Improved luminosity determination in pp collisions at √s =7 TeV using the ATLAS detector at the LHC
European Physical Journal C 73:8 (2013) 2-39
Abstract:
The luminosity calibration for the ATLAS detector at the LHC during pp collisions at √s = 7 TeV in 2010 and 2011 is presented. Evaluation of the luminosity scale is performed using several luminosity-sensitive detectors, and comparisons are made of the long-term stability and accuracy of this calibration applied to the pp collisions at √s = 7 TeV. A luminosity uncertainty of δL/L= ± 3.5 % is obtained for the 47 pb-1 of data delivered to ATLAS in 2010, and an uncertainty of δL/L= ± 1.8 % is obtained for the 5.5 fb-1 delivered in 2011.Measurement with the ATLAS detector of multi-particle azimuthal correlations in p + Pb collisions at √sNN = 5.02 TeV
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 725:1-3 (2013) 60-78
Abstract:
In order to study further the long-range correlations ("ridge") observed recently in p + Pb collisions at √sNN= 5.02 TeV, the second-order azimuthal anisotropy parameter of charged particles, v2, has been measured with the cumulant method using the ATLAS detector at the LHC. In a data sample corresponding to an integrated luminosity of approximately 1 μb-1, the parameter v2has been obtained using two- and four-particle cumulants over the pseudorapidity range |η|<2.5. The results are presented as a function of transverse momentum and the event activity, defined in terms of the transverse energy summed over 3.1 < η <4.9 in the direction of the Pb beam. They show features characteristic of collective anisotropic flow, similar to that observed in Pb + Pb collisions. A comparison is made to results obtained using two-particle correlation methods, and to predictions from hydrodynamic models of p +Pb collisions. Despite the small transverse spatial extent of the p + Pb collision system, the large magnitude of v2and its similarity to hydrodynamic predictions provide additional evidence for the importance of final-state effects in p + Pb reactions. © 2013 CERN. Published by Elsevier B.V.Evidence for a bottom baryon resonance Lambda_b* in CDF data
ArXiv 1308.176 (2013)
Abstract:
Using data from proton-antiproton collisions at Ecms=1.96 TeV recorded by the CDF II detector at the Fermilab Tevatron, evidence for the excited resonance state Lambda_b* is presented in its Lambda_b0 pi+ pi- decay, followed by the Lambda_b0 -->Lambda_c+ (-->proton K- pi+) pi- decays. The analysis is based on a data sample corresponding to an integrated luminosity of 9.6/fb collected by an online event selection based on charged-particle tracks displaced from the proton-antiproton interaction point. The significance of the observed signal is 3.5 Gaussian sigmas. The mass of the observed state is found to be 5919.22 +- 0.76 MeV in agreement with similar findings in proton-proton collision experiments.Measurement of the leptonic asymmetry in ttbar events produced in ppbar collisions at sqrt(s)=1.96 TeV
(2013)