Higher-twist contributions to large pT hadron production in hadronic collisions

The scaling behavior of large-pT hadron production in hadronic collisions is investigated. A significant deviation from the NLO QCD predictions is reported, especially at high values of xT=2pT/sqrt(s). In contrast, the prompt photon and jet production data prove in agreement with leading-twist expectations. These results are interpreted as coming from a non-negligible contribution of higher-twist processes, where the hadron is produced directly in the hard subprocess. Predictions for scaling exponents at RHIC are successfully compared to PHENIX preliminary measurements. We suggest to trigger on isolated large-pT hadron production to enhance higher-twist processes, and point that the use of isolated hadrons as a signal for new physics at colliders can be affected by the presence of direct hadron production processes.Comment: 4 pages, 2 figures. Talk given at the 45th Rencontres de Moriond QCD and High Energy Interactions, La Thuile, Italy, 13-20 March 201

Higher-Twist Dynamics in Large Transverse Momentum Hadron Production

A scaling law analysis of the world data on inclusive large-pT hadron production in hadronic collisions is carried out. A significant deviation from leading-twist perturbative QCD predictions at next-to-leading order is reported. The observed discrepancy is largest at high values of xT=2pT/sqrt(s). In contrast, the production of prompt photons and jets exhibits the scaling behavior which is close to the conformal limit, in agreement with the leading-twist expectation. These results bring evidence for a non-negligible contribution of higher-twist processes in large-pT hadron production in hadronic collisions, where the hadron is produced directly in the hard subprocess rather than by gluon or quark jet fragmentation. Predictions for scaling exponents at RHIC and LHC are given, and it is suggested to trigger the isolated large-pT hadron production to enhance higher-twist processes.Comment: 5 pages, 4 figures. Extended introduction, additional reference

Photon tagged correlations in heavy ion collisions

A detailed study of various two-particle correlation functions involving photons and neutral pions is presented in proton-proton and lead-lead collisions at the LHC energy. The aim is to use these correlation functions to quantify the effect of the medium (in lead-lead collisions) on the jet decay properties. The calculations are carried out at the leading order in QCD but the next-to-leading order corrections are also discussed. The competition between different production mechanisms makes the connection between the jet energy loss spectrum and the gamma-pi correlations somewhat indirect while the gamma-gamma correlations have a clearer relation to the jet fragmentation properties.Comment: 32 pages, 19 figures. Minor changes, published versio

Non-universality of transverse Coulomb exchange at small x

Within an explicit scalar QED model we compare, at fixed x << 1, the leading-twist K_T-dependent `quark' distribution f_q(x, K_T) probed in deep inelastic scattering and Drell-Yan production, and show that the model is consistent with the universality of f_q(x, K_T). The extension of the model from the aligned-jet to the 'symmetric' kinematical regime reveals interesting properties of the physics of Coulomb rescatterings when comparing DIS and DY processes. At small x the transverse momentum induced by multiple scattering on a single centre is process dependent, as well as the transverse momentum broadening occurring in collisions on a finite size nuclear target.Comment: 28 pages, 3 eps figure

CFD aided design and experimental validation of an innovative Air Assisted Pure Water Jet cutting system

Water jet cutting has always been a promising technology because of its extreme simplicity and flexibility, even if it often suffers a lack of control on its process parameters, especially if compared to technologies such as laser cutting or electro-discharge machining. Recent studies have showed how the presence of water inside the orifice causes disturbances and instabilities which systematically affect the jet structure, both during the jet formation and the cutting process. These disturbances can be neglected in industrial applications, but they can play a relevant role in case of high-precision water jet machining. The aim of the research presented in this paper is to develop an innovative system able to modify the orifice flow field by means of a simple modification of the standard cutting head geometry; the system allows the controlled injection of air inside the primary orifice to prevent the jet instabilities and to adapt the level of jet coherence to the specific machining operation. The fluid dynamics aspects of the outflow process are investigated by means of a 3D numerical simulation with the Ansys Fluent CFD solver, while considerable experimental efforts are provided in order to validate the numerical model and finally evaluate the system performances on real case studies

