We report the observation of Higgs boson decays to WW Ã based on an excess over background of 6.1 standard deviations in the dilepton final state, where the Standard Model expectation is 5.8 standard deviations. Evidence for the vector-boson fusion (VBF) production process is obtained with a significance of 3.2 standard deviations. The results are obtained from a data sample corresponding to an integrated luminosity of 25 fb −1 from ffiffi ffi s p ¼ 7 and 8 TeV pp collisions recorded by the ATLAS detector at the LHC. For a Higgs boson mass of 125.36 GeV, the ratio of the measured value to the expected value of the total production cross section times branching fraction is 1.09 þ0.

The Versatile Link is a bi-directional digital optical data link operating at rates up to 4.8 Gbit/s and featuring radiation-resistant low-power and low-mass front-end components. The system is being developed in multimode or singlemode versions operating at 850 nm or 1310 nm wavelength respectively. It has serial data interfaces and is protocol-agnostic, but is targeted to operate in tandem with the GigaBit Transceiver (GBT) serializer/deserializer chip being designed at CERN. This paper gives an overview of the project status three and a half years after its launch. It describes the challenges encountered and highlights the solutions proposed at the system as well as the component level. It concludes with a positive feasibility assesment and an outlook for future project development directions.

A proton pencil beam is associated with a surrounding low-dose envelope, originating from nuclear interactions. It is important for treatment planning systems to accurately model this envelope when performing dose calculations for pencil beam scanning treatments, and Monte Carlo (MC) codes are commonly used for this purpose. This work aims to validate the nuclear models employed by the Geant4 MC code, by comparing the simulated absolute dose distribution to a recent experiment of a 177 MeV proton pencil beam stopping in water. Striking agreement is observed over five orders of magnitude, with both the shape and normalisation well modelled. The normalisations of two depth dose curves are lower than experiment, though this could be explained by an experimental positioning error. The Geant4 neutron production model is also verified in the distal region. The entrance dose is poorly modelled, suggesting an unaccounted upstream source of low-energy protons. Recommendations are given for a follow-up experiment which could resolve these issues.

The radiation induced attenuation of optical fibres below −20°C exposed to lifetime HL-LHC doses at a dose rate of 700 Gy(Si)/hrTo cite this article: D Hall et al 2012 JINST 7 C01047 View the article online for updates and enhancements. Related contentThe radiation hardness of specific multimode and single-mode optical fibres at -25°C beyond a full SLHC dose to a dose of 500 kGy(Si) B T Huffman, C Issever, N C Ryder et al. -The radiation tolerance of MTP and LC optical fibre connectors to 500 kGy(Si) of gamma radiation D C Hall, P Hamilton, B T Huffman et al. ABSTRACT: The LHC luminosity upgrade, known as the HL-LHC, will require high-speed optical links to read out data from the detectors. Such links must be capable of withstanding high doses whilst being kept at low temperatures. Two single-mode and two multi-mode fibres were exposed to 200 kGy(Si) at a dose rate of about 700 Gy(Si)/hr, whilst being kept at about -25 • C. The radiation induced attenuation of these fibres was measured as the fibres accumulated dose. A conservative estimate has been made of the total attenuation expected for a realistic fibre route through the ATLAS detector after a lifetime dose at the HL-LHC. With safety factors, the maximum dose extrapolated to was 375 kGy(Si). All four fibres performed extremely well and were qualified for use at HL-LHC detectors.

Whilst Monte Carlo (MC) simulations of proton energy deposition have been well-validated at the macroscopic level, their microscopic validation remains lacking. Equally, no gold-standard yet exists for experimental metrology of individual proton tracks. In this work we compare the distributions of stochastic proton interactions simulated using the TOPAS-nBio MC platform against confocal microscope data for AlO:C,Mg fluorescent nuclear track detectors (FNTDs). We irradiated [Formula: see text] mm FNTD chips inside a water phantom, positioned at seven positions along a pristine proton Bragg peak with a range in water of 12 cm. MC simulations were implemented in two stages: (1) using TOPAS to model the beam properties within a water phantom and (2) using TOPAS-nBio with Geant4-DNA physics to score particle interactions through a water surrogate of AlO:C,Mg. The measured median track integrated brightness (IB) was observed to be strongly correlated to both (i) voxelized track-averaged linear energy transfer (LET) and (ii) frequency mean microdosimetric lineal energy, [Formula: see text], both simulated in pure water. Histograms of FNTD track IB were compared against TOPAS-nBio histograms of the number of terminal electrons per proton, scored in water with mass-density scaled to mimic AlO:C,Mg. Trends between exposure depths observed in TOPAS-nBio simulations were experimentally replicated in the study of FNTD track IB. Our results represent an important first step towards the experimental validation of MC simulations on the sub-cellular scale and suggest that FNTDs can enable experimental study of the microdosimetric properties of individual proton tracks.

Purpose To predict the organ-at-risk (OAR) dose levels achievable with proton beam therapy (PBT), solely based upon the geometric arrangement of the target volume in relation to the OARs. Comparison to an alternative therapy yields a prediction of the patient-specific benefits offered by PBT. This could enable a physician at a hospital without proton capabilities to make a better-informed referral decision, or aid patient selection in model-based clinical trials. Methods and Materials Skull-base tumors were chosen to test the method, owing to their geometric complexity and multitude of nearby OARs. By exploiting correlations between dose and distance-to-target in existing PBT plans, models were independently trained for six types of OAR: brainstem, cochlea, optic chiasm, optic nerve, parotid gland and spinal cord. Once trained, the models could estimate the feasible dose-volume histogram and generalized equivalent uniform dose (gEUD) for OAR structures of new patients. Models were trained using 20 patients and validated with a further 21 patients. Validation was achieved by comparing the predicted gEUD to that of the actual PBT plan. Results The predicted and planned gEUD were in good agreement: considering all OARs, the prediction error was +1.4 ± 5.1 Gy (mean ± SD) and Pearson’s correlation coefficient was 93%. When compared to an IMRT plan, the model could classify whether an OAR structure would experience a gain with a sensitivity of 93% (95% CI: 87% – 97%) and a specificity of 63% (95% CI: 38% – 84%). Conclusions We trained and validated models that quickly and accurately predict the patient-specific benefits of PBT for skull-base tumors. Similar models could be developed for other tumor sites. Such models are useful when an estimation of the feasible benefits of PBT is desired, but the experience and/or resources required for treatment planning are unavailable.

No abstract

The LHC luminosity upgrade, known as the High Luminosity LHC (HL-LHC), will require high-speed optical links to read out data from the detectors. The optical fibre connectors contained within such a link must have a small form factor and be capable of operating in the harsh radiation environment at the HL-LHC. MTP ribbon fibre connectors and LC single fibre connectors were exposed to 500 kGy(Si) of gamma radiation and their radiation hardness was investigated. Neither type of connector exhibited evidence for any significant radiation damage and both connectors could be qualified for use at HL-LHC detectors.