Download phys3313-fall12-112812

PHYS 3313 – Section 001
Lecture #22
Wednesday, Nov. 268, 2012
Dr. Jaehoon Yu
•
•
•
•
Wednesday, Nov. 28,
2012
Particle Accelerators
Particle Physics Detectors
Hot topics in Particle Physics
What’s coming in the future?
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
1
Announcements
• Your presentations are in classes on Dec. 3 and Dec. 5
– All presentation ppt files must be sent to me by 8pm this Sunday, Dec. 2
• Final exam is 11am – 1:30pm, Monday, Dec. 10
– You can prepare a one 8.5x11.5 sheet (front and back) of handwritten formulae
and values of constants for the exam
– No formulae or values of constants will be provided!
• Planetarium extra credit
– Tape one side of your ticket stubs on a sheet of paper with your name on it
– Submit the sheet on Wednesday, Dec. 5
• Please be sure to fill out the feedback survey.
• Colloquium this Wednesday at 4pm in SH101
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
2
Introduction
• What are elementary particles?
– Particles that make up all matters in the universe
• What are the requirements for elementary particles?
– Cannot be broken into smaller pieces
– Cannot have sizes
• The notion of “elementary particles” have changed from early
1900’s through present
– In the past, people thought protons, neutrons, pions, kaons,  mesons, etc, as elementary particles
• Why?
– Due to the increasing energies of accelerators that allowed us to
probe smaller distance scales
• What is the energy needed to probe 0.1–fm?
– From de Broglie Wavelength, we obtain
c 197fm  MeV 2000MeV / c


0.1fm c
 2012 c
PHYS 3313-001, Fall
3
P
Wednesday, Nov. 28,
2012
Dr. Jaehoon Yu

Forces and Their Relative Strengths
• Classical forces:
– Gravitational: every particle is subject to this force, including
massless ones
• How do you know?
– Electromagnetic: only those with electrical charges
– What are the ranges of these forces?
• Infinite!!
– What does this tell you?
• Their force carriers are massless!!
– What are the force carriers of these forces?
• Gravity: graviton (not seen but just a concept)
• Electromagnetism: Photons
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
4
Forces and Their Relative Strengths
• What other forces?
– Strong force
• Where did we learn this force?
– From nuclear phenomena
– The interactions are far stronger and extremely short ranged
– Weak force
• How did we learn about this force?
– From nuclear beta decay
– What are their ranges?
• Very short
– What does this tell you?
• Their force carriers are massive!
• Not really for strong forces
• All four forces can act at the same time!!!
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
5
Interaction Time
• The ranges of forces also affect interaction time
– Typical time for Strong interaction ~10-24sec
• What is this time scale?
• A time that takes light to traverse the size of a proton (~1 fm)
– Typical time for EM force ~10-20 – 10-16 sec
– Typical time for Weak force ~10-13 – 10-6 sec
• In GeV ranges, the four forces (now three since EM
and Weak forces are unified!) are different
• These are used to classify elementary particles
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
6
Elementary Particles
• Before the quark concepts, all known elementary
particles were grouped in four depending on the
nature of their interactions
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
7
Elementary Particle Interactions
• How do these particles interact??
– All particles, including photons and neutrinos, participate in
gravitational interactions
– Photons can interact electromagnetically with any particles
with electric charge
– All charged leptons participate in both EM and weak
interactions
– Neutral leptons do not have EM couplings
– All hadrons (Mesons and baryons) respond to the strong
force and appears to participate in all the interactions
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
8
Elementary Particles: Bosons and Fermions
• All particles can be classified as bosons or fermions
– Bosons follow Bose-Einstein statistics
• Quantum mechanical wave function is symmetric under exchange
of any pair of bosons
 B  x1, x2 , x3 ,...xi ...xn    B  x2 , x1 , x3 ,...xi ...xn 
• xi: space-time coordinates and internal quantum numbers of
particle i
– Fermions obey Fermi-Dirac statistics
• Quantum mechanical wave function is anti-symmetric under
exchange of any pair of Fermions
 F  x1, x2 , x3 ,...xi ...xn    F  x2 , x1, x3 ,...xi ...xn 
• Pauli exclusion principle is built into the wave function
– For xi=xj,
Wednesday, Nov. 28,
2012
 F   F
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
9
Bosons, Fermions, Particles and Antiparticles
• Bosons
– All have integer spin angular momentum
– All mesons (consists of two quarks) are bosons
• Fermions
– All have half integer spin angular momentum
– All leptons and baryons (consist of three quarks) are fermions
• All particles have anti-particles
– What are anti-particles?
• Particles that has same mass as particles but with opposite quantum numbers
– What is the anti-particle of
•
•
•
•
A 0?
A neutron?
A K0?
A Neutrino?
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
10
Quantum Numbers
• When can an interaction occur?
– If it is kinematically allowed
– If it does not violate any recognized conservation laws
• Eg. A reaction that violates charge conservation will not occur
– In order to deduce conservation laws, a full theoretical
understanding of forces are necessary
• Since we do not have full theory for all the forces
– Many of general conservation rules for particles are based on
experiments
• One of the clearest conservation is the lepton number
conservation
– While photon and meson numbers are not conserved
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
11
Baryon
Numbers

