K l p 0 nn experiment at j parc
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K L  p 0 nn experiment at J-PARC. Mitsuhiro YAMAGA Osaka Univ. Oct. 7, 2004 Workshop on Physics at an Upgraded Fermilab Proton Driver. Contents: Introduction J-PARC K L → p 0 nn experiment KEK PS-E391a At Proton Driver.

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K L  p 0 nn experiment at J-PARC

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K l p 0 nn experiment at j parc

KL  p0nn experiment at J-PARC

Mitsuhiro YAMAGA

Osaka Univ.

Oct. 7, 2004

Workshop on Physics at an Upgraded Fermilab Proton Driver

  • Contents:

  • Introduction

  • J-PARC KL → p0nn experiment

  • KEK PS-E391a

  • At Proton Driver


Golden channel in k decays

Br(KL →p0nn)=6k1(Im(VtdV*ts))2X2(xt)

~ 1.94x10-10h2A4X2

~ 3x10-11

Theoretical uncertainty is small (~1%).

Golden Channel in K Decays

_

KL→ p0nn :

  • CP violation in FCNC process.

  • Clean measurement of Im(Vtd) ~ h.

  • Test of the Standard Model

  • Clue for new physics

    in comparison with B physics.


Still room for future progress

Ligeti

Still Room for Future Progress


Remains as a frontier

Remains as a Frontier

Rare decay (Br~10-11) and no definite kinematical constraint.

KL→ p0 nn → 2 g + nothing

⇒Very difficult experiment

BG : KL→2p0 , 2g-missing

(Br ~ 10-3)

10-3 ⇒ 10-11 obtained by (10-4)2

The main concern is how we can

lower the veto threshold.

_


Two concepts

Two Concepts

Two methods have been proposed:

  • KOPIO : Kinematical constraint as much as possible

    to reduce background.

    • TOF by pulsed beam, angular measurement of g, …

    • Acceptance is not so high.

    • Low momentum KL → g inefficiency

  • E391a, J-PARC : Simply observe 2g (high PT ) + nothing.

    • High Acceptance

    • High momentum KL → Better g inefficiency


Strategy

Strategy

  • Pencil beam

    • Narrow beam for PT resolution

  • Detector system in vacuum

    • Suppress interactions with materials

  • High acceptance

    • Hermetic detector system

  • Higher energy

    • Better g-inefficiency

  • Constraints if possible.

    • Angular measurement of g.


K l p 0 nn experiment at j parc

Goal

  • Present experimental limit :

    • Br ~ 5.9 x 10-7 (KTeV)

      Goal :

  • < 10-13 of the sensitivity

  • >100 SM events

  • Dh/h < 5%

    ⇒ High-intensity machine

    is necessary.


J parc accelerator complex

J-PARC :Accelerator Complex

3x1014 ppp

  • Neutron

  • Muon


Hadron hall layout plan

Hadron Hall Layout Plan

← Phase 1 plan

KL

Phase 2 plan →


Construction schedule

Now

Construction Schedule


K l p 0 nn experiment at j parc

LOI

  • LOI was submitted for the J-PARC Kaon experiment:

    • L-05 : Measurement of the KL→p0nn Branching Ratio. [T.Inagaki(KEK)]

      Regarded as one of the highlight of experiment of the J-PARC Phase-1 by the facility committee.

  • Full proposal will be prepared within 2005.


Sensitivity estimation by mc

Sensitivity Estimation by MC

  • KL production target :

    • 50 GeV protons on 1 lI length

      of target.

    • 5° extraction to minimize

      n/KL ratio.

    • <pKL> ~ 6 GeV/c.

  • Neutral beamline :

    • 1.2 mstr of solid angle.

n/KL ratio

50GeV protons

1 lIlength target

0 5 10 15 20 25 30 35 40

ext.angle(deg)


Detector

Detector

  • 15m-long, 2m-f cylinder.

  • Located at z=50m to avoid BG from L→np0 decays.

  • Both of side- and endcap- calorimeters are the active g detectors.

