共查询到20条相似文献,搜索用时 31 毫秒
1.
O. Erriquez S. Natali S. Nuzzo A. Pullia F. Romano D.C. Colley G.T. Jones L. Lowe S. ONeale S.J. Sewell G. Bertrand-Coremans H. Mulkens J. Sacton C. Vander Velde-Wilquet J. Wickens V. Brisson P. Petiau T.W. Jones 《Physics letters. [Part B]》1978,77(2):227-232
For e+ energy > 0.3 GeV and 10 GeV < visible energy < 100 GeV we find that: (i) ; (ii) 1.2 ± 0.5 neutral strange particles are produced per μ?e+ event; (iii) the lifetime of possible positron-parent particles is < 3 × 10?10 s (90% C.L.); (iv) the cross section for direct e+ production via the neutral current is < 0.2 times that via the charged current (90% C.L.); (v) the cross section for producing heavy leptons, L+, decaying into e+ … is < 0.7 × 10?3 times that for μ?production, implying M(L+) > 10 GeV. 相似文献
2.
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
3.
A.C.David Wright 《Physics letters. [Part B]》1977,71(2):425-428
Cross sections for charmed baryon pair production near threshold in e+e? annihilation are calculated using pole-dominated form factors modified to take intoccount continuum effects. When the C0+0? production cross section is normalized with the help of data for it is found that the total charmed baryon production cross reaches a peak value of approximately 2.7 nb at √s = 5 GeV. 相似文献
4.
By also taking into account off-diagonal contributions to the virtual forward Compton amplitude, scaling in ep scattering is obtained from scaling of the total cross section for e+e? annihilation into hadrons. The parameter which sets the scale for the q2 dependence in ep scattering is calculated to be . 相似文献
5.
R. Brandelik W. Braunschweig H.-U. Martyn H.G. Sander D. Schmitz W. Sturm W. Wallraff D. Cords R. Felst R. Fries E. Gadermann H. Hultschig P. Joos W. Koch U. Kötz H. Krehbiel D. Kreinick S. Yamada 《Physics letters. [Part B]》1977,70(3):387-392
The semileptonic and leptonic decay modes of charmed hadrons produced in e+e? collisions above 4 GeV in the cm have been investigated by selecting events with a single electron plus at least two charged tracks. The electron momentum spectrum peaks near 0.5 GeV/c with few events above 0.7 GeV/c. The spectrum excludes large rates for the decays and , but is compatible with , or a mixture of both. The semileptonic branching ratio is obtained both by comparing the inclusive electron cross section with the total cross section attributable to charm, and by studying the fraction of events containing a second electron. The semileptonic charm branching ratios obtained are 0.11 ± 0.03 and 0.16 ± 0.06 respectively. A single event with three electrons and hadrons is found, consistent with the estimated background. The 90% confidence upper limit for σ(e+e? → 3e + hadrons) is 0.1 nb. 相似文献
6.
The cross section for production of single photons in the process is calculated including selectron propagator and photino mass effects and is found to be significantly smaller than the local limit for selectron masses ? 35 GeV/c2. Numerical results for the cross section are obtained as a function of selectron masses for photino masses and electron beam energies E = 14.5, 25, and 35 GeV appropriate to PEP, PETRA, and TRISTAN, respectively. 相似文献
7.
D. Bertrand G. Bertrand-Coremans R. Blaes F.W. Bullock M. Dewit B. Escoubes E. Fett A. Haatuft A. Halsteinslid T.W. Jones J.G. Morfin K. Myklebost J.M. Olsen P. Petitjean M. Pohl F. Rahimi P.N. Ratoff J. Sacton L.C. Welch 《Physics letters. [Part B]》1979,84(3):354-356
Candidates for the purely leptonic process have been searched for in the bubble chamber Gargamelle exposed to the CERN-SPS antineutrino wide-band beam. No single e?, of energy greater than 1 GeV, was found in a total of 230 000 pictures, corresponding to 7400 charged current events. This leads to an upper limit for the observed cross section of cm2 (90% C.L.). Interpretation of this value in terms of the standard W Weinberg-Salam model yields an upper limit to the mixing parameter sin2θW < 0.39 at 90% C.L. 相似文献
8.
D. Chultem V.S. Evseev V.M. Sidorov V.A. Khalkin R. Engfer H.H. Müller H.K. Walter 《Nuclear Physics A》1979,316(3):290-294
A search for the existence of the tetraneutron has been made using the double charge exchange reaction residuals for 4n production and the capture process in the same target, , for the 4n detection. No event has been found, giving an upper limit for the product of the production cross section σp, the detection cross section σd and the 4n lifetime τ. Assuming 10?18 ≦ τ ≦ 10?9 sec it follows that σpσdτ ≦ 2.5 × 10?65cm4 sec with 90 % confidence, and for with 90 % confidence. The magnitude of this value is comparable to the experimental limit of the 4He(π?, π+)4n cross section. 相似文献
9.
The 0-0, 1-1, 2-2, and 3-3 bands of the A2Π-X2Σ+ transition of the tritiated beryllium monohydride molecule have been observed at 5000 Å in emission using a beryllium hollow-cathode discharge in a He + T2 mixture. The rotational analysis of these bands yields the following principal molecular constants. From the pure electronic energy difference (EΠ - EΣ)BeT = 20 037.91 ± 1.5 cm?1 and the corresponding previously known values for BeH and BeD, the following electronic isotope shifts are derived and related to the theoretical approach given by Bunker to the problem of the breakdown of the Born-Oppenheimer approximation. 相似文献
10.
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
11.
