ハイパー核ガンマ線分光用磁気スペクトロメータ -sksminus-

ハイパー核ガンマ線分光用磁気スペクトロメータ

-SksMinus-

東北大学大学院理学研究科白鳥昂太郎

12/14 @ ATAMI

2006 Strangeness ATAMI 2

Outline

Background of experiments Requirement on setup Modification of SKS Setup : SksMinus Detectors in detail, DC, Veto counters Summary Future plan


“DAY-1” experiment E13

Several light hypernuclear gamma-ray spectroscopy experiments are planned.

(4He, 7

Li, 10B, 11

B, 19F)

Beam momentum (K-, - ) @ 1.5 GeV/c (500 k/spill, full intensity)The best sensitivity for selecting spin-flip state1.1~1.8 GeV/c beam for 4He

n


Requirement on spectrometer forhypernuclear gamma-ray spectroscopy

To analyze 1.4 GeV/c (1.1~1.8 GeV/c) scattered - by existing spectrometer system

Large acceptance ~100 msr, ~20 degree

→ Enough hypernuclear production yield. Good momentum resolution 2~4 MeV/c→ To distinguish excited states of hypernuclei

SksMinus(Superconducting Kaon Spectrometer Modified for Hypernuclear Gamma ray Spectroscopy)

SKS to SksMinus


The modification of SKS

Momentum resolution0.1%FWHM (0.72 MeV/c)

@ 720 MeV/c, 2.2T

Maximum central momentum

1.0 GeV/c @ 2.7T

Acceptance 100 msr @ 0.72GeV/c

2.2T 2.7T

~20° ~20°

Scattered particles are not focused and present drift chambers (SDC3,4) are small for large reaction angle (half acceptance).

1.05 GeV/c (+, K+) reaction (K+ 0.72 GeV/c)

Present SKS


The modification of SKS Keeping large acceptance and wide angular coverage by large drift chambers (2m×1m) (from BNL and Freiburg)

Incident beam angle and position of drift chambers are optimized by keeping acceptance for the 1.5 GeV/c beam condition.

Setup can be used for 1.1~1.8 GeV/c beam hypernuclear gamma ray spectroscopy experiment without modification.

~20°


The modification of SKS Keeping large acceptance and wide angular coverage by large drift chambers (2m×1m) (from BNL and Freiburg)



170cm

270cm

On the step, not a giant


The K1.8 Beam line and SksMinusBeam spectrometer

・ BH1,2 : Time-of

-flight

・ BAC : - veto (n=1.03)SksMinus

・ STOF : Time-of-flight

・ SAC : K- beam veto (n=1.03)

・ SFV : K- beam vetoTarget : ～ 20 g/cm2

Length : 20 cmMWPC & DC: Beam position measurement

Background Veto

・ SMF : - from K- → - +

・ SP0 : - from K- → - +

0

Hyperball-J : ray

T.Koike 12/15


SksMinus

SksMinus

・ SAC : K- beam veto (n=1.03)

・ SFV : K- beam veto・ STOF : Time-of-flight

SDC1~4: Beam position measurement

Background Veto

・ SMF : - from K- → - +

・ SP0 : - from K- → - +

0Target : ~20 g/cm2

Length : 20 cm

SksMinus performanceBasic performance

Acceptance Momentum resolution


Acceptance Acceptance at 1.4 GeV/c ～130 msr by large drift chambers (2m×1m) Angular acceptance is enough, ~ 20 degree

Acceptance is determined by SKS magnet gap and distance from SKS entrance. Higher momentum→ Cut off by SKS magnet Lower momentum→ Out of range SDC3,4


Momentum resolution

Momentum resolution at 1.4 GeV/c ~2.1 MeV/c (FWHM) , intrinsic ~1.6, MSC ~1.3 400 m DC resolution and multiple scattering (DC : Ar gas, He bag : He gas, Air)

Higher momentum→ Intrinsic resolution (bending angle) Lowe momentum→ Similar to present SKS, ~0.9 MeV/c (FWHM) @ 1.0 GeV/c

SksMinus performanceBeam decay suppression

Muon Filter PiZero Veto


Background rejection

Beam K- decay products make serious background (Trigger rate, Missing mass spectrum)

Fake trigger ~1740/spillTrue event trigger ~1000/spill(Contribution of three-body decay ~200 /spill)

Beam K

BAC SACTarget20cm

Reaction

K- → - (63.4%)

⇒Muon Filter (1390 /spill) K- → - 0 (21.1%)

⇒PiZero Veto (350 /spill)


Background rejection

K- → - (63.4%)

⇒Muon Filter (1390 /spill) K- → - 0 (21.1%)

⇒PiZero Veto (350 /spill)

