Quark-Gluon Plasma !? If physicists are able to create a QGP it will expand and decay into hadrons and will recreate the scenario that occured at about a micro-second after the Big Bang

Evolution of the Universe Too hot for quarks to bind!!! Standard Model (N/P) Physics Quark- Gluon Plasma?? Collisions of “Large” nuclei convert beam energy to temperatures above 200 MeV or 1,500,000,000,000 K ~100,000 times higher temperature than the center of our sun. “Large” as compared to mean-free path of produced particles. Too hot for nuclei to bind Nuclear/Particle (N/P) Physics Hadron Gas Transition process Nucleosynthesis builds nuclei up to He Nuclear Force…Nuclear Physics Universe too hot for electrons to bind E-M…Atomic (Plasma) Physics E/M Plasma Solid Liquid Gas Today’s Cold Universe Gravity…Newtonian/General Relativity

u d s c b t together with 6 anti-quarks Nucleon: 6 known quarks: u d s c b t together with 6 anti-quarks Nucleon: 3 quarks bound by exchange of gluons (confined) Quarks and anti-quarks can also be bound together within mesons If the temperature and the density are high enough, one can obtain a new phase of matter where quarks and gluons are deconfined quark-gluon plasma such onditions can be created in high energy heavy-ion collisions Peripheral collisions: No quark-gluon plasma Central collisions: In case of quark-gluon plasma formation: - -screening of the c-c color interaction in presence of the other quarks –no J/ produced J/ is detected by ist decay into two muons

Recall of some concepts in Hadron-Nucleon and Hadron-Nucleus interactions Laboratory System Center of Mass System Beam Target Beam Target Mass Momentum Energy Four-momentum Total momentum Total Energy

In this notation, the velocity of the CMS in the LS is The Lorentz -factor being The Lorentz transformation give: -Transverse mass LAB. System C.M. System

Collisions of two particles the collision must be analysed in the CMS of the two colliding particles. The two main reasons for this are: 1. In the CMS the energy has the smallest value of all reference systems. In the CMS the total energy is of the total energy in the LS: 2. Because in the CMS the total momentum is zero, when particles are created there are no preferential direction imposed by kinematics. Due to the energy conversation law

Inclusive Production of Particles beam+target A+ anything The cross section of particle production is usually separated into two factors: This factorization is empirical A similar factorization of the differential cross section is used: The differential cross section for the inclusive production of a particle is then written: where -Feynman‘s assumption that at high energies the function becomes assymptotically independent of the energy:

Differential cross section as a function of or It has been observed experimentally, that the Lorentz-invariant differential cross section as well as non-invariant cross section has exponential behaviour of the type:

Rapidity By definition, the rapidity of a particle is: The rapidity is connected with the longitudinal motion of the particle. The differential cross section for the particle production is: Rapidity of the CMS in the LS Relationship between the rapidity of a particle in the LS and the rapidity in the CMS of the collision

Pseudorapidity Let us assume that a particle is emitted at an angle in the LS. Then rapidity y at very high energies can be written: where is called pseudorapidity. Pseudorapidity is a very convenient variable, because it depends only on the angle of emission and is defined for any values of the mass and momentum of the particle and any value of the energy of the collision.

From Hadronic Matter to Quark-Gluon Plasma Density of nucleons in normal nuclear matter where and . Therefore, Energy density of normal nuclear matter or Taking the radius of the proton as , the energy density of a proton is Relashionship between energy and temperature Time corresponding to one fermi

Deconfinement Quantum chromodynamics predicts that at extreme high conditions of energy and /or temperature there should be a deconfinement of quarks and gluons, and hadrons should undergo a phase transition to a quark-gluon plasma (QGP) If a nucleus is put in a state in which the nucleon density becomes and the energy density becomes then deconfinement should occur. Hadron gas QGP

How to Obtain Experimentally a Hadronic State with High Energy Density or High Temperature? The only way we know today of obtaining hadronic states with high energy density and /or high temperature is with ultrarelativistic nucleus-nucleus collisions. A first generation of experiments has been done by the mid-1980s: three at Brookhaven‘s Alternating Gradient Synchrotron (AGS) E802, E810, and E814, and in Switzerland, at CERN Super Proton Synchrotron (SPS) at CERN six large ones, NA34, NA35, NA36, NA38, WA80 and WA85; at Brookhaven the AGS accelerates and ions at 14.5 Gev/nucleon; at CERN the SPS accelerates and at 200 GEV/nucleon. But those high-energy beams, colliding with stationary nuclear targets (heavy), gave rather modest center-of-mass collision energies 5 and 17 GeV, respectively, per nucleon pair.

