We present a brief description of the recently developed Fortran code TERAD91 for semi-analytical calculations of the double differential cross sections of NC and CC deep inelastic electron-proton scattering and of some related observables. The code is mainly intended for the calculations at HERA or other ep-colliders but may be also used for similar processes like muon-proton scattering in fixed-target experiments.
An introduction and overview of charm production in deep inelastic scattering at HERA is given. The existing next-to-leading order perturbative QCD calculations are then reviewed, and key results are summarized. Finally, comparisons are made with the most recent HERA data, and unresolved issues are highlighted.
Recent measurements of inclusive deep inelastic scattering differential cross-section in the range 1.5 \gev2\le Q^2\le 30000 \gev2 and 5\cdot 10^{-6}\le x\le 0.65 are presented. Phenomenological analyses performed from these measurements are also described.
After a brief introduction into the phenomenology of instantons, results from instanton perturbation theory applied to deep-inelastic electron proton scattering are summarized. Based on event signatures derived from Monte Carlo studies, strategies for enhancing instanton induced events relative to Standard Model deep-inelastic events are developed. Preliminary results for a search for such events performed with the H1 detector at HERA are given.
We give an overview of jet physics in deeply inelastic scattering at HERA. The problem of jet definitions, the scale dependence of jet cross sections and some applications are discussed. (Talk presented at the Workshop on Deeply Inelastic Scattering and QCD, Paris, April 1995. To appear in the proceedings.)
We calculate cross-sections for neutral current deep inelastic scattering at HERA with photon tagging. Both the exact lowest-order cross-section and a leading logarithmic approximation of next-order corrections are calculated. The latter amounts to less than 20% in a large kinematical range. The integrations are performed numerically but without relying on Monte Carlo methods.
The sensitivity of the Deep Inelastic Compton (DIC) scattering at HERA to the structure of the virtual photon is discussed. It is demonstrated that the gluonic content of the virtual photon can be pinned down by measuring the photons with $p_T \sim 5 $ GeV in the proton direction.
In the framework of the $k_T$-factorization approach, we analyse the inclusive and inelastic production of $J/ψ$ particles in deep inelastic $ep$ scattering. We take into account both colour-singlet and colour-octet production channels. We inspect the sensitivity of theoretical predictions to the choice of model parameters. Our theoretical results agree reasonably well with recent experimental data collected by the collaboration H1 at HERA.
The measurements of inclusive charm and beauty cross sections in deep-inelastic scattering $ep$ collisions at HERA are compared with the predictions of perturbative quantum chromodynamics from the CTEQ and MRST fitting groups, employing a range of theoretical schemes. The differences in the theoretical predictions are discussed and the theoretical uncertainties investigated.
After summarizing the results of QCD-instanton-perturbation theory for the calculation of instanton-induced effects in deep inelastic electron proton scattering, we discuss search strategies for instanton-induced effects that have been derived for HERA-conditions using the QCDINS-Monte Carlo. Recent results from the H1 collaboration are presented.
We use the BFKL equation to calculate the rate of deep inelastic scattering events containing two forward jets (adjacent to the proton remnants) at HERA. We compare the production of two forward jets with that of only one forward jet (the "Mueller" process). We obtain a stable prediction for this two to one jet ratio, which may serve as a measure of the BFKL vertex function.
We estimate the cross-section and asymmetry relevant for the production of forward jets in polarised deep inelastic scattering in the region of small values of $x$ which can be probed at possible polarised HERA measurements. The kinematical cuts implemented in our analysis are the same as those which were used in the unpolarised deep inelastic scattering at HERA. The calculations are based on the double ln^2(1/x) resummation which controls the polarised deep inelastic scattering for small values of the Bjorken parameter x. We show that this resummation substantially enhances the corresponding …
We calculate the QED corrections to deep inelastic scattering with tagged photons at HERA in the leading logarithmic approximation. Due to the special experimental setup, two large scales appear in the calculation that lead to two large logarithms of comparable size. The relation of our formalism to the conventional structure function formalism is outlined. We present some numerical results and compare with previous calculations.
