Elementary Particle Physics Research

Achim Geiser, DESY Hamburg Summer Student Lecture, 3.8.06

Scope of this lecture:

„ Introduction to particle physics for non-specialists ‰rather elementary ‰more details -> specialized lectures ‰particle physics in general thanks to B. Foster for some of the nicest slides/animations other sources: ‰some emphasis on DESY-related topics www pages of DESY and CERN

3.8.06 A. Geiser, Particle Physics 1 What is Particle Physics?

3.8.06 A. Geiser, Particle Physics 2 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 „ Modern view: particles = objects with discrete Niels quantum numbers, e.g. charge, mass, ... Bohr not necessarily located at a specific position. (Nobel 1922) (Heisenberg uncertainty principle) can also be represented by wave functions (Quantum mechanics, particle/wave duality)

Louis Werner Erwin de Broglie Heisenberg Schrödinger (Nobel 1933) (Nobel 1929) (Nobel 1932) 3.8.06 A. Geiser, Particle Physics 3 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)

3.8.06 A. Geiser, Particle Physics 4 History of basic building blocks of matter 0 − − + οο ΚΣ∆Λ+∆π − ∆− + Ω motivation: ππ∆0 p + find Κ+ Κ smallest + Super- possible number symmetry

AD

3.8.06 A. Geiser, Particle Physics 5 Which Interactions? Three

3.8.06 A. Geiser, Particle Physics 6 The Forces in Nature

at ~ 1 GeV

3.8.06 A. Geiser, Particle Physics 7 What we know today

GGrraavviittyy

g s u c t s -- r up charm top gluon r

e

e

i γ i tthhee

r

r

r

r Quarks Quarks downd s bottomb strange photon a a gghhoosstt aatt

C ν ν ν C e µ τ tthhee

e W e e-neutrino µ-neutrino τ-neutrino

c

W boson c

r r ffeeaasstt

o e µ τ Z o Leptons

F Leptons electron muon tau Z boson F II IIII IIIIII HiggsHiggs GGeenneerraattiioonnss ooff BosonBoson?BosonBoson? mmaatttteerr 3.8.06 A. Geiser, Particle Physics 8 The Power of Conservation Laws

„e.g. radioactive neutron decay: - ν not visible n p + e + e

„Pauli 1930:

Wolfgang Pauli

(Nobel 1945)

3.8.06 A. Geiser, Particle Physics 9 confirmation: neutrino detection

„e.g. reversed reaction: ν e+ n p + e extremely rare! Frederick Reines (absorption length ~ 3 light years Pb) (Nobel 1995) „first detection: 1956 (!) Reines and Cowan, neutrinos from nuclear reactor

3.8.06 A. Geiser, Particle Physics 10 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 Eugene (on the continent) Wigner „ What about basic interactions? (Nobel 1963) „ Electromagnetic and strong interactions conserve parity!

3.8.06 A. Geiser, Particle Physics 11 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 Tsung -Dao consequence: Lee neutrinos are always Chieng Shiung lefthanded ! Wu (antineutrinos righthanded) 3.8.06 A. Geiser, Particle Physics 12 The Power of Quantum Numbers

„ 1948: discovery of muon Who ordered THAT ? „ same quantum numbers as electron, except mass (Nobel 1988) I.I. Rabi (Nobel 1944) µ- ν - ν „muon decay: -> µ e e conservation of Leon M. Melvin Jack Ledermann Schwartz Steinberger „ electric charge -1 0 -1 0 „ lepton number: 1 1 1 -1 ν = ν (1955) ν ν „ „muon number“: 1 1 0 0 µ = e (1962) „ „ There is a distinct neutrino for each charged lepton 3.8.06 A. Geiser, Particle Physics 13 The Power of Precision

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

ν number of ν

ν (light) neutrino

flavours = 3 Gerardus Martinus t’Hooft Veltman (Nobel 1999)

e+e- -> Z0

3.8.06 A. Geiser, Particle Physics 14 Can we “see” particles?

Luis Walter Alvarez (Nobel 1968) we can!

bubble chamber photo

Donald Arthur Glaser (Nobel 1960) 3.8.06 A. Geiser, Particle Physics 15 A generic modern particle detector

3.8.06 A. Geiser, Particle Physics 16 Why do we need colliders?

„ early discoveries in cosmic rays, but Mont Blanc „ need controlled conditions E „ m = c 2 CERN need high energy to discover new heavy particles „ colliders = LEP/LHC microscopes (later) 3.8.06 A. Geiser, Particle Physics 17 The HERA ep Collider and Experiments

