一种在ISR能量下精确检验α_s的方法

本文用微扰QCD计算了以下过程的截面差。 (a)dσ(pp→Jet_(大PT) γ_(大PT) X)-dσ(pp→Jet_(大PT) γ_(大PT) X) (b)dσ(pp→2γ_(大PT) X)-dσ(pp→2_(大PT) X) (c)dσ(K~-p→Jet_(大PT) γ_(大PT) X)-dσ(K~ p→Jet_(大PT) γ_(大PT) X) (d)dσ(K~-p→2γ_(大PT) X)-dσ(K~ p→2γ_(大PT) X) (e)dσ(pp→2Jet_(大PT) X)-dσ(pp→2Jet_(大PT) X)发现胶子和海夸克的分布函数以及许多部分子的碎裂函数都不出现在这些截面差的计算结果中。将这些结果与实验数据作比较,在不必区分胶子喷注与夸克喷注的情况下,有可能精确测定α_s/α的比值。本文还探讨了进一步提高测量精度的可行方案。     

用喷注电荷截面方法考察胶子信息

本文通过对反应:p+p→γ+Jet+X,γ+p→2Jets+X,γ+p→h+Jet+X的喷注电荷截面的分析,分别给出了检测质子中胶子分布函数,提取胶子喷注信息以及确定胶子碎裂函数的方法。 关键词：     

e+e-对撞中夸克喷注强子化的多重数结构

本文半唯象地基于无规独立产生子夸克和相空间考虑的简单图象,计算了S^1/2～4—7GeV能区的夸克喷注强子化的强子纵动量和能量分布S/β dσ/dx_p和S/β dσ/dx_E行为。它们与实验符合得相当好,本文还给出喷注中两个粒子关联截面dσ/(dx_1Edx_2E),有待实验检验。     

非微扰QCD真空中夸克真空凝聚的结构(英文)

基于Dyson-Schwinger方程(DSEs)所确定的夸克传播子和算符成积展开(OPE),在彩虹近似下,预言了QCD真空中非定域夸克真空凝聚的结构。这种结构由夸克自能函数Af和Bf决定,通过数值求解DSEs就可以得到这些自能函数。但是,直接数值求解DSEs方程非常复杂,这里采用Roberts和Williams提出的参数化方法,用参数化的夸克传播函数σf v(p2)和σf s(p2)计算夸克自能函数。同时,也计算了定域的夸克真空凝聚值,夸克胶子混合的真空凝聚值,以及夸克的虚度。理论预言和计算结果均与标准QCD求和定则、格点QCD和瞬子模型的理论结果大致相符。和这些模型的结果相比,参数化方法得到的轻夸克(u,d,s)的定域真空凝聚偏大,这主要是由于模型依赖导致的。与u,d夸克相比,s夸克的真空凝聚比较大,这是因为s夸克自身质量较大的缘故。当然,Roberts-Williams参数化的夸克传播子只是一个经验公式,只能近似描述夸克的传播。     

γ–p碰撞中J/ψ的硬衍射产生

按着重夸克偶素产生的NRQCD因子化方案,计入qq的色八重态产生机制,采用L.Alvero等给出的三组Pomeron的部分子分布函数,在s=200GeV,4GeV相似文献   

胶子喷注和夸克喷注性质的蒙特卡洛研究

用蒙特卡洛方法研究了91.2GeV e⁺e^－碰撞产生的3喷注事件.用3个喷注之间的夹角来标识各个喷注,分别计算了3个喷注的能量及能量分布,并在相同能量下计算了3个喷注的多重数,横动量及其分布.通过与能量相同的2喷注事件中单夸克喷注的上述性质的比较,得到了从3喷注事件中挑选胶子喷注和夸克喷注的一种简便方法.这样挑选出来的胶子和夸克喷注在性质上与QCD的理论预言一致,并且胶子和夸克喷注的平均多重数比值的计算结果与实验观测值符合     

夸克喷注和胶子喷注硬度特性的研究

用蒙特卡洛模拟方法研究了Z⁰强子衰变中的三喷注事件.用b标记方法辨别,得到夸克喷注和胶子喷注.定义了一个新的物理量—硬度.分别计算了发射了胶子的夸克喷注和胶子喷注的硬度分布.通过胶子和夸克喷注的平均多重数和平均横动量对硬度的依赖性以及他们的多重数和横动量在相同硬度区间内的分布情况的计算与比较,发现夸克喷注和胶子喷注的硬度特性有显著的差别.夸克喷注的特性几乎与硬度无关,而胶子喷注的特性与硬度之间存在较强的关联.当Hd>10GeV时,胶子喷注的平均多重数和平均横动量都明显地大于夸克喷注的平均多重数和平均横动量;而当H_d<6GeV时,结果正好相反.这表明,只是对于较硬的胶子,胶子喷注比夸克喷注“胖”的结论才能成立.     

在大横动量直接光子出射过程中检验强子的胶子分布函数

本文探讨了强作用中截面差Δ_AB=dσ(AB→cγX)-dσ(AB→cγX)的物理含义, 给出了挑选对截面差有贡献的子过程的简单规则. 并建议在大横动量直接光子出射的条件下, 通过测量截面差及其组合检验强子的胶子分布函数. 同时, 还得到了这些截面组合一相应质子、中子、π介子和K介子中的胶子分布函数之间的简单关系:G_p(x)/(Δ_pp－Δ_pp)=G_n(x)/(Δ_np－Δ_np)=G_π(x)/(Δ_π+p－Δ_π－p)=G_K(x)/(Δ_K+p－Δ_K－p),它们可望在实验上得到检验.     

