STUDY OF ULTRAREAR DECAYS K0 → π0νν(bar)

(Search of K0 → π0νν(bar) decay at IHEP , project KLOD )

V.N. Bolotov

on behalf of the collaboration JINR, IHEP and INR RAS

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STATE RESEARCH CENTER OF RUSSIAINSTITUTE FOR HIGH ENERGY PHYSICS

π−

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theoretically ~00 LK

• Rare FCNC process• Purely CP-Violetting (Littenberg, 1989)

• Totally dominated from t-quark Computed in QCD (Buchalla, Buras, 1999)

Small corrections due to mt

• <π|Hweak|K> is known from K+ 0 e+ e (Ke3) No long distance contribution (Rein, L. M. Sehgal, 1989;

Marciano, Z. Parsa 1996)

• SM: Br ~ η2, 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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Experimental challenge. Must-do experiment

~00 LK signature: π0-signal + “nothing”

At least 2 charged or 4 γ’s -- veto inefficiency ~ 10-6

-- full veto coveredπ0 in 34% of decays -- PT cut (231MeV/c)

Interaction with gas -- high vacuum

Strategy:

2 γ’s in EcalNo veto-signalConstruct π0 from 2 γ’s -- reconstruct vertex-- reconstruct PT

(narrow beam approach)

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KL beam at U-70 IHEP

Beam requirements

-- very narrow (R<5cm) and well collimated-- high PT balanced-- high intensity (~108 KL/pulse)-- mean KL energy ~10 GeV-- minimal contamination of neutral unwanted particles (neutrons/KL < 10)

Sketch design completed !

KL beam optimizationconditions

-- 1013 60 GeV p/cycle(slow extraction);

-- Cu-target 25см(80% interactions);

- 35 mrad extraction angle;- 5 cm Pb-converter:- steel collimators

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KL beam at U-70 IHEP

Beam requirements

-- very narrow (R<5cm) and well collimated-- high PT balanced-- high intensity (~108 KL/pulse)-- mean KL energy ~10 GeV-- minimal contamination of neutral unwanted particles (neutrons/KL < 10)

Sketch design completed !

KL beam optimizationconditions

-- 1013 60 GeV p/cycle(slow extraction);

-- Cu-target 25см(80% interactions);

- 35 mrad extraction angle;- 5 cm Pb-converter:- steel collimators

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KL beam. Calculated parameters

Background & Fluxes per spill

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KLOD Detector Layout

Vacuum requirement: ~(10 –3 -- 10 –4) torr inside tank ~ 10 –7 torr inside internal membrane Another solutions under study

Forward CalorimeterMain Veto Veto HodoscopeForward Veto Section

Backward Veto Section

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KLOD Detector Layout

Vacuum requirement: ~(10 –3 -- 10 –4) torr inside tank ~ 10 –7 torr inside internal membrane Another solutions under study

Forward CalorimeterMain Veto Veto HodoscopeForward Veto Section

Backward Veto Section

Forward Calorimeter Requirements• Detect and resolve all clusters• In case of 2 clusters:

-- reconstruct Vertex & PT• In case of Vertex inside Decay Volume

-- define angle of gammas

~25 X0 fine sampling fast response small RM & fine transverse segmentation moderate Energy Resolution, very good angular resolution,

E/)%65(~ Emrad /10~

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KLOD Detector Layout

Vacuum requirement: ~(10 –3 -- 10 –4) torr inside tank ~ 10 –7 torr inside internal membrane Another solutions under study

Forward CalorimeterMain Veto Veto HodoscopeForward Veto Section

Backward Veto Section

Main Veto Requirements• Dominates in cost estimation

=> sampling structure• Best gamma-detection efficiency up to smallest energy

10–6 inefficiency is the target

The reasons of gamma-inefficiency:

-- “Punch-through” @>1 GeV 18 X0 8×10–7

-- Photo-nuclear reactions@(0.11)GeV (10-4 10-6) at 10 MeV threshold the smallest detection threshold (< 1MeV)

-- “Sampling”- effect @<100 MeV~1% @ 20 MeV for (1mm Pb + 5mm Scint.) “fine” sampling-structure the smallest detection threshold (< 1MeV)

