Hadrons in nuclei from high (200 GeV) to low (1 GeV) energies

The study of the interaction of hadrons, produced by introducing elementary probes into a nucleus, with the surrounding nuclear medium can give insight into two important questions. Firstly, at high energies, the production process, the time-scales connected with it, and the prehadronic interactions can be studied by using the nuclear radius as a length-scale. We do this here by analyzing data from the EMC and HERMES experiments on nuclear attenuation. Secondly, at low energies the spectral function, and thus the selfenergy of the produced hadron, can be studied. Specifically, we analyze the CBELSA/TAPS data on ω production in nuclei and discuss the importance of understanding in-medium effects both on the primary production cross section and the final state branching ratio. In both of these studies, an excellent control of the final state interactions is essential.     

Positive parity scalar mesons in the 1–2 GeV mass range

Based on the observation that K₀ ^*(1430) is lighter than its SU₃ counterpart, a₀(1450), we examine the possibility that these particles, together with f₀(1370), f₀(1500) and f₀(1710), fill a tetraquark recurrence of the sub-GeV 0⁺⁺ nonet mixed with a glueball state. We find the picture to be consistent with the known data about the three f₀ resonances, more than the qq̄ hypothesis. Conventional spin–orbit coupling suggests the qq̄, P-wave, nonet to lie around 1200 MeV. We review possible experimental indications of a scalar isovector resonance at 1.29 GeV, first observed by OBELIX in pp̄ annihilation. PACS 12.39.Mk; 12.40.-y; 13.25.Jx     

Experimental evidence for narrow baryons in the mass range 1.0≤M≤1.46 GeV

The reaction pp → pπ⁺ X was studied at different incident energies around T _p = 2 GeV. Narrow baryonic structures were observed in the missing mass M _X and in the invariant mass M _pπ{+}. The masses of these structures are 1004, 1044, 1094, 1136, 1173, 1249, 1277, and 1384 MeV (and possibly 1339 MeV). Some of them were also observed at the same masses in the missing-mass spectra of the dp → ppX reaction although with a weaker signature. Many checks were performed to make sure that these structures were not produced by experimental artifacts. Several narrow small-amplitude peaks, were also extracted using already published photonucleon cross-sections. The small widths of all these results, and the stability of the observed structures, regardless of the experiment, were used to conclude that they are genuine baryons and not merely the consequence of dynamical rescatterings. These baryons cannot be associated with classical q³ quark configurations. We associate them with two colored-quark cluster configurations. Received: 3 July 2002 / Accepted: 30 January 2003 / Published online: 5 June 2003     

Search for cosmic γ-ray bursts in the (1÷50) GeV energy range

Summary A search for cosmic gamma-ray bursts in the GeV energy range has been performed by means of the EAS-TOP Extensive Air Shower array at Campo Imperatore (Gran Sasso Laboratories) during the period March–December 1990. In 2566.5 hours of measurement the obtained upper limit to the rate of bursts of amplitude >2% of the cosmic-ray intensity and time duration τ=1 s, isR≤7.9y⁻¹ (90% c.l.). Assuming for γ-rays a differential energy spectrumS(E ₀ )≈E ₀ ^−2.5 , the corresponding upper limit to the energy flux of γ-rays with energy >5 GeV in bursts of duration τ≤1 s is Φ<8.3·10⁻⁵erg cm⁻².     

On the transverse energy distributions in the central rapidity region of 16O+Pb collisions at 200 GeV per nucleon

We point out that the recent data obtained by the NA35 collaboration at the CERN SPS on E_T distributions in ¹⁶O + Pb collisions can be understood within the wounded nucleon model with a simple geometrical calculation of the number of interacting nucleons in ¹⁶O. Although the large E_T trigger increases the average E_T per final state hadron, we are unable to explain in this way the observed rather large value of this quantity.     

Bose-einstein correlations in the target fragmentation region in 200A GeV16O+nucleus collisions

Correlations between positive pions are investigated in the target fragmentation region of 200A GeV¹⁶O+nucleus collisions. The pions are measured with the Plastic Ball detector in the WA80 experiment at the CERN SPS. The target mass dependence of the radii and the correlation strength extracted by interferometry is studied. A new approach to the fit of the correlation function is introduced. The correlation strength and both invariant and transverse radii increase with decreasing target mass. The transverse radius for¹⁶O+C reactions appears to be much larger than the geometrical radius of the nuclei involved. For the Au target only a small fraction of the measured pions contributes to the apparent correlation. Hints for a much larger second component in¹⁶O+Au reactions are observed. Rescattering phenomena may provide a clue to understand these phenomena.     

