- Email: [email protected]
Present status of the MEG experiment at PSI
Available online at www.sciencedirect.com
Nuclear Physics B (Proc. Suppl.) 221 (2011) 336 www.elsevier.com/locate/npbps
Present status of the MEG experiment at PSI F Cei1 , for the MEG Collaboration 1
Department of Physics, University of Pisa, Largo B. Pontecorvo, 3, 56127 Pisa, ITALY
E-mail: [email protected] Abstract. We describe the present status of the MEG experiment, whose aim is to search for the lepton flavour violating (LFV) process μ+ → e+ γ with a sensitivity down to 10−13 . Recent theoretical calculations indicate a strong connection between LFV processes and neutrino oscillations [1]. We discuss the detection techniques and the performances of the experiment.
The MEG experiment at PSI [2] (Fig. 1) aims to be sensitive to the μ+ → e+ γ branching ratio down to 10−13 , a level within the predictions of many SUSY theories [3] and two orders of magnitude better than the present limit [4]. A positive muon beam (≈ 108 μ+ s−1 ) will be brought to stop in a thin target, slanted by 22◦ , where muons will decay. The e+ and the γ (emitted back-to-back, both with 52.8 MeV kinetic energy) will be detected by 1) a magnetic spectrometer (composed by an almost solenoidal magnet (COBRA) with an axial gradient field and a system of 16 drift chambers, DCH) for measuring the momentum and a pair of double-layer arrays of plastic scintillators (Timing Counter, TC) for measuring the absolute timing and by 2) a ≈ 800 l volume liquid xenon (LXe) calorimeter, equipped with 846 PMTs, for the Figure 1. Layout of MEG experiment. measurement of γ energy, direction and timing. The LXe was chosen because of its large light yield, homogeneity and fast scintillation light decay time (∼ 20 ns). Challenging energy, angular and timing resolutions are required for all detectors in order to single out the possible μ+ → e+ γ candidates and reject the background. A 5 % energy and 140 ps timing resolution at 55 MeV [5] for γ’s in LXe calorimeter and a < 100 ps timing resolution (all FWHM) in TC for e+ ’s were obtained in various experimental tests. The expected resolutions for DCH system are Δp ≈ 0.7 ÷ 0.9 % and Δθ ≈ 9 ÷ 12 mrad (all FWHM). The MEG experiment is in advanced state of building and is planned to start at the end of 2006; it is expected to be completed in 2008, before the first results of LHC experiments. Liq. Xe Scintillation Detector
Liq. Xe Scintillation Detector
Muon Beam
Thin Superconducting Coil
γ
Stopping Target
+
e
Timing Counter
γ
e+
Drift Chamber
Drift Chamber
1m
References [1] [2] [3] [4] [5]
Masiero A et al 2004 JHEP 0403 046; Hisano J and Nomura D 1999 Phys. Rev. D 59 116005 MEG Collaboration, Baldini A et al , Proposal to INFN, available at the web-site: http://meg.psi.ch Barbieri R and Hall L J 1994 Phys. Lett. B 338 212; Barbieri R et al 1995 Nucl. Phys. B 445 219 MEGA Collaboration, Ahmed M et al 2002 Phys. Rev. D 65 112002 Baldini A et al 2005 Nucl. Inst. and Meth. A 545 753
0920-5632/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2011.09.035
Nuclear Physics B (Proc. Suppl.) 221 (2011) 336 www.elsevier.com/locate/npbps
Present status of the MEG experiment at PSI F Cei1 , for the MEG Collaboration 1
Department of Physics, University of Pisa, Largo B. Pontecorvo, 3, 56127 Pisa, ITALY
E-mail: [email protected] Abstract. We describe the present status of the MEG experiment, whose aim is to search for the lepton flavour violating (LFV) process μ+ → e+ γ with a sensitivity down to 10−13 . Recent theoretical calculations indicate a strong connection between LFV processes and neutrino oscillations [1]. We discuss the detection techniques and the performances of the experiment.
The MEG experiment at PSI [2] (Fig. 1) aims to be sensitive to the μ+ → e+ γ branching ratio down to 10−13 , a level within the predictions of many SUSY theories [3] and two orders of magnitude better than the present limit [4]. A positive muon beam (≈ 108 μ+ s−1 ) will be brought to stop in a thin target, slanted by 22◦ , where muons will decay. The e+ and the γ (emitted back-to-back, both with 52.8 MeV kinetic energy) will be detected by 1) a magnetic spectrometer (composed by an almost solenoidal magnet (COBRA) with an axial gradient field and a system of 16 drift chambers, DCH) for measuring the momentum and a pair of double-layer arrays of plastic scintillators (Timing Counter, TC) for measuring the absolute timing and by 2) a ≈ 800 l volume liquid xenon (LXe) calorimeter, equipped with 846 PMTs, for the Figure 1. Layout of MEG experiment. measurement of γ energy, direction and timing. The LXe was chosen because of its large light yield, homogeneity and fast scintillation light decay time (∼ 20 ns). Challenging energy, angular and timing resolutions are required for all detectors in order to single out the possible μ+ → e+ γ candidates and reject the background. A 5 % energy and 140 ps timing resolution at 55 MeV [5] for γ’s in LXe calorimeter and a < 100 ps timing resolution (all FWHM) in TC for e+ ’s were obtained in various experimental tests. The expected resolutions for DCH system are Δp ≈ 0.7 ÷ 0.9 % and Δθ ≈ 9 ÷ 12 mrad (all FWHM). The MEG experiment is in advanced state of building and is planned to start at the end of 2006; it is expected to be completed in 2008, before the first results of LHC experiments. Liq. Xe Scintillation Detector
Liq. Xe Scintillation Detector
Muon Beam
Thin Superconducting Coil
γ
Stopping Target
+
e
Timing Counter
γ
e+
Drift Chamber
Drift Chamber
1m
References [1] [2] [3] [4] [5]
Masiero A et al 2004 JHEP 0403 046; Hisano J and Nomura D 1999 Phys. Rev. D 59 116005 MEG Collaboration, Baldini A et al , Proposal to INFN, available at the web-site: http://meg.psi.ch Barbieri R and Hall L J 1994 Phys. Lett. B 338 212; Barbieri R et al 1995 Nucl. Phys. B 445 219 MEGA Collaboration, Ahmed M et al 2002 Phys. Rev. D 65 112002 Baldini A et al 2005 Nucl. Inst. and Meth. A 545 753
0920-5632/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2011.09.035