Hadronic final states in deep-inelastic scattering with Sherpa

We extend the multi-purpose Monte Carlo event generator Sherpa to include processes in deeply inelastic lepton–nucleon scattering. Hadronic final states in this kinematical setting are characterised by the presence of multiple kinematical scales, which were up to now accounted for only by specific resummations in individual kinematical regions. Using an extension of the recently introduced method for merging truncated parton showers with higher-order tree-level matrix elements, it is possible to obtain predictions which are reliable in all kinematical limits. Different hadronic final states, defined by jets or individual hadrons, in deep-inelastic scattering are analysed and the corresponding results are compared to HERA data. The various sources of theoretical uncertainties of the approach are discussed and quantified. The extension to deeply inelastic processes provides the opportunity to validate the merging of matrix elements and parton showers in multi-scale kinematics inaccessible in other collider environments. It also allows to use HERA data on hadronic final states in the tuning of hadronisation models.     

High-spin states in neutron-rich nuclei explored with deep-inelastic HI reactions

The use of deep-inelastic heavy-ion reactions for the spectroscopy of neutron-rich nuclei is discussed. Conclusions from the N/Z equilibration process studies are outlined and examples of spectroscopic results obtained for the neutron-rich spdf shell nuclei, N = 82 isotones and nuclei from the ²⁰⁸Pb region are reviewed. Received: 1 May 2001 / Accepted: 4 December 2001     

Fast-hadron formation mechanism in leptoproduction in nuclei

The mechanism of fast-hadron leptoproduction in nuclei in deep inelastic region is considered. Different possible mechansims of fast-hadron formation in the virtual-photon fragmentation region and the process of transition of the quark (quark-gluon system) through nuclear matter is analysed. The range of consistency of the SLAC and EMC CERN data on meson leptoproduction in different nuclei is obtained to be 0.2 GeV²m _c ² 0.5 GeV². It is shown that the kinematic region 0.05x _B 0.3 and (3–5)Q ²/m _c ² 100 is the most favourable for an investigation of the growth law (evolution) of the transverse dimensions of quark (quark-gluon system) produced by the virtual photon.     

Hadron formation in deep-inelastic positron scattering in a nuclear environment

The influence of the nuclear medium on the production of charged hadrons in semi-inclusive deep-inelastic scattering has been studied by the HERMES experiment at DESY using a 27.5 GeV positron beam. The differential multiplicity of charged hadrons and identified charged pions from nitrogen relative to that from deuterium has been measured as a function of the virtual photon energy and the fraction z of this energy transferred to the hadron. There are observed substantial reductions of the multiplicity ratio at low and at high z, both of which are well described by a gluon-bremsstrahlung model of hadronization. A significant difference of the -dependence of is found between positive and negative hadrons. This is interpreted in terms of a difference between the formation times of protons and pions, using a phenomenological model to describe the - and z-dependence of . Received: 20 February 2001 / Revised version: 3 May 2001 / Published online: 8 June 2001     

Hard-to-reach nuclei studied with deep-inelastic heavy-ion reactions

Spectroscopic studies performed with deep-inelastic heavy-ion reactions are reviewed for two regions of neutron-rich nuclei. The identification of isomers in nearly complete series of Sn isotopes and the resulting systematic of B(E2) values for isomeric transitions is presented and followed by the discussion of shell model states studied in neutron-rich Te isotopes including the new four neutron-hole isomers identified in ¹³⁰Te. Yrast spectroscopy studies of nuclei from the doubly magic ²⁰⁸Pb region are described by outlining the highest spin states observed in the ²⁰⁸Pb core nucleus. The E3 transitions observed abundantly in yrast decays are discussed within the framework of particle-octupole vibration coupling and the validity of a simple rule connecting energy shifts of octupole states built on one-particle states with the ones observed for two-particle states is demonstrated.Received: 15 January 2003, Published online: 23 March 2004PACS: 21.60.Cs Shell model - 23.20.Lv transitions and level energies - 27.60. + j - 27.80. + w      

Dynamical deformation of nuclei participating in deep-inelastic collisions

TheN/Z equilibration process taking place in deep-inelastic heavy ion collisions above the Coulomb barrier was studied by means of thick target gamma spectroscopy method. The analysis of gamma coincidence data obtained for four heavy ion systems gave complete distributions of primary reaction products which allowed to extract the most probableN/Z ratios as a function of mass. The comparison of experimentalN/Z values with expectations based on potential energy minimization leads to conclusion that during the crucial interaction time the involved nuclei are dynamically deformed.     