0
• Can the decay p  e   occur?
– Kinematically??
• Yes, proton mass is a lot larger than the sum of the two masses
– Electrical charge?
• Yes, it is conserved
• But this decay does not occur (<10-40/sec)
– Why?
• Must be a conservation law that prohibits this decay
– What could it be?
•
•
•
•
An additive and conserved quantum number, Baryon number (B)
All baryons have B=1
Anti-baryons? (B=-1)
Photons, leptons and mesons have B=0
• Since proton is the lightest baryon, it does not decay.
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
12
The Standard Model of Particle Physics
•
Prior to 70’s, low mass hadrons (mesons and baryons) are
thought to be the fundamental constituents of matter, despite
some new particles that seemed to have new flavors
–
Even lightest hadrons, protons and neutrons, show some indication
of substructure
•
–
•
Such as magnetic moment of the neutron
Raised questions whether they really are fundamental particles
In 1964 Gell-Mann and Zweig suggested independently that
hadrons can be understood as composite of quark
constituents
–
Recall that the quantum number assignments, such as strangeness,
were only theoretical tools rather than real particle properties
Monday, Nov. 27, 2006
PHYS 3446, Fall 2006
Jae Yu
13
The Standard Model of Particle Physics
•
In late 60’s, Jerome Friedman, Henry Kendall and
Rich Taylor designed an experiment with electron
beam scattering off of hadrons and deuterium at
SLAC (Stanford Linear Accelerator Center)
–
–
Data could be easily understood if protons and neutrons
are composed of point-like objects with charges -1/3e and
+2/3e.
A point-like electrons scattering off of point-like quark
partons inside the nucleons and hadrons
•
•
Corresponds to modern day Rutherford scattering
Higher energies of the incident electrons could break apart the
target particles, revealing the internal structure
Monday, Nov. 27, 2006
PHYS 3446, Fall 2006
Jae Yu
14
•
The Standard Model of Particle Physics
Elastic scatterings at high energies can be described well with
the elastic form factors measured at low energies, why?
–
•
Since the interaction is elastic, particles behave as if they are pointlike objects without a substructure
Inelastic scatterings cannot be described well w/ elastic form
factors since the target is broken apart
–
Inelastic scatterings of electrons with large momentum transfer (q2)
provides opportunities to probe shorter distances, breaking apart
nucleons
The fact that the form factor for inelastic scattering at large q2 is
independent of q2 shows that there are point-like object in a nucleon
–
•
•
Bjorken scaling
Nucleons contain both quarks and glue particles (gluons) both
described by individual characteristic momentum distributions
(Parton Distribution Functions)
Monday, Nov. 27, 2006
PHYS 3446, Fall 2006
Jae Yu
15
The Standard Model of Particle Physics
•
By early 70’s, it was clear that hadrons (baryons and mesons)
are not fundamental point-like objects
But leptons did not show any evidence of internal structure
•
–
–
•
•
Even at high energies they still do not show any structure
Can be regarded as elementary particles
The phenomenological understanding along with observation
from electron scattering (Deep Inelastic Scattering, DIS) and
the quark model
Resulted in the Standard Model that can describe three of the
four known forces along with quarks, leptons and gauge
bosons as the fundamental particles
Monday, Nov. 27, 2006
PHYS 3446, Fall 2006
Jae Yu
16
Quarks and Leptons
•
In SM, there are three families of leptons
 e 
  
e 
–
–
•
  
  
 
0
-1
 Increasing order of lepton masses
Convention used in strong isospin symmetry, higher member of
multiplet carries higher electrical charge
And three families of quark constituents
u 
 
d 
•
  
  
 
Q
c
 
s
t 
 
b
Q
+2/3
-1/3
All these fundamental particles are fermions w/ spin
Monday, Nov. 27, 2006
PHYS 3446, Fall 2006
Jae Yu
1
2
17
Monday, Aug. 27, 2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
18
The Standard Model
Make up most
ordinary matters
~0.1mp
Discovered
in 1995,
~175mp
• Total of 16 particles make up the matter in the universe!  Simple
and elegant!!!
Monday, Aug. 27, 2012
PHYS 3313-001, Fall 2012
19
Jaehoon Yu
• Tested to a precision of 1 partDr. per
million!
Quark Content of Mesons
•
Meson spins are measured to be integer.
–
–
•
They must consist of an even number of quarks
They can be described as bound states of quarks
Quark compositions of some mesons
–
Pions
Strange mesons
K   us
   ud
  ud
K   us

