- Email: [email protected]
A Highly intense DC muon source, MuSIC and muon CLFV search
Available online at www.sciencedirect.com
Nuclear Physics B (Proc. Suppl.) 253–255 (2014) 206–207 www.elsevier.com/locate/npbps
A Highly intense DC muon source, MuSIC and muon CLFV search Y.Hinoa , Y.Kunoa , A.Satoa , H.Sakamotoa,b , Y.Matsumotoa , N.H.Trana , I.H.Hashima , M.Fukudab , Y.Hayashidab , T.Ogitsuc , A.Yamamotoc , M.Yoshidac a Department
of Physics, osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043 Center of Nuclear Physics, 10-1 Mihogaoka, Ibaraki, Osaka 567-0047 c High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801 b Research
Abstract MuSIC is a new muon facility, which provides the world’s highest intense muon beam with continuous time structure at Research Center of Nuclear Physics (RCNP), Osaka University. It’s intensity is designed to be 108 muons per second with only 0.4 kW proton beam. Such a high intense muon beam is very important for searches of rare decay processes, for example search for the muon to electron conversion. Keywords: Muon beam, CLFV, Accelerator
1. MuSIC MuSIC project is a highly intense DC muon beam facility, which is now under construction at RCNP, Osaka University [1]. It provides about 108 muons per second, using 392 MeV and 1 μA proton beam provided by the ring cyclotron of RCNP. Such a high intense will be used in various fields, for example, not only particle physics but also nuclear physics, chemistry, material science, accelerator R&D and so on. It consists of a proton beam line, a pion production target with a capture solenoid, muon transport solenoids, and a muon storage ring. In 2009, we finished the construction of the proton beam line, pion capture solenoid, and transport solenoid up to 36 degrees out of 180 degrees. The construction of other parts will be done step by step and it will finish probably in 2015 or 2016 (Figure1). 1.1. Technical points MuSIC has some technical points: (1) Thick pion production target located in solenoidal field, (2) Curved muon transport solenoids with dipole magnetic field. The pion capture system of MuSIC is a key point to improve muon collection efficiency (per proton beam) dramatically (Table 1). In conventional muon facilities, http://dx.doi.org/10.1016/j.nuclphysbps.2014.09.051 0920-5632/© 2014 Elsevier B.V. All rights reserved.
Figure 1: Final layout of MuSIC
there is strong limitation that proton loss at the pion production target must be small (~5%), because at the downstream of it there is neutron production target. So, the target thickness is thin, typical size is 2cm, and magnetic field on the proton bean line is not allowed. On the other hand, in MuSIC, we can use all proton beams to produce pions and muons because there is only beam dump at the downstream of the pion production target. The size of target is enough thick (20cm long and φ 40mm) and it is located in a 3.5T solenoidal magnetic field. So, pions generated after proton injection into the target can be corrected with large solid angle. Second, in the curved transport solenoids, pions and
Y. Hino et al. / Nuclear Physics B (Proc. Suppl.) 253–255 (2014) 206–207
Table 1: Comparison of muon facilities in the world
Beam power Muon intensity Time struction
MuSIC 0.4 kW 108 ~109 DC
J-PARC 1000 kW ~108 pulsed
PSI 1200 kW 108 ~109 DC
muons move helically and the center of helical orbit moves to a direction perpendicular to the plane of the curved solenoid. With an additional dipole field to the same direction of the drift, the center position of the orbit is restored. The proper value of dipole field By depends on the momentum p and charge q of the particle as following equation: 1 p 1 (cosθ + ) By = qr 2 cosθ
(1)
Where r refers the radius of the torus, and theta is the particle direction. By changing the dipole field, we can select the momentum and charge of the beam particle, as shown in Figure 2.
207
Therefore discovery of the process can be an evidence of new physics beyond the SM, for example, Supersymmetric theory, Grand Unified Theory and so on. In these theories, the branching ratio of CLFV is predicted in order of 10−14 , and this is reachable sensitivity (Figure 3). To achieve this, a high intense muon source, such as MuSIC, is required.
