PHY313 - CEI544 The Mystery of Matter From Quarks to the Cosmos Fall 2005

Transcription

1 PHY313 - CEI544 The Mystery of Matter From Quarks to the Cosmos Fall 2005 Peter Paul Office Physics D PHY313 Peter Paul 10/20/05 PHY313-CEI544 Fall-05 1

2 What have we learned last time I The elements up to the tightest bound one, 56 Fe, are formed during the burning process in the star as it uses its primordial fuel, 75% hydrogen (protons) and 25% Helium. In the first step the star burns four protons into 4 He. Once sufficed 4 He is produced, 3 4 He will combine to yield 12 C. This process produces more heat. In the next step the star uses 12 C and the available hydrogen to go through the CNO cycle which produces the elements between 12 C and 16 O. This heats the star up further. One there is sufficient 16 O around the star will produce still heavier elements by using available H and 4 He to fuse with the 16 O. The process continues until the elements that are produced reach the peak of the nuclear binding energy, at Fe/Ni. Then the star cools (Red Giant). Gravitation compresses the star. The heaviest elements accumulate at the core in layers of density. Compression reheats the star. It explodes as a Supernova. Nuclear reactions occurring during this violent phase produce many neutrons. These are rapidly captured into the Fe/Ni core to produce the heavier nuclei (rprocess). Beta decay changing n p inside the nuclei moves the neutronrich nuclei toward the valley of stability. The final explosive phase spews these heavy elements into the interstellar medium. There they are incorporated into new stellar objects Peter Paul 10/20/05 PHY313-CEI544 Fall-05 2

3 What have we learned last time II The known zoo of strongly interacting particles (hadrons) was found divided into very heavy particles (Baryons) and medium heavy particles (Mesons). It became clear from the formation and decay of these particles that several hidden quantum numbers must play a role, in addition to the conservation of electric charge, such as S and B. Strangeness S and Baryon number B are always conserved in reactions that involve the strong interaction. A concept of elemental building blocks, called up, down and strange quarks, u,d,s, could explain all properties of the construction of the observed hadrons. The quarks have electric changes in units of 1/3 of the electron charge, Baryon number 1/3. and spin 1/2. All known Baryons could be constructed combining 3 quarks; all Mesons could be constructed with pairs of one quark and an anti-quark. The discovery of the predicted Ω particle, a combination of 3 s quarks, showed that there was reality behind the quark concept. Later, three heavier quarks, the charm, top and bottom quarks were discovered. The total of 6 quarks and 6 antiquarks can be grouped into three families. Quarks are bound to each other by a force that becomes stronger as the quarks are pulled apart (Confinement). Peter Paul 10/20/05 PHY313-CEI544 Fall-05 3

4 The three quark families Today we know 3 families of quarks, and 3 antiquark families. Spin Charge First family Second family Third family 1/2 +2/3 up charm top (3 MeV) (1300 MeV) (175,000 MeV) 1/2-1/3 down strange bottom (6 MeV) (100 MeV) (4,300 MeV) Note that the neutron and proton and the light mesons are all build up of the lightest quarks, the u and d quarks (and their anti-quarks in the meson case). The strange particles contain the s-quark which is much heavier Peter Paul 10/20/05 PHY313-CEI544 Fall-05 4

5 Reminder: Particles from quarks Mesons are made from quarks and anti-quarks u and anti-d = π+ d and anti-up = π- u and anti-s = K+ and so on, making hundreds of particles. Baryons are made from 3 quarks uud = proton udd = neutron uds = lambda (Λ) and so on, making hundreds of baryons Note: Anti-quarks have the opposite charge of the quarks Peter Paul 10/20/05 PHY313-CEI544 Fall-05 5

6 Quark Confinement (Repeat) The interaction between quarks binds them such that no single quark can ever be free. This is different from two charged bodies bound by the Coulomb force, which becomes weaker as the charges are separated It is similar to the binding of a magnetic northpole and a south-pole. Thus any quark that emerges from a proton will dress itself with other quarks or anti-quarks and emerge as a jet. The binding force between quarks is weak when they are close together but grows stronger as they are pulled apart. At close distances they can almost be treated as free: Asymptotic freedom Peter Paul 10/20/05 PHY313-CEI544 Fall-05 6

