Organization – Lectures, exercises and lab course

Physik-Institut

PHY213 Kern- und Teilchenphysik II (FS 2020)

Introduction

Lea Caminada

lea.caminada@physik.uzh.ch

2

CV

•  Diploma and PhD in physics at ETH Zürich

–  H1 experiment at HERA (DESY, Hamburg) –  CMS experiment at LHC (CERN, Geneva)

•  Postdoctoral Fellow at LBNL, Berkeley California (USA)

–  ATLAS experiment at LHC (CERN, Geneva)

•  Scientist at University of Zürich and PSI

–  CMS experiment at LHC (CERN, Geneva)

•  SNF Eccellenza Professorial Fellowship starting in May Current research

•  Physics analysis at LHC with a focus on Standard Model processes with heavy quarks (t,b,c) and Higgs boson

•  Development, construction and

operation of high-precision silicon pixel detectors

Introducing myself

People

Organization – Lectures, exercises and lab course

Lea Caminada lea.caminada

@physik.uzh.ch

Kyle Cormier kcormier

@physik.uzh.ch

Stefanos Leontsinis steleo

@physik.uzh.ch

Olaf Steinkamp olafs

@physik.uzh.ch

Organization – Lectures, exercises and lab course

Schedule

•  Published and continuously updated at:

https://

www.physik.uzh.ch/de/

lehre/PHY213/

FS2020.html

•  Wed 10:15-12:00

–  Lectures

•  Fri 13:00-14:45

–  Lectures and

Organization – Lectures, exercises and lab course

•  There will be 6 series of exercises:

•  Requirements: At least 60% of exercises solved (points

only if present during exercise class), at least one exercise solved at blackboard

Schedule of exercises

Hand out Hand in Discussion Exercise 1 Wed 19.2. Wed 26.2. Fri 28.2.

Exercise 2 Wed 26.2. Fri 6.3. Fri 13.3.

Exercise 3 Fri 6.3. Fri 20.3. Fri 27.3.

Exercise 4 Fri 20.3. Fri 3.4. Fri 24.4.

Exercise 5 Fri 3.4. Wed 29.4. Fri 8.5.

Exercise 6 Wed 29.4. Fri 15.5. Fri 22.5.

Organization – Lectures, exercises and lab course

•  2-hours written exam

•  Wednesday, 24.6.2020, 10:00-12:00

•  Let me know by Friday in case of conflicts

•  Final grade is composed of grade of written exam (¾) and lab report (¼)

Exam

Organization – Lectures, exercises and lab course

•  Carry out full-scale particle physics experiment at PSI High-Intensity Proton Accelerator (HIPA)

–  Experimental setup –  Testing of components

–  Electronics and readout system –  Data taking

–  Physics analysis

•  Experiment will take place during the period of 6.-19.7.2020

–  Organized in shift work

–  Detailed schedule to be worked out toward the end of the semester

•  Written report to be handed in by 31.8.2020

Lab course at PSI

Overview

•  Review of the Standard Model (SM) of particle physics

•  Theory and experiments at the three frontiers

Literature

"Teilchen und Kerne" B. Povh, K. Rith, C. Scholz, F. Zetsche Springer

"Elementarteilchenphysik" C. Berger Springer

"Particle Astrophysics" D. Perkins Oxford University Press

"Nuclear and Particle Physics" B.R. Martin Wiley

"Modern Particle Physics" M. Thomson Cambridge University Press

Mass spectrum of matter particles

(fermions) and force carriers (bosons)

Fundamental Forces

strong interaction color charge

electromagnetic interaction electromagnetic charge

weak interaction

weak charge

Range of interactions

•  Range of strong force limited by gluon self-interaction

•  Range of electromagnetic interaction is infinite

•  Range of weak interaction limited by the mass of the weak bosons

Symmetries and conservation laws

•  Noether's theorem: If a physical system is invariant under a symmetry operation, then there is a

corresponding conservation law

•  Conservation laws in the Standard Model

Conserved quantity strong int. em. int. weak int.

