Technihadron production and decay at LEP2

The simple “straw-man” model of low-scale technicolor contains light color-singlet technihadrons, which mix with the electroweak gauge bosons. We present lepton collider production rates at the parton level, and show that experiments at LEP2 may be sensitive to the presence of technirho and techniomega states with masses 10–20 GeV beyond the center-of-mass energy because of the mixing. The exact sensitivity depends on several parameters, such as the technipion mass, the technipion mixing angle, and the charge of the technifermions. In an appendix, we describe the implementation of the model into the event generator PYTHIA for particle-level studies at lepton and hadron colliders.     

Consequences of partial vector meson dominance for the phenomenology of colored technihadrons

In this paper we address the question: do the limits on technirho production at the Tevatron mean what we think they do? These limits are based on calculations that rely on vector meson dominance (VMD). VMD was invented in order to describe the interaction of electrons with hadrons (the rho meson and pions). The method has been used also as a tool in the study of technicolor phenomenology. Nevertheless there is evidence in the sense that, even in its original context, VMD is not completely realized. In this work we investigate the consequences of a deviation from complete VMD for the phenomenology of colored technihadrons. We focus specially on the production of the color octet technirho and color triplet technipions. We found that a relatively small direct coupling of the proto-technirho to quarks is enough to suppress or even eliminate the interaction among quarks and the physical technirho. On the other hand, it is possible to suppress the coupling of the physical technirho to technipions, but in this case a large interaction among the technipions and the proto-gluon must be introduced. The consequences for the limits on the mass of the color octet technirho and colored triplets technipions are also investigated.     

Discriminating scalar and pseudoscalar weak bosons via toponium → γ + boson

The production of Higg's or neutral technipion spin-zero bosons (szb) in toponium decay is examined. Different methods for determining the parity of these bosons are discussed. The decay width Γ(m³S₁ → γ + szb) is very sensitive to the parity of the szb and it is shown how comparing the widths of different toponium states can be used to determine the szb parity. The method is applicable for a szb within 30% of the toponium mass.     

The Rare DecayK+ →π+vv and Effects of Charged Technipions

In this paper we calculate the contributions to the FCNC rare decay from the charged technipion P^± and P₈^± in the frarnervork of technicolor theory. We find that: (a) P^± can provide a positive but relatively small contribution to the process; (b) the contribution is large and positive for relatively light P₈^± and becomes negative for m_p8 ≥ 531 GeV; (c) the enhancement to the ratio BR() can be as large as a factor of 30 for m_p1 = 50 GeV and m_p8 = 100 GeV; (d) the lower mass bound on m_p8 is m_p8 > 220,190 GeV for m_p1 = 50,200 GeV, respectively     

Search for heavy particles decaying into electron-positron pairs in pp collisions

We present results of searches for technirho (rho(T)), techniomega (omega(T)), and Z' particles, using the decay channels rho(T),omega(T),Z'-->e(+)e(-). The search is based on 124.8 pb(-1) of data collected by the D0 detector at the Fermilab Tevatron during 1992-1996. In the absence of a signal, we set 95% C.L. upper limits on the cross sections for the processes pp-->rho(T),omega(T),Z'-->e(+)e(-) as a function of the mass of the decaying particle. For certain model parameters, we exclude the existence of degenerate rho(T) and omega(T) states with masses below about 200 GeV. We exclude a Z' with mass below 670 GeV, assuming that it has the same couplings to fermions as the Z boson.     

最轻的中性TC介子P0和μ+μ－对撞机

在顶色辅助的多标度人工色(TOPCMTC)模型框架下,讨论了最轻的中性TC介子P⁰在μ⁺μ^－对撞机(FMC)上的s道共振产生.计算结果表明:其有效产生截面非常大,至少比标准模型中的Higgs粒子h⁰的产生截面大一个量级.因此,FMC可以用来探测TC介子的存在进而检验人工色理论.     

Precise measurement of the top-quark mass in the lepton+jets topology at CDF II

We present a measurement of the mass of the top quark from proton-antiproton collisions recorded at the CDF experiment in Run II of the Fermilab Tevatron. We analyze events from the single lepton plus jets final state (tt-->W(+)bW(-)b-->lnubqq'b). The top-quark mass is extracted using a direct calculation of the probability density that each event corresponds to the tt final state. The probability is a function of both the mass of the top quark and the energy scale of the calorimeter jets, which is constrained in situ by the hadronic W boson mass. Using 167 events observed in 955 pb(-1) of integrated luminosity, we achieve the single most precise measurement of the top-quark mass, 170.8+/-2.2(stat.)+/-1.4(syst.) GeV/c(2).     