The contribution of subleading reggeons to the diffractive structure function ${dF_{2}^D / dx_{\funp} dt}$ is estimated from the soft physics data. This contribution leads in a natural way to the violation of the factorization property of the diffractive structure function.
QCD coherence effects in initial state radiation at small x in deep inelastic scattering in HERA kinematics are studied with the help of the Monte Carlo model SMALLX. Theoretical assumptions based on the CCFM evolution equation are reviewed and the basic properties of the partonic final states are investigated. The results are compared with those obtained in the conventional DGLAP evolution scheme.
We discuss two topics in the production of heavy quarks in deep-inelastic scattering: the next-to-leading order Monte-Carlo HVQDIS and the next-to-leading logarithmic resummation of soft gluon effects, including estimates of next-to-next-to-leading order corrections therefrom.
The next-to-leading QCD calculation for the isolated photon and isolated photon plus jet photoproduction at the ep collider DESY HERA is presented. The theoretical uncertainties are discussed in details. The predictions are compared with predictions of other authors and with data. The sensitivity of the leading order cross section to the gluon density in both the real and the virtual photon is discussed as well.
The QCD analysis of deep inelastic diffractive scattering is performed assuming the dominance of the "soft" pomeron exchange and simple, physically motivated parametrization of parton distributions in a pomeron. Results of the analysis are compared with the recent data obtained by the H1 collaboration at HERA. Both the LO and NLO approximations are considered and the theoretical predictions concerning the quantity $R=F_L^D/F_T^D$ for diffractive structure functions are presented.
The H1 Collaboration recently reported a new analysis on the inelastic photo- production of J/ψmesons at DESY HERA ep collider. We show that these new experimental results are well described by the Color Evaporation Model for quarkonium production. Moreover, this new data requires the introduction of resolved photon contributions in order to explain the results on small charmonium energy fraction, indicating that colored c \bar{c} pairs also contribute to the process.
A next-to-leading order Monte Carlo program for the calculation of heavy quark cross sections in deeply inelastic scattering is described. Concentrating on charm quark and D^*(2010) production at HERA, several distributions are presented and their variation with respect to charm quark mass, parton distribution set, and renormalization-factorization scale is studied.
The coefficient functions for heavy-flavour production in deeply inelastic electron-hadron scattering have been calculated previously. Analytic expressions are impossible to publish due to their length. Therefore we have tabulated them as two-dimensional arrays as is often done for the scale-dependent parton densities. Using this computer program we present event rates for charm production at HERA in bins of $x$ and $Q^2$. These rates are insensitive to variations in the factorization and renormalization scale $μ$.
An introduction and summary is given of the main results achieved by working group 1: Structure Functions in Deep Inelastic Scattering at HERA. The prospects were discussed of future measurements of the structure functions $F_{2}, F_{L}, xG_{3}, F_{2}^{Q\overline{Q}}$ and $F_π$ at HERA. The results represent a long term programme of experimentation with high luminosity, different lepton beam charges, proton and deuteron beams, allowing for precision measurements. The theoretical investigations focussed on QED corrections, higher order QCD corrections for different observables, resummation of s…
We have substantially extended our analysis of the partonic content of the pomeron. Ambiguities in the normalization of the pomeron flux and the possiblity of a direct coupling of the pomeron to single quarks are discussed, yielding two equally possible scenarios for the parton distributions in the pomeron. We discuss various experimental tests of these scenarios.
High energy scattering processes of charged particles are accompanied by radiation of hard photons. Emission collinear to the incident particles, which leads to a reduction of the effective beam energy, and the possibility to directly measure these photons at the HERA electron-proton collider provides important physics opportunities. For deep inelastic scattering, the measurement of radiative processes extends the kinematic range accessible to the HERA experiments to lower Q^2, as well as helps in separating the proton structure functions without the need to run at different collider energies.…
In the framework of semihard (k$_T$ factorization) QCD approach, we consider the differential cross sections of $D^{*\pm}$ meson production at HERA. The consideration is based on BFKL and CCFM gluon distributions. We find that in the case of BFKL LO gluon distribution the theoretical results are sensitive to the Pomeron intercept parameter $Δ$. We present a comparison of the theoretical results with available ZEUS experimental data.