3.8.06 A. Geiser, Particle Physics 18 Particle Physics = People

3.8.06 A. Geiser, Particle Physics 19 Strong Interactions: Quarks and Colour

„ strong force in nuclear interactions = „exchange of massive pions“ between nucleons = residual Van der Waals-like interaction

Hideki Yukawa (Nobel 1949) n „ modern view: π (Quantum Chromo-Dynamics, QCD) exchange of massless gluons p between quark constituents

„similar“ to electromagnetism (Quantum Electro-Dynamics, QED) 3.8.06 A. Geiser, Particle Physics 20 The Quark Model (1964)

arrange quarks (known at that time) into flavour-triplett

=> SU(3)flavour symmetry Q=-1/3 Q=2/3

d u treat all known hadrons S=0 (protons, neutrons, pions, ...) as objects composed of two or three such quarks (antiquarks)

S=-1 s 3.8.06 A. Geiser, Particle Physics 21 The Quark Model

baryons = qqq mesons = qq

3.8.06 A. Geiser, Particle Physics 22 Colour

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

q g g q q gggg qq g g q

„ 3 coulours -> SU(3)colour qqq = qq = white!

3.8.06 A. Geiser, Particle Physics 23 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

3.8.06Sin-Itoro Julian Richard P. A. Geiser, Particle Physics 24 Tomonaga Schwinger Feynman Anti-Screening of Coulour Charge!

„ quark-antiquark pairs -> screening „ gluons carry colour -> gg pairs -> anti-screening!

asymptotic

confinement freedom

1/r2~E2,

3.8.06 A. Geiser, Particle Physics 25 3.8.06 A. Geiser, Particle Physics 26 Comparison QED / QCD

electromagnetism strong interactions

QED QCD 1 kind of charge (q) 3 kinds of charge (r,g,b) force mediated by photons force mediated by gluons photons are neutral gluons are charged (eg. rg, bb, gb) α α is nearly constant s strongly depends on distance

confinement limit:

„ The underlying theories are formally almost identical! 3.8.06 A. Geiser, Particle Physics 27 The effective potential for qq interactions

confinement

asymptotic freedom

3.8.06 A. Geiser, Particle Physics 28 Burton Heavy Quark Spectroscopy Richter

Charmonium = bound system (Nobel 1976) + - of cc quark pair Positronium = bound e e system Samuel C.C. Ting

1974

3.8.06 A. Geiser, Particle Physics 29 How to detect Quarks and Gluons?

Jets!

hadrons Example of the hadron production in e+e- q e+ e- annihilation in the JADE q detector at the PETRA e+e- collider at DESY, hadrons Germany. Georges „ cms energy 30 GeV. Charpak „ Lines of crosses - reconstructed trajectories in drift chambers (gas ionisation detectors). (Nobel 1992) „ Photons - dotted lines - detected by lead-glass Cerenkov counters. „ Two opposite jets.

3.8.06 A. Geiser, Particle Physics 30 Discovery of the Gluon (1979)

PETRA at DESY: look for

Björn Wiik Paul Söding

TASSO event picture Günter Wolf Sau Lan Wu

3.8.06 A. Geiser, Particle Physics 31 Jets in ep interactions (HERA)

3.8.06 A. Geiser, Particle Physics 32 α Runnning coupling s from jet production

HERA

(E,Q ~ 1/r)

3.8.06 A. Geiser, Particle Physics 33 α Running coupling s from other measurements

(HERA) (LEP, PETRA)

HERA = currently best place to study QCD! 3.8.06 A. Geiser, Particle Physics 34 How to determine the „size“ of a particle? microscope: resolution ~ 10-18 m = 1/1000 of size of a proton low resolution -> small instrument high resolution -> large instrument

3.8.06 A. Geiser, Particle Physics 35 How to resolve the structure of an object?

scattering image e.g. X-rays probe (Hasylab) E~ keV accelerator

-> structure of a biomolecule

3.8.06 A. Geiser, Particle Physics 36 Resolvethestructureof theproton

„ E ~ MeV resolve whole proton

„ static quark model, Jerome I. Henry W. Richard E. Friedmann Kendall Taylor valence quarks (Nobel 1990) (m ~ 350 MeV)

„ E ~ mp ~ 1 GeV resolve valence quarks and their motion

„ E >> 1 GeV resolve quark and gluon “sea”

