arXiv subjects
Publications and source records attributed to J. Kwiecinski.
The proton spin dependent structure function $g_1^p$ is analysed using the unified scheme incorporating both Altarelli-Parisi evolution and the double $ln^2(1/x)$ effects at low $x$. The latter are found to be very important in the region of $x$ which can possibly be probed at HERA. Predictions for the polarized gluon distribution $ΔG(x)$ at low $x$ are also given.
The reactions gamma-gamma to eta_c eta_c and gamma gamma to eta_c + X are discussed within the three gluon exchange model. We give predictions for the differential cross-sections and discuss feasibility of measuring these processes at LEP2 and TESLA. The total cross-sections were estimated to be approximately equal to 40 fb and 120 fb for gamma-gamma to eta_c eta_c and gamma-gamma to eta_c + X respectively assuming exchange of elementary gluons that corresponds to the odderon with intercept equal to unity. These values can be enhanced by a factor equal to 1.9 and 2.1 for LEP2 and TESLA energies if the odderon intercept is equal to 1.07. The estimate of cross-sections sigma(e^+ e^- to e^+ e^- eta_c eta_c) and sigma (e^+ e^- to e^+ e^- eta_c + X) for untagged e^+ and e^- is also given.
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.
Theory and phenomenology of the eta_c photo- and electroproduction is developed from the point of view of probing the odderon singularity in QCD which corresponds to the three gluon exchange mechanism. This mechanism leads to the cross-sections which are independent of W^2 for the exchange of three non-interacting gluons or exhibit increase with increasing W^2 (or 1/x) for the odderon intercept above unity. The η_c electroproduction in the three gluon exchange mechanism is shown to be entirely controlled by the transversely polarised virtual photons. The magnitude of the eta_c photoproduction cross-section is estimated to be around 11-45pb. The t-dependence of the differential cross-section is also discussed.
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 study the transverse momentum ($p_T$) spectrum of charged particles produced in deep inelastic scattering (DIS) at small Bjorken $x$ in the central region between the current jet and the proton remnants. We calculate the spectrum at large $p_T$ with the BFKL $\ln (1/x)$ resummation included and then repeat the calculation with it omitted. We find that data favour the former. We normalize our BFKL predictions by comparing with HERA data for DIS containing a forward jet. The shape of the $x$ distribution of DIS + jet data are also well described by BFKL dynamics.
We introduce a coupled pair of evolution equations for the unintegrated gluon distribution and the sea quark distribution which incorporate both the resummed leading $\ln (1/x)$ BFKL contributions and the resummed leading $\ln (Q^2)$ DGLAP contributions. We solve these unified equations in the perturbative QCD domain. With only two physically motivated parameters we obtain an excellent description of the HERA $F_2$ data.
We argue that the use of the universal unintegrated gluon distribution and the $k_T$ (or high energy) factorization theorem provides the natural framework for describing observables at small x. We introduce a coupled pair of evolution equations for the unintegrated gluon distribution and the sea quark distribution which incorporate both the resummed leading $ln (1/x)$ BFKL contributions and the resummed leading $ln (Q^2)$ GLAP contributions. We solve these unified equations in the perturbative QCD domain using simple parametic forms of the nonperturbative part of the integrated distributions. With only two (physically motivated) input parameters we find that this $k_T$ factorization approach gives an excellent description of the measurements of $F_2 (x,Q^2)$ at HERA. In this way the unified evolution equations allow us to determine the gluon and sea quark distributions and, moreover, to see the x domain where the resummed $ln (1/x)$ effects become significant. We use $k_T$ factorization to predict the longitudinal structure function $F_L (x,Q^2)$ and the charm component of $F_2 (x,Q^2)$.
