The ABC130 barrel module prototyping programme for the ATLAS strip tracker

For the Phase-II Upgrade of the ATLAS Detector, its Inner Detector, consisting of silicon pixel, silicon strip and transition radiation sub-detectors, will be replaced with an all new 100 % silicon tracker, composed of a pixel tracker at inner radii and a strip tracker at outer radii. The future ATLAS strip tracker will include 11,000 silicon sensor modules in the central region (barrel) and 7,000 modules in the forward region (end-caps), which are foreseen to be constructed over a period of 3.5 years. The construction of each module consists of a series of assembly and quality control steps, which were engineered to be identical for all production sites. In order to develop the tooling and procedures for assembly and testing of these modules, two series of major prototyping programs were conducted: an early program using readout chips designed using a 250 nm fabrication process (ABCN-25) and a subsequent program using a follow-up chip set made using 130 nm processing (ABC130 and HCC130 chips). This second generation of readout chips was used for an extensive prototyping program that produced around 100 barrel-type modules and contributed significantly to the development of the final module layout. This paper gives an overview of the components used in ABC130 barrel modules, their assembly procedure and findings resulting from their tests.Comment: 82 pages, 66 figure

Analysis of Time Resolution in HGCAL Testbeam

Using data from a 250 GeV electron run during the November 2016 HGCAL testbeam, the time resolution of the High Granularity hadronic endcap Calorimeter, HGCAL, was investigated, looking at the seven innermost Si cells, and using them as reference timers for each other. Cuts in the data was applied based on signal amplitude,$0.05 \hspace{1mm} V < A < 0.45 \hspace{1mm} V$, position of incoming beam particle,$0 \hspace{1mm} mm < TDCx < 22\hspace{1mm} mm$ and $-7\hspace{1mm} mm <TDCy < 11\hspace{1mm} mm$ and size of the time difference between two cells, $\vert t_1 - t_2 \vert < 200 \hspace{1mm} ps.$ Timewalk corrections, wrt in-cell amplitude, were applied to the cut data, with the Photek as reference.\\ Gaussian functions were fitted to the corrected $\Delta t$ distributions, and a time resolution of $15-50$ $ps$ was obtained, depending on which two cells were compared, and how the low-statistics cut were placed. We also confirmed a slight correlation between time resolution and distance between the two cells compared. \end{abstract

Testbeam studies of irradiated modules for the ATLAS ITk Strip upgrade

To cope with the occupancy and radiation environment expected at the High-Luminosity LHC, the ATLAS experiment will replace its Inner Detector with an all-silicon Inner Tracker (ITk), containing pixel and strip subsystems. The strip subsystem will be built from modules, consisting of one or two n+-in-p silicon sensor(s), one or two PCB hybrid(s) containing the front-end read-out electronics, and one powerboard with high voltage, low voltage, and monitoring electronics. The sensors in the central barrel region of the detector will use a simple rectangular geometry, while those in the forward end-cap regions will use a radial geometry with a built-in stereo angle. To validate the expected performance of the ITk strip detector, a series of testbeam campaigns has been performed over several years at the DESY-II testbeam facility. Tracking was provided by EUDET telescopes, consisting of six Mimosa26 pixel planes. An additional FE-I4 pixel plane was used to provide sufficient timing resolution for the telescope. In the years 2021-2022, the focus of testbeam campaigns has been on assessing module performance post-irradiation, using the final production versions of the sensors, and most recent versions of front-end electronics. Three modules of differing geometry were built from irradiated components; a barrel Short Strip (SS), an end-cap R0, and an end-cap R5 - the first "split" module (containing two sensors) to be tested at testbeam. Measurements of the collected charge, detection efficiency, and noise occupancy were performed on all tested modules, as well as of the tracking performance in various sensor regions. The results give confidence in the operability of the detector across its lifetime

Developing Module Assembly and Quality Control Procedures for the HL-LHC Upgrade of the ATLAS Inner Tracker

To further probe the fundamental structures of matter, the Large Hadron Collider (LHC) at CERN is undergoing a programme of upgrades aimed at increasing the instantaneous luminosity by a factor 5 − 7. In lieu of this High Luminosity upgrade (HL-LHC), the current ATLAS Inner Detector will be replaced by a new large area all-silicon tracker - the Inner Tracker (ITk). This is a vast and complex undertaking, requiring the involvement of many institutes worldwide. A modular design philosophy is employed, such that the ITk will consist of 19.000 independent sensor modules, facilitating the need for mass-production, with pixel and microstrip n-on-p based sensor technologies being utilised. The Scandinavian ITk Cluster, consisting of physicists and engineers from Copenhagen, Lund, Oslo and Uppsala University, will be responsible for producing ∼ 600 of the microstrip type modules, in a close collaboration between academia and industry. This partnership has re- quired a redesign of many ITk baseline assembly procedures - to better suit the production line-up in industry. The work carried out during this project touched upon several aspects of the production pro- cedure. The primary product of the research effort described in this thesis, is the development of a robot for high precision high accuracy glue dispensing, both as to regards the placement and amount of glue. The two-component epoxy glue can be delivered with a precision of 2 mg, with clear avenues of improvement, over a time period of 50 min. It will be used in mounting the read-out, powering and control electronics on to the surface of silicon microstrip sensors - a most critical step of the assembly procedure. In addition to this, a study of early onset micro-discharge, seen in IV curves of the ITk silicon sensors labelled ATLAS12EC, has been carried out. Using NRA analysis techniques, we could show that the top oxide layers of several mini sensors had been contaminated with up to ∼ 7% hydrogen by atomic fraction, most likely due to prolonged humidity exposure - hinting at humidity being the cause for this early onset phenomenon

