Deep inelastic scattering cross section measurements previously published by the H1 and ZEUS collaborations are combined. The procedure takes into account the systematic error correlations in a coherent way, leading to a significantly reduced overall cross section uncertainty. The combined H1 and ZEUS measurements of the inclusive neutral and charged current cross sections are used to perform a common NLO QCD fit. The consistent treatment of systematic uncertainties in the joint data set ensures that the resulting set of parton density functions (PDFs) have a much reduced experimental uncertainty compared to the previous PDF extractions performed separately by the H1 and ZEUS collaborations.
Measurements of jet production in the photoproduction region at HERA are presented, which are sensitive to the underlying event structure. It is argued that in the photoproduction region a significant amount of multi-parton interactions in the collinear factorisation ansatz are needed to describe the measurement. A different approach for higher order parton radiation (CCFM parton showers) can also describe the measurement.
Heavy quark structure functions from HERA provide a direct handle on the medium and small-x gluon PDF. In this contribution, we discuss ongoing progress on the implementation of the FONLL General-Mass scheme with running heavy quark masses, and of its benchmarking with the HOPPET and OpenQCDrad codes, and then present the impact of the recently released combined HERA charm production cross sections in the NNPDF2.3 analysis. We find that the combined charm data contribute to constraining the gluon and quarks at small values of Bjorken-x.
Recent structure function results from H1 and ZEUS are presented. The data have been recorded in e+p and e-p collisions for both Neutral Current and Charged Current reactions, covering a wide kinematic range of squared four-momentum transfers Q2, from 0.2GeV2 to 30000GeV2, and Bjorken x between ~5*10-6 and 0.65. Data from both experiments have been combined, leading to significantly reduced experimental uncertainties. The combined measurements are analysed in a NLO QCD fit, and a set of parton density functions, HERAPDF1.0, is extracted from these data alone. New direct measurements of the str…
We study the photoproduction of isolated prompt photons associated with hadron jets in the framework of the parton Reggeization approach. The cross section distributions in the transverse energies and pseudorapidities of the prompt photon and the jet as well as the azimuthal decorrelation variables measured by the H1 and ZEUS collaborations at DESY HERA are nicely described by our predictions. The main improvements with respect to previous studies in the $k_T$-factorization framework include the application of the Reggeized-quark formalism, the generation of exactly gauge-invariant amplitudes …
Charged particle multiplicity distributions in positron-proton deep inelastic scattering at a centre-of-mass energy $\sqrt{s}=319$ GeV are measured. The data are collected with the H1 detector at HERA corresponding to an integrated luminosity of $136$ pb${}^{-1}$. Charged particle multiplicities are measured as a function of photon virtuality $Q^2$, inelasticity $y$ and pseudorapidity $η$ in the laboratory and the hadronic centre-of-mass frames. Predictions from different Monte Carlo models are compared to the data. The first and second moments of the multiplicity distributions are determined …
Measurement of $α_S$ from Jet Rates in Deep Inelastic Scattering at HERA
利用HERA ZEUS探测器收集的3.2~pb $^{-1}$的积分光度数据，研究了$120<Q^2<3600$ ~ GeVPDMATHABMN的深非弹性散射中喷流的产生。射流采用JADE算法进行识别。在$γ^*$ -部分子质心系统中部分子发射的角分布上的切割使确定喷流率的实验和理论不确定性最小化。喷气式飞机的速度，与${\cal O}$相比，（$α_{s}$ ^2 $) perturbative QCD calculations, allow a precise determination of $ α_{s}（Q）$ in three $ Q^2 $-intervals. The values are consistent with a running of $ $-intervals. The values are consistent with a running of $ α_{s}（Q）$, as expected from QCD. Extrapolating to $ Q= M_{Z^0} $ yields $ α_{s}（M_{Z^0}）= 0.117~ \pm ~0.005~（stat）~^{+0.004}_{-0.005}~（syst_{exp}）~{\pm ~0.007}~（syst_{theory}）$。
The parton distribution functions (PDFs) are a non-negotiable input to almost all theory predictions at hadron colliders. In this talk, I introduce PDF determination by global analysis and discuss selected topics concerning recent relevant data from HERA and the Tevatron, before giving some prospects for the LHC. The combination of H1 and ZEUS cross sections reduces uncertainties and will be an important input to future global PDF analyses. The theoretical description of the heavy-quark contribution to structure functions at HERA has a significant influence on predictions at the LHC. New W and…
Recent measurements of inclusive and semi-inclusive deep inelastic scattering in electron-proton collisions at HERA are reviewed. These measurements are used to determine the parton distribution functions (PDFs) of the proton, a necessary input to theory predictions for hadron colliders. An introduction to the PDF determination with an emphasis on HERA PDFs is presented. Theory predictions based on HERAPDF are compared to a selection of recent LHC and Tevatron measurements. The impact of jet and charm production measurements on the PDFs is discussed.
