Banco didáctico para ensayo de torsión en barras

El presente trabajo se basó en la construcción de un banco didáctico para realizar pruebas de torsión estática de barras de diferente material y sección transversal; correspondientes a probetas macizas cuadradas y circulares de latón y aluminio; y una probeta tubular de aluminio, las dimensiones de las probetas se establecieron en el rango de medidas de 650mm de longitud y 40 mm2 de área, la condición de diseño era probar materiales de aproximadamente 200Mpa de esfuerzo ultimo a cortante teniendo en cuenta posibles pruebas de torsión a la rotura. Inicialmente realizamos una búsqueda bibliográfica acerca de las diferentes máquinas de torsión de barras que se han desarrollado con el paso del tiempo hasta la actualidad, así mismo analizamos su funcionamiento y el procedimiento que se llevaba a cabo para realizar pruebas de torsión de barras, esto para ampliar los conocimientos sobre el tema de interés. De la búsqueda bibliográfica se seleccionaron 4 alternativas de bancos de pruebas de torsión, de las cuales se analizaron sus ventajas y desventajas teniendo en cuenta costos, construcción y ambiente, posteriormente elegimos como alternativa de solución y referencia para construcción del banco, el modelo comercial SE110.29 ya que este modelo se asemejaba a los requerimientos que se habían planteado inicialmente

Banco didáctico para ensayo de torsión en barras

El presente trabajo se basó en la construcción de un banco didáctico para realizar pruebas de torsión estática de barras de diferente material y sección transversal; correspondientes a probetas macizas cuadradas y circulares de latón y aluminio; y una probeta tubular de aluminio, las dimensiones de las probetas se establecieron en el rango de medidas de 650mm de longitud y 40 mm2 de área, la condición de diseño era probar materiales de aproximadamente 200Mpa de esfuerzo ultimo a cortante teniendo en cuenta posibles pruebas de torsión a la rotura. Inicialmente realizamos una búsqueda bibliográfica acerca de las diferentes máquinas de torsión de barras que se han desarrollado con el paso del tiempo hasta la actualidad, así mismo analizamos su funcionamiento y el procedimiento que se llevaba a cabo para realizar pruebas de torsión de barras, esto para ampliar los conocimientos sobre el tema de interés. De la búsqueda bibliográfica se seleccionaron 4 alternativas de bancos de pruebas de torsión, de las cuales se analizaron sus ventajas y desventajas teniendo en cuenta costos, construcción y ambiente, posteriormente elegimos como alternativa de solución y referencia para construcción del banco, el modelo comercial SE110.29 ya que este modelo se asemejaba a los requerimientos que se habían planteado inicialmente

Multiplicity dependence of light (anti-)nuclei production in p–Pb collisions at sNN=5.02 TeV

The measurement of the deuteron and anti-deuteron production in the rapidity range −1 < y < 0 as a function of transverse momentum and event multiplicity in p–Pb collisions at √sNN = 5.02 TeV is presented. (Anti-)deuterons are identified via their specific energy loss dE/dx and via their time-of- flight. Their production in p–Pb collisions is compared to pp and Pb–Pb collisions and is discussed within the context of thermal and coalescence models. The ratio of integrated yields of deuterons to protons (d/p) shows a significant increase as a function of the charged-particle multiplicity of the event starting from values similar to those observed in pp collisions at low multiplicities and approaching those observed in Pb–Pb collisions at high multiplicities. The mean transverse particle momenta are extracted from the deuteron spectra and the values are similar to those obtained for p and particles. Thus, deuteron spectra do not follow mass ordering. This behaviour is in contrast to the trend observed for non-composite particles in p–Pb collisions. In addition, the production of the rare 3He and 3He nuclei has been studied. The spectrum corresponding to all non-single diffractive p-Pb collisions is obtained in the rapidity window −1 < y < 0 and the pT-integrated yield dN/dy is extracted. It is found that the yields of protons, deuterons, and 3He, normalised by the spin degeneracy factor, follow an exponential decrease with mass number

Real-time data processing in the ALICE High Level Trigger at the LHC

International audienceAt the Large Hadron Collider at CERN in Geneva, Switzerland, atomic nuclei are collided at ultra-relativistic energies. Many final-state particles are produced in each collision and their properties are measured by the ALICE detector. The detector signals induced by the produced particles are digitized leading to data rates that are in excess of 48 GB/s. The ALICE High Level Trigger (HLT) system pioneered the use of FPGA- and GPU-based algorithms to reconstruct charged-particle trajectories and reduce the data size in real time. The results of the reconstruction of the collision events, available online, are used for high level data quality and detector-performance monitoring and real-time time-dependent detector calibration. The online data compression techniques developed and used in the ALICE HLT have more than quadrupled the amount of data that can be stored for offline event processing

Λ3H^3_\Lambda\mathrm{H} and Λˉ3H‾^3_{\bar{\Lambda}}\mathrm{\overline{H}} lifetime measurement in Pb-Pb collisions at sNN=\sqrt{s_{\mathrm{NN}}} = 5.02 TeV via two-body decay

International audienceAn improved value for the lifetime of the (anti-)hypertriton has been obtained using the data sample of Pb–Pb collisions at sNN=5.02 TeV collected by the ALICE experiment at the LHC. The (anti-)hypertriton has been reconstructed via its charged two-body mesonic decay channel and the lifetime has been determined from an exponential fit to the d N /d( ct ) spectrum. The measured value, τ=242−38+34 (stat.) ± 17 (syst.) ps, is compatible with representative theoretical predictions, thus contributing to the solution of the longstanding hypertriton lifetime puzzle

