First results from ALICE

The Large Hadron Collider provides p-p and Pb-Pb collisions at the highest centre-of-mass energies to date, which allow to study high-pT particle, jet and heavy-quark properties in a new energy regime. We present first results from both p-p and Pb-Pb collisions that provide a first characterization of the properties of the matter formed in these collisions

Azimuthal Asymmetries: Access to Novel Structure Functions

One of the most interesting consequence of non-zero intrinsic transverse momentum of partons in the nucleon is the nontrivial azimuthal dependence of the cross section of hard scattering processes. Many of the observable asymmetries contain unknown functions which provide essential information on the quark and gluon structure. Several of them have been studied in the last few years; we discuss their qualitative and quantitative features in semi-inclusive DIS.Comment: 6 pages, LaTeX, 7 eps figures, Talk presented at the 15th International Spin Physics Symposium, Spin 2002, Brookhaven National Laboratory, September 9-14, 200

Proces hadronizacije u duboko-neelastičnom raspršenju u eksperimentu HERMES

The influence of the nuclear medium on lepto-production of hadrons was studied in the HERMES experiment at DESY in semi-inclusive deep-inelastic scattering of 27.6 GeV and 12 GeV positrons off deuterium, and off light and heavy targets. The differential multiplicity for nuclei relative to that of deuterium has been measured for the first time for various identified hadrons (π +, π −, π 0 , K+, K−, p and ¯p) as a function of the virtual photon energy ν, the fraction z of this energy transferred to the hadron, and the hadron transverse momentum squared p 2 t .Proučavamo utjecaj nuklearne tvari na leptonsku tvorbu hadrona u mjerenju HERMES u DESYu poluinkluzivnim duboko-neelastičnim raspršenjem pozitrona energije 27.6 GeV i 12 GeV u deuteriju, te lakim i teškim metama. Načinili smo prva mjerenja omjera diferencijalne višestrukosti za jezgre u odnosu prema deuteriju za više utvrđenih hadrona (π +, π −, π 0 , K+, K−, p and ¯p) u ovisnosti o virtualnoj energiji fotona ν, dijela te energije z predane hadronu i kvadrata poprečnog impulsa pt2

Proces hadronizacije u duboko-neelastičnom raspršenju u eksperimentu HERMES

The influence of the nuclear medium on lepto-production of hadrons was studied in the HERMES experiment at DESY in semi-inclusive deep-inelastic scattering of 27.6 GeV and 12 GeV positrons off deuterium, and off light and heavy targets. The differential multiplicity for nuclei relative to that of deuterium has been measured for the first time for various identified hadrons (π +, π −, π 0 , K+, K−, p and ¯p) as a function of the virtual photon energy ν, the fraction z of this energy transferred to the hadron, and the hadron transverse momentum squared p 2 t .Proučavamo utjecaj nuklearne tvari na leptonsku tvorbu hadrona u mjerenju HERMES u DESYu poluinkluzivnim duboko-neelastičnim raspršenjem pozitrona energije 27.6 GeV i 12 GeV u deuteriju, te lakim i teškim metama. Načinili smo prva mjerenja omjera diferencijalne višestrukosti za jezgre u odnosu prema deuteriju za više utvrđenih hadrona (π +, π −, π 0 , K+, K−, p and ¯p) u ovisnosti o virtualnoj energiji fotona ν, dijela te energije z predane hadronu i kvadrata poprečnog impulsa pt2

Hadron production in deep inelastic lepton-nucleus scattering

Predictions for semi-inclusive deep inelastic lepton-nucleus scattering are presented. Both the effects of gluon radiation by the struck quark and the absorption of the produced hadron are considered. The gluon radiation covers a larger window in virtuality $Q^2$ because of the increased deconfinement of quarks inside nuclei. The absorption of hadrons formed inside the nucleus is described with a flavor dependent cross section. Calculations for rescaled fragmentation functions and nuclear absorption are compared with the EMC and HERMES data for N, Cu and Kr targets with respect to the deuteron target. Predictions for Ne and Xe targets in the HERMES kinematic regime are given.Comment: 27 pages, 12 figures. Section 2 on rescaling modified. Extended discussion of the results in Sec. 5 and 6. To be published in Nucl.Phys.

Low energy onset of nuclear shadowing in photoabsorption

The early onset of nuclear shadowing in photoabsorption at low photon energies has recently been interpreted as a possible signature of a decrease of the rho meson mass in nuclei. We show that one can understand this early onset within simple Glauber theory if one takes the negative real part of the rho N scattering amplitudes into account, corresponding to a higher effective mass of the rho meson in nuclear medium.Comment: REVTEX, 9 pages, including 4 eps figure

Performance of the Electromagnetic Calorimeter of the HERMES Experiment

The performance of the electromagnetic calorimeter of the HERMES experiment is described. The calorimeter consists of 840 radiation resistant F101 lead-glass counters. The response to positrons up to 27.5 GeV, the comparison between the measured energy and the momentum reconstructed from tracking, long-term stability, hadron rejection and neutral meson invariant mass reconstruction are shown.Comment: 22 pages, 13 figures, LaTeX, accepted by NI

Atomic Mass Dependence of Hadron Production in Deep Inelastic Scattering on Nuclei

Hadron production in lepton-nucleus deep inelastic scattering is studied in an absorption model. In the proposed model, the early stage of hadronization in the nuclear medium is dominated by prehadron formation and absorption, controlled by flavor-dependent formation lengths and absorption cross sections. Computations for hadron multiplicity ratios are presented and compared with the HERMES experimental data for pions, kaons, protons and antiprotons. The mass-number dependence of hadron attenuation is shown to be sensitive to the underlying hadronization dynamics. Contrary to common expectations for absorption models, a leading term proportional to A^{2/3} is found. Deviations from the leading behavior arise at large mass-numbers and large hadron fractional momenta.Comment: 30 pages, 10 figures, v2: minor changes (legend in figs 5 & 6 is added), v3: additional explanations are added, v4: Version combines v3 and the erratum hep-ph/050803

Hadron formation in high energy photonuclear reactions

We present a new method to account for coherence length effects in a semi-classical transport model. This allows us to describe photo- and electroproduction at large nuclei (A>12) and high energies using a realistic coupled channel description of the final state interactions that goes beyond simple Glauber theory. We show that the purely absorptive treatment of the final state interactions can lead to wrong estimates of color transparency and formation time effects in particle production. As an example, we discuss exclusive rho^0 photoproduction on Pb at a photon energy of 7 GeV as well as K^+ production in the photon energy range 1-7 GeV.Comment: 14 pages, 6 figures, version published in Phys. Rev.