Target fragmentation in proton-nucleus and16O-nucleus reactions at 60 and 200 GeV/nucleon

Target remnants withZ<3 from proton-nucleus and¹⁶O-nucleus reactions at 60 and 200 GeV/nucleon were measured in the angular range from 30° to 160° (?1.7<η<1.3) employing the Plastic Ball detector. The excitation energy of the target spectator matter in central oxygen-induced collisions is found to be high enough to allow for complete disintegration of the target nucleus into fragments withZ<3. The average longitudinal momentum transfer per proton to the target in central collisions is considerably higher in the case of¹⁶O-induced reactions (≈300 MeV/c) than in proton-induced reactions (≈130 MeV/c). The baryon rapidity distributions are roughly in agreement with one-fluid hydrodynamical calculations at 60 GeV/nucleon¹⁶O+Au but are in disagreement at 200 GeV/nucleon, indicating the higher degree of transparency at the higher bombarding energy. Both, the transverse momenta of target spectators and the entropy produced in the target fragmentation region are compared to those attained in head-on collisions of two heavy nuclei at Bevalac energies. They are found to be comparable or do even exceed the values for the participant matter at beam energies of about 1–2 GeV/nucleon.     

Fragmentation cross sections of16O at 60 and 200 GeV/nucleon

We used CR39 plastic nuclear track detectors (C₁₂H₁₈O₇) in combination with automatic track measurement to determine total charge changing and partial cross sections for the production of fragments of chargeZ=6 andZ=7 in collisions of¹⁶O beam nuclei at energies of 60 GeV/nucleon and 200 GeV/nucleon in targets H, C, CR39, CH₂, Al, Cu, Ag and Pb. Total charge changing cross sections due to the process of electromagnetic dissociation are calculated based on a theoretical model and found to be consistent with total and partial electromagnetic dissociation cross sections derived from this experiment. The energy dependence of pure nuclear fragmentation is investigated.     

Concept of a coming accelerator complex and design study for heavy ions and intense protons

It is emphasized that a coming accelerator complex should be designed by wide application of beam manipulation. On the basis of this opinion, conceptual designs of two kinds of accelerator complexes of a 30 GeV/nucleon uranium-ion collider and of an intense 30 GeV proton accelerator are studied independently of each other. Moreover, it is shown from these designs that an accelerator complex with accelerator parameters common to both is possibly designed with the help of good beam manuipulation if mutual concessions of beam parameters of heavy ions and of intense protons are accepted. The optimum accelerator complex consists of at least three synchrotrons and three dc rings. The expected beam performance is 450 MeV/nucleon and 30 GeV/nucleon for uranium ions as a typical example of heavy ions, and 150 A below 2.7 GeV and 10 A below 30 GeV for intense protons.     

Six “beyond Collins and Sivers” transverse spin asymmetries at COMPASS

COMPASS is a fixed-target high energy physics experiment at the SPS at CERN [1]. One of the important objectives of the experiment is the exploration of the transverse spin structure of the nucleon via spin dependent azimuthal asymmetries in single-hadron production in deep inelastic scattering of polarized leptons off transversely polarized target. For this purpose a series of measurements were made in COMPASS, using 160 GeV/c longitudinally polarized muon beam and transversely polarized ⁶LiD (in 2002, 2003 and 2004) and NH₃ (in 2007 and 2010) targets. Till now main attention was focused on Collins and Sivers asymmetries and obtained results play an important role in the general understanding of the three-dimensional nature of the nucleon and mechanism of SIDIS processes in terms of Transverse Momentum Dependent (TMD) Parton Distribution Functions (PDFs) and Fragmentation Functions (FFs). In addition to these two measured leading-twist effects, the SIDIS cross-section counts six more target transverse spin dependent azimuthal effects, which have their own well defined leading or higher-twist interpretation in terms of QCD parton model. So far COMPASS presented preliminary results for these asymmetries from deuteron [2, 3] and “proton-2007” data [4]. In this contribution we review the results obtained with the last “proton-2010” data sample.     

Optimization of accelerated charged particle beam for ADS energy production

A comparative analysis and optimization of energy efficiency for proton and ion beams in ADS systems is performed via simulation using a GEANT4 code with account for energy consumption for different accelerator types. It is demonstrated that for light nuclei, beginning from ⁷Li, with energies above 1 GeV/nucleon, ion beams are considerably (several times) more efficient than the 1–3 GeV proton beam. The possibility of achieving energy deposition equivalent to 1 GeV protons in a quasi-infinite uranium target with higher efficiency (and twice as small accelerator size) in the case of acceleration of light ions is substantiated.     

