4,515 research outputs found
Multiparton scattering at the LHC
The large parton flux at high energy gives rise to events where different
pairs of partons interact contemporarily with large momentum exchange. A main
effect of multiple parton interactions is to generate events with many jets at
relatively large transverse momenta. The large value of the heavy quarks
production cross section may however give also rise a sizable rate of events
with several -quarks produced. We summarize the main features of multiparton
interactions and make some estimate of the inclusive cross section to produce
two pairs within the acceptance of the ALICE detector.Comment: 10 pages, 4 figures, contribution to ALICE PP
Optimal generation of entanglement under local control
We study the optimal generation of entanglement between two qubits subject to
local unitary control. With the only assumptions of linear control and unitary
dynamics, by means of a numerical protocol based on the variational approach
(Pontryagin's Minimum Principle), we evaluate the optimal control strategy
leading to the maximal achievable entanglement in an arbitrary interaction
time, taking into account the energy cost associated to the controls. In our
model we can arbitrarily choose the relative weight between a large
entanglement and a small energy cost.Comment: 4 page
Production and detection of doubly charmed tetraquarks
The feasibility of tetraquark detection is studied. For the cc\bar{u}\bar{d}
tetraquark we show that in present (SELEX, Tevatron, RHIC) and future
facilities (LHCb, ALICE) the production rate is promising and we propose some
detectable decay channels.Comment: 6 pages, 5 figure
Possible explanations for different surface quality in laser cutting with 1 micron and 10 microns beams
In laser cutting of thick steel sheets, quality difference is observed between cut surfaces obtained with 1 micron and 10 micron laser beams. This paper investigates physical mechanisms for this interesting and important problem of the wavelength dependence. First, striation generation process is described, based on a 3D structure of melt flow on a kerf front, which was revealed for the first time by our recent experimental observations. Two fundamental processes are suggested to explain the difference in the cut surface quality: destabilization of the melt flow in the central part of the kerf front and downward displacement of discrete melt accumulations along the side parts of the front. Then each of the processes is analyzed using a simplified analytical model. The results show that in both processes, different angular dependence of the absorptivity of the laser beam can result in the quality difference. Finally we propose use of radial polarization to improve the quality with the 1 micron wavelength
b \bar b b\bar b production in proton-nucleus collisions at the LHC
A sizable rate of events, with several pairs of -quarks produced
contemporarily by multiple parton interactions, may be expected at very high
energies as a consequence of the large parton luminosities. The production
rates are further enhanced in hadron-nucleus reactions, which may represent a
convenient tool to study the phenomenon. We compare the different contributions
to production, due to single and double parton
scatterings, in collisions of protons with nuclei at the CERN-LHC.Comment: 13 pages, 4 figure
Fractional momentum correlations in multiple production of W bosons and of b-anti_b pairs in high energy pp collisions
Multiple parton collisions will represent a rather common feature in pp
collisions at the LHC, where regimes with very large momentum transfer may be
studied and events rare in lower energy accelerators might occur with a
significant rate. A reason of interest in large p_t regimes is that,
differently from low p_t, evolution will induce correlations in x in the
multiparton structure functions. We have estimated the cross section of
multiple production of W bosons with equal sign, where the correlations in x
induced by evolution are particularly relevant, and the cross section of
b-bar_b b-bar_b production, where the effects of evolution are much smaller.
Our result is that, in the case of multiple production of W bosons, the terms
with correlations may represent a correction of the order of 40% of the cross
sections, for pp collisions at 1 TeV c.m. energy, and a correction of the order
of 20% at 14 TeV. In the case of b-bar_b pairs the correction terms are of the
order of 10-15% at 1 TeV and of the order of 5% at 14 TeV.Comment: Submitted to Phys. Rev.
Photometry of supernovae in an image series : methods and application to the Supernova Legacy Survey (SNLS)
We present a technique to measure lightcurves of time-variable point sources
on a spatially structured background from imaging data. The technique was
developed to measure light curves of SNLS supernovae in order to infer their
distances. This photometry technique performs simultaneous PSF photometry at
the same sky position on an image series. We describe two implementations of
the method: one that resamples images before measuring fluxes, and one which
does not. In both instances, we sketch the key algorithms involved and present
the validation using semi-artificial sources introduced in real images in order
to assess the accuracy of the supernova flux measurements relative to that of
surrounding stars. We describe the methods required to anchor these PSF fluxes
to calibrated aperture catalogs, in order to derive SN magnitudes. We find a
marginally significant bias of 2 mmag of the after-resampling method, and no
bias at the mmag accuracy for the non-resampling method. Given surrounding star
magnitudes, we determine the systematic uncertainty of SN magnitudes to be less
than 1.5 mmag, which represents about one third of the current photometric
calibration uncertainty affecting SN measurements. The SN photometry delivers
several by-products: bright star PSF flux mea- surements which have a
repeatability of about 0.6%, as for aperture measurements; we measure relative
astrometric positions with a noise floor of 2.4 mas for a single-image bright
star measurement; we show that in all bands of the MegaCam instrument, stars
exhibit a profile linearly broadening with flux by about 0.5% over the whole
brightness range.Comment: Accepted for publication in A&A. 20 page
Correlation between hormone dependency and the regulation of epidermal growth factor receptor by tumor promoters in human mammary carcinoma cells.
The Chances to Produce and Detect the b-b-ubar-dbar Tetraquark at LHC
In the LHC collider a significant rate of events with double parton
scattering is expected. This will be the leading mechanism for production of
two b-bbar pairs. We estimate the probability of binding two b quarks into a
diquark and the probability of dressing this diquark into a b-b-ubar-dbar
ISP=01+ tetraquark. Calculations shows that that this bound state of two B
mesons is stable against the strong interaction and has a life time of the
order of ps. We estimate that the production rate at luminosity L=0.1 events
per second will be about 6 tetraquarks per hour or more.Comment: Contributed talk at the XVIII European Conference on Few-Body
Problems in Physics, September 8-14, Bled, Slovenia, 4 pages LaTe
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