{s} \simeq 189\text{--}209$ GeV
A search for pair-produced leptoquarks is performed using
collision events collected by the OPAL detector at LEP at centre-of-mass energies between 189 and 209 GeV. The data sample corresponds to a total integrated luminosity of 596 pb-1. The leptoquarks are assumed to be produced via couplings to the photon and the Z0. For a given search channel only leptoquark decays involving a single lepton generation are considered. No evidence for leptoquark pair production is observed. Lower limits on masses for scalar and vector leptoquarks are calculated. The results improve most of the LEP limits derived from previous searches for the pair production process by 10-25 GeV, depending on the leptoquark quantum numbers.Received: 6 May 2003, Published online: 24 October 2003 相似文献
4.
The DELPHI experiment at the LEP e + e- collider collected almost 700 pb-1 at centre-of-mass energies above the Z0 mass pole and up to 208 GeV. Those data were used to search for SUSY in the Anomaly Mediated SUSY Breaking (AMSB) scenario with a flavour independent common sfermion mass parameter. The searches covered several possible signatures experimentally accessible at LEP, with either the neutralino, the sneutrino or the stau being the Lightest Supersymmetric Particle (LSP). They included: the search for nearly mass-degenerate chargino and neutralino, which is a typical feature of AMSB; the search for Standard-Model-like or invisibly decaying Higgs boson; the search for stable staus; the search for cascade decays of SUSY particles resulting in the LSP and a low multiplicity final state containing neutrinos. No evidence of a signal was found, and thus constraints were set in the space of the parameters of the model.Received: 3 September 2003, Revised: 3 February 2004, Published online: 9 March 2004 相似文献
5.
The ALEPH Collaboration A. Heister et al. 《The European Physical Journal C - Particles and Fields》2003,28(1):1-13
Events containing only energetic photons are analysed in a sample of of data recorded from collisions at centre-of-mass energies between 189 and 209 GeV by the ALEPH detector at LEP. The and cross sections are measured and found to be in agreement with the standard model predictions. The number of light
neutrino generations is determined to be . Upper limits are derived on the cross sections for photon production in the context of several supersymmetric models. Limits
are also set on the parameters of models with extra spatial dimensions, with contact interactions and with excited electrons.
Received: 27 May 2002 / Published online: 14 March 2003 相似文献
6.
The measurement of $\alpha_s$ from event shapes with the DELPHI detector at the highest LEP energies
Searches for pair-production of supersymmetric particles under the assumption of non-conservation of R-parity with a dominant LL
or
term have been performed using the data collected by the DELPHI experiment at LEP in e + e- collisions at centre-of-mass energies from 192 up to 208 GeV. No excess of data above Standard Model expectations was observed. The results were used to constrain the MSSM parameter space and to derive limits on the masses of supersymmetric particles.Received: 4 March 2004, Revised: 5 May 2004, Published online: 23 June 2004An Erratum to this article can be found at 相似文献
7.
The OPAL Collaboration G. Abbiendi et al. 《The European Physical Journal C - Particles and Fields》2003,27(4):467-481
Charged particle momentum distributions are studied in the reaction hadrons, using data collected with the OPAL detector at centre-of-mass energies from 192 GeV to 209 GeV. The data correspond
to an average centre-of-mass energy of 201.7 GeV and a total integrated luminosity of 433 pb-1. The measured distributions and derived quantities, in combination with corresponding results obtained at lower centre-of-mass
energies, are compared to QCD predictions in various theoretical approaches to study the energy dependence of the strong interaction
and to test QCD as the theory describing it. In general, a good agreement is found between the measurements and the corresponding
QCD predictions.
Received: 17 July 2002 / Published online: 3 March 2003 相似文献
8.
The OPAL Collaboration G. Abbiendi et al. 《The European Physical Journal C - Particles and Fields》2003,27(4):483-495
We have analysed the data collected by OPAL at centre-of-mass energies between 189 and 209 GeV searching for Higgs boson
candidates from the process followed by the decay of where is the CP-odd Higgs boson. The search is done in the region where the mass, , is below the production threshold for , and the CP-even Higgs boson mass is within the range 45-86 GeV/c
2
. In this kinematic range, the decay of may be dominant and previous Higgs boson searches have very small sensitivities. This search can be interpreted within any
model that predicts the existence of at least one scalar and one pseudoscalar Higgs boson. No excess of events is observed
above the expected Standard Model backgrounds. Model-independent limits on the cross-section for the process are derived assuming 100% decays of the into and 100% decays of the into each of the following final states: , , , , and . The results are also interpreted in the CP-conserving no-mixing MSSM scenario, where the region and is excluded.
