Evaluation of novel KEK/HPK n-in-p pixel sensors for ATLAS upgrade with testbeam
A new type of n-in-p planar pixel sensors have been developed at KEK/HPK in order to cope with the maximum particle fluence of 1–3×1016 1 MeV equivalent neutrons per square centimeter ( n eq / cm 2 ) in the upcoming LHC upgrades. Four n-in-p devices were connected by bump-bonding to the new ATLAS Pixel front-end chip (FE-I4A) and characterized before and after the irradiation to 2×1015 n eq / cm 2 . These planar sensors are 150 μ m thick, using biasing structures made out of polysilicon or punch-through dot and isolation structures of common or individual p-stop. Results of measurements with radioactive 90Sr source and with a 120 GeV/c momentum pion beam at the CERN Super Proton Synchrotron (SPS) are presented. The common p-stop isolation structure shows a better performance than the individual p-stop design, after the irradiation. The flat distribution of the collected charge in the depth direction after the irradiation implies that the effect of charge trapping is small, at the fluence, with the bias voltage well above the full depletion voltage.

title: TCAD simulations of silicon strip and pixel sensor optimization
abstract: Technology computer-aided design (TCAD), used in the semiconductor industry, simulates the semiconductor manufacturing process and the resulting device performance. We have used a device simulator to develop a highly radiation-tolerant n-in-p silicon strip and pixel sensors, both of which can operate at a very high voltage of up to 1000 V. We analyzed the electric field in the pstop structures, novel punch-through-protection (PTP) structures, breakdown in the edge region, etc. and compared the analysis results with the measurement results of test structures; our findings contributed to the development of guiding principles for optimizing the critical structures. The TCAD device simulator is a valuable and effective tool as long as relevant semiconductor physics models and their parameters are implemented. We have yet to understand the modeling of the surface-bulk interplay after proton irradiation, the leakage current generation in the dicing edge, and other phenomena.

title: Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC
abstract: A search for the Standard Model Higgs boson in proton–proton collisions with the ATLAS detector at the LHC is presented. The datasets used correspond to integrated luminosities of approximately 4.8 fb−1 collected at View the MathML source in 2011 and 5.8 fb−1 at View the MathML source in 2012. Individual searches in the channels H→ZZ(⁎)→4l, H→γγ and H→WW(⁎)→eνμν in the 8 TeV data are combined with previously published results of searches for H→ZZ(⁎), WW(⁎), View the MathML source and τ+τ− in the 7 TeV data and results from improved analyses of the H→ZZ(⁎)→4l and H→γγ channels in the 7 TeV data. Clear evidence for the production of a neutral boson with a measured mass of View the MathML source is presented. This observation, which has a significance of 5.9 standard deviations, corresponding to a background fluctuation probability of 1.7×10−9, is compatible with the production and decay of the Standard Model Higgs boson.

title: Evaluation of slim-edge, multi-guard, and punch-through-protection structures before and after proton irradiation
abstract: Planar geometry silicon pixel and strip sensors for the high luminosity upgrade of the LHC (HL-LHC) require a high bias voltage of 1000 V in order to withstand a radiation damage caused by particle fluences of 1×10 16 1 MeV n eq /cm 2 and 1×10 15 1 MeV n eq /cm 2 for pixel and strip detectors, respectively. In order to minimize the inactive edge space that can withstand a bias voltage of 1000 V, edge regions susceptible to microdischarge (MD) should be carefully optimized. We fabricated diodes with various edge distances (slim-edge diodes) and with 1–3 multiple guard rings (multi-guard diodes). AC coupling insulators of strip sensors are vulnerable to sudden heavy charge deposition, such as an accidental beam splash, which may destroy the readout AC capacitors. Thus various types of punch-through-protection (PTP) structures were implemented in order to find the most effective structure to protect against heavy charge deposition. These samples were irradiated with 70 MeV protons at fluences of 5×10 12 1 MeV n eq /cm 2 –1×10 16 1 MeV n eq /cm 2 . Their performances were evaluated before and after irradiation in terms of an onset voltage of the MD, a turn-on voltage of the PTP, and PTP saturation resistance.