The QCD expectations for the behaviour of the deep inelastic scattering structure functions in the region of small values of the Bjorken parameter $x$ are summarized. The Balitzkij, Lipatov, Fadin, Kuraev (BFKL) equation which sums the leading powers of $α_s ln(1/x)$ is described and confronted with the "conventional" formalism based on the leading order QCD evolution equations. The small $x$ behaviour of the spin dependent structure function $g_1$ is also discussed. The dedicated measurements of the hadronic final state in deep inelastic scattering at small $x$ probing the QCD pomeron are described. This includes discussion of the deep inelastic scattering accompanied by forward jets as well as production of forward prompt photons and $π^0$-s. Finally the basic facts concerning the deep inelastic diffraction are briefly summarized.
We predict the rate of deep inelastic scattering (DIS) events containing an identified forward $π^0$ that is expected in the experiments at the HERA electron-proton collider, in order to see if this process can be used as an indicator of the underlying small $x$ dynamics. We determine the background due to deep inelastic events containing forward photons which are fragments of the forward jet. We compare the DIS + $π^0$ cross section with that of the DIS + parent jet process.
Elements of the pomeron phenomenology within the Regge pole exchange picture are recalled. This includes discussion of the high energy behaviour of total cross-sections, the triple pomeron limit of the diffractive dissociation and the single particle distributions in the central region. The BFKL pomeron and QCD expectations for the small $x$ behaviour of the deep inelastic scattering structure functions are discussed. The dedicated measurements of the hadronic final state in deep inelastic scattering at small $x$ probing the QCD pomeron are described. The deep inelastic diffraction is also discussed.
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.
The theory of deep inelastic scattering structure functions is reviewed with an emphasis put on the QCD expectations of their behaviour in the region of small values of the Bjorken parameter $x$.
We derive a modified form of the BFKL equation which enables the structure of the gluon emissions to be studied in small $x$ deep inelastic scattering. The equation incorporates the resummation of the virtual and unresolved real gluon emissions. We solve the equation to calculate the number of small $x$ deep-inelastic events containing 0,1,2 ...resolved gluon jets, that is jets with transverse momenta $q_{T} > μ$. We study the jet decomposition for different choices of the jet resolution parameter $μ$.
We calculate the rate of producing deep inelastic events containing an energetic isolated forward photon at HERA. We quantify the enhancement arising from the leading $\log 1/x$ gluon emissions with a view to using such events to identify the underlying dynamics.
A model for the longitudinal structure function $F_L$ at low $x$ and low $Q^2$ is presented, which includes the kinematical constraint $F_L \sim Q^4$ as $Q^2 \rightarrow 0$. It is based on the photon-gluon fusion mechanism suitably extrapolated to the region of low $Q^2$. The contribution of quarks having limited transverse momentum is treated phenomenologically assuming that it is described by the soft pomeron exchange mechanism. The ratio $R={F_L/(F_2-F_L)}$, with the $F_2$ appropriately extrapolated to the region of low $Q^2$, is also discussed.
The BFKL and the unified angular-ordered equations are solved to determine the gluon distribution at small $x$. The impact of kinematic constraints is investigated. Predictions are made for observables sensitive to the gluon at small $x$. In particular comparison is made with measurements at the HERA electron-proton collider of the proton structure function $F_2 (x, Q^2)$ as a function of $\ln Q^2$, the charm component, $F_2^c(x,Q^2)$ and diffractive $J/ψ$ photoproduction.
The perturbative QCD predictions concerning deep inelastic scattering at low $x$ are summarized. The theoretical framework based on the leading log $1/x$ resummation and $k_t$ factorization theorem is described and some recent developments concerning the BFKL equation and its generalization are discussed. The QCD expectations concerning the small $x$ behaviour of the spin dependent structure function $g_1(x,Q^2)$ are briefly summarized and the importance of the double logarithmic terms which sum contributions containing the leading powers of $α_s ln^2(1/x)$ is emphasised. The role of studying final states in deep inelastic scattering for revealing the details of the underlying dynamics at low $x$ is pointed out and some dedicated measurements, like deep inelastic scattering accompanied by an energetic jet, the measurement of the transverse energy flow etc., are briefly discussed.