The study of magnetic field for COMET experiment Weichao Yao - PowerPoint PPT Presentation

The study of magnetic field for COMET experiment Weichao Yao 12/23/2019 Year-End Presentation

Contents • The magnet used in particle physics experiment • Introduction to motion of charged particle in magnetic field • The optimization of muon target of COMET experiment • Summary

Introduction to LHC & BESIII • Main Dipoles • there is a 27 km long underground tunnel, the Main Bends(MBs, dipole magnets) fill more than 2/3 of the ring • Nominal magnetic filed 8.33T, ultimate field 9 T. • ATLAS • 1 Barrel Toroid, 2 End Cap Toroids and 1 1T SC magnetic Central Solenoid • 2T inner detector • 1T for muon detectors • 4.1T peak in winding

The magnet used In COMET Experiment 5T 1 1 2 2 3T 3T 3 3 4 Here will be 5 4 introduced in this slide 5 ~1.08T 6 1T 6

The motion of charged particle in magnetic field

The distribution of magnetic field Item Material aluminium Shape flat disk Radius 100 mm disk Thickness 200 μ m Number of disks 17 Disk spacing 50 mm 3.214 • The total length of stopping target section is 5m • The default position of Stopping target is 3.214 m • Position? uniform field, slope field

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Energy deposit in target disks θ • If there is no magnetic field, the initial angle larger than θ , the hit number of particles is zero. The gap between disks more large more better. • The energy loss of electron with 105MeV in Aluminium : • βγ =105MeV/0.51=205.88, dE/dx ≈ -2.18 (MeV/g cm2), so Edep is 2.18 × 2.7= 5.86 MeV/cm: if the thickness is 0.2mm, then edep is 117.72 keV • There magnetic field in this section, the motion of charged particle will be helix

<latexit sha1_base64="W4OM/b/oSgKv39ecA4jFkiU1Hes=">ACOXicbVDLSgMxFM3UV62vqks3wSK4KGWmCroRSt24rGAf0Kklk2ba0GQmJlCGfJbvwLd4IbF4q49QdMH4vaeiBwOdcbu4JBKNKu+6rk1lb39jcym7ndnb39g/yh0cNFScSkzqOWSxbAVKE0YjUNdWMtIQkiAeMNIPh7cRvjohUNI4e9FiQDkf9iIYUI2lbr7m8+TGDyXCKYejbuoWfUGkMI9p2Zi0DKtWMmYxIajGgyJciU1Y7r5gltyp4CrxJuTApij1s2/+L0YJ5xEGjOkVNtzhe6kSGqKGTE5P1FEIDxEfdK2NEKcqE46vdzAM6v0YBhL+yINp+riRIq4UmMe2CRHeqCWvYn4n9dOdHjdSWkEk0iPFsUJgzqGE5qhD0qCdZsbAnCktq/QjxAtiRty87ZErzlk1dJo1zyLkrl+8tCpTqvIwtOwCk4Bx64AhVwB2qgDjB4Am/gA3w6z8678+V8z6IZz5zDP7A+fkFwGquHw=</latexit> <latexit sha1_base64="2ywr5fC9OtEoFeDx9Ic4UEjXI0=">ACEnicbVC7SgNBFJ31GeMramkzGISkCbtR0EYIsbGMYB6QjWF2MpsMmZ1dZu4KYdlvsPFXbCwUsbWy82+cJFto4oHLPZxzLzP3eJHgGmz721pZXVvf2Mxt5bd3dvf2CweHLR3GirImDUWoOh7RTHDJmsBsE6kGAk8wdre+Hrqtx+Y0jyUdzCJWC8gQ8l9TgkYqV8ou74iNKn3EztNpy3iQEdpeuVqLvF9Uk1LowYkHK/ULQr9gx4mTgZKaIMjX7hyx2ENA6YBCqI1l3HjqCXEAWcCpbm3ViziNAxGbKuoZIETPeS2UkpPjXKAPuhMiUBz9TfGwkJtJ4EnpkMCIz0ojcV/O6MfiXvYTLKAYm6fwhPxYQjzNBw+4YhTExBCFTd/xXRETEZgUsybEJzFk5dJq1pxzirV2/NirZ7FkUPH6ASVkIMuUA3doAZqIoe0TN6RW/Wk/VivVsf89EVK9s5Qn9gf4AgSud+Q=</latexit> The charged particle in gradient field: Mirror effect • the magnetic moment is considered the lowest- order approximation of the adiabatic invariant • At the reverse point, the ν ⫽ =0. • Magnetic moment is conserved mv 2 mv 2 ν 0 , ⊥ pitch, ⊥ µ = = ν ⊥ 2 B 0 2 B pitch θ • Therefore B ν ⫽ B 0 = sin 2 ( θ ) B pitch • Particles with appropriate angle will mirror in regions of higher B, If θ is too small, particle does not mirror. • Bmax =3T: • If B=1.5T, θ =45 degree; if B=2.1T, then θ =56.8 degree; if B=2.5T, then θ =66 degree • the particle within angle> θ could be reflected. 9

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Reflected rate of electron velocity v v z θ mirror e ff ect axis • The definition of the angle θ • Cos θ = v z / v • The maximum v z corresponding to to pitch angle upstream, reflected • if θ > pitch angle, the charged particle could be reflected, Downstream however if the θ is too large, it also could not be reflected θ >40 degree 11

The charged particle motion w/wo gradient field 2T with slope field 2T uniform • The mirror e ffi ciency will be e ff ected by the gradient field • If using the uniform field, the electron with small angle will be lost. The gradient field is necessary

The study of the optimization of stopping target • Purpose: • Increasing the muons yield in stopping target • improving the signal acceptance • Method: • Magnetic field option • The parameters of Stopping target: Number disks, Position, disks gap etc.

The options of Magnetic field • Using the gradient field • The default: center 1.8T, dB/dm=1.343 • Case1: center 2T, gradient < default • Improving the average field during • Case2: center 2.1T, gradient< default the Stopping target • Case3:center 2T, gradient ~> default • Changing the slope rate • Case4: center 2T, gradient > default • Changing the position