Collisions between two excited atoms leading to an increase in the excitation energy of the particles have been under investigation. All measurements were made in the afterglow of gas-discharge plasma. The cross sections of the following reactions have been determined: . The cross section of the first reaction for different transitions lies in the region (2?35) × 10?15 cm2 and the cross section of the second, in (0.2?2.4) × 10?16 cm2. Possible systematic errors and the role of cascade transitions are discussed. Cross sections of the Penning reaction Hem + Xe0 → He0 + Xe+ + e have also been measured. The result is σ (23S) = (1.4 ± 0.2) × 10?15 cm2, σ (21S) = (1.2 ± 0.3) × 10?15 cm2. 相似文献
12.
J.C.D. Brand U.D. Deshpande A.R. Hoy S.M. Jaywant E.J. Woods 《Journal of Molecular Spectroscopy》1983,99(2):339-347
Molecular constants of the first E 0+ ion-pair state of IBr vapor have been determined using polarization-labeling spectroscopy applied to the sequential transitions E 0+ ← B′ 0+ ← X 0+, while the second f 0+ ion-pair state is reported and characterized for the first time. A least-squares, simultaneous analysis of data for the I79Br and I81Br isotopes gives the following constants (in cm?1) for I79Br: , , . , . Preliminary data for the first ion-pair state, accessed in the sequence , indicate that Te is ?30 cm?1 higher in energy than that of the E state. 相似文献
13.
The present article is a review of phenomena connected with neutrino oscillations. Mixing of two neutrinos (Majorana as well as Dirac) with masses m1 and m2 is considered in detail. It is shown that the hypothesis of lepton mixing is not in contradiction with the existing data if |m12?m22| ? 1 (eV)2. Possible experiments designed to reveal neutrino oscillations at reactor, meson factory and high energy accelerator facilities are considered. In such experiments oscillation might be found if . The possibilities of searching for oscillations by experiments on cosmic ray neutrinos and especially on solar neutrinos are discussed in detail. The last experiments have an incredible high sensitivity from the point of view of testing the lepton mixing hypothesis (oscillation effects might be observable if ). The “solar neutrino puzzle” is also discussed from the point of view of lepton mixing. Neutrino oscillations are considered then in the case where in nature there exist N ? 2 neutrino types.In conclusion the case of heavy lepton mixing is considered. It is shown that in a concrete scheme with right-handed currents, the probabilities of such processes as μ → eγ, μ → 3e etc. can be close to existing experimental upper limits, provided the heavy lepton masses are of an order of a few GeV, whereas the probabilities of the above processes are entirely negligible if only neutrinos are mixed. 相似文献
14.
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
15.
A weak emission spectrum of I2 near 2770 Å is reanalyzed and found to to minate on the A(1u3Π) state. The assigned bands span v″ levels 5–19 and v′ levels 0–8. The new assignment is corroborated by isotope shifts, band profile simulations, and Franck-Condon calculations. The excited state is an ion-pair state, probably the 1g state which tends toward . In combination with other results for the A state, the analysis yields the following spectroscopic constants: T″e = 10 907 cm?1, ″e = 1640 cm?1, ω″e = 95 cm?1, ; T′e = 47 559.1 cm?1, ω′e = 106.60 cm?1, . 相似文献
16.
P. Fayet 《Physics letters. [Part B]》1982,117(6):460-466
We evaluate cross sections for the two processes e+e? → γ-photino-antiphotino, e+e? → γ-gravitino-antiphotino. In the local limit approximation they are proportional to (spin-0 electron) and (gravitino), respectively. I If spin-0 electrons have masses between 16 and , the γ-photino-antiphotino production cross section would be of the order of 0.4 to 0.1 pb at , with the cuts indicated in the text. Detecting this process is within the range of possibilities at PETRA. If no such signal is found the existence of light photinos coupled to spin-0 electrons lighter than , or to gravitinos lighter than , would be excluded. 相似文献
17.
L.M. Sehgal 《Nuclear Physics B》1975,84(1):122-126
In the presence of neutral lepton currents, the characteristics of the reaction are modified from those expected in the conventional V-A theory. We show that in a very general class of intermediate boson theories, the modification produced can be specified entirely in terms of the cross sections for . Such a constraint does not necessarily exist in models with four-fermion interaction. 相似文献
18.
The radiative corrections of O(α) to the final electron spectrum and the total cross sections for the processes are studied in the framework of the SU(2)L ? U(1) theory. The electroweak corrections to the fisrt two processes are presented in two equivalent schemes in terms of (Gμ, sin2θw) and . As a byproduct, the relationship to O(α) between the basic parameters (defined by modified minimal subtraction) is explicitly given. The QED corrections are evaluated in the extreme relativistic (ER) regime of the final electron (E′e ? me) for the situation in which the bremsstrahlung photons are unobserved and unrestricted. The ER approximation allows us to obtain simple analytic expressions for the differential electron spectrum and the total cross sections. The relationship to O(GFα) between the spin-averaged differential cross sections for the above processes in the ER regime is derived. 相似文献
19.
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
20.
J.P. Berge D. Bogert R. Hanft D. Hamilton G. Harigel J.A. Malko G.I. Moffatt F.A. Nezrick J. Wolfson V.V. Ammosov A.G. Denisov P.F. Ermolov G.S. Gapienko V.A. Gapienko V.I. Klukhin V.I. Koreshev P.V. Pitukhin V.I. Sirotenko E. Wang 《Physics letters. [Part B]》1979,84(3):357-359
We have searched for candidates for the weak neutral leptonic current reaction in the Fermilab 15 ft bubble chamber filled with a heavy neon-hydrogen mix. Based on zero observed events of this type we find the 90% confidence level upper limit for the rate for this reaction relative to the total antineutrino charged current rate to be 3.9 × 10?4 and, in the Weinberg-Salam model, sin2θW ? 0.37. 相似文献