고에너지 물리 특강
DESCRIPTION
고에너지 물리 특강. Lecture 1: Experimental Tools for HEP - Accelerators & Detectors - Observation of fundamental particles Lecture 2: Some recent/future HEP experiments - Belle for heavy-flavor physics and CP violation - COREA for UHECR. Experiments of High-Energy Physics. - PowerPoint PPT PresentationTRANSCRIPT
고에너지 물리 특강Experiments of High-Energy Experiments of High-Energy
PhysicsPhysicsLecture 1: Experimental Tools for HEP
- Accelerators & Detectors - Observation of fundamental particles
Lecture 2: Some recent/future HEP experiments- Belle for heavy-flavor physics and CP violation- COREA for UHECR
High-Energy Physics / Experimental Tools Mar.15, 2005 Youngjoon Kwon (Yonsei Univ.) 2
theory
physicalobservables
QFT
calculate
experimentwith any necessary
approximations
Theory vs. Experiment
,L
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Experimental tools Particle Accelerators
Particle interactions inside matter
Particle detectors
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Particle Accelerators
“precision instruments constructed on a gigantic scale” particles are traversing ~106 km for a few seconds
while maintaining the path within ~m “modern accelerators are like great Gothic cathedrals
of mediaeval Europe…” (R. Wilson) Why accelerate?
the more energy, the deeper structure we can prober p ħ/2
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Why not use high-E particles
in the cosmic ray? low flux ; energies cannot be controlled
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T = qVlimited to ~ 1 MeV voltage breakdown & discharge
Electrostatic Accelerators
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potential difference b/w the ends of drift tubes the fields oscillate, but the particles are protected (from decelerating
phase) by the metallic drift tube the distance b/w gap increases but soon saturates
an everyday proof of special relativity!
Linear Accelerator
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An example: Stanford Linear
Accelerator Center
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SLAC linear acc.
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cyclotron
Circular Accelerators
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Cyclotron
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Cyclotron[Ex] a cyclotron, with extraction radius R = 0.4 m & B = 1.5T fAC = ? Tmax = ? (for p)
fAC = fc = qB/2m = 22.9 MHz
Tmax = (qBR)2/2m = 17 MeV
As we increase the energy, relativity must be considered. fixed freq. cyclotron would not work for very high E synchronous acceleration is needed!
13High-Energy Physics / Experimental Tools Mar.15, 2005 Youngjoon Kwon (Yonsei Univ.)
Synchrotron
Consider we already attained the desired energy (= constant)and the particle goes through a circular orbit under B
f or B (or both) should be changed synchronously with the particle velocity; hence it is called a “synchrotron”
14High-Energy Physics / Experimental Tools Mar.15, 2005 Youngjoon Kwon (Yonsei Univ.)
a “magic formula” for charged particles
Then, for v c,
and we obtain a very useful formula
B
p
3.0
(GeV)
[Ex] p = 3 GeV/c, B = 2T; R = ?
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SynchrotronIf we build a cyclotron-style machine, too much steel (and cost!) is needed…hence, a new design!
The beam particles take many turns to achieve the design energy.Q: is it possible to maintain the beam size (within the vac. chamber) for so many turns? beam stability ??
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Focusing of beams
Phase stability edge focusing
Strong focusing - FODO lattice
F O D O
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focusing with quadrupole magnet
flux return steel
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Collider vs. fixed target
How to derive ?
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Livingston Plot
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Colliders
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Particle Detectors
Detector system: an overview Particle interaction inside matter
– dE/dx
– Multiple Coulomb scattering
– photon interaction inside matter Charged particle detection : Neutral particle detection : Detector system for real experiment
ppxx ,
EExx ,
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On experimental resolution
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Detector System What do we want to measure in a detector system?
positionposition ; event topology, intermediate particle state momentummomentum ; need “tracking” energyenergy ; deposited in a localized place ; “calorimetry” massmass ; i.e. particle identification (PID) chargecharge ; from the curve orientation in the tracking chamber
px
Constructing (E, ) 4-vector for each particle: charged : tracking & PID => , m => E=(p2+m2) neutral : (E, , ) => is deduced by assuming m and origin
p
p
p
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How a detector system works
For colliding beam experiments
For fixed-target experiments
Pt=0.3BR
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26High-Energy Physics / Experimental Tools Mar.15, 2005 Youngjoon Kwon (Yonsei Univ.)
Particle interaction inside matter
Energy loss of charged particle– Before a particle can be detected,
it must first undergo some sort of interaction in the material of a detector.
