pegasus
is a parton-level Monte-Carlo event generator designed to calculate cross sections for a wide range of hard QCD processes at high energy
pp
and
p
p
¯
collisions, which incorporates the ...dynamics of transverse momentum dependent (TMD) parton distributions in a proton. Being supplemented with off-shell production amplitudes for a number of partonic subprocesses and provided with necessary TMD gluon density functions, it produces weighted or unweighted event records which can be saved as a plain data file or a file in a commonly used Les Houches Event format. A distinctive feature of the
pegasus
is an intuitive and extremely user friendly interface, allowing one to easily implement various kinematical cuts into the calculations. Results can be also presented “on the fly” with built-in tool
pegasus plotter
. A short theoretical basis is presented and detailed program description is given.
We uncover the fine structure of a silicon vacancy in isotopically purified silicon carbide (4H-SiC28 ) and reveal not yet considered terms in the spin Hamiltonian, originated from the trigonal ...pyramidal symmetry of this spin-3/2 color center. These terms give rise to additional spin transitions, which would be otherwise forbidden, and lead to a level anticrossing in an external magnetic field. We observe a sharp variation of the photoluminescence intensity in the vicinity of this level anticrossing, which can be used for a purely all-optical sensing of the magnetic field. We achieve dc magnetic field sensitivity better than 100nT/Hz within a volume of 3×10−7mm3 at room temperature and demonstrate that this contactless method is robust at high temperatures up to at least 500 K. As our approach does not require application of radio-frequency fields, it is scalable to much larger volumes. For an optimized light-trapping waveguide of 3mm3 , the projection noise limit is below 100fT/Hz .
We consider the production of hadrons containing two charmed quarks in
pp
and
ee
collisions. We perform a numerical comparison of the fragmentation approach with the full calculation at
O
(
α
s
4
)
. ...We conclude that the non-fragmentation contributions remain important up to transverse momenta as large as about 40 GeV, thus making questionable the applicability of the fragmentation approximation at smaller transverse momenta.
One of the challenges in the field of quantum sensing and information processing is to selectively address and coherently manipulate highly homogeneous qubits subject to external perturbations. Here, ...we present room-temperature coherent control of high-dimensional quantum bits, the so-called qudits, associated with vacancy-related spins in silicon carbide enriched with nuclear spin-free isotopes. In addition to the excitation of a spectrally narrow qudit mode at the pump frequency, several other modes are excited in the electron spin resonance spectra whose relative positions depend on the external magnetic field. We develop a theory of multipole spin dynamics and demonstrate selective quantum control of homogeneous spin packets with sub-MHz spectral resolution. Furthermore, we perform two-frequency Ramsey interferometry to demonstrate absolute dc magnetometry, which is immune to thermal noise and strain inhomogeneity.
We report a giant thermal shift of 2.1 MHz/K related to the excited-state zero-field splitting in the silicon vacancy centers in 4H silicon carbide. It is obtained from the indirect observation of ...the optically detected magnetic resonance in the excited state using the ground state as an ancilla. Alternatively, relative variations of the zero-field splitting for small temperature differences can be detected without application of radiofrequency fields, by simply monitoring the photoluminescence intensity in the vicinity of the level anticrossing. This effect results in an all-optical thermometry technique with temperature sensitivity of 100 mK/Hz(1/2) for a detection volume of approximately 10(-6) mm(3). In contrast, the zero-field splitting in the ground state does not reveal detectable temperature shift. Using these properties, an integrated magnetic field and temperature sensor can be implemented on the same center.
Quantum systems can provide outstanding performance in various sensing applications, ranging from bioscience to nanotechnology. Atomic-scale defects in silicon carbide are very attractive in this ...respect because of the technological advantages of this material and favorable optical and radio frequency spectral ranges to control these defects. We identified several, separately addressable spin-3/2 centers in the same silicon carbide crystal, which are immune to nonaxial strain fluctuations. Some of them are characterized by nearly temperature independent axial crystal fields, making these centers very attractive for vector magnetometry. Contrarily, the zero-field splitting of another center exhibits a giant thermal shift of -1.1 MHz/K at room temperature, which can be used for thermometry applications. We also discuss a synchronized composite clock exploiting spin centers with different thermal response.
We discuss the fine structure and spin dynamics of spin‐3/2 centers associated with silicon vacancies in silicon carbide. The centers have optically addressable spin states which makes them highly ...promising for quantum technologies. The fine structure of the spin centers turns out to be highly sensitive to mechanical pressure, external magnetic and electric fields, temperature variation, etc., which can be utilized for efficient room‐temperature sensing, particularly by purely optical means or through the optically detected magnetic resonance. We discuss the experimental achievements in magnetometry and thermometry based on the spin state mixing at level anticrossings in an external magnetic field and the underlying microscopic mechanisms. We also discuss spin fluctuations in an ensemble of vacancies caused by interaction with environment.
Atomic‐scale defects in silicon carbide, a widely used material in semiconductor industry, have been recently recognized to reveal high potential for quantum technologies. The paper reviews quantum spin properties of these defects and discusses how they can be utilized for environment sensing with very high accuracy. The achievements in sensing magnetic field and temperature fluctuations as well as the underlying mechanisms and microscopic theory are discussed in detail.
We reconsider the associated
Z
boson and charm or beauty jet production at the LHC by paying special attention to the formation dynamics of heavy jets. Two different approaches are studied: first ...one, where heavy quarks are produced in the hard scattering subprocesses, implemented in the Monte-Carlo generator
pegasus
, and another method, where the hard scattering is calculated at NLO with
MadGraph5_aMC@NLO
and TMD parton shower is included (implemented in the Monte-Carlo generator
Cascade3
). We compare the predictions obtained in both schemes with latest experimental data for associated
Z
+
b
production cross sections and the relative production rate
σ
(
Z
+
c
)
/
σ
(
Z
+
b
)
collected by the ATLAS and CMS Collaborations at
s
=
13
TeV. We introduce two kinematic observables (denoted as
z
b
and
p
T
rel
) which can be used to discriminate between the heavy jet production mechanisms. Using these variables we trace the shape of the simulated
b
-jet events and recommend that these observables be taken into consideration in the forthcoming experimental analyses.
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