Mesonic processes in deep-inelastic electron scattering from nuclei

Inelastic electron scattering is considered in the energy and momentum transfer region associated with the quasielastic and 3-3 resonance pion electroproduction peaks. Calculations of two-nucleon ejection via two-body meson-exchange currents (MEC) and of pion electroproduction from threshold through the 3-3 resonance are presented using the Fermi gas model of the nucleus. The MEC contribution is found to be significant in this region, and helps to account for the discrepancy between theory and experiment in the “dip” between the quasielastic and 3-3 resonance peaks.     

Hadron resonances as rovibrational states

A rovibrational model,including anharmonic,centrifugal,and Coriolis corrections,is used to calculate π,K,N, and Σ orbital and radial resonances.The four orbital excitations of the π meson correspond to the b(1235),π_2(1670),b_3(2030),and π_4(2250) resonances.Its first four radial excitations correspond to the π(1300),π(1800),π(2070),and π(2360) resonances.The orbital excitations of the K meson are interpreted as the K_1(1270),K_2(1770),K_3(2320),and K_4(2500) resonances;its radial excitations correspond to the K(1460) and K(1830) resonances.The N orbital excitations are identified with the N(1520),N(1680),N(2190),N(2220),and N(2600) resonances.The first four radial excitations of the N family correspond to the N(1440),N(1880),N(2100),and N(2300) resonances.The orbital excitations of the Σ baryon are associated with the Σ(1670),Σ(1915),Σ(2100),and Σ(2250) resonances,whereas its radial excitations are identified with the Σ(1660),Σ(1770),and Σ(1880) resonances.The proposed rovibrational model calculations show a good agreement with the corresponding experimental values and allow for the prediction of hadron resonances,thereby proving to be useful for the interpretation of excited hadron spectra.     

Method of estimation of hadron attenuation in leptoproduction from nuclei

Results of estimation of hadron attenuation in the process of leptoproduction from nuclei are presented, obtained on the basis of the improved numerical method proposed in [1] with allowance for predictions of the string model. Definition of the concepts of production time and formation time are given. The developed methodology of calculations is described. Plots of hadron attenuations versus the energy of the virtual photon and the fraction of energy retained by the hadron are presented.     

The yrast spectroscopy of neutron-rich nuclei produced in deep-inelastic processes

The highly sensitive GASP array at the INFN Legnaro Laboratory was used to study the -ray de-excitation of neutron-rich nuclei produced in the deep-inelastic processes which occur when 230 MeV ³⁶S ions interact with a target of ¹⁷⁶Yb. Yrast decay schemes were identified in over forty target-like fragments and in over twenty projectile-like fragments. Analysis of the data has resulted in extensions to the yrast decay sequences of the target-like species, ¹⁷⁶Hf, ¹⁶⁶Er, ¹⁷²Yb, and ¹⁵²Sm. New transitions have also been observed in a number of projectile-like species including ³⁴P and ⁴¹Cl. Experimental results are compared with the results of shell model calculations.Received: 29 October 2002, Published online: 17 February 2004PACS: 23.20.Lv Gamma transitions and level energies - 27.40. + z - 27.70. + q      

High-spin states in neutron-rich Dy isotopes populated in deep-inelastic reactions

High-spin states in neutron-rich Dy isotopes, populated in deep-inelastic processes produced by the interaction of 234 MeV ³⁷Cl ions with a ¹⁶⁰Gd target, have been studied using the highly sensitive EUROBALL IV gamma-ray detector array. The previously known level schemes for ^{159,160,161,162}Dy have been extended to significantly higher spin ( ? 30?) and the i _13/2 band crossing in ¹⁵⁹Dy has been observed for the first time. The experimental results are discussed within the framework of cranked shell model and projected shell model calculations with particular reference to the observed delayed band crossing in ¹⁶²Dy. Received: 20 October 2000 / Accepted: 16 January 2001     

Entropy and equilibrium property of QCD-instanton induced final state in deep-inelastic scattering

The scaling and additivity properties of Rényi entropy in rapidity space of the instanton final state (IFS) and current jet identified by the r-sorting method from the QCDINS Monte Carlo event sample are to saturation with decreasing phase space scale. Furthermore, it is found that the additivity of H2 holds well for the IFS in narrow rapidity windows at different positions. These results indicate that the IFS produced in the instanton-induced process of deep inelastic scattering has reached local equilibrium.     