The quark condensate in relativistic nucleus-nucleus collisions

We compute the modification of the quark condensate <ˉq q> in relativistic nucleus-nucleus collisions and estimate the 4-volume, where the quark condensate is small (<ˉqq>/<ˉqq>⁰≤ 0.1–0.3) using hadron phase-space distributions obtained with the quark-gluon string model. As a function of the beam energy the 4-volume rises sharply at a beam energy E^lab/A ≃ (2–5) GeV, remains roughly constant up to beam energies ≃ 20 GeV and rises at higher energies. At low energies the reduction of the condensate is mainly due to baryons, while at higher energies the rise of the 4-volume is due to the abundant mesons produced. Based on our results we expect that moderate beam energies on the order of 10 GeV per nucleon are favourable for studying the restoration of chiral symmetry in a baryon-rich environment in nucleus-nucleus collisions. Received: 4 December 1997 / Revised version: 31 July 1998     

Cumulative protons in the 9Be(12C,p)X reaction at 0.2–3.2 GeV/nucleon

The spectra of protons were measured in fragmentation of ¹²C ions in the cumulative region at energies of 0.2–3.2 GeV/nucleon. The energy dependence of the slope parameters in the obtained spectra was traced. The probability of the existence of two- and three-nucleon clusters in the carbon nucleus was estimated within the model of quark-gluon strings.     

Shock waves and mach cones in fast nucleus-nucleus collisions

Mach shock waves and head shock waves occur during the interpenetration of a light high energetic nucleus with a heavy one. Collisions of¹⁶O,¹²C and⁴He ions at energies between 0.25 and 2.1 GeV/N with Ag and Cl nuclei have been investigated. The theoretical concepts and the experiment are presented and interpreted. From that a velocity of first sound in nuclear matterc _s ≈0.19c, a Mach shock velocityv _s ≈0.58c and a nuclear compression constantK=300 MeV are deduced.     

Measuring the cross sections of heavy-metal spallation induced by deuterons with energies of 2, 2.94, and 3.5 GeV per nucleon

The cross sections for the spallation of the heavy-metal nuclei ¹⁸¹Ta, ¹⁹⁷Au, ²⁰⁷Pb, ²⁰⁹Bi, ²³²Th, and ²³⁸U induced by relativistic deuterons with energies of 2, 2.94, and 3.5 GeV per nucleon are measured using the deuteron beam from the Nuclotron accelerator of the JINR Laboratory of High Energy Physics in Dubna, Russia. The cross-section measurements employ a combined experimental technique involving the solidstate nuclear-track detectors and the activation gamma spectrometry. Adding our measurements to the database of experimental nuclear data will make it possible to test the computer codes used for selecting the parameters of the ADS-type facilities.     

Booster synchrotron of NICA accelerator complex

NICA is a new accelerator complex being constructed at the Joint Institute for Nuclear Research; the main task of this complex is to perform collider experiments for ion beams up to uranium with energies of up to 3.5 × 3.5 GeV/nucleon. This complex includes an electron string ion source, a 6 MeV/nucleon linear accelerator, a booster, the Nuclotron, and a collider with an average luminosity of 10²⁷ cm² s^?1. The main tasks of the booster are to accumulate up to 4 × 10^{9 197}Au³²⁺ ions, to accelerate to 600 MeV/nucleon (sufficient enough energy for completely stripping nuclei), to reduce the requirements of vacuum conditions for the Nuclotron, and to form the necessary beam emittance using an electron cooling system. The specific features of the NICA booster and the requirements for the basic systems of the synchrotron and their parameters are presented in this paper.     

Lead beam experiments at the CERN SPS

The acceleration in 1986 of¹⁶O beams to 200 GeV/nucleon at the CERN SPS created a new frontier of particle and nuclear physics, namely the study of high energy density systems with hundreds of quarks and gluons created in the central collisions of nuclei with heavy targets. In order to produce the largest piece of “quark matter”, beams as heavy as²⁰⁸Pb are needed. The Lead-Injector Project that would provide them is presented. Possible experimental approaches to extract the physics from collisions with thousands of produced particles are discussed.     

Coulomb and photo cross sections for nucleon emission from relativistic O projectiles

Coulomb cross sections for nucleon emission out of ¹⁶O projectiles scattered with laboratory energies of 2.1, 60 and 200 GeV/nucleon on various target nuclei are calculated in first-order perturbation theory by using the corresponding photo cross sections. The photo cross sections are obtained with an 1-particle-1-hole basis in the giant resonance region and with the quasi-deuteron model up to photon energies of 140 MeV. Whereas the 2.1 GeV/nucleon results agree well with the experimental data points, the 60 and 200 GeV/nucleon cross sections are roughly one quarter lower than the measured ones, because also photons with energies higher than 140 MeV contribute at these incident energies.     

Measurement of the azimuthal anisotropy coefficient <Emphasis Type="Italic">v</Emphasis><Subscript>2</Subscript> for the emission of α particles in nucleus-nucleus collisions at energies 1.88–10.6 GeV/nucleon

The azimuthal anisotropy of the emission of α particles in collisions of the ²²Ne, ²⁴Mg, ⁵⁶Fe, and ¹⁹⁷Au nuclei with photoemulsion nuclei has been measured at projectile energies E_pr = 1.88–10.6 GeV/nucleon. The results are compared with similar measurements for protons. It has been found that the ratio of the azimuthal anisotropy coefficients v₂ for α particles and protons is equal to 6 ± 2 at low energies E_pr ≈ 2 GeV/nucleon, whereas these coefficients coincide with each other for energies E_pr ≥ 4 GeV/nucleon. This difference may indicate that, at low projectile energies, α particles are formed predominantly at the early stage of a collective flow. Formation of α particles for E_pr ≥ 4 GeV/nucleon likely occurs at the stage of nuclear matter scattering.     

