Elementary Particle Physics Research Achim Geiser, DESY Hamburg Summer Student Lecture, 21.-22.7.15

Scope of this lecture: Introduction to particle physics for non-specialists rather elementary more details -> specialized lectures particle physics in general some emphasis on DESY-related topics 21.-22.7.15

A. Geiser, Particle Physics

thanks to B. Foster for some of the nicest slides/animations other sources: www pages of DESY and CERN

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What is Particle Physics?

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What is “science”? Wikipedia.org:

Science (from Latin scientia, meaning "knowledge") is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe.

First large scale scientific experiment:

proposal: Galilei 1632 Galileo Galilei realisation: Pierre Gassendi 1640 French navy Galley with international crew of ~100 people

^ recorded historically

M. Risch Physik in Unserer Zeit 38 (5) (2007) 249

cannon ball

(fraction of students not reported)

=>

5 m/s

?

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What is a „particle“? Classical view: particles = discrete objects. energy concentrated into finite space with definite boundaries. Particles exist at a specific location. -> Newtonian mechanics Isaac Newton (Principia 1687) Modern view: particles = objects with discrete quantum numbers, e.g. charge, mass, ...

Niels Bohr

not necessarily located at a specific position, (Heisenberg uncertainty principle) can also be represented by wave functions. (Quantum mechanics, particle/wave duality)

Louis de Broglie (Nobel 1929)

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Werner Heisenberg (Nobel 1932)

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(Nobel 1922)

Erwin Schrödinger (Nobel 1933)

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What is „elementary“? Greek: atomos = smallest indivisible part Dmitry Ivanowitsch Mendeleyev 1868 (elements) Ernest Rutherford 1911 (nucleus) (Nobel 1908)

Murray Gell-Mann 1962 (quarks) (Nobel 1969)

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History of basic building blocks of matter

Σ∆ π Λ∆Ω ∆ Κ πΚπ∆pΚ

0 − − + οο + − − 0+ + + +

motivation: find smallest possible number

Supersymmetry

AD

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Which “interactions”? at ~ 1 GeV

-2

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Leptons Quarks

What we know today

u c t g γ s d b

up

down

charm

top

strange bottom

gluon

photon

νe νµ ντ W

e-neutrino µ-neutrino τ-neutrino

e µ τ

electron

muon tau

W boson

Z Z boson Higgs Boson

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The Power of Conservation Laws e.g. radioactive neutron decay:

n

p

+e +

νe

not visible

Pauli 1930: Wolfgang Pauli (Nobel 1945)

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confirmation: neutrino detection e.g. reversed reaction:

νe+ n

p +e

extremely rare! (absorption length ~ 3 light years Pb)

Frederick Reines (Nobel 1995)

first detection: 1956 Reines and Cowan, neutrinos from nuclear reactor

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The power of symmetries: Parity

Will physical processes look the same when viewed through a mirror?

In everyday day life: violation of parity symmetry is common „natural“: our heart is on the left „spontaneous“: cars drive on the right (on the continent)

Eugene Wigner

What about basic interactions? Electromagnetic and strong interactions conserve parity! (Nobel 1963)

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The power of symmetries: Parity Lee & Yang 1956:

weak interactions violate Parity

experimentally verified

by Wu et al. 1957: Chen Ning Yang (Nobel 1957)

spin consequence:

Tsung -Dao Lee

neutrinos are always lefthanded !

Chieng Shiung Wu

(antineutrinos righthanded) 21.-22.7.15

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The Power of Quantum Numbers 1948: discovery of muon same quantum numbers as electron, except mass

Who ordered THAT ?