7 Peter Paul 10/20/05 PHY313-CEI544 Fall-05 7

8 Color in the Strong Interaction Some particles are made up of 3 identical quarks, like the Ω-: s s s This contradicts Pauli Principle because two would have the same QN. Therefore, in addition to their regular quantum properties, like spin and electric charge, quarks must have another property that differentiates them from each other. This property is called Color. There are 3 colors : Red, Green and Blue (these are just stand-in names). Thus the proton could look like this uud or any other color combination. A particle in the real world, like a proton (u-u-d) cannot show any color. It must appear white, i.e. it must be made of quark combinations that contain all 3 colors equally. The colored Quarks interact with each other through the exchange of gluons, which exchange color between the quarks (Color interaction). The Theory that describes the Color interaction iscalled Quantum Chromo Dynamics (QCD) Peter Paul 10/20/05 PHY313-CEI544 Fall-05 8

9 The Force Carriers of the Strong Interaction The Strong Interaction involves the exchange of gluons The Gluons, which are mass less, exchange color between quarks There are 9 color-anti-color combinations, but only 8 quarks, since the 9 th combination contains all colors and thus is white. greenanti-green redanti-red blueanti-blue greenanti-red redanti-blue blueanti-red greenanti-blue redanti-green blueanti-green Peter Paul 10/20/05 PHY313-CEI544 Fall-05 9

10 Can we ever set quarks free? Setting a quark free means breaking the connection to its partner quarks. This cannot happen in free space, but it could happen in a medium. This is analogous to the situation in Water: In ice the molecules are strictly bound and ordered into a crystal. Even in liquid form the molecules feel an interaction between each other. Only when we evaporate the water are the molecules free. Can we evaporate quark matter? Peter Paul 10/20/05 PHY313-CEI544 Fall-05 10

11 Example: The Phases of Water As water changes from Ice to Vapor, the binding between molecules is first weakened, then broken Peter Paul 10/20/05 PHY313-CEI544 Fall-05 11

12 Evolution of the Universe ~ 10 µs after Big Bang T = K (~ 170 MeV) T = 10 9 K Hadron Synthesis strong force binds quarks and gluons in massive objects: p & n; mass ~ 1 GeV ~ 100 s after Big Bang Nucleon Synthesis strong force binds protons and neutrons into nuclei QCD: Quantum Chromo Dynamics Two puzzles: Confinement & Chiral Symmetry Can we undo confinement? Unbound quark ~1 MeV (Higgs mass) Constituent quarks ~ 300 MeV Peter Paul 10/20/05 PHY313-CEI544 Fall-05 12

13 Explore QCD (Nuclear) Matter at High Temperature and Density nuclear matter p, n density or temperature Quark-Gluon Plasma q, g QCD potential: in vacuum: linear increase with distance from color charge strong attractive force confinement of quarks to hadrons : baryons (qqq) and mesons (qq-bar) in dense and hot matter screening of color charges; Debye screening potential vanishes for large distance deconfinement of quarks QGP Peter Paul 10/20/05 PHY313-CEI544 Fall-05 13

14 QCD predictions for the Phase Transition Results from lattice QCD establish the QCD phase transition and chiral symmetry transition. Karsch, Laermann, Peikert (99) ε C = 0.6 GeV/fm 3 T C ~ 170 MeV jump in energy density predicted at: T C ~ 170 MeV ε C = 0.6 GeV/fm 3 T ~ 220 MeV ε = 3.5 GeV/fm 3 Peter Paul 10/20/05 PHY313-CEI544 Fall-05 14

15 Phase Diagram for Quark Matter Phase transition temperature T = 170 MeV ~ Kelvin Peter Paul 10/20/05 PHY313-CEI544 Fall-05 15

16 Use energetic Gold collisions to. Create nuclear matter in the combined volume of the 2 Gold ions (2x 200 nucleons!) to create the medium in which quarks could be deconfined. Bring in enough energy to compress the nuclear matter and to heat it to several 100 MeV in temperature. In the parlance of the scientists: Create QGP as transient state in heavy ion collisions up to 400 nucleons in close proximity verify experimentally existence of QGP study QCD confinement of quarks to hadrons study how hadrons get their masses Retrace spontaneous breaking of chiral symmetry Turn free quarks ( ~ 5 MeV for u,d ) into constituent quarks ( ~ 300 MeV for u,d) Peter Paul 10/20/05 PHY313-CEI544 Fall-05 16

