Manfred Jeitler The Physics of LHC Baikal Physics School 2011 1 LHC/LEP SPS CMS ATLAS ALICE LHCb THE...

Manfred Jeitler The Physics of LHC Baikal Physics School 2011 1

LHC/LEP SPS

CMS

ATLAS

ALICE

LHCb

THE PHYSICS OF LHCM

anfr

ed J

eitle

r


БАК (Большой Адронный Коллайдер)


THE PHYSICS CASE


aims of accelerators

energy frontier– find new particles

– learn about basics of interactions» “unification” at higher energies: electroweak interactions, grand unification

– cosmology: what the universe looked like soon after the Big Bang

intensity frontier – high-precision experiments


Vom Urknall bis zum ...?


fermions (spin ½)

charge

0

-1

+2/3

-1/3

d

uu

du

d

leptons quarks

the Standard Model

+1 0 proton neutron

baryons

interactions

strong

weak

gravitation?

weakW, Z

electromagnetic

strongg

force carriers = bosons (spin 1)

e

e

u c t

d s b


completing the Standard Model:the W± and Z0 bosons (1983)

CERN SPS


completing the Standard Model:the top quark (1995)

Tevatron (Fermilab, Chicago)


fermions (spin ½)

charge

0

-1

+2/3

-1/3

leptons quarks

the Standard Model

interactions

strong

weak

gravitation?

weakW, Z

electromagnetic

strongg

e

e

u c t

d s b

Astro

Accelerator


The Higgs boson

For the Standard Model to be consistent, there has to exist one more particle: the Higgs boson. It has not been found yet. However, many other high-precision measurement have confirmed the Standard Model in an impressive way.


Peter Higgs in front of LHC-experiment ATLAS


• the Standard Model works only with particles which are originally massless!• mass is created through interaction with a (hypothetical) Higgs field• due to spontaneous symmetry breaking this field is present everywhere in the universe• “oscillations” in the Higgs field manifest themselves as Higgs particles, which should be observed at LHC / CERN over the next few years

spontaneous symmetry breaking

energy

Higgs field

hot universe(soon after big bang)

cold universe(condensates in an asymmetric state with Higgs field)0

v

particles are massless

particles acquire mass

the Higgs boson


The Higgs boson

cannot be lighter than 114.4 GeV/c2

– excluded by direct searches (LEP, “Large Electron-Positron collider, CERN)

– some people thought they caught a glimpse of it at LEP (but then LEP was turned off)

should not be too heavy

– else problems arise with the physics it’s supposed to explain

maybe “just around the corner” ?

– not so good for LHC (“Large Hadron Collider”, CERN): hard to disentangle from background

– have to study lots of possible decay channels !

– Fermilab (“Tevatron” collider, Chicago) has been trying hard to find it


Supersymmetry (“SUSY”) another 2 open problems in

Standard Model: “running coupling

constants” of electromagnetic, weak and strong interactions meet almost but not completely at the same point

to avoid quadratic divergences in Higgs mass, “fine-tuning” is needed

both problems can be solved by introducing a symmetry between bosons and fermions


bosons

SUSY

SUSY particles. green: known particles of the Standard Model red: hypothetical new particles

for each known elementary particle there should exist a supersymmetric partner

fermions

Supersymmetry


Atome (Bekannte Materie)

3% Dunkle Materie23%

Dunkle Energie74%

massive astrophysical cosmic halo objects?weakly interacting massive particles?

questions of cosmology to particle physics:Why is there more matter than anti-matter in the universe?

What is the universe made of? What is dark matter?What is dark energy?

answers to these questions concerning the largest scales might come from the physics of the smallest scales - elementary particle physics

dark matter: MACHOS vs WIMPS


experimental observation of SUSY particles ?

Looking for these new supersymmetric particles was/is one of the most important tasks of the major experiments at the Tevatron in Chicago, USA, at the LHC at CERN (Geneva, Switzerland) and at the planned e+ e- linear collider.