(Nobel 1988)

I.I. Rabi (Nobel 1944)

muon decay:

µ- -> νµ e- νe

conservation of electric charge

-1

0

-1

0

lepton number:

1

1

1

-1

„muon number“:

1

1

0

0

Leon M. Melvin Jack Ledermann Schwartz Steinberger

ν=ν νµ = νe

(1955) (1962)

There is a distinct neutrino for each charged lepton 21.-22.7.15

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The Power of Precision Precision measurements of shape and height of Z0 resonance at LEP I (CERN 1990’s)

number of (light) neutrino flavours = 3

ν ν ν

Gerardus Martinus t’Hooft Veltman (Nobel 1999)

e+e- -> Z0

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Can we “see” particles? Luis Walter Alvarez

(Nobel 1968)

we can! bubble chamber photo

Donald Arthur Glaser 21.-22.7.15

(Nobel 1960)

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A typical particle physics detector

see e.g. ARGUS near DESY entrance 21.-22.7.15

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Why do we need colliders? early discoveries in cosmic rays, but need controlled conditions

E m= 2 c

Mont Blanc

V.F. Hess (Nobel 1936)

CERN

Albert Einstein (Nobel 1921)

need high energy to discover new heavy particles colliders = microscopes (later) 21.-22.7.15

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LEP/LHC

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The HERA ep Collider and Experiments Data taking stopped summer 2007. Data analysis ongoing until 2014 and beyond.

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Particle Physics = People

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Strong Interactions: Quarks and Colour strong force in nuclear interactions = „exchange of massive pions“ between nucleons = residual Van der Waals-like interaction Hideki Yukawa

n π p

(Nobel 1949)

modern view: (Quantum Chromo-Dynamics, QCD) exchange of massless gluons between quark constituents „similar“ to electromagnetism (Quantum Electro-Dynamics, QED)

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The Quark Model (1964) arrange quarks (known at that time) into flavour-triplet => SU(3)flavour symmetry Q=-1/3

Q=2/3

d

u S=0

treat all known hadrons (protons, neutrons, pions, ...) as objects composed of two or three such quarks (antiquarks)

S=-1 s 21.-22.7.15

Murray Gell-Mann (Nobel 1969)

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The Quark Model baryons = qqq

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mesons = qq

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Colour Quark model very successful, but seems to violate quantum numbers (Fermi statistics), e.g. ∆ ++ = uuu ↑↑↑ => introduce new degree of freedom: q q

g

q

g

g q

q

gg g

g g

q

3 coulours -> SU(3)colour 21.-22.7.15

qqq = qq = white!

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Screening of Electric Charge electric charge polarises vacuum -> virtual electron positron pairs positrons partially screen electron charge effective charge/force (Nobel 1965)

decreases at large distances/low energy (screening) increases at small distance/large energy

Sin-Itoro Julian Richard P. 21.-22.7.15 A. Geiser, Particle Physics Tomonaga Schwinger Feynman

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Anti-Screening of Coulour Charge! quark-antiquark pairs -> screening gluons carry colour -> gg pairs -> anti-screening!

confinement

(Nobel 2004)

asymptotic freedom

1/r2~E2, 21.-22.7.15

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Comparison QED / QCD electromagnetism

strong interactions

QED 1 kind of charge (q) force mediated by photons photons are neutral α is nearly constant

QCD 3 kinds of charge (r,g,b) force mediated by gluons gluons are charged (eg. rg, bb, gb) αs strongly depends on distance confinement limit:

The underlying theories are formally almost identical! 21.-22.7.15

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The effective potential for qq interactions

confinement

asymptotic freedom

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lattice gauge calculation

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Burton Richter

Heavy Quark Spectroscopy Positronium = bound e+e- system

Charmonium = bound system of cc quark pair

(Nobel 1976)

Samuel C.C. Ting

1974

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calculation of proton mass in QCD from lattice gauge theory:

p

spontaneous breakdown of “chiral symmetry” (left-right-symmetry) yields QCD “vacuum” expectation value

⇒ proton mass, ⇒ mass of the visible part of the universe ! 21.-22.7.15

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Yoichiro Nambu (Nobel 2008)

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How to detect Quarks and Gluons? Jets! hadrons q

e+ q

hadrons

e-

Example of the hadron production in e+eannihilation in the JADE detector at the PETRA e+e- collider at DESY, Germany. Georges Charpak

cms energy 30 GeV. Lines of crosses - reconstructed trajectories in drift chambers (gas (Nobel 1992) ionisation detectors). Photons - dotted lines - detected by lead-glass Cerenkov counters. Two opposite jets. 21.-22.7.15

