TeV能区物理

文章简要介绍研究TeV能区物理的意义、重要性和当前国际上的发展形势,以及清华大学粒子物理理论组为发展TeV能区物理研究所做的工作和取得的成果.     

TeV能区物理的进展

综述近年各种TeV能量对撞机的计划和建造情况,TeV能区物理的理论研究进展和TeV能区物理的发展前景.     

New physics at 1 TeV?

If decays of a heavy particle S are responsible for the diphoton excess with invariant mass 750 GeV observed at the 13 TeV LHC run, it can be easily accommodated in the Standard Model. Two scenarios are considered: production in gluon fusion through a loop of heavy isosinglet quark(s) and production in photon fusion through a loop of heavy isosinglet leptons. In the second case, many heavy leptons are needed or/and they should have large electric charges in order to reproduce experimental data on σ_{pp → SX} · Br(S → γγ).     

10TeV宇宙线时间变化研究

利用羊八井ASγ二期阵列实验数据,分析研究了10TeV宇宙线时间变化,以10.4σ和9.6σ的显著性发现了10TeV宇宙线流强气象效应修正后的半太阳日和太阳日周期变化,没有发现有恒星日变化.同时发现10TeV宇宙线流强有7天左右周期变化的迹象.     

观测来自银道面的TeV γ射线

给出来自银经79.3866°的银道面的TeV γ射线的观测结果.数据是在1995年10月至1998年11月间的晴朗无月夜,用兴隆站的大气契伦科夫望远镜ACT2和ACT3以向源–背景(ON–OFF)观测方式取得的,总观测时间为224.4h.在望远镜计数服从高斯分布的情况下,导出了最大似然比λ的表达式,它直接给出显著性水平的概率.用它分析观测资料,在统计误差范围内没发现有来自银道面的TeV γ射线.     

寻找10TeV能区的γ射线暴

利用西藏羊八井大气簇射实验数据,开展了对10TeV能区γ暴的全天区搜寻. 分析了4亿个簇射事例,找出在给定的时间间隔和给定的小天区内出现的簇射事例团. 采用等天顶角方法来估计背景. 有少量事例团显示了对背景的超出,但它们的显著性还不够高,尚不足以认定为γ暴. 讨论了羊八井二期阵列实验对寻找10TeVγ暴所具有的高灵敏度.     

Is strong gravitational radiation predicted by TeV gravity?

In TeV-gravity models, the gravitational coupling to particles with energies ∼ m _Pl ∼ 10 TeV is not suppressed by powers of ultra-small ratio /M _Pl with M _Pl ∼ 10¹⁹ GeV. Therefore, one could imagine strong synchrotron radiation of gravitions by the accelerating particles to become the most pronounced manifestation of TeV-gravity at LHC. However, this turns out to be not true: considerable damping continues to exist, only the place of /M _Pl is taken by a power of a ratio ϑω/ , where the typical frequency ω of emitted radiation, while increased by a number of γ-factors, cannot reach /ϑ unless particles are accelerated by nearly critical fields. Moreover, for currently available magnetic fields B ∼ 10 T, multidimensionality does not enhance gravitational radiation at all even if TeV-gravity is correct. The text was submitted by the authors in English.     

Leptonic Origin of TeV Gamma-Ray Emission from Crab Nebula

We study the nonthermal emission of the Crab nebula in the bands from radio to TeV γ-ray on a simplified timedependent injection model. In this model, relativistic electrons in the Crab nebula consists of two components and their injected spectrum is a broken power law with different indices and a break energy. The relativistic electrons emit nonthermal photons through synchrotron and inverse Compton scattering off soft photon fields inside the nebula. The resulting spectrum calculated with the model is well consistent with the observed data ranging from radio to very high energy γ-rays for the Crab nebula, where the emission from radio to medium γ-rays is from electron＇s synchrotron emission, whereas the emission above ～ 100 MeV primarily comes from the inverse Compton scattering of the relativistic electrons on synchrotron photons.     

