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| Author | : Giovanni Gallucci |
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| Release | : 2011 |
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| Author | : Giovanni Gallucci |
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| Release | : 2011 |
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| Author | : Luca Galli |
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| Release | : 1986 |
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This Letter reports a new experimental search for the family-number-nonconserving decay ..mu.. ..-->.. e..gamma ... There is no evidence for the presence of this decay mode. The upper limit for the branching ratio is GAMMA(..mu.. ..-->.. e..gamma..)/GAMMA(..mu.. ..-->.. enu anti nu)
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| Total Pages | : 12 |
| Release | : 1989 |
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This report describes the status of the MEGA experiment, which is a search for the decay [mu] → e[gamma] with a branching ratio sensitivity of approximately 10−13. The observation of this decay would contradict the empirically established rule of lepton family number conservation and would indicate the existence of physics outside the standard model of electroweak interactions. The experimental design employs highly modular, fast detectors, state-of-the-art electronics, and a staged trigger with online filters. The detectors are contained in a 15 kG solenoidal field produced by a superconducting magnet. Positrons are confined to the central region and are measured by a set of thin MWPCs. Photons are measured by one of four layers of pair spectrometers in the outer region. Most aspects of the detector design have been validated in engineering runs; data taking will begin in 1990 with the electron arm and one pair spectrometer layer installed. 9 refs., 1 fig.
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| Release | : 2006 |
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The MEGA experiment is a search for the decay [mu] [r-arrow] e[gamma]. Even though there is no fundamental reason to expect lepton number to be a conserved quantity, processes such as [mu] [r-arrow] e[gamma] have not been observed. (The present upper limit for the branching ratio for [mu] [r-arrow] e[gamma] is 4.9 x 10[sup [minus]11].) The minimal standard model of electroweak interactions, which is enormously successful, builds in lepton number conservation. However, the decay [mu] [r-arrow] e[gamma] is expected in many extensions to the standard model, in particular in supersymmetry models. The experimental signature for [mu] [r-arrow] e[gamma] from decays at rest is the observation of a positron and photon, each of 52.8 MeV, that are back-to-back, in time coincidence, and originate from a common spatial point. The MEGA detector consists of two spectrometers designed to measure the kinematic characteristics of positrons and photons to search for events with this signature. The primary difficulty in the analysis of these data has been the development of reconstruction algorithms that balance efficiency and resolution. Also, many calibrations and corrections are needed to get optimum resolutions. Most surviving candidate events are accidentals. Results of analysis are given.
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| Release | : 2006 |
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The MEGA experiment is designed to search for the lepton-flavor number non-conserving rare decay [mu] [yields] [ital e][gamma]. Data- taking is complete, with 450 million events on tape taken over approximately 10[sup 7] seconds. A small portion of the data sample has been processed through the complete event reconstruction codes to search for the [mu] [yields] [ital e][gamma] process. No evidence for the [mu] [yields] [ital e][gamma] decay is observed at a sensitivity of [approximately]7 x 10[sup -11] (90% confidence).
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| Release | : 1988 |
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The MEGA experiment is designed to search for the .mu. .-->. e.gamma. process with a branching ratio sensitivity of 10−13. This decay violates the empirically established rule of lepton family number conservation and lies outside the Standard Model of electroweak interactions. In order for the experiment to make a factor of 500 improvement over the existing limit, a new design was adopted that employs highly modular, fast detectors and state-of-the-art electronic readout. The detectors are contained in a 15 kG solenoidal field produced by a superconducting magnet. The central region is a positron spectrometer, and the outer region is four layers of pair spectrometers. Data taking is expected to commence in 1989. 6 refs., 3 figs.
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| Release | : 2005 |
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The MEGA -experiment is a search for the decay [mu] [yields] [gamma], for which the present upper limit for the branching ratio is 4.9 [times] 10[sup [minus]11]. The observation of this decay would indicate the existence of physics outside the standard model of electroweak interactions. The experiment employs highly modular, fast detectors, state-of-the-art electronics, and a staged trigger with on-line filters. The detectors are contained in a 1.5 T solenoidal field produced by a superconducting magnet. Positrons axe confined to the central region and axe measured by a set of thin MWPCs with a designed energy resolution of 350 keV FWHM and angular resolution of 1 deg FWHM. Photons are measured by one of three layers of pair spectrometers in the outer region. The total photon detection efficiency is about 6%; the expected photon energy resolution is 1.7 MeV FWHM and the angular resolution is 10 deg FWHM. The time resolution between the photon and electron is 0.8 ns FWHM. About 10[sup 8] events that passed the on-line inters were recorded during the 1993 run. These data should have a branching ratio sensitivity approximately fifteen times better than the present limit. The measured resolutions are approaching the design values.
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| Release | : 1987 |
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An experimental search for the lepton-family number nonconserving decay, .mu. .-->. e.gamma gamma., has been conducted at the Clinton P. Anderson Meson Physics Facility (LAMPF) using the Crystal Box detector. The detector consists of a modular NaI(Tl) calorimeter, scintillator hodoscope, and a high-resolution, cylindrical drift chamber. It provides a large solid-angle for detecting three-body decays and has good resolutions in the time, position, and energy measurements to eliminate unwanted backgrounds. No evidence for .mu.+ .-->. e+.gamma gamma. is found, giving an upper limit for the branching ratio of GAMMA(.mu. .-->. e.gamma gamma.)/GAMMA(.mu. .-->. e nu anti nu) less than or equal to 7.2 x 10−11 (90% C.L.). This result is an improvement of more than two orders of magnitude in the existing limit. 109 refs., 39 figs.
