Recreating the Birth of the Universe

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Recreating the Birth of the Universe

• T.K HemmickUniversity at Stony Brook

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The Beginning of Time

• Time began with the Big Bang
• All energy (matter) of the universe concentrated
  at a single point in space and time.
• The universe expanded and cooled up to the
  present day
• 3 Kelvin is the temperature of most of the
  universe.
• Except for a few hot spots where the expanding
  matter has collapsed back in upon itself.
• How far back into time can we explain the
  universe based upon our observations in the Lab?
• What Physics do we use to explain each stage?

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Evolution of the Universe
Too hot for quarks to bind!!! Quark
PlasmaStandard Model Physics
Too hot for nuclei to bind Hadronic
GasNuclear/Particle Physics
Nucleosynthesis builds nuclei up to Li Nuclear
ForceNuclear Physics
Universe too hot for electrons to bind E-MAtomic
(Plasma) Physics

• Universe Expands and Cools
• GravityNewtonian/General Relativity

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Standard Model (simplified)

• Imagine a college campus on a warm summer day
• Students are uniformly distributed in an open
  field.

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Standard Model II

• Students who interact with the FRISBEE form a
  group.
• These students are charged
• Other students dont interact with the FRISBEE.
• neutral or nerds

• Now introduce CHESS into the campus!

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Standard Model III

• Some charged and some neutral students decide to
  play chess
• Very short range interaction
• More than one type of exchange particle

• Finally, introduce LOVE into the college campus

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Standard Model IV

• All the remaining students form into tightly
  bound pairs
• (and triples)
• If you break up with one partner, you immediately
  find another (confinement)
• Force grows stronger with separation

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Decoding the Analogy
Sport Force ExchangeParticle Strength Range Calculable?
FRISBEE Electro-Magnetic(QED) Photon Moderate Infinite Most accurate theory ever devised
CHESS Weak Force (unified w/ EM) W, W-, Z0 Weak Short Perfect
LOVE Strong Force (QCD) 8 gluons Strong Infinite Nearly incalculable except for REALLY VIOLENT COLLISIONS!
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Electric vs. Color Forces

• Electric Force
• The electric field lines can be thought of as the
  paths of virtual photons.
• Because the photon does not carry electric
  charge, these lines extend out to infinity
  producing a force which decreases with
  separation.,

• Color Force
• The gluon carries color charge, and so the force
  lines collapse into a flux tube.
• As you pull apart quarks, the energy in the flux
  tube becomes sufficient to create new quarks.

• Trying to isolate a quark is as fruitless as
  trying to cut a string until it only has one end!

CONFINEMENT
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What about this Quark Soup?

• If we imagine the early state of the universe, we
  imagine a situation in which protons and neutrons
  have separations smaller than their sizes.
• In this case, the quarks would be expected to
  lose track of their true partners.
• They become free of their immediate bonds, but
  they do not leave the system entirely.
• They are deconfined, but not isolated
• similar to water and ice, water molecules are not
  fixed in their location, but they also do not
  leave the glass.

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Phase Diagrams
Nuclear Matter
Water
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Making Plasma in the Lab

• Extremes of temperature/density are necessary to
  recreate the Quark-Gluon Plasma, the state of our
  universe for the first 10 microseconds.
• Density threshold is when protons/neutrons
  overlap
• 4X nuclear matter density touching.
• 8X nuclear matter density should be plasma.
• Temperature threshold should be located at
  runaway particle production.
• The lightest meson is the pion (140 MeV/c2).
• When the temperature exceeds the mc2 of the pion,
  runaway particle production ensues creating
  plasma.
• The necessary temperature is 1012 Kelvin.
• Question Where do you get the OVEN?
• Answer Heavy Ion Collisions!

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RHIC

• RHIC Relativistic Heavy Ion Collider
• Located at Brookhaven National Laboratory

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RHIC Specifications

• 3.83 km circumference
• Two independent rings
• 120 bunches/ring
• 106 ns bunch crossing time
• Can collide any nuclear species on any other
  species
• Top Center-of-Mass Energy
• 500 GeV for p-p
• 200 GeV/nucleon for Au-Au
• Luminosity
• Au-Au 2 x 1026 cm-2 s-1
• p-p 2 x 1032 cm-2 s-1 (polarized)

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RHICs Experiments
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RHIC Video
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How is RHIC Different?