K 0  ds

1
uu  dd
 
2
0
Monday, Nov. 27, 2006

K 0  ds
PHYS 3446, Fall 2006
Jae Yu
20
Quark Content of Baryons
•
Baryon spins are measured to be ½ integer.
–
–
•
They must consist of an odd number of quarks
They can be described as bound states of three quarks based on the
studies of their properties
Quark compositions of some baryons
–
–
Nucleons
p  uud
n  udd
•
Strange baryons
s=1
s=2
0  uds
  uus
0  uds
  dds
  uss
  dss
0
Other Baryons
   uuu
Since baryons have B=1, the quarks must have baryon
number 1/3
Monday, Nov. 27, 2006
PHYS 3446, Fall 2006
Jae Yu
21
Z and W Boson Decays
•
The weak vector bosons (discovered in early 1980’s) couple
quarks and leptons
–
•
Thus they decay to a pair of leptons or a pair of quarks
Since they are heavy, they decay instantly to the following
channels and their branching ratios
– Z bosons: MZ=91GeV/c2
– Z 0 ® qq 69.9%
– Z 0 ® l + l - (3.37% for each charged lepton species)
– Z 0 ® n n (20%)
l l
– W bosons: MW=80GeV/c2
– W ± ® qq¢ 68%
–
±
±
(
)
(
)
W ® l n l (~10.6% for each charged lepton species)
Monday, Nov. 27, 2006
PHYS 3446, Fall 2006
Jae Yu
22
Z and W Boson Search Strategy
•
The weak vector bosons have masses of 91 GeV/c2 for Z and 80
GeV/c2 for W
While the most abundant decay final state is qqbar (2 jets of
particles), the multi-jet final states are also the most abundant in
collisions
•
–
•
Background is too large to be able to carry out a meaningful search
The best channels are using leptonic decay channels of the bosons
–
•
Especially the final states containing electrons and muons are the cleanest
So what do we look for as signature of the bosons?
–
–
For Z-bosons: Two isolated electrons or muons with large transverse momenta
(PT)
For W bosons: One isolated electron or muon with a large transverse
momentum along with a signature of high PT neutrino (Large missing ET).
Monday, Nov. 27, 2006
PHYS 3446, Fall 2006
Jae Yu
23
What do we need for the experiment to
search for vector bosons?
•
We need to be able to identify isolated leptons
–
–
•
We need to be able to measure transverse
momentum well
–
•
Good electron and muon identification
Charged particle tracking
Good momentum and energy measurement
We need to be able to measure missing transverse
energy well
–
Good coverage of the energy measurement (hermeticity)
to measure transverse momentum imbalance well
Monday, Nov. 27, 2006
PHYS 3446, Fall 2006
Jae Yu
24
Particle Accelerators
• How can one obtain high energy particles?
– Cosmic ray  Sometimes we observe 1000TeV cosmic rays
• Low flux and cannot control energies too well
• Need to look into small distances to probe the fundamental
constituents with full control of particle energies and fluxes
– Particle accelerators
• Accelerators need not only to accelerate particles but also to
– Track them
– Maneuver them
– Constrain their motions to the order of 1 m or better
• Why?
– Must correct particle paths and momenta to increase fluxes and control
momenta
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
25
Particle Accelerators
• Depending on what the main goals of physics are, one needs
different kinds of accelerator experiments
• Fixed target experiments: Probe the nature of the nucleons 
Structure functions
– Results also can be used for producing secondary particles for further
accelerations  Tevatron anti-proton production
• Colliders: Probes the interactions between fundamental
constituents
– Hadron colliders: Wide kinematic ranges and high discovery potential
• Proton-anti-proton: TeVatron at Fermilab, Sp pSat CERN
• Proton-Proton: Large Hadron Collider at CERN (turned on early 2010)
– Lepton colliders: Very narrow kinematic reach, so it is used for precision
measurements
• Electron-positron: LEP at CERN, Petra at DESY, PEP at SLAC, Tristan at KEK,
ILC in the med-range future
• Muon-anti-muon: Conceptual accelerator in the far future
– Lepton-hadron colliders: HERA at DESY
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
26
Electrostatic Accelerators: Cockcroft-Walton
• Cockcroft-Walton Accelerator
– Pass ions through sets of aligned DC electrodes at successively
increasing fixed potentials
– Consists of ion source (hydrogen gas) and a target with the electrodes
arranged in between
– Acceleration Procedure
• Electrons are either added or striped off of an atom
• Ions of charge q then get accelerated through series of electrodes, gaining kinetic
energy of T=qV through every set of electrodes
• Limited to about 1MeV acceleration due to
voltage breakdown and discharge beyond
voltage of 1MV.
• Available commercially and also used as the
first step high current injector (to ~1mA).
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
27
Electrostatic Accelerators: Van de Graaff
• Energies of particles through DC accelerators are
proportional to the applied voltage
• Robert Van de Graaff developed a clever mechanism to
increase HV
– The charge on any conductor resides on its outermost
surface
– If a conductor carrying additional charge touches another
conductor that surrounds it, all of its charges will transfer to
the outer conductor increasing the charge on the outer
conductor, thereby increasing voltage higher
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
28
Electrostatic Accelerators: Van de Graaff
• Sprayer adds positive charge to
the conveyor belt at corona points
• Charge is carried on an insulating
conveyor belt
• The charges get transferred to the
dome via the collector
• The ions in the source then gets
accelerated to about 12MeV
• Tandem Van de Graff can
accelerate particles up to 25 MeV
• This acceleration normally occurs
in high pressure gas that has very
high breakdown voltage
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
29
Resonance Accelerators: Cyclotron
• Fixed voltage machines have intrinsic
limitations in their energy due to
breakdown
• Machines using resonance principles
can accelerate particles to even
higher energies
• Cyclotron developed by E. Lawrence
is the simplest and first of these
• The accelerator consists of
– Two hallow D shaped metal chambers
connected to alternating HV source
– The entire system is placed under
strong magnetic field
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
30
Resonance Accelerators: Cyclotron
• While the D’s are connected to HV sources,
there is no electric field inside the chamber
due to Faraday effect
• Strong electric field exists only in the gap
between the D’s
• An ion source is placed in the gap
• The path is circular due to the
perpendicular magnetic field
• Ion does not feel any acceleration inside a
D but gets bent due to magnetic field
• When the particle exits a D, the direction of
voltage can be changed and the ion gets
accelerated before entering into the D on
the other side
• If the frequency of the alternating voltage is
just right, the charged particle gets
accelerated continuously until it is extracted
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
31
Resonance Accelerators: Cyclotron
• For non-relativistic motion, the frequency appropriate for
alternating voltage can be calculated from the fact that the
magnetic force provides centripetal acceleration for a circular
orbit
v qB
v2
vB
m
r
q
r
c