ILC——TeV能量正负电子直线对撞机计划

 2004年8月20日,在北京举行的第32届世界高能物理大会结束的前两天,国际未来加速器委员会(ICFA)主席乔纳森·多芬(JonathanDorfan)在大会上宣布:国际未来加速器委员会已经批准了国际技术推荐专家委员会(InternationalTechnologyRecommendationPanel)的推荐,专家委员会正式推荐在未来的正负电子直线对撞机上采用"冷技术"。     

寻找来自原始黑洞蒸发的TeV γ射线暴

用兴隆站的两台大气切伦科夫望远镜ACT2和ACT3在1995—1997年间的观测数据,寻找来自原始黑洞(PBH)蒸发终态的0.1sTeVγ射线暴.分析这些资料没发现有这样的γ射线暴.据此估算出在太阳系附近、在99%的置信水平下原始黑洞的蒸发率-密度的上限为3×10⁸/年·pc3.     

10TeV宇宙线的太阳阴影与太阳活动的关联

利用1990年6月至1993年10月间采集的数据,西藏空气簇射阵列(海拔高度4300m)以5.7σ、7.1σ的显著性观测到了10TeV宇宙线的太阳阴影和月亮阴影;研究发现,行星际磁场效应使太阳阴影偏向西0.62°,南0.22°:仔细研究了太阳阴影与太阳活动及其不对称性的关联,对太阳阴影位置的偏转发其变化行为给出了新的定性解释.     

蟹状星云脉冲星的TeV γ射线周期发射

利用自行研制的两台大气切伦科夫望远镜(ACT2和ACT3),在1995年秋至1996年春的观测季节对蟹状星云脉冲星进行了168小时(ACT2)和126小时(ACT3)的跟踪观测.分析这些数据没有发现有月或天时间尺度稳定的33ms周期的TeVγ射线发射,但发现两段持续几十分钟的暴发样本具有33ms周期.     

2.76 TeV铅-铅碰撞中带电粒子的方位角分布

利用多源热模型分析了ATLAS实验组2.76 TeV 铅-铅碰撞中产生的、带电粒子在多个不同中心度事例中的方位角分布,并与n=2,4,6 和n=2 的傅里叶级数形式的方位角分布进行了比较。同时,利用由多源热模型得到的散射源在横动量空间的结构参数,计算了散射源在横动量空间的各向异性率和相对膨胀率,且与相关傅里叶系数进行了比较。在各个中心度区间,横动量空间的各向异性率和相对膨胀率都小于相应的傅里叶系数,椭圆各向异性是末态方位角分布中最主要的成分,其他成分的各向异性在各中心度区间的贡献不同且作用不可忽视。We analyze the azimuthal distributions of charged particles produced in 2.76 TeV Pb-Pb collisionsfrom ATLAS experimental group in eight different centralities by using the multi-source thermal model. Themodeling results are compared with the results from Fourier series forms with n = 2,4,6 and n = 2. Meanwhile,the anisotropy ratios and the relative expansion rates of scattering source in transverse momentum space are  calculated applying the transverse structural parameters of multi-source thermal model, and the modeling results are compared with the associated fourier coefficients. The anisotropy ratios and the relative expansion rates are less than the corresponding fourier coefficients in transverse momentum space in different center intervals. Elliptical anisotropy is main component in azimuthal distribution. Other anisotropies have different contributions in different centralities, and these contributions cannot be neglected.     

TeV γ 暴搜寻中最优窗口角半径的探讨

作为搜寻TeVγ暴最主要的观测手段—广延大气簇射阵列,其阵列角分辨值常用于确定搜寻窗口的大小.为了在一个合理大小的窗口内对TeVγ暴进行搜寻,本文从理论上推导出一个统计意义上的最优窗口角半径,然后用Monte Carlo方法进行了模拟验证.结合入射信号强度、背景强度、计算显著性的不同方法等因素,进一步对窗口角半径进行了讨论.并在小统计情况下,给出了计算显著性的经验公式.     

