Rare decay

Rare decayOpportunities at U-70 Accelerator (IHEP, Protvino)

~00 LK

Experiment KLODJoint Project : IHEP, Protvino JINR, Dubna

INR, Moscow, 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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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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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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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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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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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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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










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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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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Summary.

•It is possible to make registration of K0 → π0νν(bar)decays at IHEP setup .• Sensitivity of setup allows for reasonable time(100 days) to register about 30 (SM) decays at alevel of a background nearly 9 decays.• R&D for production and test prototypes of thebasic detectors is necessary. Some of detectors were tested and the results coincide with calculations.• The further simulation for more exact calculationof signals and background processes isnecessary.

Rare decay

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