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Title: Dielectron Production in {sup 12}C+{sup 12}C Collisions at 2A GeV with the HADES Spectrometer

Abstract

The invariant-mass spectrum of e{sup +}e{sup -} pairs produced in {sup 12}C+{sup 12}C collisions at an incident energy of 2 GeV per nucleon has been measured for the first time. The measured pair production probabilities span over 5 orders of magnitude from the {pi}{sup 0}-Dalitz to the {rho}/{omega} invariant-mass region. Dalitz decays of {pi}{sup 0} and {eta} account for all the yield up to 0.15 GeV/c{sup 2}, but for only about 50% above this mass. A comparison with model calculations shows that the excess pair yield is likely due to baryon-resonance and vector-meson decays. Transport calculations based on vacuum spectral functions fail, however, to describe the entire mass region.

Authors:
; ; ; ; ; ; ; ; ; ;  [1]; ; ; ; ; ; ; ; ;  [2]
  1. II.Physikalisches Institut, Justus Liebig Universitaet Giessen, 35392 Giessen (Germany)
  2. Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Sud, 95125 Catania (Italy) (and others)
Publication Date:
OSTI Identifier:
20955421
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Letters; Journal Volume: 98; Journal Issue: 5; Other Information: DOI: 10.1103/PhysRevLett.98.052302; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; CARBON 12 BEAMS; CARBON 12 REACTIONS; CARBON 12 TARGET; COLLIDING BEAMS; ELECTRON-POSITRON INTERACTIONS; ELECTRONS; ETA MESONS; MASS SPECTRA; PAIR PRODUCTION; PARTICLE DECAY; PIONS NEUTRAL; POSITRONS; PROBABILITY; RESONANCE PARTICLES; SPECTRAL FUNCTIONS; SPECTROMETERS; VECTOR MESONS