The main experimental results on jet production at HERA are reviewed. A study of jet shapes shows that the internal structure of jets is well understood. The potential to accurately determine the strong coupling constant using jet rates is discussed. First attempts to extract the gluon density in next-to-leading order are presented. Although fixed order perturbative QCD is able to describe the shape of most variables associated to the hard subprocess leading to jets, it does not reproduce the absolute dijet rate over a large phase space region.
We calculate the cross section of beauty production in electron-proton deep inelastic scattering at HERA collider in the framework of the kt-factorization approach. The unintegrated gluon distributions in a proton are obtained from the full CCFM, from unified BFKL-DGLAP evolution equations as well as from the Kimber-Martin-Ryskin prescription. We investigate different production rates and study the b-quark contribution to the inclusive proton structure function F2(x,Q2) at small x and at moderate and high values of Q2. Our theoretical results are compared with the recent experimental data take…
Two-jet cross sections in deep inelastic scattering at HERA are calculated in next-to-leading order. The importance of higher order corrections and recombination scheme dependencies is studied for various jetalgorithms. Some implications for the determination of $α_s(μ_R^2)$, the determination of the gluon density and the associated forward jet production in the low $x$ regime at HERA are briefly discussed.
The luminosity of the electron-proton collider, HERA, will be increased by a factor of five during the long shutdown starting September 2000. At the same time longitudinal lepton beam polarisation will be provided for the collider experiments H1 and ZEUS. These far reaching upgrades to the machine will be matched by upgrades to the detectors. The result will be a unique facility for the study of the structure of the proton and the nature of the strong and electroweak interactions. The physics potential of the upgraded accelerator is discussed here.
We compare recent experimental results for one-particle-inclusive processes in deeply inelastic scattering at HERA with theoretical predictions in next-to-leading-order QCD perturbation theory, and study the factorization scale dependence of cross sections and charged multiplicities. In the future, for the HERA machine running at design luminosity, scaling violations of fragmentation functions permit the measurement of the strong coupling constant. We estimate the size of the statistical error of $α_s$ that can be achieved, and study the theoretical error due to the various parton density para…
We present results from NLO QCD calculations on the production of jets in ep collisions at HERA in a continuous range of photon virtuality Q^2. Special attention is given to the collinear singularities from the virtual photon and the resolved virtual photon component of the cross sections. Comparisons with dijet data from H1 are shown and the infrared sensitivity of dijet cross sections is discussed.
The numerical study of QED radiative corrections in the low x region for the H1 experiment at HERA was performed. The analytical program TERAD91 was used to obtain the values of the radiative correction factor for the first measurement of the proton structure function F2(x,Q2) in the range x= 10^{-2} - 10^{-4} and 5 < Q2 < 80 GeV2.
We present a BFKL phenomenology of structure functions in the framework of the generalized BFKL equation for the dipole cross section proposed by us recently. We show that the HERA measurements of excitation of charm at $Q^{2} \lsim $10 GeV$^{2}$ allow determination of the intercept of the BFKL pomeron. A comparison with the experimental data suggests a large contribution from the nonperturbative cross section for colour dipoles of large size $r$.
The diffraction dissociation of virtual photons is considered in the framework of conventional Regge theory. It is shown that the recent HERA data on large rapidity gap events can be successfully described in terms of the Pomeron structure function. Using Regge factorization, the latter can be related to the deuteron structure function. The parameters which relate these two structure functions are determined from soft hadronic diffraction data. The size of the shadowing corrections at low x and large Q**2 is also obtained.
