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

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. 06.06.2017 BNO-50

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 06.06.2017 BNO-50

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. 06.06.2017 BNO-50

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 06.06.2017 BNO-50

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 06.06.2017 BNO-50

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 06.06.2017 BNO-50

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 06.06.2017 BNO-50

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 06.06.2017 BNO-50

RICH STRAW station are backed-up by a ring-imaging Čerenkov (RICH) counter to identify pions with respect to muons 06.06.2017 BNO-50

CHOD Charged-particle hodoscope (CHOD), to detect photon conversion and hadron interactions of particles in the material upstream 06.06.2017 BNO-50

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 06.06.2017 BNO-50

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. 06.06.2017 BNO-50

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) 06.06.2017 BNO-50

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 06.06.2017 BNO-50

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 06.06.2017 BNO-50

Scintillators, photosensors and fibers SensL MicroFC-30035-SMT 3x3 mm2 The tiles are made of polymerized scintillator produced in IHEP Fiber Kuraray Y11 d = 1 mm 06.06.2017 BNO-50

Assembly of the New CHOD Wrapped: combination of Tyvek and 70μm Al-Mylar 06.06.2017 BNO-50

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) 06.06.2017 BNO-50

Time resolution of the New CHOD 06.06.2017 BNO-50

Time resolution of the New CHOD 06.06.2017 BNO-50

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 06.06.2017 BNO-50

Efficiency of the New CHOD New CHOD efficiency on average is close to 99% 06.06.2017 BNO-50

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 06.06.2017 BNO-50

Background 06.06.2017 BNO-50

Readout electronics 06.06.2017 BNO-50

Kuraray Y11 Fibers: Kuraray Y11 multiclad Diameter : 1 mm Cladding : double clad Decay time : ~12 ns Emission peak : 476 nm Attenuation length: 3.5-4 m 06.06.2017 BNO-50

Photodiodes SensL MicroFC-30035-SMT SPECIFICATION from datasheet (at 21oC): Sensitive area size : 3x3 mm2 Number of pixels : 4774 Pixel size : 35x35 µm2 Gain : 3 x106 Operating voltage: VBR+2.5 V Dark count rate: 300 kHz (typ.) Crosstalk: 7% (typ.) Peak spectral sensitivity: 420 nm PDE at 520 nm: ~20% 06.06.2017 BNO-50

Photodiodes SensL MicroFC-30035-SMT 06.06.2017 BNO-50

Background decays 06.06.2017 BNO-50