17 Schematic View of a Heavy Ion Collision projectile J/ψ p several 1000 particles produced in central collision π π b ~ 0 cc Κ π π π target p e e + hadrons π, K, p -lots, produced late when particles stop to interact (freezeout) thermal equilibrium and collective behavior ( flow ) strangeness equilibration Correlated systems from dense system(j/ψ, Jets) electro-magnetic radiation γ, e + e, µ + µ -few, emitted any time ; black body radiation π π Peter Paul 10/20/05 PHY313-CEI544 Fall-05 17

18 Violent collisions produce lots of particles Amazingly, these particles can all be recorded simultaneously Peter Paul 10/20/05 PHY313-CEI544 Fall-05 18

19 The Relativistic Heavy Ion Collider at BNL Peter Paul 10/20/05 PHY313-CEI544 Fall-05 19

20 Gold Ion Collisions in RHIC PHOBOS 10:00 o clock High Int. Proton Source Pol. Proton Source PHENIX 8:00 o clock LINAC BAF (NASA) BOOSTER µ g-2 12:00 o clock RHIC STAR 6:00 o clock U-line AGS 9 GeV/u Q = +79 HEP/NP 4:00 o clock BRAHMS 2:00 o clock Six collision regions Four detectors Design Parameters: Beam Energy = 100 GeV/u No. Bunches = 57 No. Ions /Bunch = T store = 10 hours L ave = cm -2 sec -1 1 MeV/u Q = +32 TANDEMS Peter Paul 10/20/05 PHY313-CEI544 Fall-05 20

21 Basic Principle of Acceleration: Use Electric Force Voltage - Two charged particles electrons Battery + Voltage In ~1920 s Cockcroft and Walton invented the first particle accelerator: The electrostatic accelerator. It uses the fact that bodies with electric charges interact with each other: They feel a force. 1. Equally charged particles repel each other, 2. Oppositely charged particles attract each other. Peter Paul 10/20/05 PHY313-CEI544 Fall-05 21

22 Acceleration with DC or AC Electric Fields Acceleration is done by the Coulomb force acting on the positive or negative charge of the accelerated particle. Acceleration principle is very simple: E= q V where q = n x e. V can be a positive or negative voltage. Typical voltages can be 1 MV/m or even 70 MV/m Acceleration in a DC field produces a steady beam. Acceleration in an AC or rf field produces bunches of accelerated particles. Particle beam Peter Paul 10/20/05 PHY313-CEI544 Fall-05 22

23 The Van de Graaf Accelerator Van de Graaf invented a simple electrostatic aacacelerator: It was the first accelerator to reach large energies by the use of very high voltages. It uses an insulated conveyor belt to shuffle positive (or negative) charges into an insulated dome. This builds up voltage as high as 20 Million Volts (20 MV). If the dome is positively charged, protons will be accelerated downward; if the dome is negatively charged, electrons can be accelerated downward. Today thousands of these accelerators from a few 100 kv to 20 MV are used all over the world. Positive Protons accelerated downward Peter Paul 10/20/05 PHY313-CEI544 Fall-05 23

24 Modern Tandem at Oak Ridge Peter Paul 10/20/05 PHY313-CEI544 Fall-05 24

25 Circular Accelerators: The Cyclotron The Cyclotron was invented at Berkeley in the 1930 s by E. Lawrence. It runs particle bunches in circles many time through the same electric field. The electric field is timed so that each time a bunch enters into one of two gaps, it gets an accelerating kick. This requires a resonance condition between the path of the beam bunch and the accelerating wave. Peter Paul 10/20/05 PHY313-CEI544 Fall-05 25

26 The latest stage: Sector focusing superconducting cyclotrons Peter Paul 10/20/05 PHY313-CEI544 Fall-05 26

27 Synchrotrons One can cut out the center of the cyclotron magnet if the particles can be made to stay on a fixed orbit as they get accelerated. This requires that the Magnetic Field be increased linearly with the velocity gain of the beam during acceleration. Removing the center part of the magnet eliminates huge amount of weight and cost for steel. Most modern particle accelerators are synchrotrons. Extracted beam Circling beam RF voltage Peter Paul 10/20/05 PHY313-CEI544 Fall-05 27