ITER磁体支撑316LN U型支撑夹制造研究

通过焊接和"整体环形锻造+线切割"两种制造方案对ITER磁体支撑U型支撑夹(PFCS2 U)的制造进行了研究.在采用TIG焊接方案时,通过对组件进行双面和单面焊接,结合多种辅助工装和热处理,最终可将尺寸控制在要求范围内,77K时焊缝的夏比冲击性能低于100J;在采用"整体环形锻造+狭缝线切割"的制造方案时,U型支撑夹的...     

Search for a fourth-generation quark more massive than the Z0 boson in p&pmacr; collisions at radicals = 1.8 TeV

We present the results of a search for pair production of a fourth-generation charge -1 / 3 quark (b(')) in sqrt[s] = 1.8 TeV p&pmacr; collisions using 88 pb(-1) of data obtained with the Collider Detector at Fermilab. We assume that both quarks decay via the flavor-changing neutral current process b(')-->bZ(0) and that the b(') mass is greater than m(Z)+m(b). We studied the decay mode b(')b(');-->Z(0)Z(0)b&bmacr; where one Z0 decays into e(+)e(-) or &mgr;(+)&mgr;(-) and the other decays hadronically, giving a signature of two leptons plus jets. An upper limit on the sigma(p&pmacr;-->b(')b(');)x[B(b(')-->bZ(0))](2) is established as a function of the b(') mass. We exclude at 95% confidence level a b(') quark with mass between 100 and 199 GeV/c(2) for B(b(')-->bZ(0)) = 100%.     

Identifying new physics contributions in the Higgs sector at linear <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> colliders

Loop-driven decay modes of the Higgs are sensitive to new physics contributions because of new particles in the loops. To highlight this we look at the dilepton-dijet signal in the dominant Higgs production channel at a linear e ⁺ e ⁻ collider. We show that by taking a simple ratio between cross-sections of two different final states such contributions can be very easily identified.      

Scalar field theory in the strong self-interaction limit

We revisit the monophoton plus missing energy signature at \(e^+e^-\) colliders in supersymmetric (SUSY) models where the gravitino is very light. There are two possible processes which provide the signal: gravitino pair production and associated gravitino production with a neutralino, leading the monophoton final state via an additional photon radiation and via the neutralino decay, respectively. By using the superspace formalism, we construct a model that allows us to study the parameter space for the both processes. We show that the signal cross section and the photon spectra provide information on the masses of the SUSY particles as well as the SUSY breaking scale.     

Heavy charged Higgs boson production at next generation e^\pm\gamma colliders

We assess the potential of future electron-positron linear colliders operating in the mode in detecting charged Higgs bosons with mass around and larger than the top quark mass, using Compton back-scattered photons from laser light. We compare the pair production mode, , to a variety of channels involving only one charged Higgs scalar in the final state, such as the tree-level processes ( and ) and ( and ) as well as the loop-induced channel . We show that, when the charged Higgs boson mass is smaller than or comparable to half the collider energy, , single production cross sections are of the same size as the pair production rate, whereas, for charged Higgs boson masses larger than , all processes are heavily suppressed. In general, production cross sections of charged Higgs bosons via scatterings are smaller than those induced at an collider and the latter represents a better option to produce and analyse such particles. Received: 29 August 2001 / Published online: 23 November 2001     

Search for gauge mediated SUSY breaking topologies at \sqrt{{\mathrm s}} \sim 189 GeV

Searches for topologies characteristic of Gauge Mediated SUSY Breaking models (GMSB) are performed by analysing 173.6 of data collected at = 188.6 GeV with the ALEPH detector. These topologies include acoplanar photons, non-pointing single photon, acoplanar leptons, large impact parameter leptons, detached slepton decay vertices, heavy stable charged sleptons and four leptons plus missing energy final states. No evidence for these new phenomena is observed and limits on production cross sections and sparticle masses are derived. A scan of a minimal GMSB parameter space is performed and model dependent lower limits of about 45 GeV/ on the next-to-lightest supersymmetric particle (NLSP) mass and of about 9 TeV on the mass scale parameter are derived, independently of the NLSP lifetime. Received: 30 November 1999 / Published online: 14 April 2000     

Charm,bottom and top production in high energy electron proton collisions

Differential cross sections for electroproduction of charm, bottom and top quarks are calculated via all contributing 2 → 2 and 2 → 3 QCD subprocesses. Fragmentation of heavy quarks to heavy hadrons and effects due to weak chain decays of the heavy quarks are taken into account. We also calculated background contributions given by the production of two or three light-quark jets both via the neutral and charged current processes. We point out that, similarly to the case of hadron colliders, it will be necessary to require final state lepton(s) to suppress the jet background. To separate charm and bottom production we have to require at least one hard muon or two isolated leptons and one jet in the final state. We show that two or more jet production via the charged current mechanism and bottom production with hard gluon bremssrahlung are the most important background contributions in top search. However, we also show that they become negligible by requiring one lepton, two or three jets and large missing energy in the final state. We estimate that the discovery limit on the top quark mass value is about 70 GeV at HERA.     

