北京谱仪积分亮度测量的新方法

介绍了利用e⁺e^－对撞中双μ产生和双γ产生两种QED过程来测量积分亮度的新思路.前者的特色在于用单根径迹选择双μ事例,后者则是首次利用双γ事例测定亮度.两种方法分别用于1998年春季北京谱仪(BES)R值扫描6个能量点的积分亮度测量,所得结果的误差分别小于8.0%和7.5%,在误差范围内与大角度巴巴事例积分亮度值一致.     

Photon events with missing energy at \sqrt{s} =183 to 189 GeV

The production of single photons has been studied in the reaction at centre-of-mass energies of 183 GeV and 189 GeV. A previously published analysis of events with multi-photon final states accompanied by missing energy has been updated with 189 GeV data. The data were collected with the DELPHI detector and correspond to integrated luminosities of about 51 pb and 158 pb at the two energies. The number of light neutrino families is measured to be . The absence of an excess of events beyond that expected from Standard Model processes is used to set limits on new physics as described by supersymmetric and composite models. A limit on the gravitational scale is also determined. Received: 28 January 2000 / Revised version: 27 April 2000 / Published online: 26 July 2000     

Measurement of triple gauge-boson couplings at LEP energies up to 189 GeV

The triple gauge-boson couplings involving the W are determined using data samples collected with the ALEPH detector at mean centre-of-mass energies of 183 GeV and 189 GeV, corresponding to integrated luminosities of 57 pb and 174 pb, respectively. The couplings, , and , are measured using W-pair events, single-{\it W} production and single- production. Each coupling is measured individually with the other two couplings fixed at their standard model value. Including ALEPH results from lower energies, the 95% confidence level intervals for the deviation to the standard model are , , and . Fits are also presented where two or all three couplings are allowed to vary. In addition, W-pair events are used to set limits on the C- or P-violating couplings , , , and , where V denotes either or Z. No deviations from the standard model expectations are observed. Received: 28 February 2001 / Published online: 24 August 2001     

Measurement of the ratio of inclusive cross sections sigma(pp --> Z + b jet)/sigma(pp --> Z + jet) at square root(s) = 1.96 TeV

Using the data collected with the D0 detector at square root(s) = 1.96 TeV, for integrated luminosities of about 180 pb(-1), we have measured the ratio of inclusive cross sections for pp --> Z + b jet to pp --> Z + jet production. The inclusive Z + b-jet reaction is an important background to searches for the Higgs boson in associated ZH production at the Fermilab Tevatron collider. Our measurement is the first of its kind, and relies on the Z --> e+ e- and Z --> mu+ mu- modes. The combined measurement of the ratio yields 0.021+/-0.005 for hadronic jets with transverse momenta pT > 20 GeV/c and pseudorapidities absolute value(eta) < 2.5, consistent with next-to-leading-order predictions of the standard model.     

R值扫描中积分亮度的测量

在R值扫描中利用大角度Bhabha事例测量积分亮度,较之以往的同类过程积分亮度的测量,在事例选择和探测效率的确定方面都作了较大的改进. 用不同的测量方法对本文的结果进行了检查,发现几种结果在误差范围内是一致的. 但本文的测量优化了事例选择条件,所以在一定程度上改善了系统误差.     

A Study of the Processes of e+e－→e+e－,μ+μ－ at Large Angle and Measured Luminosities

Using the BES data collected at √S=4.03GeV.the QED processes of e⁺e^－→e⁺e^－,μ⁺μ^－ have been studied. Our measurements agree with the QED prediction,and luminosities obtained from these two final states are compatible at a level of 4%.The total integrated luminosity of 23.1pb^－1 was given for all data collected at this energy region from the calculation.     

T-odd quarks at the large hadron collider: 2010-2012

We study the potential of the current Large Hadron Collider (LHC) 7 TeV run to search for heavy, colored vector-like fermions, which are assumed to carry a conserved Z₂ quantum number forcing them to be pair-produced. Each fermion is assumed to decay directly into a Standard Model quark and an invisible stable particle. T-odd quarks and the lightest T-odd particle (LTP) of the Littlest Higgs model with T-parity provide an example of this setup. We estimate the bounds based on the published CMS search for events with jets and missing transverse energy in the 35 pb−1 data set collected in the 2010 run. We find that T-odd quark masses below about 450 GeV are ruled out for the LTP mass about 100 GeV. This bound is somewhat stronger than the published Tevatron constraint. We also estimate the reach with higher integrated luminosities expected in the 2011-2012 run. If no deviation from the SM is observed, we expect that a bound on the T-odd quark mass of about 650 GeV, for the LTP mass of 300 GeV and below, can be achieved with 1 fb−1 of data. We comment on the possibility of using initial-state radiation jets to constrain the region with nearly-degenerate T-odd quark and LTP.     

