1. STUDY OF ULTRAREAR DECAYS K 0 → π 0 νν(bar) (Search of K 0 → π 0 νν(bar) decay at IHEP, project KLOD ) V.N. Bolotov on behalf of the collaboration JINR, IHEP and INR RAS

2. 29.11.20152

3. 3 STATE RESEARCH CENTER OF RUSSIA INSTITUTE FOR HIGH ENERGY PHYSICS

4. 29.11.20154 theoretically Rare FCNC process Purely CP-Violetting (Littenberg, 1989) Totally dominated from t-quark  Computed in QCD (Buchalla, Buras, 1999)  Small corrections due to m t is known from K +   0 e + e (K e3 )  No long distance contribution (Rein, L. M. Sehgal, 1989; Marciano, Z. Parsa 1996) SM: Br ~ η 2, CP violating parameter (Buchalla, Buras, PR, 1996) Sensitive to the new heavy objects  New physics Theoretically clean process, ~1% SM: Br = (2.8±0.4)×10 −11 (Buras et al., hep-ph/0603079)

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10. 10 Experimental challenge. Must-do experiment signature: π 0 -signal + “nothing” At least 2 charged or 4 γ’s -- veto inefficiency ~ 10 -6 -- full veto covered π 0 in 34% of decays -- P T cut (231MeV/c) Interaction with gas -- high vacuum Strategy: 2 γ’s in Ecal No veto-signal Construct π 0 from 2 γ’s -- reconstruct vertex -- reconstruct P T (narrow beam approach)

11. 29.11.201511 K L beam at U-70 IHEP Beam requirements -- very narrow (R<5cm) and well collimated -- high P T balanced -- high intensity (~10 8 K L /pulse) -- mean K L energy ~10 GeV -- minimal contamination of neutral unwanted particles (neutrons/K L < 10) Sketch design completed ! K L beam optimization conditions -- 10 13 60 GeV p/cycle (slow extraction); -- Cu-target 25см (80% interactions); - 35 mrad extraction angle; - 5 cm Pb-converter: - steel collimators

12. 29.11.201512 K L beam at U-70 IHEP Beam requirements -- very narrow (R<5cm) and well collimated -- high P T balanced -- high intensity (~10 8 K L /pulse) -- mean K L energy ~10 GeV -- minimal contamination of neutral unwanted particles (neutrons/K L < 10) Sketch design completed ! K L beam optimization conditions -- 10 13 60 GeV p/cycle (slow extraction); -- Cu-target 25см (80% interactions); - 35 mrad extraction angle; - 5 cm Pb-converter: - steel collimators

13. 29.11.201513 K L beam. Calculated parameters Background & Fluxes per spill

14. 29.11.201514 KLOD Detector Layout Vacuum requirement: ~(10 –3 -- 10 –4 ) torr inside tank ~ 10 –7 torr inside internal membrane Another solutions under study Forward CalorimeterMain VetoVeto HodoscopeForward Veto SectionBackward Veto Section

15. 29.11.201515 KLOD Detector Layout Vacuum requirement: ~(10 –3 -- 10 –4 ) torr inside tank ~ 10 –7 torr inside internal membrane Another solutions under study Forward CalorimeterMain VetoVeto HodoscopeForward Veto SectionBackward Veto Section

16. 29.11.201516 KLOD Detector Layout Vacuum requirement: ~(10 –3 -- 10 –4 ) torr inside tank ~ 10 –7 torr inside internal membrane Another solutions under study Forward CalorimeterMain VetoVeto HodoscopeForward Veto SectionBackward Veto Section

17. 29.11.201517 KLOD Detector Layout Vacuum requirement: ~(10 –3 -- 10 –4 ) torr inside tank ~ 10 –7 torr inside internal membrane Another solutions under study Forward CalorimeterMain VetoVeto HodoscopeForward Veto SectionBackward Veto Section

18. 29.11.201518 KLOD Detector Layout Vacuum requirement: ~(10 –3 -- 10 –4 ) torr inside tank ~ 10 –7 torr inside internal membrane Another solutions under study Forward CalorimeterMain VetoVeto HodoscopeForward Veto SectionBackward Veto Section