  • Beam-anti completely dead due to high rate (~GHz).


Event selection

Event Selection

Reconstruct p0 from two g’s by assuming p0-mass.

  • Signal : KL→p0nn

  • Background : KL→2p0, 2g-missing.

    Selection Criteria :

  • Eg> 100 MeV

  • 135 < pT < 240 MeV/c

  • Z-vertex:

    SS : 210 < z < 795 cm

    SE : 210 < z < 975 cm

    EE : 210 < z < 1050 cm

    (Determined to give best Dh/h)

SS: Side-Side

SE: Side-Endcap

EE: Endcap-Endcap

_

e = 1 for Eg<2 MeV


Event selection cont d

Event Selection (cont’d)

KL→p0nn

KL→2p0

Zvtx

Zvtx

pT

pT


Sensitivity

Sensitivity

  • At 2x1014 ppp intensity,

    • 1.8x1021 protons / 3 years(=3x107 sec)

    • 1.5x1015 KL / 3 years@ z=50m

    • 10 MHz of KL decay rate @ fiducial (52~60m)

      ⇒ Signal yield ~900 events/3years (3x10-14 of s.e.s).

      S/N ~ 3.

      → Dh/h ~ 4%

      (Optimization still underway)


Kek ps e391a a pilot experiment

First run:

Feb.18 – June 30, 2004

KEK PS-E391a : A pilot experiment


E391a apparatus

E391a apparatus

K0 beam line

  • Pencil beam

    • 2mrad of beam aperture

      =12mstr of solid angle.

  • Detector system in vacuum

    • Differential pumping

    • Whole detector system: low vacuum < 0.1Pa

    • Decay region: high vacuum ~ 10-5 Pa

  • Hermetic veto system

    • Double decay chamber

      • Reject KLdecay in front of

        fiducial region

E391a detector

n

g

g

KL

n


Detector integration

Detector Integration

Jan 22, 2004


Data taking

X-Y coe

mass

COE-X

COE-Y

Vertex

Momentum

Data taking

Online monitoring using KL 3p0 decay

12 GeV incident protons

2.2 X 1012/spill at target

2s spill length

4s repetition

KL Yield in front of detector

5x105 /spill

peak momentum : 2 GeV/c

DAQ live-time ratio : 75 %

Vacuum pressure : 1X10-5 Pa


Performance

Performance

KL→3p0

Clean neutral beam

s ~ 6 MeV/c2

KL→2p0


E391a status prospects

E391a status & prospects

  • First physics run Feb-June this year

    • 2.21012 POT, 50% duty factor

    • 5 105 KL/pulse

    • Detector worked well

    • Analysis underway

    • Nominal s.e.s. ~ 410-10

    • First sight of the enemy

      • Halo neutrons, self-vetoing, etc.

  • Second run proposed for next year.

    Good start for p0nn experiment.


At proton driver

At Proton Driver

What can we do after J-PARC experiment ?

  • 120 GeV, 2 MW beam at Proton Driver :

    • Intensity ~ 1.5x1014 ppp : Half of the J-PARC

      • Statistic enhancement might not be big.

    • Higher energy :

      • Better n/KL ratio, g-inefficiency → better S/N, Dh/h.

    • Optimum detector design might be different from J-PARC due to the decay kinematics of higher-energy KL :

      KAMI–type ?

      • ~1000 Event at 120GeV in 3 years (KAMI).

      • Huge (~100m of calorimeter cylinder).


Summary

Summary

  • KL →p0nn decay is pure and clean mode to measure a basic parameter of the SM and to look for new physics.

  • At J-PARC 50 GeV PS, we will achieve the goal of <10-13 sensitivity (~900 SM events with S/N~3).

  • KEK PS-E391a, a pilot experiment, is the first dedicated experiment for this decay. Run-1 was successfully carried out from Feb. to June 2004. We are asking to double the statistics by Run-2 in 2005.

  • At Proton Driver, better S/N and Dh/h might be expected.


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