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Hunting for Free Quarks

Helen Caines Relativistic Heavy Ion Group WNSL - West. Hunting for Free Quarks. The RHI Physics Group. The Actors Faculty : Helen Caines John Harris Thomas Ullrich 1 Research Scientists: Jaroslav Bielcik 2 Jana Bielcikova

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Hunting for Free Quarks

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  1. Helen Caines Relativistic Heavy Ion Group WNSL - West Hunting for Free Quarks

  2. 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

  3. Some Terminology partons hadrons quarks quarks gluons mesons baryons nucleons pions, kaons, .. protons, neutrons, ... protons neutrons

  4. 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

  5. Why We Don’t 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 Earth’s surface Quarks exert 16 metric tons of force on each other!

  6. Evolution of the Universe The universe gets cooler ! Reheating Matter ? ? Need temperatures around 1.5·1012 K (200 MeV)

  7. 2 concentric rings of 1740 superconducting magnets 3.8 km circumference counter-rotating beams of ions from p to Au RHIC @ Brookhaven National Lab BRAHMS PHOBOS PHENIX STAR Long Island • Au+Au @ sNN= 200 GeV • p+p @ s = 200 GeV

  8. 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 What Do Those Numbers Mean?

  9. How Much Is That? • Central Au+Au Collision: • NColl. sNN = 40 TeV ~ 6 mJoule Sensitivity of human ear: 10-11 erg = 10-18 Joule = 10-12mJoule Indeed a pretty “Loud Bang“ if E  Sound Most goes into particle creation

  10. Aftermath of a Collision End-on view of high energy gold-gold collision • >5000 particles • Only charged particles seen here (there are also lots of neutral particles) • Neutrals don’t ionise the gas so are not “seen” by the detector. As seen by STAR experiment at RHIC

  11. 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

  12. Determining the Temperature intensity  Phobos Preliminary Systematic Errors not shown transverse momentum  From transverse momentum distribution deduce temperature ~ 120 MeV Close to Temperature we needed

  13. A typical approach use calorimeters to measure energy emitted from collision estimate the volume of the collision What’s the Energy Density? pR2 The PHENIX Calorimeter R~6.5 fm Time it takes to thermalize system (t0 ~ 1 fm/c) 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

  14. 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:

  15. One Way To Dig Even Deeper - Jets • Possible for “knock-on” collisions of partons • Seen in high-energy physics experiments since mid-1970’s • A real particle physics phenomenon that can be used to probe the trillion degree material we create hadron hadron

  16. 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

  17. “is this thing on?” First beam - least know the source is on. Second beam intensity tells you a lot about matter passed through Case study: opacity of fog ? Predictions QGP: the “backwards” jet will be absorbed by the medium Hadron gas: the “backwards” jet be less affected by the medium

  18. Jets in Heavy Ion Collisions? e+e- q q (OPAL@LEP) p-p jet+jet (STAR@RHIC) Au-Au ??? (STAR@RHIC) Jets in Au-Au hopeless Task? No, but a bit tricky…

  19. Jets & 2-particle Azimuthal Distributions central Au+Au collisions min. bias p+p collisions trigger Phys Rev Lett 90, 082302 ? p+p  dijet Df 0: central Au+Au similar to p+p Df p: strong suppression of back-to-back correlations in central Au+Au • Trigger: highest pT track • Δ distribution:

  20. We now know that Au+Au 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 Have we found the Quark Gluon Plasma? 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)

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