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Introduction to Particle Physics 1Spring 2012, period III

Lecturer: Katri Huitu, C325, puh 191 50677, katri.huitu@helsinki.fi

Assistant: Asli Sabanci, C304, puh 191 50705, asli.sabanci@helsinki.fi

Lectures: Tue 12-14, Wed 10-12

Exercises: ?, return homework by ? noon on the second floor,

20 % of the total grade

Textbooks: Martin, Shaw: Particle physics (John Wiley and sons, Inc)Griffiths: Introduction to elementary particles (Wiley-VCH verlag)Halzen, Martin: Quarks and leptons (John Wiley and sons, Inc) Perkins: Introduction to particle physics (Addison-Wesley Publishing Company, Inc) Bettini: Introduction to elementary particle physics (Cambridge University Press)

Examinations:

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Course outline:

Intro 1Introduction. Short history. Particles. Interactions.

Symmetries: P, C, T. Isospin. G-parity. Quark model. Color factor. Confinement.

Cross sections and decay rates. Invariant variables. Experimental detection.

Intro 2 Dirac equation. QED. Feynman rules. Parton model. Deep inelastic scattering. Color interaction. QCD.

Weak interaction. V-A theory of weak interactions. Weak mixing angles. GIM.

Electroweak interactions. Gauge symmetries. The Standard Model.

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Theoretical High Energy Physics in Finland:Beyond the Standard Model phenomena: K. Huitu (AFO), K. Tuominen (JU)

Hadron physics and QCD: P. Hoyer (AFO), D.-O. Riska (HIP), M. Sainio (HIP)

Computational field theory: K. Rummukainen (AFO)

String theory and quantum field theory: E. Keski-Vakkuri (HIP), A. Tureanu (AFO)

Cosmology: K. Enqvist (AFO), K. Kainulainen (JU), H. Kurki-Suonio (AFO), T. Multamäki (TU), I. Vilja (TU)

Neutrino physics: J. Maalampi (JU)

Ultrarelativistic heavy ion collisions: K.J. Eskola (JU)

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Experimental High Energy Physics in Finland:

CERN LHC (Switzerland):

-CMS-experiment (Paula Eerola, Ritva Kinnunen, Veikko Karimäki,…)

-TOTEM-experiment (Risto Orava, Kenneth Österberg, …)

-ALICE-experiment (Juha Äystö, Jan Rak, …)

Fermilab Tevatron (USA):

-CDF-experiment (Risto Orava, …)

Linear collider:

-CERN CLIC-experiment (Kenneth Österberg,…)

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AFO summer internships:

http://www.particle.physics.helsinki.fi/kesatyopaikat.html

Application deadline 8.2.

HIP and CERN summer internships:

http://www.hip.fi/educations/kesaharjottelu.html

Application deadline 31.1.

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Basic tools:Quantum mechanics

Special relativity

-Group theory

-Relativistic kinematics

-Spinor algebra

-Path integrals

-…

Quantum Field Theory

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INTRODUCTIONPartly from

http://www.cern.ch/ and

http://particleadventure.org/particleadventure/

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Found in 1995

Found in 2000

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Size in atoms Size in meters

at most

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Leptons and quarks have in addition antiparticles (with opposite electric charge).

All the quark ’flavours’ have three ’colours’ :

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Matter particles are fermions: they obey the Pauli exclusion principle – identical particles are not in the same place.

Particles mediating interactions are bosons, which do not obey the Pauli exclusion principle.

Quarks are always bound together by strong interactions:

Two bound quarks: mesons (pion, kaon,...)Three bound quarks: baryons (proton, neutron,...)

Of the observable particles, the stable ones are:

electron, positron, proton, neutrinos, photon

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Heavy unstable particlesIn nature heavy particles can be found in cosmic rays.

85% protons, 12% alpha particles (=helium nuclei), 1% heavier nuclei, 2% electrons collide in the air

, K, other

+(-) +(-)+(anti-)

0 e+e-

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Do we know that there are three generations of particles?

At CERN (Geneva, Switzerland) in the LEP-experiments (1989-2000) it was found that the number of almost massless neutrino generations is three.

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Particle properties (Particle Data Group, http://pdg.lbl.gov/)

neutrino masses very small (<0.2 eV/c2, the masses are very small, but >0), charge=0

electron: 0.5 MeV, life time > 4 108 y, charge=-1muon (1936): 106 MeV, life time 2 10-6 s, charge=-1 tau (1976): 1777 MeV, life time 3 10-13 s, charge=-1

up-quark: 5 MeV, charge =+2/3 down-quark: 8 MeV, charge =-1/3 charm-quark (1974): 1.2 GeV, charge =+2/3 strange-quark: 160 MeV , charge =-1/3 top-quark (1995): 175 GeV~3.17 10-25 kg, charge =+2/3 bottom-quark (1977): 4.2 GeV, charge =-1/3

proton mass ~1 GeV

gauge bosons: W: 80.4 GeV, Z: 91.2 GeV, ,g massless

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Relative strengths of interactions

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Amaldi, de Boer, Furstenau, Phys. Lett. B 260 (1991) 447

Standard Model Supersymmetric model

Are the interactions remnants of one basic interaction? Here 1 describes the strength of electromagnetic interaction, 2 the strength of the weak and 3 the strength of the strong interaction.

