Kaon beam at K1.1BR KEK Jun Imazato

Hadron Hall

K1.1-BR beam Low momentum K± beam for stopped beam experiments Only the possibility in Phase-1 Hadron Hall Common use of T1 with K1.8/K1.8BR and KL Branch of K1.1 or K1.1 as a future extension TREK experiment is the only experiment there now but the group will propose a new experiment soon. 6° T1 Layout of K1.1BR (K0.8)

Beam optics design of K1.1-BR Designed by Dr.Doornbos Beam momentum pmax = 0.8 GeV/c Common use of the upstream part up to MS1 Macroscopic time sharing with K1.1 in future Effective use of IFY Moderate K/p ratio with a single-stage ESS Beam optics design was performed in detail based on the K1.1 design at 2005. Although the B1 distance from the target was changed in 2007, the essential points are the same.

K1.1-BR Beam envelop @ 0.8 GeV/c x’=35 mr y’= 9 mr x = 3.5 mm y = 2.0 mm Dp/p = 0, ±3% Length = 20.3 m Acc = 4.5 msr % Dp/p

Momentum dispersion K1.1 R16(FF) = 0 R26(FF) ≠0 R16 K1.1-BR

IFY profile ZGOUBI calculation Source size y [mm] Dx = 2 mm Dy = 2 mm Q fringing field Up to 5th order x [cm]

MS1 profile DCS = 550 kV/10cm Pion kick = 2.2 mr ZGOUBI calculation y [mm] y [mm]

Pion/muon suppression at K1.1-BR Effective use of wedge focus to make HFOC Suppression of slit-scattered pions at HFOC Suppression of muons also at HFOC These three points are different from K1.8BR Cloud pion source definition by IFY Good K/p ratio in spite of single ESS HFOC Sector dipole IFY Reduction of cloud pions Direct pions from target @target-y @HFOC

HFOC profile ZGOUBI calculation Y「cm」 Pions = direct pions from the target x [cm] x[cm] y[cm]

Final focus ZGOUBI calculation R16 = 0 cf. R16≠0 y [cm] @ K5 → source of systematic errors R26 ≠0 less problematic longer target y [cm] x [cm]

Pion contamination Three sources: Higher order aberration simulation by ZGOUBI 2. Slit scattering 3. Cloud pions from Ks (ct =2.7 cm) simulation by REVMOC Aberration: 　y = R33y0 + R34 f + A1fq + A2fq2 + B1fd + B2fd2 + ・・ A1, B1 = 0 by adjusting the sextupoles S1 and S2 A2, B2 were minimized by optimizing the octupole O1

Rejection of slit-scattered pions x-profile at HFOC Slit scattering simulation with REVMOC from IFY and MS1 with 30 cm thickness tapered (20 mr at both ends) HFOC is effective ! x[cm] x[cm]

Rejection of cloud pions Accepted y region at the production target Pion source of x = ±2 cm y = ±2 cm was assumed. ( c.f. ct = 2.7 cm) IFY = 5 mm MS1 = 4 mm HFOC = 1.6 cm HFOC is effective !

Kaon yield and p/K ratio

Scattered pions Pi/K

Cloud pion contamination Pi/K~5 Pi/K~0.16

Muon contamination

Summary of the K1.1BR beam c.f. Acc (K1.1) ~ 2 msr % Dp/p Acc = 4.5 msr % Dp/p c.f. Acc (K1.1) ~ 2 msr % Dp/p Acc (LESB3) ~ 50 msr % Dp/p IK+ ~ 2.1 × 106/s @ 270 kW p+(m+)/K+ ~ 0.6 assuming sp/sK = 600 Beam spot : dx ~ dy ~ 1 cm << @K5 (old calculation)

Problems with K1.1-BR Single ESS Small acceptance 4.5 msr(Dp/p)% How effective IFY is？ Small acceptance 4.5 msr(Dp/p)% Time sharing with K1.1 in the future

Acceptance of K1.1-BR The first element B1 cannot be put closer to the target due to the conflict with K1.8 B1. Distance to B1 from T1= 2.0 m (1.2 m before) W(K1.1-BR) = 6.0 msr%(Dp/p) W(K1.1-BR) = 4.5 msr%(Dp/p)