Search for resonant $\tilde\nu$ production at $\sqrt{s} = $ 183 to 208 GeV

Searches for resonant production in e ⁺ e ^- collisions under the assumption that R-parity is not conserved and that the dominant R-parity violating coupling is or used data recorded by DELPHI in 1997 to 2000 at centre-of-mass energies of 183 to 208 GeV. No deviation from the Standard Model was observed. Upper limits are given for the and couplings as a function of the sneutrino mass and total width. The limits are especially stringent for sneutrino masses equal to the centre-of-mass energies with the highest integrated luminosities recorded. Received: 14 January 2003 / Published online: 14 March 2003     

Luminosity monitoring and calibration of BLM

The BEPCⅡLuminosity Monitor(BLM)monitors relative luminosity per bunch.The counting rates of gamma photons,which are proportional to the luminosities from the BLM at the center of mass system energy of the ψ(3770)resonance,are obtained with a statistical error of 0.01% and a systematic error of 4.1%.Absolute luminosities are also determined by the BESⅢ End-cap Electro-Magnetic Calorimeter(EEMC)using Bhabha events with a statistical error of 2.3% and a systematic error of 3.5%.The calibration constant between the luminosities obtained with the EEMC and the counting rates of the BLM are found to be 0.84±0.03(x1026 cm-2·count-1).With the calibration constant,the counting rates of the BLM can be scaled up to absolute luminosities.     

Exclusive photoproduction of J/\psi mesons at HERA

The exclusive photoproduction of mesons, , has been studied in ep collisions with the ZEUS detector at HERA, in the kinematic range 20<W<290 GeV, where W is the photon-proton centre-of-mass energy. The mesons were reconstructed in the muon and the electron decay channels using integrated luminosities of 38 and 55,respectively. The helicity structure of production shows that the hypothesis of s-channel helicity conservation is satisfied within two standard deviations. The total cross section and the differential cross-section , where t is the squared four-momentum transfer at the proton vertex, are presented as a function of W, for |t|<1.8 GeV². The t distribution exhibits an exponential shape with a slope parameter increasing logarithmically with W with a value at . The effective parameters of the pomeron trajectory are and . Received: 1 February 2002 / Published online: 22 May 2002     

Search for associated higgs boson production WH-->WWW*-->l+/-nul'+/-nu'+X in pp collisions at square root s=1.96 Te V

We present a search for associated Higgs boson production in the process pp-->WH-->WWW*-->l;+/-nul'+/-nu'+X in final states containing two like-sign isolated electrons or muons (e+/-e;+/-, e+/-micro+/-, or micro+/-micro+/-). The search is based on D0 run II data samples corresponding to integrated luminosities of 360-380 pb-1. No excess is observed over the predicted standard model background. We set 95% C.L. upper limits on sigma(pp-->WH)xBr(H-->WW*) between 3.2 and 2.8 pb for Higgs boson masses from 115 to 175 GeV.     

A study of the measurement precision of the Higgs boson decaying into tau pairs at the ILC

We evaluate the measurement precision of the production cross section times the branching ratio of the Higgs boson decaying into tau lepton pairs at the International Linear Collider (ILC). We analyze various final states associated with the main production mechanisms of the Higgs boson, the Higgs-strahlung and WW-fusion processes. The statistical precision of the production cross section times the branching ratio is estimated to be 2.6 and 6.9 % for the Higgs-strahlung and WW-fusion processes, respectively, with the nominal integrated luminosities assumed in the ILC Technical Design Report; the precision improves to 1.0 and 3.4 % with the running scenario including possible luminosity upgrades. The study provides a reference performance of the ILC for future phenomenological analyses.     

Search for lepton flavor violation in ep collisions at 300 GeV center of mass energy

Using the ZEUS detector at the HERA electronproton collider, we have searched for lepton flavor violation in ep collisions at a center—of—mass energy ($sqrt S$) of 300 GeV. Events of the type e + p → ? + X with a final—state lepton of high transverse momentum, ? = μ or τ, were sought. No evidence was found for lepton flavor violation in the combined 1993 and 1994 data samples, for which the integrated luminosities were 0.84 pb{?1}for e{～p collisions and 2.94 pb{?1} for e⁺p collisions. Limits on coupling vs. mass are provided for leptoquarks and R—parity violating squarks. For flavor violating couplings of electromagnetic strength, we set 95% confidence level lower limits on leptoquark masses between 207 GeV and 272 GeV, depending on the leptoquark species and final—state lepton. For leptoquark masses larger than 300 GeV, limits on flavor—changing couplings are determined, many of which supersede prior limits from rare decay processes.     