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One particle is still missing:

the Higgs boson gives mass to all particles in the Standard Model

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As a physical system, the Universe is in the lowest possible energy state. The minimum of potential energy is not at the point where the Higgs field vanishes.

The expectation value of the Higgs field in the minimum is not zero!The interaction between particles and Higgs field is called mass. Through the self-interaction also the Higgs boson becomes massive.

2020

Interactions between particles

214.12.2009 21

LEP: MH>114.4 GeV

Higgs mass limits [ 1 GeV/c2=1.78 x 10-27 kg; c=1 ]

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Higgs particle is searched for in the Large HadronCollider, which started operation in 2009

Light Higgs decays mostly to two b-quarks and heavy to weak gauge bosons.

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Fig. 1. a) Standard Model Higgs exclusion limit at 95% confidence level for 4.7 fb-1 proton-proton data collected by CMS in 2010 and 2011, showing the lower mass region, as of 13 December 2011.

Fig. 1. b) A typical Higgs candidate event including two high-energy photons.

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Accelerators (not a complete story)Synchrotrons: p(GeV)=0.3 B(T) R(m)

uniform magnetic field; beam pipe with good vacuum;accelerating cavities; RF pushes to particles in bunches

1952 Brookhaven Cosmotron, proton p=3 GeV1954 Berkeley Bevatron, p=7 GeV1960 CERN(CPS), Brookhaven (AGS) p=30 GeV1971 Fermilab, Main Ring p=500 GeV

Storage rings or colliders1961 Frascati, ADA Ecm=500 MeV (e+e-)1976 CERN, SPS Ecm=540 GeV (p anti-p)1983 Fermilab, Tevatron Ecm=2 TeV (p anti-p) 20111989 CERN, LEP Ecm>200 GeV (e+e-, practical limit)1991 DESY, HERA 30 GeV + 920 GeV (e p)2009 CERN, LHC Ecm=7 TeV (pp)

Linear colliders1987 Stanford, SLC Ecm=91.2 GeV (e+e-)???? ILC, CLIC Ecm= 300 GeV – 3 TeV ??

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CERN in Geneva

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Aerial picture of CERN

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High Energy Physics laboratories. Finland participates in experimental work at CERN and at Fermilab.

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Identified in the detector:

Photon – energy in em calorimeter, but not in the hadron calorimeter, no track

Electron – energy in em calorimeter, but not in the hadron calorimeter, leaves a track

Muon – leaves only little energy in the calorimeters, leaves a track and goes all the way to the muon chambers

Jets = quarks and gluons, which hadronize to jets. A group of particles which are seen in the hadron calorimeter. The decay vertex can be seen for heavy quarks.

Typical detector:

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LHC: 7 TeV pp-collisions in 2010-11, 8 TeV in 2012?, 14 TeV ?

Kuva: CERN

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Not all the events are investigated!Triggering

When the proton beams meet, approximately 108 collisions per second, of which 102 can be kept.

Most of these test the Standard Model, which is background from the new physics point of view!

It has to be decided beforehand, which is important and interesting and only such events are written: triggering

This can be done mechanically or by software, e.g. only such electrons or muons are considered, which clearly can be isolated, and certain momentum for a particle is required.

Background

Standard Model is background for the new physics – it is well known and can be predicted. A model for new physics has to be separated from the Standard Model by various distributions, like distributions of leptons, jets, and missing energy.

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36 nationalities160 institutes2008 researchers

E=mc2

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Golden mode: H ZZ l+l-l’+l’-

p pZ

Z

-

+

+

-

all energy can be identified

Simulation of Higgs decay in ATLAS detector

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LEP: E=mc2

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A detector at LEP

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e+e- Z* ZH qqq’q’ ?

August 2000

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Bubble chamber, around 1970

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Some unsolved mysteries:

Why three generations?

How is mass generated?

What is dark matter?

Why is there matter?

Are quarks and leptons elementary? (Strings?)

How to explain gravity?

Are the interactions united at higher energies?

More profound theories: grand unified theories, supersymmetric models, string theories, …

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How do we know this?

The elements in galaxies would fly apart, unless there is enough material!

Most of the matter in the universe is dark: it does not radiate.

L. Bergström, Rep.Prog.Phys. 2000

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In spring 2005 a galaxy containing only dark matter was found:

A hydrogen cloud with mass ~108M was investigated, but it was deduced that the whole galaxy mass is ~1011M .

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Direct observational proof of dark matter through gravitational lense effect.D. Clowe et al, ApJ Letters, astro-ph/0608407.

Two groups of galaxies collided 100 million years ago. The ordinary matter (pink) slows down, while the weakly interacting dark matter goes through.

Wilkinson Microwave Anisotropy Probe (WMAP) has measured the dark matter and dark energy of the universe starting in 2001.

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Theories of particle physics have a large number of suitable candidates for dark matter, which can also provide the observed structure of the universe.

Diemand, Moore, Stadel, Nature 433 (2005) 389.

Particle physics Cosmology

Dark matter

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Short history of particle physicsfrom

http://particleadventure.org/particleadventure/other/history/

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1964 Higgs, and separately Englert and Brout develop the Higgs mechanism.

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