19. 29.11.201519 KLOD Detector Layout Vacuum requirement: ~(10 –3 -- 10 –4 ) torr inside tank ~ 10 –7 torr inside internal membrane Another solutions under study Forward CalorimeterMain VetoVeto HodoscopeForward Veto SectionBackward Veto Section

20. 29.11.201520 Forward Calorimeter Size across the beam Radiation length, X 0 Size along the beam Cell size # channels Full length of fibers Total weight of lead  120 cm 13 mm 312 mm 15 mm 1920 220 km 700 kg Entered circle 24 X 0 160 (per plane) × 3 (X,U,W) × 4 (long. segments) Resolutions energy  E /E  5.5%/√E spatial 2.5mm/√E angular 20mrad/√E (X+U+W)×80=240 layers Single “spaghetti”– like layer “X” “U” “W” 1.3 mm

21. 29.11.201521 Main Veto (1) “Shashlyk” – calorimeter (0.3mm Pb + 1.5мм molding Scint.) 30000 photons per 1 GeV  -shower 5.5 ph.e – per single Sc. plate for mip 18 ph.e – per 1 MeV of “visible” energy  E /E  3%/sqrt(E) Module size along the beam Module size across the beam Scintillator thickness Lead thickness Radiation length, X 0 Module length (active part) Module full length Module weight Fibers length (per module) # modules in Main Veto Fibers length in Main Veto 300 mm 200 mm 1.5 mm 0.275 mm 35.5 mm 500 mm 600 mm 80 kg 268 m 1400 375 km Segmentation along the beam – 100 mm Segmentation across the beam – 200 mm 0.55 mm for the rear part 17.75 mm for the rear part (355 + 145) mm, (10 + 8) X 0 Without photodetector All loops including (28 – across beam) х (50 – along beam) Loops Mirrored

22. 29.11.201522 Main Veto (1) “Shashlyk” – calorimeter (0.3mm Pb + 1.5мм molding Scint.) 30000 photons per 1 GeV  -shower 5.5 ph.e – per single Sc. plate for mip 18 ph.e – per 1 MeV of “visible” energy  E /E  3%/sqrt(E) Module size along the beam Module size across the beam Scintillator thickness Lead thickness Radiation length, X 0 Module length (active part) Module full length Module weight Fibers length (per module) # modules in Main Veto Fibers length in Main Veto 300 mm 200 mm 1.5 mm 0.275 mm 35.5 mm 500 mm 600 mm 80 kg 268 m 1400 375 km Segmentation along the beam – 100 mm Segmentation across the beam – 200 mm 0.55 mm for the rear part 17.75 mm for the rear part (355 + 145) mm, (10 + 8) X 0 Without photodetector All loops including (28 – across beam) х (50 – along beam) Loops Mirrored

23. 29.11.201523 Main Veto (2)

24. 29.11.201524 In Beam Veto Calorimeter 1-st idea :to use Cherenkov light quartz fibers are only sensitive to em shower component CMS HF: e/h ~ 5, NIM A399 (1997) 202 2-nd idea: Dual Readout (Scint.+Ch.) DREAM calorimeter, NIM A536 (2005) 29 Purpose is to measure f em event by event & eliminate dominant source of fluctuations for hadrons. They succeed ! Hadron Blind Calorimeter ? Not our goal ! But... -- look at Ch/Sc signals ratio & its behavior in transverse and longitudinal directions Possible problem : not enough Ch. light => 45 deg. turn => more quartz fibers (more loose structure) The goal is not to measure E but to identify γ’s Not Hadron-Blind but Hadron-Distinguishable Calorimeter Suitable for our goal prototype is under construction

25. In Beam Veto Calorimeter 1-st idea :to use Cherenkov light quartz fibers are only sensitive to em shower component CMS HF: e/h ~ 5, NIM A399 (1997) 202 2-nd idea: Dual Readout (Scint.+Ch.) DREAM calorimeter, NIM A536 (2005) 29 Purpose is to measure f em event by event & eliminate dominant source of fluctuations for hadrons. They succeed ! Hadron Blind Calorimeter ? Not our goal ! But... -- look at Ch/Sc signals ratio & its behavior in transverse and longitudinal directions Possible problem : not enough Ch. light => 45 deg. turn => more quartz fibers (more loose structure) The goal is not to measure E but to identify γ’s Not Hadron-Blind but Hadron-Distinguishable Calorimeter Suitable for our goal prototype is under construction

