Hunting for Free Quarks

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Hunting for Free Quarks

• Helen Caines
• Relativistic Heavy Ion Group
• WNSL - West

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The RHI Physics Group
The Actors Faculty Helen Caines
John Harris Thomas
Ullrich1 Research Scientists Jaroslav
Bielcik2 Jana Bielcikova
Matthew Lamont Nikolai Smirnov
Richard Witt3
Grad. Students Stephen Baumgardt (1) Betty
Bezverkhny (5) Oana Catu (3) Jonathan Gans
(Ph.D 04) Michael Miller (Ph,D
04) Christine Nattrasse (2) Sevil Salur (5)
1 Adjunct, Scientist at BNL 2 Joint
appointment with BNL 3 Visiting, Scientist at
University of Bern, Switzerland
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Some Terminology
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More About Quarks
Ordinary matter made of up and down quarks

• Quarks interact by exchanging gluons
• Nucleons are held together by gluons
• Free quarks have never been seen - distinctive
  non-integer charge

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Why We Dont See Free Quarks
The size of a nucleus is 1.2A1/3 fm where A is
the mass number and a fm is 10-15 m
gluons
quark
quark
Compare to gravitational force at Earths surface
Quarks exert 16 metric tons of force on each
other!
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Evolution of the Universe
10-44 sec Quantum Gravity Unification of all 4 forces 1032 K
10-35 sec Grand Unification E-M/Weak Strong forces 1027 K
10-35 sec ? Inflation universe exponentially expands by 1026 1027 K
2 10-10 sec Electroweak unification E-M weak force 1015 K
210-6 sec Proton-Antiproton pairs creation of nucleons 1013 K
6 sec Electron-Positron pairs creation of electrons 6 x 109 K
3 min Nucleosynthesis light elements formed 109 K
106 yrs Microwave Background recombination - transparent to photons 3000 K
109 yrs ? Galaxy formation bulges and halos of normal galaxies form 20 K
Reheating Matter ?
The universe gets cooler !
? Need temperatures around 1.51012 K (200 MeV)

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RHIC _at_ Brookhaven National Lab

• 2 concentric rings of 1740 superconducting
  magnets
• 3.8 km circumference
• counter-rotating beams of ions from p to Au

BRAHMS
PHOBOS
PHENIX
STAR
Long Island

• AuAu _at_ ?sNN 200 GeV
• pp _at_ ?s 200 GeV

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What Do Those Numbers Mean?

• Energies are measured in electron volts
• 1 eV is the energy acquired by a particle with
  charge 1 accelerated across a voltage of 1 volt
• keV - 1000 eV
• MeV - 1,000,000 eV, 1 million eV
• GeV - 1,000,000,000 eV, 1 billion eV
• The binding energy of a nucleus is about 8
  MeV/nucleon
• Beam energies are often given in GeV/nucleon
• RHIC is one nucleus with 100 GeV/nucleon
  colliding with another nucleus with 100
  GeV/nucleon going the opposite direction

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How Much Is That?

• Central AuAu Collision
• NColl.? ?sNN 40 TeV 6 mJoule

Sensitivity of human ear 10-11 erg
10-18 Joule 10-12 mJoule Indeed a pretty Loud
Bang if E ? Sound
Most goes into particle creation
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Aftermath of a Collision
End-on view of high energy gold-gold collision

• gt5000 particles
• Only charged particles seen here (there are
  also lots of neutral particles)
• Neutrals dont ionise the gas so are not seen
  by the detector.

As seen by STAR experiment at RHIC
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Blackbody Radiation
Planck distribution describes intensity as a
function of the wavelength of the emitted
radiation
Blackbody radiation is the spectrum of
radiation emitted by an object at temperature T
1/Wavelength ? Frequency ? E ? p
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Determining the Temperature
From transverse momentum distribution deduce
temperature 120 MeV
Close to Temperature we needed
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Whats the Energy Density?

• A typical approach
• use calorimeters to measure energy emitted from
  collision
• estimate the volume of the collision

In Central Collision E 650 GeV
V 130 fm3
eBJ ? 5.0 GeV/fm3
30 times normal nuclear density 5 times above
ecritical from
lattice QCD
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5 GeV/fm3. Is that a lot?
Last year, the U.S. used about 100 quadrillion
BTUs of energy
At 5 GeV/fm3, this would fit in a volume of
Or, in other words, in a box of the following
dimensions
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One Way To Dig Even Deeper - Jets

• Possible for knock-on collisions of partons
• Seen in high-energy physics experiments since
  mid-1970s
• A real particle physics phenomenon that can be
  used to probe the trillion degree material we
  create

hadron
hadron
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Creating a jet of particles

• As connection between quarks breaks up, most of
  the motion stays close to direction of the
  original quarks

pion
pion
pion
kaon

• The fragmented bits appear as normal
  subatomic particles
• pions, kaons,etc

kaon

• Jets commonly come in
• pairs

pion
pion
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Case study opacity of fog

• First beam - least know the source is on.
• Second beam intensity tells you a lot about
  matter passed through

• is this thing on?

Predictions QGP the backwards jet
will be absorbed by the medium Hadron gas the
backwards jet be less affected by the medium
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Jets in Heavy Ion Collisions?
ee- ? q q (OPAL_at_LEP)
p-p ?jetjet (STAR_at_RHIC)
Au-Au ???? (STAR_at_RHIC)
Jets in Au-Au hopeless Task?
No, but a bit tricky
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Jets 2-particle Azimuthal Distributions
pp ? dijet
Df ? 0 central AuAu similar to pp Df ? p
strong suppression of back-to-back
correlations in central AuAu

• Trigger highest pT track
• ?? distribution

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Have we found the Quark Gluon Plasma?

• We now know that AuAu collisions generate a
  medium that is dense (pQCD theory many times
  cold nuclear matter density)
• exhibits behaviour of very hot, thermalized
  source that is dissipative

This represents significant progress in our
understanding of strongly interacting matter

• We have yet to prove that
• Dissipation occurs at the partonic stage
• The system is deconfined and thermalized
• A transition occurs can we turn the effects off
  ?

Not yet, still work to do (but getting closer)