• Its dedicated to High Energy Heavy Ion Physics
• Heavy ions will run 20-30 weeks/year
• Its a collider
• Detector systematics independent of ECM
• (No thick targets!)
• Its high energy
• Access to non-perturbative phenomena
• Jets (very violent calculable processes in the
  mix)
• Non-linear dE/dx
• Its detectors are comprehensive
• All final state species measured with a suite of
  detectors that nonetheless have significant
  overlap for comparisons

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RHIC in Fancy Language

• Explore non-perturbative vacuum by melting it
• Temperature scale
• Particle production
• Our perturbative region is filled with
• gluons
• quark-antiquark pairs
• A Quark-Gluon Plasma (QGP)
• Experimental method
• Energetic collisions of heavy nuclei
• Experimental measurementsUse probes that are
• Auto-generated
• Sensitive to all time/length scales

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RHIC in Simple Language

• Suppose
• You lived in a frozen world where water existed
  only as ice
• and ice comes in only quantized sizes ice cubes
• and theoretical friends tell you there should be
  a liquid phase
• and your only way to heat the ice is by colliding
  two ice cubes
• So you form a bunch containing a billion ice
  cubes
• which you collide with another such bunch
• 10 million times per second
• which produces about 1000 IceCube-IceCube
  collisions per second
• which you observe from the vicinity of Mars
• Change the length scale by a factor of 1013
• Youre doing physics at RHIC!

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Natures providence

• How can we hope to study such a complex system?

g, ee-, mm-
p, K, h, r, w, p, n, f, L, D, X, W, D, d, J/Y,
PARTICLES!
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Deducing Temperature from Particles

• Maxwell knew the answer!
• Temperature is proportional to mean Kinetic
  Energy
• Particles have an average velocity (or momentum)
  related to the temperature.
• Particles have a known distribution of velocities
  (momenta) centered around this average.
• All the RHIC experiments strive to measure the
  momentum distributions of particles leaving the
  collision.
• Magnetic spectrometers measure momentum of
  charged particles.
• A variety of methods identify the particle
  species once the momentum is known
• Time-of-Flight
• dE/dx

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Magnetic Spectrometers

• Cool Experiment
• Hold a magnet near the screen of a BW TV.
• The image distorts because the magnet bends the
  electrons before they hit the screen.
• Why?

1 meter of 1 Tesla field deflects p 1 GeV/c by
17O
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Particle Identification by TOF

• The most direct way
• Measure b by distance/time
• Typically done via scintillators read-out with
  photomultiplier tubes
• Time resolutions 100 ps

p
e
K
p

• Exercise Show

• Performance
• dt 100 ps on 5 m flight path
• P/K separation to 2 GeV/c
• K/p separation to at least 4 GeV/c

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Particle Identification by dE/dx

• Elementary calculation of energy loss
• Charged particles traversing material give
  impulse to atomic electrons

• dE/dx
• The 1/ b2 survives integration over impact
  parameters
• Measure average energy loss to find b
• Used in all four experiments

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Measuring Sizes

• Borrow a technique from Astronomy
• Two-Particle Intensity Interferometry
• Hanbury-Brown Twiss or HBT
• Bosons (integer spin particles like photons,
  pions, Kaons, ) like each other
• Enhanced probability of close-by emission

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Measuring Shapes

• Momentum difference can be measured in all three
  directions
• This yields 3 sizes
• Long (along beam)
• Out (toward detector)
• Side (left over dimension)
• Conventional wisdom
• The Long axis includes the memory of the
  incoming nuclei.
• The Out axis appears longer than the Side
  axis thanks to the emission time

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Run-2000

• First collisions15-Jun-00
• Last collisions 04-Sep-00
• RHIC achieved its First Year Goal (10 of design
  Luminosity).
• Most of the data were recorded in the last few
  weeks of the run.
• The first public presentation of RHIC results
  took place at the Quark Matter 2001 conference.
• January 15-20
• Held at Stony Brook University

• Recorded 5M events

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Jet Quenching

• At RHIC energies, some of the processes are
  calculable from first principles
• Hard scattering
• Jets
• Violent collisions between quarks and gluons.
• Excess yield at high momentum.
• One effect of Plasma is the quenching of these
  jets.
• They lose their energy while crossing the plasma.
• They cool down to the soup temperature.

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Jet Quenching Observed

• Stony Brook Postdoc Federica Messer, presented
  PHENIX spectra of charged particles.
• (should be dominated by pions).
• BNL scientist (formed SB student) Gabor David
  presented measurements of neutral, IDENTIFIED
  pions.

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Identified Particle Spectra

• Stony Brook Postdoc Julia Velkovska presented
  identified charged particle spectra at high
  momentum
• The proton production EXCEEDS the pion production
  at high momentum
• NOONE PREDICTED THAT!
• This causes the divergence between all-charged
  and neutral pions.

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Where are the Jets?
Expectation

• Charged particle production falls below the
  expectations by about a factor of two despite the
  proton contamination.
• Neutral pion production is a factor of 10 below
  predictions.

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Another Surprise!

• RoutltRside!!!!!
• Normal theory cannot account for this
• Imaginary times of emission!!

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Possible Explanation??

• Stony Brook theory student Derek Teaney (advisor
  E. Shuryak) calculated an exploding ball of QGP
  matter.
• The exploding ball drives an external shell of
  ordinary matter to high velocities
• Rout is the shell thickness
• Rside is the ball size

Plasma
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Is it Soup Yet?