3.8.06 A. Geiser, Particle Physics 37 Inside the proton

Heisenberg’s UP Low Q2 (large λ) allows gluons, and qq Medium Q2 (medium λ) pairs to be produced for a very short time. Large Q2 (short λ)

At higher and higher resolutions, the quarks emit gluons, which also emit gluons, which emit quarks, which……. 2 -18 3.8.06At highest A. Geiser, Q , Particleλ ~ 1/Q Physics ~ 10 m 38 Deep Inelastic ep Scattering at HERA

q p p remnant e e

3.8.06 A. Geiser, Particle Physics 39 Deep Inelastic Scattering (DIS)

3.8.06 A. Geiser, Particle Physics 40 The Proton Structure

structure functions quark and gluon densities

3.8.06 A. Geiser, Particle Physics 41 Kinematic regions: HERA vs. LHC

„ proton structure measured directly for large part of LHC phase space

„ QCD evolution LHC Tevatron successful -> safely extrapolate to high Q2 or low x

HERA fixed target

3.8.06 A. Geiser, Particle Physics 42 Example: Higgs cross section at LHC

3.8.06 A. Geiser, Particle Physics 43 Weak Interactions

The Theory of GLASHOW, SALAM and WEINBERG ~ 1959-1968

(Nobel 1979)

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

3.8.06 A. Geiser, Particle Physics 44 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! Z0 -> e+e- UA1 -> first W and Z produced 1982/83 (Nobel 1984)

Simon Carlo van der Rubbia Meer

3.8.06 A. Geiser, Particle Physics 45 Three Boson Coupling @ LEP

W/Z bosons carry electroweak charge (like gluons) -> measure rate of W pair production at LEP II

No ZWW vertex only ν exchange

3.8.06 A. Geiser, Particle Physics 46 Electroweak Physics at HERA

Neutral Current (NC) interactions

e

Charged Current (CC) interactions

e

3.8.06 A. Geiser, Particle Physics 47 Weak interactions are "left-handed"

„ lefthanded electrons interact (CC) Polarized CC Cross Sections - e- e

„ righthanded electrons do not! e-

+ „ cross section linearly proportional e σ to polarization

± ± left polarization e p = ± ⋅σ e p right polCC (1 Pe) unpolCC

3.8.06 A. Geiser, Particle Physics 48 Electroweak Unification

NC

CC

2 MW 3.8.06 A. Geiser, Particle Physics 49 The Quest for Unification of Forces

Electroweak Unification

Grand Unified Theories ?

Superstring Theories ?

Maxwell’s equations

strong Big Bang electric

magnetic

weak gravity

3.8.06 A. Geiser, Particle Physics 50 α s from HERA and Grand Unification

HERA prel.: ± ± αS(MZ) = 0.1186 0.0011(exp) 0.0050(th)

± world average: αS(MZ) = 0.1182 0.0027 NNLO, MSbar Bethke , hep-ex/0407021

3.8.06 A. Geiser, Particle Physics 51 Antimatter relativistic Schrödinger equation P.A.M. (Dirac equation) Dirac two solutions: (Nobel 1933) one with positive, one with negative energy Dirac: interpret negative solution as 1932 antielectrons (positrons) found in conversion of energy into matter 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 3.8.06 A. Geiser, Particle Physics 52 Pair Production

+ − e.g. γ → e + e

3.8.06 A. Geiser, Particle Physics 53 Annihilation

+ − e + e → 2hf

3.8.06 A. Geiser, Particle Physics 54 The Matter Antimatter Puzzle

Why does the Universe look like this not that?

As far as we can see in universe, no large-scale antimatter.

3.8.06-> need A. Geiser, CP Particle violation! Physics 55 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

3.8.06 A. Geiser, Particle Physics 56 CP symmetry

Parity (reflection)

Charge (black → C Conjugation white)

P

Like weak interaction, symmetric under CP (at first sight!) Note interesting new physics ! 3.8.06 A. Geiser, Particle Physics 57 CP violation in B decays e+ e− First B Second B decays decays (B0) Decay length ~ 1/4 mm t1 t2 0 0 d b B d (orB d ) B0 - B0 Asymmetry()t = B0 + B0 c c ds Simply count decays as function of t! ψ 0 3.8.06J/ K s A. Geiser, Particle Physics 58 CP violation in B decays

Current state of the art from BaBar at SLAC (also Belle at KEK)

B and anti-B are indeed different

(also found earlier for K decays: )

Val Logsdon Fitch

James Watson Cronin (Nobel 1980) 3.8.06 A. Geiser, Particle Physics 59 contribution to the antimatter puzzle from HERA?

