Experimentat J-PARC
山鹿光裕
大阪大学
2005年3月7日, 科研費特定領域研究会

Golden Channel in K Decays_:• CP violation in FCNC process.
• Clean measurement of Im(Vtd) ~η.
• Test of the Standard Model• Clue for new physics
in comparison with B physics.
Br() = 6κ1(Im(VtdV*ts))2X2(xt)~ 1.94x10-10η2A4X2~ 3x10-11
Theoretical uncertainty is small(~1%).

Ligeti

Still Room for Future Progress

Remains as a Frontier• Rare decay (Br～10-11)_• No definite kinematical constraint.
⇒ 2 γ + nothing
Very difficult experiment• Large BG.
KL→2π0 , 2γ-missing(Br ~ 10-3)
10-3 → 10-11 : 10-8 of reduction⇒ (10-4)2 of γ inefficiency

γ detection inefficiency

Two Concepts for the Experiment• KOPIO : Kinematical constraint as much as possible
to reduce backgrounds.
– TOF by bunched-beam, angular measurement of γ,– Acceptance is not so high.
– Low momentum KL → γ inefficiency• E391a, J-PARC : Simply observe 2γ + nothing.
– High acceptance.
– High momentum KL → Better γ inefficiency

Goal• Present experimental limit– Br ~ 5.9 x 10-7 (KTeV)• KEK PS-E391a : ~ 10-10

Goal :• < 10-13 of the sensitivity• > 100 SM events• ∆η/η < 5%
⇒ High-intensity machine is necessary.

High-Intensity Machine :J-PARC

J-PARC : Accelerator Complex ＠TokaiAccelerator Layouts

3.3x1014 ppp

Proton accelerator in the worldx100 intensityof KEK-PS

ScheduleFeb. 2005
Linac

3GeV RCS

50GeV MRnowHadron Hall Layout PlanKL

Phase 2 →• B-line (exclusive).
• Optimum designfor KL exp.

← Phase 1• A-line only
• T1-target only
• Shared beam
• Not optimum for
KL exp.

KL

Concept for J-PARC KLexperiment

What we need• Many signal events– KL flux• proton flux, energy, targeting angle, beam size,– High acceptance• Less background events– Veto efficiencies–– Neutrons–

KL flux(MC study)• 50 GeV protons on 1 λΙ length of target.
– 5° extraction to minimize n/KL ratio.
→ <pKL> ~ 5.8 GeV/c.

• 50m of Neutral beamline :n/KL ratio
50GeV protons
1 λΙ length target– 1 µstr of solid angle (7cmφ at detector)

3.3 x1014 ppp for 3 years (3x107 sec)
⇒ ~5x1014 KL @ detector

0 5 10 15 20 25 (deg)• 30 GeV protons ⇒ ~60% of KL yield• A-line (30GeV, 16deg extraction, T1 target, 7cmφbeam)⇒ ~7 % of KL yield.

High acceptance• Geometrical acceptance– Long pipe-like calorimeter (e.g. 15m-long)KLγ• Less accidental vetoing• Less self vetoingγ– Shower leakage kills the signal event.

Shower-leakage effect# of leakage / incident γ• Shallow incident angle→ Larger # of leakage

1 GeV
500 MeV
100 MeV50 MeV# of recon’d event / decay (MC)EESSES
TotalShowerleakage
6%2%
4%12%Noleakage
7%9%
12%
28%

0Side detector kills many signals.

20406080 (deg)
incident angle

For high acceptance ..
• Larger-radius detector→ More hits to Endcap

EndcapSide
radiusLess leakage# of recon’d event / decay (MC)Better acceptanceNo leakage
With leakage

Larger-radius might be better.
0 50 100 150 200 250 300 350 400
Radius (cm)Background•, 2γ-missing

Detector for photon-angle measurementPrototype module

MC study underway.
Beam test in next fiscal year

Sensitivity• 50 GeV primary protons• Full intensity (3.3x1014 ppp) for 3 years• 15m-long, 3m-φ detector⇒ S/N = 206/180 ~ 1.1∆η/η ~ 5%• With γ angular measurement :– Odd-pair BG=1/3, Even :Odd ~ 1:1

BG → 70% ⇒ S/N ~ 1.6∆η/η ~ 4%Other considerations / developments• PMT development– High quantum-efficiency• Prism-PMT (NIM A522 (2004) 477)
• Muiti-alkali Multi-anode-PMT– High-rate resistant PMT• Cockcroft-Walton-type devider• Charged Tracker by straw-chamber– Useful for calibration by e.g. KL→π+π−π0.
– Charged veto

• DAQ
– Pipeline readouts for ADC/TDC.

Things to study• Extraction beamline and beam dump for B-line.
• Collimating scheme for neutral beam.
– How to clean-up the beam halo.

• Neutral beam size
– Large solid angle → more KL yield.
– PT resolution ?

• …

Step by Step in reality• Step1 : A-line– 30 GeV protons– E391a detector + some modifications– Good to test new components– ~1 SM events• Step 2 : B-line– 30 (or 50) GeV protons– Optimum beamline and collimator– Fully upgraded detector– ~200 SM events, ∆η/η < ~5%Summary• High-Intensity machine is necessary tomeasure the golden mode,.
• Conceptual designing underway.
– R&D for detectors, PMT, DAQ, …

• B-line at Phase-2 would be needed to achieve
our final goal.
Step by Step in reality is good for the test.
• Full proposal will be prepared within 2005.