28 Beam deflection in magnets Lorentz Force F L = qbv A magnetic field deflects but does not accelerate. The force acts perpendicular to the direction of flight. It bends a charge beam. The bending power is directly proportional to the magnetic field strength B This can be used in particle accelerators to bend and/or focus beams It is also used to deflect beams in detectors Peter Paul 10/20/05 PHY313-CEI544 Fall-05 28

29 Electrostatic fields and beam focusing Electric fields widely used for beam focusing (TV picture tubes!), similar to the use of lenses for light focusing. Charged particles follow trajectories that are perpendicular to the line of equal voltage It is weak focusing because one cannot achieve very high electric DC fields: ~ 1 MV/m Peter Paul 10/20/05 PHY313-CEI544 Fall-05 29

30 Strong focusing with magnetic quadrupoles Magnetic quadrupole lens focuses in one direction but defocuses in the other. However, a sequence of two lenses with a drift space in between has a net focus on two dimensions Focusing strength of a single lens is proportional to the magnetic field f = p qbl = x f y X-focusing Y-focusing Peter Paul 10/20/05 PHY313-CEI544 Fall-05 30

31 Strong focusing of particle beams Magnetic Quadrupole fields have a strong focusing action. They are the work horse of all modern machines. A single quadrupole focuses in one direction, defocuses in the orthogonal direction. Thus two lenses must always be paired Strongest lenses can be made with superconductors and with very mall dimensions Beam system for CEBAF accelerator Peter Paul 10/20/05 PHY313-CEI544 Fall-05 31

32 Radiofrequency waves E z c z Electromagnetic waves are electromagnetic fields that change with time. They can travel in free space or in resonator cavities that contain them. E z ct = λ 2 c c A charged particle can ride on this wave like a surfer, either at the peak or a little in front of it. Staying a bit ahead of the wave is more stable. z Peter Paul 10/20/05 PHY313-CEI544 Fall-05 32

33 The skill of the Surfer By staying ahead of the peak of the wave the surfer makes sure he does not fall off the wave backwards. He cannot fall forward since the wave will catch up with him. The stability of his position requires that his/her speed is matched to the speed of the wave. The same synchronization condition applies to the particle beam (=surfer) and the electromagnetic wave. In free space the EM wave would travel with the speed of light. But in a resonator cavity it can be slowed down to match the changing speed of the particle beam. Peter Paul 10/20/05 PHY313-CEI544 Fall-05 33

34 Linear accelerators Resonators filled with such traveling waves are used in linear Accelerators. The particle bunches travel on a linear path through a series of resonators, being pushed forward in each resonator. Linear accelerators are used for very high particle currents, e.g. in neutron spallation sources They are the basis for the most modern proposed accelerator, the International Linear Collider (ILC). RF power supply Particle beam Resonators Peter Paul 10/20/05 PHY313-CEI544 Fall-05 34

35 Superconducting resonators made from Nb have achieved the highest quality and highest electric field. Superconducting resonators Since electric currents experience almost no resistive losses in superconducting materials, such cavities can achieve large accelerating fields with little electric power. The preparation of these resonators requires ultimate cleanliness and surface smoothness Peter Paul 10/20/05 PHY313-CEI544 Fall-05 35

36 Particle Colliders When a beam has been accelerated in a synchrotron ring, it can be stored and let to coast for many hours. The beams of 2 rings can then be crossed and made to collide If both beams have the same energy the collision of 2 particles, one from each ring, brings them to a stop. This is a very efficient transformation of beam energy into reaction energy (or heat of the reaction zone). All modern HEP accelerators are colliders. Look at for more information The Large Hadron Collider (LHC) at CERN carries two beams in one magnet ring and collides them in 4 crossings. It will begin operation in Peter Paul 10/20/05 PHY313-CEI544 Fall-05 36