Beam K- decay products make serious background (Trigger rate, Missing mass spectrum)

Fake trigger ~1740/spillTrue event trigger ~1000/spill(Contribution of three-body decay ~200 /spill)

Beam K

BAC SACTarget20cm

Decay


Muon Filter -SMF-

86% of can be rejected in the trigger @ 1.5 GeV/c beam Stopped cannot be rejected. (In the offline analysis >99%) Over kill for true π ~2.5%

- (passing through)- (stopped in the iron)

Not need to change iron thickness, 1.1~1.8 GeV/c beam

momentum

Stopping points


Muon Filter -SMF-

86% of can be rejected in the trigger @ 1.5 GeV/c beam Stopped cannot be rejected. (In the offline analysis >99%) Over kill for true π ~2.5%

Not need to change iron thickness, 1.1~1.8 GeV/c beam

momentum

Stopping points

-

-

X

Z


PiZero veto -SP0-

78% of 0 can be detected by 6 sets of 5 mm lead plate and scintillation counter layer at 1.5 GeV/c beam. (85% of from 0 hit the SP0)

Reaction - pass through the window.

Acceptance 85%


Trigger rate @ 1.5 GeV/c beam

(K-,π-) Reaction rate ~1000 /spill K-→- ~1390 /spill K-→- 0 ~350 /spill K- Beam ~30 /spill 3-body decay ~200 /spill

~2970 /spillw/o Veto counters

True trigger ~500 /spillw/ Ge trigger and fake trigger greatly decreased (1/4).

~1320/spillw/ Veto counters

~570/spillw/ Ge trigger

(K-, - ) at pK = 1.5 GeV/c (500 k/spill)

Comparable to the present trigger rate

(K-,π-) Reaction rate ~950 /spill K-→- ~190 /spill K-→- 0 ~80 /spill K- Beam ~30 /spill 3-body decay ~70 /spill


4He experiment

Energy spacing of 4He(1+) → 4

He(0+), (4H(1+)

→ 4H(0+) : (K-, 0 ), no charge and SP0 ?)

@ 1.5 GeV/c beam M.Ukai 12/15

Spin-flip measurement• Momentum (1.1), 1.3, 1.5, 1.8 GeV/c→Acceptance and momentum resolution are enough.• PID counters→STOF, SAC and SFV are enough.• Veto counters→More study is needed : Trigger rate @ 1.8 GeV/c.

n


Summary Several hypernulcear gamma-ray experiments are

planned at the J-PARC K1.8 beam line (4He, 7

Li, 10

B, 11B, 19

F).

SksMinus is sufficient for hypernuclear gamma-ray spectroscopy at 1.5 GeV/c beam. Acceptance 130 msr, 20 degree. Momentum resolution 2.1 MeV/c.

Simulations in progress show a good veto counter efficiency at 1.5 GeV/c beam, SMF ~86%, SP0 ~78%.

SksMinus can be used for 1.1~1.8 GeV/c beam.


Future Plan

Determination of the final SksMinus design SDC3&4 shipped from BNL and Freiburg and

repaired in 2007 PMT for TOF and Cherenkov from BNL D6

beam line and Range counter (E559) in 2007 Design and construction of SMF, SP0 and

other counters in 2007~2008

Backup


Particle identification (K-, - ) → - or K-

Beam K- can greatly be decreased by SAC (n=1.03) and SFV→ less than 30 trigger /spill (500 k/spill beam)

Time resolution of STOF ~150 ps (rms) For B(M1) measurement, dual SAC is planned because of saving forward events.


Magnetic field

Calculated magnetic filed map is used in simulations.


The modification of SKSLarge acceptance and wide angular coverage by large drift chambers (2m×1m)




Beam VetoSAC efficiency ～ 99%→5k trigger /spill @ 500k/spill

SFV → ～ 10 trigger Reduction of acceptance 7.5%

Beam size σx=19.8 mmσy=3.2 mm(u=0.02, v=0.002)

SBS

SBSK- beam directly hit SDC3,4.↓Scattering beam particles by some material (Pb, W)300kHz → 60kHz @ 20mm cell


SMF & SP0 performance @ 1.1~1.8 GeV/c beam

It is difficult to suppress trigger rate at higher beam intensity…

- ~580 trigger/spill @ 1.8 GeV/c beam(~4300 trigger)

- ~360 trigger/spill @ 1.8 GeV/c beam(~1200 trigger)

SMF SP0


3-body Decay

K-→π-π-π+ (5.58%)K-→e-π0ν (4.87%)K-→μ-π0ν (3.27%)K-→π-π0π0 (1.73%)

ハイパー核ガンマ線分光用 磁気スペクトロメータ -sksminus-

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ハイパー核ガンマ線分光用磁気スペクトロメータ -sksminus-