Figure 3: Feynman diagrams of CLFV in theory beyond SM: (a) Loop dirgram with supersymmetric particles, (b) Tree diagram of 4 fermion interaction mediated by a new boson
At MuSIC, we are planning to carry out some experiments to search muon CLFV decay, for example μ → eee [2] [3]. The aiming sensitivity is calculated as B(μ → eee)=10−14 , using beam intensity of 108 muons per second. Advantages of MuSIC for CLFV search experiments • High intense DC muon beam • Possible to select muon charge and momentum • Beam has large diameter, φ = 400mm
Figure 2: Momentum distribution of positive and negative muons, and their intensities, simulated by g4beamline
1.2. Beam test at MuSIC In 2009, present equipment was constructed. Then, we carried out five beam tests. The aim of the tests is to check performance of MuSIC systems and to compare with designed performance. By the measurement of the muon lifetime and muonic X-rays, we estimated the number of positive and negative muons, and furthermore, we tried the operation with high proton beam current (1 μA) with additional concrete shielding. As a result, we confirmed that MuSIC worked successfully, even if with high power, and ~108 muons/sec with 1 μA (=0.4kW) proton beam is achievable. 2. CLFV search at MuSIC The charged lepton flavor violation (CLFV) processes are forbidden by the Standard Model (SM).
Because of large beam size, the target and detector must be also big, but itfs convenient to identify vertexes of muon decay, especially when hit rate is high. In the measurement of μ → eee, the muon decay in orbit (μ → eeeνν), where two neutrinos carry very little energy, and accidental background (two normal decay and 1 electron) can mimic the signal. Those background can be suppressed by improving energy and position resolution of detectors. Now, wefre discussing detector requirements and aiming to complete MuSIC system. References [1] A.Sato, Y.Kuno, et al, Proceeding of IPAC2011, San Sebastian, Spain, pages 820-822 (2011) [2] A.Schoning, et al, Physics Procedia 00 (2010) 1-10 [3] U.Bellgardt, et al, Nucl. Phys. B229 (1988) 1-6
Nuclear Physics B (Proc. Suppl.) 253–255 (2014) 206–207 www.elsevier.com/locate/npbps
A Highly intense DC muon source, MuSIC and muon CLFV search Y.Hinoa , Y.Kunoa , A.Satoa , H.Sakamotoa,b , Y.Matsumotoa , N.H.Trana , I.H.Hashima , M.Fukudab , Y.Hayashidab , T.Ogitsuc , A.Yamamotoc , M.Yoshidac a Department
of Physics, osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043 Center of Nuclear Physics, 10-1 Mihogaoka, Ibaraki, Osaka 567-0047 c High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801 b Research
Abstract MuSIC is a new muon facility, which provides the world’s highest intense muon beam with continuous time structure at Research Center of Nuclear Physics (RCNP), Osaka University. It’s intensity is designed to be 108 muons per second with only 0.4 kW proton beam. Such a high intense muon beam is very important for searches of rare decay processes, for example search for the muon to electron conversion. Keywords: Muon beam, CLFV, Accelerator
1. MuSIC MuSIC project is a highly intense DC muon beam facility, which is now under construction at RCNP, Osaka University [1]. It provides about 108 muons per second, using 392 MeV and 1 μA proton beam provided by the ring cyclotron of RCNP. Such a high intense will be used in various fields, for example, not only particle physics but also nuclear physics, chemistry, material science, accelerator R&D and so on. It consists of a proton beam line, a pion production target with a capture solenoid, muon transport solenoids, and a muon storage ring. In 2009, we finished the construction of the proton beam line, pion capture solenoid, and transport solenoid up to 36 degrees out of 180 degrees. The construction of other parts will be done step by step and it will finish probably in 2015 or 2016 (Figure1). 1.1. Technical points MuSIC has some technical points: (1) Thick pion production target located in solenoidal field, (2) Curved muon transport solenoids with dipole magnetic field. The pion capture system of MuSIC is a key point to improve muon collection efficiency (per proton beam) dramatically (Table 1). In conventional muon facilities, http://dx.doi.org/10.1016/j.nuclphysbps.2014.09.051 0920-5632/© 2014 Elsevier B.V. All rights reserved.
