北京 , 2002. 5. 19

北京北京 , 2002. 5. 19., 2002. 5. 19. 北京北京 , 2002. 5. 19., 2002. 5. 19. 中国科学院高能物理研究所中国科学院高能物理研究所 , , 黄光顺黄光顺中国科学院高能物理研究所中国科学院高能物理研究所 , , 黄光顺黄光顺

http://pony2.ihep.ac.cn/~besr/ppt/hepintro.ppt


高能物理又称粒子物理，是研究物质的基本组元和它们之间相互作用规律的一门学科。

高能是指研究粒子物理需要高能加速器实验手段，能量一般大于 1 GeV (10 9电子伏 ) 。

高能物理研究的内容涉及到基本的物质结构及其相互作用规律，因而在人们认识世界和改造世界过程中起

到很大作用。她始终处于科学的前沿。 “ ” 她总结出的标准模型是物理的基础。她把人们的认识水平推进到 10 –19 米。

什么是高能物理？


10 7 m (10000000米 )

Large structures and Orders of Magnitude

地球


Sun (Eclipse)

corona

10 9 m

Sun ≈ 2x1030 kg ≈ 1057 (protons + neutrons)

nucleons


10 11 m

Earth Orbit


Milky Way (银河系 )


Spiral Galaxy

100 000 light years = 10 21 m

10 11 stars


Spiral Galaxy

100 000 light years = 10 21 m

10 11 stars


Hubble Deep Field


A Foamy Universe (bubbles 200 Mly across)


10 21 m 10 22 m 10 23 m

10 24 m 10 25 m 10 26 m

10 11

galaxies

10 22

stars

Summary of the largest structures

1080

nucleons


客体尺度与观测手段


Dominated by Matter and Gravity ** (1011 galaxies, 1022 stars)

Described by General Relativity (or Newtonian Mechanics)

** This is far from the whole truth !!


Where it all came from

15 billions = 1.5 x 10 12

years ago and since then ever expanding


Will the Expansion ever stop ?

Inflation predicts a flat universe. This means that the Density of Matter and Energy equals the so called critical density Ordinary Matter can account for only up to

5% of the critical density

Dark Matter Problems


The First Dark Matter problem: these Galaxies should simply not exist !

Need a spherical halo of matter around the galaxySo: is thereinvisible (dark) matteraround the galaxy ?


speed

200km/s

distance from center

predicted

measured


Gravitational lensing

Distant galaxy

Foreground cluster

Observer

109 light years

2x 109 light years


Large amounts of invisible (dark) matter Can NOT be ordinary matter : - does not interact with light - does not interact with ordinary matter - does concentrate around galaxies and in galaxy clusters.

What is it ??? If the answer is Super Symmetric Particles,

How can we find it? LHC !!


The Second Dark Matter problem: The dark matter seems to make up only 30-50% of the critical density This may be linked with observations of a possible accelerating expansion of the universe at large distances. Study of type 1a Supernovae (1a Supernovae ≈ standard light sources)


1a Supernova:

white dwarf accompanying star


Far away* supernovae seem to be too far away ! Very difficult observations, but if true could mean: Resurrection of Einstein’s Cosmological Constant, or “Qintessence” - one more possibility of

Exotic Matter ???? Need more astronomical data Need more powerful accelerator for a better understanding of dark matter * for specialists - red shifts z ≈ 1


Matter

Anti Matter What happened to the Anti Matter ?


Electrons (10-18 m ) 电子

Atom nucleus nucleon quark 原子核子 (质子 ,中子 ) 核子夸克

10-10 m 10-14 m 10-15 m 10-18 m

物质的组成单元see


“ ” “ ”有味道和颜色的夸克

六味

三色


Ingredients of the Standard Model

To explain all matter we need three generations of quarks We also have three generations of leptons.

THE COMPLETE PICTURE: Quarks Leptons

charges: 2/3 -1/3 0 -1 up down e electron (e) charm strange muon ()

top bottom tau Two different sorts of Matter particles: -composite particles made up of quarks (called HADRONS) -non composite particles like electrons and neutrinos (LEPTONS)

粒子物理标准模

型


u

d

c

s

t

b

e

e

Charge

+2/3

-1/3

0

-1

quarks (q)

leptons

“Fundamental” Matter Particles

heavier


Stable (ordinary) matter:

one up quark (charge +2/3)

one down quark (charge -1/3)

one electron (charge -1)

one neutrino (no charge, “no” mass)

proton

neutron

But for what do we need the neutrino??

leptons

composite particles

nucleons


Can not use light microscopes to study atoms !!!

Quantum mechanics tells us that particles behave like waves and visa versa:

h/p

Use electron microscopes

为什么需要加速器？高能加速器是威力巨大的

” “ 电子显微镜

electron


electron

quark

New Stuff from E = Mc2

New, unstable particles, can NOT be explained as made up of up and down quarks only.

