Measurement of the Higgs boson mass in the H→ZZ∗→4ℓH \rightarrow ZZ* \rightarrow 4\ell decay channel with s=13\sqrt{s} = 13 TeV pppp collisions using the ATLAS detector at the LHC

The mass of the Higgs boson is an important parameter in the Standard Model as it affects the predictions of observables related to the Higgs boson. Higher precision measurements of its mass are therefore of fundamental importance. The $H \rightarrow ZZ* \rightarrow 4\ell$ channel ($\ell = e,\mu$) provides a fully reconstructable final state with good resolution and a high signal-to-background ratio. Using the proton-proton collision data delivered by the Large Hadron Collider at a centre-of-mass energy of 13 TeV and recorded by the ATLAS detector between 2015-2018, we present the most recent measurement of the Higgs Boson mass in this final state. Using this 139 fb$^{-1}$ dataset, we are able to reduce the uncertainty in the mass measurement by almost a factor of 2

Combined Higgs boson measurements at the ATLAS experiment

The most precise measurements of Higgs boson cross sections obtained combining of the measurements performed in the different Higgs boson decay channels. This talk presents the combined measurements, as well as their interpretations

ATLAS ITk strip sensor quality assurance tests and results of ATLAS18 pre-production sensors

Towards the high luminosity (HL) operation of the Large Hadron Collider (LHC), the inner tracking system of the ATLAS detector is replaced by a fully silicon-based inner tracker (ITk). Its outer region consists of 17,888 $n^+$-in-$p$ silicon strip sensors. In order to confirm key properties of the production sensors as well as to establish a solid workflow of quality inspection and monitoring of the various sensor properties, about 5\% of the total strip sensors were produced in 2020 as a pre-production run. As a quality assurance (QA) program, irradiation of dedicated QA test pieces was periodically performed. The fluences of proton, neutron and $\gamma$-ray irradiations were up to $1.6 \times 10^{15}$ 1-MeV neutrons$/\mathrm{cm}^2$ and 0.66 MGy, which are equivalent to the maximum expected radiation fluences at the HL-LHC operation with a safety factor of 1.5. Results from 154 QA test pieces demonstrated high quality of the strip sensors through the pre-production. Detailed understanding of post-irradiated strip sensors was acquired, and the procedures of irradiation and post-irradiation QA testing were fully established. Consequently, the 3.8-year project of the strip sensor production for the ATLAS ITk detector was initiated in July 2021

First bulk and surface results for the ATLAS ITk stereo annulus sensors

A novel microstrip sensor geometry, the “stereo annulus”, has been developed for use in the end-cap of the ATLAS experiment’s strip tracker upgrade at the High-Luminosity Large Hadron Collider (HL- LHC). The radiation-hard, single-sided, ac-coupled, n + -in-p microstrip sensors are designed by the ITk Strip Sensor Collaboration and produced by Hamamatsu Photonics. The stereo annulus design has the potential to revolutionize the layout of end-cap microstrip trackers promising better tracking performance and more complete coverage than the contemporary configurations. These advantages are achieved by the union of equal length, radially oriented strips with a small stereo angle implemented directly into the sensor surface. The first-ever results for the stereo annulus geometry have been collected across several sites world- wide and are presented here. A number of full-size, unirradiated sensors were evaluated for their mechanical, bulk, and surface properties. The new device, the ATLAS12EC, is compared against its conventionally shaped predecessors, the ATLAS07 and ATLAS12, for realistic evaluation of the sensor design. The bulk character of the unirradiated sensors has been determined from IV curve, CV curve, and metrology studies. The leakage current and full depletion voltage characteristics have been obtained and compared with the strict specifications required by the next-generation tracker. Interstrip capacitance and resistance in the four segments of strips, each with equal length constituents and a constant angular pitch, have also been ascertained and are compared to expectations. Long-term leakage current stability tests under various humidity conditions have been conducted to investigate more closely the surface and edge processing. These also allow the determination of any high electric field gradients in the synthesis of stereo radial strips with a tracking coverage enhancing slim edge- width. The impact of the novel stereo annulus sensor geometry on the operation of the detector has been evaluated in these studies. The suitability of the optimized sensor shape for the ATLAS HL-LHC upgrade and future end-cap microstrip trackers will be discussed

First bulk and surface results for the ATLAS ITk Strip stereo annulus sensors

A novel microstrip sensor geometry, the stereo annulus, has been developed for use in the end-cap of the ATLAS experiment's strip tracker upgrade at the HL-LHC. Its first implementation is in the ATLAS12EC sensors a large-area, radiation-hard, single-sided, ac-coupled, \ninp design produced by the ITk Strip Sensor Collaboration and fabricated by Hamamatsu Photonics in early 2017. The results of the initial testing of two ATLAS12EC batches are presented here with a comparison to specification. The potential of the new sensor shape to reinvigorate endcap strip tracking is explained and its effects on sensor performance are isolated by comparing the bulk mechanical and electrical properties of the new sensor to the previous iteration of prototype, the conventional barrel ATLAS12A sensor. The surface properties of the new sensor are evaluated for full-size unirradiated sensors as well as for mini sensors unirradiated and irradiated with $p^{+}$ up to a fluence of $2.2 \times 10^{15}$\neqsq. The results show that the new stereo annulus ATLAS12EC sensors exhibit excellent performance and the expected irradiation evolution

