The construction and first proton beam tests of a demonstrator dedicated to the beam ballistic control in hadrontherapy cancer treatments are described. This cost-effective demonstrator, called large ...area pixelized detector, is a PET-like detector used for in-beam ballistic control. It was built to test the feasibility of monitoring in real time, during irradiation, the ion range in the patient through the measurement of the beam-induced β + activity distribution. Achieving this goal necessitates to overcome several challenges. One of them is the rejection of the beam-induced background. Another one is the definition of fast event selection and reconstruction techniques so that real time monitoring is possible. Strategies employed to tackle these problems are presented and tested with the 65 MeV Medicyc proton beam of the cancer treatment center in Nice, France. In particular, an original fast reconstruction technique is presented. First performances obtained during irradiation of polymethyl methacrylate targets are described.
We present the first results obtained with a detector, called Large Area Pixelized Detector (LAPD), dedicated to the study the ballistic control of the beam delivered to the patient by in-beam and ...real time detection of secondary particles, emitted during its irradiation in the context of hadrontherapy. These particles are 511keV γ from the annihilation of a positron issued from the β+ emitters induced in the patient tissues along the beam path. The LAPD basic concepts are similar to a conventional PET camera. The 511keV γ are detected and the reconstructed lines of response allow to measure the β+ activity distribution. Nevertheless, when trying to use γ from positron annihilation for the ballistic control in hadrontherapy, the large prompt γ background should be taken into account and properly rejected. First reconstruction results, obtained with a phantom filled with a high intensity FDG source at the cancer research centre of Clermont-Ferrand are shown. We also report results of measurements performed at the Heidelberg Ion-Beam Therapy Centre with one third of the detector, using proton and carbon ion beams.
Searches are performed for resonant and non-resonant Higgs boson pair production in the hh to gamma gamma b bbar final state using 20 fb-1 of proton--proton collisions at a center-of-mass energy of 8 ...TeV recorded with the ATLAS detector at the CERN Large Hadron Collider. A 95% confidence level upper limit on the cross section times branching ratio of non-resonant production is set at 2.2 pb, while the expected limit is 1.0 pb. The corresponding limit observed for a narrow resonance ranges between 0.8 and 3.5 pb as a function of its mass.
Measurements of fiducial and differential cross sections of Higgs boson production in the ${H \rightarrow ZZ ^{*}\rightarrow 4\ell}$ decay channel are presented. The cross sections are determined ...within a fiducial phase space and corrected for detection efficiency and resolution effects. They are based on 20.3 fb$^{-1}$ of $pp$ collision data, produced at $\sqrt{s}$=8 TeV centre-of-mass energy at the LHC and recorded by the ATLAS detector. The differential measurements are performed in bins of transverse momentum and rapidity of the four-lepton system, the invariant mass of the subleading lepton pair and the decay angle of the leading lepton pair with respect to the beam line in the four-lepton rest frame, as well as the number of jets and the transverse momentum of the leading jet. The measured cross sections are compared to selected theoretical calculations of the Standard Model expectations. No significant deviation from any of the tested predictions is found.
A search for excited states of the Bc+/- meson is performed using 4.9 inv. fb of 7 TeV and 19.2 inv. fb of 8 TeV pp collision data collected by the ATLAS experiment at the LHC. A new state is ...observed through its hadronic transition to the ground state, with the latter detected in the decay Bc+/- --> J/psi pi+/-. The state appears in the m(Bc+/- pi+ pi-) - m(Bc+/-) - 2m(pi+/-) mass difference distribution with a significance of 5.2 standard deviations. The mass of the observed state is 6842 +/- 4 +/- 5 MeV, where the first error is statistical and the second is systematic. The mass and decay of this state are consistent with expectations for the second S-wave state of the Bc, Bc(2S).
This letter presents a search for new resonances decaying to final states with a vector boson produced in association with a high transverse momentum photon, $V\gamma$, with $V= W(\rightarrow \ell ...\nu)$ or $Z(\rightarrow \ell^{+} \ell^{-})$, where $\ell = e$ or $\mu$. The measurements use 20.3 fb$^{-1}$ of proton-proton collision data at a center-of-mass energy of $\sqrt{s}=8$ TeV recorded with the ATLAS detector. No deviations from the Standard Model expectations are found, and production cross section limits are set at 95% confidence level. Masses of the hypothetical $a_{T}$ and $\omega_{T}$ states of a benchmark Low Scale Technicolor model are excluded in the ranges 275,960 GeV and $200,700\cup750,890$ GeV, respectively. Limits at 95% confidence level on the production cross section of a singlet scalar resonance decaying to $Z\gamma$ final states have also been obtained for masses below 1180 GeV.
This Letter presents a search for quantum black-hole production using 20.3 inverse fb of data collected with the ATLAS detector in pp collisions at the LHC at sqrt(s) = 8 TeV. The quantum black holes ...are assumed to decay into a lepton (electron or muon) and a jet. In either channel, no event with a lepton-jet invariant mass of 3.5 TeV or more is observed, consistent with the expected background. Limits are set on the product of cross sections and branching fractions for the lepton+jet final states of quantum black holes produced in a search region for invariant masses above 1 TeV. The combined 95% confidence level upper limit on this product for quantum black holes with threshold mass above 3.5 TeV is 0.18 fb. This limit constrains the threshold quantum black-hole mass to be above 5.3 TeV in the model considered.
The production of a W boson in association with a single charm quark is studied using 4.6 fb^-1 of pp collision data at sqrt(s)=7 TeV collected with the ATLAS detector at the Large Hadron Collider. ...In events in which a W boson decays to an electron or muon, the charm quark is tagged either by its semileptonic decay to a muon or by the presence of a charmed meson. The integrated and differential cross sections as a function of the pseudorapidity of the lepton from the W-boson decay are measured. Results are compared to the predictions of next-to-leading-order QCD calculations obtained from various parton distribution function parameterisations. The ratio of the strange-to-down sea-quark distributions is determined to be 0.96 +0.26 -0.30 at Q^2=1.9 GeV^2, which supports the hypothesis of an SU(3)-symmetric composition of the light-quark sea. Additionally, the cross-section ratio sigma(W^+ + bar{c})/sigma(W^- + c) is compared to the predictions obtained using parton distribution function parameterisations with different assumptions about the s-bar{s} quark asymmetry.
A measurement of the mass difference between top and anti-top quarks is presented. In a 4.7 fb-1 data sample of proton--proton collisions at sqrt(s) = 7 TeV recorded with the ATLAS detector at the ...LHC, events consistent with ttbar production and decay into a single charged lepton final state are reconstructed. For each event, the mass difference between the top and anti-top quark candidate is calculated. A two b-tag requirement is used in order to reduce the background contribution. A maximum likelihood fit to these per-event mass differences yields mt-mtbar = 0.67 +/- 0.61 (stat) +/- 0.41 (syst) GeV, consistent with CPT invariance.
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