This paper presents the electron and photon energy calibration achieved with the ATLAS detector using about 25 fb −1 of LHC proton-proton collision data taken at centre-of-mass energies of √ s = 7 and 8 TeV. The reconstruction of electron and photon energies is optimised using multivariate algorithms. The response of the calorimeter layers is equalised in data and simulation, and the longitudinal profile of the electromagnetic showers is exploited to estimate the passive material in front of the calorimeter and reoptimise the detector simulation. After all corrections, the Z resonance is used to set the absolute energy scale. For electrons from Z decays, the achieved calibration is typically accurate to 0.05 % in most of the detector acceptance, rising to 0.2 % in regions with large amounts of passive material. The remaining inaccuracy is less than 0.2-1 % for electrons with a transverse energy of 10 GeV, and is on average 0.3 % for photons. The detector resolution is determined with a relative inaccuracy of less than 10 % for electrons and photons up to 60 GeV transverse energy, rising to 40 % for transverse energies above 500 GeV.
The luminosity calibration for the ATLAS detector at the LHC during pp collisions at 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 . A luminosity uncertainty of is obtained for the 47 pb−1 of data delivered to ATLAS in 2010, and an uncertainty of is obtained for the 5.5 fb−1 delivered in 2011.
A new measurement of proton resonance scattering on 7 Be was performed up to the center-of-mass energy of 6.7 MeV using the low-energy RI beam facility CRIB (CNS Radioactive Ion Beam separator) at the Center for Nuclear Study of the University of Tokyo. The excitation function of 7 Be+p elastic scattering above 3.5 MeV was measured successfully for the first time, providing important information about the resonance structure of the 8 B nucleus. The resonances are related to the reaction rate of 7 Be(p,γ) 8 B, which is the key reaction in solar 8 B neutrino production. Evidence for the presence of two negative parity states is presented. One of them is a 2 − state observed as a broad s-wave resonance, the existence of which had been questionable. Its possible effects on the determination of the astrophysical S-factor of 7 Be(p,γ) 8 B at solar energy are discussed. The other state had not been observed in previous measurements, and its J π was determined as 1 − .
Six laser-resonant transitions have been detected in metastable antiprotonic helium atoms produced at the CERN Antiproton Decelerator. They include UV transitions from the last metastable states in the y n 2 ᐉ 2 1 0 and 1 cascades. Zero-density frequencies were obtained from measured pressure shifts with fractional precisions between 1.3 3 10 27 and 1.6 3 10 26 . By comparing these with QED calculations and the antiproton cyclotron frequency, we deduce that the antiproton and proton charges and masses agree to within 6 3 10 28 with a confidence level of 90%. Two transitions were in the previously unstudied UV region; two others were to final states with large Auger widths which provide particularly stringent tests of such calculations. These studies were done using the Antiproton Decelerator (AD) recently built at CERN.A variety of antiprotonic atoms exists for every element, but only p He 1 atoms have microsecond-scale lifetimes against annihilation. This extreme longevity (typically t 3 4 ms) arises because antiprotons in states with large principal ͑n ϳ 38͒ and angular momentum ͑ᐉ ϳ n͒ quantum numbers (see Fig. 1) cannot easily deexcite by Auger emission of the electron. With this electron in place, the atom is protected against collisional Stark mixing with low-ᐉ states, which overlap with the nucleus. It deexcites by radiating a series of optical-frequency photons, as the antiproton traverses a constant y n 2 ᐉ 2 1 cascade of these metastable states.Recent variational calculations [3-5] claim a precision of ,1 3 10 27 , for radiative transition frequencies involving states with small natural widths (G # 50 MHz). Relativistic [4] and one-loop QED corrections [5] are taken into account, as well as nuclear size and order-a 4 effects. Another calculation using the nonadiabatic coupledrearrangement-channel method [6] has also been made. The two calculations agree within #2 3 10 27 for transitions with natural widths of G , 50 MHz, while a larger difference is seen ͑.2 3 10 26 ͒ for states having large Auger widths (G $ 15 GHz).As in previous experiments [7,8], we measured the delayed annihilation time spectrum (the distribution of the number of annihilations, as a function of the time elapsed since p He 1 formation). We tuned pulsed laser beams to stimulate antiproton transitions from metastable states to levels that are not protected in the way described above, thereby revealing the resonance condition between the laser beam and the atom as a sharp peak in the annihilation rate (see Fig. 2). We have already measured one such transition frequency of ͑n, ᐉ͒ ͑39, 35͒ ! ͑38, 34͒ to an accuracy of 5 3 10 27 , which agreed with theoretical calculations at a level of 2 3 10 26 [9].The present experiments were done during the first months of operation at the AD, which provided a pulsed beam containing 2 3 10 7 antiprotons, with an energy of 5.3 MeV, a pulse length of 250 ns, and a repetition rate of 1 pulse per 2 min. Metastable p He 1 atoms were produced by stopping the antiproton pulses in a cryogenic helium
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