Specifications and Pre-Production of n+-in-p Large-format Strip Sensors fabricated in 6-inch Silicon Wafers, ATLAS18, for Inner Tracker of ATLAS Detector for High-Luminosity Large Hadron Collider

The full volume of the inner tracker of the ATLAS experiment will be replaced with new all-Silicon detectors for HL-LHC. The strip detectors, in the radial extent of 40 to 100 cm, are made of four layers of cylindrical-structures in the barrel and six layers of disk-structures in the endcap section with 2 layers of strip sensors for stereo-viewing in each layer-structure. The corresponding area of strip sensors, at 165 m^2, will be covered with 10976 barrel and 6912 endcap sensors. A new approach is adopted to use p-type material to be more radiation-tolerant, making the readout in n-strips, so-called n+-in-p sensors, to cope with the fluence of 9.7×10^14　(1.6×10^15) 1-MeV neutron-equivalent (neq)/cm^2 and ionizing dose of 44 (66) Mrad at the maximum in the barrel (endcap in the parenthesis) section, for its lifetime including a safety factor of 1.5. The readout is AC-coupled and the strips are biased via Polysilicon resistors for all sensors. In the barrel sensors, the geometry is square, 9.8×9.8 cm^2, to have the largest area of sensor possible from a 6-inch wafer. The strips are laid out in parallel with a strip pitch of 75.5 µm and 4 or 2 rows of strip segments in two types of sensors, "short strips (SS)" for the inner 2 layers and "long strips (LS)" for the outer 2, respectively. In the endcap, we have designed roughly trapezoidal sensors with built-in stereo angle, curved edges along the circumference, and in 6 unique shapes in each radial extent, R0 to R5. The strips are in fan geometry, with a mean pitch of approximately 75 µm and 4 or 2 rows of strip segments. The sensors of this specification are labelled as "ATLAS18xx" where xx stands for SS, LS, Rx (x=0 to 5). With the specifications of mechanical features and electrical performance, CAD files for processing were laid out by following successful designs of ATLAS07, ATLAS12 and ATLAS17LS of the barrel sensors, and ATLAS12EC/R0 of the R0 endcap sensors, together with a number of optimizations. "Pre-Production" amount of 1041 wafers were fabricated and delivered with the tests carried out by vendor. The quality of the sensors was reviewed through the data as provided by the vendor. These sensors were used for establishing and exercising acceptance procedures, and subsequently to be used for pre-production of strip modules and layer structures

Specifications and Pre-production of n+^{+}-in-p Large-format Strip Sensors fabricated in 6-inch Silicon Wafers, ATLAS18, for the Inner Tracker of the ATLAS Detector for High-Luminosity Large Hadron Collider

The ATLAS experiment is constructing new all-silicon inner tracking system for HL-LHC. The strip detectors cover the radial extent of 40 to 100 cm. A new approach is adopted to use p-type silicon material, making the readout in n$^+$-strips, so-called n$^+$-in-p sensors. This allows for enhanced radiation tolerance against an order of magnitude higher particle fluence compared to the LHC. To cope with varying hit rates and occupancies as a function of radial distance, there are two barrel sensor types, the short strips (SS) for the inner 2 and the long strips (LS) for the outer 2 barrel cylinders, respectively. The barrel sensors exhibit a square, 9.8$\times$9.8 cm$^2$, geometry, the largest possible sensor area from a 6-inch wafer. The strips are laid out in parallel with a strip pitch of 75.5 µm and 4 or 2 rows of strip segments. The strips are AC-coupled and biased via polysilicon resistors. The endcap sensors employ a "stereo-annulus" geometry exhibiting a skewed-trapezoid shapes with circular edges. They are designed in 6 unique shapes, R0 to R5, corresponding to progressively increasing radial extents and which allows them to fit within the petal geometry and the 6-inch wafer maximally. The strips are in fan-out geometry with an in-built rotation angle, with a mean pitch of approximately 75 µm and 4 or 2 rows of strip segments. The eight sensor types are labeled as ATLAS18xx where xx stands for SS, LS, and R0 to R5. According to the mechanical and electrical specifications, CAD files for wafer processing were laid out, following the successful designs of prototype barrel and endcap sensors, together with a number of optimizations. A pre-production was carried out prior to the full production of the wafers. The quality of the sensors is reviewed and judged excellent through the test results carried out by vendor. These sensors are used for establishing acceptance procedures and to evaluate their performance in the ATLAS collaboration, and subsequently for pre-production of strip modules and stave and petal structures