共查询到20条相似文献,搜索用时 31 毫秒
1.
Searches for topologies characteristic of Gauge Mediated SUSY Breaking models (GMSB) are performed by analysing 173.6 of data collected at = 188.6 GeV with the ALEPH detector. These topologies include acoplanar photons, non-pointing single photon, acoplanar leptons,
large impact parameter leptons, detached slepton decay vertices, heavy stable charged sleptons and four leptons plus missing
energy final states. No evidence for these new phenomena is observed and limits on production cross sections and sparticle
masses are derived. A scan of a minimal GMSB parameter space is performed and model dependent lower limits of about 45 GeV/ on the next-to-lightest supersymmetric particle (NLSP) mass and of about 9 TeV on the mass scale parameter are derived, independently of the NLSP lifetime.
Received: 30 November 1999 / Published online: 14 April 2000 相似文献
2.
G. Abbiendi et al. 《The European Physical Journal C - Particles and Fields》1999,11(4):619-642
Searches for pair-produced charginos and neutralinos with R-parity violating decays have been performed using a data sample corresponding to an integrated luminosity of 56 pb collected with the OPAL detector at LEP at a centre-of-mass energy of 183 GeV. An important consequence of R-parity violation is that the lightest supersymmetric particle becomes unstable. The searches have been performed under the
assumptions that the lightest supersymmetric particle promptly decays and that only one R-parity violating coupling is dominant for each of the decay modes considered. Such processes would yield multiple leptons,
jets plus leptons, or multiple jets with or without significant missing energy in the final state. No excess of such events
above Standard Model backgrounds has been observed. Limits are presented on the production cross-sections of gauginos in R-parity violating scenarios. Limits are also presented in the framework of the Minimal Supersymmetric Standard Model.
Received: 14 December 1998 / Published online: 14 October 1999 相似文献
3.
A. Heister et al. 《The European Physical Journal C - Particles and Fields》2002,25(3):339-351
A total of 628 bp-1 of data collected with the ALEPH detector at centre-of-mass energies from 189 to 209 GeV is analysed in the search for gauge
mediated SUSY breaking (GMSB) topologies. These topologies include two acoplanar photons, non-pointing single photons, acoplanar
leptons, large impact parameter leptons, detached slepton decay vertices, heavy stable charged sleptons and multi-leptons
plus missing energy final states. No evidence is found for new phenomena, and lower limits on masses of supersymmetric particles
are derived. A scan of a minimal GMSB parameter space is performed and lower limits are set for the next-to-lightest supersymmetric
particle (NLSP) mass at 54 GeV/c2 and for the mass scale parameter at 10 TeV/c2, independently of the NLSP lifetime. Including the results from the neutral Higgs boson searches, a NLSP mass limit of 77
GeV/c2 is obtained and values of up to 16 TeV/c2 are excluded.
Received: 14 March 2002 / Published online: 20 September 2002 相似文献
4.
We propose a left-right model of quarks and leptons based on the gauge group SU(3)(C)xSU(2)(L)xSU(2)(R)xU(1)(B-L), where the scalar sector consists of only two doublets: (1,2,1,1) and (1,1,2,1). As a result, any fermion mass, whether it be Majorana or Dirac, must come from dimension-five operators. This allows us to have a common view of quark and lepton masses, including the smallness of Majorana neutrino masses as the consequence of a double seesaw mechanism. 相似文献
5.
Searches for unstable neutral and charged heavy leptons, N and , and for excited states of neutral and charged leptons, , , , and , have been performed in collisions using data collected by the OPAL detector at LEP. The data analysed correspond to an integrated luminosity of
about 58 pb at a centre-of-mass energy of 183 GeV, and about 10 pb each at 161 GeV and 172 GeV. No evidence for new particles was found. Lower limits on the masses of unstable heavy and excited
leptons are derived. From the analysis of charged-current, neutral-current, and photonic decays of singly produced excited
leptons, upper limits are determined for the ratio of the coupling to the compositeness scale, , for masses up to the kinematic limit. For excited leptons, the limits are established independently of the relative values
of the coupling constants f and .
Received: 29 November 1999 / Published online: 6 March 2000 相似文献
6.
Frank Cuypers Sacha Davidson 《The European Physical Journal C - Particles and Fields》1998,2(3):503-528
We define bileptons to be bosons coupling to a pair of leptons and construct the most general dimension four lagrangian involving
scalar and vector bileptons. We concentrate on fields with lepton number 2, and derive model independent bounds on their masses
and couplings from low-energy data. In addition, we study their signals in high-energy experiments and forecast the discovery
potential of future colliders.