mc

• In a constant angular speed,  =v/r. The frequency of the
motion is
qB

1  q B
f
2


2 mc 2  m  c
• Thus, to continue accelerating the particle, the electric field
should alternate in this frequency, cyclotron resonance
frequency
• The maximum kinetic energy achievable for an cyclotron with
2
radius R is
 qBR 
1
1
Wednesday, Nov. 28,
2012
2
2 2
Tmax  mvmax

m

R2012
PHYS 3313-001, Fall
2
mc 2
Dr.2Jaehoon Yu
32
Resonance Accelerators: Linear Accelerator
• Accelerates particles along a linear path using resonance principle
• A series of metal tubes are located in a vacuum vessel and connected
successively to alternating terminals of radio frequency oscillator
• The directions of the electric fields changes before the particles exits the
given tube
• The tube length needs to get longer as the particle gets accelerated to
keep up with the phase
• These accelerators are used for accelerating light particles to very high
energies
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
33
Synchroton Accelerators
• For very energetic particles, the relativistic effect must be taken
into account
• For relativistic energies, the equation of motion of a charge q
under magnetic field B is
dv
v´B
mg
dt
= mg v ´ v = q
• For v ~ c, the resonance frequency becomes
c
v 1 æ qö 1 B
n=
= ç ÷
2p 2p è m ø g c
• Thus for high energies, either B or  should increase
• Machines with constant B but variable  are called synchrocyclotrons
• Machines with variable B independent of the change of  is
called synchrotrons
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
34
Synchroton Accelerators
• Electron synchrotrons, B varies while  is held
constant
• Proton synchrotrons, both B and  varies
• For v ~ c, the frequency of motion can be expressed
• For an electron
1 n
c
f=
»
2p R 2p R
p  GeV / c 
pc
R(m) 

qB 0.3B Tesla) 
• For magnetic field strength of 2Tesla, one needs radius
of 50m to accelerate an electron to 30GeV/c.
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
35
Synchroton Accelerators
• Synchrotons use magnets
arranged in a ring-like
fashion.
• Multiple stages of
accelerations are needed
before reaching over GeV
ranges of energies
• RF power stations are
located through the ring to
pump electric energies into
the particles
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
36
Comparisons between Tevatron and LHC
• Tevatron: A proton-anti proton collider at 2TeV
– Need to produce anti-protons using accelerated protons at
150GeV
– Takes time to store sufficient number of anti-protons
• Need a storage accelerator for anti-protons
– Can use the same magnet and acceleration ring to circulate
and accelerator particles
• LHC: A proton-proton collier at 14TeV design energy
– Protons are easy to harvest
– Takes virtually no time to between a fresh fill of particles into
the accelerator
– Must use two separate magnet and acceleration rings
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
37
•
Fermilab Tevatron and
LHC
at
CERN
• World’s Highest Energy p-p collider
World’s Highest Energy proton-anti-proton collider
– 27km circumference, 100m underground
– Design Ecm=14 TeV (=44x10-7J/p 362M
Joules on the area smaller than 10-4m2)
 Equivalent to the kinetic energy of a B727
(80tons) at the speed 193mi/hr  312km/hr
– 4km circumference
– Ecm=1.96 TeV (=6.3x10-7J/p 13M Joules on the
area smaller than 10-4m2)
– Equivalent to the kinetic energy of a 20t truck at the
speed 81mi/hr 130km/hr
•
~100,000 times the energy density at the ground 0 of the
Hiroshima atom bomb
– Was shut down at 2pm CDT, Sept. 30, 2011
– Vibrant other programs running!!
p
Tevatron
Monday, Aug. 27, 2012
•
•
Chicago
CDF

