41 research outputs found
Evidence of dynamical dipole excitation in the fusion-evaporation of the 40Ca +152Sm heavy system
The excitation of the dynamical dipole mode along the fusion path was investigated for the first time
in the formation of a heavy compound nucleus in the
A
∼
190 mass region. The compound nucleus was
formed at identical conditions of excitation energy and spin from two entrance channels: the charge-asymmetric
40
Ca
+
152
Sm and the nearly charge-symmetric
48
Ca
+
144
Sm at
E
lab
=
11 and 10.1 MeV
/
nucleon, respectively.
High-energy
γ
rays and light charged particles were measured in coincidence with evaporation residues by
means of the MEDEA multidetector array (Laboratori Nazionali del Sud, Italy) coupled to four parallel plate
avalanche counters. The charged particle multiplicity spectra and angular distributions were used to pin down
the average excitation energy, the average mass, and the average charge of the compound nucleus. The
γ
-ray
multiplicity spectrum and angular distribution related to the nearly charge-symmetric channel were employed to
obtain new data on the giant dipole resonance in the compound nucleus. The dynamical dipole mode excitation in
the charge-asymmetric channel was evidenced, in a model-independent way, by comparing the
γ
-ray multiplicity
spectra and angular distributions of the two entrance channels with each other. Calculations of the dynamical
dipole mode in the
40
Ca
+
152
Sm channel, based on a collective bremsstrahlung analysis of the reaction dynamics,
are presented. Possible interesting implications in the superheavy-element quest are discussed
Characterizing the initial conditions of heavy-ion collisions at the LHC with mean transverse momentum and anisotropic flow correlations
Correlations between mean transverse momentum and anisotropic flow coefficients or are measured as a function of centrality in Pb–Pb and Xe–Xe collisions at sqrt(sNN) = 5.02 TeV and 5.44 TeV, respectively, with ALICE. In addition, the recently proposed higher-order correlation between [pt], v2, and v3 is measured for the first time, which shows an anticorrelation for the presented centrality ranges. These measurements are compared with hydrodynamic calculations using IP-Glasma and TRENTO initial-state shapes, the former based on the Color Glass Condensate effective theory with gluon saturation, and the latter a parameterized model with nucleons as the relevant degrees of freedom. The data are better described by the IP-Glasma rather than the TRENTO based calculations. In particular, Trajectum and JETSCAPE predictions, both based on the TRENTO initial state model but with different parameter settings, fail to describe the measurements. As the correlations between [pt] and vn are mainly driven by the correlations of the size and the shape of the system in the initial state, these new studies pave a novel way to characterize the initial state and help pin down the uncertainty of the extracted properties of the quark–gluon plasma recreated in relativistic heavy-ion collisions
Hypertriton Production in p-Pb Collisions at √sNN = 5.02 TeV
The study of nuclei and antinuclei production has proven to be a powerful
tool to investigate the formation mechanism of loosely bound states in
high-energy hadronic collisions. The first measurement of the production of
in p-Pb collisions at = 5.02
TeV is presented in this Letter. Its production yield measured in the rapidity
interval -1 < y < 0 for the 40% highest multiplicity p-Pb collisions is . The measurement is compared with the expectations of statistical
hadronisation and coalescence models, which describe the nucleosynthesis in
hadronic collisions. These two models predict very different yields of the
hypertriton in small collision systems such as p-Pb and therefore the
measurement of is crucial to distinguish between them.
The precision of this measurement leads to the exclusion with a significance
larger than 6 of some configurations of the statistical hadronisation,
thus constraining the production mechanism of loosely bound states
General balance functions of identified charged hadron pairs of (pi,K,p) in Pb-Pb collisions at 2.76 TeV
First measurements of balance functions (BFs) of all combinations of identified charged hadron ( π , K, p)
pairs in Pb–Pb collisions at √sNN = 2.76 TeV recorded by the ALICE detector are presented. The BF
measurements are carried out as two-dimensional differential correlators versus the relative rapidity
(delta-y) and azimuthal angle (delta-φ) of hadron pairs, and studied as a function of collision centrality. The delta-φ
dependence of BFs is expected to be sensitive to the light quark diffusivity in the quark–gluon plasma.
While the BF azimuthal widths of all pairs substantially decrease from peripheral to central collisions, the
longitudinal widths exhibit mixed behaviors: BFs of π π and cross-species pairs narrow significantly in
more central collisions, whereas those of KK and pp are found to be independent of collision centrality.