– EM interaction is the most important Energy loss as a function of travel distance
dE/dx
0.000
2.000
4.000
6.000
8.000
10.000
12.000
14.000
0.000 2.000 4.000 6.000 8.000 10.000 12.000
232
ln1
~/ vv
dxdE vs./ dxdE
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dE/dx (brief derivation) Coulomb interaction b/w incident charged particle &
another charged particle in the detector material by transverse p
TE
22
221
2
bmv
)z2(z
2m
ΔpΔE m = target mass
Then, in the Lab. frame, (t=0 @ r=b)
dtEqp T
(Jackson)
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[Ex] energy loss due to bound electrons vs. nuclei
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dE/dx (brief derivation) For dE/dx,
count the number of interacting particles in the target!
dxdbbnN e 2
min
max2
221
max
min 22
221 ln
)()(/
b
b
mv
ZZdb
b
b
mv
ZZdxdE
b
b
bmin and bmax ?
A
NZnZn A
atome
22
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bmax for dE/dx consider interaction w/ free electron
only if motion orbitalcollision Tt
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bmin for dE/dx E cannot exceed the max. allowed energy transfer
for a head-on collision
(let Z2 = 1)
2
1
23
2
421 ln
4/
eZ
mv
mv
eZndxdE e
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Bethe-Bloch formula dE/dx calculation with quantum correction
2
23
2
421 2
ln4
/ I
mv
mv
eZndxdE e
I = ionization potential
For small v,
For large v,“relativistic rise”
minimum ionization
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Particle ID by dE/dx
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Additional tools for charged particle ID
• Time of flightvxt /
p from trackingmass
• Cherenkov radiation
p
I K p
n
c
vc
1cos
Mass (GeV)
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Multiple Coulomb scattering
energy loss in Coulomb collision with nuclei is small
Note: Rutherford scattering formula
as / dd
ping-pong ball bowling ball
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Multiple Coulomb scattering
In any given layer of material,the net scattering is the result ofa large # of small-angle deviations (indep. of one another)
=> “ Multiple Scattering ”
ddP
2
2
2exp
2)(
a Gaussian distribution
for details, see “Intro. to Exp. P.P.” by R. Fernow, Sec.2-7
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Multiple Coulomb scattering
In a layer of thickness
deflection angle
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Multiple Coulomb scattering
Ec = “critical energy”
39High-Energy Physics / Experimental Tools Mar.15, 2005 Youngjoon Kwon (Yonsei Univ.)
Multiple Coulomb scattering
In practice, multiple scattering limits the precision of p
[ex] determine inside of a solenoidp
B
if no scattering, pc = BeR (Gaussian unit)
or p = BeR (SI unit)
Traversing a distance x, the angular deflection is
p
Bxx
cp
Be
R
xB
300
)(
[ p(MeV/c), x(m), B(T) ]
619
819
10106.1)GeV(
)m/s(100.3)m()C(106.1)(
pc
xTB
B
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Tracking error due to multiple scattering
Compare with scat B
0
rmsscat
1
2
21
2
X
x
pv
where
why 1/2 ? consider only projection onto the plane of the trajectory
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Energy loss via radiation
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Photon interactions in matter
C Pb
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Pair production
In the high energy limit (E>>2me),
the mean distance a photon will travel before pair producing is
Note: Why are XP and X0 similar?=> because bremsstrahlung and pair production are simply time and space rearrangements of the same process
0)7/9(~ XX P“conversion length”
Photon interactions in matter
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Calorimetry Most calorimeters measure the ionization energy
deposited by all the charged particles in the "showers" produced as the particle is absorbed. – EM shower– Hadronic shower
The scale length– EM: radiation length, X0 (~2cm in Fe);
relevant for both bremsstrahlung & pair production
– Hadronic: mean hadronic interaction length, I (0.2m in Fe).
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Scintillation detectors
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PhotoMultiplier Tube
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Belle EM Calorimeter
Tower structure projected to the vicinity of IP. 30 cm long (16.2 X0),
8736 CsI(Tl) crystals (6624 in barrel). 12< < 155 (lab frame)
Inner radius – 1250 mm
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How to detect a charged track?
E ~ 10 kV/cmcharge amplification ~ 105
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Ionization and detectionsensitive medium +V
V
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Multi-Wire Proportional Chamber
Charpak, 1992 Nobel physics prize
x ~ O(wire spacing)
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MWPC
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Drift Chamber
in each cell, the combination of (+) and () HV wiresprovides a relatively uniform E (= V/x)in a direction to normal incdidence
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drift distance measurement
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Drift Chamber
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Field lines inside Drift Chamber
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Precision Vertex Detection
Particles with c (charm) or b (bottom) quarks have lifetimes ~ 10-12 s
[Ex] In the Belle experiment, e+ (3.5GeV) and e (8 GeV) beams are collided and a pair of B mesons (mB = 5.28 GeV/c2) are produced.