~3M times the energy density at the ground 0 of the
Hiroshima atom bomb
First 7TeV collisions on 3/30/10  The highest energy
humans ever achieved!!
First 8TeV collisions in 2012 on April 5, 2012
DØ
p
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
38
LHC @ CERN Aerial View
CMS
France
Geneva
Airport
ATLAS
Monday, Aug. 27, 2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
Swizerland
39
Particle Detectors
• Subatomic particles cannot be seen by naked eyes but can be
detected through their interactions within matter
• What do you think we need to know first to construct a
detector?
– What kind of particles do we want to detect?
• Charged particles and neutral particles
– What do we want to measure?
•
•
•
•
•
Their momenta
Trajectories
Energies
Origin of interaction (interaction vertex)
Etc
– To what precision do we want to measure?
• Depending on the answers to the above questions we use
different detection techniques
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
40
Particle Detection Techniques
Energy
Scintillating Fiber
Silicon Tracking
Calorimeter (dense)
Interaction
Point
B
EM
Muon Tracks
Magnet
Charged Particle Tracks
hadronic
electron
photon
Wire Chambers
jet
neutrino -- or any non-interacting
particle missing transverse momentum
Monday, Nov. 27, 2006
muon
We know x,y starting momenta is zero, but
along the z axis it is not, so many of our
measurements are in the xy plane, or
transverse
PHYS 3446, Fall 2006
Jae Yu
41
The ATLAS and CMS Detectors
•
•
•
•
•
Fully multi-purpose detector with emphasis on lepton ID & precision E & P
Weighs 7000 tons and 10 story tall
Records 200 – 400 collisions/second
Records approximately 350 MB/second
Record over 2 PB per year  200*Printed material of the US Lib. of Congress
Monday, Aug. 27, 2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
42
Scintillation Counters
• Two types of scintillators
– Organic or plastic
•
•
•
•
Tend to emit ultra-violate
Wavelength shifters are needed to reduce attenuation
Faster decay time (10-8s)
More appropriate for high flux environment
– Inorganic or crystalline (NaI or CsI)
• Doped with activators that can be excited by electron-hole
pairs produced by charged particles in the crystal lattice
• These dopants can then be de-excited through photon
emission
• Decay time of order 10-6sec
• Used in low energy detection
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
43
Scintillation Detectors & Photo-multiplier Tube
• Scintillation detectors consist of a doped plastic that
emits lights when a particle loses its energy via atomic
excitation and transition back to lower energy states
• The light produced by scintillators are usually too weak to
see
– Photon signal needs amplification through photomultiplier
tubes
• Gets the light from scintillator directly or through light guide
– Photocathode: Made of material in which valence electrons are loosely bound
and are easy to cause photo-electric effect (2 – 12 cm diameter)
– Series of multiple dynodes that are made of material with relatively low workfunction
» Operating at an increasing potential difference (100 – 200 V) difference
Wednesday, Nov. 28, between dynodes
PHYS 3313-001, Fall 2012
44
2012
Dr. Jaehoon Yu
Scintillation Detector Structure
HV PS
Scintillation
Counter
Light Guide/
Wavelength PMT
Shifter
Readout
Electronics
Scope
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
45
Some PMT’s
Super-Kamiokande detector
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
46
Time of Flight
• Scintillator + PMT can provide time resolution of 0.1 ns.
– What position resolution does this corresponds to?
• 3cm
• Array of scintillation counters can be used to measure
the time of flight (TOF) of particles and obtain their
velocities
– What can this be used for?
• Can use this to distinguish particles with about the same momentum
but with different mass
– How?
• Measure
– the momentum (p) of a particle in the magnetic field
– its time of flight (t) for reaching some scintillation counter at a distance L from
the point of origin of the particle
– Determine the velocity of the particle and its mass
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
47
Cerenkov Detectors
• What is the Cerenkov radiation (covered in CH2)?
– Emission of coherent radiation from the excitation of atoms and
molecules
• When does this occur?
– If a charged particle enters a dielectric medium with a speed faster
than light in the medium
– How is this possible?
• Since the speed of light is c/n in a medium with index of refraction n, if the
particle’s >1/n, its speed is larger than the speed of light
• Cerenkov light has various frequencies but blue and ultraviolet
band are most interesting
– Blue can be directly detected w/ standard PMTs
– Ultraviolet can be converted to electrons using photosensitive
molecules mixed in with some gas in an ionization chamber
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
48
Cerenkov Detectors
• Threshold counters
– Particles with the same momentum but with different mass will start emitting
Cerenkov light when the index of refraction is above a certain threshold
– These counters have one type of gas but could vary the pressure in the chamber to
change the index of refraction to distinguish particles
– Large proton decay experiments use Cerenkov detector to detect the final state
particles, such as p  e+0
• Differential counters
– Measure the angle of emission for the given index of refraction since the emission
angle for lighter particles will be larger than heavier ones
• Ring-imaging Cerenkov Counters (RICH)
– An energetic charged particle can produce multiple UV distributed about the
direction of the particle
– The now stopped BaBar experiment at Stanford Linear Accelerator Center (SLAC)
used RICH as the primary detector system
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
49