带头对数近似下的π介子价夸克分布函数的QCD行为和有关的微分截面

本文利用我们已经给出的在带头对数近似下强子价夸克分布函数的解析表达式^[11], 讨论了π介子价夸克分布函数的QCD行为, 很好地解释了现有的π介子价夸克分布函数数据. 同时预言了Drell-Yan机制产生大质量轻子对的微分截面M³ dσ/dM, 并和现有的实验数据进行了比较.     

Some consequences of the quark parton model in inclusive electroproduction

Consequences of the quark parton model proposed by Feynman for inclusive electroproduction are studies. We show that the SLAC experiment γ_v+p(n) → h^±+anything which distinguishes the outcoming hdrons by their charges only gives the possibility to check sum rules with fractional quark quantum numbers, to determine the charge of the proton quark (neutron quark) and to measure the valence distribution function directly. We predict the multiplicity difference for the charged hadrons as the function of q² which agrees well with the experimental data published recently.     

Muon-electron universality at high energies and hadronic corrections to e+e− → μ+μ−

It is argued that unitarity and muon-electron universality are sufficient to determine the contribution of hadrons to the imaginary part of the forward amplitude for the process e⁺e^? → μ⁺μ^?. With these assumptions Im T₁^h(e⁺e^? → μ⁺μ^?) = sσ(e⁺e^? → hadrons) to all orders in α. Some consequences of this formula are discussed.     

A measurement of σtot(e+e− → hadrons) for cm energies between 12.0 and 36.7 GeV

The ration R = σ(e⁺e^? → hadrons)σ_μμ was measured between 12.0 and 36.7 GeV c.m. energy W with a precision of typically ± 5.2%. R is found to be constant with an average R = 4.01 ± 0.03 (stat) ± (syst.) for W ? 14 GeV. Quarks are found to be point-like, the mass parameter describing a possible quark form-factor being larger than 186 GeV. Fits including QCD corrections and a weak neutral-current contribution are presented.     

Study of electron-positron collisions at the highest PETRA energy

We report on the results of the study of e⁺e^? collisions at the highest PETRA energy of √s = 31.57 GeV, using the 4π sr, electromagnetic and calorimetric detector Mark J. Based on 88 hadron events, and an integrated luminosity of 243 nb^?1 we obtain R = σ(e⁺e^? → hadrons)/σ(e⁺e^? → μ⁺μ^?) = 4.0 ± 0.5 (statistical) ± 6 (systematic). The R value, the measured thrust distribution and average spherocity show no evidence for the production of new quark flavors.     

Parton model predictions for two-particle correlations in e+e− annihilation

The parton model predicts a jet structure for e⁺e^? annihilation into hadrons. This is obscured at low energies by the presence of finite transverse momentum effects. We suggest studying e+⁺e^? → h₁+h₂+X, where at least one hadron is near the kinematical boundary; this defines a jet axis. Numerous predictions for correlations among mesons follow from Feynman's parton fragmentation suggestion. We also give sum rules which check for the quantum numbers of the partons.     

Jets in pp collisions: Radiation zeroes and the electric charges of colored quarks

Measurements involving more than one photon (e.g., γγ → hadrons, e⁺e^- → q$\text{q}$γ) can determine the electric charge of colored quarks rather than the color-averaged value measured, for example, by the R-value in e⁺e^- → hadrons. We draw attention to the fact that this measurement of the absolute quark charges can be performed in hadron collisions via the process qq → qqγ. The charge signature is dramatic due to the appearance of radiation zeroes whose position depends on the values of the electric charges. This can be exploited to perform such measurements with a detector lacking γ/π⁰ separation capability. Such experiments also study the interface of color and electromagnetic amplitudes and can further elucidate the QCD origin of jets.     

Production of the exotic 1(--) hadrons ϕ(2170), X(4260), and Y(b)(10890) at the LHC and Tevatron via the Drell-Yan mechanism

We calculate the Drell-Yan production cross sections and differential distributions in the transverse momentum and rapidity of the J(PC) = 1(--) exotic hadrons ?(2170), X(4260), and Y(b)(10890) at the LHC and the Tevatron. These hadrons are tetraquark (four-quark) candidates, with a hidden ss, cc, and bb quark pair, respectively. In deriving the distributions, we include the order α(s) QCD corrections, resum the large logarithms in the small transverse momentum region in the impact-parameter formalism, and use the state of the art parton distribution functions. Production rates for the processes pp(p) → ?(2170)× (→ ?(1020)π+ π- → K+ K- π+ π-) +…, pp(p) → X(4260)(→J/ψπ+ π- → μ+ μ- π+ π-)+…, and pp(p) → Y(b)(10890)(→ Υ(1S,2S,3S)π+ π- → μ+ μ- π+ π-) +… are presented. Their measurements will help in understanding the dynamics of these exotic hadrons.     

Remark on the production cross section of J particles in hadron-hadron collisions according to the statistical bootstrap model

Heavy J particles decaying into e⁺e^? were recently found in p-Be collisions [1] as well as in e⁺e^? annihilations [2, 3], where also the decay into hadrons with a branching ratio of about $\text{σ(}\text{J}\text{→}\text{h}\text{)}\text{σ(}\text{J}\text{→}\text{e}{}^{\mathrm{+}}\text{e}{}^{\mathrm{?}}\text{) = 15}$ was observed.     

QCD estimates for associated charm production by weak neutral currents

We give quantitative estimates for associated charm production in neutrino and antineutrino induced neutral current interactions, based on (a) quantum chromodynamics (QCD) and (b) the quark parton model (QPM) and a phenomenological generalization thereof. We emphasize the need for a precise measurement of the ratio σ(v_μN→v_μe⁺X)/σ(v_μN→μ^?X) and the corresponding ratio for antineutrinos, as these can provide clean tests of certain characteristic features of QCD. Bounds are obtained for single charm production by charm-changing neutral currents.