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CMS. SPS. LHC/LEP. ATLAS. THE PHYSICS OF LHC. Manfred Jeitler. LHCb. ALICE. БАК (Большой Адронный Коллайдер). THE PHYSICS CASE. aims of accelerators. energy frontier find new particles learn about basics of interactions

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Lhc lep

CMS

SPS

LHC/LEP

ATLAS

THE PHYSICS OF LHC

Manfred Jeitler

LHCb

ALICE


Lhc lep

БАК

(Большой Адронный

Коллайдер)


The physics case

THE PHYSICS CASE


Aims of accelerators

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


Lhc lep

VomUrknallbiszum ...?


Lhc lep

t

ne

nm

nt

interactions

u

c

strong

g

strong

g

electromagnetic

u

u

d

d

u

d

d

s

b

m

t

e

weak

W, Z

?

gravitation

weak

force carriers = bosons

(spin 1)

the Standard Model

fermions (spin ½)

leptons

quarks

charge

0

+2/3

-1

-1/3

+1

0

proton

neutron

baryons


Completing the standard model the w and z 0 bosons 1983

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

CERN SPS


Completing the standard model the top quark 1995

completing the Standard Model:the top quark (1995)

Tevatron (Fermilab, Chicago)


Lhc lep

t

ne

nm

nt

interactions

u

c

strong

g

strong

g

electromagnetic

d

s

b

m

t

e

weak

W, Z

?

gravitation

weak

the Standard Model

fermions (spin ½)

leptons

quarks

charge

0

+2/3

-1

-1/3

Astro

Accelerator


Lhc lep

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.


Lhc lep

Peter Higgs in front of LHC-experiment ATLAS


Lhc lep

the Higgs boson

  • 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

hot universe

(soon after big bang)

energy

particles are massless

cold universe

(condensates in an asymmetric state with Higgs field)

particles acquire mass

0

Higgs field

v


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

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


Lhc lep

Supersymmetry

SUSY

bosons

fermions

for each known elementary particle there should exist a supersymmetric partner

SUSY particles.

green: known particles of the Standard Model

red: hypothetical new particles


Lhc lep

dark matter:MACHOS vs WIMPS

  • 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


Experimental observation of susy particles

experimental observation of SUSY particles ?

SUSY particles may show very clear signatures due to cascade decays

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.


Lhc lep

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

ACCELERATORS


Lhc lep

Cockroft-Walton accelerator at CERN


Lhc lep

inside of an Alvarez-type

accelerating structure


Lhc lep

Synchrotron

elements of a

synchrotron

quadrupole magnet: focussing

dipole magnet: to keep particles on track

high-frequency accelerating cavity


Lhc lep

SPS Tunnel

Super-Proton-Synchrotron (Geneva)


Lhc lep

Professor Baikalix

Professor Cernix

Summer student

in Bolshie Koty

Astroparticles with

1019 eV !!

Collisions at

7 TeV !!


Lhc lep

quadrupole

dipole

resonator

reaction products

interaction zone

layout of a circularcollider


Lhc lep

first electron-electron collider: Novosibirsk / Russia

VEP-1

130+130 MeV


Superconducting rf cavity from lep

superconducting RF cavity from LEP


Electrons vs protons

+30 MinBias

electronsvs.protons


Elementary particle or not

elementary particle or not?

  • 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


Synchrotron radiation

synchrotron radiation

  • scales with 4th power of Lorentz factor

  • energy loss per turn:

  • or


Lhc lep

velocity


Synchrotron radiation1

synchrotron radiation

  • 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


Collisions at the tev scale

Collisions at the TeV scale


Example simulated higgs event

Example: simulated Higgs event

LHC

ILC

e– e+Z H

Ze– e+, H b b …


What do you spend your money on electricity bill

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

  • 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”


Discovery vs precision machine

“discovery” vs. “precision” machine

  • 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


Question homework

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 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

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?


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