K. Jakobs

Higgs boson searches at hadron colliders

The investigation of the dynamics responsible for electroweak symmetry breaking is one of the prime tasks of experiments at present and future colliders. Experiments at the Tevatron Collider and at the CERN Large Hadron Collider (LHC) must be able to discover a Standard Model Higgs boson over the full mass range as well as Higgs bosons in extended models. In this review, the discovery potential for the Standard Model Higgs boson and for Higgs bosons in the Minimal Supersymmetric extension is summarized. Emphasis is put on those studies which have been performed recently within the experimental collaborations using a realistic simulation of the detector performance. This includes a discussion of the search for Higgs bosons using the vector boson fusion mode at the LHC, a discussion of the measurement of Higgs boson parameters as well as a detailed review of the MSSM sector for different benchmark scenarios. The Tevatron part of the review also contains a discussion of first physics results from data taken in the ongoing Run II.

The process gg ? WW as a background to the Higgs signal at the LHC

The production of W pairs from the one-loop gluon fusion process is studied. Formulas are presented for the helicity amplitudes keeping the top mass finite, but all other quark masses zero. The correlations among the leptons coming from the W bosons are kept. The contribution of this background to the Higgs boson search in the WW decay mode at the LHC is estimated by applying the cuts foreseen in experimental searches using the PYTHIA Monte Carlo program. Kinematic distributions for the final state leptons are compared to those of the Higgs boson signal and of the q qbar -> WW background. After applying final cuts, the gg background is found to be large, at the level of 35% of the q qbar background.The characteristics of the gg background are very similar to those of the signal. Therefore, an experimental normalization of this background component appears to be very difficult and the uncertainty must largely be determined by theory. As a result, the significance of a Higgs signal in the gg -> H -> WW mode at the LHC is reduced.

Test beam results of 3D silicon pixel sensors for the ATLAS upgrade

Results on beam tests of 3D silicon pixel sensors aimed at the ATLAS Insertable B-Layer and High Luminosity LHC (HL-LHC) upgrades are presented. Measurements include charge collection, tracking efficiency and charge sharing between pixel cells, as a function of track incident angle, and were performed with and without a 1.6 T magnetic field oriented as the ATLAS inner detector solenoid field. Sensors were bump-bonded to the front-end chip currently used in the ATLAS pixel detector. Full 3D sensors, with electrodes penetrating through the entire wafer thickness and active edge, and double-sided 3D sensors with partially overlapping bias and read-out electrodes were tested and showed comparable performance.

Beam Test Measurements With Planar and 3D Silicon Strip Detectors Irradiated to sLHC Fluences

The planned luminosity upgrade of the CERN LHC to the super LHC (sLHC) requires investigation of new radiation hard tracking detectors. Compared to the LHC, tracking detectors must withstand a 5-10 times higher radiation fluence. Promising radiation hard options are planar silicon detectors with n-side readout and silicon detectors in 3D technology, where columnar electrodes are etched into the silicon substrate. This article presents beam test measurements per formed with planar and 3D n-in-p silicon strip detectors. The detectors were irradiated to different fluences, where the maximum fluence was 3 × 1015 1 MeV neutron equivalent particles per square centimeter (neq/cm2) for the planar detectors and 2 × 1015 neq/cm2 for the 3D detectors. In addition to signal measurements, charge sharing and resolution of both detector technologies are compared. An increased signal from the irradiated 3D detectors at high bias voltages compared to the signal from the unirradiated detector indicates that charge multiplication effects occur in the 3D detectors. At a bias voltage of 260 V, the 3D detector irradiated to 2 × 1015 neq/cm2 yields a signal almost twice as high as the signal of the unirradiated detector. Only 30% of the signal of an unirradiated detector could be measured with the planar detector irradiated to 3 × 1015 neq/cm2 at a bias voltage of 600 V, which was the highest bias voltage applied to this sensor.

