893 research outputs found
First measurement of the rho spectral function in nuclear collisions
The NA60 experiment has studied low-mass muon pairs in 158 AGeV Indium-Indium
collisions at the CERN SPS. A strong excess of pairs is observed above the
expectation from neutral meson decays. The unprecedented sample size of 360 000
events and the good mass resolution of about 2% allow to isolate the excess by
subtraction of the known sources. The shape of the resulting mass spectrum is
consistent with a dominant contribution from pi+ pi- -> rho -> mu+ mu-
annihilation. The associated rho spectral function shows a strong broadening,
but essentially no shift in mass.Comment: 4 pages, 3 figures, Proceedings of Quark Matter 2005, Budapes
Piezoelectric nonlinearity and frequency dispersion of the direct piezoelectric response of BiFeO3 ceramics
We report on the frequency and stress dependence of the direct piezoelectric
d33 coefficient in BiFeO3 ceramics. The measurements reveal considerable
piezoelectric nonlinearity, i.e., dependence of d33 on the amplitude of the
dynamic stress. The nonlinear response suggests a large irreversible
contribution of non-180{\deg} domain walls to the piezoelectric response of the
ferrite, which, at present measurement conditions, reached a maximum of 38% of
the total measured d33. In agreement with this interpretation, both types of
non-180{\deg} domain walls, characteristic for the rhombohedral BiFeO3, i.e.,
71{\deg} and 109{\deg}, were identified in the poled ceramics using
transmission electron microscopy (TEM). In support to the link between
nonlinearity and non-180{\deg} domain wall contribution, we found a correlation
between nonlinearity and processes leading to deppining of domain walls from
defects, such as quenching from above the Curie temperature and
high-temperature sintering. In addition, the nonlinear piezoelectric response
of BiFeO3 showed a frequency dependence that is qualitatively different from
that measured in other nonlinear ferroelectric ceramics, such as "soft"
(donor-doped) Pb(Zr,Ti)O3 (PZT); possible origins of this dispersion are
discussed. Finally, we show that, once released from pinning centers, the
domain walls can contribute extensively to the electromechanical response of
BiFeO3; in fact, the extrinsic domain-wall contribution is relatively as large
as in Pb-based ferroelectric ceramics with morphotropic phase boundary (MPB)
composition, such as PZT. This finding might be important in the search of new
lead-free MPB compositions based on BiFeO3 as it suggests that such
compositions might also exhibit large extrinsic domain-wall contribution to the
piezoelectric response.Comment: 38 pages, 11 figure
In-medium vector mesons and low mass lepton pairs from heavy ion collisions
The rho and omega meson self-energy at finite temperature and baryon density
have been analysed for an exhaustive set of mesonic and baryonic loops in the
real time formulation of thermal field theory. The large enhancement of
spectral strength below the nominal rho mass is seen to cause a substantial
enhancement in dilepton pair yield in this mass region. The integrated yield
after space-time evolution using relativistic hydrodynamics with quark gluon
plasma in the initial state leads to a very good agreement with the
experimental data from In-In collisions obtained by the NA60 collaboration.Comment: Invited Talk at the DAE-BRNS Workshop on Hadron Physics, Bhabha
Atomic Research Centre, Mumbai, India, October 31-November 4, 201
Dileptons from the nonequilibrium Quark-Gluon Plasma
According to the dynamical quasiparticle model (DQPM) -- matched to reproduce
lattice QCD results in thermodynamic limit, -- the constituents of the strongly
interacting quark-gluon plasma (sQGP) are massive and off-shell quasi-particles
(quarks and gluons) with broad spectral functions. In order to address the
electromagnetic radiation of the sQGP, we derive off-shell cross sections of
, and () reactions taking into account the effective propagators
for quarks and gluons from the DQPM. Dilepton production in In+In collisions at
158 AGeV is studied by implementing these processes into the
parton-hadron-string dynamics (PHSD) transport approach. The microscopic PHSD
transport approach describes the full evolution of the heavy-ion collision:
from the dynamics of quasi-particles in the sQGP phase (when the local energy
density is above GeV/fm) through hadronization and to the
following hadron interactions and off-shell propagation after the
hadronization. A comparison to the data of the NA60 Collaboration shows that
the low mass dilepton spectra are well described by including a collisional
broadening of vector mesons, while the spectra in the intermediate mass range
are dominated by off-shell quark-antiquark annihilation, quark Bremsstrahlung
and gluon-Compton scattering in the nonperturbative QGP. In particular, the
observed softening of the spectra at intermediate masses (1 GeV 3 GeV) is approximately reproduced.Comment: 8 pages, 8 figures, to be published in the Proceedings of the 26th
Winter Workshop on `Nuclear Dynamics', Ochto Rios, Jamaica, 2-9 January, 201
Interpretation of Recent SPS Dilepton Data
We summarize our current theoretical understanding of in-medium properties of
the electromagnetic current correlator in view of recent dimuon data from the
NA60 experiment in In(158 AGeV)-In collisions at the CERN-SPS. We discuss the
sensitivity of the results to space-time evolution models for the hot and dense
partonic and hadronic medium created in relativistic heavy-ion collisions and
the contributions from different sources to the dilepton-excess spectra.Comment: To appear in the proceedings of the 19th International Conference on
Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter 2006) v2:
references added, minor typos correcte
Using Touch Technology to Foster Storytelling in the Preschool Classroom
This practitioner research explores ways children engage in literacy learning through storytelling with the use of touch technology in a VPK (Voluntary Pre-Kindergarten) classroom. With access to diverse touch technology devices but no experience using these technologies, a VPK teacher explored strategies to use the resources to enhance literacy learning in the classroom with the support of a professional learning community (PLC). The PLC consisted of a master’s student, university faculty, school director, and a technology liaison. The implementation of this study took place over three weeks, and every week children created a different story. Collected data include photographs, student voice recordings, anecdotal notes, and a reflective journal. The three weeks of implementation data showed how touch technology provided a new modality of learning representation for young children in my classroom. The findings suggest that multiliteracies complemented traditional literacy, storytelling enhanced children’s communication, and touch technology functionality went beyond literacy skills
What to learn from dilepton transverse momentum spectra in heavy-ion collisions?
Recently the NA60 collaboration has presented high precision measurements of
dimuon spectra double differential in invariant mass and transverse pair
momentum in In-In collisions at . While the
-dependence is important for an understanding of in-medium changes of light
vector mesons and is integrated insensitive to collective expansion, the
-dependence arises from an interplay between emission temperature and
collective transverse flow. This fact can be exploited to derive constraints on
the evolution model and in particular on the contributions of different phases
of the evolution to dimuon radiation into a given window. We present
arguments that a thermalized evolution phase with leaves
its imprint on the spectra.Comment: Contributed to 19th International Conference on Ultrarelativistic
Nucleus-Nucleus Collisions: Quark Matter 2006 (QM 2006), Shanghai, China, 14-
20 Nov 200
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