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.     

Photoproduction of πΔ(1.232) from hydrogen in the energy range 2.4–4.8 GeV

We present differential cross sections andΔ ⁺⁺ spin density matrix elements for the photoproduction processγp→π ^? Δ ⁺⁺ and differential cross sections for the processγp→π ⁺ Δ ⁰. The incident photon energy dependence is studied and a comparison is made with previous experiments and with the predictions of a theoretical model.     

Charged-particle distributions in 16O induced nuclear reactions at 60 and 200 A GeV

Results from ¹⁶O induced nuclear interactions with C, Cu, Ag and Au targets at 60 and 200 A GeV are presented. Multiplicity and pseudorapidity-density distributions of charged particles and their dependence on the target mass number are reported. The increase in the particle density with increasing centrality, characterized by the energy flux at zero degrees, is investigated. Comparisons with the Fritiof model reveal systematic differences.     

The structure of the forward elastic cross section in (10–14) GeV range

The logarithmic slope of the differentical cross section for K^±p elastic scattering at 10 and 14 GeV, and for π^±p and p^±p at 10GeV has been measured. Rich structure is observed in the forward slope for all processes, which is well accounted for by the properties of a peripheral exchange amplitude for the nonexotic reactions, and by a peripheral component of the diffractive amplitude as clearly seen in the exotic processes, K^±p and pp.     

Strange and non-strange (Anti-) baryon production at 200 A GeV/c

Rapidity distributions of net hyperons $\left( {\Lambda - \bar \Lambda } \right)$ are compared to distributions of participant protons $\left( {p - \bar p} \right)$ . Strangeness production (mean multiplicities of produced Λ/Σ⁰ hyperons and $\left\langle {K + \bar K} \right\rangle $ in central nucleusnucleus collisions is shown for different collision systems at different energies. An enhanced production of $\bar \Lambda $ compared to $\bar p$ is observed at 200 GeV per nucleon.     

Nuclear interactions of 200 GeV protons in emulsion

Proton-nucleus interactions have been studied in nuclear emulsion exposed to the NAL 200 GeV proton beam. The inelastic mean free path is found to be 35.5 ± 0.8 cm and the average shower particle multiplicity is 12.9 ± 0.2. The angular distribution reveals some characteristics features of proton-nucleus interactions.     

Pseudorapidity distributions from pion-emulsion interactions in the energy range 60 GeV to 300 GeV

The analysis of experimental data for pion-nucleus interactions in the energy range 60 GeV–300 GeV is presented. The pseudorapidity distributions of shower particles are analyzed in terms of pion energy and the average number of intra-nuclear collisions of the projectile. The particle densities in the projectile fragmentation region are compared to predictions of the additive quark model. The relation between the average number of wounded quarks in the projectile and the number of fast protons emitted from the struck nucleus is derived and used to extract from the experimental π^?-emulsion data the fragmentation functions for both wounded and spectator quarks. These functions are then used to described the results of independent π^?-proton and π^?-deuteron experiments.     

Search for long-lived particles in 200 GeV/c proton-nucleon collisions

A search for long-lived particles (τ ? 10^?8 sec), with changes $\text{±}\text{2}\text{3}\text{, ± 1, ±}\text{4}\text{3}\text{and}\text{± 2}$, produced in 200 GeV pN collisions was performed at the CERN-SPS in a secondary beam equipped with superconducting r.f. separators. Upper limits were obtained for the production of long-lived hadrons and leptons. For charge - 1 particles the limits are at the level of 10^?7 of the pions at a mass m = 0.2 GeV and reach the 10^?11 level from $\text{3}\text{to}\text{8}\text{GeV}$. The production of light antinuclei was measured. The cross sections for ³He production are (1.3 ± 0.3) and (1.9 ± 0.3) × 10^?34 cm²/sr · GeV/c at 21 and 47.4 GeV/c respectively; for t the cross section is (7.6 ± 0.9) × 10^?34 cm²/sr · GeV/c at 23.7 GeV/c.     

Search for enhancements in the nucleon-nucleon mass distributions in the dp breakup reaction in the momentum range 2.0–3.7 GeV/c

We have investigated the dp → ppn non-spectator breakup reaction obtained from the KEK l m liquid hydrogen bubble chamber exposed to a beam of deuterons at ten momenta in the range 2.0–3.7 GeV/c. The pn and pp effective mass distributions in the two momentum regions 2.0–2.9 GeV/c and 3.0–3.7 GeV/c show no structure.