Received: 13 March 2002 / Published online: 26 February 2003 相似文献
9.
Measurements of on-shell ZZ production are described, using data from the DELPHI experiment at LEP in e
+
e
- collisions at centre-of-mass energies between 183 and 209 GeV, corresponding to an integrated luminosity of about 665 pb-1. Results obtained in each of the final states
,
,
,
,
, l
+
l
-
l
+
l
-, and
(with
) are presented. The measured production cross-sections are consistent with the Standard Model expectations. These results update and supersede those already published at 183 and 189 GeV.Received: 3 March 2002, Revised: 28 May 2003, Published online: 19 September 2003 相似文献
10.
J. Abdallah et al. 《The European Physical Journal C - Particles and Fields》2006,45(2):273-289
The production of single charged and neutral intermediate vector bosons in e + e- collisions has been studied in the data collected by the DELPHI experiment at LEP at centre-of-mass energies between 183
and 209 GeV, corresponding to an integrated luminosity of about 640 pb-1. The measured cross-sections for the reactions, determined in limited kinematic regions, are in agreement with the Standard
Model predictions.
Arrival of the final proofs: 21 November 2005 相似文献
11.
A search for excited lepton production in e+e- collisions was performed using the data collected by the DELPHI detector at LEP at centre-of-mass energies ranging from 189 GeV
to 209 GeV, corresponding to an integrated luminosity of approximately 600 pb-1. No evidence for excited lepton production was found. In searches for pair-produced excited leptons, lower mass limits were
established in the range 94–103 GeV/c2, depending on the channel and model assumptions. In searches for singly-produced excited leptons, upper limits on the parameter
f/Λ were established as a function of the mass. 相似文献
12.
《The European Physical Journal C - Particles and Fields》2007,49(2):411-437
Cross sections, angular distributions and forward-backward asymmetries are presented, of two-fermion events produced in e+e- collisions at centre-of-mass energies from 189 to 209 GeV at LEP, measured with the ALEPH detector. Results for e+e-, μ+μ-, τ+τ-, qq̄, bb̄ and cc̄ production are in agreement with the standard model predictions. Constraints are set on scenarios of new
physics such as four-fermion contact interactions, leptoquarks, Z′ bosons, TeV-scale quantum gravity and R-parity violating squarks and sneutrinos.
Dedicated to the memory of John Strong who died on July 31, 2006 相似文献
13.
《Physics letters. [Part B]》1999,446(1):75-91
An update of the searches for charginos and neutralinos is presented, based on a data sample corresponding to the 53.9 pb−1 recorded by the DELPHI detector in 1997, at a centre-of-mass energy of 183 GeV. No evidence for a signal was found. The lower mass limits are 4–5 GeV/c2 higher than those obtained at a centre-of-mass energy of 172 GeV. The (μ,M2) domain excluded by combining the neutralino and chargino searches implies a limit on the mass of the lightest neutralino which, for a heavy sneutrino, is constrained to be above 29.1 GeV/c2 for tanβ≥ 1. 相似文献
14.
DELPHI data collected at centre-of-mass energies up to 208 GeV have been analysed to search for charginos, neutralinos and sfermions in the framework of the Minimal Supersymmetric Standard Model (MSSM) with R-parity conservation. No evidence for a signal was found in any of the channels. The results of each search were used to derive limits on production cross-sections and particle masses. In addition, the combined result of all searches excludes regions in the parameter space of the constrained MSSM, leading to limits on the mass of the Lightest Supersymmetric Particle and other supersymmetric particles.Received: 22 February 2003, Revised: 24 July 2003, Published online: 12 November 2003 相似文献
15.
