Modern Accelerators for High Energy Physics

Transcription

1 Modern Accelerators for High Energy Physics 1. Types of collider beams 2. The Tevatron 3. HERA electron proton collider 4. The physics from colliders 5. Large Hadron Collider 6. Electron Colliders A.V. Tollestrup Aug. 2004

2 6 different colliders Pbar-P P- P Heavy Ion e+/- Proton e + - e - Linear e + e - Tevatron FNAL LHC at CERN RHIC BNL HERA DESY B-factories NLC TESLA CLIC 1.96 TeV 14 TeV 100 GeV/nucleon 30 GeV e by 920 GeV P 2 x B mass 9.4 GeV 500 GeV cm to 5 TeV cm They interact with each other by means of the bosons. The photons carry the electromagnet force, the gluons, the strong force and the W/Z the weak force. The quarks and leptons shown at left behave like point particles! ACCELERATORS ONLY ACCELERATE CHARGED PARTICLES! The electrons are the only point particles that accelerators in the above table can accelerate. Protons are composites ( u, u, d) and Nuclei are even more complicated as they are composed of neutrons and protons.

3 Tevatron proton and anti proton collision LHC: anti proton replaced by a proton Electron collider Proton U U D Quarks gluons Anti proton U U D Anti quarks gluons e + e - p n p n n p n p p n p n n p n p HERA e p collider Proton Z protons N neutrons Z protons N neutrons U U D quarks e + / - RHIC HEAVY ION COLLIDER

4 COLLIDE TWO PARTICLES AND WATCH TEHM SCATTER P4 P1 P2 Probability Scatting probability P3 SCATTERING OF TWO PARTICLES: KINEMATICS FIXED BY THE CONSERVATION OF ENERGY AND MOMENTUM λ = h/ p High momentum makes short wavelength 0 O ANGLE 180 O BEAM A BEAM B

5 COLLIDE TWO PARTICLES AND MAKE NEW PPARTICLES E=MC 2 Beam a P1, E1 Beam b P2, E2 PARTICLES a AND b COLLIDE AND INTERACT STRONGLY MAKING NEW PARTICLES. IF P1 = - P2, THEN THE TOTAL ENERGY AVAILABLE IS E1 +E2. THE PROPERTIES OF THE NEW PARTICLES ARE MEASURED IN THE DETECTOR. FOR THE ACCELERATORS WE LISTED ON SLIDE 1, THERE ARE FOUR CASES. 1. Positron-electron colliders. Point like particles collide and convert all of their energy into new particles. SLC, LEP and B-Factories. 2. HERA: e P collider. Point electrons collide with quarks inside the proton. 3. TEVATRON: pbar p collider. Quarks inside proton collide with anti quarks in the anti proton. 4. RHIC: Heavy Ion Collider. Complex collision!

6 Distribution of momentum in the proton SCATTERING e P electron u u d proton Jet of particles Scattered electron Relative Probilit y Fraction of proton momentum PRODUCTION OF NEW PARTICLES q qbar Production and decay of a top quark top b quark Lifetime ~ sec. U Ubar top W boson top bar Decays to an electron and neutrino 10.5%

7 DETECTORS A DETECTORS USE CONSERVATION OF ENERGY AND MOMENTUM TO RECONSTRUCT WHAT HAPPENS IN A COLLISION: 1. QUARKS CLOTH THEMSELVES AND TURN INTO HADRONS ( STATES OF 3 QUARKS) OR MESONS (QUARK ANTI QUARK PAIRS). 2. SINCE ENERGY AND MOMENTUM MUST BE CONSERVED, THE SHOWER OF MESONS AND HADRON AROUND THE QUARK DIRECTION CARRY THE MOMENTUM AND ENERGY OF THE ORIGINAL QUARK. WHEN THE MESONS AND HADRONS PASS THRU A SOLID THEY LOOSE A FRACTION OF THEIR ENERGY BY IONIZING THE ATOMS. THIS IONIZATION CAN BE MEASURE ELECTRONICALLY AND CAN BE CALIBRATED TO GIVE THE TOTAL ENERGY OF THE ORIGINAL QUARK. 3. HIGH ENERGY PHOTONS LOOSE ENERGY BY MAKING SHOWER OF e + e - in a HIGH Z MATERIAL. THE INTERACTION OF THE ELECTRONS WITH THE MATERIAL MAKES SCINTILLATION LIGHT OR IONIZATION. EITHER CAN BE DETECTED ELECTRONICALLY. 4. SINGLE MUONS OR ELECTRONS CAN BE MEASURED BY BENDING THEM IN A MAGNET FIELD AND MEASURING THE RADIUS OF CURVTURE OF THE TRAJECTORY WHICH IS PROPORTIONAL TO THE MOMENTUM. B C 3 position measurements will determine the curvature. High precision measurement of momentum requires many more than 3 points.