Search for a new scalar resonance in flavour-changing neutral-current top-quark decays t \u86-&gt; qX (q = u, c), with X -&gt;\u86\u92 b(b)over-bar, in proton-proton collisions at root \u88\u9as=13 TeV with the ATLAS detector

A search for flavour-changing neutral-current decays of a top quark into an up-type quark (either up or charm) and a light scalar particle X decaying into a bottom anti-bottom quark pair is presented. The search focuses on top-quark pair production where one top quark decays to qX, with X -&gt; b (b) over bar, and the other top quark decays according to the Standard Model, with the W boson decaying leptonically. The final state is thus characterised by an isolated electron or muon and at least four jets. Events are categorised according to the multiplicity of jets and jets tagged as originating from b-quarks, and a neural network is used to discriminate between signal and background processes. The data analysed correspond to 139 fb(-1) of proton-proton collisions at a centre-of-mass energy of 13TeV, recorded with the ATLAS detector at the LHC. The 95% confidence-level upper limits between 0.019% and 0.062% are derived for the branching fraction B(t -&gt; uX) and between 0.018% and 0.078% for the branching fraction B(t -&gt; cX), for masses of the scalar particle X between 20 and 160 GeV.For complete list of authors see http://dx.doi.org/10.1007/JHEP07(2023)199</p

Search for new phenomena in multi-body invariant masses in events with at least one isolated lepton and two jets using root \u88\u9as=13 TeV proton-proton collision data collected by the ATLAS detector

A search for resonances in events with at least one isolated lepton (e or mu) and two jets is performed using 139 fb(-1) of root s = 13 TeV proton-proton collision data recorded by the ATLAS detector at the LHC. Deviations from a smoothly falling background hypothesis are tested in three- and four-body invariant mass distributions constructed from leptons and jets, including jets identified as originating from bottom quarks. Model-independent limits on generic resonances characterised by cascade decays of particles leading to multiple jets and leptons in the final state are presented. The limits are calculated using Gaussian shapes with different widths for the invariant masses. The multi-body invariant masses are also used to set 95% confidence level upper limits on the cross-section times branching ratios for the production and subsequent decay of resonances predicted by several new physics scenarios.For complete list of authors see http://dx.doi.org/10.1007/JHEP07(2023)202</p

Measurement of the polarisation of Wbosons produced in top-quark decays using dilepton events at â\u88\u9as=13TeV with the ATLAS experiment

A measurement of the polarisation of Wbosons produced in top-quark decays is presented, using proton-proton collision data at a centre-of-mass energy of v s= 13TeV. The data were collected by the ATLAS detector at the Large Hadron Collider and correspond to an integrated luminosity of 139fb(-1). The measurement is performed selecting t tevents decaying into final states with two charged leptons (electrons or muons) and at least two b-tagged jets. The polarisation is extracted from the differential cross-section distribution of the cos theta* variable, where theta(*) is the angle between the momentum direction of the charged lepton from the Wboson decay and the reversed momentum direction of the b-quark from the top-quark decay, both calculated in the Wboson rest frame. Parton-level results, corrected for the detector acceptance and resolution, are presented for the cos theta* angle. The measured fractions of longitudinal, left- and right-handed polarisation states are found to be f(0) = 0.684 +/- 0.005 (stat.)+/- 0.014 (syst.), f(L)= 0.318 +/- 0.003 (stat.)+/- 0.008 (syst.) and f(R)=-0.002 +/- 0.002 (stat.)+/- 0.014 (syst.), in agreement with the Standard Model prediction. (c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP(3).For complete list of authors see http://dx.doi.org/10.1016/j.physletb.2023.137829</p

Observation of WWW Production in pp Collisions at √s=13 TeV with the ATLAS Detector

This Letter reports the observation of WWW production and a measurement of its cross section using detector at the Large Hadron Collider. Events with two same-sign leptons (electrons or muons) and at least two jets, as well as events with three charged leptons, are selected. A multivariate technique is then used to discriminate between signal and background events. Events from WWW production are observed with a significance of 8.0 standard deviations, where the expectation is 5.4 standard deviations. The inclusive WWW production cross section is measured to be 820 ??? 100 ??stat?? ??? 80 ??syst?? fb, approximately 2.6 standard deviations from the predicted cross section of 511 ??? 18 fb calculated at next-to-leading-order QCD and leading-order electroweak accuracy.For complete list of authors see http://dx.doi.org/10.1103/PhysRevLett.129.061803</p

Search for leptoquarks decaying into the bt final state in pp collisions at â\u88\u9as=13 TeV with the ATLAS detector

A search for leptoquarks decaying into the b tau final state is performed using Run 2 proton-proton collision data from the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb(-1) at root s = 13TeV recorded by the ATLAS detector. The benchmark models considered in this search are vector leptoquarks with electric charge of 2/3e and scalar leptoquarks with an electric charge of 4/3e. No significant excess above the Standard Model prediction is observed, and 95% confidence level upper limits are set on the cross-section times branching fraction of leptoquarks decaying into b tau. For the vector leptoquark production two models are considered: the Yang-Mills and Minimal coupling models. In the Yang-Mills (Minimal coupling) scenario, vector leptoquarks with a mass below 1.58 (1.35) TeV are excluded for a gauge coupling of 1.0 and below 2.05 (1.99) TeV for a gauge coupling of 2.5. In the case of scalar leptoquarks, masses below 1.28 (1.53) TeV are excluded for a Yukawa coupling of 1.0 (2.5). Finally, an interpretation of the results with minimal model dependence is performed for each of the signal region categories, and limits on the visible cross-section for beyond the Standard Model processes are provided.For complete list of authors see http://dx.doi.org/10.1007/JHEP10(2023)001</p