1、季向东季向东 上海交通大学上海交通大学Outline Particle CosmologyWIMPs 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,ext
2、ra 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 earl
3、y universe is an important lab for particle physics The Cooking recipeAssuming Standard Cosmology+(nearly)thermal equilibriumThe third magic assumption!Throw in some particles,everything that we know,quarks+leptons+.,forming the energy-momentum density Solve the Einstein equation.Particle and intera
4、ctions gravity weak strong e/mQuarks Lepton+(W,H+)Neutrinos (Z,H0)Photons Gluons Gravitons Symmetries:spacetime+gauge symmetries+otherThere are unknowns Heavy particles that live short.In the GUT model,there are GUT scales multiplets which play important role in the very early universeHeavy right-ha
5、nded neutrinosParticles that are weakly interacting and live long AxionsSterile neutrinosGravitino WIMPs.Particles that live longElectron:lightest charged particle(charge conservation)Proton:baryon number symmetry breaking interaction is small.Neutrinos:lightest fermionPhoton and graviton:cannot dec
6、ay due to energy-momentum conservationParticles that drop out of thermal equilibrium Standard Boltzmann equation approachDepend on the rate of annihilation and recombinationCan trace out particles cosmic history fairly accurately Baryon Asymmetry and Leptogenesis Understanding baryon-antibaryon asym
7、metry in the present universe,why matter dominates over antimatter?Heavy right-handed neutrino required by seasaw might play a very important roleConstraint on the CP violation parameter in the lepton sector What is dark matter?AxionSterile neutrinosGravitinosWIMPs Non-particle possibilities Graviti
8、no 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 inflationGravitino will be regenerated through reheating process.If gravitino decays,its life
9、 time will be around M2pl/M3,which could affect BBN.Gravitino dark matter?If gravitino is the lightest supersymmetric particle,it lives longHowever,decay(to gravitino)of the next-to-the lightest supersymmetric particles can affect BBNThis problem can be solve through small R-parity breaking decays,w
10、hich lead to a gravitino with life time much longer than that of the universe.WIMPsWIMPs 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 Reli
11、cs in the UniverseT M,WIMPs in thermal equilibrium T M,number density becomes Boltzmann suppressedT M/20,Hubble expansion dominates over annihilations freeze-out occursPrecise temperature at which freeze-out occurs,and the density which results,depends on the WIMPs annihilation cross sectionWIMP Mir
12、acleTo 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 interaction
13、s,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 WIMPsCollider searchIndirect searchDirect searchReview by 倪凯旋（上海交通大学）PandaX ExperimentAn experiment that designed to look
14、 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 experimentFormed in 2009Shanghai Jiaotong UniversityShanghai Institue of Applied Physics,CASShangdong UniversityPeking University(University
15、 of Maryland)The technologyPandaX:Particle AND Astrophysical Xenon TPC can be used for both dark matter search and double beta decay searchFollowing 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 collect
16、ion efficiency so as to enhance the sensitivity to low-mass WIMPs 2.It can accommodate a ton-scale experimentPandaX 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 jinp
17、ing 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summaryGreat things happen now at the intersection of particle physics and cosmologyA lot of challengeCosmological constantDark matterGrand unification?Extra dimension?
