Teorías de la teatroterapia

Time of Flight Detectors (TOF)

Three time of flight detectors, identified in Figure 2.5 as TOF 0, 1 and 2, serve several purposes. Their most important use is to provide particle identification information by measuring the time of flight between two TOF stations. They can also serve as an experimental trigger, and during Step I the first measurement of emittance was made using the TOFs. An example of the time of flight distributions between TOF0 and TOF1 during Step I is shown in Figure 2.15

The TOFs are composed of slabs of scintillating material arranged in two planes, orientated in X and Y. TOF0,1, and 2 have active areas of 40×40 cm2, 42×42 cm2, and 60×60 cm2 respectively. The slabs in TOF0 are 4 cm wide, while the slabs of TOF1 and TOF2 are 6 cm wide [37]. respectively. The strip width is 4 cm for TOF0 and 6 cm for the other two stations. Readout is performed by photo-multiplier tubes (PMTs). TOF0,1, and 2 have timing resolutions of 51 ps, 58 ps and 52 ps respectively, consistent with design requirements. TOF0 and TOF1 are placed upstream of the cooling channel, and TOF2 is downstream of the channel, mounted in front of the KL, as shown in Figure 2.16.

Figure 2.15: Time of flight between TOF0 and TOF1 for a muon beam (left) and pion beam (right) [38]. In the muon beam, a small electron peak can be seen at 26 ns, while the pion contamination of the beam is contained within the muon peak. For the pion beam, the electron, muon, and pion peaks are clearly separated, at 26, 29, and 31 ns respectively.

(a) Front view of one of the Cherenkov de- tectors.

(b) Both Cherenkov detectors in place in the beamline.

Figure 2.17: Cherenkov detectors in MICE

Cherenkov Detectors

Cherenkov light is produced when a charged particle passes through a medium with a speed that is greater than the speed of light in that medium. In a Cherenkov detector, this light is then converted by a photomultiplier tube into an electrical signal that is proportional to the intensity of the light produced.

At higher momenta, muons and pions cannot be easily distinguished by their time of flight. MICE has two Cherenkov detectors (CkovA and CkovB) with dif- ferent refractive indices (1.07 and 1.12 respectively), immediately downstream of TOF0, which can distinguish between particle types due to their different values of relativisticβ.

The refractive indices of the Cherenkovs have been selected such that, for a 200 MeV/c beam, muons will produce a signal in CkovB, but not CkovA, and pions will produce no signal. For a 240 MeV/c beam, pions will produce a signal in CkovB, whereas muons will produce a signal in both detectors. At 140 MeV/c, neither muons or pions will produce a signal in the Cherenkovs, however TOF separation is sufficient at this lower momentum. Figure 2.18 shows the Cherenkov response with respect to the particle time of flight. The efficiencies of CkovA and CkovB are shown in Figure 2.19.

KLOE Light (KL) Calorimeter

Figure 2.18: The number of photoelectrons produced in the Cherenkovs with respect to the time of flight. A clear separation between the different particle species can be seen [25].

Figure 2.19: The efficiencies of CkovB (solid line) and CkovA (dashed line), as a function of the particle time of flight (in ns) [39].

Figure 2.20: Layout of the KL extruded lead and fibres [38].

has an active volume of 93 x 93 x 4 cm3 and is composed of 21 cells of scintillating fibres within extruded lead foils, shown in Figure 2.20, and scintillation light is readout by 42 Hamamatsu R1355 PMTs. Figure 2.21 shows an exploded view of the KL readout [38], while an exploded view of the KL assembly is shown in Figure 2.21. The signal from the PMTs is shaped and extended in time to match the sampling rate of flash ADCs. The measurement quantity of interest from the KL is the ADC charge product, which is the product of the digitised signals from either side of the cell, divided by their sum, and with a factor of 2 for normalisation, which is of more use than just the ADC charge as it compensates for light attenuation [25].

ADCprod= 2×ADClef t×ADCright/(ADClef t+ADCright) (2.1)

The response of the KL to muons, pions, and electrons of different momenta is shown in Figure 2.22.

Electron Muon Ranger (EMR)

The EMR is a totally active scintillator detector, that can distinguish between muons and electrons produced by muon decay in the channel, based upon the range of the particle in the detector, and the characteristics of the energy loss of the particle in the detector. Extruded triangular shaped scintillating plastic bars are arranged in a x-y geometry into 48 planes of 59 bars each. The scintillator light is carried by wavelength shifting fibres, and readout by multi-anode PMTs on both sides. Figure 2.24 shows the EMR in the MICE hall.

Muons and electrons have distinctively different behaviours in the EMR. A muon will leave a single track in the EMR before either stopping, decaying, or exiting the detector, whereas electrons will create an electromagnetic shower. Event displays of a muon track in the EMR are shown in Figure 2.25, and of a showering

Figure 2.21: An exploded view of a single KL module (which contains 3 cells), with the light guides (A), metal shielding (B), PMTs (C) and voltage dividers (D) [25].

Figure 2.22: KL response for different muon and pion momenta, and for 80 MeV/c electrons, taken from [25].

Figure 2.23: Exploded view of KL assembly. The seven strips in the centre contain the active cells. The red bars cover the light guides, the dark blue is the magnetic shielding for the PMTs, the green is the iron bars that house the PMT voltage dividers, and the mechanical support for the KL is in yellow [25].

Figure 2.24: EMR detector.

electron in Figure 2.26. For a particle that stops in the EMR, it is also possible to determine the momentum of the particle, with a resolution of 3 MeV/c [40]