~18 X0 fine sampling fast response reasonable segmentation

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KLOD Detector Layout

Vacuum requirement: ~(10 –3 -- 10 –4) torr inside tank ~ 10 –7 torr inside internal membrane Another solutions under study

Forward CalorimeterMain Veto Veto HodoscopeForward Veto Section

Backward Veto Section

Veto Hodoscope Requirements• To prevent misidentification of charge clusters in FCal as a gammas• Inefficiency for Charged by Scintillator is small

-- see Table (for 1GeV particles, 1cm Plastic Scintillator)(Inagaki et al., NIM, A359 (1995)

• Exclusion --

Solutions:=> reduce the threshold=> increase scintillator thickness=> place hodoscope by ~0.5m in front of FCal=> small RM & fine segmentation of FCal

eKL0

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KLOD Detector Layout

Vacuum requirement: ~(10 –3 -- 10 –4) torr inside tank ~ 10 –7 torr inside internal membrane Another solutions under study

Forward CalorimeterMain Veto Veto HodoscopeForward Veto Section

Backward Veto Section

Forward Veto Section Requirements• Aperture Calorimeters goal:

-- kill any from beam transport pipe (target -- 32m)which may hit FCal.Mainly to suppress 2- background (not from one 0)

• Forward Barrel Veto:-- KL decays just in front of Main Decay Volume

Also for gammas originated not from one 0

Aperture & Position – from geometrical considerations Requirements for gamma detection inefficiency are not so high

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KLOD Detector Layout

Vacuum requirement: ~(10 –3 -- 10 –4) torr inside tank ~ 10 –7 torr inside internal membrane Another solutions under study

Forward CalorimeterMain Veto Veto HodoscopeForward Veto Section

Backward Veto Section

Backward Veto Section Requirements

In Beam Veto Calorimeter – real challenge

1. -detection from background KL decays inside Decay Volume-- main problem

-- (18% of them have at least 1 in the FCal beam hole)=> shift “InBeamVeto” apart FCal=> Back Veto Calorimeters

-- still 2% of have 2 ’s (0) at InBeamVetosuch topology should be suppressed, 10-6 !!!

hard spectrum (fortunately)2. avoid “over-veto” (acceptance lost) from beam particles (n, , KL )

-flux huge but soft => (Ethreshold > 250 MeV) => ~106 /spill-- helps against beam ’s-- doesn’t affect detection efficiency of ’s from background decays-- doesn’t help against neutrons

-- Beam neutrons are major problem~300 MHz => Neutron Blind Detector

+ enough amount of X0’s+ small amount of ’s+ very fast+ segmentations+ no dead time readout (FADC)

000 LK

000 LK

-spectra from at condition“2 ’s hit Forward Calorimeter”

000 LK

(1) – @ Main Veto(2) – @Hole in FCal(3) – @ InBeamVetoCal.

@ InBeamVetoCal.+ “2 ’s hit InBeamVetoCal”(1) – E(); (2) – E(1)+E(2)

+ “2 ’s are from one 0”(3) – E(); (4) – E(1)+E(2)

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Forward Calorimeter

Size across the beamRadiation length, X0

Size along the beam Cell size# channelsFull length of fibersTotal weight of lead

120 cm13 mm312 mm15 mm1920220 km700 kg

Entered circle 24 X0

 160 (per plane) × 3 (X,U,W) × 4 (long. segments)

Resolutions

• energy E/E5.5%/√E

• spatial 2.5mm/√E

• angular 20mrad/√E

(X+U+W)×80=240 layers

Single “spaghetti”– like layer

“X”

“U”

“W”

1.3

mm

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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/E3%/sqrt(E)

Module size along the beamModule size across the beamScintillator thicknessLead thicknessRadiation length, X0

Module length (active part)Module full lengthModule weightFibers length (per module)# modules in Main VetoFibers length in Main Veto

300 mm200 mm1.5 mm0.275 mm35.5 mm500 mm600 mm80 kg268 m1400375 km

Segmentation along the beam – 100 mmSegmentation across the beam – 200 mm  0.55 mm for the rear part17.75 mm for the rear part(355 + 145) mm, (10 + 8) X0

