K+e+γ using OKA detector Международная сессия-конференция Секции ядерной физики ОФН РАН «Физика фундаментальных взаимодействий» 6-8 июня 2017 г. A.Polyarush INR RAS On behalf of «OKA» collaboration (IHEP-INR-JINR) K+e+γ using OKA detector The talk layout OKA detector Ke3 and Ke3γ decays selection Background suppression Results Conclusions 1

Radiative K+e+γ decay «Физика фундаментальных взаимодействий» 6-8 июня 2017 г Radiative K+e+γ decay A.Polyarush INR RAS 2 06/06/17

Radiative K+e+γ decay «Физика фундаментальных взаимодействий» 6-8 июня 2017 г. Radiative K+e+γ decay The radiative K+e+γ decay allow as to perform quantitative tests CHPT, thanks to theoretical developments over the past couple of decades as well as recent and ongoing high-statistics experimental studies. The first complete analysis within CHPT to O(p4) order was performed by Bijinens et al. [Nucl. Phys. B396 (1993) 81]. Recently, the CHPT analysis was revisited and extended to O(p6) Kubis et al. [Eur Phys. J. C50 (2007) 557]. K+e+γ decay is one of kaon decays where new physics beyond Standard model can be probed. This decay is especially interesting as it is sensitive to T-odd contributions. According to CPT theorem, observation of T violation is equivalent to observation of CP-violating effects. 06/06/17 A.Polyarush INR RAS 3

OKA: search for T-violation in K+ decays PDG 2016 «Физика фундаментальных взаимодействий» 6-8 июня 2017 г OKA: search for T-violation in K+ decays   PDG 2016 Br(K+e+γ ) = (2.56 ± 0.16)·10 -4 A(ξ) = - 0.022 ± 0.024 A.Polyarush INR RAS 4 06/06/17

OKA detector ffff 1. Beam spectrometer:1mm pitch PC, ~1500 channels; Cherenkov counters 2. Decay volume with Veto system: 11m; Veto: 670 Lead-Scintillator sandwiches 20* (5mm Sc+1.5 mmPb), WLS readout 3. PC's and DT's for magnetic spectrometer: ~5000 ch. PC (2 mm pitch) + 1300 DT (1 and 3 cm) 4. Pad(Matrix) Hodoscope ~300 ch. WLS+SiPM readout 5. Magnet: aperture 200*140 cm2 6. Gamma detectors: GAMS2000, EHS-backward EM cal. ~ 4000 LG. 7. Muon identification: GDA-100 HCAL+ 4 muon trigger counters behind 06/06/17 A.Polyarush INR RAS 5 5

Decay volume with Veto System «Физика фундаментальных взаимодействий» 6-8 июня 2017 г. Decay volume with Veto System Decay volume Veto System Decay volume inside view Veto System A.Polyarush INR RAC 06/06/17 6

«Физика фундаментальных взаимодействий» 6-8 июня 2017 г. Statistics OKA collaboration operate at IHEP PS U-70 in Protvino, Moscow region. Detector is located in positive RF-separated beam with 12.5% of K-meson. Nov 2010 Nov 2011 Nov 2012 Apr 2013 Dec 2015 Total Beam, GeV/c 12.5+17.7 17.7 17.7 +12.5 12.5 Live Kaons, 109 6.2 5.1 17.4 12.2 6.7 47.8 K2π, 106 15.2 15.5 61 42 16 ~150 Ke3, 106 2.5 2.0 8.1 ~5 2.8 ~20 7 06/06/17 A.Polyarush INR RAS 7

«Физика фундаментальных взаимодействий» 6-8 июня 2017 г. IHEP PS U-70 U-70 ring IHEP Protvino accelerator ring length 1.5 km the size of the magnet as a truck A.Polyarush INR RAS 06/06/17 8

Ke3 decay selection 2812875 Ke3 events with Eγ > 0.5GeV 1 ch. track 2mrad point to em-shower in ECAL: (r<4cm) .8 <E/P<1.2 2 extra showers (ncl >3); 0.12 <M<0.15 GeV -angle between pK and pe 2mrad 2C -constrained fit χ2<20 2812875 Ke3 events with Eγ > 0.5GeV 0.8 <E/P<1.2 0.11 <M<0.16 GeV  - angle between pK and pe2mrad M2mis = (pK - pe 06/06/17 A.Polyarush INR RAS 9 9

K+e+γ events selection «Физика фундаментальных взаимодействий» 6-8 июня 2017 г. K+e+γ events selection 1) One positive charged track detected in tracking system and 4 showers detected in electromagnetic calorimeters GAMS- 2000 and EGS. 2) One shower must be associated with charged track. 3) Charged track is identified as positron. 4) Vertex situated within the decay volume. 5) The effective mass Mγγ for one γγ –pair is 0.12 <M<0.15 GeV. . 06/06/17 A.Polyarush INR RAS 10

Background suppression «Физика фундаментальных взаимодействий» 6-8 июня 2017 г. Background suppression The main background channels for the decay K+e+γ are: 1) K+e+ with extra photon. The main source of extra photons are an interactions of electrons in the detector material. 2) K++ where one  photons not detected and + decays to e+ or misidentified as positron. 3) K++ with fake photon and + decayed or misidentified as positron. Fake photon clusters can come from + hadron interaction in the detector, external bremsstrahlung, accidentals. All these sources are included in our MC calculations. 4) K++γ when + decays or is miss-identified as an positron. 5) K+e+ when one γ is lost. 06/06/17 A.Polyarush INR RAS 11