„ CP violation measured so far not strong enough to explain matter-antimatter asymmetry „ way out: CP violation in neutrino oscillations (see later) and/or strong lepton number asymmetry in early universe. „ Standard Model predicts baryon and lepton number violation through so-called „sphaleron“ tunneling process: converts 3 leptons into 3 baryons! „ rare process at very high energy -> not observable so far

u ud „ related process: QCD „instantons“ d s „ in principle observable at HERA! I s c „ still searching ... c b b 3.8.06 A. Geiser, Particle Physics 60 The Mystery of Mass

topt charmc upu d s down strange

. ν e e-neutrino ν b . µ bottom e µ-neutrino electron . ν µ τ τ-neutrino muon τ 3.8.06 A. Geiser, Particle Physics tau 61 Fermion Mass from Higgs field?

very brilliant scientist (fermion) works with speed of light! room = vacuum -> “massless” people = Higgs vacuum expectation value

3.8.06 A. Geiser, Particle Physics 62 Fermion Mass from Higgs field?

scientist becomes famous! enters room with people

3.8.06 A. Geiser, Particle Physics 63 Fermion Mass from Higgs field?

people cluster around him hamper his movement/working speed -> he becomes “massive”!

3.8.06 A. Geiser, Particle Physics 64 How much do Neutrinos weigh?

Standard Model has mν = 0

-> evidence for mν = 0 forces

nothing ? or almost nothing?

3.8.06 A. Geiser, Particle Physics 65 Neutrinos in Cosmology artist‘s view of the Big Bang

~400 ν’s / cm3 ! dark matter??

3.8.06 A. Geiser, Particle Physics 66 Neutrinos from the Sun

Raymond Davis Jr

(Nobel 2002) Masatoshi Koshiba

The sun in neutrino “light” (Super-Kamiokande)

~7 x 1010 ν’s / cm2 s measure ~ half predicted!? 3.8.06 A. Geiser, Particle Physics 67 Neutrinos from Cosmic Rays

(atmospheric neutrinos) Super Kamio- kande ν rate from below only ~half of above ??

3.8.06 A. Geiser, Particle Physics 68 Solution: Neutrino Oscillations simplified case: two neutrino flavours, simple quantum mechanics ⎛ν ⎞ ⎛ cosθ sinθ⎞ ⎛ν ⎞ e = 1 ⎜ν ⎟ ⎜− θ θ⎟ ⎜ν ⎟ ⎝ µ ⎠ ⎝ sin cos ⎠ ⎝ 2 ⎠ flavour mass eigenstates eigenstates time evolution: ν = θ ⋅ − ν + θ ⋅ − ν e (t) cos exp( iE1t) 1 sin exp( iE2t) 2 average ~ 50% if m1 = m2 -> E1 = E2 -> ⎛ ⋅ ⋅∆ 2 2 ⎞ 2 2 1.27 L(m) m (eV ) Pν →ν = sin 2θ ⋅sin e µ ⎜ ⎝ Eν (MeV) ⎠

3.8.06 A. Geiser, Particle Physics 69 Solution for “Solar” Neutrinos

SNO, Solarsin Neutrino2θ is determined by SK/SNO Observatory

KamLAND KamLand, ν ν SK/SNO Reactor Neutrino e → x Experiment

3.8.06 A. Geiser, Particle Physics 70 Solution for “Atmospheric” Neutrinos

ν ν µ → x also MINOS/Fermilab

3.8.06 A. Geiser, Particle Physics 71 Seven Questions

„ Dirac or Majorana? „ Absolute mass scale? θ „ How small is 13? „ CP Violation? „ Mass hierarchy? „ Verify Oscillation? „ LSND? Sterile neutrino(s)? CPT violation?

3.8.06 A. Geiser, Particle Physics 72 Conclusions for Neutrinos

Neutrino flavour transitions established ->

->

How? -> see lecture C. Hagner

Important consequences e.g. for CP violation

3.8.06 A. Geiser, Particle Physics 73 The quest for the top quark

Electroweak precision measurements at LEP/CERN sensitive to top quark mass and Higgs mass (indirect effects)

-> Mt ~ 170 GeV 3.8.06 A. Geiser, Particle Physics 74 The Tevatron (Fermilab)

3.8.06 A. Geiser, Particle Physics 75 Top quark discovery (Fermilab 1995)

Top quark actually found where expected!