Citation Formats

Agakichiev, G., Gilardi, C., Kuehn, W., Lehnert, J., Lins, E., Metag, V., Pechenov, V., Perez, T., Ritman, J., Spruck, B., Toia, A., Agodi, C., Bellia, G., Coniglione, R., Cosentino, L., Finocchiaro, P., Maiolino, C., Piattelli, P., Sapienza, P., and Vassiliev, D. Dielectron Production in {sup 12}C+{sup 12}C Collisions at 2A GeV with the HADES Spectrometer. United States: N. p., 2007. Web. doi:10.1103/PHYSREVLETT.98.052302.
Agakichiev, G., Gilardi, C., Kuehn, W., Lehnert, J., Lins, E., Metag, V., Pechenov, V., Perez, T., Ritman, J., Spruck, B., Toia, A., Agodi, C., Bellia, G., Coniglione, R., Cosentino, L., Finocchiaro, P., Maiolino, C., Piattelli, P., Sapienza, P., & Vassiliev, D. Dielectron Production in {sup 12}C+{sup 12}C Collisions at 2A GeV with the HADES Spectrometer. United States. doi:10.1103/PHYSREVLETT.98.052302.
Agakichiev, G., Gilardi, C., Kuehn, W., Lehnert, J., Lins, E., Metag, V., Pechenov, V., Perez, T., Ritman, J., Spruck, B., Toia, A., Agodi, C., Bellia, G., Coniglione, R., Cosentino, L., Finocchiaro, P., Maiolino, C., Piattelli, P., Sapienza, P., and Vassiliev, D. Fri . "Dielectron Production in {sup 12}C+{sup 12}C Collisions at 2A GeV with the HADES Spectrometer". United States. doi:10.1103/PHYSREVLETT.98.052302.
@article{osti_20955421,
title = {Dielectron Production in {sup 12}C+{sup 12}C Collisions at 2A GeV with the HADES Spectrometer},
author = {Agakichiev, G. and Gilardi, C. and Kuehn, W. and Lehnert, J. and Lins, E. and Metag, V. and Pechenov, V. and Perez, T. and Ritman, J. and Spruck, B. and Toia, A. and Agodi, C. and Bellia, G. and Coniglione, R. and Cosentino, L. and Finocchiaro, P. and Maiolino, C. and Piattelli, P. and Sapienza, P. and Vassiliev, D.},
abstractNote = {The invariant-mass spectrum of e{sup +}e{sup -} pairs produced in {sup 12}C+{sup 12}C collisions at an incident energy of 2 GeV per nucleon has been measured for the first time. The measured pair production probabilities span over 5 orders of magnitude from the {pi}{sup 0}-Dalitz to the {rho}/{omega} invariant-mass region. Dalitz decays of {pi}{sup 0} and {eta} account for all the yield up to 0.15 GeV/c{sup 2}, but for only about 50% above this mass. A comparison with model calculations shows that the excess pair yield is likely due to baryon-resonance and vector-meson decays. Transport calculations based on vacuum spectral functions fail, however, to describe the entire mass region.},
doi = {10.1103/PHYSREVLETT.98.052302},
journal = {Physical Review Letters},
number = 5,
volume = 98,
place = {United States},
year = {Fri Feb 02 00:00:00 EST 2007},
month = {Fri Feb 02 00:00:00 EST 2007}
}
  • We present the inclusive di-electron invariant-mass spectrum from p+p interactions at 3.5 GeV kinetic beam energy. It is a very important reference for the study of vector meson production off the nucleus, recently investigated by HADES in p+{sup 93}Nb reactions at the same beam energy. Up to invariant masses of 0.6 GeV/c{sup 2} the main contributions to the e{sup +}e{sup -} spectrum are {pi}{sup 0},{eta}, {omega} and {Delta} Dalitz decays. In the vector-meson region a clear peak corresponding to the {omega} direct decay is reconstructed with {approx_equal}2% mass resolution. Subtracting this peak from the spectrum allows to investigate additional sources,more » in particular the {rho} meson. Indeed, the latest results from HSD and UrQMD calculations show different distributions for the shape of the {rho} meson at these energies. Therefore it is important to experimentally understand the production mechanism of the {rho} meson in elementary reactions. Besides the spectral shape of the mesons, their inclusive production cross sections are also not known at these energies. Due to the large and flat acceptance of the HADES spectrometer for e{sup +}e{sup -} masses above 0.2 GeV/c{sup 2} and for P{sub T}<1GeV/c, acceptance corrections are to a large extent model independent. This allows us to extract the preliminary inclusive cross section values for the meson productions at these energies.« less
  • No abstract prepared.
  • The experimental transverse momentum distributions of negative pions produced in d{sup 12}C, {sup 4}He{sup 12}C, and {sup 12}C{sup 12}C collisions at 4.2 A GeV/c were analyzed in the framework of Hagedorn Thermodynamic Model. The spectral temperatures of {pi}{sup -} mesons as well as their relative contributions to the total multiplicity of {pi}{sup -} mesons were extracted from fitting the p{sub t} spectra by two-temperature Hagedorn function. The results were compared systematically with the earlier results obtained from analysis of non-invariant center-of-mass energy spectra of negative pions produced in the analyzed collisions.
  • A phenomenological analysis of the channel involving the production of three alpha particles in collisions of relativistic oxygen nuclei with protons is performed for the first time. It is shown that one-third of it is saturated by the decay of an excited nucleus {sup 12}C{sup *}, while the remaining part is due to direct Fermi breakup or the quasielastic knockout of one alpha-particle cluster from a loosely bound residual nucleus consisting of three alpha particles. The results obtained by simulating the decay of the excited system involving three alpha particles for an isotropic phase space describe experimental data satisfactorily atmore » moderate values of the excitation energy ({delta}E{sup *} < 15 MeV)« less
  • The interference of secondary negative pions produced in collisions of carbon nuclei of energy 4.2 GeV/c per nucleon with tantalum nuclei has been investigated. The radius of the region of production of these particles has been found to be r=3.3 +- 0.6 F.