Super Kamiokande
A Differential Water Cerenkov Detector
•Kamioka zinc mine, Japan
• 1000m underground
•40 m (d) x 40m(h) SS
•50,000 tons of ultra pure H2O
•11200(inner)+1800(outer) 50cm
PMT’s
•Originally for proton decay
experiment
•Accident in Nov. 2001, destroyed
7000 PMT’s
•Dec. 2002 resumed data taking
•This experiment was the first to
show the neutrinos oscillate
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
50
Super-K Event Displays
Stopping 
Wednesday, Nov. 28,
2012
3
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
51
Semiconductor Detectors
• Semiconductors can produce large signal (electron-hole pairs)
for relatively small energy deposit (~3eV)
– Advantageous in measuring low energy at high resolution
• Silicon strip and pixel detectors are widely used for high
precision position measurements
– Due to large electron-hole pair production, thin layers (200 – 300  m)
of wafers sufficient for measurements
– Output signal proportional to the ionization loss
– Low bias voltages sufficient to operate
– Can be deposit in thin stripes (20 – 50  m) on thin electrode
– High position resolution achievable
– Can be used to distinguish particles in multiple detector configurations
• So what is the catch?
– Very expensive  On the order of $30k/m2
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
52
DØ Silicon Vertex Detector
8
1 9
11
12 0
6
7
5
2
43
Barrels
1
1
1
2
F-Disks
H-Disks
Channels
387120
258048
147456
Modules
432
144
96
Inner R
2.7 cm
2.6 cm
9.5 cm
Outer R
9.4 cm
10.5 cm
26 cm
6
One Si detector
3
4
Wednesday, Nov. 28,
2012
Barrel
Disk
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
53
Calorimeters
• Magnetic measurement of momentum is not sufficient
for physics, why?
– The precision for angular measurements gets worse as
particles’ momenta increases
– Increasing magnetic field or increasing precision of the
tracking device will help but will be expensive
– Cannot measure neutral particle momenta
• How do we solve this problem?
– Use a device that measures kinetic energies of particles
• Calorimeter
– A device that absorbs full kinetic energy of a particle
– Provides signal proportional to deposited energy
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
54
Calorimeters
• Large scale calorimeter were developed during 1960s
– For energetic cosmic rays
– For particles produced in accelerator experiments
• How do high energy EM (photons and electrons) and
Hadronic particles deposit their energies?
– Electrons: via bremsstrahlung
– Photons: via electron-positron conversion, followed by
bremsstrahlung of electrons and positrons
– These processes continue occurring in the secondary
particles causing an electromagnetic shower losing all of its
energy
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
55
Electron Interactions in material (showering)
Photon, 
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
56
Calorimeters
• Hadrons are massive thus their energy deposit via brem is
small
• They lose their energies through multiple nuclear collisions
• Incident hadron produces multiple pions and other secondary
hadrons in the first collision
• The secondary hadrons then successively undergo nuclear
collisions
• Mean free path for nuclear collisions is called nuclear
interaction lengths and is substantially larger than that of EM
particles
• Hadronic shower processes are therefore more erratic than
EM shower processes
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
57
Sampling Calorimeters
• High energy particles require large
calorimeters to absorb all of their
energies and measure them fully in
the device (called total absorption
calorimeters)
• Since the number of shower particles
is proportional to the energy of the
incident particles
• One can deduce the total energy of
the particle by measuring only the
fraction of their energy, as long as the
fraction is known  Called sampling
calorimeters
– Most the high energy experiments use
sampling calorimeters
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
58
How particle showers look in detectors
Hadron
EM
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
59
Principles of Calorimeters
Total absorption
calorimeter: See
the entire
shower energy
Sampling
calorimeter: See
only some fraction
of shower energy
For EM
Absorber plates
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
E  fEvis 
For HAD E  fEvis
X 0vis
X 0abs + X 0vis
Evis
l0vis
 abs vis Evis
l0 +60
l0
Example Hadronic Shower (20GeV)
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
61
Conventional Neutrino Beam
Good
target
Good
beam
focusing
Sufficient
dump
p
Long
decay
region
• Use large number of protons on target to produce many
secondary hadrons (, K, D, etc)
• Let  and K decay in-flight for   beam
–  +  99.99%, K   63.5%
– Other flavors of neutrinos are harder to make
• Let the beam go through thick shield and dirt to filter out
 and remaining hadrons, except for 
– Dominated by  
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
62
How can we select sign of neutrinos?
• Neutrinos are electrically neutral
• Need to select the charge of the secondary hadrons
from the proton interaction on target
• NuTeV experiment at Fermilab used a string of magnets
called SSQT (Sign Selected Quadrupole Train)
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
63
A Typical Neutrino Detector: NuTeV
•
Calorimeter
– 168 FE plates & 690tons
– 84 Liquid Scintillator
– 42 Drift chambers interspersed
Wednesday, Nov. 28,
2012
• Solid Iron Toroid
• Measures Muon momentum
• p/p~10%
Continuous test beam for in-situ calibration
64
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
How Do Neutrino Events Look?
Charged
Current
Events
Neutral
Current
Events
Wednesday, Nov. 28,
2012
y-view
Nothing is
coming
in!!!
x-view
y-view
Nothing is
coming
in!!!
x-view
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu


