Introduction to Particle Physics 1

Transcription

1 Introduction to Particle Physics 1 Spring 2011, period III Lecturer: Katri Huitu, C325, puh , katri.huitu@helsinki.fi Assistant: Asli Sabanci, C304, puh , asli.sabanci@helsinki.fi Lectures: Tue 12-14, Wed Exercises:?, return homework by? noon on the second floor, 20 % of the total grade Textbooks: Bettini: Introduction to elementary particle physics (Cambridge University Press) Martin, Shaw: Particle physics (John Wiley and sons, Inc) Halzen, Martin: Quarks and leptons (John Wiley and sons, Inc) Perkins: Introduction to particle physics (Addison-Wesley Publishing Company, Inc) Examinations: 1

2 Course outline: Intro 1 Introduction. 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. 2

3 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) 3

4 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, ) 4

5 CERN summer student programme Application deadline end of January. 5

6 Basic tools: Quantum mechanics Special relativity Quantum Field Theory -Group theory -Relativistic kinematics -Spinor algebra -Path integrals - 6

7 INTRODUCTION Partly from and 7

8 Found in 2000 Found in

9 Size in atoms Size in meters at most 9

10 Leptons and quarks have in addition antiparticles (with opposite electric charge). All the quark flavours have three colours : 10

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12 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 12

13 Heavy unstable particles In 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 - 13

14 Do we know that there are three generations of particles? At CERN (Geneva, Switzerland) in the LEP-experiments ( ) it was found that the number of almost massless neutrino generations is three. 14

15 Particle properties (Particle Data Group, neutrino masses very small (<0.2 ev/c 2, the masses are very small, but >0), charge=0 electron: 0.5 MeV, life time > y, charge=-1 muon (1936): 106 MeV, life time s, charge=-1 tau (1976): 1777 MeV, life time 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~ 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 15

16 Relative strengths of interactions 16

17 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. Standard Model Supersymmetric model Amaldi, de Boer, Furstenau, Phys. Lett. B 260 (1991)

18 One particle is still missing: the Higgs boson gives mass to all particles in the Standard Model 18

19 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. 19

20 Interactions between particles 20

21 Higgs mass limits [ 1 GeV/c 2 =1.78 x kg; c=1 ] LEP: M H >114.4 GeV Katri Huitu, Fysikaalisten tieteiden esittely 21

22 Higgs particle will be searched for in the accelerators, e.g. in the Large Hadron Collider, which started operation in 2009 Light Higgs decays mostly to two b- quarks and heavy to weak gauge bosons. 22

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24 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 GeV 1954 Berkeley Bevatron, p=7 GeV 1960 CERN(CPS), Brookhaven (AGS) p=30 GeV 1971 Fermilab, Main Ring p=500 GeV Storage rings or colliders 1961 Frascati, ADA E cm =500 MeV (e + e - ) 1976 CERN, SPS E cm =540 GeV (p anti-p) 1983 Fermilab, Tevatron E cm =2 TeV (p anti-p) CERN, LEP E cm >200 GeV (e + e -, practical limit) 1991 DESY, HERA 30 GeV GeV (e p) 2009 CERN, LHC E cm =7 TeV (pp) Linear colliders 1987 Stanford, SLC E cm =91.2 GeV (e + e - )???? ILC, CLIC E cm = 300 GeV 3 TeV?? 24

25 CERN in Geneva 25

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28 Aerial picture of CERN 28

29 High Energy Physics laboratories. Finland participates in experimental work at CERN and at Fermilab. 29

30 Typical detector: 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. 30

31 LHC: 7 TeV pp-collisions in 2010, 8 TeV in , 14 TeV? Kuva: CERN 31

32 Not all the events are investigated! Triggering When the proton beams meet, approximately 10 8 collisions per second, of which 10 2 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. 32

33 E=mc 2 36 nationalities 160 institutes 2008 researchers 33

34 Golden mode: H ZZ l + l - l + l p Z p + Z - all energy can be identified Simulation of Higgs decay in ATLAS detector 34

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37 LEP: E=mc 2 37

38 A detector at LEP 38

39 e + e - Z * ZH qqq q? August

40 Bubble chamber, around

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42 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, 42

43 Most of the matter in the universe is dark: it does not radiate. How do we know this? The elements in galaxies would fly apart, unless there is enough material! L. Bergström, Rep.Prog.Phys

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45 In spring 2005 a galaxy containing only dark matter was found: A hydrogen cloud with mass ~10 8 M. was investigated, but it was deduced that the whole galaxy mass is ~10 11 M. 45

46 Direct observational proof of dark matter through gravitational lense effect. D. Clowe et al, ApJ Letters, astro-ph/ Wilkinson Microwave Anisotropy Probe (WMAP) has measured the dark matter and dark energy of the universe starting in Two groups of galaxies collided 100 million years ago. The ordinary matter (pink) slows down, while the weakly interacting dark matter goes through. 46

47 Particle physics Cosmology Dark matter 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)

48 Short history of particle physics from /other/history/ 48

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56 1964 Higgs, and separately Englert and Brout develop the Higgs mechanism. 56

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