Di-Boson production at hadron colliders with general triple gauge boson couplings. Analytic expressions of helicity amplitudes and cross-sections

We discuss the tests of general Triple Gauge Boson Vertices (TGV) through bosonic pair production at present and future hadron colliders. All bosonic final states are reviewed via the tree level quark-antiquark annihilation sub-processes. The full analytic expressions of the helicity amplitudes and cross-sections are given. These expressions should be useful in any attempt to disentangle the effects of the most general non standard WWV(V = γ,Z) vertices including 14 free parameters. We investigate the sensitivity of the invariant mass and transverse momentum distributions to the full set of anomalous couplings including final state polarization structures. We particularly consider these features at the projected CERN Large Hadron Collider (LHC) energy scale.     

Prospects of squark and slepton searches at a gamma–gamma collider

We examine the prospects of detecting sfermions at a gamma–gamma collider. Once produced, a slepton can decay into a pair of quarks (jets) through R-parity violating interactions. Similarly, a squark may decay into a lepton–quark pair. Analyzing the corresponding Standard Model backgrounds, namely 4-jet and dilepton plus dijet final states respectively, we show that the sfermion can be detected almost right upto the kinematic limit and its mass determined to a fair degree of accuracy. Similar statements also hold for nonsupersymmetric leptoquarks and diquarks.     

Prospects for observation of double parton scattering with four-muon final states at LHCb

We study the prospects for observing double parton scattering through four-muon final states, forming two opposite-sign muon pairs, in the LHCb experiment in pp collisions at 14 TeV centre of mass energy. We consider two special cases, namely double Drell–Yan and J/ψ-pair production. The kinematic properties and prospects for observing these processes are discussed. We find that the production rate depends strongly on the origin of the four muons, while many kinematic properties can be used to help identify the presence of double parton scattering events.     

Results for all reactions e^+ e^- \rightarrow 4{\rm f}, 4{\rm f}\gamma with nonzero fermion masses

We accomplish our efforts to obtain predictions for all four–fermion final states of –annihilation and the corresponding bremsstrahlung reactions which are possible in the framework of the Standard Model. For this purpose we have developed a program ee4 . Our predictions are valid for fermions of arbitrary masses and we can obtain results for total cross sections without any collinear cut. Keeping exact fermion masses is of course required for top quark production. We give a detailed phenomenological analysis of fermion mass effects and real photon radiation for all channels of four–fermion production at LEP-II and next linear collider energies. Received: 2 October 2001 / Revised version: 2 January 2002 / Published online: 1 March 2002     

Limits on light gravitino production and new processes with large missing transverse energy in p&pmacr; collisions at sqrt

Events collected by the Collider Detector at Fermilab (CDF) with an energetic jet plus large missing transverse energy can be used to search for physics beyond the standard model. We see no deviations from the expected backgrounds and set upper limits on the production of new processes. We consider in addition the production of light gravitinos and set a limit at 95% confidence level on the breaking scale sqrt[F]>/=217 GeV, which excludes gravitino masses smaller than 1.1x10(-5) eV/c(2).     

Heavy quark and quarkonium production at CERN LEP2: <Emphasis Type="Italic">k</Emphasis><Subscript>T</Subscript>-factorization versus data

We present calculations of heavy quark and quarkonium production at CERN LEP2 in the k _T-factorization QCD approach. Both direct and resolved photon contributions are taken into account. A conservative error analysis is performed. The unintegrated gluon distribution in the photon is obtained from the full CCFM evolution equation. The traditional color-singlet mechanism to describe the non-perturbative transition of a -pair into a final quarkonium is used. Our analysis covers the polarization properties of heavy quarkonia at moderate and large transverse momenta. We find that the total and differential open charm production cross sections are consistent with the recent experimental data taken by the L3, OPAL and ALEPH collaborations. At the same time the DELPHI data for the inclusive production exceed our predictions, but experimental uncertainties are too large to claim a significant inconsistency. The bottom production in photon-photon collisions at CERN LEP2 is hard to explain within the k _T-factorization formalism.Received: 22 December 2004, Revised: 15 February 2005, Published online: 12 April 2005