This dichotomy is qualitatively consistent with the presence of strong radial flow effects and the existence
of two stages of quark production in relativistic heavy-ion collisions. Finally, the first measurements of
the collision centrality evolution of BF integrals are presented, with the observation that charge balancing
fractions are nearly independent of collision centrality in Pb–Pb collisions. Overall, the results presented
provide new and challenging constraints for theoretical models of hadron production and transport in
relativistic heavy-ion collisions
Measurement of the non-prompt D-meson fraction as a function of multiplicity in proton-proton collisions at = 13 TeV
The fractions of non-prompt (i.e. originating from beauty-hadron decays) D0
and D+ mesons with respect to the inclusive yield are measured as a function of the
charged-particle multiplicity in proton-proton collisions at a centre-of-mass energy of √s =
13 TeV with the ALICE detector at the LHC. The results are reported in intervals of
transverse momentum (pT) and integrated in the range 1 < pT < 24 GeV/c. The fraction
of non-prompt D0 and D+ mesons is found to increase slightly as a function of pT in
all the measured multiplicity intervals, while no significant dependence on the charged-
particle multiplicity is observed. In order to investigate the production and hadronisation
mechanisms of charm and beauty quarks, the results are compared to PYTHIA 8 as well
as EPOS 3 and EPOS 4 Monte Carlo simulations, and to calculations based on the colour
glass condensate including three-pomeron fusion
K∗(892)0 and φ(1020) production in p-Pb collisions at √s NN = 8.16 TeV
The production of K*(892)(0) and phi(1020) resonances has been measured in p-Pb collisions at root s(NN) = 8.16 TeV using the ALICE detector. Resonances are reconstructed via their hadronic decay channels in the rapidity interval -0.5 8 GeV/c), the R-pPb values of all hadrons are consistent with unity within uncertainties. The R-pPb of K*(892)(0) and phi(1020) at root s(NN) = 8.16 and 5.02 TeV show no significant energy dependence
Inclusive and multiplicity dependent production of electrons from heavy-flavour hadron decays in pp and p-Pb collisions
Measurements of the production of electrons from heavy-flavour hadron decays in pp collisions at root s = 13 TeV at midrapidity with the ALICE detector are presented down to a transverse momentum (p(T)) of 0.2 GeV/c and up to p(T) = 35 GeV/c, which is the largest momentum range probed for inclusive electron measurements in ALICE. In p-Pb collisions, the production cross section and the nuclear modification factor of electrons from heavy-flavour hadron decays are measured in the p(T) range 0.5 < p(T) < 26 GeV/c at root s(NN) = 8.16 TeV. The nuclear modification factor is found to be consistent with unity within the statistical and systematic uncertainties. In both collision systems, first measurements of the yields of electrons from heavy-flavour hadron decays in different multiplicity intervals normalised to the multiplicity-integrated yield (self-normalised yield) at midrapidity are reported as a function of the self-normalised charged-particle multiplicity estimated at midrapidity. The self-normalised yields in pp and p-Pb collisions grow faster than linear with the self-normalised multiplicity. A strong p(T) dependence is observed in pp collisions, where the yield of high-p(T) electrons increases faster as a function of multiplicity than the one of low-p(T) electrons. The measurement in p-Pb collisions shows no p(T) dependence within uncertainties. The self-normalised yields in pp and p-Pb collisions are compared with measurements of other heavy-flavour, light-flavour, and strange particles, and with Monte Carlo simulations
Effects of waveform model systematics on the interpretation of GW150914
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Wei54, M Weinert10, A J Weinstein1, R Weiss12, L Wen52, P Weßels10, T Westphal10, K Wette10, J T Whelan107, B F Whiting6, C Whittle120, D Williams36, R D Williams1, A R Williamson94, J L Willis142, B Willke10,19, M H Wimmer10,19, W Winkler10, C C Wipf1, H Wittel10,19, G Woan36, J Woehler10, J Worden37, J L Wright36, D S Wu10, G Wu7, W Yam12, H Yamamoto1, C C Yancey64, M J Yap22, Hang Yu12, Haocun Yu12, M Yvert8, A Zadrożny118, L Zangrando42, M Zanolin103, J-P Zendri42, M Zevin85, L Zhang1, M Zhang129, T Zhang36, Y Zhang107, C Zhao52, M Zhou85, Z Zhou85, S J Zhu10,29, X J Zhu52, M E Zucker1,12, J Zweizig1 (LIGO Scientific Collaboration, Virgo Collaboration), M Boyle143, T Chu97, D Hemberger51, I Hinder29, L E Kidder143, S Ossokine29, M Scheel51, B Szilagyi51, S Teukolsky143 and A Vano Vinuales94 Hide full author list Published 12 April 2017 • © 2017 IOP Publishing Ltd Classical and Quantum Gravity, Volume 34, Number 10 Focus Issue: Gravitational Waves Article PDF Figures References Citations PDF 258 Total downloads Cited by 1 articles Article has an altmetric score of 3 Turn on MathJax Get permission to re-use this article Share this article Article information Abstract Parameter estimates of GW150914 were obtained using