In the framework of k_T-factorization QCD approach and the colour singlet model we consider J/ψinelastic photo- and leptoproduction processes at HERA. We investigate the dependences of the single differential and double differential cross section on different forms of the unintegrated gluon distribution. The z and p_T dependences of the spin aligment parameter αare presented also. Our theoretical predictions agree well with recent data taken by the H1 and ZEUS collaborations at HERA. It is shown that experimental study of the polarization J/ψmesons at low Q^2 < 1 GeV^2 is an additional test of…
The measurement of the inelastic photoproduction of charmonium at HERA seems to have ignited a new charmonium crisis. The (already discredited) color singlet model fits the data for large charmonium energy fraction z, where the NRQCD model qualitatively fails. We here point out that by the straightforward inclusion of color singlet and octet processes in the soft color (color evaporation) scheme, the HERA data can be accommodated for all z. We anticipate that the color singlet model will fail at low z, as it does in hadroproduction.
The uncertainties involved in the calculation of bottom quark cross-sections in deep-inelastic scattering at HERA are studied in different phase space regions. Besides the inclusive bottom quark cross-section, definitions closer to the detector acceptance requiring at least one high energetic muon from the semi-leptonic \bquark decay or a jet with high transverse energy are investigated. For each case the uncertainties due to the choice of the renormalisation and factorisation scale as well as the \bquark mass are estimated in the perturbative NLO QCD calculation and furthermore uncertainties …
We consider J/Psi meson production in $ep$ deep inelastic scattering in the colour singlet model using the k_T-factorization QCD approach. We investigate the z-, Q^2-, p_T^2-, y^*- and W-dependences of inelastic J/Psi production on different forms of the unintegrated gluon distribution. The p_T^2- and Q^2-dependences of the J/Psi spin aligment parameter alpha are presented also. We compare the theoretical results with recent experimental data taken by the H1 and ZEUS collaborations at HERA. It is shown that experimental study of the polarization J/Psi mesons at Q^2 < 1 {GeV}^2 is an additional…
The measurements of the hadronic final state in deep inelastic scattering at HERA are reviewed and discussed in the context of QCD. Covered are the general event properties in terms of energy flows, charged particle production, and charm and strangeness production. Quark fragmentation properties are studied in the Breit frame. Event shape measurements allow "power corrections" to be applied and the strong coupling alpha_s to be extracted. Other alpha_s measurements are based on dijet rates. Jet rates as well as charm production have been used to determine the gluon density in the proton. Indic…
We investigate the prompt photon production in deep inelastic scattering at HERA in the framework of kt-factorization QCD approach. Our study is based on the off-shell partonic amplitude e q* -> e gamma q, where the photon radiation from the leptons as well as from the quarks is taken into account. The unintegrated quark densities in a proton are determined using the Kimber-Martin-Ryskin prescription. The conservative error analisys is performed. We investigate both inclusive and jet associated prompt photon production rates. Our predictions are compared with the recent experimental data taken…
The "triple-Regge" analysis of subleading Reggeon contributions to the diffractive structure function in DIS at HERA is presented. The recently published data allow to estimate the only free parameter of the analysis related to the ratio of the RRP and PPP couplings. The large value of this ratio is prefered which is in agreement with analyses of soft hadronic interactions. The role of the subleading Reggeons as well as pions for the fast forward neutron production in diffractive processes is estimated. The forward piN state production is also discussed.
