Stopped K beam at J-PARC

Designed by J.Doornbos1) Optics design of a K0.8 branch2) Performance3) Pion contamination 4) Comments on K1.1

Nov. 4, 2005Korea J-PARC seminar

- A branch option of K1.1 -

LoI’s with stopped K beam

LoI-04 Study of the Rare Decay K ＋→＋ with Stopped Kaon Beam at J-PARC

LoI-05 Measurement of the K0L→ Branching Rati

o

LoI-16 Study the Kaon Decay Physics at JHF

LoI-19 Search for T-violation in K ＋ decays

LoI-20 Precise Measurement of the K ＋→ 0e ＋ (Ke3) Branching Ratio

Possibility of a stopped beam in Phase 1

K0 Line（ KL beam）

E391a detector

K0.8 Line（ stopped K±) as a branch of K1.1 Use of K1.1 by lowering

beam momentum

Phase-2 Hall

Hall size = 60m (W) x 100 m (L) More than 2 target stations

K0.8

Use of T2

Can we use K1.1?

A branch option of K1.1designed by J.Doornbos

• A branch of K1.1 at B3• Common use of the upstream part up to MS1• Macroscopic time sharing with K1.1• Effective use of IFY• Single-stage DCS

• Moderate beam intensity -> Feasibility to start the T-violation experiment with minor upgrades of the Toroidal Detector

Layout of the K0.8 branch

Design principle

Effective use of wedge focus to make HFOC Suppression of slit-scattered pions at HFOC Cloud pion source definition by IFY

Replacement of B3

Beam optics

First order beam envelop@ 0.8 GeV/c

x’= 43 mr y’= 9 mr

x = 3.5 mm y = 2.0 mm

p/p = 0

Length = 19.06 m

Momentum dispersion

R16(FF) = 0R26(FF) ≠0

Beamline elements

IFY profile

ZGOUBI calculation

Source size x = 2 mm y = 2 mm

MS1 profile

DCS = 550 kV/10cmPion kick = 2.2 mr

ZGOUBI calculation

HFOC profileZGOUBI calculation

Final focus

ZGOUBI calculation

R16 = 0

cf. R16≠0 @ K5 → source of systematic errors

R26 ≠0• less problematic• longer target

p/p momentum acceptance

Angle acceptance

Pion contamination

1. Higher order aberration2. Slit scattering3. Cloud pions from Ks (c=2.7 cm)

simulation by ZGOUBI

Aberration:　 y = R33y0 + R34 + A1 + A22 + B1 + B22 + ・・

A1, B1 = 0 by adjusting the sextupoles S1 and S2 A2, B2 were minimized by optimizing the octupole O1

Rejection of slit-scattered pions

Slit scattering simulation with REVMOC

IFY and MS1

with 30 cm thickness tapered (20 mr at both ends)

x-profile at HFOC

Rejection of cloud pions

Accepted y region at the production target

IFY = 5 mmMS1 = 4 mmHFOC = 1.6 cm

HFOC is effective !

Pion source of x = -2 ~ +2 cm y = -1 ~ +3 cm was assumed. ( c.f. c = 2.7 cm)

Kaon yield and /K ratio

Cloud pion contamination

Summary of the K0.8 beam

Acc = 6 msr % p/p c.f. Acc (K1.1) ~ 4 msr % p/p Acc (LESB3) ~ 50 msr % p/p IK+ ~ ( 1~ a few) × 106/s

+/K+ < 0.5 assuming /K = 500

Beam spot : dx ~ dy ~ 1 cm << @K5

Further studies

Realistic source distribution in T11. rotating target angle2. cloud pion source

Effects of proton beam halo /K ratio optimization

Comments on the K1.1 optics

Sector type B4 with HFOC

effective suppression of +

/K separation at MS1

MS2 profile

Final focus of the new design

Rejection of cloud pion by HFOC

Conclusion

The C-type branch of K1.1 for stopped beam is feasible

The intermediate vertical focus IFY plays an important

role.

The installation of an IFY slit is very necessary.

A switching mechanism has to be considered for B3+Q7. We will propose this option of the low momentum separate K-line together with the experiment proposal

There is no concrete plan yet for funding.