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Discovery of the Gluon PETRA at DESY:

(1979)

look for

αs Björn Wiik

Paul Söding

Günter Wolf

Sau Lan Wu

TASSO event picture

(EPS prize 1995)

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Jets in ep and pp interactions LHC HERA

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Running strong coupling „constant“ αs e.g. from jet production at e+e-, ep, and pp at DESY, Fermilab and CERN (HERA) (LEP, PETRA)

similar for ATLAS

courtesy T. Dorigo

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How to determine the „size“ of a particle? microscope: low resolution -> small instrument

resolution ~ 10-18 m = 1/1000 of size of a proton

high resolution -> large instrument

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How to resolve the structure of an object? e.g. X-rays (Hasylab, FLASH, PETRA III, XFEL)

scattering image probe

accelerator

E~ keV

-> structure of a biomolecule Ada Yonath (Nobel 2009)

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Resolve the structure of the proton E ~ MeV resolve whole proton static quark model, valence quarks (m ~ 350 MeV)

Jerome I. Henry W. Richard E. Friedmann Kendall Taylor (Nobel 1990)

E ~ mp ~ 1 GeV resolve valence quarks and their motion E >> 1 GeV resolve quark and gluon “sea” 21.-22.7.15

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Inside the proton Low Q2 (large λ)

Heisenberg’s UP allows gluons, and qq pairs to be produced for a very short time.

Medium Q2 (medium λ)

Large Q2 (short λ)

At higher and higher resolutions, the quarks emit gluons, which also emit gluons, which emit quarks, which……. 21.-22.7.15

At highest QA.2,Geiser, λ ~ 1/Q 10-18 m Particle~Physics

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Deep Inelastic ep Scattering at HERA

q

p remnant

p

e e

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Deep Inelastic Scattering (DIS)

(in QPM)

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The Proton Structure structure functions

quark and gluon densities

Amanda Cooper-Sarkar (Chadwick medal 2015)

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Kinematic regions: HERA vs. LHC proton structure measured directly for large part of LHC phase space

LHC

HERA

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Tevatron

QCD evolution successful -> safely extrapolate to higher Q2

fixed target

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Example: Higgs cross section at LHC H -> γγ in ATLAS

Kerstin Tackmann (Hertha Sponer prize 2013)

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Intermediate summary Particle physics: Symmetries and conservation laws are important many exciting results at DESY, CERN and elsewhere! HERA closed down, but particle physics at DESY alive and well tomorrow: weak interactions, Higgs, (neutrinos), cosmology, future of particle physics 21.-22.7.15

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Weak Interactions The Theory of

~ 1959-1968

GLASHOW, SALAM and WEINBERG

(Nobel 1979)

Theory of the unified weak and electromagnetic interaction, transmitted by exchange of “intermediate vector bosons”

mass generated by Higgs field 21.-22.7.15

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Discovery of the W and Z

(1983)

To produce the heavy W and Z bosons (m ~ 80-90 GeV) need high energy collider! 1978-80: conversion of SPS proton accelerator at CERN into proton-antiproton collider challenge: make antiproton beam! success! -> first W and Z produced 1982/83

Z0 -> e+e- UA1

(Nobel 1984)

Carlo Rubbia

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Simon van der Meer

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Z production at LHC

Now millions of events … yesterday’s signal is today’s background and tomorrow’s calibration 21.-22.7.15

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Three Boson Coupling @ LEP W/Z bosons carry electroweak charge (like colour for gluons) -> measure rate of W pair production at LEP II

only ν exchange

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No ZWW vertex

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Electroweak Physics at HERA Neutral Current (NC) interactions

e

Charged Current (CC) interactions

e

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Weak interactions are "left-handed" lefthanded electrons interact (CC)

e-

erighthanded electrons do not!

e-

e+ cross section linearly proportional to polarization

e± p

e± p

σ polCC = (1 ± Pe) ⋅ σ unpolCC 21.-22.7.15

left

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polarization

right

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Electroweak Unification NC

CC

MW2 21.-22.7.15

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The Quest for Unification of Forces Electroweak Unification

LHC

Grand Unified Theories ? Superstring Theories ? Maxwell’s equations

HERA

strong

Big Bang

electric magnetic weak gravity 21.-22.7.15

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αs running and Grand Unification with SUSY (see later):

?