Data on the hadronic final state of deep-inelastic events at the ep collider HERA are reviewed. Fragmentation properties in the current region extracted from charged particle spectra are compared to e+e- and fixed target experiments at lower center of mass energies. A measurement of the strong coupling constant from integrated jet rates is presented and prospects to extract the gluon density in the proton by tagging vector mesons are discussed. Data on the inclusive mean transverse energy together with the transverse momentum distribution of single charged particles indicate an increased gluon…
The distribution of transverse energy, $E_T$, which accompanies deep-inelastic electron-proton scattering at small $x$, is predicted in the central region away from the current jet and proton remnants. We use BFKL dynamics, which arises from the summation of multiple gluon emissions at small $x$, to derive an analytic expression for the $E_T$ flow. One interesting feature is an $x^{-ε}$ increase of the $E_T$ distribution with decreasing $x$, where $ε= (3α_s/π)2\log 2$. We perform a numerical study to examine the possibility of using characteristics of the $E_T$ distribution as a means of ident…
We recently derived explicit solutions of the leading-order Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) equations for the $Q^2$ evolution of the singlet structure function $F_s(x,Q^2)$ and the gluon distribution $G(x,Q^2)$ using very efficient Laplace transform techniques. We apply our results here to a study of the HERA data on deep inelastic $ep$ scattering as recently combined by the H1 and ZEUS groups. We use initial distributions $F_2^{γp}(x,Q_0^2)$ and $G(x,Q_0^2)$ fixed by a global fit to the HERA data. From $F_2^{γp}(x,Q_0^2)$ we obtain the singlet quark distribution $F_s(x,Q_0^…
We perform a calculation on the polarization of J/psi production in deep inelastic scattering in the HERA energy range. For the inclusive production distributions, we find that the color-singlet contributions are consistent with the experimental data in the major region of z (z>0.4). Only in low z regions, there are some hints of the need of the color-octet contributions to describe the experimental data. For the polarization of J/psi in DIS processes, we find the parameter alpha changes with Q^2. Especially, at higher Q^2, difference on alpha between color-singlet and color-octet contribution…
Since its commissioning in 1991, the ep collider HERA has been running successfully for almost a decade without stopping improving its performance. In this report, the inclusive cross section and structure function measurements for the deep inelastic scattering of neutral and charged current processes in the full HERA kinematic domain are reviewed. The results are compared with the Standard Model expectations for the deep inelastic scattering processes. The new insights into the proton structure and on the underlying strong and electroweak interactions are discussed.
The structure of the hadronic final state in deep inelastic scattering at HERA is studied on the level of the Monte Carlo event generator. Special emphasis is given to the colour coherence phenomenon in the current fragmentation region. It is shown that results of perturbative QCD recently tested in $e^+e^-$ annihilation at LEP also describe production of hadrons in current fragmentation region of deep inelastic scattering.
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 addre…
We calculate the cross section of J/psi plus jet associated production in ep deep-inelastic scattering within the factorization formalism of nonrelativistic quantum chromodynamics. Our analytic results disagree with previous analyses, both for the colour-singlet and colour-octet channels. Our theoretical predictions agree reasonably well with recent data taken by the H1 Collaboration at DESY HERA, significantly better than those obtained within the colour-singlet model.
In scenarios motivated by string theories, it is possible to have extra Kaluza-Klein dimensions compactified to rather large magnitudes, leading to large effects of gravity at scales down to a TeV. The effect of the spin-2 Kaluza-Klein modes on the deep-inelastic cross-section at HERA is investigated. We find that the data can be used to obtain bounds on the effective low energy scale, $M_S$.
We propose a method to assess the quality of geometrical scaling in Deep Inelastic Scattering and apply it to the combined HERA data on $γ^{\ast}p$ cross-section. Using two different approaches based on Bjorken $x$ binning and binning in $γ^{\ast}p$ scattering energy $W$, we show that geometrical scaling in variable $τ\sim Q^{2} x^λ$ works well up to Bjorken $x$'s 0.1. The corresponding value of exponent $λ$ is 0.32 -- 0.34.
We present the first study of the QCD corrections to the color-singlet (CS) $J/ψ$ production in deeply inelastic $ep$ scattering at HERA. The $K$-factor ranges from $0.85$ to $2.38$ in the kinematic regions we study. In low transverse momentum regions, the $K$-factors is even smaller, and close to 1, which indicates good convergence of the perturbative expansion. With the QCD corrections, the CS cross section is still below the data. At least at QCD next-to-leading order, the color-octet mechanism is necessary to describe the data.