8 HOW TO MEASURE A PARTICLES TRAJECTORY TRACKING CHAMBERS SILICON TRACKERS TRACK IONIZES THE GAS ATOMS AND THE ELECTRONS DRIFT TO THE WIRES AND MAKE AN AVALANCH. MEASURE THE DRIFT TIME TO GET DISTANCE FROM THE WIRE E WIRE PLANE -- HV THE PARTICLE PASSES THRU THE SILICON MAKING ELECTRON-HOLE PAIRS. THE CHARGE IS COLLECTED ON THE STRIPS THAT ARE SPACED MICRONS AND CAN BE 10 CM LONG. THE SILICON IS MICRONS THICK. THE SIGNAL IS ABOUT 1 mv SO EACH STRIP MUCT BE DIRECTLY CONNECTED TO AN AMPLIFIER.

9 CDF DETECTOR FNAL

10 CDF DETECTOR END VIEW

11 CDF DETECTOR END VIEW

12 CDF DETECTOR END VIEW

13 Jet event from cdf

14

15 Gold-gold cllision RHIC STAR detector

16 CMS DETECTOR CERN/LHC

17 CMS DETECTOR CERN/LHC

18 ATLAS CERN/LHC

19 MACHINES 1. TEVATRON 2. LHC 3. ELECTRON MACHINES OF THE FUTURE

20

21 HERA e P COLLIDER, HAMBURG HERA e P RADIUS 1 km 30 GeV e 920 GeV P

22 C = 27 km Originally LEP e+ e- RING 100 X 100 GeV Now replaced by LHC p p collider 7 x 7 TeV SC magnets 8.3 T Start to commission 2007 LHC LAYOUT

23 The Tevatron THE TEVATRON WAS THE FIRST ACCELERATOR TO USE SC MAGNETS. IT IS THE HIGHEST ENERGY SYNCHROTRON SOME STATISTICS: 1. COLLIDES PROTRONS WITH ANTI PROTONS 980 X 980 GeV METER DIPOLES AND 200 FOCUSING QUADRUPOLES. 3. CIRCUMFERENCE 6.28 km. 4. PROTON BEAM 36 BUNCHES 2.8 E 11 / BUNCH PBAR BEAM 4.6 E 10 / BUNCH 5. TWO LARGE DETECTORS CDF AND D0. 6. PBAR P COLLISIONS PER SEC. = 4 E t tbar PAIRS MADE PER SECOND = 4 e -4. RATIO 10 10!! 7 ENERGY STORED IN A SINGLE BEAM IS ALMOST 1 MJ. 8 ENERGY TO QUENCH A MAGNET IS A FEW mj/cc FOOT MODEL MAGNETS FIRST BEAM JULY FIRST PBAR P COLLISIONS OCT TOP DISCOVERY 1995.

24 j x B Azimuthal compression B B= 4 T Coils carry current perpendicular to plane of drawing 1200 kg 1200 kg -j _ + +j Energy stored Per magnet 1 e 6 J Cross section of Tevatron Magnet Coil