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Antimatter relativistic Schrödinger equation (Dirac equation) two solutions: one with positive, one with negative energy Dirac: interpret negative solution as

P.A.M. Dirac (Nobel 1933)

1932 antielectrons (positrons) found in conversion C.D.Anderson of energy into matter (Nobel 1936)

1995 antihydrogen consisting of antiprotons and positrons produced at CERN In principle: antiworld can be built from antimatter In practice: produced only in accelerators and in cosmic rays 21.-22.7.15

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Pair Production e.g.

+

γ →e +e

−

when radiation 21.-22.7.15

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Annihilation +

−

e + e → 2 hf

radiation 21.-22.7.15

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The Matter Antimatter Puzzle Why does the Universe look like not this

that?

As far as we can see in universe, no large-scale antimatter. -> need CP violation! 56 21.-22.7.15 A. Geiser, Particle Physics

The Matter Antimatter Puzzle -> particles, anti-particles and photons in thermal equilibrium – colliding, annihilating, being re-created etc. Slight difference in fundamental interactions between matter and antimatter (“CP violation”) ? -> matter slightly more likely to survive Ratio of baryons (e.g. p, n) to photons today tells us about this asymmetry - it is about 1:109 21.-22.7.15

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CP symmetry

graphics: M.C. Escher

Parity (reflection)

Charge Conjugation

(black → white)

C P

Like weak interaction, symmetric under CP (at first sight!) Can there be small deviations from this symmetry? 21.-22.7.15

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CP violation in B meson decays

e

+

e

−

Second B decays (B )

First B decays t

0

Decay length ~ 1/4 mm

0 1 Bd

(or B 0d )

d b

Asymmetry ( t )

c c

d s

J/ψ

0 K

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t2 =

B0 - B0 B0 + B0

Simply count decays as function of t!

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CP violation in B meson decays Example: measurement from BaBar at SLAC (also Belle at KEK)

B and anti-B are indeed different (also found earlier for K decays: )

Val L. Fitch James W. Cronin 21.-22.7.15

(Nobel 1980)

data taking stopped. Belle/Super-Belle continuing. A. Geiser, Particle Physics

M. Kobayashi

T. Maskawa

(Nobel 2008)

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DESY contribution to the antimatter puzzle? CP violation measured so far not strong enough to explain matter-antimatter asymmetry way out: CP violation in neutrino oscillations and/or strong lepton number asymmetry in early universe. Sphaleron Standard Model predicts baryon and lepton number violation through Instanton so-called „sphaleron“ process: converts 3 leptons into 3 baryons! rare process at very high energy -> not observable so far related process: QCD „instantons“ in principle observable at HERA or LHC still searching ...

u

u

d d s

I

s c c b b

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The Mystery of Mass

t

c

u

charm

d

s

top

up

down .

strange

νe

e-neutrino

e

electron

.

νµ

bottom

µ-neutrino

µ

muon

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b

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ντ

τ-neutrino

τ

tau

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The Mass (BEH) Mechanism P. Higgs et al. (1964-66,71) Brout, Englert, Guralnik, Hagen, Kibble, …

many subvariants which is right?

Peter Higgs

François Englert (Nobel 2013)

source: viXra blog 21.-22.7.15

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Fermion Mass from Higgs field? very brilliant scientist (fermion) works with speed of light! room = vacuum -> “massless”

people = Higgs vacuum expectation value

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Fermion Mass from Higgs field? scientist becomes famous! enters room with people

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Fermion Mass from Higgs field? people cluster around him hamper his movement/working speed -> he becomes “massive”!

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How much do Neutrinos weigh? from the lightest ...

