POLENKEVICH IRINA (JINR, DUBNA) ON BEHALF OF THE NA62 COLLABORATION XXI INTERNATIONAL WORKSHOP ON HIGH ENERGY PHYSICS AND QUANTUM FIELD THEORY (QFTHEP'2013) 23 – 30 JUNE, 2013 Prospects for K  →   observation at CERN

Outline Motivation Principles of NA62 Sensitivity Studies Results from the 2012 Technical Run Conclusions 2 Irina Polenkevich QFTHEP'2013, June

K →  : a theoretical clean environment FCNC processes described with penguin and box diagrams Very clean theoretically: SD contributions dominate BR proportional to |V ts *V td | 2 → theoretical clean V td dependence SM predictions [Brod, Gorbahn, Stamou, Phys. Rev. D 83, (2011)] :  BR(K L →  0 ) = (2.43 ±0.39 ±0.06) × Pure theoretical error, mostly LD corrections  BR (K  →   ) = (7.81 ± 0.75 ± 0.29)× Parametric error dominated by V cb,  Present experimental results:  BR(K  →   ) = (17.3 − )×10 −11 [E787, E959]  BR(K L →   ) < 2.6×10 −8 [E391a] 3 Irina Polenkevich QFTHEP'2013, June

Irina Polenkevich 4 Experimental Measurements and Techniques Stopped Work in kaon frame High kaon purity Compact detectors In-Flight Decays in vacuum Separated or not separated beams Extended decay regions Upcoming experiments: CERN JPARC Fermilab

The NA62 detector for K  →   Goal: 10% precision branching ratio measurement of K  →    O(100) SM K  →   events (2 years of data) Requirements  Statistics: BR(SM)  8 x  K decays (2 years):  Acceptance:  10%  Systematics:  >10 12 background rejection (<20% background)  <10% precision background measurement Technique  “High” momentum K + beam Kaon intensity Signal efficiency Signal purity Detector redundancy Decay in flight 5 Irina Polenkevich QFTHEP'2013, June

SPS proton 400 GeV/c Proton on target: 1.1 x / s P secondary charged beam 75 GeV/c Momentum bite 1% Angular spread in X and Y < 100 mrad beam tracker: 5.5 x 2.2 cm 2 beam tracker: 750 MHz 6% K + (others:  +, proton) Rate downstream 10 MHz (K + decay mainly) K decay rates / year: 4.5 x10 12 (60 m decay volume) Beam line Irina Polenkevich QFTHEP'2013, June

Detectors 7 The CEDAR – differential Cerenkov counter  K + components in the beam GTK – Gigatracker  3 Si micro-pixel station  Time, direction and momentum of the beam particle The STRAW Tracker  4 Chambers inside the high vacuum (  ) tank  Coordinate and momentum of secondary charged particles from decay volume The RICH detector  17m long radiator filled with neon Gas at 1 atm, THE MUV – Muon-Veto Detectors  2-part hadron calorimeter, iron and a transversally-segmented hodoscope  Separate pions and muons between 15 and 35 Gev/c System of Photon-Veto detectors:  The LKR – high resolution Liquid Krypton electro-magnetic calorimeter  IRC and SAC– Intermediate Ring and Small-Angle Calorimeters  12 annular photon-veto LAV detectors  Hermetic coverage 0-50 mrad angles from the decay region Counters CHANTI and charge-particle hodoscope CHOD Acceptance High-performance trigger and Data- acquisition (TDAQ) system Irina Polenkevich QFTHEP'2013, June

Scheme for  Selection One reconstructed track in the Straw (  + track) Signal in RICH compatible with only 1  + hypothesis Signal in Calorimeters (CHOD, LKr, MUV1,2,3) compatible with only 1  + hypothesis No clusters in LKr compatible with  hypothesis No signals in LAVs, IRC, SAC compatible with  hypotesis At least one track in Gigatracker matched in space and time with the  + track (K + track) and compatible with the beam parameters (75 GeV/c) No extra activity in CHANTI compatible with a MIP signal Signal in KTAG compatible with a K hypothesis Z vertex in the first 60 m of the decay volume 15 < P  + < 35 GeV/c Irina Polenkevich QFTHEP'2013, June

Signal and Background Signal  Kinematic variable : Background 1) K + decay modes 2) Accidental single track matched with a K-like track Signal signature:  Incoming high momentum(75 GeV/c) K +  Outcoming low momentum(<35 GeV/c)  + in time with the incoming K + 9 Irina Polenkevich QFTHEP'2013, June

10 Background Rejection Decay BR K + →  +(K 2 ) 0.64 K + →  +  0 (K 2 ) 0.21 K+→++K+→+00K+→++K+→+0 Irina Polenkevich QFTHEP'2013, June ~92% of kaon decays separated by kinematical cut

11 Particle Identification K + positive identification (CEDAR)  /  separation (RICH)  /e separation (E/p) DecayBR K + →   e +(K e3 ) K + →  0  +(K 3 ) K + →  + (K 2 )6.210 -3 K + →  +  - e + (K e4 )4.110 -5 K + →  +  -  + (K 4 )1.4  Irina Polenkevich QFTHEP'2013, June

Physics Sensitivity Decay event/year K + → π + ν ν [SM] (flux 4.5x10 15 ) 45 K + → π + π 0 5 K + → μ + ν 1 K + → π + π - π + < 1 K + → π + π - e + ν + other 3-track decays < 1 K + → π + π 0 γ (IB) 1.5 K + → μ + ν γ (IB) 0.5 K + → π 0 e + (μ + ) ν, other decays negligible Total background < 10 Cut & count analysis without any optimization e.g. Use of the 2 shape to add further signal/background discrimination The background must be measured with at least 10% precision Background evaluation to be done on data 12 Irina Polenkevich QFTHEP'2013, June

Results from the 2012 Technical Run Goals: Analysis of the time and spatial correlation between the subdetectors Estimation of the time resolution and efficiency of the subdetectors Partial set –up: KTAG (50% PMs), 1 straw plane, CHOD, LKr (30% readout), MUV2, MUV3 Analysis Method: selection of K +  +  0 events Selection based on the Liquid Kripton Calorimeter Photon tagging from the shape of the reconstructed clusters  0 reconstruction: Z vertex from 2  on the LKr assuming m  0 X and Y vertex from the assumed K direction K momentum (P K ) and divergence well defined by the beam line P  + = (P K - -P  0 )  P 2  + = m 2  + for K +  +  0 13 Irina Polenkevich QFTHEP'2013, June

The Final K +  +  0 Sample  Exploit the timing and spatial correlations between the subdetectors to define a Kaon candidate, pion candidate and a muon candidate.  Signal region:  0 < m 2 miss < 0.04 GeV 2 /c 4  % level   m miss 2  =(0.0199±0.0005) GeV 2 /c 4   (m miss 2 ) =3.8  GeV 2 /c 4  m 2 (  + )= GeV 2 /c 4  Time resolution: KTAG 150 ps, LKr 350 ps, CHOD 400 ps, MUV3 450 ps  KTAG efficiency about 87% (corresponding to 95% for a fully instrumented detector)  6% of events with a muon in-time (upper limit to the punch-through)  This analysis will be used in the final analysis to monitor the tails of the m miss 2 reconstructed with the tracking system. 14 Irina Polenkevich QFTHEP'2013, June

Conclusions The Na62 will allow us:  10% precision BR(K  →   ) measurement in two years of data taking  observe and study of other rare decays 15 to fulfill a strong test for the SM or to indicate a new physics We look forward to the 2014 data Irina Polenkevich QFTHEP'2013, June

Thank you