1. Kaon beam at K1.1BR
KEK
Jun Imazato

2. Hadron Hall

3. 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)

4. 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.

5. 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

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

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

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

9. 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

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

11. 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]

12. 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

13. 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]

14. 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 !

15. Kaon yield and p/K ratio

16. Scattered pions
Pi/K

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

18. Muon contamination

19. 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 × 270 kW
p+(m+)/K+ ~ assuming sp/sK = 600
Beam spot : dx ~ dy ~ 1 cm
(old calculation)

20. 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

21. 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)

22. 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

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

24. 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

25. 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

26. 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)

27. 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

28. K1.1BR experimental area
Tentative structure for test experiments

29. 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

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

31. 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

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

33. 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

34. Hodoscope

35. 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

36. 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 × 270 kW
p+(m+)/K+ ~ assuming sp/sK = 600
Beam spot : dx ~ dy ~ 1 cm
Beam spot at final focus x y
R26 = 0
R16 = 0

37. K/p separation at the 550 MeV/c lineQ8
MS1
MS2
MS1×MS2=0.01
MS1×MS2 ×Q8 = ?
Q8-Entrance is effective to cut pions