Context.
Peta-eV (PeV) astronomy emerged in 2021 with the discovery of ultra-high-energy gamma-ray sources associated with powerful natural particle accelerators known as PeVatrons. In order to ...determine the nature of their emission, namely whether it has a hadronic or leptonic origin, it is essential to characterise the physical parameters of the environment where it originates.
Aims.
We unambiguously confirm the association of molecular gas with the PeVatron candidate
LHAASO J2108+5157
using unprecedented high angular-resolution (17″)
12, 13
CO(
J
= 1 → 0) observations carried out with the Nobeyama 45m radio telescope.
Methods.
We characterised a molecular cloud in the vicinity of the PeVatron candidate
LHAASO J2108+5157
by determining its physical parameters from our
12, 13
CO(
J
= 1 → 0) line observations. We used an updated estimation of the distance to the cloud, which provided a more reliable result. The molecular emission was compared with excess gamma-ray images obtained with
Fermi
-LAT at energies above 2 GeV to search for spatial correlations and test a possible hadronic (
π
0
decay) origin for the gamma-ray emission.
Results.
We find that the morphology of the spatial distribution of the CO emission is strikingly similar to that of the
Fermi
-LAT excess gamma ray. By combining our observations with archival 21 cm HI line data, the nucleons (HI + H
2
) number density of the target molecular cloud is found to be 133.0 ± 45.0 cm
−3
, for the measured angular size of 0.55 ± 0.02° at a distance of 1.6 ± 0.1 kpc. The resulting total mass of the cloud is
M
(HI + H
2
) = 7.5±2.9×10
3
M
⊙
. Under a hadronic scenario, we obtain a total energy of protons of
W
p
= 4.3 ± 1.5 × 10
46
erg with a cutoff of 700±300 TeV, which reproduces the sub-PeV gamma-ray emission.
Conclusions.
We identified a molecular cloud in the vicinity of LHAASO J2107+5157 as the main target where cosmic rays from an unknown PeVatron produce the observed gamma-ray emission via
π
0
decay.
Andes Large-area PArticle detector for Cosmic-ray physics and Astronomy (ALPACA) is an international experiment that applies southern very-high-energy (VHE) gamma-ray astronomy to determine the ...origin of cosmic rays around the knee energy region (10
15
eV − 10
16
eV). The experiment consists of an air shower (AS) array with a surface of 83,000m
2
and an underground water Cherenkov muon detector (MD) array covering 5,400m
2
. The experimental site is at the Mt. Chacaltaya plateau in La Paz, Bolivia, with an altitude of 4,740m corresponding to 572g/cm
2
atmospheric thickness. As the prototype experiment of ALPACA, the ALPAQUITA experiment aims to begin data acquisition in late 2021. The ALPAQUITA array consists of a smaller AS array (18,450m
2
) and underground MD (900m
2
), which are now under construction. ALPAQUITA’s sensitivity to gamma-ray sources is evaluated with Monte Carlo simulations. The simulation finds that five gamma-ray sources observed by H.E.S.S. and HAWC experiments will be detected by ALPAQUITA beyond 10TeV and ne out of these five - HESS J1702-420A - above 300 TeV in one calendar year observation. The latter finding means that scientific discussions can be made on the emission mechanism of gamma rays beyond 100TeV from southern sources on the basis of the observational results of this prototype experiment.
Observation techniques of high-energy gamma rays using air showers have remarkably progressed via the Tibet AS
γ
, HAWC, and LHAASO experiments. These observations have significantly contributed to ...gamma-ray astronomy in the northern sky’s sub-PeV region. Moreover, in the southern sky, the ALPACA experiment is underway at 4,740 m altitude on the Chacaltaya plateau in Bolivia. This experiment estimates the gamma-ray flux from the difference between the number of on-source and off-source events by real data, utilizing the gamma-ray detection efficiency calculated through Monte Carlo simulations, which in turn depends on the hadronic interaction models. Even though the number of cosmic-ray background events can be experimentally estimated, this model dependence affects the estimation of gamma-ray detection efficiency. However, previous reports have assumed that the model dependence is negligible and have not included it in the error of gamma-ray flux estimation. Using ALPAQUITA, the prototype experiment of ALPACA, we quantitatively evaluated the model dependence on hadronic interaction models for the first time. We evaluate the model dependence on hadronic interactions as less than 3.6 % in the typical gamma-ray flux estimation performed by ALPAQUITA; this is negligible compared with other uncertainties such as energy scale uncertainty in the energy range from 6 to 300 TeV, which is dominated by the Monte Carlo statistics. This upper limit of 3.6 % model dependence is expected to apply to ALPACA.
