Biomedical subjects

H J Specht

Publications and source records attributed to H J Specht.

5 recordsLinked to original sources

PubMed2006

First measurement of the rho spectral function in high-energy nuclear collisions.

We report on a precision measurement of low-mass muon pairs in 158 AGeV indium-indium collisions at the CERN SPS. A significant excess of pairs is observed above the yield expected from neutral meson decays. The unprecedented sample size of 360,000 dimuons and the good mass resolution of about 2% allow us to isolate the excess by subtraction of the decay sources. The shape of the resulting mass spectrum is consistent with a dominant contribution from pi+pi- -->rho -->mu+mu- annihilation. The associated space-time averaged spectral function shows a strong broadening, but essentially no shift in mass. This may rule out theoretical models linking hadron masses directly to the chiral condensate.

Journal Article↗

PubMed2004

Semihard scattering unraveled from collective dynamics by two-pion azimuthal correlations in 158A GeV/c Pb+Au collisions.

Elliptic flow and two-particle azimuthal correlations of charged hadrons and high-p(T) pions (p(T)>1 GeV/c) have been measured close to midrapidity in 158A GeV/c Pb+Au collisions by the CERES experiment. Elliptic flow (v(2)) rises linearly with p(T) to a value of about 10% at 2 GeV/c. Beyond p(T) approximately 1.5 GeV/c, the slope decreases considerably, possibly indicating a saturation of v(2) at high p(T). Two-pion azimuthal anisotropies for p(T)>1.2 GeV/c exceed the elliptic flow values by about 60% in midcentral collisions. These nonflow contributions are attributed to nearside and back-to-back jetlike correlations, the latter exhibiting centrality dependent broadening.

Journal Article↗

PubMed2003

Enhanced production of low-mass electron-positron pairs in 40-AGeV Pb-Au collisions at the CERN SPS.

We report on first measurements of low-mass electron-positron pairs in Pb-Au collisions at the CERN SPS beam energy of 40 AGeV. The observed pair yield integrated over the range of invariant masses 0.2 e(+)e(-) annihilation with a modified rho propagator. They may be linked to chiral symmetry restoration and support the notion that the in-medium modifications of the rho are more driven by baryon density than by temperature.

Journal Article↗

PubMed2003

Universal pion freeze-out in heavy-ion collisions.

Based on an evaluation of data on pion interferometry and on particle yields at midrapidity, we propose a universal condition for thermal freeze-out of pions in heavy-ion collisions. We show that freeze-out occurs when the mean free path of pions lambda(f) reaches a value of about 1 fm, which is much smaller than the spatial extent of the system at freeze-out. This critical mean free path is independent of the centrality of the collision and beam energy from the Alternating Gradient Synchrotron to the Relativistic Heavy Ion Collider.

Journal Article↗

PubMed2003

Additional neuromagnetic source activity outside the auditory cortex in duration discrimination correlates with behavioural ability.

In magneto- and electroencephalographic experiments on an oddball paradigm we compared the components of the auditory evoked fields and potentials of "attend" with "nonattend" conditions in 17 subjects. The former consisted of the performance of a duration discrimination task, where we observed augmented activity for the auditory sustained response. A multiple source analysis showed this effect mainly stemming from a third source outside the auditory cortices. The dipole moment of this specific activation was increased by 150% under the attend condition. Having anatomical 3D MRI data sets of 12 subjects the likely location of the third source was shown to be within the area of the precuneus or the posterior cingulate gyrus, which, along with its waveform, suggests it to be a CNV equivalent. Further, the dipole moment is correlated significantly to the subjects' psychometrically derived discriminative abilities.

Acoustic Stimulation↗