Without photodetector  All loops including(28 – across beam) х (50 – along beam) 

Loops

Mirrored

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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/E3%/sqrt(E)

Module size along the beamModule size across the beamScintillator thicknessLead thicknessRadiation length, X0

Module length (active part)Module full lengthModule weightFibers length (per module)# modules in Main VetoFibers length in Main Veto

300 mm200 mm1.5 mm0.275 mm35.5 mm500 mm600 mm80 kg268 m1400375 km

Segmentation along the beam – 100 mmSegmentation across the beam – 200 mm  0.55 mm for the rear part17.75 mm for the rear part(355 + 145) mm, (10 + 8) X0

Without photodetector  All loops including(28 – across beam) х (50 – along beam) 

Loops

Mirrored

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Main Veto (2)

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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 fem 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

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 fem 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

Transverse profiles of 80 GeV showersN.Akchurin, R.Wigmans Rev.Sci.Instrum., Vol.74, 2003

No such difference for -showers !

+ very different behavior for & hadron showersin longitudinal direction

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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 fem 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

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Monte-Carlo ~00 LK

Resolutions

-- σ(Z) ≈ 15 cm (without beam contribution)

Dominated by FCal energy resolution

-- σ(PT) ≈ 6 MeV/cDefined by beam angular spread

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For 1 SM decay

KL 0.1Br = 5.7 x 10-4

KL 0 0 ~ 0.26Br = 9.1 x 10-4

Max(Pt)=209 МэВ/c

KL 0 0 0 0.1Br = 21.6%Max(Pt)=139 МэВ/c

KL - е+ 0.1Br = 38.7%

Main cuts

• E(1), E(2) > 0.15 GeVbetter 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 π0

• Energy gravity Center > 20 cm from beam axis

• Dist(γ1-γ2) > 15 cmaccidentals, γ’s from different π0’s

Background & Sensitivity Estimation

eK L0

20 LK

Acceptance – 18 (15) %4.8% KL decays in Main Volume@ 108 (5.4×107) KL/spill

10 days sensitivity (~ 104 spills/day)

10×(104)×( 108 )×(4.8×10-2)×(1.8×10-1)×Br(2.8×10-11) ≈ 2.4 events10×(104)×(5.4×107)×(4.8×10-2)×(1.5×10-1)×Br(2.8×10-11) ≈ 1.1 events

~00 LK

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For 1 SM decay

KL 0.1Br = 5.7 x 10-4

KL 0 0 ~ 0.26Br = 9.1 x 10-4

Max(Pt)=209 МэВ/c

KL 0 0 0 0.1Br = 21.6%Max(Pt)=139 МэВ/c

KL - е+ 0.1Br = 38.7%

Main cuts

• E(1), E(2) > 0.15 GeVbetter 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 π0

• Energy gravity Center > 20 cm from beam axis

• Dist(γ1-γ2) > 15 cmaccidentals, γ’s from different π0’s

Background & Sensitivity Estimation

eK L0

20 LK

Acceptance – 18 (15) %4.8% KL decays in Main Volume@ 108 (5.4×107) KL/spill

10 days sensitivity (~ 104 spills/day)

10×(104)×( 108 )×(4.8×10-2)×(1.8×10-1)×Br(2.8×10-11) ≈ 2.4 events10×(104)×(5.4×107)×(4.8×10-2)×(1.5×10-1)×Br(2.8×10-11) ≈ 1.1 events

~00 LK

background (instrumental effects included)“2 ’s hit Forward Calorimeter”

000 LK

’s are not from one 0 Distances between ’s at front of FCal

’s are not from one 0 (low histogram)

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Summary• There is a possibility to make at IHEP setup forregistration of K0 → π0νν decays.• Sensitivity of setup allows for reasonable time(100 days) to register about 30 (SM) decays at alevel of a background near 9 decays.• R&D for production and test of prototypes of thebasic detectors is necessary.• The further simulation for more exact calculationof signals and background processes isnecessary.