Some aspects on four quarks recombination Sánchez, G. Toledo; Juárez, I. A. Toledano
Journal of physics. Conference series,
10/2016, Letnik:
761, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We have performed a 3-D Monte Carlo simulation of a system composed of two identical light quarks (qq) and two identical antiquarks (QQ) and determined whether it is energetically more favorable to ...form a tetraquark or two mesons, as a function of the interparticle separation distance which, for a fixed number of particles, can be identified as a particle density. In this proceedings, we highlight the main results and elaborate on the implications in properties like the correlation function for two-mesons and characterize the isolated diquark correlation function. We analize the four-body potential evolution and exhibit its linear behavior as a function of the invariant distance. We track the dynamical flipping among configurations to determine the recombination probability, exhibiting the importance of the tetraquark state.
We study the formation of a tetraquark state from the presence of two initially uncorrelated states, using a Monte Carlo simulation based on a QCD-inspired model (String-Flip), incorporating an ...effective many-body potential between particles. In a first step we study a two body system linked by a linear potential and elaborate on how to built a variational wave function that can mimic the exact result and from general requirements we propose an anzats for a four body system that can be bound either as two mesons or as a tetraquark. We present preliminary results of the implementation of these ideas and the procedure to evaluate the 4-body potential.
We perform a variational Monte Carlo simulation of a system consisting of two quarks and two antiquarks. Using a dynamical model of the strong interaction (string-flip model) we explore the formation ...of mesons and/or a tetraquark for a set different different density conditions. We characterize the single properties of these states and the modifications upon the mixing. The competition among the different configurations and its implications on several observables are exhibited.
We consider a system composed of two identical light quarks (\(qq\)) and two identical antiquarks (\(\bar Q\bar Q\)) that can be linked either as two mesons or as a tetraquark, incorporating quantum ...correlations between identical particles and an effective many-body potential between particles. We perform a 3-D Monte Carlo simulation of the system, considering the configurations allowed to form: i) Only two mesons, ii) Only tetraquark and iii) two mesons and tetraquark . We characterize each case and determine whether it is energetically more favorable to form a tetraquark or two mesons, as a function of the interparticle separation distance which, for a fixed number of particles, can be identified as a particle density. We determine how the two mesons, which dominate the low density regime, mixes with a tetraquark state as the density increases. Properties like the mean square radius and the two-particle correlation function are found to reflect such transition, and we provide a parameterization of the diquark correlation function in the isolated case. We track the dynamical flipping among configurations to determine the recombination probability, exhibiting the importance of the tetraquark state. We analize the four-body potential evolution and show that its linear behavior is preserved, although the slope can reflect the presence of a mixed state. Results are shown for several light-quarks to heavy-antiquarks mass ratios whenever they are found to be relevant.
We have performed a 3-D Monte Carlo simulation of a system composed of two identical light quarks (\(qq\)) and two identical antiquarks (\(\bar Q\bar Q\)) and determined whether it is energetically ...more favorable to form a tetraquark or two mesons, as a function of the interparticle separation distance which, for a fixed number of particles, can be identified as a particle density. In this proceedings, we highlight the main results and elaborate on the implications in properties like the correlation function for two-mesons and characterize the isolated diquark correlation function. We analize the four-body potential evolution and exhibit its linear behavior as a function of the invariant distance. We track the dynamical flipping among configurations to determine the recombination probability, exhibiting the importance of the tetraquark state.
Andes Large-area PArticle detector for Cosmic-ray physics and Astronomy (ALPACA) is an international experiment that applies southern very-high-energy (VHE) gamma-ray astronomy to determine the ...origin of cosmic rays around the knee energy region (\(10^{15}\, {\rm eV} - 10^{16}\, {\rm eV}\)). The experiment consists of an air shower (AS) array with a surface of \(83, 000\, {\rm m}^2\) and an underground water Cherenkov muon detector (MD) array covering \(5, 400\, {\rm m}^2\). The experimental site is at the Mt. Chacaltaya plateau in La Paz, Bolivia, with an altitude of \(4, 740\, {\rm m}\) corresponding to \(572\, {\rm g}/{\rm cm}^2\) atmospheric thickness. As the prototype experiment of ALPACA, the ALPAQUITA experiment aims to begin data acquisition in late 2021. The ALPAQUITA array consists of a smaller AS array (\(18, 450\, {\rm m}^2\)) and underground MD (\(900\, {\rm m}^2\)), which are now under construction. ALPAQUITA's sensitivity to gamma-ray sources is evaluated with Monte Carlo simulations. The simulation finds that five gamma-ray sources observed by H.E.S.S. and HAWC experiments will be detected by ALPAQUITA beyond 10 TeV and one out of these five - HESS J1702-420A - above 300 TeV in one calendar year observation. The latter finding means that scientific discussions can be made on the emission mechanism of gamma rays beyond 100 TeV from southern sources on the basis of the observational results of this prototype experiment.
PDF
