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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 -
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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
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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
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Phase-2 Hall Hall size = 60m (W) x 100 m (L) More than 2 target stations K0.8 Use of T2
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Can we use K1.1?
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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
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Layout of the K0.8 branch
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Design principle Effective use of wedge focus to make HFOC Suppression of slit-scattered pions at HFOC Cloud pion source definition by IFY
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Replacement of B3
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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
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Momentum dispersion R 16 (FF) = 0 R 26 (FF) ≠0
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Beamline elements
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IFY profile ZGOUBI calculation Source size x = 2 mm y = 2 mm
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MS1 profile DCS = 550 kV/10cm Pion kick = 2.2 mr ZGOUBI calculation
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HFOC profile ZGOUBI calculation
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Final focus ZGOUBI calculation R 16 = 0 cf. R 16 ≠0 @ K5 → source of systematic errors R 26 ≠0 less problematic longer target
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p/p momentum acceptance
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Angle acceptance
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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
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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
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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)
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Kaon yield and / K ratio
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Cloud pion contamination
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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 << @K5
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Further studies Realistic source distribution in T1 1. rotating target angle 2. cloud pion source Effects of proton beam halo /K ratio optimization
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Comments on the K1.1 optics Sector type B4 with HFOC effective suppression of +
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/K separation at MS1
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MS2 profile
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Final focus of the new design
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Rejection of cloud pion by HFOC
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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.
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