Multi-object tracking can be achieved by detecting objects in individual frames and then linking detections across frames. Such an approach can be made very robust to the occasional detection ...failure: If an object is not detected in a frame but is in previous and following ones, a correct trajectory will nevertheless be produced. By contrast, a false-positive detection in a few frames will be ignored. However, when dealing with a multiple target problem, the linking step results in a difficult optimization problem in the space of all possible families of trajectories. This is usually dealt with by sampling or greedy search based on variants of Dynamic Programming which can easily miss the global optimum. In this paper, we show that reformulating that step as a constrained flow optimization results in a convex problem. We take advantage of its particular structure to solve it using the k-shortest paths algorithm, which is very fast. This new approach is far simpler formally and algorithmically than existing techniques and lets us demonstrate excellent performance in two very different contexts.
We outline the many physics opportunities offered by a multi-purpose fixed-target experiment using the proton and lead–ion beams of the LHC extracted by a bent crystal. In a proton run with the LHC ...7 TeV beam, one can analyze pp, pd and pA collisions at center-of-mass energy sNN≃115GeV and even higher using the Fermi motion of the nucleons in a nuclear target. In a lead run with a 2.76 TeV-per-nucleon beam, sNN is as high as 72 GeV. Bent crystals can be used to extract about 5×108 protons/s; the integrated luminosity over a year reaches 0.5 fb−1 on a typical 1 cm long target without nuclear species limitation. We emphasize that such an extraction mode does not alter the performance of the collider experiments at the LHC. By instrumenting the target-rapidity region, gluon and heavy-quark distributions of the proton and the neutron can be accessed at large x and even at x larger than unity in the nuclear case. Single diffractive physics and, for the first time, the large negative-xF domain can be accessed. The nuclear target-species versatility provides a unique opportunity to study nuclear matter versus the features of the hot and dense matter formed in heavy-ion collisions, including the formation of the quark–gluon plasma, which can be studied in PbA collisions over the full range of target-rapidity domain with a large variety of nuclei. The polarization of hydrogen and nuclear targets allows an ambitious spin program, including measurements of the QCD lensing effects which underlie the Sivers single-spin asymmetry, the study of transversity distributions and possibly of polarized parton distributions. We also emphasize the potential offered by pA ultra-peripheral collisions where the nucleus target A is used as a coherent photon source, mimicking photoproduction processes in ep collisions. Finally, we note that W and Z bosons can be produced and detected in a fixed-target experiment and in their threshold domain for the first time, providing new ways to probe the partonic content of the proton and the nucleus.
Given two to four synchronized video streams taken at eye level and from different angles, we show that we can effectively combine a generative model with dynamic programming to accurately follow up ...to six individuals across thousands of frames in spite of significant occlusions and lighting changes. In addition, we also derive metrically accurate trajectories for each of them. Our contribution is twofold. First, we demonstrate that our generative model can effectively handle occlusions in each time frame independently, even when the only data available comes from the output of a simple background subtraction algorithm and when the number of individuals is unknown a priori. Second, we show that multiperson tracking can be reliably achieved by processing individual trajectories separately over long sequences, provided that a reasonable heuristic is used to rank these individuals and that we avoid confusing them with one another.
We propose a parametrization of the nuclear absorption mechanism relying on the proper time spent by
c
c
¯
bound states travelling in nuclear matter. Our approach could lead to the extraction of ...charmonium formation time. It is based on a large amount of proton-nucleus data, from nucleon-nucleon center-of-mass energies
s
NN
=
27
Ge
V
to
s
NN
=
5.02
Te
V
, collected in the past 30 years, and for which the main effect on charmonium production must be its absorption by the nuclear matter it crosses.
We outline the many quarkonium-physics opportunities offered by a multi-purpose fixed-target experiment using the
p
and Pb Large Hadron Collider (LHC) beams extracted by a bent crystal. This provides ...an integrated luminosity of 0.5 fb
−1
per year on a typical 1 cm-long target. Such an extraction mode does not alter the performance of the collider experiments at the LHC. With such a high luminosity, one can analyse quarkonium production in great details in
pp
,
pd
and
pA
collisions at
GeV and at
GeV in Pb
A
collisions. In a typical
pp
(
pA
) run, the obtained quarkonium yields per unit of rapidity are 2–3 orders of magnitude larger than those expected at RHIC and about, respectively, 10(70) times larger than for ALICE. In Pb
A
, they are comparable. By instrumenting the target-rapidity region, the large negative-
x
F
domain can be accessed for the first time, greatly extending previous measurements by Hera-B and E866. Such analyses should help resolving the quarkonium-production controversies and clear the way for gluon PDF extraction via quarkonium studies. The nuclear target-species versatility provides a unique opportunity to study nuclear matter and the features of the hot and dense matter formed in Pb
A
collisions. A polarised proton target allows the study of transverse-spin asymmetries in
J
/
ψ
and
production, providing access to the gluon and charm Sivers functions.