Received: 24 April 1997 / Published online: 20 February 1998 相似文献
7.
Fang-xiao Dong 《理论物理通讯》1991,15(1):53-64
We discuss the relations between the K-M matrix and the masses of the quarks and leptons in the case of four generations, and give the exact expression of the K-M matrix in terms of the masses of quarks and leptons. The requirement that the theoretical and experimental values of the K-M ,matrix are consistent leads to an allowed range of quark masses of the fourth generation mt'~400-1000 GeV, mb'~50-130 GeV. In the leptonic sector.in comparison I with the neutrino oscillation experiments and supernova it seems that neutrino masses must have hierarchy as charged leptons. 相似文献
8.
String consistency conditions are stronger than anomaly cancellation and can require the addition of exotics in the visible sector. We study such exotics and demonstrate that they may account for the modest excess at 750 GeV in recent diphoton resonance searches performed by the ATLAS and CMS collaborations. In a previous analysis of type II MSSM D‐brane quivers we systematically added up to five exotics for the sake of satisfying string consistency conditions. Using this dataset, we demonstrate that 89780 of the 89964 quivers have exotics, 78155 of which include singlets that may couple to MSSM or exotic multiplets with coupling structures governed by U(1) symmetries that are often anomalous. We demonstrate that certain sets of exotics are far preferred over others and study the structure of singlet couplings to heavy exotics carrying standard model charges. Typical possibilities include singlets that may decay to vector‐like quarks and/or vector‐like leptons and subsequently to two photons. We show that a narrow width diphoton excess can be accounted for while evading existing bounds if multiple exotics are added, with vector‐like leptons of mass GeV and vector‐like quarks with masses up to ≃ 3 TeV. However, a large width , as suggested by the ATLAS data, cannot be easily accommodated in this framework. Renormalization group equations with GUT‐scale boundary conditions show that these supersymmetric models are perturbative and stable. Type IIA compactifications on toroidal orbifolds allow for O(10) Yukawa couplings in the ultraviolet. We also discuss the possibility of accounting for the diphoton excess in a low string scale scenario via the decay of string axions. 相似文献
9.
We calculate the CP-violating electric and weak dipole form factors of the top quark and the tau lepton in models with scalar
leptoquarks coupling only to the third generation of quarks and leptons. We obtain numerical values of the real and imaginary
parts of these form factors at various energies for different values of leptoquark masses and couplings. The existing limits
on the tau electric and weak dipole form factors allow us to put a limit on the masses and couplings of such leptoquarks and
therefore on the top electric and weak dipole form factors. We also discuss constraints on the form factors coming from indirect
limits on leptoquark masses and couplings deduced from LEP results on Z properties. 相似文献
10.
A search for unstable heavy fermions with the DELPHI detector at LEP is reported. Sequential and non-canonical leptons, as
well as excited leptons and quarks, are considered. The data analysed correspond to an integrated luminosity of about 48 pb at an centre-of-mass energy of 183 GeV and about 20 pb equally shared between the centre-of-mass energies of 172 GeV and 161 GeV. The search for pair-produced new leptons establishes
95% confidence level mass limits in the region between 70 GeV/ and 90 GeV/, depending on the channel. The search for singly produced excited leptons and quarks establishes upper limits on the ratio
of the coupling of the excited fermion to its mass () as a function of the mass.
Received: 30 October 1998 / Published online: 1 March 1999 相似文献
11.
In models with a low quantum gravity scale, fast proton decay can be avoided by localizing quarks and leptons to separated positions in an extra 1/TeV sized dimension with gauge and Higgs fields living throughout. Black holes with masses of the order of the quantum gravity scale are therefore expected to evaporate nonuniversally, preferentially radiating directly into quarks or leptons but not both. Should black holes be copiously produced at a future hadron collider, we find the ratio of final state jets to charged leptons to photons is 113:8:1, which differs from previous analyses that assumed all standard model fields live at the same point in the extra dimensional space. 相似文献
12.
R. Barate et al. 《The European Physical Journal C - Particles and Fields》2000,17(2):241-261
The mass of the W boson is determined in ee collisions at LEP by the direct reconstruction of W decays in and events, supplemented by measurements using the kinematic properties of the leptons in the
decay channel. The main sample of W pairs is selected from an integrated luminosity of 174 pb collected with the ALEPH detector in 1998 at a centre-of-mass energy of 188.63 GeV. The combined result from all channels
is
where FSI represents the possible effects of final state interactions in the channel. In a second two-parameter fit to the , and channels, where the W mass and width are decoupled, the average W width is found to be { GeV/}, consistent with the Standard Model prediction. The combination of the mass measurement presented in this paper together
with those derived previously from the W pair cross section at 161 and 172 GeV and direct reconstruction at 172 and 183 GeV
gives
Received: 15 March 2000 / Published online: 8 September 2000 相似文献
13.