Supersymmetric lepton flavor violation in a linear collider: the role of charginos

The occurrence of significant supersymmetric lepton flavor violation at laboratory energies, through – mixing, has become a realistic possibility in the wake of the super-Kamiokande atmospheric neutrino result. This effect can be observed in an linear collider with the distinct final state . We show that the pair production of charginos can make an important contribution to this process and has to be taken into account in addition to that of sneutrinos or charged sleptons. Some case studies are presented with CM energies of 500 and 800GeV and integrated luminosities of 50, 500 and 1000. Received: 14 March 2001 / Published online: 19 July 2001     

Comparative study of the relationships between CO isotopic luminosities and infrared luminosity for the Galactic dense cores

Combining the 12CO(1-0),13CO(1-0),and C18O(1-0) data with IRAS four band data,we here estimate the physical parameters such as size,viral mass,and CO J=1-0 isotopic and infrared luminosities for 29 dense molecular clouds from two published CO samples. We further analyze the various correlations between CO J=1-0 isotopic luminosities and infrared luminosity(star formation rate,SFR) and discuss the relationships between the molecular gas tracers and SFR. The results show that 12CO(1-0),13CO(1-0) and C18O(1-0) luminosities have tight correlations with each other. CO J=1-0 isotopic luminosities and SFR show weak correlations with larger scatter than the HCN-IR correlations of 47 dense cores in the Galaxy and 65 external star-forming galaxies. This might be interpreted as that both the SFR and star formation efficiency are mainly determined by the molecular gas at high volume density rather than high column density.     

Higgs and background production in the reactione^ + e^ - \to b\bar b + 2 jets at LEPII and NLC energies

A complete tree-level Standard Model calculation of the reaction $e^ + e^ - \to b\bar b + 2$ jets in the energy range of LEPII and the Nexte ⁺e^? Linear Collider is presented. The 2-jet system represents either aq $\bar q$ pair or two gluons. The matrix elements were calculated by means of the package CompHEP, and phase space integration and event generation were carried out with the computer programs BASES/SPRING. Cross sections of the Higgs boson, the total background and important subsets of background are studied as functions of the c.m.s. energy and the Higgs mass, taking into account possible interferences. Various event distributions calculated for realistic integrated luminosities indicate encouraging prospects regarding the extraction of the Higgs signal.     

Gamma-ray bursts at high and very high energies

Gamma-Ray Bursts (GRBs) are extra-galactic and extremely energetic transient emissions of gamma rays, which are thought to be associated with the death of massive stars or the merger of compact objects in binary systems. Their huge luminosities involve the presence of a newborn stellar-mass black hole emitting a relativistic collimated outflow, which accelerates particles and produces non-thermal emissions from the radio domain to the highest energies. In this article, I review recent progresses in the understanding of GRB jet physics above 100 MeV, based on Fermi observations of bright GRBs. I discuss the physical implications of these observations and their impact on GRB modeling, and I present some prospects for GRB observation at very high energies in the near future.     

Bottonium production at LEP

We investigate the production of Υ(³ S ₁) and η _b (¹ S ₀) with two gluons from Z decay. We find that at LEP luminosities experimental detection will hardly be feasible.     

Measurements of the integrated muon intensity at large zenith angles

Precision measurements of the zenith-angle distributions of muons in the range 61°–89° are performed using the DECOR coordinate detector. The total number of selected events is more than 20 million. The dependence of the integrated muon intensity on the zenith angle is determined for several threshold energies in the range from 1.7 to 7.2. GeV. The experimental results in these ranges of zenith angles and threshold energies are obtained for the first time. It is demonstrated that the dependence of the integrated muon intensity on the zenith angle is adequately described by a simple analytical relationship.     

Collider physics at high energies and low luminosities

While very high acceleration gradients are expected in novel accelerating schemes such as those discussed by IZEST, generating high luminosities will be extremely challenging and will likely require a separate technology revolution. It is important to determine if a low-luminosity but high energy collider would have serious interest from a particle physics perspective. We consider a process involving physics beyond the Standard Model that would be detectable at high energies without requiring the types of luminosities normally quoted for future colliders, “classicalization”. In this example, scattering cross sections grow with a power of the center-of-mass energy, thereby reducing the luminosity requirement at high energies. Another process discussed is deep-inelastic-scattering of electrons on protons, where a precision measurement of the energy dependence of the scattering cross section could yield information about physics processes at much higher scales.