A phenomenological model of deep-inelastic collisions between complex nuclei

A simple model of heavy-ion collisions is proposed. Classical equations of motion with inclusion of a phenomenological two-body friction force are integrated numerically along trajectories. The nucleus-nucleus interaction potential which is used in the calculations includes deformation degrees of freedom in the exit channel. Both entrance and exit channel potentials are based on the boundary conditions following the liquid-drop model. The energy-angle distributions of deep-ineIastic reactions are very well reproduced by the model. The existing data on fusion cross sections are compared with the model predictions. This comparison indicates that in the nucleus-nucleus potential a repulsive core is present.     

Comparison of 147 GeV/c π− p low transverse momentum hadron production with deep-inelastic leptoproduction

Zeitschrift für Physik C Particles and Fields - Distributions with respect toz andz R for the fastest and second fastest particles produced in both beam and target hemispheres from 147 GeV/c...     

深度非弹性散射中QCD-瞬子末态的熵及热平衡性质

在蒙特-卡洛产生器 QCDINS 产生的瞬子参与的e-P深度非弹性散射事件中,用$r$ 排序法得到瞬子末态和喷注样本。研究了 R\'enyi熵$H_2$在快度空间中的标度性和相加性。在瞬子末态中观察到了 $H_2$ 随着相空间尺度的减小展现出来的渐进标度性。相比之下,喷注的$H_2$在相空间尺度减小时呈现出饱和趋势。而且,在瞬子末态中还观察到在不同快度位置的窄窗口中$H_2$的相加性很好地成立。这些结果表明,在瞬子参与的深度非弹性散射中的瞬子末态达到了局域平衡。     

Unitarity constraints for deep-inelastic scattering on nuclei: Predictions for electron-ion colliders

Future electron-ion colliders will focus on the unitarity properties of deep inelastic scattering in the limit of strong nuclear absorption. Strong nuclear shadowing and a large abundance of coherent diffraction are the most striking consequences of unitarity. Quantitative predictions for these effects in the kinematical range of the planned electron-ion colliders are reported. The text was submitted by the authors in English.     

Multiplicity structure of the hadronic final state in diffractive deep-inelastic scattering at HERA

The multiplicity structure of the hadronic system X produced in deep-inelastic processes at HERA of the type , where Y is a hadronic system with mass GeV and where the squared momentum transfer at the pY vertex, t, is limited to , is studied as a function of the invariant mass of the system X. Results are presented on multiplicity distributions and multiplicity moments, rapidity spectra and forward-backward correlations in the centre-of-mass system of X. The data are compared to results in annihilation, fixed-target lepton-nucleon collisions, hadro-produced diffractive final states and to non-diffractive hadron-hadron collisions. The comparison suggests a production mechanism of virtual photon dissociation which involves a mixture of partonic states and a significant gluon content. The data are well described by a model, based on a QCD-Regge analysis of the diffractive structure function, which assumes a large hard gluonic component of the colourless exchange at low . A model with soft colour interactions is also successful. Received: 27 April 1998 / Published online: 3 September 1998     

Hadron scattering by light nuclei and the spectroscopic approach

The spectroscopic approach is applied to describing elastic hadron scattering by light nuclei. The study shows that application of the spectroscopic approach enables us to reproduce the process of elastic scattering of different hadrons by several nuclei of the 1p shell, to analyze the calculated characteristics in detail, and to obtain good agreement with the experimental data.     

Comment on azimuthal dependence in leptoproduction

It is pointed out that in the conventional calculation a large part of 〈cosφ〉 in leptoproduction comes from configurations in which the outgoing partons have small p_T. This indicates that the conventional QCD prediction for 〈cosφ〉 is not reliable in the experimentally available Q² regions at present.