SUSY particles may show very clear signatures due

to cascade decays


important questions of today’s particle physics(ongoing experiments)

• Where do particles get their mass from? (by interaction with the Higgs particle?)

• Why are these masses so different?

• Is there an overall (hidden) symmetry such as supersymmetry (SUSY) “mirror world” of all known particles?.

• What is the nature of “dark matter” and “dark energy” in the universe?

• Why is there more matter than anti-matter?

• Why have neutrinos such small mass?

• Is there a Grand Unification which combines all interactions, including gravitation?

• Are there extra dimensions, D > 4 ? ( string theory, …)


ACCELERATORS

Manfred Jeitler The Physics of LHC Baikal Physics School 2011 21 21

Cockroft-Walton accelerator at CERN


inside of an Alvarez-typeaccelerating structure


Synchrotron

elements of a synchrotron

quadrupole magnet: focussing

dipole magnet: to keep particles on track

high-frequency accelerating cavity


SPS Tunnel Super-Proton-Synchrotron (Geneva)


Professor Baikalix Professor Cernix

Astroparticles with

1019 eV !!

Collisions at7 TeV !!

Summer student in Bolshie Koty


quadrupole

dipoleresonator

reaction products

interaction zone

layout of a circular collider


first electron-electron collider: Novosibirsk / Russia

VEP-1 130+130 MeV


superconducting RF cavity from LEP


electrons

vs.

protons


electrons (or other leptons): elementary– no substructure

– few tracks

– sharp energy

protons (hadrons): compounds made up of quarks– what collides is one quark or gluon with another quark or gluon

– lots of other “spectators”» mess up the picture

– never know collision energy of interacting constituents» only maximum

elementary particle or not?


scales with 4th power of Lorentz factor

energy loss per turn:

or

synchrotron radiation


velocity


to lose less energy you may– make particles heavier (4th power!)

– make accelerator bigger (only linear)

electron synchrotron with same losses as LHC :– LHC circumference: 27 km

27 * 20004 ~ 4 * 1014 km ~ 40 lightyears

synchrotron radiation


Collisions at the TeV scale


LHC ILCe– e+ Z H

Z e– e+, H b b …

Example: simulated Higgs event

–


electron colliders: accelerating RF-cavities to make up for synchrotron losses

proton colliders: dipole magnets to keep protons on a circular track– conventional (“warm”) magnets: ohmic losses

– superconducting magnets: cryogenics » LHC cryogenics: ~30 MW out of total of 180 MW for all of CERN

– “there is no such thing as a free lunch”

what do you spend your money on(electricity bill)?


proton colliders are “discovery” machines– proton-antiproton or proton-proton

– SPS: W, Z bosons» Super Proton Synchrotron, CERN

– Tevatron: top quark» Fermilab, Chicago

– LHC, CERN: ???» Large Hadron Collider

electron-positron colliders allow for precision measurements– LEP: precision measurments of Z mass

» Large Electron-Positron Collider, CERN

“discovery” vs. “precision” machine


question (homework)

a text in a Cern exhibition states: “the force of the LHC beam is comparable to that of a herd of running elephants”

is this correct?

help: what could be meant by “force”?

– momentum?

– kinetic energy?

remember the energy and number of particles in LHC– 3.5 TeV, 1011 protons per bunch, ~3000 bunches

how heavy and fast is an elephant?– which kind? Indian / African / Siberian?


another question (more homework)

another text says: “the energy of a particle in LHC is the same as that of a flying mosquito”

is this correct? is there a contradiction to the statement about elephants?

help: how heavy and fast is a mosquito?

– Siberian mosquito compared to Indian elephant


yet another question (still more homework)

the frequency of the LHC clock at “flat top” (3.5 TeV) is roughly 40 MHz

does the clock frequency at injection (450 GeV) have to be different?– why?

if yes, what is the change of clock frequency during the “ramp” ?– acceleration period, when particle energy and magnetic field rise

could this be a problem?

Manfred Jeitler The Physics of LHC Baikal Physics School 2011 1 LHC/LEP SPS CMS ATLAS ALICE LHCb THE...

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