(1) Find for each B meson?
(2) How far will it travel before it decays?
(3) spatial resolution to measure B meson decay position?
60High-Energy Physics / Experimental Tools Mar.15, 2005 Youngjoon Kwon (Yonsei Univ.)
Precision Vertex Detection
To detect heavy-flavor particles (c or b), we need a position measurement of ~ 100 m resolution or better
Near the collision point, the density of particle tracks is very high
Surround the collision point with a high-resolution silicon sensors
Why silicon?
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Silicon Vertex Detector To create a electron-hole pair in a semiconductor (e.g.
Si or Ge), only ~ 3 eV is needed large signals with very little energy deposition
Very thin wafer (~ 0.3 mm) is enough to achieve good signals
Conducting electrodes are implanted in separated stripes, orthogonally for p and n sides HV
n
p
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Track finding & fitting
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Detector System What do we want to measure in a detector system?
positionposition ; event topology, intermediate particle state momentummomentum ; need “tracking” energyenergy ; deposited in a localized place ; “calorimetry” massmass ; i.e. particle identification (PID) chargecharge ; from the curve orientation in the tracking chamber
px
Constructing (E, ) 4-vector for each particle: charged : tracking & PID => , m => E=(p2+m2) neutral : (E, , ) => is deduced by assuming m and origin
p
p
p
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putting things together…
quiz time!
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The Belle Detector
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Particle Flavor Q/|e| e –1
leptons e 0
u c t +2/3 quarks
d s b –1/3
The fundamental fermions
1st 2nd 3rdgenerations
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Heavy quarks ( c, b, t )
As of 1974…
sdu
e
e
?
GIM mechanism predicted the 4-th quark
which was named “charm”
because it did some good things…
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November, 1974!
SLACB. Richter
MITS. Ting
ffee Xeep Be
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J/ - the quantum #?
Interference with a photon
same quantum # as photon
interference
After heated discussion among theorists, it was concluded that J/ is a bound state.cc
The 4-th quark was discovered!
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' : 1st radial excitation of J/
)1(/)2( SJS
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One amazing feature about J/ was its long lifetime
(J/875 keV
(150 MeV
But the partial decay width to e+e was similar to other vector (JP = 1) mesons
Lifetime of J/
keV )32.077.6()(keV )37.026.5()/(
eeeeJ
Something special about J/ hadronic decays?– OZI suppression!
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OZI suppression in J/ decays
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4 quarks & 4 leptons - are we happy?
af
Reines & Cowan (1950’s)
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Leptons and their mystery
so similar?
But, then why do we not see ewhile seeing plenty of ? ee
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The 3rd charged lepton
)missing( eeeWhat could this be?
77High-Energy Physics / Experimental Tools Mar.15, 2005 Youngjoon Kwon (Yonsei Univ.)
The 3rd charged lepton
)missing( eee What could this be?
eeee
Martin Perl (1975)
??
sc
du
e
e
So, in less than a year...
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Upsilon resonances
anythingPt Cu, Be, pLederman (1977)
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Upsilon resonanceswith better resolutions
2mB
BBS )4(
OZI suppression -> narrow resonances
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What about the 6th quark?
bsc
du
e
e
?
Indirect evidences of “top” quark
Vtd
Vtd ARGUS (1987)
(1) B mixing
1.0)(
)(
XB
XB
(2) Kane-Peskin limit (1982)
81High-Energy Physics / Experimental Tools Mar.15, 2005 Youngjoon Kwon (Yonsei Univ.)
Double pendulum as a mechanical analog of flavor-
mixing
-1.500
-1.000
-0.500
0.000
0.500
1.000
1.500
0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0
Pendulum 1
Pendulum 2
1 2
k
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The 6th quarkCDF & D0 (both at Fermilab) in 1995
How to see the top quark?
LLLbt
sc
du
''' W
t b'
W+
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How to see “top” quarks?
Xttpp
or '
qqW
bWt
or '
qqW
bWt
and
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CDF DetectorCDF Detector
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“top” quark event : one lepton + 4 jets
CDF
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“top” quark event : di-lepton + 2 jets
CDF
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Mass of top quark
CDF, PRL (1998)
Each top candidate is fit to obtain Mrec
kinematical constraints tob-jets and light-q-jets
missing transverse energy for neutrino max. likelihood fit to obtain mass
from a sample of candidate events
1.53.174
(GeV) 3.58.49.175)(
tm
world average
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How about gauge bosons?
WWee 0Zee