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Register a new userDeep inelastic inclusive and diffractive scattering at $Q^2$ values from 25 to 320 GeV$^2$ with the ZEUS forward plug calorimeter
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Deep inelastic scattering and its diffractive component, $ep to e^{prime}gamma^* p to e^{prime}XN$, have been studied at HERA with the ZEUS detector using an integrated luminosity of 52.4 pb$^{-1}$. The $M_X$ method has been used to extract the diffractive contribution. A wide range in the centre-of-mass energy $W$ (37 -- 245 GeV), photon virtuality $Q^2$ (20 -- 450 GeV$^2$) and mass $M_X$ (0.28 -- 35 GeV) is covered. The diffractive cross section for $2 < M_X < 15$ GeV rises strongly with $W$, the rise becoming steeper as $Q^2$ increases. The data are also presented in terms of the diffractive structure function, $F^{rm D(3)}_2$, of the proton. For fixed $Q^2$ and fixed $M_X$, $xpom F^{rm D(3)}_2$ shows a strong rise as $xpom to 0$, where $xpom$ is the fraction of the proton momentum carried by the Pomeron. For Bjorken-$x < 1 cdot 10^{-3}$, $xpom F^{rm D(3)}_2$ shows positive $log Q^2$ scaling violations, while for $x ge 5 cdot 10^{-3}$ negative scaling violations are observed. The diffractive structure function is compatible with being leading twist. The data show that Regge factorisation is broken.
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High Q^2 NC and CC cross-sections as measured at HERA can give information on two distinct areas of current interest. Firstly, supposing that all the electroweak parameters are well known, these cross-sections may be used to give information on parton distributions at high x and high Q^2. Secondly, supposing that parton distributions are well known, after evolution in Q^2 from the kinematic regime where they are already measured, these cross-sections can be used to give information on electroweak parameters in a process where the exchanged boson is `spacelike rather than `timelike. WG1 addressed itself to clarifying the limits of our present and possible future knowledge on both these areas.
This contribution covers three recent results on deep-inelastic scattering at HERA: (i) new measurements of the proton longitudinal structure function $F_L$ from H1 and ZEUS experiments, (ii) a dedicated NC cross section measurement from ZEUS in the region of high Bjorken $x$, and (iii) preliminary combination results of all HERA inclusive data published up to now by H1 and ZEUS, taking into account the experimental correlations between measurements.
New results on diffractive deep-inelastic $e p$ scattering at HERA are presented using data taken in 1994 with the H1 detector. The cross section for diffractive deep-inelastic scattering is measured in terms of a diffractive structure function $F_2^{D(3)}(beta,Q^2,xpom)$ over an extended kinematic range. The dependence of $F_2^{D(3)}$ on $xpom$ is found not to depend on $Q^2$, but to depend on $beta$. Therefore the $xpom$ dependence no longer factorizes. The $Q^2$ and $beta$ dependence of $F_2^{D(3)}$ is analyzed after an integration over the dependence on $xpom$. For fixed $beta$ a clear rise with $log Q^2$ is observed, persisting up to high values of $beta$. In terms of the Altarelli-Parisi (DGLAP) QCD evolution equations, these scaling violations give clear indications for a gluon dominated process. Subsequently an attempt is made to quantify the parton content of the diffractive exchange using the DGLAP evolution. At the starting scale a ``leading gluon distribution is found which contributes about $80 %$ of the momentum in the diffractive exchange. Measurements of the hadronic final state (energy flow and production of $D^{*}$ mesons) are found to be consistent with the predictions of a model of deep-inelastic electron pomeron scattering using the information on the parton content obtained.
In the QCD evolution of transverse momentum dependent parton distribution and fragmentation functions, the Collins-Soper evolution kernel includes both a perturbative short-distance contribution as well as a large-distance non-perturbative, but strongly universal, contribution. In the past, global fits, based mainly on larger $Q$ Drell-Yan-like processes, have found substantial contributions from non-perturbative regions in the Collins-Soper evolution kernel. In this article, we investigate semi-inclusive deep inelastic scattering measurements in the region of relatively small $Q$, of the order of a few GeV, where sensitivity to non-perturbative transverse momentum dependence may become more important or even dominate the evolution. Using recently available deep inelastic scattering data from the COMPASS experiment, we provide estimates of the regions of coordinate space that dominate in TMD processes when the hard scale is of the order of only a few GeV. We find that distance scales that are much larger than those commonly probed in large $Q$ measurements become important, suggesting that the details of non-perturbative effects in TMD evolution are especially significant in the region of intermediate $Q$. We highlight the strongly universal nature of the non-perturbative component of evolution, and its potential to be tightly constrained by fits from a wide variety of observables that include both large and moderate $Q$. On this basis, we recommend detailed treatments of the non-perturbative component of the Collins-Soper evolution kernel for future TMD studies.
We report preliminary $R$ values for all 85 energy points scanned in the energy region of 2-5 GeV with the upgraded Beijing Spectrometer (BESII) at the Beijing Electron Positron Collider (BEPC). The typical uncertainty on the R values we measured is about 7%. The new R values have a significant impact on the predicted mass of the Higgs coming from the global fit to the electroweak data, and will also contribute to the interpretation of the E821 g-2 experiment.
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