High Energy electron-proton scattering


Einstein: E = Mc2

pc

use units such that c =1 E (GeV or MeV) p (GeV/c or MeV/c) M (GeV/c2 or MeV/c2)

M0c2 Mproton = 0.931 GeV/c2 ≈ 1 GeV/c2

Melectron = 0.5 MeV/c2

( Mtop = 170 GeV/c2 )

proton diameter = length scale: 10-15 m = 1 fermi (femtometer)

E

Special Relativity: ( E2= (pc)2 + (M0c2)2 )


Creating New Matter with Accelerator

Need two more generations of quarks


electron (energy U)

U= 1 eV = 1.6x10-19J (speed at positive plate 18 000 km/s)

1 keV = 103 eV 1 MeV = 106 eV 1 GeV = 109 eV 1 TeV = 1012 eV BEPC = 3 GeV LEP = 209 GeV LHC = 14 TeV

Practical Units

- +

1 Volt


自然界中的四种相互作用

重力

弱作用

强作用

电磁作用


Forces of Nature

name of field (wave) force carrier (particle) gravitational field graviton (?) electromagnetic field (a) (photon) weak field Z0, W+, W- strong (color) field 8 gluons, g higgs field (*) h0, H0, H+, H-.. (*)Unifying the weak and the electromagnetic fields giving mass to the Z and the W’s - all other particles !!! (a) Electric and Magnetic Fields Unified by Maxwell (1864) Big Question: Can all Force Fields be unified ?

(*)


the Strong Field (gluons) couple to Quarks the Weak field (W’s and Z) couple to Leptons the Electromagnetic field couple to Charge

(classical: F = qE) the Gravitational field couple to Mass

(Newton: F = mg) the Higgs field couple to Mass ! ! ! In fact the Higgs field is responsible for the mass ! Can detailed studies of large number of Higgs Particles give us the explanation why we have three families of quarks and leptons, and why they have such enormous mass differences ??

How the forces work Higgs粒子存在吗？


q q q

Composite Matter Particles (hadrons) made out of quarks ( q ) and anti quarks ( q )

Baryons Mesons

q q q q q

Anti Baryons Hundreds of possible

combinations or particles

hadrons


Higgs Hunting with LEP (Total energy 206.6 GeV)

e- e+H (115 GeV)

Z (91 GeV)

two Higgs jets containing B-particles

two Z jets

2.5 effect for a Higgs Particle at 115 GeV

(e- + e+) -----> (Z0 + H) -----> 4 jets


ALEPH DELPHI


How the forces vary with distance

Classical electrostatics (Coulomb’s law):

F = k (q1 q2)/r2

Classical gravitation (Newton):

F = (M1 M2)/r2

In a quantum field theory the “constants” k and will vary with energy (Vacuum Polarization)

Is it possible that all the forces of Nature have the same strength at a certain (very high) energy?


The “strength” of the strong force (running of the Coupling “Constant” S)


Unification of the Coupling Constants in the SM and the minimal MSSM


Unification of Gravity with the other forces From a simple extrapolation this should happen at an energy scale of 1019 GeV or a length scale of 10-35 m

But only superstring theory is capable of unifying all the forces. Superstring theory contains supersymmetry. Superstrings are objects with 1 spatial dimension moving in a world of 9, but where all but three dimensions are curled up on an unobservable scale ! The # of dim. for the EM field is tested to be 3 down to 10-18 m, but gravity is tested only down to mm scale ! ! Is unification of all the forces possible at the TeV scale ?


How many macroscopic dimensions can we “see”?

gravitation and light (electromagnetism) tell us: three macroscopic dimensions

In N dimensions: field lines spread out, i.e. field weakens as

1/rN-1



Particles as Super Strings

Strings and extra dimensions:

.. . .

Two-dimensional (“normal”) Space

Extra Dimension Graviton


1 mm

1 mm

billions of light years

Parallel universes gravity curled up at millimeter scale

Gravity from galaxy on neighboring sheet may be weakly felt


1 mm

1 mm

One universe (folded) Gravity from galaxy on neighboring sheet (mm distance ) can be weakly felt. Light has to go billions of light years.

billions of light years


高能加速器和探测器规模巨大

欧洲核子中心 LEP/LHC 储存环直径 9 公里！


建造中的 ATLAS 探测器


北京正负电子对撞机（ BEPC）鸟瞰图


北京正负电子对撞机（ BEPC）示意图

注入器长 202米

储存环的周长为 240.4 米

对撞能量 2-5GeV 物理目标


侧面

图

端面

图

7X6X7米 3， 500吨


北京谱仪轻子质量测量精度比国外平均水平提高 10倍，下图是质量、探测器探测效率和最大似然函数值的三维图像


北京谱仪 R值测量： 2-5 GeV能区 R值精度比国外平均水平提高 2~3倍，意义重大影响深远。


妙趣横生的高能物理！

仍需探索的问题：物质的最小单元是什么？质量的起源在哪里？轻子和夸克为什么有三代？它们的质量差别为什么那么大？中微子究竟是否存在？反物质、暗物质的疑问？有没有其他形式的物质？

几十年来高能物理实验研究和理论探索对提高人类认识水平作出了重大贡献。从 1901 年开始颁发诺贝尔奖起，已有一百多位物理学家获得了诺贝尔物理奖，其中有 41位与粒子物理有关，是物理学中获诺贝尔奖最多的一门分支。

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北京 , 2002. 5. 19