Bayesian inference, based on three semi-analytic waveform models for binary black hole coalescences. These waveform models differ from each other in their treatment of black hole spins, and all three models make some simplifying assumptions, notably to neglect sub-dominant waveform harmonic modes and orbital eccentricity. Furthermore, while the models are calibrated to agree with waveforms obtained by full numerical solutions of Einstein's equations, any such calibration is accurate only to some non-zero tolerance and is limited by the accuracy of the underlying phenomenology, availability, quality, and parameter-space coverage of numerical simulations. This paper complements the original analyses of GW150914 with an investigation of the effects of possible systematic errors in the waveform models on estimates of its source parameters. To test for systematic errors we repeat the original Bayesian analysis on mock signals from numerical simulations of a series of binary configurations with parameters similar to those found for GW150914. Overall, we find no evidence for a systematic bias relative to the statistical error of the original parameter recovery of GW150914 due to modeling approximations or modeling inaccuracies. However, parameter biases are found to occur for some configurations disfavored by the data of GW150914: for binaries inclined edge-on to the detector over a small range of choices of polarization angles, and also for eccentricities greater than ~0.05. For signals with higher signal-to-noise ratio than GW150914, or in other regions of the binary parameter space (lower masses, larger mass ratios, or higher spins), we expect that systematic errors in current waveform models may impact gravitational-wave measurements, making more accurate models desirable for future observations
All-sky search for long-duration gravitational wave transients in the first Advanced LIGO observing run
We present the results of a search for long-duration gravitational wave transients in the data of the LIGO Hanford and LIGO Livingston second generation detectors between September 2015 and January 2016 , with a total observational time of 49 d. The search targets gravitational wave transients of 10 – 500 s duration in a frequency band of 24 – 2048 Hz, with minimal assumptions about the signal waveform, polarization, source direction, or time of occurrence. No significant events were observed. As a result we set 90% confidence upper limits on the rate of long-duration gravitational wave transients for different types of gravitational wave signals. We also show that the search is sensitive to sources in the Galaxy emitting at least ∼ 10 − 8 M c 2 in gravitational waves
Directly comparing GW150914 with numerical solutions of Einstein's equations for binary black hole coalescence
We compare GW150914 directly to simulations of coalescing binary black holes in full general relativity, including
several performed specifically to reproduce this event. Our calculations go beyond existing semianalytic
models, because for all simulations – including sources with two independent, precessing spins – we perform
comparisons which account for all the spin-weighted quadrupolar modes, and separately which account for all
the quadrupolar and octopolar modes. Consistent with the posterior distributions reported in LVC-PE[1] (at
the 90% credible level), we find the data are compatible with a wide range of nonprecessing and precessing
simulations. Followup simulations performed using previously-estimated binary parameters most resemble the
data, even when all quadrupolar and octopolar modes are included. Comparisons including only the quadrupolar
modes constrain the total redshifted mass Mz ∈ [64M� − 82M�], mass ratio 1/q = m2/m1 ∈ [0.6, 1], and
effective aligned spin χeff ∈ [−0.3, 0.2], where χeff = (S1/m1 + S2/m2) · Lˆ /M. Including both quadrupolar
and octopolar modes, we find the mass ratio is even more tightly constrained. Even accounting for precession,
simulations with extreme mass ratios and effective spins are highly inconsistent with the data, at any mass.
Several nonprecessing and precessing simulations with similar mass ratio and χeff are consistent with the data.
Though correlated, the components’ spins (both in magnitude and directions) are not significantly constrained
by the data: the data is consistent with simulations with component spin magnitudes a1,2 up to at least 0.8, with
random orientations. Further detailed followup calculations are needed to determine if the data contain a weak
imprint from transverse (precessing) spins. For nonprecessing binaries, interpolating between simulations, we
reconstruct a posterior distribution consistent with previous results. The final black hole’s redshifted mass is
consistent with Mf,z
in the range 64.0M� − 73.5M� and the final black hole’s dimensionless spin parameter is
consistent with af = 0.62 − 0.73. As our approach invokes no intermediate approximations to general relativity
and can strongly reject binaries whose radiation is inconsistent with the data, our analysis provides a valuable
complement to LVC-PE[1]