2,891 research outputs found
Dynamical Monte Carlo investigation of spin reversals and nonequilibrium magnetization of single-molecule magnets
In this paper, we combine thermal effects with Landau-Zener (LZ) quantum
tunneling effects in a dynamical Monte Carlo (DMC) framework to produce
satisfactory magnetization curves of single-molecule magnet (SMM) systems. We
use the giant spin approximation for SMM spins and consider regular lattices of
SMMs with magnetic dipolar interactions (MDI). We calculate spin reversal
probabilities from thermal-activated barrier hurdling, direct LZ tunneling, and
thermal-assisted LZ tunnelings in the presence of sweeping magnetic fields. We
do systematical DMC simulations for Mn systems with various temperatures
and sweeping rates. Our simulations produce clear step structures in
low-temperature magnetization curves, and our results show that the thermally
activated barrier hurdling becomes dominating at high temperature near 3K and
the thermal-assisted tunnelings play important roles at intermediate
temperature. These are consistent with corresponding experimental results on
good Mn samples (with less disorders) in the presence of little
misalignments between the easy axis and applied magnetic fields, and therefore
our magnetization curves are satisfactory. Furthermore, our DMC results show
that the MDI, with the thermal effects, have important effects on the LZ
tunneling processes, but both the MDI and the LZ tunneling give place to the
thermal-activated barrier hurdling effect in determining the magnetization
curves when the temperature is near 3K. This DMC approach can be applicable to
other SMM systems, and could be used to study other properties of SMM systems.Comment: Phys Rev B, accepted; 10 pages, 6 figure
Determination of the X(3872) Meson Quantum Numbers
The Large Hadron Collider beauty (LHCb) is one of the several experiments located at the ring of the Large Hadron Collider (LHC) in Geneva. The LHCb detector is a single arm forward spectrometer and is designed to perform high precision measurements of Charge Parity (CP) violation parameters and rare decays of the beauty and charm hadrons. The detector was successfully operated at a center-of-mass energy of 7 TeV in 2010 and 2011 and at 8 TeV in 2012. Over 3 fb-1 of data has been collected by the LHCb. The LHCb experiment is also well suited for studies on hadron spectroscopy.
Besides the well established mesons consisting of quark-antiquark pairs (qq-bar), it has been proposed that exotic qqq-barq-bar mesons could exist. One of the candidates for a four-quark state is the charmonium-like state X(3872) which was first observed by the Belle experiment in 2003. This narrow state has a mass of about 3872 MeV which is located in a region of excited charmonium states (cc-bar). However its mass does not match to any theoretically predicted charmonium state. In order to investigate the nature of this anomalous state, we analyze its quantum number which is the key for its interpretation. The X(3872) events are reconstructed from B+-\u3eX(3872)K+, where X(3872)-\u3epi+ pi- J/psi , J/psi-\u3emu+mu-; based on 1 fb-1 of 2011 data collected by LHCb detector. We implement a method which is guaranteed by statistics to be the most powerful way to discriminate between spin hypotheses; namely unbinned likelihood ratio test using full angular phase-space. The 5-dimensional analysis shows that 1++ hypothesis is preferred with overwhelming significance. The only alternative assignment allowed by the previous measurements, JPC = 2-+, is rejected with a confidence level equivalent to more than eight Gaussian standard deviations. This result favors exotic explanations of the X(3872) state, such as a mesonic molecule or a tetraquark
Convergence of Sewing Conformal Blocks
In recent work, Damiolini-Gibney-Tarasca showed that for a -cofinite
rational CFT-type vertex operator algebra , sheaves of conformal
blocks are locally free and satisfy the factorization property. In this
article, we use analytic methods to prove that sewing conformal blocks is
convergent, solving a conjecture proposed by Zhu and Huang.Comment: 62 pages, reference added. The assumptions of CFT-type and
rationality are completely removed in the main results. Logarithmic modules
are treated. A new proof is written for multiple sewing (Sec. 13) since the
original inductive proof does not apply to logarithmic modules. (Note that
our results do not cover the pseudotraces of intertwining operators.
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