M. Dubinin H. J. Schreiber A. Vologdin 《The European Physical Journal C - Particles and Fields》2003,30(3):337-344
We examine the prospects for measuring the
coupling of a standard model-like Higgs boson with a mass between 120 and 160 GeV at the future TESLA linear e
+
e
- collider, assuming an integrated luminosity of 1 ab-1 and a center-of-mass energy of 500 GeV. We consider the Higgs boson produced in association with
via the W W fusion reaction
, followed by the rare decay into a Z boson and a photon,
. Accounting for all main background contributions, a precision of 27% can be achieved in unpolarized e
+
e
- collisions for M
H
= 140 GeV. With appropriate initial state polarisations
BF(
)/BF(
), or the precisions on the
partial width, can be improved to 17% and provide valuable information on the
coupling. For M
H
= 120 and 160 GeV, the small significance of the signals in unpolarized collisions sets upper limits of 79% respectively 72% at 90% confidence level on the
branching fraction.Received: 5 March 2003, Revised: 14 July 2003, Published online: 5 September 2003 相似文献
16.
Multi-ring signatures of
appearance via the oscillation
are formulated for a water Cherenkov detector. These signatures are appropriate for long-baseline neutrino experiments operating at relatively high neutrino energies
GeV that emphasize the matter effect. The NC background is less for selected multi-ring events than for 1e-like events, and may be directly estimated from the data. Our results suggest that best sensitivity to
and to the sign of
can be reached with baselines over some 6000 km.Received: 14 April 2003, Revised: 19 June 2003, Published online: 26 September 2003M.A. Kubantsev: Now at Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208, USA 相似文献
17.
J. Gluza A. Hoefer S. Jadach F. Jegerlehner 《The European Physical Journal C - Particles and Fields》2003,28(2):261-278
Final state radiation (FSR) in pion pair production cannot be calculated reliably because of the composite structure of the
pions. However, FSR corrections have to be taken into account for a precise evaluation of the hadronic contribution to g-2 of the muon. The role of FSR in both energy scan and radiative return experiments is discussed. It is shown how FSR influences
the pion form factor extraction from experimental data and, as a consequence, the evaluation of . In fact the FSR corrections should be included to reach the precision we are aiming at. We argue that for an extraction of the desired
FSR-inclusive cross section a photon-inclusive scan measurement of the ”” cross section is needed. For exclusive scan and radiative return measurements in contrast we have to rely on ad hoc FSR
models if we want to obtain either or the FSR-exclusive cross section . We thus advocate to consider seriously precise photon-inclusive energy scan measurements at present and future low energy
e
+
e
-
-facilities. Then together with radiative return measurements from DANE and BABAR and forthcoming scan measurements at VEPP-2000 we have a good chance to substantially improve the evaluation
of in the future.
Received: 2 January 2003 / Published online: 24 March 2003 相似文献
18.
The OPAL Collaboration G. Abbiendi et al. 《The European Physical Journal C - Particles and Fields》2002,23(1):1-11
A search for first generation scalar and vector leptoquarks (LQ) as well as for squarks () in R-parity violating SUSY models with the direct decay of the into Standard Model particles has been performed using ee collisions collected with the OPAL detector at LEP at an ee centre-of-mass energy of 189 GeV. The data correspond to an integrated luminosity of about 160 pb. The dominant process for this search is , where a photon, which has been radiated by one of the beam electrons, serves as a source of quarks. The numbers of selected
events found in the two decay channels are in agreement with the expectations from Standard Model processes. This result allows
to set lower limits at the 95% confidence level on the mass of first generation scalar and vector leptoquarks, and of squarks
in R-parity violating SUSY models. For Yukawa couplings to fermions larger than , the mass limits range from 121 GeV to GeV ( GeV to GeV) depending on the branching ratio of the scalar (vector) leptoquark state. Furthermore, limits are set on the Yukawa couplings for leptoquarks and for squarks, and on as a function of the scalar leptoquark/squark mass.
Received: 22 May 2001 / Published online: 25 January 2002 相似文献
19.
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
20.
Complementing the preceding study of charged scalar leptons, the sector of the neutral scalar leptons, sneutrinos, is investigated in a high-precision analysis for future e
+
e
- linear colliders. The theoretical predictions for the cross-sections are calculated at the thresholds for non-zero widths and in the continuum including higher-order corrections at the one-loop level. Methods for measuring the sneutrino masses and the electron-sneutrino-gaugino Yukawa couplings are presented, addressing theoretical problems specific for the sneutrino channels.Received: 10 September 2004, Revised: 11 October 2004, Published online: 3 March 2005 相似文献