8.882 LHC Physics Experimental Methods and Measurements Heavy Ion Physics Overview [Lecture 4, February 17, 2009] with a 'thank you' to Bolek and Gunther for material and explanations - PowerPoint PPT Presentation


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8.882 LHC Physics Experimental Methods and Measurements Heavy Ion Physics Overview [Lecture 4, February 17, 2009] with a 'thank you' to Bolek and Gunther for material and explanations


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Title: 8.882 LHC Physics Experimental Methods and Measurements Heavy Ion Physics Overview [Lecture 4, February 17, 2009] with a 'thank you' to Bolek and Gunther for material and explanations

8.882 LHC PhysicsExperimental Methods and
MeasurementsHeavy Ion Physics OverviewLecture
4, February 17, 2009with a 'thank you' to
Bolek and Gunther for material and explanations
Organizational Issues
  • Course and recitation
  • new students Michael and Erik
  • please make sure to catch up on recitation
  • any questions
  • Matthew is expert in setting up windows machines
    if needed
  • Recitation
  • Friday at 1200 noon in 24-414

Lecture Outline
  • Heavy Ion Physics Overview
  • general introduction
  • the strong force and QCD
  • state diagram
  • real life heavy ion physics
  • variables and their implementation
  • measurements
  • experimental status

Particle Physics
  • Searching for the smallest constituents
    elementary particle
  • un-dividable unit(s)?
  • the atomos in the true sense of the word
  • water droplet ? water molecule ? hydrogen atom ?
    proton ? quarks
  • Search for the fundamental forces or interactions

Current Elementary Particles
  • Matter particles
  • fermions (half integer spin)?
  • Force carriers
  • bosons (integer spin)?
  • Fermions organized
  • generations, families
  • higher generations unstable decay to lowest
  • 1st generation makes up almost all we see

Particle Physics and the Universe
  • Heavy ion physics after elementary particle
    formation but before nucleon formation (1 GeV)?

The Strong Force
  • Heavy Ion Physics is all about the strong force
  • Examples of strong force
  • binding of nucleons into the atom core protons
    repel each other (electromagnetic charge),
    neutrons need to be added
  • strong force in core let's proton decay (weak
  • binding force of the proton itself (three quarks
  • binding force of the pion (two quarks inside)?
  • in fact binds all hadrons

Quantum Chromo Dynamics (QCD)?
  • What is QCD? Theory of the strong force!
  • fermions quarks fractional electric charge u
    2/3, d -1/3
  • force carrier is the gluon (8)?
  • charge (QED) ? color charge (QCD) red-green-blue
  • asymptotic freedom
  • quarks free to move when they are close
  • coupling large no perturbative solution

Nobel Price 2004
  • The Nobel Prize in Physics 2004
  • Gross, Politzer, Wilczek for the discovery of
    asymptotic freedom in the theory of the strong

H. David Politzer
Frank Wilczek
David J. Gross
the younger Wilczek
  • Interesting to read
  • http//nobelprize.org/nobel_prizes/physics/laureat
  • http//nobelprize.org/nobel_prizes/physics/laureat
  • http//nobelprize.org/nobel_prizes/physics/laureat

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Nobel Price 1990
  • The Nobel Prize in Physics 1990
  • Friedman, Kendall, Taylor for their pioneering
    investigations concerning deep inelastic
    scattering of electrons on protons and bound
    neutrons, which have been of essential importance
    for the development of the quark model in
    particle physics

Henry W. Kendall
Richard E. Taylor
Jerome I. Friedman
  • Interesting to read
  • http//nobelprize.org/nobel_prizes/physics/laureat
  • http//nobelprize.org/nobel_prizes/physics/laureat
  • http//nobelprize.org/nobel_prizes/physics/laureat

Strong Force
  • Paradox
  • weakly bound proton constituents can be seen in
    high-energy scattering, but cannot be liberated
    even in most violent collisions
  • Confinement
  • direct search for quarks were performed without
  • why can they not be found by themselves?
  • answer confinement - objects are always
  • mesons quark-antiquark no color, ex. pion
  • baryons green-blue-red white, ex. proton
    uud, neutronudd

The Color String Flux Tube
  • The Color String
  • overall colorless
  • stores energy when quark-antiquark are pulled
  • breaks up when enough energy stored
    fragmentation ? quarks look like jets
  • baryons are formed when three quarks are close in
    phase space

Observation of the Gluon
  • Gluon confined as the quarks
  • indirect observation only
  • gluon looks like a quark jet
  • three jet events are signature
  • first shown by TASSO experiment at PETRA
  • detailed flow of fragmentation very interesting
  • independent versus string fragmentation
  • PETRA built to discover top