Background suppression «Физика фундаментальных взаимодействий» 6-8 июня 2017 г. Background suppression Emiss > 0.5GeV, Eveto < 50 MэВ, -2200<Zvx<-950, Eγ > 0.5GeV; | Δy | = | y γ - y e+ | > 4 cm, Δy - vertical distance in GAMS plane; |x,y| of reconstructed “ν” < 100cm in GAMS-2000 plane; | M2miss (p0e+γ )|< 0.003 GeV2; MK > 0.45GeV; 4 mrad < θeγ < 40 mrad, where M2miss (p0e+γ ) = (PK – Pπº – Pe – Pγ)2 , MK - K meson mass recovered, mass of the (e+γ)- system, assuming mν=0 . 06/06/17 A.Polyarush INR RAS 12

Experimental data K+ e+γ cut 1 cut 2 1) Emiss > 0.5GeV and … 2) | Δy | = | y γ - y e+ | > 4 cm 3) |x,y| in GAMS-2000 of reconstructed “ν” < 100cm 4) |M2miss (π0e+γ )|< 0.003 GeV2 5) MK > 0.45GeV 6) 4 mrad < θeγ < 40 mrad cut 3 cut 4 cut 5 cut 6 M2miss(π0e+γ ) 06/06/17 A.Polyarush, INR RAS 13

Experimental data K+ e+γ 1) Emiss > 0.5GeV and … 2) | Δy | = | y γ - y e+ | > 4 cm 3) |x,y| in GAMS-2000 of reconstructed “ν” < 100cm 4) |M2miss (π0e+γ )|< 0.003 GeV2 5) MK > 0.45GeV 6) 4 mrad < θeγ < 40 mrad MK 06/06/17 A.Polyarush, INR RAS 14

MC signal Experimental data 06/06/17 θeγ A.Polyarush INR RAS 15

Background suppression «Физика фундаментальных взаимодействий» 6-8 июня 2017 г Background suppression Cut Real data Ke3 Kπ3 Kπ2 Signal Emiss > 0.5GeV, Z, veto 515612 395930 19869 7138 62670 Δy > 4 cm 65093 10396 13975 1373 29190 |x,y| “ν” < 100cm 44363 7385 8726 1027 21950 MK > 0.045GeV 23446 3801 2901 333 17030 |M2 miss (e+γ )|< 0.005 GeV2 20739 3520 398 298 16120 4 mrad < θeγ < 40 mrad 13118 1239 225 138 12040 Table 1 06/06/17 A.Polyarush INR RAS 16

«Физика фундаментальных взаимодействий» 6-8 июня 2017 г Results Experiment Bg + signal Background 06/06/17 A.Polyarush INR RAS 17

«Физика фундаментальных взаимодействий» 6-8 июня 2017 г Results After applying cuts 1 to 6, we received 13,118 candidates. For E*γ > 10MeV and 0.6 <cos*θ <0.9 we have 3435 selected events with 252 background events. Comparing this after efficiency correction with ours 2812875 Ke3 events, for the relative branching ratio we got R=Г(K+e+γ ) / Г(K+e+) = (0.59 ± 0.02 ±0.03) ·10-2 Systematic errors are estimated by variation of cuts of Table 1 and using two different ways of backgrounds normalization. Theoretical prediction for R from CHPT is R = 0.56 ·10-2 For T-odd asymmetry we got: Aξ = 𝟏𝟔𝟐𝟐−𝟏𝟓𝟔𝟏 𝟑𝟏𝟖𝟑 =− 0.019± 0.020 ± 0.030 Theoretical prediction in Standard Model is Aξ = −0.59·10 −4 . 06/06/17 A.Polyarush INR RAS 18

«Физика фундаментальных взаимодействий» 6-8 июня 2017 г Results Nev R exp · 10 -2 Reference 3435 0.59 ± 0.02 ± 0.03 This work 1456 0.48 ± 0.02 ± 0.03 ISTRA+ 82 0.46 ± 0.08 XEBC 192 0.56 ± 0.04 ISTRA 13 0.76 ± 0.28 HLBC Table 20 06/06/17 A.Polyarush INR RAS 19

«Физика фундаментальных взаимодействий» 6-8 июня 2017 г Summary 1) collaboration, operating at IHEP Protvino U-70 PS in RF-separated beam, has accumulated large statistics of K+ decays. 2) K+e+γ decay signal is extracted with a low background. 3) R = Г(K+e+γ ) / Г(K+e+) = (0.59 ± 0.02 ±0.03) ·10-2 for the region E*γ > 10 MeV and 0.6 <cos*θ eγ <0.9 at statistic 3435 events. 4) Asymmetry in the T-odd variable ξ A(ξ) = - 0.019 ± 0.020± 0.03 for the region E*γ > 10 MeV and 0.6 <cos*θ eγ <0.9 Next step – to measure SD terms. 06/06/17 A.Polyarush INR RAS 20 20