Nothing is
going
out!!!
65
Source of Cleaner Neutrino Beam
Muon storage ring can generate 106 times higher flux and well
understood, high purity neutrino beam  significant
reduction in statistical uncertainty
But  e and   from muon decays are in the beam at all times
 Deadly for traditional heavy target detectors
Wednesday, Nov. 28,
2012
PHYS 3313-001, Fall 2012
Dr. Jaehoon Yu
66
What’s the current hot issues?
• Why is the mass range so large (0.1mp – 175 mp)?
• How do matters acquire mass?
- Higgs
mechanism,
we find
theHiggs?
Higgs?
– Higgs
mechanism
butdid
where
is the
• Why is the matter in the universe made only of particles?
• Neutrinos have mass!! What are the mixing parameters, CP
violations and mass ordering?
• Why are there only three apparent forces?
• Is the picture we present the real thing?
– What makes up the 96% of the universe?
– How about extra-dimensions?
• Are there any other theories that describe the universe better?
– Does the super-symmetry exist?
• Where is new physics?
April 24, 2012
Searchees for the Higgs and the Future
Dr. Jaehoon Yu
67
What is the Higgs and What does it
do?
• When there is perfect symmetry, one cannot tell
directions!
• Only when symmetry is broken, can one tell directions
• Higgs field works to break the perfect symmetry and
give mass
– This field exists right now amongst us so that we have mass
• Sometimes, this field spontaneously generates a
particle, the Higgs particle
• So the Higgs particle is the evidence of the existence
of the Higgs field!
July 6, 2012
Is the Higgs particle discovered? Dr.
Jaehoon Yu
68
How do we look for the Higgs?
• Higgs particle is so heavy they decays into some
other particles very quickly
• When one searches for a new particle, you look for
the easiest way to get at them
• Of these the many signatures of the Higgs, some
states are much easier to find, if it were the
Standard Model one
–
–
–
–
H 
H  ZZ*  4e, 4 , 2e2 , 2e2 and 2 2
H WW*2e2 and 2 2
And many more complicated signatures
July 6, 2012
Is the Higgs particle discovered? Dr.
Jaehoon Yu
69
How do we look for the Higgs?
• Identify the Higgs candidate events
e+ (μ+)
e- (μ-)
e+
• Understand fakes (backgrounds)
e-
• Look for a bump!!
July 6, 2012
Is the Higgs particle discovered? Dr.
Jaehoon Yu
70
The ATLAS and CMS Detectors
Sub System
ATLAS
CMS
Solenoid (within EM Calo) 2T
3 Air-core Toroids
Solenoid 3.8T
Calorimeters Inside
Inner Tracking
Pixels, Si-strips, TRT
PID w/ TRT and dE/dx
Pixels and Si-strips
PID w/ dE/dx
EM Calorimeter
Lead-LAr Sampling
w/ fine longitudinal segmentation
Lead-Tungstate Crys. Homogeneous
w/o longitudinal segmentation
Design
Magnet(s)
Hadronic Calorimeter
Fe-Scint. & Cu-Larg (fwd)
Instrumented Air Core (std. alone)
Muon Spectrometer System
Acc. ATLAS 2.7 & CMS 2.4
4
11
Brass-scint.
& Tail Catcher
Instrumented Iron return yoke
Amount of LHC Data
2012:16 ~17fb-
Max inst. luminosity:
~ 7.7 x1033 cm-2 s-1
1
at 8 TeV thus far
~1fb-1//week
Superb performance!!
4th July
announcement
2011
5.6 fb-1
at 7 TeV
2010
0.05 fb-1
at 7 TeV
Oct. 23, 2012
Recent LHC Higgs Results
LCWS12, Jae Yu, U. Texas at Arlington
72
The BIG challenge in 2012: PILE-UP
Experiment’s
design value
(expected to be
reached at L=1034 !)
Z   event from 2012 data with 25 reconstructed vertices
Z  
73
After all selections: 59059 events
“raw” mass spectrum
weighted: wi ~S/B in each category i
Data sample mH of max
significance
2011
126 GeV
2012
127 GeV
2011+2012 126.5 GeV
2011+2012
125.5GeV
local significance
obs. (exp. SM H)
3.4 σ (1.6)
3.2 σ (1.9)
4.5 σ(2.5) ATLAS
4.1 σ(2.8) CMS
peak above a large smooth background,
relies upon excellent mass resolution
2e2 candidate event w/ M2e2 =123.9GeV
pT (e,e,μ,μ)= 18.7, 76, 19.6, 7.9 GeV, m (e+e-)= 87.9 GeV, m(μ+μ-) =19.6 GeV
12 reconstructed vertices
75
All Channel Combined Exclusion
Excluded at 95% CL:
112-122, 131-559 GeV
Only little sliver in 122 – 135 GeV and high mass left
All Channel Combined Significance
ATLAS
CMS
5.9σ
ATLAS and CMS Combined Higgs – end of 2011
Standard Model Higgs excluded in 110.0 <MH<117.5 GeV, 118.5
<MH< 122.5 GeV, and 129<MH<539 GeV & 127.5<MH<543GeV
Oct. 23, 2012
Recent LHC Higgs Results
LCWS12, Jae Yu, U. Texas at Arlington
