Study On Dark Matter Search

Variety of evidences from astrophysical and cosmological observations confirm that there are a large number of non-baryonic dark matter in the universe,whose mass accounts for nearly 85%of the total mass of the matter in the universe.ACDM is an extremely successful model for the large scale structure of the uni-verse,but does not correctly reproduce the observed structure at the galactic and sub-galactic scales.In order to solve the problems of matter-antimatter asymme-try and hierarchical structure,etc.,which cannot be answered by the standard model,people have proposed a variety of beyond-standard models,such as super-symmetry model,extra dimensions model and littlest Higgs model.These new models can also give the candidate particles that satisfy the characteristics of dark matter.Nowadays,the study of the nature of dark matter has become one of the most important issues in the frontier of modern cosmology and particle physics.In this paper,we study the issues related to dark matter based on the direct detection and collider detection of dark matter.The method of direct detection experiments is to measure the small recoil energy of a nucleus in an underground detector after a collision with a dark matter particle.Weakly interacting massive particles(WIMPs)are one of the most popular dark matter candidates.In the more than 30-year history of dark matter direct detection,only DAMA,CRESST-II,CoGeNT and CDMS-II-Si have reported potential dark matter signals,while other experiments have only presented null results and given the upper exclusion limit of the dark matter in mass-cross section parameter spaces.In order to reconcile the conflicts among the experiments,several mechanisms have been proposed,such as isospin-violating interactions,inelastic scatterings,the light mediators and non-stand halo model,etc.As with the direct detection,dark matter has to interact sufficiently strongly with the standard model particles to yield observable signatures at colliders.Future election-positron colliders with high luminosity,high precision and clean environment can play an important role in detecting dark matter and new mediators.Dark matter collider detection experiments are independent of the dark matter distribution,and can complement and check with the results of direct detection experiments.The main research contents of this paper are as follows:(1)We investigate the compatibility of the event excess observed by the CDMS-?-Si experiment in 2013 with the latest constraints from DarkSide-50 and XENON1T in an extended effective operator framework with isospin violating interaction and light mediators.We consider three different situations corresponding to three sets of parameters:?=-0.7,m?=200 MeV;?=-0.7,m??1 MeV;?=-0.82,m?=1 MeV.In the situation of spin-independent interaction,we find that XENON1T and DarkSide-50 are complementary to each other in limiting the theory.Fixing the isospin-violation parameter at ?=-0.70(-0.82),the constraint from XENON1T(DarkSide-50)is maximally weakened.For the type-I operator,when we choose ?=-0.7 and m?=1 MeV,DarkSide-50 can give more stringent constraints in the region mx?20 GeV;when we choose ?=-0.82 and m?=1 MeV,DarkSide-50 can give stringent limits in a smaller range mx?5 GeV.For the type-II and type-III operators,we obtain the similar conclusions.We find that for isospin violating interaction with light mediator there is no parameter space which can be compatible with the positive signals from CDMS-II-Si.As a concrete example of the general dark matter model,we investigate the dark photon model in detail.In the(mA',?)plane,we show the new upper limits on the kinetic mixing parameter ?.We find that for dark matter mx<6 GeV,DarkSide-50 can give more stringent upper limits in the dark photon mass range[1 MeV,1 GeV].In the(mx,mA')plane,we also show the new limits on the parameters of dark matter and dark photon.(2)The dark sector may consist of not only dark matter but also of one or more new force-carrying mediators which couple to the standard model particles.The mediators can be vector A',scalar ?,pseudoscalar a,axial-vector Z' and even fermions N.We investigate the production of the dark photon A' and the dark scalar mediator ? via the processes e+e-?qqA' and e+e-?qq? at future electron-positron colliders,and we calculate the cross section and analyze the kinematic distributions.We find that the kinematic distributions of the two-jet system in the final state can be used to identify the dark photon and the dark scalar mediator,by imposing appropriate kinematic cuts.Then we investigate the discovery potential of the dark photon at CEPC with the hypothesis that dark photon interact only with dark matter and standard model quarks.We choose DM mass mx=8.6 GeV which is favored by CDMS-II-Si,and obtain the 90%C.L.upper limits of the combined parameter ???2 based on direct detection results,and analyse the branching ratios of A'? ??.We find that,with CEPC running at ?=91.2 GeV,it would be possible to perform a decisive measurement of the massive dark photon[20,60]GeV in less than one operating year.But in this assumption,for the higher ?,the cross section of the signal process will become smaller while the cross section of the background process will become larger.Therefore,with CEPC running at higher ?(such as ?=240 GeV),it would be difficult to discover this massive dark photon.