Being used in the fixed-target mode, the multi-TeV LHC proton and lead beams allow for studies of heavy-flavour hadroproduction with unprecedented precision at backward rapidities, far negative ...Feynman-x, using conventional detection techniques. At the nominal LHC energies, quarkonia can be studied in detail in p+p, p+d, and p+A collisions at sNN≃115 GeV and in Pb + p and Pb + A collisions at sNN≃72 GeV with luminosities roughly equivalent to that of the collider mode that is up to 20 fb−1 yr−1 in p+p and p+d collisions, up to 0.6 fb−1 yr−1 in p+A collisions, and up to 10 nb−1 yr−1 in Pb + A collisions. In this paper, we assess the feasibility of such studies by performing fast simulations using the performance of a LHCb-like detector.
Cold nuclear matter effects on J/ψ production in proton–nucleus and nucleus–nucleus collisions are evaluated taking into account the specific J/ψ-production kinematics at the partonic level, the ...shadowing of the initial parton distributions and the absorption in the nuclear matter. We consider two different parton processes for the cc¯-pair production: one with collinear gluons and a recoiling gluon in the final state and the other with initial gluons carrying intrinsic transverse momentum. Our results are compared to RHIC observables. The smaller values of the nuclear modification factor RAA in the forward rapidity region (with respect to the mid rapidity region) are partially explained, therefore potentially reducing the need for recombination effects.
We study the effect of nuclear matter in
ϒ
production in
d
Au collisions at RHIC and
p
Pb collisions at the LHC. We find that the nuclear modification factor,
, measured at RHIC is not satisfactorily ...reproduced by the conventional effects used in the literature, namely the modification of the gluon distribution in bound nucleons and an—effective—survival probability for a bound state to escape the nucleus. In particular, we argue that this probability should be close to 1 as opposed to the
J
/
ψ
case. We note that, at backward rapidities, the unexpected suppression of
observed by PHENIX hints at the presence of a gluon EMC effect, analogous to the quark EMC effect—but likely stronger. Further nuclear matter effects, such as saturation and fractional energy loss, are discussed, but none of them fit in a more global picture of quarkonium production. Predictions for
ϒ
(
nS
) for the forthcoming
p
Pb run at 5 TeV at the LHC are also presented.
We report on the opportunities for spin physics and Transverse-Momentum Dependent distribution (TMD) studies at a future multi-purpose fixed-target experiment using the proton or lead ion LHC beams ...extracted by a bent crystal. The LHC multi-TeV beams allow for the most energetic fixed-target experiments ever performed, opening new domains of particle and nuclear physics and complementing that of collider physics, in particular that of RHIC and the EIC projects. The luminosity achievable with AFTER@LHC using typical targets would surpass that of RHIC by more that 3 orders of magnitude in a similar energy region. In unpolarised proton-proton collisions, AFTER@LHC allows for measurements of TMDs such as the Boer-Mulders quark distributions, the distribution of unpolarised and linearly polarised gluons in unpolarised protons. Using the polarisation of hydrogen and nuclear targets, one can measure transverse single-spin asymmetries of quark and gluon sensitive probes, such as, respectively, Drell-Yan pair and quarkonium production. The fixed-target mode has the advantage to allow for measurements in the target-rapidity region, namely at large x↑ in the polarised nucleon. Overall, this allows for an ambitious spin program which we outline here.
Transverse-momentum dependence of J/ψ shadowing effects Ferreiro, E. G.; Fleuret, F.; Rakotozafindrabe, A.
European physical journal. C, Particles and fields (Print),
06/2009, Volume:
61, Issue:
4
Journal Article, Conference Proceeding
Peer reviewed
Open access
We present a new approach to estimate the effect of gluon shadowing in nucleus + nucleus collisions and its consequences on the
J
/
ψ
production yield. Using kinematical information available from ...the measured
J
/
ψ
production in proton + proton collisions at
GeV, we build a Glauber Monte Carlo code which takes into account shadowing in two alternative ways: multiple-scattering corrections or
Q
2
evolution of parton densities. We exploit the dependence of these different parameterizations to the
J
/
ψ
transverse momentum and we give the first predictions on the resulting
p
T
dependence of the nuclear modification factor in deuteron + gold collisions at the same energy.
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