v>c/n

素粒子を捉える
ＫＥＫ
幅淳二
その前にまず素粒子を作る（加速器）
s= (p1 +p2)2
N= s x L
実効エネルギー
ルミノシティー（輝度）
高エネルギー加速器研究機構（KEK）
CERN
モンブラン
レマン湖
ジュネーブ
周長２７ｋｍ
地下１００ｍ
素粒子反応を観測するということ
electron
8GeV
positron
3.5 GeV
素粒子反応を観測するということ２
?
We can’t see
the interaction itself.
We only observe
the final state particles
outside the beam pipe
素粒子反応を観測するということ３
• Reconstruction of the interaction should be
done with the information measured outside.
• Kinematical information of all the outgoing
particles is necessary.
Determine four momentum (E,px,py,pz) with the help
of E2=(mc2) 2+(pc)2
Momentum measurement
Energy measurement
m can be fixed if we identify the particle species like e,
m, p, K…..
Particle identification
素粒子現象を観測するということ
1. 発生した素粒子を検知する
2. 素粒子の状態を測る
– 運動量、速度
– 電荷
3. 素粒子の種別・質量を特定する
4. 素粒子の発生・崩壊を再構成
素粒子を検知する
• 素粒子は見えません。
• 素粒子は触れません。
素粒子が残した痕跡を見つける。（電離・分
子の励起）
古典的：霧箱、泡箱、スパークチェンバー
現代：ドリフトチェンバー、シリコン検出器、シンチ
レータ・・・・・・
素粒子が発する微弱光を捉える。
チェレンコフ検出器、遷移放射検出器
どうやって測定するか?
• Momentum is measured as a curvature of
Energy is measured
with a calorimeter
the• trajectory
of the particles
in a strong
• where
Particle
identified by
measuring its
it isis converted
to scintillation
light.
magnetic
fieldwith timeCharged
velocity
of flight,particle
Cherenkov
Neutral partcile (photon)
radiation or energy loss rate…
B
霧箱（cloud chamber）
Video Clip
泡箱（bubble chamber）
Spark Chamber
現代の測定器システム一例
Ｂｅｌｌｅ
Belle detector components
Silicon 検出器
150mm
半導体検出器の仕組み
空乏層
－
－
－
－
＋
＋
＋
＋
－
－
－
－
＋
＋
＋
＋
－
－
－
－
＋
＋
＋
＋
Ｐ型半導体
－アクセプタ
正孔
Ｎ型半導体
+ ドナー
電子
逆バイアス
ドリフトチェンバー
(momentum,PID)
•
•
•
Belle CDC consists of three parts(Main, Inner and Cathode).
Curved Aluminum enplates for the main part.
– Thickness : 10mmt
Conical endplates for the inner part to give a space for accelerator
components.
• Wires
– 30mmf Au-W for sense
wire
– 126mmf Al for field wire
• Square cells
– 16mm(r)X~18mm(rf)
– 50 layers in total
X-T relation (drift time vs
position)
•
•
•
•
•
He(50%)-C2H6(50%)
B=1.5Tesla
HV : 2.3KV
Cell Size:18mm
Maximum Drift Time :
~400nsec
+
+
+
+
+
+
cell
dE/dx Measurement
Energy loss in material depends on
its velocity. PID
80%
truncated
mean
log10P(GeV/c)
粒子の識別
Aerogel Cherenkov and ToF
Cherenkov counter
Cherenkov radiation
emitted for velocity
Radiator
v>c/n
Select on velocity
by choosing n of
radiator
(c: velocity of light,
n: refractive index)
Cherenkov Light
Charged Particles
Photon sensors
Cherenkov Radiation (1)
• Moving charge in matter
at rest
slow
fast
Cherenkov Radiation (2)
• Wave front comes out at certain angle
cos c 
• That’s the trivial result!
1
n
Silica Aerogel Cherenkov
radiator
Colloidal form of SiO2.
r0.1g/cc n=1.006 ~ 1.06
Hydrophobic
Fractal structure
Number of photoelectrons
(v<c/n)
(v~c>c/n)
Number of photons
ToF (Time of Flight) 飛行時間測定
• The most direct way to measure the
velocity of particles.
velocity=flight length/flight time
ToF counter
Flight length
ToF counter (cont’d)
有機シンチレータの一例
PMT
Plastic scintillator
ToF resolution
Timing accuracy
Particle identification
(mc2)2=E2(1-(v/c)2)
ガンマ線を捉える
（カロリメータ）無機シンチレータの一例
• Total number of crystals = ８，７３６
• Total weight is ~43ton
barrel
(6,624)
r=1.25m
Backward endcap
(960)
z~ -1m
e-
e+
Forward endcap
(1,152)
z~+2m
Structure of CsI counter
Preamp. cards
Preamp box
CsI(Tl) crystal
~60x60x300mmL
(16.2 X0)
Mother board
Photodiodes
S2744-08
（1cm x 2cm）
CsI counter
Aluminized
Mylar sheet
po reconstruction
Hadron events
sp0(MeV/c2)
7
6
5
4
0.1
1.0
Eg(GeV)
(momentum)
Super conducting solenoid
• 3.8 mf x 3.9 m
wound with
3x33mm conductor
• 6 ton (cold mass)
• 1.5T with 4400 A
• Stored energy
35MJ
Solenoid installation
Magnetic field generated
Iron flex return
Non-uniformity below 5% inside tracking volume.
Field mapping with 0.3% precision.
KLM (KL and m detector)
14 x 47mmt iron plates
(magnetic flux return)
15 RPC super layers
Inserted
(PID)
RPC super layer
India Ink
Signal pickup (x)
Glass plates
8 kV
Signal pickup (y)
India Ink
Spacers
+++
+++++++++++++++
+++++++++++++++
+++++
_________ __ __ __ __ __ __ __ __
The
discharge is
is induced
quenched
when
An avalanche
and
A charged particle passes. 2
all
of
the locallyinto
(A~0.1cm
then develops
a spark. )
available charge is consumed.
The discharged area recharges slowly through the
high-resistivity glass plates.
KLM fabrication in US
KL detection
The systems also are used to
reconstruct
B 0  J / K L
events by detecting the
direction of the KL.
KL hits
KL
An ideal example
fully reconstructed events
B1
B2

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