3,236 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
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.
Double parton distributions in the leading logarithm approximation of perturbative QCD
Recent CDF measurements of the inclusive cross section for a double parton
scattering attach a great importance to any theoretical calculations of
two-particle distribution functions. Using a parton interpretation of the
leading logarithm diagrams of perturbative QCD theory, generalized
Lipatov-Altarelli-Parisi-Dokshitzer equations for the two-parton distributions
are re-obtained. The solutions of these equations are not at all the product of
two single-parton distributions what is usually applied to the current analysis
as ansatz.Comment: 8 pages, LaTe
Scale Factor in Double Parton Collisions and Parton Densities in Transverse Space
The scale factor , which characterizes double parton collisions
in high energy hadron interactions, is a direct manifestation of the
distribution of the interacting partons in transverse space, in such a way that
different distributions give rise to different values of in
different double parton collision processes. We work out the value of the scale
factor in a few reactions of interest, in a correlated model of the
multi-parton density of the proton recently proposed.Comment: 10 pages, 2 figure
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
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
Same-sign W pair production as a probe of double parton scattering at the LHC
We study the production of same-sign W boson pairs at the LHC in double
parton interactions. Compared with simple factorised double parton
distributions (dPDFs), we show that the recently developed dPDFs, GS09, lead to
non-trivial kinematic correlations between the W bosons. A numerical study of
the prospects for observing this process using same-sign dilepton signatures,
including same-sign WWjj, di-boson and heavy flavour backgrounds, at 14 TeV
centre-of-mass energy is then performed. It is shown that a small excess of
same-sign dilepton events from double parton scattering over a background
dominated by single scattering WZ(gamma*) production could be observed at the
LHC.Comment: 14 pages, 8 figures. Added references, slight changes in the text
Cone-beam computed tomography accuracy in pulp chamber size evaluation: An ex vivo study
This study aimed to assess ex vivo the accuracy of cone-beam computed tomography (CBCT), as compared to operative microscope, for evaluating pulp chamber size. A total of forty teeth were extracted for periodontal reasons and a horizontal section was done at the most apical level of the cement-enamel junction. The pulp chamber was photographed using a digital camera connected to an optical microscope. Then, the tooth was scanned with CBCT and the horizontal slide matching the anatomical section of pulp chamber was digitally stored. The pulp chamber section area was measured through image analysis software. The two methods provided similar results, either for monoradicular (P = 0.14) or multiradicular teeth (P = 0.93). Correlation was statistically significant (P < 0.0001), being the coefficient r = 0.89 and 0.94 for monoradicular and multiradicular teeth, respectively. Conclusively, CBCT is suitable for pulp chamber morphology evaluation. However, it has limitations in detecting the anatomical variability of small branches in root canal system
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