Figure 1: Final layout of MuSIC
there is strong limitation that proton loss at the pion production target must be small (~5%), because at the downstream of it there is neutron production target. So, the target thickness is thin, typical size is 2cm, and magnetic field on the proton bean line is not allowed. On the other hand, in MuSIC, we can use all proton beams to produce pions and muons because there is only beam dump at the downstream of the pion production target. The size of target is enough thick (20cm long and φ 40mm) and it is located in a 3.5T solenoidal magnetic field. So, pions generated after proton injection into the target can be corrected with large solid angle. Second, in the curved transport solenoids, pions and
Y. Hino et al. / Nuclear Physics B (Proc. Suppl.) 253–255 (2014) 206–207
Table 1: Comparison of muon facilities in the world
Beam power Muon intensity Time struction
MuSIC 0.4 kW 108 ~109 DC
J-PARC 1000 kW ~108 pulsed
PSI 1200 kW 108 ~109 DC
muons move helically and the center of helical orbit moves to a direction perpendicular to the plane of the curved solenoid. With an additional dipole field to the same direction of the drift, the center position of the orbit is restored. The proper value of dipole field By depends on the momentum p and charge q of the particle as following equation: 1 p 1 (cosθ + ) By = qr 2 cosθ
(1)
Where r refers the radius of the torus, and theta is the particle direction. By changing the dipole field, we can select the momentum and charge of the beam particle, as shown in Figure 2.
207
Therefore discovery of the process can be an evidence of new physics beyond the SM, for example, Supersymmetric theory, Grand Unified Theory and so on. In these theories, the branching ratio of CLFV is predicted in order of 10−14 , and this is reachable sensitivity (Figure 3). To achieve this, a high intense muon source, such as MuSIC, is required.
Figure 3: Feynman diagrams of CLFV in theory beyond SM: (a) Loop dirgram with supersymmetric particles, (b) Tree diagram of 4 fermion interaction mediated by a new boson
At MuSIC, we are planning to carry out some experiments to search muon CLFV decay, for example μ → eee [2] [3]. The aiming sensitivity is calculated as B(μ → eee)=10−14 , using beam intensity of 108 muons per second. Advantages of MuSIC for CLFV search experiments • High intense DC muon beam • Possible to select muon charge and momentum • Beam has large diameter, φ = 400mm
Figure 2: Momentum distribution of positive and negative muons, and their intensities, simulated by g4beamline
1.2. Beam test at MuSIC In 2009, present equipment was constructed. Then, we carried out five beam tests. The aim of the tests is to check performance of MuSIC systems and to compare with designed performance. By the measurement of the muon lifetime and muonic X-rays, we estimated the number of positive and negative muons, and furthermore, we tried the operation with high proton beam current (1 μA) with additional concrete shielding. As a result, we confirmed that MuSIC worked successfully, even if with high power, and ~108 muons/sec with 1 μA (=0.4kW) proton beam is achievable. 2. CLFV search at MuSIC The charged lepton flavor violation (CLFV) processes are forbidden by the Standard Model (SM).
Because of large beam size, the target and detector must be also big, but itfs convenient to identify vertexes of muon decay, especially when hit rate is high. In the measurement of μ → eee, the muon decay in orbit (μ → eeeνν), where two neutrinos carry very little energy, and accidental background (two normal decay and 1 electron) can mimic the signal. Those background can be suppressed by improving energy and position resolution of detectors. Now, wefre discussing detector requirements and aiming to complete MuSIC system. References [1] A.Sato, Y.Kuno, et al, Proceeding of IPAC2011, San Sebastian, Spain, pages 820-822 (2011) [2] A.Schoning, et al, Physics Procedia 00 (2010) 1-10 [3] U.Bellgardt, et al, Nucl. Phys. B229 (1988) 1-6