Exploration of jet substructure using iterative declustering in pp and Pb–Pb collisions at LHC energies

The ALICE collaboration at the CERN LHC reports novel measurements of jet substructure in pp collisions at $\sqrt{s}$= 7 TeV and central Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 2.76 TeV. Jet substructure of track-based jets is explored via iterative declustering and grooming techniques. We present the measurement of the momentum sharing of two-prong substructure exposed via grooming, the $z_{\rm{g}}$, and its dependence on the opening angle, in both pp and Pb-Pb collisions. We also present the first measurement of the distribution of the number of branches obtained in the iterative declustering of the jet, which is interpreted as the number of its hard splittings. In Pb-Pb collisions, we observe a suppression of symmetric splittings at large opening angles and an enhancement of splittings at small opening angles relative to pp collisions, with no significant modification of the number of splittings. The results are compared to predictions from various Monte Carlo event generators to test the role of important concepts in the evolution of the jet in the medium such as color coherence

Measurement of charged jet cross section in pp collisions at √s = 5.02 TeV

The cross section of jets reconstructed from charged particles is measured in the transverse momentum range of 5<pT<100 GeV/c in pp collisions at the center-of-mass energy of s√=5.02 TeV with the ALICE detector. The jets are reconstructed using the anti-kT algorithm with resolution parameters R=0.2, 0.3, 0.4, and 0.6 in the pseudorapidity range |η|<0.9−R. The charged jet cross sections are compared with the leading order (LO) and to next-to-leading order (NLO) perturbative Quantum ChromoDynamics (pQCD) calculations. It was found that the NLO calculations agree better with the measurements. The cross section ratios for different resolution parameters were also measured. These ratios increase from low pT to high pT and saturate at high pT, indicating that jet collimation is larger at high pT than at low pT. These results provide a precision test of pQCD predictions and serve as a baseline for the measurement in Pb−Pb collisions at the same energy to quantify the effects of the hot and dense medium created in heavy-ion collisions at the LHC

Global polarization of ΛΛˉ\Lambda \bar \Lambda hyperons in Pb-Pb collisions at sNN\sqrt {s_{NN}} = 2.76 and 5.02 TeV

International audienceThe global polarization of the $\Lambda$ and $\overline\Lambda$ hyperons is measured for Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 2.76 and 5.02 TeV recorded with the ALICE at the LHC. The results are reported differentially as a function of collision centrality and hyperon's transverse momentum ($p_{\rm{T}}$) for the range of centrality 5-50%, $0.5 < p_{\rm{T}} <5$ GeV/$c$, and rapidity $|y|<0.5$. The hyperon global polarization averaged for Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 2.76 and 5.02 TeV is found to be consistent with zero, $\langle P_{\rm{H}}\rangle$ (%) $\approx$ 0.01 $\pm$ 0.06 (stat.) $\pm$ 0.03 (syst.) in the collision centrality range 15-50%, where the largest signal is expected. The results are compatible with expectations based on an extrapolation from measurements at lower collision energies at RHIC, hydrodynamical model calculations, and empirical estimates based on collision energy dependence of directed flow, all of which predict the global polarization values at LHC energies of the order of 0.01%

Multiplicity dependence of (anti-)deuteron production in pp collisions at s\sqrt{s} = 7 TeV

In this letter, the production of deuterons and anti-deuterons in pp collisions at $\sqrt{s}$ = 7 TeV is studied as a function of the charged-particle multiplicity density at mid-rapidity with the ALICE detector at the LHC. Production yields are measured at mid-rapidity in five multiplicity classes and as a function of the deuteron transverse momentum ($p_{\rm T}$). The measurements are discussed in the context of hadron–coalescence models. The coalescence parameter B$_2$ , extracted from the measured spectra of (anti-)deuterons and primary (anti-)protons, exhibits no significant $p_{\rm T}$-dependence for $p_{\rm T}$ < 3 GeV/c , in agreement with the expectations of a simple coalescence picture. At fixed transverse momentum per nucleon, the B$_2$ parameter is found to decrease smoothly from low multiplicity pp to Pb–Pb collisions, in qualitative agreement with more elaborate coalescence models. The measured mean transverse momentum of (anti-)deuterons in pp is not reproduced by the Blast-Wave model calculations that simultaneously describe pion, kaon and proton spectra, in contrast to central Pb–Pb collisions. The ratio between the $p_{\rm T}$-integrated yield of deuterons to protons, d/p, is found to increase with the charged-particle multiplicity, as observed in inelastic pp collisions at different centre-of-mass energies. The d/p ratios are reported in a wide range, from the lowest to the highest multiplicity values measured in pp collisions at the LHC

Coherent J/ψ\psi photoproduction at forward rapidity in ultra-peripheral Pb-Pb collisions at sNN=5.02\sqrt{s_{\rm{NN}}}=5.02 TeV

The ALICE collaboration performed the first rapidity-differential measurement of coherent J/ψ photoproduction in ultra-peripheral Pb–Pb collisions at a center-of-mass energy $\sqrt{s_{\rm NN}}$ = 5.02 TeV. The J/ψ is detected via its dimuon decay in the forward rapidity region (−4.0 < y <−2.5 ) for events where the hadronic activity is required to be minimal. The analysis is based on an event sample corresponding to an integrated luminosity of about 750 $\mu$b$^{-1}$ . The cross section for coherent J/ψ production is presented in six rapidity bins. The results are compared with theoretical models for coherent J/ψ photoproduction. These comparisons indicate that gluon shadowing effects play a role in the photoproduction process. The ratio of ψ′ to J/ψ coherent photoproduction cross sections was measured and found to be consistent with that measured for photoproduction off protons