共查询到20条相似文献,搜索用时 31 毫秒
1.
Heavy J particles decaying into e+e? were recently found in p-Be collisions [1] as well as in e+e? annihilations [2, 3], where also the decay into hadrons with a branching ratio of about was observed. 相似文献
2.
We consider the possibility that the scalar partners of the neutrinos are the least massive supersymmetric partners, and show that this alternative is compatible with cosmological constraints, which put a significant lower bound on photino masses but not on masses. Various consequences are examined: the photon counting rate for may be large; the rate for by exchange is enhaced; Z0→ increases Γ(Z0) by about 0.25 GeV; may be enhanced; the decay may be detectable; there can be additional contributions to the rare decay ; restrictions on gluino masses, which depend on photinos interacting before they decay, have to be re-examined; scalar neutrinos have suitable characteristics as candidates for dark matter in the universe. We discuss one currently fashionable class of models that can predicr a light . 相似文献
3.
4.
The simplest four-quark SU(2) ? U(1) models with an anomally-free heavy lepton sector can have two charged heavy leptons and one or two neutral leprons. Such models also explain the rise in R (the ratio of hadronic to muon pair production in e+e? collisions). We study some consequences of different choices of leptonic numbers for L1 and L2. In particular, we derive, the leptonic decay width when several final-stae leptons are massive; the cross section for production; the branching ratio for . 相似文献
5.
We report on the final analysis of a search for the decay μ+→e+γ performed at SIN. No evidence for the existence of the process has been found. An upper limit for the branching ratio of 1.0 × 10?9 (90% confidence) is presented. The measured positron-photon energy distributions are completely described by the decay and accidental coincidences. 相似文献
6.
K.S. Heard J. Heintze G. Heinzelmann P. Igo-Kemenes W. Kalbreier E. Mittag H. Rieseberg B. Schürlein H.W. Siebert V. Soergel K.P. Streit A. Wagner A.H. Walenta 《Physics letters. [Part B]》1975,55(3):327-330
The branching ratio has been measured on the basis of 534 observed K+ → e+v decays. The K+ decay at rest; the momenta of the e+ and μ+ are measured in a magnetic spectrometer using multiwire driftchambers, and the electrons are identified in a gas Cerenkov counter. The result is R = (2.37 ± 0.17_× 10?5. The value predicted for pure axial-vector interaction and μ-e-universality is R = 2.57 × 10?5. 相似文献
7.
A. Ali J.G. Körner Z. Kunszt E. Pietarinen G. Kramer G. Schierholz J. Willrodt 《Nuclear Physics B》1980,167(3):454-478
We have calculated the four-jet production processes and to lowest-order QCD perturbation theory. We find that (qq) production is small compared to the dominant process which can in part be traced to the fact that the latter process is more singular as the 2- and 3-jet phase-space limits are approached. We present differential 4-jet acoplanarity distributions and compare them with non-perturbative acoplanarity distributions at maximum PETRA and PEP energies. Leading log cross-section formulae are derived for various cut-off procedures and are compared to the results of our numerical integrations. We also present results on associated heavy quark production in e+e? annihilation. 相似文献
8.
O. Dumbrajs R. Koch H. Pilkuhn G.C. Oades H. Behrens J.J. de Swart P. Kroll 《Nuclear Physics B》1983,216(2):277-335
The electron capture decay occurs with a record low energy release, Q ~ 2.6 keV. The daughter DyH atom has an electron hole, H, and predominantly decays by electron ejection DyH→DyH1H2+e?. We investigate the neutrino mass sensitivity of the electron spectrum in the overall process Ho→DyH1H2+e?+νe. In this spectrum, the fraction of events sensitive to a fixed non-zero neutrino mass in one to two orders of magnitude smaller than in the standard case of tritium β decay. But the electron energies in 163Ho decay are considerably smaller than in 3H decay (Q ~ 18 keV). This suggests experiments whose energy resolution could be much better than that of the magnetic spectrometers conventionally used in the tritium case. 相似文献
9.
D. Bollini P. Giusti T. Massam L. Monari F. Palmonari G. Valenti A. Zichichi 《Physics letters. [Part B]》1976,61(1):96-98
The analysis of the reaction e+e?→π+π? measured at the e+e? colliding beam machine ADONE shows that, if ?′ and ?″ exist, the cross sections compare as follows (taking the ? as the reference point): : σ(e+e? → ?′ → π+π?): σ(e+e? → ?″ → π+π?) = 1: (7 ± 4) × 10?3: (1 ± 5) × 10?4. The square of the product of their couplings to the photon (γ?) and the γγ system (g?ππ) are derived. 相似文献
10.
J. Burmester L. Criegee H.C. Dehne K. Derikum R. Devenish G. Flügge J.D. Fox G. Franke Ch. Gerke P. Harms G. Horlitz Th. Kahl G. Knies M. Rössler R. Schmitz U. Timm H. Wahl K. Wacker 《Physics letters. [Part B]》1977,68(3):301-304
Events of the type have been observed in the magnetic detector PLUTO at the storage ring DORIS at DESY. The data support the hypothesis of the pair production of heavy leptons, and allow to determine decay parameters. Decay rates into muons and electrons are equal within error, and argue for a new lepton number of the heavy lepton. 相似文献
11.
