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ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Escobar, C., et al. (2011). Luminosity determination in pp collisions at sqrt(s)=7 TeV using the ATLAS detector at the LHC. Eur. Phys. J. C, 71(4), 1630–37pp.
Abstract: Measurements of luminosity obtained using the ATLAS detector during early running of the Large Hadron Collider (LHC) at root s = 7 TeV are presented. The luminosity is independently determined using several detectors and multiple algorithms, each having different acceptances, systematic uncertainties and sensitivity to background. The ratios of the luminosities obtained from these methods are monitored as a function of time and of mu, the average number of inelastic interactions per bunch crossing. Residual time- and mu-dependence between the methods is less than 2% for 0 < μ< 2.5. Absolute luminosity calibrations, performed using beam separation scans, have a common systematic uncertainty of +/- 11%, dominated by the measurement of the LHC beam currents. After calibration, the luminosities obtained from the different methods differ by at most +/- 2%. The visible cross sections measured using the beam scans are compared to predictions obtained with the PYTHIA and PHOJET event generators and the ATLAS detector simulation.
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n_TOF Collaboration(Guerrero, C. et al), Giubrone, G., & Tain, J. L. (2011). Characterization of the New n_TOF Neutron Beam: Fluence, Profile and Resolution. J. Korean Phys. Soc., 59(2), 1624–1627.
Abstract: After a halt of four years, the nTOF spallation neutron facility at CERN has resumed operation in November 2008 with a new spallation target characterized by an improved safety and engineering design, resulting in a more robust overall performance and efficient cooling. The first measurement during the 2009 run has aimed at the full characterization of the neutron beam. Several detectors, such as calibrated fission chambers, the nTOF Silicon Monitor, a MicroMegas detector with (10)B and (235)U samples, as well as liquid and solid scintillators have been used in order to characterize the properties of the neutron fluence. The spatial profile of the beam has been studied with a specially designed “X-Y” MicroMegas which provided a 2D image of the beam as a function of neutron energy. Both properties have been compared with simulations performed. with the FLUKA code. The characterization of the resolution function is based on results from simulations which have been verified by the study of narrow capture resonances. of (56)Fe, which were measured as part of a new campaign of (n,gamma) measurements on Fe and Ni isotopes.
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n_TOF Collaboration(Chiaveri, E. et al), Giubrone, G., & Tain, J. L. (2011). Past, Present and Future of the n_TOF Facility at CERN. J. Korean Phys. Soc., 59(2), 1620–1623.
Abstract: The nTOF spallation neutron facility is operating at CERN since 2001. Neutrons are produced with a very wide energy range, from thermal up to 1 GeV and with a very high instantaneous flux (10(5)n/cm(2)/pulse at 200 m from target) thanks to the high intensity (7 x 10(12) protons/pulse) and low repetition rate of the Proton Synchrotron (PS) which is delivering protons to a lead spallation target. The experimental area is located at 200 m from the target, resulting in a very good energy resolution and beam quality thanks to the adoption of an optimal collimation system. At the end of 2008 the nTOF facility has resumed operation after a halt of 3 years due to technical issues. This contribution will outline the main physics results obtained by the facility since its inception in 1999, and show the importance of the measured nuclear data in the field of Nuclear Astrophysics and Nuclear Technology. Then it will present the future perspectives of the facility, aiming mainly in the direction of measuring highly radioactive samples, for which the facility has unique capabilities, with a lower background.
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Perez-Ramos, R. (2011). The Internal Structure Of Jets At Colliders: Light And Heavy Quark Inclusive Hadronic Distributions. Int. J. Mod. Phys. E, 20(7), 1616–1622.
Abstract: In this paper, we report our results on charged hadron multiplicities of heavy quark initiated jets produced in high energy collisions. After implementing the so-called dead cone effect in QCD evolution equations, we find that the average multiplicity decreases significantly as compared to the massless case. Finally, we discuss the transverse momentum distribution of light quark initiated jets and emphasize the comparison between our predictions and CDF data.
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ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Escobar, C., et al. (2011). Studies of the performance of the ATLAS detector using cosmic-ray muons. Eur. Phys. J. C, 71(3), 1593–36pp.
Abstract: Muons from cosmic-ray interactions in the atmosphere provide a high-statistics source of particles that can be used to study the performance and calibration of the ATLAS detector. Cosmic-ray muons can penetrate to the cavern and deposit energy in all detector subsystems. Such events have played an important role in the commissioning of the detector since the start of the installation phase in 2005 and were particularly important for understanding the detector performance in the time prior to the arrival of the first LHC beams. Global cosmic-ray runs were undertaken in both 2008 and 2009 and these data have been used through to the early phases of collision data-taking as a tool for calibration, alignment and detector monitoring. These large datasets have also been used for detector performance studies, including investigations that rely on the combined performance of different subsystems. This paper presents the results of performance studies related to combined tracking, lepton identification and the reconstruction of jets and missing transverse energy. Results are compared to expectations based on a cosmic-ray event generator and a full simulation of the detector response.
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