PHYS 3313 – Section 001 Lecture #22

Wednesday, Nov. 28, 2012

PHYS 3313-001, Fall 2012 Dr. Jaehoon Yu

1

PHYS 3313 – Section 001Lecture #22

Wednesday, Nov. 268, 2012Dr. Jaehoon Yu

• Particle Accelerators• Particle Physics Detectors• Hot topics in Particle Physics• What’s coming in the future?



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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


3Wednesday, Nov. 28, 2012

• 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, ρ-

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

Introduction

P

c

c

2000 /MeV c197fm0.1fm

MeVc



• 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

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!!!

Forces and Their Relative Strengths



• 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

Interaction Time



• Before the quark concepts, all known elementary particles were grouped in four depending on the nature of their interactions

Elementary Particles



• 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

Elementary Particle Interactions



• 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

• 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

• Pauli exclusion principle is built into the wave function– For xi=xj,

Elementary Particles: Bosons and Fermions

1 2 3, , ,... ...B i nx x x x x

1 2 3, , ,... ...F i nx x x x x

F

1 32 , ,... ., ..B i nx xx x x

1 32 , ,... ., ..F i nx xx x x

F



• 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 π0?• A neutron?• A K0?• A Neutrino?

Bosons, Fermions, Particles and Antiparticles



• 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

Quantum Numbers



• Can the decay 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.

Baryon Numbers0p e π

13Monday, Nov. 27, 2006 PHYS 3446, Fall 2006Jae Yu

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


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


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 point-

like 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)


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


Quarks and Leptons• In SM, there are three families of leptons

– 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

• All these fundamental particles are fermions w/ spin

e

e

ud

cs

tb

+2/3

-1/3

Q

0-1

Q

Monday, Aug. 27, 2012 PHYS 3313-001, Fall 2012 Dr. Jaehoon Yu

18

The Standard Model


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Discovered in 1995, ~175mp

• Total of 16 particles make up the matter in the universe! Simple and elegant!!!

• Tested to a precision of 1 part per million!

Make up most ordinary matters ~0.1mp


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

π

π

0π

ud

ud

12uu dd

K

K 0K 0K

us

us

ds

ds


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 Strange baryons Other Baryons– s=1 s=2

• Since baryons have B=1, the quarks must have baryon number 1/3

p

n

uud

udd

0 0

udsuusudsdds

0

ussdss

uuu


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 – – – – W bosons: MW=80GeV/c2

– –


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).


What do we need for the experiment to search for vector bosons?

• We need to be able to identify isolated leptons– Good electron and muon identification– Charged particle tracking

• We need to be able to measure transverse momentum well– 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



• 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 1m or better

• Why?– Must correct particle paths and momenta to increase fluxes and control

momenta

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, at 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

Particle Accelerators



• 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

Electrostatic Accelerators: Cockcroft-Walton

• 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).



• 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

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

Electrostatic Accelerators: Van de Graaff



• 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

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




• 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

• In a constant angular speed, ω=v/r. The frequency of the motion is

• 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 radius R is


2vmr

v qBr mc

2f

π

22 2 2

max max 21 12 2

qBRT mv m R

mc

vBqc

ω

2qBmcπ

12

q Bm cπ



• 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

Resonance Accelerators: Linear Accelerator



• 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

• For v ~ c, the resonance frequency becomes

• Thus for high energies, either B or should increase• Machines with constant B but variable are called synchro-

cyclotrons• Machines with variable B independent of the change of is

called synchrotrons

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

• For magnetic field strength of 2Tesla, one needs radius of 50m to accelerate an electron to 30GeV/c.


/( )

0.3 )p GeV cpcR m

qB B Tesla



• 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


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



37


Fermilab Tevatron and LHC at CERN• World’s Highest Energy proton-anti-proton collider

– 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!!

Chicago

Tevatron p

p CDF DØ

• World’s Highest Energy p-p 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 ~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

38


39

LHC @ CERN Aerial View

Geneva Airport

ATLAS

CMS

France

Swizerland



• 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

Particle Detectors


Particle Detection Techniques

InteractionPoint

electron

photon

jet

muonneutrino -- or any non-interacting particle missing transverse momentum

B

Scintillating FiberSilicon Tracking

Charged Particle Tracks

Calorimeter (dense)

EM hadronic

Energy

Wire Chambers

Mag

net

Muon Tracks

We know x,y starting momenta is zero, butalong the z axis it is not, so many of our measurements are in the xy plane, or transverse


The ATLAS and CMS Detectors

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• 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



• 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

Scintillation Counters



• 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 work-function» Operating at an increasing potential difference (100 – 200 V) difference

between dynodes

Scintillation Detectors & Photo-multiplier Tube



Scintillation Detector Structure

Scintillation Counter

PMT

Readout Electronics

HV PS

Light Guide/WavelengthShifter

Scope



Some PMT’sSuper-Kamiokande detector



• 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

Time of Flight



• 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 β>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

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+π0

• 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

Cerenkov Detectors



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



Super-K Event Displays

Stopping 3



• 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

Semiconductor Detectors



DØ Silicon Vertex Detector234

9 811

1

67

5

1012

1

6…...

