Correlations between and Multiplicity in a Single BFKL Pomeron
Strong correlations are obtained between the number and the average transverse momentum of jets emitted by the exchange of a single BFKL Pomeron.
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arXiv subjects
C. Merino
Publications and source records attributed to C. Merino.
Theoretical Approaches to HERA Physics
A review is presented of the different theoretical models proposed to approach consistently the interplay between soft and hard physics, that can now be studied experimentally at HERA for the first time.
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Correlations between and jet multiplicities from the BFKL chain
Strong correlations between the number of emitted jets and their average transverse momentum are found for the events resulting from the exchange of a single BFKL pomeron. transverse momentum are found for the events resulting from the exchange.
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Jet Asymmetry in High Energy Diffractive Production
We propose the asymmetry in the fractional energy of charm versus anticharm jets produced in high energy diffractive photoproduction as a sensitive test of the interference of the Odderon (C = -) and Pomeron (C = +) exchange amplitudes in QCD. If measured at HERA, this asymmetry could provide the first experimental evidence of the Odderon.
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On the Behavior of F2 and its Logarithmic Slopes
It is shown that the CKMT model for the nucleon structure function F2, taken as the initial condition for the NLO evolution equations in perturbative QCD, provides a good description of the HERA data when presented in the form of the logarithmic slopes of F2 vs x and Q2 (Caldwell-plot), in the whole available kinematic ranges. Also the results obtained for the behavior of the gluon component of a nucleon are presented.
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THE CKMT Model and the Theoretical Description of the Caldwell-plot
The CKMT model for the nucleon structure function F_2 is in good agreement with the HERA data at low and moderate Q^2. The fit to the same data obtained with a modified version of the model in which a logarithmic dependence on Q^2 has been included is also discussed. Finally, we show how the parametrization of the CKMT model for the nucleon structure function F_2 describes the HERA data when presented in the Caldwell-plot as the behavior of the logarithmic slopes of F_2 vs x and Q^2.
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Perturbative QCD relations inspired by hypothetical tau leptons
We review our recent works on tests of perturbative QCD, inspired by the relation between the hadronic decay of the tau lepton and the e+ e- annihilation into hadrons. First, we present a set of commensurate scale relations that probe the self-consistency of leading-twist QCD predictions for any observable which defines an effective charge. These tests are independent of the renormalization scheme and scale, and are applicable over wide data ranges. As an example we apply this approach to R_{e+ e-}. Second, using a differential form of these conmensurate scale relations, we present a method to measure the QCD Gell-Mann--Low Psi function.
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Measuring the QCD Gell Mann-Low $Ψ$-function
We present a general method for extracting the Gell Mann-Low logarithmic derivative of an effective charge of an observable directly from data as a mean for empirically verifying the universal terms of the QCD $β$-function. Our method avoids the biases implicit in fitting to QCD-motivated forms as well as the interpolation errors introduced by constructing derivatives from discrete data. We also derive relations between moments of effective charges as new tests of perturbative QCD.
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Theoretical description of the HERA data on $F_2$
It is shown that the CKMT model for the nucleon structure function $F_2$ gives a good description of the recent HERA data at low and moderate $Q^2$. Also the fit to the same data obtained with a modified version of the model in which a logarithmic dependence on $Q^2$ has been included, is presented. For moderate values of $Q^2$, in the current available range of $x$, the first parametrization leads to a better description of the data.
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Structure Functions of Nuclei at Small x and Diffraction at HERA
Gribov theory is applied to investigate the shadowing effects in the structure functions of nuclei. In this approach these effects are related to the process of diffractive dissociation of a virtual photon. A model for this diffractive process, which describes well the HERA data, is used to calculate the shadowing in nuclear structure functions. A reasonable description of the $x$, $Q^2$ and A-dependence of nuclear shadowing is achieved.
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Structure Functions of Nuclei at Small x and Diffraction at HERA
Gribov theory is applied to investigate the shadowing effects in the structure functions of nuclei. In this approach these effects are related to the process of diffractive dissociation of a virtual photon. A model for this diffractive process, which describes well the HERA data, is used to calculate the shadowing in nuclear structure functions. A reasonable description of the x, Q^2 and A-dependence of nuclear shadowing is achieved.
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Strange Baryon Production in Heavy Ion Collisions
The rapidity distribution of $Λ$ and $\barΛ$ produced in nucleus-nucleus collisions at CERN energies is studied in the framework of an independent string model - with quark-antiquark as well as diquark-antidiquark pairs in the nucleon sea. It is shown that, besides the $Λ$-$\barΛ$ pair production resulting from the fragmentation of sea diquarks, final state interactions of co-moving secondaries $π+ N \to K + Λ$ and $π+ \bar{N} \to K + \barΛ$ are needed in order to reproduce the data. Predictions for $Pb$-$Pb$ collisions are presented.
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Hard Diffraction at HERA and the Gluonic Content of the Pomeron
We show that the previously introduced CKMT model, based on conventional Regge theory, gives a good description of the HERA data on the structure function F_2^D for large rapidity gap (diffractive) events. These data allow, not only to determine the valence and sea quark content of the Pomeron, but also, through their Q^2 dependence, give information on its gluonic content. Using DGLAP evolution, we find that the gluon distribution in the Pomeron is very hard and the gluons carry more momentum than the quarks. This indicates that the Pomeron, unlike ordinary hadrons, is a mostly gluonic object. With our definition of the Pomeron flux factor the total momentum carried by quarks and gluons turns out to be 0.3-0.4 - strongly violating the momentum sum rule.
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Diffractive Dissociation in Deep Inelastic Scattering at HERA
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.
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Structure functions and low x physics
In the framework of conventional Regge theory we present a common description of total photon-proton cross-section and proton structure functions in the region $0 \leq Q^2 \leq 5 \ {\rm GeV}^2$. Using it as an initial condition in the perturbative QCD evolution equation, we describe structure functions at any $Q^2$ and $x$ - including the small $x$ region explored at HERA.
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