Energy/momentum ✔ ✔ ✔

Charge ✔ ✔ ✔

Baryon number ✔ ✔ ✔

Lepton number ✔ ✔ ✔

I (isospin) ✔ ✗ ✗

S (strangeness) ✔ ✔ ✗

P (parity) ✔ ✔ ✗

C (C-parity) ✔ ✔ ✗

Local symmetries

•  Local symmetry: Transformation can be chosen

differently at each point in space-time à this freedom comes at a price

QED

To define phase in each point in space-time

à have to introduce γ (vector boson) Corresponds to 1D rotation: U(1)

Weak isospin

To have charged current in each point in space-time

à have to introduce W^- (vector boson) Corresponds to 2D rotation: SU(2)

QCD

To have color flow in each point in space-time

à have to introduce g (octet of bi- colored vector bosons)

e- e^-

γ

e- ν^e

W-

g^ij

Gauge group of the Standard Model

SU(3)

x SU(2)

x U(1)

QCD Electroweak theory

Gauge group of the Standard Model

SU(3)

x SU(2)

x U(1)

QCD Electroweak theory

Model which treats electromagnetic and weak interaction as two aspects of the

same force

•  1960-1970: Different aspects of weak

interaction observed in experimental data (parity violation, charged and neutral

currents, neutrino helicity,..)

•  1967/68: Formulation of the electroweak theory by Glashow, Salam & Weinberg (Nobel prize in 1979)

•  1971: Demonstration of renormalizibility ('t Hooft, Veltman, Nobel prize in 1999)

Weak isospin T

•  Define weak isospin T (in analogy to isospin I in strong interaction)

•  Each family of left-handed (LH) quarks and leptons forms a duplet of fermions

–  can be converted by the absorption/emission of a W boson –  weak isospin T=1/2 with 3^rd component T₃=±1/2

–  DIfference in charge within the same dublet is one unit

•  Right-handed (RH) fermions do not couple to W^± and are described as singlets

–  T=T₃=0

•  Weak isospin is conserved for weak, electromagnetic and strong interaction

•  SU(2)

is the gauge group corresponding to the

Weak hypercharge Y

•  U(1)_Y group couples to LH doublets and RH singlets

•  Gell-Mann and Nishijima: Q = T₃ + ½ Y

charge 3^rd component of the weak isospin

Multiplets of the electroweak interaction

Triplet and singlet of weak isospin

21

Charged current interaction: T

is conserved à T

(W

) = -1

T

(W

)=+1

There should be a third state W

with T=1 and T

=0.

W

couples with same strength (g) to fermions (as W

) à cannot be Z

(W

, W

, W

) form a triplet of the weak isospin

Postulate an additional state B

with T=0 and

T

=0 which is a singlet of the weak isospin with

corresponding coupling g'

Idea of electroweak unification

•  W only couples to LH fermions

•  Photon field A couples equally to LH/RH fermions

•  Z couples differently to LH/RH fermions

–  as observed e.g. from Z branching ratios

à A and Z are generated in mixing of a B and W⁰ (orthogonal linear combination)

•  θ

: weak mixing angle or Weinberg angle

| γ > = cos θ

| B

> + sin θ

| W

>

| Z

> = -sin θ

| B

> + cos θ

| W

>

Relation between θ

, g and g'

•  Electroweak unification predicts the following relations:

Together with: gives m_W and since

• 

Electroweak theory is predictive:

Once θ_W is measured à m_Z and m_W are predicted

Successfully tested to high precision at LEP, Tevatron, LHC also gives m_Z

However...

24

•  There is an issue with the electroweak theory:

•  SU(2)_LxU(1)_Y gauge theory with massless vector fields

•  However, experiment shows:

–  m_W = 80 GeV/c², m_Z = 91 GeV/c²

à

Solution: Masses introduced through concept of spontaneous symmetry breaking (SSB)

à Introduce a duplet of scalar particles (Higgs)

which generate through self-interaction the masses

of the W and Z boson