Nuclear activation studies of heavy ion reactions

The identification of the residues which are produced in a nuclear interaction, and the measurement of their recoil range and angular distribution provides useful information on the reaction mechanism. If the residues are radioactive this information may be easily obtained by measuring off beam the activity they induce both in the target and a suitable set of catchers. This experimental technique is discussed together with the results of a systematic study of the interaction of¹²C and¹⁶O ions, with heavy nuclei at low incident energies.     

Interactions of relativistic heavy ions in thick heavy element targets and some unresolved problems

Interactions of relativistic heavy ions with total energies above 30 GeV in thick Cu and Pb targets (≥ 2 cm) have been studied with various techniques. Radiochemical irradiation experiments using thick Cu targets, both in a compact form or as diluted “2π-Cu targets” have been carried out with several relativistic heavy ions, such as 44 GeV ¹²C (JINR, Dubna, Russia) and 72 GeV ⁴⁰Ar (LBL, Berkeley, USA). Neutron measuring experiments using thick targets irradiated with various relativistic heavy ions up to 44 GeV ¹²C have been performed at the JINR. In addition, the number of “black prongs” in nuclear interactions (due to protons with energies less than 30 MeV and emitted from the target-like interaction partner at rest) produced with 72 GeV ²²Ne ions in nuclear emulsion plates has been measured in the first nuclear interaction of the primary ²²Ne ion and in the following second nuclear interaction of the secondary heavy (Z > 1) ion. Some essential results have been obtained. (1) Spallation products produced by relativistic secondary fragments in interactions ([44 GeV ¹²C or 72 GeV ⁴⁰Ar] + Cu) within thick copper yield fewer products close to the target and many more products far away from the target as compared to primary beam interactions. This applies also to secondary particles emitted into large angles (Θ > 10°). (2) The neutron production of 44 GeV ¹²C within thick Cu and Pb targets is beyond the estimated yield as based on experiments with 12 GeV ¹²C. These rather independent experimental results cannot be understood within well-accepted nuclear reaction models. They appear to present unresolved problems. The text was submitted by the authors in English.     

Neutrino—nucleon cross-section at ultra-high energies in models with large extra dimensions

We examine whether the models with large extra dimensions can provide an explanation for the GZK violating ultra-high energy cosmic rays (UHECR). In these models the neutrino—nucleon cross-section rises rapidly with energy and hence cosmic rays might be identified with neutrinos. We calculate the neutrino-nucleon cross-section at ultra high energies by assuming that it is dominated by the production ofp-branes. We perform the calculation in a generalized Randall-Sundrum model and Lykken-Randall model and find cross-sections of the order of 100 mb at neutrino energies of 10²⁰ eV, which is required for explaining UHECR events.     

Intermittency in relativistic heavy-ion collisions

Corrected scaled-factorial-moments are calculated for the multiplicity distributions of shower particles in different phase spaces. An intermittency power-law is observed in the central collisions of³²S and¹⁶O at 200A GeV,¹⁶O at 60A GeV and²⁸Si at 14.5A GeV in nuclear emulsion.     

Total interaction and proton-removal cross-section measurements for the proton-rich isotopes 7Be, 8B,and 9C

In an experiment performed at the FRS of GSI, we measured total interaction cross sections for ⁷Be, ⁸B, and ⁹C, one-proton-removal cross sections for ⁸B and ⁹C as well as two-proton-removal cross sections for ⁹C on targets ranging from carbon to lead at an energy of 285 MeV/nucleon. In addition, we performed measurements at 142 MeV/nucleon for ⁸B. The experimental results are compared to different calculations. Glauber-type calculations with different model·density distributions show that, down to incident energies of about 50 MeV/nucleon, total interaction cross-section measurements with light targets are not sensitive to an extended proton distribution in ⁸B. However, at lower incident energies, a tail in the proton density distribution is needed to explain the total interaction cross sections. Total interaction cross-section measurements with high-Z targets in the present experiment show a significant increase of the cross sections due to low-lying electromagnetic strength.     

Mass yield distributions of target fragments from the reactions of iron with 135 MeV/nucleon 12C and 80 MeV/nucleon 16O ions

Cross sections for the production of target fragments in the reactions of iron with 135 MeV/nucleon ¹²C and 80 MeV/nucleon ¹⁶O ions have been measured by off-line γ-ray spectroscopy. Through these data, the mass yield distributions have been obtained. The result of the experiment for the reaction with 135 MeV/nucleon ¹²C ions is compared with theoretical calculations using the fusion-fragmentation model and the GEMINI code for sequential binary decay, following a calculation with the fireball model. Reveived: 24 March 1999 / Revised version: 16 July 1999