12

34

Barrels F-Disks H-DisksChannels 387120 258048 147456Modules 432 144 96I nner R 2.7 cm 2.6 cm 9.5 cmOuter R 9.4 cm 10.5 cm 26 cm

One Si detector

BarrelDisk



• 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

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

Calorimeters



Electron Interactions in material (showering)

Photon, γ



• 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

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

Sampling Calorimeters



EM

Hadron

How particle showers look in detectors



Principles of Calorimeters

Total absorption calorimeter: See the entire shower energy

Sampling calorimeter: See only some fraction of shower energy

For EM

Absorber plates

visE fE

For HAD visE fE



Example Hadronic Shower (20GeV)



Conventional Neutrino Beam

• Use large number of protons on target to produce many secondary hadrons (π, K, D, etc)

• Let π and K decay in-flight for beam– π+ 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

p

Good target

Good beam focusing

Long decay region

Sufficient dump



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)



• Calorimeter– 168 FE plates & 690tons– 84 Liquid Scintillator– 42 Drift chambers interspersed

A Typical Neutrino Detector: NuTeV

• Solid Iron Toroid• Measures Muon momentum• p/p~10%

Continuous test beam for in-situ calibration



Charged Current Events

Neutral Current Events

How Do Neutrino Events Look?

x-view

y-view

x-view

y-viewNothing is coming in!!!

Nothing is coming in!!!

Nothing is going out!!!



Source of Cleaner Neutrino BeamMuon 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

• Why is the mass range so large (0.1mp – 175 mp)?• How do matters acquire mass?

– Higgs mechanism but where is the Higgs?• 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

What’s the current hot issues?

67

- Higgs mechanism, did we find the Higgs?

Is the Higgs particle discovered? Dr. Jaehoon Yu

68July 6, 2012

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!


69July 6, 2012

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 γγ– H ZZ* 4e, 4, 2e2, 2e2 and 22 – H WW*2e2 and 22 – And many more complicated signatures


70July 6, 2012

How do we look for the Higgs?• Identify the Higgs candidate events

• Understand fakes (backgrounds)

• Look for a bump!!

e- (μ-)e+ (μ+)

e-

e+

The ATLAS and CMS DetectorsSub System ATLAS CMS

Design

Magnet(s) Solenoid (within EM Calo) 2T3 Air-core Toroids

Solenoid 3.8TCalorimeters Inside

Inner TrackingPixels, Si-strips, TRTPID w/ TRT and dE/dx

Pixels and Si-stripsPID w/ dE/dx

EM CalorimeterLead-LAr Sampling

w/ fine longitudinal segmentationLead-Tungstate Crys. Homogeneous

w/o longitudinal segmentation

Hadronic Calorimeter Fe-Scint. & Cu-Larg (fwd) Brass-scint. & Tail Catcher

Muon Spectrometer SystemAcc. ATLAS 2.7 & CMS 2.4

Instrumented Air Core (std. alone) Instrumented Iron return yoke411

Oct. 23, 2012 Recent LHC Higgs Results LCWS12, Jae Yu, U. Texas at Arlington

72

Amount of LHC Data

20100.05 fb-1

at 7 TeV

2012:16 ~17fb-1

at 8 TeV thus far~1fb-1//week

20115.6 fb-1

at 7 TeV

4th July announcement

Max inst. luminosity:~ 7.7 x1033 cm-2 s-1

Superb performance!!

73

Experiment’s design value (expected to bereached at L=1034 !)

Z event from 2012 data with 25 reconstructed vertices

The BIG challenge in 2012: PILE-UP

Z

“raw” mass spectrum

weighted: wi ~S/B in each category i

After all selections: 59059 events

peak above a large smooth background,relies upon excellent mass resolution

Data sample mH of max local significance significance obs. (exp. SM H) 2011 126 GeV 3.4 σ (1.6) 2012 127 GeV 3.2 σ (1.9) 2011+2012 126.5 GeV 4.5 σ(2.5) ATLAS2011+2012 125.5GeV 4.1 σ(2.8) CMS

75

pT (e,e,μ,μ)= 18.7, 76, 19.6, 7.9 GeV, m (e+e-)= 87.9 GeV, m(μ+μ-) =19.6 GeV12 reconstructed vertices

2e2 candidate event w/ M2e2=123.9GeV

76

Excluded at 95% CL:112-122, 131-559 GeV

All Channel Combined Exclusion

Only little sliver in 122 – 135 GeV and high mass left

77

5.9σ

All Channel Combined Significance

ATLAS

CMS

ATLAS and CMS Combined Higgs – end of 2011

Oct. 23, 2012 78Recent LHC Higgs Results LCWS12, Jae Yu, U. Texas at Arlington

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

79

Evolution of the excess with time

80


81


82


07/12 CERN Prel.

83


07/12 CERN Prel.

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 84Is the Higgs particle discovered? Dr. Jaehoon Yu

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


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

July 6, 2012

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


87

Circumference ~6.6km~300 soccer fields

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

GEM Application Potential FAST X-RAY IMAGING

Using the lower GEM signal, the readout can be self-triggered with energy discrimination:

A. Bressan et al, Nucl. Instr. and Meth. A 425(1999)254F. Sauli, Nucl. Instr. and Meth.A 461(2001)47

9 keV absorption radiography of a small mammal (image size ~ 60 x 30 mm2)

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

– At 5.9σ/5.0σ significance, corresponds to 1.7x10-9 bck fluctuation probability!– Compatible with production and decay of SM Higgs boson

• 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 Arlington90

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PHYS 3313 – Section 001 Lecture #22

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