Tevatron at Fermilab (CDF + D0)

most recent mass value: (ICHEP06) = ± 2 Mtop 171.4 2,1 GeV/c

3.8.06 A. Geiser, Particle Physics 76 Precision @ LEP and Higgs

insert measured top mass into precision measurements at LEP -> now sensitive to Higgs mass (last undetected particle of Standard Model!)

mH < 219 GeV at 95% CL

current direct lower limit:

mH > 114 GeV at 95% CL

3.8.06 A. Geiser, Particle Physics 77 The LHC Project

scheduled startup: 2007!

3.8.06 A. Geiser, Particle Physics 78 The Quest for the Higgs at LHC

Higgs production:

Higgs decay: depending on mass, Higgs might be found within first year of LEP LHC physics operation!

3.8.06 A. Geiser, Particle Physics 79 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

3.8.06 A. Geiser, Particle Physics 80 Supersymmetry

„double number of particles:

„ not seen at LEP, HERA, Tevatron ... -> must be heavy! „ some hope to see them at LHC!

3.8.06 A. Geiser, Particle Physics 81 The case for an e+e- Linear Collider

see also lecture E. Elsen this morning „ 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)

3.8.06 A. Geiser, Particle Physics 82 The case for an e+e- Linear Collider

„ to complement LHC, need >= 500 GeV CMS energy „ circular colliders have reached end of technical possibilities (bremsstrahlung energy loss) „ => go for Linear Collider! „ TESLA project at DESY: (TDR 2001) ... too early

„ current project: International Linear Collider (ILC) based on TESLA technology

3.8.06 A. Geiser, Particle Physics 83 Why/what is ILC?

„ If LHC finds Higgs ILC will study its detailed properties „ If LHC does not find Higgs -> Problem with Standard Model, only ILC can study why (precision measurements) „ If LHC finds SUperSYmmetery ILC will study SUSY particles, and potentially find/distentangle many more „ If LHC does not find SUperSYmmetry ILC might provide indirect evidence (precision measurements) „ + potential unexpected discoveries ... Compositeness, Large Extra Dimensions, indirect effects from Superstrings, ...

3.8.06 A. Geiser, Particle Physics 84 Unification and Superstrings

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

3.8.06 A. Geiser, Particle Physics 85 Superstring interaction

3.8.06 A. Geiser, Particle Physics 86 Extra Dimensions?

„ Superstrings require more than 3+1 dimensions „ additional “extra” dimensions -> “curled up” - could be as large as a mm!

potentially measurable effects, even at HERA!

3.8.06 A. Geiser, Particle Physics 87 Large extra dimensions: virtual graviton exchange

Virtual graviton exchange in t-channel interferes with Deep Inelastic Scattering (DIS) Q2 = (k-k’)2 ,KK

Exchange of Kaluza-Klein tower (KK) affects Q2 distribution at high Q2

Compare dσ/dQ2 to what is K e K expected from SM e

p jet

3.8.06 A. Geiser, Particle Physics 88 Large extra dimensions: virtual graviton exchange

1/2 -1 Zeus s (GeV) Lint(pb ) e+ p 301/319 112 e- p 319 16

dσ/dQ2 used in binned likelihood => 95% CL limits on

MS (TeV)

λ = - 1 : MS > 0.79 TeV λ = + 1 : MS > 0.78 TeV

3.8.06 A. Geiser, Particle Physics 89 General search for deviations from SM at high pT

H1

3.8.06 A. Geiser, Particle Physics 90 Cosmology

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

3.8.06 A. Geiser, Particle Physics 91 ElectroweakGrand AtomsProtonseraGalaxyunification and and Hasylab, lightNucleineutronsera era are form XFEL formation3000001010-10-4 syearss formed300000-35 years formed100010 M yearss HERA/LEP QuarksThe Universe combine tobecomes make protons and100 neutrons s InflationGalaxiestransparentElectroweak ceases, begin and force to expansion fills form splits with LHC/ILC continues.lightProtons Grand and neutrons Unification breaks.combine Strong to andform helium electroweaknuclei forces become distinguishable You!

3.8.06 A. Geiser, Particle Physics 92 Elementary Particle Physics is exciting!

„ We already know a lot, but many open issues

I am b sti ut n ll co ow nfu I a sed at m c , a m onf uch use hig d le her vel!

„ Exciting new insights expected for the coming decade!

3.8.06 A. Geiser, Particle Physics 93