This paper presents the result of a search for a narrow strange baryonic state in the invariant-mass distribution of $pK^0_S(\overline{p}K^0_S)$ in HERA II data (2003-2007). The search was performed in the deep inelastic scattering (DIS) data with photon virtuality, $Q^2$, between 20 and 100 GeV. The analysis in HERA II period has improvements over the previous ZEUS analysis in HERA I period (1996-2000). These consist of large statistics and improved particle identification performance by using both of the CTD $dE/dx$ and the MVD $dE/dx$ in this search. Contrary to evidence for such an exotic …
We use recently proposed method of ratios to assess the quality of geometrical scaling in deep inelastic scattering for different forms of the saturation scale. We consider original form of geometrical scaling (motivated by the Balitski-Kovchegov (BK) equation with fixed coupling) studied in more detail in our previous paper, and four new hypotheses: phenomenologically motivated case with $Q^2$ dependent exponent $λ$ that governs small $x$ dependence of the saturation scale, two versions of scaling (running coupling 1 and 2) that follow from the BK equation with running coupling, and diffusive…
A first measurement of the 1-jettiness event shape observable $τ_1^b$ in neutral-current deep inelastic scattering is presented. For the measurement, the equivalence of $τ_1^b$ to the DIS thrust observable defined in the Breit frame is utilised. The data were taken by the H1 experiment at HERA from 2003 to 2007 at a centre of mass energy of $\sqrt{s}=319 \text{ GeV}$. The data amount to an integrated luminosity of $351.6\text{ pb}^{-1}$. The triple-differential cross sections are presented as a function of the 1-jettiness $τ^1_b$, the virtuality of the exchanged boson $Q^2$ and the inelasticit…
We determine the charm-quark mass mc(mc) in the MS-bar scheme using measurements of charm production in deep-inelastic ep scattering at HERA in the kinematic range of photon virtuality from 5 to 1000 GeV squared and Bjorken scaling variable from 0.0001 to 0.5. The extraction of charm quark mass from this process with space-like kinematics provides complementary information to results from hadronic processes. The QCD analysis of the HERA data yields a value of mc(mc) of 1.27 plus minus 0.05(exp) plus 0.06 minus 0.01(scale) GeV at next-to-leading order and mc(mc) of 1.36 plus minus 0.04(exp) plu…
Measurements of open charm and beauty production cross sections in deep inelastic $ep$ scattering at HERA from the H1 and ZEUS Collaborations are combined. Reduced cross sections are obtained in the kinematic range of negative four-momentum transfer squared of the photon $2.5$ GeV$^2<Q^2<2000$ GeV$^2$ and Bjorken scaling variable $3\cdot10^{-5}<x_{\text{Bj}}<5\cdot10^{-2}$. The combination method accounts for the correlations of the statistical and systematic uncertainties among the different datasets. Perturbative QCD calculations are compared to the combined data. A next-to-leading order QCD…
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…
A phenomenological study of the final combined HERA data on inclusive deep inelastic scattering (DIS) has been performed. The data are presented and investigated for a kinematic range extending from values of the four-momentum transfer, $Q^2$, above 10$^4$ GeV$^2$ down to the lowest values observable at HERA of $Q^2$ = 0.045 GeV$^2$ and Bjorken $x$, $x_{\rm Bj}$ = 6 $\cdot$ 10$^{-7}$. The data are well described by fits based on perturbative quantum chromodynamics (QCD) using collinear factorisation and evolution of the parton densities encompassed in the DGLAP formalism from the highest $Q^2$…
The parameters of the electroweak theory are determined in a combined electroweak and QCD analysis using all deep-inelastic $e^+p$ and $e^-p$ neutral current and charged current scattering cross sections published by the H1 Collaboration, including data with longitudinally polarised lepton beams. Various fits to Standard Model parameters in the on-shell scheme are performed. The mass of the $W$ boson is determined as $m(W)=80.520\pm 0.115$ GeV. The axial-vector and vector couplings of the light quarks to the $Z$ boson are also determined. Both results improve the precision of previous H1 deter…
After fifteen years of running and a further five years of analysis, the final inclusive deep inelastic scattering cross sections from H1 and ZEUS have been published. Measurements of neutral current and charged current processes in ep collisions at HERA are presented. These provide us with the most valuable information on the structure of the proton, which tells us about the fundamental structure of matter and is essential for understanding processes at proton colliders such as the Large Hadron Collider. The measurements also demonstrate the chiral structure of the weak force and give a beaut…