The data collected by the OPAL experiment at GeV were used to search for Higgs bosons which are predicted by the Standard Model and various extensions, such as general
models with two Higgs field doublets and the Minimal Supersymmetric Standard Model (MSSM). The data correspond to an integrated
luminosity of approximately 54 pb. None of the searches for neutral and charged Higgs bosons have revealed an excess of events beyond the expected background.
This negative outcome, in combination with similar results from searches at lower energies, leads to new limits for the Higgs
boson masses and other model parameters. In particular, the 95% confidence level lower limit for the mass of the Standard
Model Higgs boson is 88.3 GeV. Charged Higgs bosons can be excluded for masses up to 59.5 GeV. In the MSSM, GeV and GeV are obtained for , no and maximal scalar top mixing and soft SUSY-breaking masses of 1 TeV. The range is excluded for minimal scalar top mixing and GeV. More general scans of the MSSM parameter space are also considered.
Received: 27 October 1998 / Published online: 19 February 1999 相似文献
14.
R. N. Mohapatra 《Pramana》2004,62(2):319-333
We discuss ways to understand large neutrino mixings using new symmetries of quarks and leptons beyond the standard model
for the three allowed patterns of neutrino masses: normal, inverted hierarchy and degenerate masses. 相似文献
15.
We discuss the theoretical expectations and phenomenological evidence for the lightest glueballs and the members of the meson
nonet with quantum numbers . We reconsider the recent evidence for candidate states with masses below 1700 MeV, but include also the results from earlier phase-shift analyses. Arguments are presented to classify the scalars
and as members of the nonet, with a mixing rather similar to that of the pseudoscalars and . The S-wave states called and are considered as different signals from a single broad resonance, which we take to be the lowest-lying glueball. This state together with and with spin form the basic triplet of binary gluonic bound states. We argue that these hypotheses are consistent with what can be expected
theoretically.
Received: 30 November 1998 / Revised version: 17 February 1999 / Published online: 27 April 1999 相似文献
16.
Chandra Raju 《International Journal of Theoretical Physics》1987,26(6):575-581
In this note, we arrange equal mass for all the four leptons,e,, and their neutrinos through their coupling to a Higg's quartet. In addition, the electron and muon are coupled to the left handed and right handed Higgs doublets. This is a pseudo scalar coupling. This enables these charged leptons to attain different masses. Their masses are arranged to be proportional to their neutrino mass. The mass of the electron or muon neutrino turns out to be 6.3 eV. 相似文献
17.
Gerald Rosen 《Central European Journal of Physics》2011,9(1):45-48
Without Higgs field interaction, accurate pole mass values are obtained for the charged leptons and quarks from a Z3-symmetric linear superposition self-interference of the Dirac fields in the effective free-field Lagrangian. The charged
lepton and quark pole masses evidence the discrete Z3 symmetry, the theoretical-experimental deviations δm/m are $
\mathcal{O}
$
\mathcal{O}
(10−5) for all three charged leptons, and the quark pole masses are in very satisfactory overall agreement with the experimental
data. 相似文献
18.
H. Fritzsch 《Progress in Particle and Nuclear Physics》2010,64(2):313-314
We study a model for the mass matrices of the leptons, based on texture zero elements. We are able to relate the mass eigenvalues of the charged leptons and of the neutrinos to the mixing angles, and can predict the masses of the neutrinos. We find a normal hierarchy—the masses are 0.005 eV, 0.01 eV and 0.05 eV. Predictions for the double beta decay and the reactor neutrino experiments are made. 相似文献
19.
J. I. Aranda O. A. Sampayo R. Martínez 《Zeitschrift fur Physik C Particles and Fields》1996,72(3):479-483
Composite models predict the existence of excited quarks and leptons. We find bounds for the masses of possible excited leptons and for the substructure scale by using radiative corrections at theZ scale. A non-decoupling scenario arises naturally which induces upper bounds on these masses as a function of the substructure scale. 相似文献
20.
R. Barate et al. 《The European Physical Journal C - Particles and Fields》1998,4(4):571-590
Extensive searches for evidence of compositeness of quarks and leptons have been made in the complete set of ALEPH data from
LEP running at the Z peak. These include searches for radiative and weak decays of excited fermions, produced either in pairs
or singly, and a scalar partner of the Z. Coupling and branching ratio limits deduced from these searches are presented.
Received: 6 February 1998 / Published online: 2 July 1998 相似文献