Short strips for the SLHC: A P-Type Silicon microstrip detector in 3D-technology

The luminosity upgrade of the Large Hadron Collider (LHC), the sLHC, will constitute an extremely challenging radiation environment for tracking detectors. With respect to the LHC, massive improvements in radiation hardness are required. In this paper we investigate the superior radiation hardness of the 3D-design, where rows of 3D-columns are etched in substrate material and joined together to form strips. To demonstrate the feasibility of 3D silicon strip detectors (SSDs) for the sLHC, we have built prototype modules using 3D single type column (3D-STC) strip detectors with short strips and front-end electronics from the present ATLAS SemiConductor Tracker (SCT). The modules were tested with a beta source setup before and after irradiation to sLHC fluences with 26 MeV protons. We report on the performance of these 3D-modules, compare it to the results prior to irradiation, and draw conclusions about options for using 3D SSDs for tracking at the sLHC.

Beam Test Measurements With 3D-DDTC Silicon Strip Detectors on n-Type Substrate

For the planned luminosity upgrade of the CERN LHC to the sLHC new radiation hard technologies for the tracking detectors are investigated. Corresponding to the luminosity increase, the radiation dose will be approximately a factor of ten higher than for the detectors currently installed in the LHC experiments. One option for radiation tolerant detectors are 3D silicon detectors with columnar electrodes penetrating into the silicon bulk. This article reports results of beam test measurements performed with 3D-DDTC (Double-Sided, Double Type Column) silicon strip detectors, where the columns do not pass through the detector completely. The devices were produced by IMB-CNM (Barcelona, Spain) and by FBK-irst (Trento, Italy). Important properties like space-resolved charge collection and efficiency are investigated.

Short Strips for the sLHC: A P-Type Silicon Microstrip Detector in 3-D Technology

The luminosity upgrade of the Large Hadron Collider (LHC), the sLHC, will constitute an extremely challenging radiation environment for tracking detectors. With respect to the LHC, large improvements in radiation hardness are required. In this paper, we investigated the expected radiation hardness of the 3-D-design, where rows of 3-D-columns are etched in substrate material and joined together to form strips. To investigate the feasibility of 3-D silicon strip detectors (SSD) for the sLHC, we have built prototype modules using 3-D single type column (3-D-STC) strip detectors with short strips and front-end electronics from the present ATLAS SemiConductor Tracker (SCT). The modules were tested with a beta source setup before and after irradiation to sLHC fluences with 26 MeV protons. We report on the performance of these 3-D-modules, compare it to the results prior to irradiation, and draw conclusions about options for using 3-D SSD detectors for tracking at the sLHC.

PROSPECTS FOR HIGGS BOSON SEARCHES AT THE LHC

The investigation of the dynamics responsible for electroweak symmetry breaking is one of the prime tasks of experiments at the CERN Large Hadron Collider (LHC). The experiments ATLAS and CMS have been designed to be able to discover a Standard Model Higgs boson over the full mass range as well as Higgs bosons in extended models. In this paper, the prospects for Higgs boson searches at the LHC are reviewed. In addition, the potential for the measurement of Higgs boson parameters is discussed.

First Beam Test Characterisation of a 3D-stc Silicon Short Strip Detector

The planned upgrade to the CERN Large Hadron Collider (LHC), the Super-LHC (sLHC) will increase its luminosity by a factor of ten. This necessitates the development of silicon tracking detectors that are significantly more radiation resistant than the ones employed at the LHC. Currently, new detector technologies are being developed to cope with the increased levels of radiation damage at the sLHC. A possible radiation hard option for silicon short strip devices (SSD) in the inner layers of sLHC trackers are 3-D detectors with rows of columnar electrodes processed into the bulk material. These are joined together to form strips. While the excellent radiation hardness of this design has been proven before in lab experiments, a 3-D SSD prototype has now been investigated for the first time in a beam test with pions of a nominal energy of 180 GeV. The use of analog LHC-speed electronics, a beam telescope and time-resolved measurements allowed for detailed studies of the signal behavior on the hit strip and its neighboring strips. Charge collection and efficiency were as well measured with respect to time and point of incidence of the beam particles on the detector. The results of these measurements are presented in this paper.

Higgs-Boson Physics at the LHC

The discovery of a Higgs boson or the exclusion of such a particle in a wide mass range from 100 to 1000 GeV was a major design goal of the LHC and the experiments ATLAS and CMS. The discovery of a Higgs-like particle at a mass around 125 GeV marked the beginning of a new era in particle physics. A snapshot of early results at the time of discovery and detailed investigations of the properties of the new particle with the full LHC data set taken in the years 2010–2012 at centre-of-mass energies of 7 and 8 TeV as well as remaining open questions are the main focus of this chapter.