37 Energy Frontier of Colliders LHC at CERN, E cm = 14 TeV Peter Paul 10/20/05 PHY313-CEI544 Fall-05 37

38 Gold Ion Collisions in RHIC PHOBOS 10:00 o clock High Int. Proton Source Pol. Proton Source PHENIX 8:00 o clock LINAC BAF (NASA) BOOSTER µ g-2 12:00 o clock RHIC STAR 6:00 o clock U-line AGS 9 GeV/u Q = +79 HEP/NP 4:00 o clock BRAHMS 2:00 o clock Six collision regions Four detectors Design Parameters: Beam Energy = 100 GeV/u No. Bunches = 57 No. Ions /Bunch = T store = 10 hours L ave = cm -2 sec -1 1 MeV/u Q = +32 TANDEMS Peter Paul 10/20/05 PHY313-CEI544 Fall-05 38

39 RHIC Pictures (1) Blue and yellow rings Injection arcs to blue and yellow rings Peter Paul 10/20/05 PHY313-CEI544 Fall-05 39

40 RHIC Pictures (2) Rf storage cavities Installation of final focussing triplets Peter Paul 10/20/05 PHY313-CEI544 Fall-05 40

41 Bringing beams precisely into collision Beam in blue ring Beam in yellow ring 200 ns (60 m) Beams in collision at the interaction regions 200 ns (60 m) Peter Paul 10/20/05 PHY313-CEI544 Fall-05 41

42 Stored beams in a Collider (RHIC) Coll. rate / Blue Ions / Yellow Ions [Hz/10 18 ] Beams in a collider die because of scattering of the particles within each bunch and the scattering of the bunches with rest gas in the beam pipe Peter Paul 10/20/05 PHY313-CEI544 Fall-05 42

43 The PHENIX Detector at RHIC This detector surrounds the collision point and tracks all particles coming from the center. It can track several thousand particles simultaneously and identify their energy and charge. A good fraction of it was built by students at Stony Brook. Peter Paul 10/20/05 PHY313-CEI544 Fall-05 43

44 East carriage Installation of PHENIX Drift Chambers West carriage and Magnet in IR Drift chamber + Pad chamber 1 Peter Paul 10/20/05 PHY313-CEI544 Fall-05 44

45 Detection of charged particles Charged particlesnize gases. The degree of ionization depends on the charge of the particle and its velocity. The particle ionizes throughout its path, but most heavily at the end of its path. The ionization products than be deflected by an electric or a magnetic field toward sensors Such detectors are wire chambers or time projection chambers (TPC). Bragg Curve of an Iron beam Peter Paul 10/20/05 PHY313-CEI544 Fall-05 45

46 Operation of gas drift chamber Peter Paul 10/20/05 PHY313-CEI544 Fall-05 46

47 Combined Identification of different particle species Tracking Beam-Beam Counter Time-of-Flight array provides excellent hadron identification over broad momentum band: Peter Paul 10/20/05 PHY313-CEI544 Fall-05 47

48 The Power of Modern Tracking Peter Paul 10/20/05 PHY313-CEI544 Fall-05 48

49 The STAR TPC Detector Peter Paul 10/20/05 PHY313-CEI544 Fall-05 49

50 First events in STAR: Big Time Projection Chamber First Events June first Au-Au collisions at STAR June 12 Brookhaven Science Associates U.S. Department of Energy 44 Peter Paul 10/20/05 PHY313-CEI544 Fall-05 50

51 Detention of Gamma rays Gamma rays can be detected with very high efficiency and resolution by use of semiconductor detectors, such as Germanium crystals. Peter Paul 10/20/05 PHY313-CEI544 Fall-05 51

52 Seventh Homework, due Oct. 27, The Lambda particle has a mass of about 1,200 MeV/c2 and zero electric charge. It behaves strangely. 1. Is it a Baryon or a Lepton: Explain your answer. 2. What combination of quarks does it contain. 2. Describe how one attempts to free up (deconfine) individual quarks and what temperatures are required to achieve that goal. 3. How long after the initial Big Bang did the quarks freeze into nucleons and mesons? 4. What force is used to accelerate charged particles? Can we build accelerators for both negatively charged particles (electrons) and for positively charge particles (protons)? 5. Describe the principle of a Synchrotron and explain the basis for its name. 6. How do we detect charged particles is used to detected them and measure their charge and velocity? Peter Paul 10/20/05 PHY313-CEI544 Fall-05 52