Transcript ppt
季向东
上海交通大学
PARTICLE COSMOLOGY
Outline
Particle Cosmology
WIMPs Miracle
PandaX
What is particle cosmology?
Can particle physicists say something about
cosmology? Or vice versa, can cosmologists
say something about particle physics?
Particle Physics = Standard Model
+ a bunch of untested ideas
(planck scale, GUT, SUSY,
extra dimension, LR symmetry,
techni-color, little Higgs…)
Importance issues
What is dark matter? Why there is 23% dark
matter?
Why there is 4% baryonic matter?
Can particle physicists say something about
cosmological constant?
Other questions:
What is the role of neutrinos?
Particle physics from cosmology? The early
universe is an important lab for particle physics
…
The Cooking recipe
Assuming Standard Cosmology + (nearly)
thermal equilibrium…
The third magic assumption!
Throw in some particles, everything that we
know, quarks+leptons+…., forming the energymomentum density
Solve the Einstein equation.
Particle and interactions
gravity
weak
strong
e/m
Quarks
Lepton+
(W, H+)
Neutrinos
(Z, H0)
Photons
Gluons
Gravitons
Symmetries: spacetime + gauge symmetries +
other
There are unknowns
Heavy particles that live short.
In the GUT model, there are GUT scales multiplets
which play important role in the very early universe
Heavy right-handed neutrinos…
Particles that are weakly interacting and live
long
Axions
Sterile neutrinos
Gravitino
WIMPs
...
Particles that live long
Electron: lightest charged particle (charge
conservation)
Proton: baryon number symmetry breaking
interaction is small.
Neutrinos: lightest fermion
Photon and graviton: cannot decay due to
energy-momentum conservation
Particles that drop out of
thermal equilibrium
Standard Boltzmann equation approach
Depend on the rate of annihilation and
recombination
Can trace out particle’s cosmic history fairly
accurately
Baryon Asymmetry and
Leptogenesis
Understanding baryon-antibaryon
asymmetry in the present universe, why
matter dominates over antimatter?
Heavy right-handed neutrino required by
seasaw might play a very important role
Constraint on the CP violation parameter in
the lepton sector
What is dark matter?
Axion
Sterile neutrinos
Gravitinos
WIMPs
…
Non-particle possibilities
Gravitino dark matter?
Because of its weak gravity coupling,
gravitino decouples from the rest of the world
very early, left with a huge quantity (it must
be very light to avoid over-closure).
It can be diluted through inflation
Gravitino will be regenerated through
reheating process.
If gravitino decays, its life time will be around
M2pl/M3, which could affect BBN.
Gravitino dark matter?
If gravitino is the lightest supersymmetric
particle, it lives long
However, decay (to gravitino) of the next-tothe lightest supersymmetric particles can
affect BBN
This problem can be solve through small Rparity breaking decays, which lead to a
gravitino with life time much longer than that
of the universe.
WIMPs
WIMPs are particles that have mass on the
order of electroweak symmetry breaking
scale and has only weak interactions
WIMPs has long life-time due to certain
symmetry
Z2 symmetry, U(1) symmetry
R-parity
Dark Matter Relics in the
Universe
T ≫ M, WIMPs in thermal
equilibrium
T < M, number density
becomes Boltzmann
suppressed
T ~ M/20, Hubble expansion
dominates over annihilations
freeze-out occurs
Precise temperature at
which freeze-out occurs, and
the density which results,
depends on the WIMP’s
annihilation cross section
WIMP Miracle
To understand the percent of DM energy in the
universe today, we need the DM particles having
annihilation cross sections on the order of
~ 10-40 cm2
Therefore, apart from the gravitational
interactions, the DM particles probably have
weak interactions as well!
If DM particles do have weak interactions, they
may have something to do with the electroweak
symmetry breaking!
WIMP Miracle might be the most exciting
thing the cosmology teaches us about
particle physics!
Searching for WIMPs
Collider search
Indirect search
Direct search
Review by 倪凯旋(上海交通大学)
PandaX Experiment
An experiment that designed to look for
WIMPs through direct search
PandaX collaboration (30+ people)
上海交通大学
中科院上海应用物理研究所
山东大学
北京大学
We are considering other institution to join from China
and US
PandaX experiment
Formed in 2009
Shanghai Jiaotong University
Shanghai Institue of Applied Physics, CAS
Shangdong University
Peking University
(University of Maryland)
The technology
PandaX: Particle AND Astrophysical Xenon TPC
can be used for both dark matter search and
double beta decay search
Following the preceding experiments: Zeplin,
XENON, and LUX, build a state-of-art large size
xenon dual phase TPC detector.
Two features:
1. It emphasizes light collection efficiency so as to
enhance the sensitivity to low-mass WIMPs
2. It can accommodate a ton-scale experiment
PandaX 实验是怎么工作的?
在一个大的、高纯度的容器装入2吨的氙、并冷
却到零下100度。
在液氙的上部和下部装上大量的光电管,可以
探测到单个光子
在液氙的中心加上10万伏的高压,单个电子可
以其中漂移80cm 以上
液氙必须不断更新提纯,去除从容器壁渗进的
杂质。
探测容器必须放在高真空和由聚乙烯和铅做成
的上百吨的屏蔽体中。
整个实验必须放在至少2公里深的地下。
Layout of jinping lab
PandaX 实验进展
PandaX 首个100公斤级探测器设计已经完成,
正在建造中,预计6月可以完成。
已购买了所有的光电管和500公斤氙气
十万伏高测试正在进行中
屏蔽体设计已经完成,正在采购材料, 准备
安装
电子学信号采集系统正在建设中
Sensitivity plot
PandaX funding
科技部973
自然科学基金委
上海交通大学
山东大学
北京大学
summary
Great things happen now at the intersection
of particle physics and cosmology
A lot of challenge
Cosmological constant
Dark matter
Grand unification? Extra dimension?