• RHIC physics in some reminds me of the
  explorations of Christopher Columbus
• He had a strong feeling that the earth was round
  without having detailed calculations to back him
  up.
• He traveled in exactly the wrong direction, as
  compared to conventional wisdom.
• He discovered the new world
• But he thought it was India!
• Our status
• We see jet quenching for the first time.
• We see results which defy all predictions
• Hard proton production exceeds pion production
• Imaginary emission time
• We could be in India (QGP), the New World, or
  just a place in Europe where the customs are VERY
  strange.

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Next Steps

• Simple Language
• After the icecubes collide and melt, fragments
  leave which are frozen by the time they reach us,
  masking the true nature of the early state.
• Lesson Dont look at the fragments of frozen
  water which leave the collision, take a picture
  using light while the system is melted!
• Sophisticated Language
• Since hadrons are made of quarks, they reform and
  thereby lose information from the early stage.
• Photons and leptons leave the plasma directly and
  give detailed information from the center of the
  collision!
• Photons and leptons are rare and require more
  RHIC running.

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Summary

• Extreme Energy Density is a new frontier for
  explorations of the state of the universe in the
  earliest times.
• The RHIC machine has just come on line
• The machine works
• The experiments work
• The data from signatures of QGP as well as
  outright surprises
• Its not your Fathers Nuclear Matter anymore!
• The real look into the system will come in the
  next run (May 2001)
• Electrons, Photons, Muons
• We dream of India as our glorious destination
• But maybe.
• Well find the new world instead.

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Electron Identification

• Problem Theyre rare

• Solution Multiple methods
• Cerenkov
• E(Calorimeter)/p(tracking) matching

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Why electrons?

• One reason sensitivity to heavy flavor production

• Other reasons vector mesons, virtual photons ?
  ee-

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p0 Reconstruction

• A good example of a combinatoric background
• Reconstruction is not done particle-by-particle
• Recall p0 ? gg and there are 200 p0 s per unit
  rapidity
• So p0 1 ? g1A g 1B p0 2 ? g2A g
  2B p0 3 ? g3A g 3B p0 N ? gNA g
  NB
• .Unfortunately, nature doesnt use subscripts on
  photons
• N correct combinations (g1A g 1B), (g2A g 2B),
  (gNA g NB),
• N(N-1)/2 N incorrect combinations (g1A g 2A),
  (g1A g 2B),
• Incorrect combinations N2 (!)
• Solution Restrict N by pT cuts
  use high granularity, high resolution detector

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BRAHMS

• An experiment with an emphasis
• Quality PID spectra over a broad range of
  rapidity and pT
• Special emphasis
• Where do the baryons go?
• How is directed energy transferred to the
  reaction products?
• Two magnetic dipole spectrometers in classic
  fixed-target configuration

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PHOBOS

• An experiment with a philosophy
• Global phenomena
• large spatial sizes
• small momenta
• Minimize the number of technologies
• All Si-strip tracking
• Si multiplicity detection
• PMT-based TOF
• Unbiased global look at very large number of
  collisions (109)

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PHOBOS Details

• Si tracking elements
• 15 planes/arm
• Front Pixels (1mm x 1mm)
• Rear Strips(0.67mm x 19mm)
• 56K channels/arm
• Si multiplicity detector
• 22K channels
• h lt 5.3

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PHOBOS Results

• First results on dNch/dh
• for central events
• At ECM energies of
• 56 Gev
• 130 GeV
• (per nucleon pair)
• To appear in PRL
• (hep-ex/0007036)

X.N.Wang et al.
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STAR

• An experiment with a challenge
• Track 2000 charged particles in h lt 1

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STAR Challenge
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STAR Event
Data Taken June 25, 2000. Pictures from Level 3
online display.
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STAR Reality
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PHENIX
GlobalMVD/BB/ZDC

• An experiment with something for everybody
• A complex apparatus to measure
• Hadrons
• Muons
• Electrons
• Photons
• Executive summary
• High resolution
• High granularity

Muon Arms Coverage (NS) -1.2lt y lt2.3 -p lt
f lt p DM(J/y )105MeV DM(g) 180MeV 3
station CSC 5 layer MuID (10X0) p(m)gt3GeV/c
West Arm
East Arm
South muon Arm
North muon Arm
Central Arms Coverage (EW) -0.35lt y lt 0.35
30o ltf lt 120o DM(J/y ) 20MeV DM(g) 160MeV
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PHENIX Design
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PHENIX Reality
January, 1999
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PHENIX Results

• (See nucl-ex/0012008)
• Multiplicity grows significantly faster than
  N-participants
• Growth consistent with a term that goes as
  N-collisions (as expected from hard scattering)

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Summary

• The RHIC heavy ion community has
• Constructed a set of experiments designed for the
  first dedicated heavy ion collider
• Met great challenges in
• Segmentation
• Dynamic range
• Data volumes
• Data analysis
• Has begun operations with those same detectors
• Quark Matter 2001 will
• See the first results of many new analyses
• See the promise and vitality of the entire RHIC
  program