The NA62 rare kaon decay experiment Photon Veto System Vito Palladino for NA62 Coll.

The NA62 experiment aims to measure the Branching Ratio of the ultrarare decay K + → π + νν. The theoretical estimation in the SM is (8.22±0.84)x10 -11, thus a precise measurement will allow us to be sensitive to: Vito Palladino for NA62 Coll.2 Physics Precise Measurement of CKM matrix element V td which is the less well known one. Evidence of Physics Beyond the SM if deviation to expectations. BR(K + → πνν) SM = (8.22 ± 0.84) × 10 −11 BR(K + → πνν) Mis = ( ) × 10 − BR(K + → πνν) SM / BR(K + → πνν) SUSY  (0.65, 1.03) Minimal SUSY Prediction

Vito Palladino for NA62 Coll.3 The Photon Veto System LARGE ANGLE VETOES REQUESTS: Photon inefficiency: for 50MeV < E < 1GeV Energy Resolution: 10% at 1 GeV Time Resolution: better than 1ns Blue Tube LAV

Vito Palladino for NA62 Coll.4 The Large Angle Veto (LAV) The LAV system will be composed of 13 stations, in the beam direction we want O(20) X 0 in order to have the desired inefficiency values. The ring inner radius will range from 60 to 120 cm depending on the station position, the overall front surface is about 30m 2. During an intense R&D period 3 different technologies were tested: Lead + Scintillating Fibers (constructed from scratch) Lead + Scintillating Tiles (FNAL loan) Lead Glass (OPAL gift)

Vito Palladino for NA62 Coll.5 Lead + ScFibers Solution This solution is based on the realization of a sampling detector whose active material is a matrix of scintillating fibers (1mm Ø) glued between thin (0.5 mm thickness) lead layers. The ring may be made by superimposing two U shaped modules. SIDE

Vito Palladino for NA62 Coll.6 Lead + ScTiles Solution This solutions was designed by CKM Collaboration (FNAL). It consist of a sampling calorimeter that alternate lead (1mm) and scintillator (5mm) tiles. The ring was 16 X 0 long, and was made by 16 sectors. The scintillating layers was read by Wave Length Shifters Fibers. WLS One sector with staggered layers

Vito Palladino for NA62 Coll.7 Lead Glass This solution is based on the reuse of the Lead glass blocks that formed the barrel of OPAL electromagnetic calorimeter. Our request on the efficiency is reached rearranging the LGs in a configuration formed by 5 staggered layers so to have at least three modules involved in detection. The number three is in order to have at least 20 X 0 needed for the inefficiency requests.

Vito Palladino for NA62 Coll.8 Large Angle Veto Tests Tests were made to measure the performances of the detectors. The tests location was the Test Beam Facility (BTF) at Laboratori Nazionali di Frascati, that provide a beam of electrons with energy from 100 to 500 MeV. The BTF has a tagging system that provide to define events of Single Electron, this is a mandatory request for the efficiency measurement. Beam 90 cm Calorimeter The BTF Tagging System Finger Hole

Vito Palladino for NA62 Coll.9 Lead+ScFibers Test Beam Energy Resolution Time Resolution Beam Energy[MeV]Tagged EventsEvent with E<50MeV1-  (Inefficiency) x x x

Vito Palladino for NA62 Coll.10 Lead+ScTiles Test Beam Results (Preliminary) Beam Energy[MeV]Tagged EventsEvent with E<50MeV1-  (Inefficiency) x x x

Vito Palladino for NA62 Coll.11 Lead Glass Tests Beam First test was made using a simple geometrical LG arrangement of four of them, disposed transversally to the beam direction with central beam incidence Second one (February 2008) is made using a LGs staggered configuration similar that will be used in the final device. Both central and on edge incidences of the beam have been tested.

Vito Palladino for NA62 Coll.12 Lead Glass Results (Preliminary) First test Beam Energy[MeV]Tagged EventsEvent with E<50MeV1-  (Inefficiency) x x Second Test Beam Energy[MeV]Tagged EventsEvent with E<50MeV1-  (Inefficiency) x Beam Energy[MeV]Tagged EventsEvent with E<50MeV1-  (Inefficiency) x Central Incidence On edge Incidence

Vito Palladino for NA62 Coll.13 Lead Glass Time and Energy Resolution (Preliminary) Energy Resolution Time Resolution σ E /E = 9.7% Time Resolution will be subtracted by the fingers one (174ns). σ Time = 591ps Energy Resolution will be computed using data from other energies.

Vito Palladino for NA62 Coll.14 Conclusions All our tests have shown that the prototypes characteristics were at level (and beyond !) our specifications for the inefficiency on low energy electrons. Due to the availability of a large amount of Lead Glass blocks originally used by OPAL, we choose this as our baseline solution for the realization of the LAV system.

Vito Palladino for NA62 Coll.15 Future Plans Next months will be full of events: After some problems with the storage of the LGs (the storage area has been flooded), we are working for defining a procedure for cleaning and test half of the LGs needed for the whole project (~1000). Starting from September is scheduled a test of a sector of a ring at CERN on a K + beam to evaluate the performance of the device for photons and investigate the effects of the muon halo. In the same period of the test we will start the realization of the first prototype (Module 0) of the whole ring. This prototype will be used as one of the LAV station of the apparatus.

Thanks Vito Palladino for NA62 Coll.16

Spares Vito Palladino for NA62 Coll.17

Vito Palladino for NA62 Coll.18 The Signal Background Ratio Kinematical rejection S/B≈10

Vito Palladino for NA62 Coll.19 The Signal Background Ratio PId rejection BR(K + → πνν) SM = (8.0 ± 1.1) × 10 −11

Vito Palladino for NA62 Coll.20 The Beam North Area Momentum75 GeV/c K + decays for year4.8 x K + → π + νν events for year (BR = , accep. = 10%)48 K + /Total Flux5.5 x K + /π x 10 -2

Vito Palladino for NA62 Coll.21 Liquid Kripton (LKr)

Vito Palladino for NA62 Coll.22 Small and Inner Radius Calorimeters (SAC and IRC)

23 Lead+ScFibers Construction Glue Distribution Fibers Positioning Fibers Ordering Lead Cables Positioning Layer aspect after fiber and cables positioning Next Lead Leyer Positioning

24 Lead+ScFibers Construction Vito Palladino for NA62 Coll.