78
Evolution of the excess with time
79
Evolution of the excess with time
80
Evolution of the excess with time
81
Evolution of the excess with time
07/12 CERN Prel.
82
Evolution of the excess with time
07/12 CERN Prel.
83
So have we seen the Higgs particle?
• The statistical significance of the finding is over 5 standard
deviation
– Level of significance: 99.99994%
– We can be wrong once if we do the same experiment 1,740,000 times
• So did we find the Higgs particle?
– We have discovered a new particle, the heaviest boson we’ve seen
thus far
• Since this particle decays to two spin 1 particles, the possible spin states of this
new boson is either 0 or 2!
– It has some properties consistent with the Standard Model Higgs
particle
– We, however, do not have enough data to precisely measure all the
properties – mass, life time, the rate at which this particle decays to
certain other particles, etc – to definitively determine
July 6, 2012
Is the Higgs particle discovered?
Dr. Jaehoon Yu
84
So why is this discovery important?
• This is the giant first in completing the Standard
Model
• Will help understand the origin of mass and the
mechanism at which mass is acquired
• Will help understand the origin and the structure of
the universe and the inter-relations of the forces
• Will help us make our lives better
• Generate excitements and interests on science and
train the next generation
July 6, 2012
Is the Higgs particle discovered?
Dr. Jaehoon Yu
85
Long Term LHC Plans
• 2012 run will end with ~25fb-1
– Combined with 2011 run (5.6fb-1), a total of 30fb-1
• 2013 – 2014: shutdown (LS1) to go to design energy
(13 – 14TeV) at high inst. Luminosity
• 2015 – 2017: √s=13 – 14TeV, L~1034, ~100fb-1
• 2018: Shut-down (LS2)
• 2019 – 2021: √s~=13 – 14TeV, L~2x1034, ~300fb-1
• 2022 – 2023: Shut-down (LS3)
• 2023 – 2030(?): √s=13 – 14TeV, L~5x1034 (HL-LHC),
~3000fb-1
Oct. 23, 2012
Recent LHC Higgs Results
LCWS12, Jae Yu, U. Texas at Arlington
86
What next? Future Linear Collider
• Now that we have found a new boson, precision measurement of the
particle’s properties becomes important
• An electron-positron collider on a straight line for precision
measurements
• 10~15 years from now (In Dec. 2011, Japanese PM announced that
they would bid for a LC in Japan)
• Takes 10 years to build the detector
L~31km
Circumference ~6.6km
~300 soccer fields
July 6, 2012
Is the Higgs particle discovered? Dr.
Jaehoon Yu
87
Bi-product of High Energy Physics Research
Can you see what the object is?
WWW Came from HEP!!!
July 6, 2012
Is the Higgs particle discovered? Dr.
Jaehoon Yu
88
GEM Application Potential
FAST X-RAY IMAGING
Using the lower GEM signal, the
readout can be self-triggered with
energy discrimination:
9 keV absorption
radiography of a small
mammal (image size ~
60 x 30 mm2)
A. Bressan et al,
Nucl. Instr. and Meth. A 425(1999)254
F. Sauli, Nucl. Instr. and Meth.A 461(2001)47
July 6, 2012
Is the Higgs particle discovered? Dr.
Jaehoon Yu
89
•
So what?
The LHC opened up a whole new kinematic regime
–
The LHC performed extremely well in 2011 and 2012!
•
•
•
•
•
•
Accumulated 22fb-1 thus far, and still have a weeks to go – additional ~1fb-1 expected!
Searches conducted with 4.8fb-1 at 7TeV and 5.8fb-1 at 8TeV of data
Observed a neutral boson couple to vector bosons and whose measured mass is
M ATLAS = 126.0 ± 0.4 ( stat.) ± 0.4 ( syst.)
M CMS = 125.6 ± 0.4 ( stat.)-0.3 ( syst.)
–
At 5.9/5.0 significance, corresponds to 1.7x10-9 bck fluctuation probability!
–
Compatible with production and decay of SM Higgs boson
+0.4
Excluded MH=112 – 122 and 131 – 559GeV (ATLAS) @95% CL
Linear collider and advanced detectors are being developed for future precision
measurements of Higgs and other newly discovered particles
Outcome and the bi-product of HEP research impacts our daily lives
– WWW came from HEP
– GEM will make a large screen low dosage X-ray imaging possible
•
•
Many technological advances happened through the last 100 years & coming 100 yrs
Continued sufficient investment to forefront scientific endeavors are absolutely
necessary for the future!
Oct. 23, 2012
Recent LHC Higgs Results
LCWS12, Jae Yu, U. Texas at Arlington
90