26. 29.11.201526 In Beam Veto Calorimeter 1-st idea :to use Cherenkov light quartz fibers are only sensitive to em shower component CMS HF: e/h ~ 5, NIM A399 (1997) 202 2-nd idea: Dual Readout (Scint.+Ch.) DREAM calorimeter, NIM A536 (2005) 29 Purpose is to measure f em event by event & eliminate dominant source of fluctuations for hadrons. They succeed ! Hadron Blind Calorimeter ? Not our goal ! But... -- look at Ch/Sc signals ratio & its behavior in transverse and longitudinal directions Possible problem : not enough Ch. light => 45 deg. turn => more quartz fibers (more loose structure) The goal is not to measure E but to identify γ’s Not Hadron-Blind but Hadron-Distinguishable Calorimeter Suitable for our goal prototype is under construction

27. 29.11.201527 Monte-Carlo Resolutions -- σ(Z) ≈ 15 cm (without beam contribution) Dominated by FCal energy resolution -- σ(P T ) ≈ 6 MeV/c Defined by beam angular spread

28. 29.11.201528 For 1 SM decay K L    0.1 Br = 5.7 x 10 -4 K L   0  0 ~ 0.26 Br = 9.1 x 10 -4 Max(Pt)=209 МэВ/c K L   0  0  0  0.1 Br = 21.6% Max(Pt)=139 МэВ/c K L   - е +  0.1 Br = 38.7% Main cuts E  (1), E  (2) > 0.15 GeV better FCal performances, γ’s from excitation E  (1), E  (2) < 6 GeV Pt > 120 MeV/c Reconstructed Vertex inside Main Decay Volume γ’s pointed to the reconstructed Vertex (+/- 0.5 m) works for γ’s not from one π 0 Energy gravity Center > 20 cm from beam axis Dist(γ1-γ2) > 15 cm accidentals, γ’s from different π 0 ’s Background & Sensitivity Estimation Acceptance – 18 (15) % 4.8% K L decays in Main Volume @ 10 8 (5.4×10 7 ) K L /spill 10 days sensitivity (~ 10 4 spills/day) 10×(10 4 )×( 10 8 )×(4.8×10 -2 )×(1.8×10 -1 )×Br(2.8×10 -11 ) ≈ 2.4 events 10×(10 4 )×(5.4×10 7 )×(4.8×10 -2 )×(1.5×10 -1 )×Br(2.8×10 -11 ) ≈ 1.1 events

29. 29.11.201529 For 1 SM decay K L    0.1 Br = 5.7 x 10 -4 K L   0  0 ~ 0.26 Br = 9.1 x 10 -4 Max(Pt)=209 МэВ/c K L   0  0  0  0.1 Br = 21.6% Max(Pt)=139 МэВ/c K L   - е +  0.1 Br = 38.7% Main cuts E  (1), E  (2) > 0.15 GeV better FCal performances, γ’s from excitation E  (1), E  (2) < 6 GeV Pt > 120 MeV/c Reconstructed Vertex inside Main Decay Volume γ’s pointed to the reconstructed Vertex (+/- 0.5 m) works for γ’s not from one π 0 Energy gravity Center > 20 cm from beam axis Dist(γ1-γ2) > 15 cm accidentals, γ’s from different π 0 ’s Background & Sensitivity Estimation Acceptance – 18 (15) % 4.8% K L decays in Main Volume @ 10 8 (5.4×10 7 ) K L /spill 10 days sensitivity (~ 10 4 spills/day) 10×(10 4 )×( 10 8 )×(4.8×10 -2 )×(1.8×10 -1 )×Br(2.8×10 -11 ) ≈ 2.4 events 10×(10 4 )×(5.4×10 7 )×(4.8×10 -2 )×(1.5×10 -1 )×Br(2.8×10 -11 ) ≈ 1.1 events

30. 29.11.201530 Summary There is a possibility to make at IHEP setup for registration of K 0 → π 0 νν decays. Sensitivity of setup allows for reasonable time (100 days) to register about 30 (SM) decays at a level of a background near 9 decays. R&D for production and test of prototypes of the basic detectors is necessary. The further simulation for more exact calculation of signals and background processes is necessary.