RHIC ERA BEGINS Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory- The largest US facility for basic research in nuclear and particle physics, which provides experiments with colliding beams of heavy nuclei at ultrarelativistic energies as high as 100 Gev per nucleon. 1000 nuclear collisions per second

Relativistic Heavy Ion Collider (RHIC) Pioneering High Energy Nuclear Interaction eXperiment (PHENIX) 2 counter-circulating rings, 3.8 km circumference Any nucleus on any other. Top energies (each beam): 100 GeV/nucleon Au-Au. 250 GeV polarized p-p. Maximal Set of Observables Photons, Electrons, Muons, ID-hadrons Highly Selective Triggering High Rate Capability. Rare Processes.

Gold-Gold Ion Collision at Phobos in the July 18, 2001 at Highest RHIC Energies: 100 GeV/nucleon Central and Peripheral Collisions It is important to distinguish central and peripheral collisions because of the density of energy released. This density is small in a peripheral collisions and is usually large in a central collisions Mainly mesons

Theoretical Models Coherent Collisions - Incoherent Collisions- They are either thermodynamical or hydrodynamical, or both (Bjorken‘s , Landau models). Thermodynamics takes into an account the exchange energy and temperature, whereas hydrodynamics takes into an account mechanical motion of expansion and compression of the hadronic matter Incoherent Collisions- Succession of independent nucleon-nucleon interactions (LUND, DUAL PARTON models).

What is measured in an experiment ? Energy (with electromagnetic or a hadronic calorimeter) Multiplicity of the secondary particles (with visual detectors of tracks or with electronic devices) Particle momentum and sign of electrical charge (with the trajectory of the particle in a magnetic field) Particle trajektory (given by visual detectors of multiplicity, or drift chambers) Particle velocity (with Cherenkov counters) Time of flight (between two counters) Energy and direction of a single photon (this can be measured with a modular electromagnetic calorimeter).

Signatures of the Quark-Gluon Plasma Distributions Suppression of the production Jet quenching Direct photons Production of strange particles Bose-Einstein interferometry

Transverse Momentum Distribution as a Signature of QGP Rapid increase Fig. Cosmic ray interactions with nuclear emulsions

Suppression of the J/Ψ production as a Signature of QGP J/Ψ suppression because colour screening hinders the quarks from binding J/Ψ interacts inelastically with some dense hadronic matter created in the collision

Jet Quenching as a Signature of QGP leading particle hadrons Hard scatterings (HS) in nucleon collisions produce jets of particles In a colour deconfined medium the partons (quarks+gluons) strongly interact and loose energy (~GeV/fm) by gluon radiation HS near the surface can give a jet in one direction, while the other side is quenched hadrons leading particle

The “Away-Side” Jet Escaping Jet “Near Side” d+Au Au+Au Min Bias 60-90% 0-10% Lost Jet “Far Side” Near Far Near Far PHENIX Preliminary PHENIX Preliminary Jets produced on the periphery of the collision zone coming out should survive. However, their partner jet will necessarily be pointed into the collision zone and be absorbed. Peripheral Au+Au similar to d+Au Central Au+Au shows distinct reduction in far side correlation. Away-side Jet is missing in Au+Au

Direct photons as a Signature of QGP If a photon is produced in a QGP it leaves the hot plasma with a small probability of interacting in the outer freeze-out region (200-300 times smaller than that of hadron) . It would keep the memory of the temperature in which it was created.

Production of strange particles as a Signature of QGP As the QGP cools quarks are once again bound within hadrons but the increased strange quark yield remains. The strange quark mass is 150 MeV, whereas the energy needed to produce a strange quark in a hadron gas is at least 530 MeV via And to produce an anti-strange quark requires 1.5 GeV through Figure. The mid-rapidity strange particle yields versus the negative hadron yield as measured by STAR in Au-Au collisions at sqrt(s)=130 GeV. All measured particles reveal a smooth, near linear, increase.

Bose-Einstein interferometry as a Signature of QGP Allows a measurement of the sizes of the interaction region from which the bosons are emitted , as well as the measurement of interaction time. The squared amplitude for two bosons wave functions is , which has a modulation with maxima at

Conclusions No one of carried out experiment can claim unambiguosly for QGP detection, but there are a number of promising observations A lot of useful information has been obtained which may be used to answer some of the key questions of nuclear and particle physics