title: Search for diphoton events with large missing transverse momentum in 7 TeV proton-proton collision data with the ATLAS detector
abstract: A search for diphoton events with large missing transverse momentum has been performed using proton-proton collision data at is root s = 7 TeV recorded with the ATLAS detector, corresponding to an integrated luminosity of 4.8 fb(-1). No excess of events was observed above the Standard Model prediction and model-dependent 95% confidence level exclusion limits are set. In the context of a generalised model of gauge-mediated supersymmetry breaking with a bino-like lightest neutralino of mass above 50 GeV, gluinos (squarks) below 1.07 TeV (0.87 TeV) are excluded, while a breaking scale Lambda below 196 TeV is excluded for a minimal model of gauge-mediated supersymmetry breaking. For a specific model with one universal extra dimension, compactification scales 1/R < 1.40 TeV are excluded. These limits provide the most stringent tests of these models to date.

title: Development of novel n+-in-p Silicon Planar Pixel Sensors for HL-LHC
abstract: We have been developing highly radiation-tolerant n + -in-p planar pixel sensors for use in the high-luminosity LHC. Novel n + -in-p structures were made using various combinations of the bias structures (punch-through or polysilicon resistor), isolation structures (p-stop or p-spray), and thicknesses ( 320 μ m or 150 μ m ). The 1-chip pixel modules with thin FE-I4 pixel sensors were evaluated using test beams, before and after 2 × 10 15 n eq / cm 2 irradiation. The full depletion voltages were estimated to be 44±10 V and 380±70 V, in the non-irradiated and the irradiated modules, respectively. A reduction of efficiency was observed in the vicinity of the four pixel corners and underneath the bias rail after the irradiation. The global efficiencies were > 99 % and > 95 % in the non-irradiated and the irradiated modules, respectively. The collected charges were uniform in the depth direction at bias voltages well above the full depletion voltages. The encapsulation of vulnerable edges with adhesive or parylene prevented HV sparking. Bump bonding with the SnAg solder bumps was performed at HPK with 150 μ m - and 320 μ m - thick sensors and chips. No disconnection of bumps was observed after 10 thermal cycles between −40 and +50 °C, with a temperature slew rate of > 70 K / min .

title: Effective theories for dark matter nucleon scattering
abstract: A bstractWe reformulate the calculation of the dark matter-nucleon scattering cross sections based on the method of effective field theories. We assume that the scatterings are induced by the exchange of colored mediators, and construct the effective theories by integrating out the colored particles. All of the leading order matching conditions as well as the renormalization group equations are presented. We consider a Majorana fermion, and real scalar and vector bosons for the dark matter and show the results for each case. The treatment for the twist-2 operators is discussed in detail, and it is shown that the scale of evaluating their nucleon matrix elements does not have to be the hadronic scale. The effects of the QCD corrections are evaluated on the assumption that the masses of the colored mediators are much heavier than the electroweak scale. Our formulation is systematic and model-independent, and thus suitable to be implemented in numerical packages, such as micrOMEGAs and DarkSUSY.

title: Does unitarity imply finiteness of electroweak oblique corrections at one-loop? — constraining extra neutral Higgs bosons —
abstract: Introducing arbitrary number of neutral Higgs bosons in the electroweak symmetry breaking sector, we derive a set of conditions among Higgs couplings which need to be satisfied to maintain the unitarity of the high energy scattering amplitudes of weak gauge bosons at the tree level (unitarity sum rules). It is shown that the unitarity sum rules require the tree levelparameter to be 1, without explicitly invoking the custodial symmetry arguments. The one-loop finiteness of the electroweak oblique corrections is automatically guaranteed once these unitarity sum rules are imposed among Higgs couplings. Severe constraints on the lightest Higgs coupling (125GeV Higgs coupling) and the mass of the second lightest Higgs boson are obtained from the unitarity and the results of the electroweak precision tests (oblique parameter measurements). These results are compared with the effective theory of the light Higgs boson, and we find simple relationships between the mass of the second lightest Higgs boson in our framework and the ultraviolet cutoff in the effective theory framework.