1. The New CHOD detector for the NA62 experiment at CERN S
The New CHOD detector for the NA62 experiment at CERN S. Fedotov (INR) for NA62 collaboration

2. NA62 experiment Collaboration NA62: Number of institutes: 29
Number of authors: 226
Number of participants: 347
Number of countries: 13
The main goal of NA62 experiment is to study very rare kaon decays K+→π+νν with 10% precision. This decay mode is strongly suppressed in Standard Model (SM) and can be very precisely calculated in terms of SM parameters. Branching ratio of BR(K+→π+νν)=7.81·10−11 makes it sensitive for search the New Physics beyond SM.
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3. Rare Kaon decay (K+→π+νν̃)
Theoretically clean (~10%)
Main contribution from Short Distance
Hadronic matrix elements related to well known decay K+→e+νπ0
Sensitive to New Physics
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4. NA62 experiment
A few candidates for the decay have been observed in BNL experiments E787 and E949, but the error in measured branching ratio was too large. Only the measurement of the branching ratio with at least 10% accuracy can be a significant test of new physics.
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5. CEDAR
An intense, momentum-selected hadron beam of secondary particles. The K+ component in the beam is positively identified with respect to the other beam particles by an upgraded differential Čerenkov (CEDAR) counter
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6. GTK
The coordinates and momentum of individual beam particles are registered before entering the decay region by 3 silicon pixel tracking detectors (GTK) tracking detectors
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7. CHANTI
The Charged ANTI (CHANTI) detector is required in order to reduce critical background induced by inelastic interactions of the beam with the collimator and the Gigatracker (GTK) stations as well as to tag beam halo muons in the region immediately close to the beam
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8. LAV
The Large Angle Veto (LAV) detector is one part of the overarching photon veto system in the NA62 experiment. It consists of 12 stations distributed along the decay volume. In this configuration the LAV covers the angular region between 8.5 mr and 50 mrad
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9. STRAW
A large-acceptance, magnetic spectrometer with tracking detectors(STRAW Tracker) in vacuum are required to detect and measure the coordinates and momentum of charged particles originating from the decay region
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10. RICH
STRAW station are backed-up by a ring-imaging Čerenkov (RICH) counter to identify pions with respect to muons
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11. CHOD
Charged-particle hodoscope (CHOD), to detect photon conversion and hadron interactions of particles in the material upstream
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12. LKr
The Liquid Krypton (LKr) calorimeter is a quasi-homogeneous electromagnetic calorimeter which ensures a very good intrinsic energy resolution for the experiment. It is key for vetoing photons from Kaon decays. The LKr covers the angular region between 1.0 mr and 8.5 mrad
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13. MUV
The LKr calorimeter is backed up by muon-veto detectors (MUV), composed of a two-part hadron calorimeter followed by additional iron and a transversally-segmented hodoscope.
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14. Problems with CHOD Problems with CHOD:
low online resolution (two layer of scintillation)
large number of events the central region of the detector
Solution: creation of a new detector (New CHOD)
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15. New Charged particle HODoscope
Location: installed between RICH and last station LAV
The main function:
To identify trigger topologies with charged particles in the fiducial volume
To detect photon conversion and hadron interactions of particles in the material upstream
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16. Structure of the New CHOD
Tiles: 268×108 mm2 on periphery and 134×108 mm2 at the center region
Number of tiles: 152
Covers the area: 140 mm < R < 1070 mm
Readout: two readout channels for each tile
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17. Scintillators, photosensors and fibers
SensL MicroFC SMT 3x3 mm2
The tiles are made of polymerized scintillator produced in IHEP
Fiber Kuraray Y11 d = 1 mm
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18. Assembly of the New CHOD
Wrapped: combination of Tyvek and 70μm
Al-Mylar
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19. Rates in CHOD tiles at nominal beam intensity (in MHz)
Rates in the New CHOD
Rates in CHOD tiles at nominal beam intensity (in MHz)
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20. Time resolution of the New CHOD
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21. Time resolution of the New CHOD
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22. Time resolution of the old CHOD
Time spectra of the CHOD :
Before T0-correction
After first T0-correction
After second T0-correction
Online time resolution of CHOD ~ 3ns
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23. Efficiency of the New CHOD
New CHOD efficiency on average is close to 99%
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24. Summary The New CHOD detector: installed in the experimental hall
integrated in NA62 Data Acquisition and Detector Control systems
included in L0-trigger
For the single track events:
Time resolution ~ 1 ns
Efficiency ~ 99%
Cordially acknowledged
I. Mannely for tips and help; S. Kholodenko for his work with New CHOD; Yu. Kudenko for collaboration in all steps
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25. Background
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26. Readout electronics
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27. Kuraray Y11 Fibers: Kuraray Y11 multiclad Diameter : 1 mm
Cladding : double clad
Decay time : ~12 ns
Emission peak : 476 nm
Attenuation length: m
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28. Photodiodes SensL MicroFC-30035-SMT
SPECIFICATION from datasheet (at 21oC):
Sensitive area size : x3 mm2
Number of pixels :
Pixel size : x35 µm2
Gain : x106
Operating voltage: VBR+2.5 V
Dark count rate: kHz (typ.)
Crosstalk: % (typ.)
Peak spectral sensitivity: nm
PDE at 520 nm: ~20%
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29. Photodiodes SensL MicroFC-30035-SMT
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30. Background decays
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