Stopped K beam at J-PARC Designed by J.Doornbos 1)Optics design of a K0.8 branch 2)Performance 3)Pion contamination 4)Comments on K1.1 Nov. 4, 2005 Korea 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 K 0 L →   Branching Ratio 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 ＋ →  0 e ＋ (Ke3) Branching Ratio

Possibility of a stopped beam in Phase 1 K0 Line （ K L 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 K1.1 designed 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 0.8 GeV/c x’= 43 mr y’= 9 mr x = 3.5 mm y = 2.0 mm  p/p = 0 Length = m

Momentum dispersion R 16 (FF) = 0 R 26 (FF) ≠0

Beamline elements

IFY profile ZGOUBI calculation Source size  x = 2 mm  y = 2 mm

MS1 profile DCS = 550 kV/10cm Pion kick = 2.2 mr ZGOUBI calculation

HFOC profile ZGOUBI calculation

Final focus ZGOUBI calculation R 16 = 0 cf. R 16 K5 → source of systematic errors R 26 ≠0 less problematic longer target

 p/p momentum acceptance

Angle acceptance

Pion contamination 1.Higher order aberration 2.Slit scattering 3.Cloud pions from Ks (c  =2.7 cm) simulation by ZGOUBI Aberration: y = R 33 y 0 + R 34  + A 1  + A 2  2 + B 1  + B 2  2 + ・・ A 1, B 1 = 0 by adjusting the sextupoles S1 and S2 A 2, B 2 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 mm MS1 = 4 mm HFOC = 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 I K + ~ ( 1~ a few) × 10 6 /s  + /K + < 0.5 assuming   /  K = 500 Beam spot : d x ~ d y ~ 1 cm

Further studies Realistic source distribution in T1 1. rotating target angle 2. 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.