Is Low-Frequency-Peaked BL Lac Object OJ 287 a TeV Emitter？

It is well known that there are only two low-frequency-peaked BL Lac objects （LBLs： BL Lacertae and S5 0716＋714） and one flat spectrum radio quasar （FSRQ： 3C 279） among more than 30 active galactic nuclei （AGNs） with detected TeV emissions. We study the spectral energy distribution （SED） of a famous LBL OJ 287, whose light curve has a 12-y period. Using a homogeneous one-zone synchrotron ＋ synchrotron-self Compton model, we model the quasi-simultaneous broad-band SED of OJ 287. With some reasonable assumptions, we extrapolate the model to the high state of OJ 287 and predict its γ？ray emissions. Taking into account the absorption of γ-ray by the extragalactic background light （EBL）, we find that the TeV emission of OJ 287 in high state is slightly higher than the sensitivity of H.E.S.S. The study on SEDs of OJ 287 has implications to unveil the origin of jet activity during its 12-y period and the properties of EBL.     

寻找BATSEγ暴的TeV能区伴随γ暴

利用西藏ASγ实验三期阵列的重建数据，对25个BATSEγ暴的TeV能区伴随γ暴进行了符合寻找。在BATSEγ暴方向的90％误差范围内，找出在给定的小天区和时间间隔内出现的显著性较高的TeV事例团，并采用“等天顶角方法”来估计背景。发现少量事例团对背景有明显超出，考虑试验次数后，其超出还不足以认定为γ暴。通过Monte Carlo模拟给出了95％置信水平下流强上限的估计值为7．1×10^-9photons／（cm^2·s）。Searching for TeV burst-like events coincident with the BATSE GRBs data was made by using the ASγ （Tibet-Ⅲ） data. In the period we analysed, there were 25 BATSE GRBs in the field view of Tibet. A search region was defined by the BATSE 90% confidence level positioning error. A GRB candidate was chosen as a shower cluster appearing in a given small sky window and a given time interval. An equi-zenith-angle method was used to estimate the background. No significant TeV GRBs were detected. The flux upper limit at the 95% confidence level was estimated to be about 7.1×10^-9 γ（cm^2·s） by Monte Carlo simulation.     

用地面阵列寻找TeV能区γ点源的方法探讨

文中探讨搜寻TeV能区γ点源的方法.讨论利用student变量t判断来自源区及背景区宇宙线事例的统计差别,并由Bayes定理与MonteCarlo模拟相结合计算源区各能段的信号数,推算蟹状星云在TeV能区的γ射线微分能谱     

Dijet azimuthal decorrelations in pp collisions at √s=7 TeV

Measurements of dijet azimuthal decorrelations in pp collisions at √s=7 TeV using the CMS detector at the CERN LHC are presented. The analysis is based on an inclusive dijet event sample corresponding to an integrated luminosity of 2.9 pb?1. The results are compared to predictions from perturbative QCD calculations and various Monte Carlo event generators. The dijet azimuthal distributions are found to be sensitive to initial-state gluon radiation.     

Dijet angular distributions at \sqrt{s}=14 TeV

We present a Monte Carlo study of dijet angular distributions at $\sqrt{s}=14$  TeV. First we perform a next-to-leading order QCD study; we calculate the distributions in four different bins of dijet invariant mass using different Monte Carlo programs and different jet algorithms, and we also investigate the systematic uncertainties coming from the choice of the parton distribution functions and the renormalization and factorization scales. In the second part of this paper, we present the effects on the distributions coming from a model including gravitational scattering and black hole formation in a world with large extra dimensions. Assuming a 25% systematic uncertainty, we report a discovery potential for the mass bin 1<M _jj <2 TeV at 10 pb^?1 integrated luminosity.