Heavy Ion Physics
  • Goals
  • find regime to set the quarks and gluons free
  • we know, they are asymptotically free (QCD)?
  • matter has to be extremely dense that protons
    break up
  • recreates phase of the universe close to big bang
  • quark-gluon-plasma (quark gluon gas, weakly
  • Implementation
  • accelerates many neutrons and protons to very
    large energies and collide them
  • best done by using heavy ions (heavy large A)?
  • ions to accelerate, electrons completely removed

Key Word State Transition
  • From Thermodynamic
  • phase or state transition
  • sudden change of an observable with respect to a
    state parameter
  • first order discontinuous
  • second order discontinuous first derivative
  • cross over smooth transition
  • Random example
  • Argon ice
  • gas-fluid-liquid

State Transition Quark-Gluon Plasma
  • What would one expect to happen?
  • phase transition of some observable
  • hadron regime ? free gluon-quark regime
  • observable should show sudden change of behavior
  • What are observables in heavy ion collisions?
  • normalized number of particles produced
  • ratio of kaons to pions
  • normalized number of heavy onia
  • smart ideas might make you a hero in HI physics!

Quark Gluon Plasma or what?
  • Expected to find Quark-Gluon Plasma
  • gas in which quarks and gluons are free
  • naïve starting point put quarks/gluons close
    together but give them lots of energy (10-20
    times than in proton)?
  • expect asymptotic freedom to do the rest
  • subtle balance between energy and force required
  • problem calculations are close to impossible
  • Experiments find
  • no quark-gluon plasma
  • instead quark-gluon conglomerate behaves like a

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A Typical Heavy Ion Collision
  • Sequence of events
  • Consider
  • luminosity low one collision per event
  • need to extrapolate back from freeze out
  • detailed collision parameters are crucial

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Determine Number of Participants
  • Fixed target experiments
  • measure energy of spectators
  • nParticipants (1 Ecal/Ebeam) A
  • Non trivial problem for collider (boot strap)?
  • use Monte Carlo to determine impact parameter
  • measure tracks in forward region, N (different
  • Determine b impact parameter when fMC fData
  • assume N related with b by monotonous function
  • systematics has to be evaluated?

Impact Parameter from N Particles
Variables of Interest
  • Number of particles seen from collisions
  • very straight forward quantity to measure
  • natural comparison is pp collision
  • neutron or proton should have very similar
    behavior concerning the strong force
  • independent collisions could be directly compared
  • normalize to number of participants (participant
    can have several collisions
  • phase transition should appear by adding all
    experiments together
  • Our first measurement
  • use CDF data at 2 TeV proton-antiproton collisions

Status after RHIC Published
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Jet Quenching, Confirmed
  • Analysis outline
  • define main direction by leading trigger particle
  • count number of particles in azimuthal angle
  • expect to find opposite side jet as expected from
  • Analysis result
  • find particles around leading particle (jet)
  • opposite side activity significantly reduced
    compared with corresponding pp data

  • Heavy Ion physics
  • create matter state close to the beginning of the
    universe this is about strong interaction (QCD)?
  • no sharp state transition observed
  • number of particle produced on a smooth curve
  • quark-gluon plasma not so gas like but rather
    like liquid
  • jet quenching
  • elliptic flow (not discussed here)?
  • a surprise but not inconceivable theory could
    not make precise predictions
  • exciting experiences expected from the LHC

Next Lecture
  • Charge multiplicity measurements
  • introduction to observables and experimental
  • the CDF data and how they are organized
  • trigger conditions and information
  • contents of the ntuple
  • prototype analysis
  • main components for full analysis
  • pile up events
  • secondary interactions

Particle Physics
Explain in 60 Seconds
  • Quarks are fundamental building blocks of matter.
    They are most commonly found inside protons and
    neutrons, the particles that make up the core of
    each atom in the universe. Based on current
    experimental evidence, quarks seem to be truly
    fundamental particles they cannot be further

Protons and neutrons mainly contain two types of
quarks. These are called up and down quarks. For
reasons still unknown, nature also designed two
copies each of the up and down quarks, identical
except for having larger masses. The heavier
copies of the up quark are called charm and top
quarks the copies of the down quark are named
strange and bottom quarks. Converting energy into
mass, accelerators produce these heavier,
short-lived quarks through particle
collisions. Quark masses span an enormous range.
The heaviest quark is the top quark, which is
about 100,000 times more massive than the two
lightest types, up and down. The explanation for
this hierarchy is a deep mystery, but the top
quarks huge mass could turn out to be a virtue.
Probing the detailed properties of the top may
shed light on the origins of mass itself in the
universe. Jay Hubisz, Fermilab
The Universe
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