New CHOD detector for the NA62 experiment at CERN
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w CHOD Detector for the NA62 Experiment at CERN S. A. Fedotov*, A. A. Kleymenova, and A. N. Khotjantsev Institute for Nuclear Research, Russian Academy of Sciences, Moscow, 117312 Russia *e-mail: [email protected] Abstract⎯The New CHOD is a scintillation hodoscope with a pad structure featuring a total of 148 counters. The signal from each pad is read out using wavelength-shifting fibers and two or four SensL SiPMs with a sensitive area of 3 × 3 mm2. This photodetector has 4774 pixels 35 × 35 μm2 in size. The key parameters (photon detection efficiency, dark current, crosstalk, and gain) were measured for 500 SiPMs. DOI: 10.1134/S1063779618010094
plastic scintillators of various sizes that cover the area around the beam. The detector is to operate in a highintensity mode with a reasonable count rate per channel and should provide high time resolution. The key functions of CHOD are to provide the signal in the level-0 trigger system and to veto efficiently the probable interactions in the mirror region of the RICH detector.
NA62 EXPERIMENT The NA62 experiment [1] is focused on the investigation of the very rare kaon decay (K+ → π +νν ). This decay is strongly suppressed and is calculated accurately in the Standard Model (SM). Therefore, the experimental measurement of its branching ratio provides an opportunity both to verify the correctness of the Standard Model itself and to obtain data regarding new physics beyond the SM. Seven decays of this type have already been detected in the Е949 experiment [2, 3]. This number is not sufficient to validate the SM predictions. A 10-percent measurement precision is expected to be achieved in the NA62 experiment. The experiment layout is shown in Fig. 1. The NA62 setup features many detectors. The charged-particle hodoscope (CHOD), which vetoes a huge number of muon decays, is one of these detectors. The CHOD has a pad structure and is made of
NEW CHOD DETECTOR Several problems with CHOD were identified in experimental runs in a kaon beam. Issues (related to the two-layer structure of this detector) in the operation of the detector firmware were found. High count rates in the central region of the detector did also cause problems. It was then decided that a new detector (New CHOD) should be constructed. Veto Photons and Muons
Hadron beam 750 MHz
π identification
CHATI
Kaon identification GTK CEDAR RICH Fiducial region 65 m
STRAW Tracker
Total length 270 m Fig. 1. Layout of the NA62 experiment [3].
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LKR MUV CHOD
NEW CHOD DETECTOR FOR THE NA62 EXPERIMENT AT CERN
(a)
(b)
HDDD1
HDDD2
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HDDD2
HDDD1
Fig. 2. (a) Diagram of the CHOD detector with a two-layer strip structure. (b) Pad structure of the New CHOD; a quarter of the hodoscope, which is symmetric with respect to the beam axis, is shown.
STRUCTURE OF THE NEW CHOD The New CHOD serves the same purpose as the old detector, but differs (Fig. 2а) in its design: instead of two layers of scintillation strips, it features a singlelayer pad structure (Fig. 2b). This provides an opportunity to resolve the firmware iss
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