Systematic study of high-pTp_T hadron and photon production with the PHENIX experiment

The suppression of hadrons with large transverse momentum ($p_{\rm T}$) in central Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV compared to a binary scaled p+p reference is one of the major discoveries at RHIC. To understand the nature of this suppression PHENIX has performed detailed studies of the energy and system-size dependence of the suppression pattern, including the first RHIC measurement near SPS energies. An additional source of information is provided by direct photons. Since they escape the medium basically unaffected they can provide a high $p_{\rm T}$ baseline for hard-scattering processes. An overview of hadron production at high $p_{\rm T}$ in different colliding systems and at energies from $\sqrt{s_{\rm NN}} = 22.4 - 200$ GeV will be given. In addition, the latest direct photon measurements by the PHENIX experiment shall be discussed.Comment: 6 pages, 3 figures, Proceeding for the Conference Strangeness in Quark Matter, Levoca, Slovakia, June 24-29, 200

Single inclusive pion pT-spectra in proton-proton collisions at sqrt(s) = 22.4GeV: data versus perturbative QCD calculations

We compare the inclusive transverse momentum spectra of single pions above pT = 3 GeV/c measured in proton-proton (p-p) collisions at sqrt(s) = 21.7 - 23.8 GeV, with next-to-leading order (NLO) perturbative QCD (pQCD) predictions using recent parametrizations of the parton densities and parton-to-pion fragmentation functions. Although the dependence on the theoretical scales is large, the calculations can reproduce the experimental results both in magnitude and shape. Based on the existing data and on a pQCD $\sqrt{s}$-rescaling of the measured spectra, we provide a practical parametrization of the baseline p-p pion transverse momentum spectrum to be compared to nucleus-nucleus collisions data at sqrt(s_NN) = 22.4 GeV.Comment: 16 pages, 7 figure

Deciphering the properties of the medium produced in heavy ion collisions at RHIC by a pQCD analysis of quenched large p⊥p_{\perp} π0\pi^0 spectra

We discuss the question of the relevance of perturbative QCD calculations for analyzing the properties of the dense medium produced in heavy ion collisions. Up to now leading order perturbative estimates have been worked out and confronted with data for quenched large $p_{\perp}$ hadron spectra. Some of them are giving paradoxical results, contradicting the perturbative framework and leading to speculations such as the formation of a strongly interacting quark-gluon plasma. Trying to bypass some drawbacks of these leading order analysis and without performing detailed numerical investigations, we collect evidence in favour of a consistent description of quenching and of the characteristics of the produced medium within the pQCD framework.Comment: 10 pages, 3 figure

Design methodology for the development of variable stiffness devices based on layer jamming transition

Variable stiffness mechanisms as Jamming Transition draw huge attention recently in Soft Robotics. This paper proposes a comprehensive design methodology for developing variable stiffness devices based on layer jamming. Starting from pre-existing modelling, we highlight the design parameters that should be considered, extracting them from literature and our direct experience with the phenomenon. Then we validated the methodology applying the design process to previous layer jamming cases presented in literature. The comparison between the results obtained from our methodology and those presented in the analyzed previous works highlights a good predictive capability, demonstrating that this methodology can be used as a valid tool to design variable stiffness devices based on layer jamming transition. Finally, in order to provide the scientific community with an easily usable tool to design variable stiffness structures based on layer jamming transition, we have elaborated a Matlab script that guides the user through the main design parameters implementing the proposed methodology in an interactive process

Charmonium suppression in p-A collisions at RHIC

We discuss charmonium production in proton-nucleus collisions at RHIC energies under the assumption of xF and x2 scaling. We find that all the ambiguities due to energy loss are gone at this energy and therefore data will reveal the scaling law, if any. These p-A data will also be crucial to interpret nucleus-nucleus data with respect to a possible formation of a quark gluon plasma because the extrapolations for charmonium production from the present p-A data to RHIC energies, based on the two scaling laws, differ by a factor of four.Comment: 6 pages, 3 figures. New section on shadowing and energy loss, References adde