Standard Model has mν = 0 -> evidence for mν = 0 forces

this year no special neutrino lecture, sorry 21.-22.7.15

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The quest for the top quark Electroweak precision measurements at LEP/CERN sensitive to top quark mass and Higgs mass (indirect effects) ... to the heaviest

-> Mt ~ 170 GeV 21.-22.7.15

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The Tevatron (Fermilab) data taking ended in 2011 analysis still ongoing

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Top quark discovery (Fermilab 1995) Top quark actually found where expected! Tevatron at Fermilab (CDF + D0) measured mass value: (PDG12)

M top = 173.5 ± 1.0 GeV/c

2

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Precision @ LEP and Higgs insert measured top mass into precision measurements at LEP -> now sensitive to Higgs mass mH < 182 GeV at 95% CL LEP direct lower limit: mH > 114 GeV at 95% CL

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Precision @ LEP and Higgs at LHC

H->ZZ*-> 4 leptons

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Special Fundamental Physics Prize 2013 for their leadership role in the scientific endeavour by the Milner Foundation that led to the discovery of the new Higgs-like particle by the ATLAS and CMS collaborations at CERN's Large Hadron Collider.

Peter Jenni,

Tejinder Singh Virdee,

Lyn Evans,

Fabiola Gianotti,

Joe Incandela,

ATLAS

CMS

LHC

ATLAS

CMS

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Michel Della Negra

Guido Tonelli,

CMS

CMS

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Higgs production at LHC measure as many as possible to check Higgs properties 21.-22.7.15

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The LHC Project Just restarted @ 13 TeV

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The DESY CMS group Installation & Commissioning Computing Tracking, Tracker upgrade Beam Condition Monitor Forward detectors (CASTOR) Data Quality Monitoring building 1a, first floor

Physics Standard Model Forward Physics Top + Higgs Supersymmetry 21.-22.7.15

CMS remote center at DESY

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The DESY ATLAS group Trigger Computing Lumi monitor (ALFA) sLHC upgrade Physics: Standard Model Top quarks Supersymmetry Higgs 21.-22.7.15

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Supersymmetry A way to solve theoretical problems with Unification of Forces: Supersymmetry For each existing particle, introduce similar particle, with spin different by 1/2 unit

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Supersymmetry double number of particles:

not seen at LEP, HERA, Tevatron ... -> must be heavy! (still) hope to see them at LHC ! 21.-22.7.15

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Unification and Superstrings To include gravity in unification of forces, need Superstrings (Supersymmetric strings)

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Superstring interaction

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Extra Dimensions? Superstrings require more than 3+1 dimensions additional “extra” dimensions -> “curled up” - could be as large as a mm (?)

potentially measurable effects, e.g. at LHC! 21.-22.7.15

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extra dimensions -> micro black holes? extremely short-lived - no indications so far

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The case for an e+e- Linear Collider for more see lectures K. Büsser Historically, hadron (proton) and electron colliders have yielded great symbiosis: hadron colliders: discoveries at highest energies electron colliders: discoveries and precision measurements latest example: Tevatron/LEP (top), now Higgs at LHC => International Linear Collider! 25

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The ILC

Technical Design Report released (June 2013) Hosting in Japan being discussed 21.-22.7.15

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Example: Higgs Physics at the ILC Top-Yukawa coupling

Self coupling Gauge couplings e+

Ζ

Ζ e– H

e– e–

e+

Ζ

Ζ H

e+

Ζ

t

H

H

e– H

t

ν W W

e+

H ν

Yukawa couplings f f

all measurable with high precision! 21.-22.7.15

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Cosmology

increasing energy -> going further backwards in time in the universe -> getting closer to the Big Bang 21.-22.7.15

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Grand Electroweak Protons and Atoms and unification era Galaxy neutrons form Nuclei are light era era formation -4 years 300000 -10 10 s 10 300000 -35 years formed 10 s 1000 M years

Hasylab, FLASH, PETRA III, XFEL HERA/LEP

Quarks combine to make The Universe becomes 100 s protons and neutrons transparent and fills with

Galaxies Electroweak beginforce toexpansion form splits Inflation ceases, ProtonsGrand and neutrons light continues. Unification breaks. Strong combine toand form helium electroweak nuclei forces become distinguishable 21.-22.7.15

LHC/ILC

You!

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Elementary Particle Physics is exciting! We already know a lot, but many open issues

Exciting new insights expected for the coming decade! 21.-22.7.15

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