25 COILS FOR MODEL MAGNET

26 1 FOOT LONG MODEL MAGNET 1976

27 Applying Steel Banding 1975

28 R. R. WILSON WINDING A COIL 1976

29 TEVATRON MAGNET CROSS SECTION FIRST BEAM JULY 3, 1984

30 Cross section of LHC

31 FLUX LINES IN THE LHC MAGNET.

32 WHY DO WE NEED HIGHER ENERGY? OVER THE PAST 50 YEARS ACCELERATORS HAVE EXPLORED THE ENERGY RANGE FROM 1 MeV IN NUCLEAR REACTIONS UP TO ABOUT 500 GeV AT THE TEVATRON. WE HAVE A REMARKABLY ACCURATE THEORY TO PREDICT AND EXPLAIN WHAT WE SEE AT PRESENT. BUT: 1. THERE IS NO UNDERSTANDING OF MASS. QUARKS RANGE FROM A FEW MeV FOR THE u/d TO 180 GeV FOR THE TOP. WHY? 2. WHY ARE THERE SO MANY DIFFERENT PARTICLES (57)? ARE THERE MORE? SOME THINK SO HIGGS AND SUSY WOULD DOUBLE THE NUMBER AND RESTORE A SYMETRY BETWEEN FERMIONS AND BOSONS. 3. WHERE DID ALL THE ANTI MATTER GO? WHAT IS DARK MATTER? 4. WE DON T EVEN KNOW HOW MANY DIMENSIONS WE LIVE IN! HOW CAN ONE HAVE A THEORY OF PARTICLES IF ONE DOESN T EVEN KNOW WHAT OUR SPACE IS LIKE? WE DON T UNDERSTAND DARK ENERGY

33 Consistency of Standard Model Parameters Winter 2004 Measurement Fit O. meas O fit /σ meas α (5) had (m Z ) ± m Z [GeV] ± Γ Z [GeV] ± σ 0 had [nb] ± R l ± A 0,l fb ± A l (P τ ) ± R b ± R c ± A 0,b fb ± A 0,c fb ± A b ± A c ± A l (SLD) ± sin 2 θ lept eff (Q fb ) ± m W [GeV] ± Γ W [GeV] ± m t [GeV] ± THE PLOT AT THE LEFT SHOWS (MEAS-FIT) / SIGMA. OF THE 17 PARAMETERS ONLY 5 DEVIATE BY MORE THAN 1 STANDARD DEVIATION FROM OVERALL FIT TO THE STANDARD MODEL

34 5. WHAT IS DARK MATTER AND DARK ENERGY?

35 THE STANDARD MODEL DOESN T ANSWER THESE QUESTIONS. HOWEVER, IT DOES STRONGLY SUGGEST THAT AT ENERGIES OF THE ORDER OF 1 TeV IN THE CM THAT SOME KIND OF NEW PHYSICS WILL EMERGE. THE TEVATRON IS PUSHING THIS LIMIT NOW. THE LHC WILL EXPLORE IT IN SOME DETAIL. THERE ARE THOUSANDS OF PAPERS BY THEORITICAL PHYSICISTS SUGGESTING DIRECTIONS THAT NATURE COULD TAKE, BUT UNTIL WE HAVE MORE EXPERIMENTS TO GUIDE THE WAY, IT WILL REMAIN UNKNOWN TERRITORY! WHAT ACCELERATORS ARE BEING PLANNED? 1. A LINEAR e+ e- COLLIDER WITH Ecm ABOUT 1 TeV. TWO TECHNOLOGIES EXIST. CHOICE BEING MADE BY AN INTERNATIONAL SELECTION COMMITTEE. (TESLA SC CAVITIES AND NLC COPPER CAVATIES.) 2. A VERY HIGH CURRENT LOW ENERGY PROTON ACCELERATOR TO MAKE MORE INTENSE NEUTRINO BEAMS.

36 ELECTRONS ELECTRONS RADIATE LIGHT WHEN BENT BY A MAGNET!!! 1 e a γ v W= where a= πε0 c ρ For instance for a ring with radius 1 km like the Tevatron or HERA 1 TeV protons radiate about 9 ev / Turn. The electrons in the HERA electron ring have an energy of 30 GeV and radiate about 70 MeV / Turn! LEP AT 100 GeV PER BEAM RADIATED ABOUT 2 GeV / TURN FOR A TOTAL RADIATED POWER OF THE ORDER OF 5 MW! High energy electron accelerators above 50 GeV are straight!

37 NLC TESLA Warm RF cavities SC RF cavities

38 NLC TESLA

39 So? Experiments are needed to guide theory and new machines will provide the necessary tools. Machines have become very expensive $ n Each HEP lab can no longer go its own way. Machines are becoming a world effort. The US must improve its skills as a host country. We need to interest students in accelerator science. Very exciting connection between the large universe km and quarks cm. MAYBE IN 20 YEARS WE WILL KNOW HOW MANY DIMENSIONS WE LIVE IN, WHY WE HAVE MASS AND WHERE ALL THE ANTI PARTICLES WENT.