Recent structure function results from the H1 and ZEUS Collaborations are presented. The data cover a wide kinematic range of squared four-momentum transfers Q^2, from 0.2 GeV^2 to 30000 GeV^2, and Bjorken x between 5*10^-6 and 0.65. Data from both experiments have been combined, leading to significantly reduced experimental uncertainties. The combined measurements are analysed using a NLO QCD fit, and a set of parton density functions, HERAPDF1.0, is extracted. New direct measurements of the structure function F_L, making use of dedicated low energy runs of the HERA machine, are also presente…
The kinematic region covered by the LHC experiments probes low values of Bjorken-$x$. At the scale relevant for $W$ and $Z$ production the central rapidity region covers $10^{-3} < x < 10^{-1}$. This means that it is the HERA data which give the most insight into the behaviour of parton distribution functions (PDFs) for the early phase of running at the LHC. The H1 and ZEUS experiments are combining their data so as to provide a legacy of HERA results. The present status of the data combinations and the impact of these data on our knowledge of parton distribution functions is explored.
We present a determination of the parton distribution functions of the proton in which NLO and NNLO fixed-order calculations are supplemented by NLLx small-x resummation. Deep inelastic structure functions are computed consistently at NLO+NLLx or NNLO+NLLx, while for hadronic processes small-x resummation is included only in the PDF evolution, with kinematic cuts introduced to ensure the fitted data lie in a region where the fixed-order calculation of the hard cross-sections is reliable. In all other respects, the fits use the same methodology and are based on the same global dataset as the re…
A QCD fit analysis to the combined HERA-I inclusive deep inelastic cross sections measured by the H1 and ZEUS collaborations for $e^\pm p$ scattering resulting into a competitive NLO PDF set, HERAPDF1.0 is presented. HERAPDF at NNLO fits are presented as well, resulting, however, in a worse description of the combined HERA data. In addition, a preliminary analysis including the HERA II measurements of lower proton-beam energies is performed. The effect of including the new data on the determination of HERA parton distribution functions is analysed, using fits similar to those performed for HER…
This review is devoted to the study of charm production in ep and pp collisions. The total set of measurements obtained by the two collaborations H1 and ZEUS from HERA and their combination is outlined, as well as complementary data obtained by the LHCb collaboration at the LHC. After fitting the parton distribution functions the charm production cross sections are predicted within perturbative QCD at next-to-leading order using the fixed-flavour-number scheme. Agreement with the data is found. The combined HERA charm data are sensitive to the $c$-quark mass and enabled its accurate determinat…
Recent measurements of jet cross sections at HERA, the Tevatron and the LHC that provide constraints on parton distribution functions and allow for determinations of the strong coupling constant are presented.
The combination is presented of all inclusive deep inelastic scattering cross sections previously published by the H1 and ZEUS collaborations at HERA for neutral and charged current $ep$ scattering for zero beam polarisation. The data were taken at proton beam energies of 920, 820, 575 and 460 GeV and an electron beam energy of 27.5 GeV. The data correspond to an integrated luminosity of about 1 fb$^{-1}$ and span six orders of magnitude in negative four-momentum-transfer squared, $Q^2$, and Bjorken $x$. The correlations of the systematic uncertainties were evaluated and taken into account for…
Recent experimental and theoretical results presented in the working group "Parton densities from DIS and hadron colliders to LHC" at the DIS2010 workshop are summarized in this contribution.
Starting in 2008 the H1 and ZEUS experiments have been combining their data in order to provide the most complete and accurate set of deep-inelastic data as the legacy of HERA. The present review presents these combinations, both published and preliminary, and explores how they have been used to give information on the structure of the proton. The HERAPDF parton distribution functions (PDFs) are presented and compared with other current PDFs and with data from the Tevatron and LHC colliders.