J. Kapusta 《Physics letters. [Part B]》1984,136(3):201-203
Chiral symmetry in the high-temperature plasma phase of QCD is consistent with at least three qualitatively different quark dispersion relations. The rate for , with zero total momentum of the e+e? pair in the plasma rest frame is direct measure of the quark dispersion relation. For the three plausible dispersion relations the rates differ by orders of magnitude when the e+e? invariant mass M < 2T. 相似文献
12.
We calculate the production of narrow resonances with even charge conjugation in e+e? annihilation in the quarkonium and vectordominance models. We give unitarity bounds for in terms of and . The electromagnetic production dominates through the neutral current at low energies independent of details of the model. For masses above 10 GeV the situation is reversed. 相似文献
13.
R. Abela G. Backenstoss W. Kowald J. Wüest H.G. Seiler M. Seiler L.M. Simons 《Physics letters. [Part B]》1980,95(2):318-322
An upper limit for μ? → e+ conversion has been established by searching for specific decay properties of the expected final state nucleus. We obtain with 90% c.l. 相似文献
14.
R. Gatto 《Physics letters. [Part B]》1974,51(4):371-375
If the hadronic contribution to vacuum polarization, which is proportional to the ration of e+e? annihilation into hadrons to that into μ+μ? rises asymptotically as a power of the squared four-momentum, the ratio point is bound to be less than and this limit is approached sooner for higher β. Other models of vacuum polarizations are also considered together with their possible origin and implications. 相似文献
15.
C. Bacci G. Parisi G. Penso G. Salvini B. Stella R. Baldini Celio G. Capon C. Mencuccini G.P. Murtas M. Spinetti A. Zallo 《Physics letters. [Part B]》1973,44(6):530-532
The cross section for the reaction e++e?→e++e?+γ has been measured at the Adone storage ring. The results in agreement with the QED predictions, establish a new limit for the mass and the coupling constant of a heavy electron e1. 相似文献
16.
J. Heintze G. Heinzelmann P. Igo-Kemenes R. Mundhenke H. Rieseberg B. Schürlein H.W. Siebert V. Soergel H. Stelzer K.-P. Streit A.H. Walenta 《Nuclear Physics B》1979,149(3):365-380
The decay K+ → e+υγ has been investigated. For the structure-dependent part with positive γ-helicity (SD+) the branching ratio is obtained from 51 ± 3 events observed in the kinematical region Ee ? 235 MeV, Eγ > 48 MeV and θeγ > 140°. For the corresponding part with negative γ-helicity we obtain an upper limit Γ(SD?)/Γ(SD+) < 11 (90% CL) from the sample of electrons with energies 220 MeV ? Ee < 230 MeV and with no γ in the backward direction. This upper limit implies that the ratio of structure-dependent axial vector amplitudes lies outside the region .For the decay the limit 90% confidence level) was found. 相似文献
17.
The energy spectrum and the angular distribution of the muon in the reaction are calculated in the framework of the Weinberg-Salam model. It is shown that the signal is well above the conventional backgrounds and thus could provide a clean signature for real W+W? production at LEP energies. Other distributions are briefly described. 相似文献
18.
We present a complete set of rotationally invariant observables (Hl) which characterizes the ‘shapes’ of final states in e+e? annihilation. They are infrared stable when calculated in QCD perturbation theory. We compare the ‘shapes’ of final states from the processes and from the three-gluon decays of heavy vector mesons. We also consider the production and decay of heavy quarks and leptons. Using a realistic model for the development of hadron jets, we find that for c.m. energies above about 10 GeV, these processes may be clearly distinguished by their distributions in the Hl. We indicate how our analysis may be extended to deep inelastic lepton-hadron interactions and hadron-hadron collisions involving large transverse momenta. 相似文献
19.
R. Budny 《Physics letters. [Part B]》1973,45(4):340-344
General cross-sections are given for annihilation via one photon and W0 exchange. Effects of the W0 in the special cases e+e?→μ+μ? and at high energies are discussed. These effects are estimated to be comparable to the effects from one γ exchange at energies accesible in NAL and SPS. 相似文献
20.
R.J. Hemingway R. Armenteros C. Dionisi Ph. Gavillet A. Gurtu S.O. Holmgren M.J. Losty J.C. Marin M. Mazzucato L. Montanet M. Banting R. Blokzijl A.J. De Groot B. Jongejans J.C. Kluyver W.M. Van Leeuwen G.G.G. Massaro J. Wells 《Nuclear Physics B》1978,142(3):205-219
Forty events have been observed in a large (133 events/βb) experiment at 4.2 GeV/c incident K? momentum. Thirty nine of the events come from the three-body reaction . The is mainly produced in the forward hemisphere (direction of the incident K?). The lifetime is measured to be τ = (0.75 +0.14?0.11 × 10?10 sec substantially less than the Particle Data Group value of (1.3 ?0.3+0.2) × 10?10 sec. The mass is determined to be 1671.7 ± 0.6 MeV, in good agreement with other determinations. The decay asymmetry parameter α (for the decay mode ) is found to be ?0.2 ± 0.4. 相似文献