LESB3 at BNL Zero degree ２stages of ESS K/p ~2.4 @ 0.8GeV/c Large acceptance 48 msr %[Dp/p] Hight K+stop rate Not very long compared with K1.1BR Successfully used for E787 and E949 for ~20 years

Low momentum beam proposed at FNAL zero degree p= 550 MeV/c; L = 13.74 m 2 stages of ESS very large acceptance: 120 msr-%(Dp/p)

Comparison of stopped K+ beams K1.1-BR LESB3 FNAL pmax (MeV/c) 800 800→710 550 Length (m) 20.3 19.6 13.7 Separator 1 (+IFY) 2 K+/p+ ratio >2* 2.4 at 800 MeV/c > 1?* Dp/p (%) ±2.5 ±2.0 ± 3.0 Acceptance (msr-%[Dp/p]) 4.5 48 120 Survival rate (%) 3.38 3.81→ 2.52 3.58 * Simulation calculation

Choice of beam momentum Relevant factors : 　Production cross section : high p is favorable 　Survival rate : high p is favorable 　K/p separation : low p is favorable 　Reactions : low p is favorable 　Stopping efficiency : low p is favorable 　Simulation calculation of stopping rate according to the actual stopping target becomes necessary 　E949 intended lower momentum 　At FNAL further down to 550 MeV/c

Stopping rate simulation in TREK GEANT3 calculation p-dependence proper length of the BeO degrader three different target radius R=4cm R=3cm R=2cm FOM Max. at 800 MeV/c estop=0.25~0.30 (taking into account also the survival rate)

Construction of K1.1BR Started this month Will be completed by summer Modifications from the optics design Length of ESS = 2.0 m instead of 2.5 m B3 bending angle of 45 degrees instead of 50 degrees Thick steal wall after Q8, which kills the possibility to put a experimental target at the FF. Beam commissioning in October. We should be responsible for that. Use of the beam for detector tests for nearly one year

K1.1BR experimental area Tentative structure for test experiments

In 2011 (after about one year) New application for radiation safety conditions Removal of the shielding after Q8 Reconstruction of the total area B3 bending angle of 50 degrees (back to the original design value) Construction of rails on the floor and a movable table Installation of SCTM and He refrigerator cold box A detector system for the new proposal will be installed following these. Angle Shield Table Rails

Beam commissioning K+ beam survey and tuning pion beam tuning for the test beam MWPC2 MWPC1 Fitch Cherenkov TOF C Gas Cherenkov C C

MWPC-1 Now being fabricated at REPIC Will be completed by the end of this month 2 mm wire spacing 250 x 250 mm2 5 cm thick

MWPC-2 Borrowed from the SKS group Broken wires will be replaced in April 1 mm wire spacing 128 x 128 mm2

Others A. Toyoda Gas Cherenkov counter borrowed from somewhere Cherenkov of Fitch type A. Toyoda Gas Cherenkov counter borrowed from somewhere TOF counters to be made Counter stands Data taking Y. Igarashi’ All the detector elements should be made ready by summer Cabling and electronics set up in September

Hodoscope

Schedule toward beam commissioning Beamline Construction now; will be completed by Summer Detectors Assembly of F-Cherenkov : this week Fabrication and test of MWPCs : March - May Hodoscope : May-June Gas Cherenkov : July - August TOF :May - June DAQ : August - September Installation : September before closing shielding Beam test : October Manpower 60 man-day from TREK, HBLG, + Liq.Ar ? A few foreign groups from Canada and USA

Summary of the K1.1BR beam IK+ ~ 2.1 × 106/s @ 270 kW Acc = 4.5 msr % Dp/p at 6° c.f. Acc (K1.1) ~ 2 msr % Dp/p IK+ ~ 2.1 × 106/s @ 270 kW p+(m+)/K+ ~ 0.5 assuming sp/sK = 600 Beam spot : dx ~ dy ~ 1 cm << @K5 Beam spot at final focus x y R26 = 0 R16 = 0

K/p separation at the 550 MeV/c line Q8 MS1 MS2 MS1×MS2=0.01 MS1×MS2 ×Q8 = ? Q8-Entrance is effective to cut pions