International Linear Collider
Not a member yet
509047 research outputs found
Sort by
Search for dark matter produced in association with one or two top quarks in proton-proton collisions at 13 TeV
No full textA search is performed for dark matter (DM) produced in association with a single top quark or a pair of top quarks using the data collected with the CMS detector at the LHC from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to 138 fb of integrated luminosity. Events are classified into zero-lepton, single-lepton, and two-lepton final states. The results are derived from the combination of these different categories. An excess of events with respect to the background-only prediction is searched for in events with a large imbalance in the transverse momentum. Novel multivariate techniques are used to take advantage of the differences in kinematic properties between the two DM production mechanisms. No significant deviations with respect to the standard model predictions are observed. The results are interpreted in the context of a simplified model in which either a scalar or pseudoscalar mediator couples to top quarks and to DM fermions, as well as for axion-like particles that are coupled to top quarks and DM fermions. Expected exclusion limits of 410 and 380 GeV for scalar and pseudoscalar mediator masses, respectively, are set at the 95% confidence level. A DM particle mass of 1 GeV is assumed, with mediator couplings to fermions and DM particles set to unity. A small signal-like excess is observed in data. Because of this excess, mediator masses are only excluded below 310 (320) GeV for the scalar (pseudoscalar) mediator. The results are also translated into model-independent 95% confidence level upper limits on the visible cross section of DM production in association with top quarks, ranging from 1 pb to 0.02 pb
Charged particles tracking in heavy ion collisions for ATLAS in Run 4
No full textLHC Run 4 will provide additional challenges in the already demanding field of charged particle track reconstruction. The Inner Detector of the ATLAS experiment will be replaced by an all-silicon inner tracker (ITk) that will consist of Pixels and Strips providing greater coverage in pseudorapidity spanning up to 8 units. The ACTS Common Tracking Software (ACTS) is the toolkit of choice that will be used to perform track reconstruction, and it is expected to meet the new challenges. The physics of heavy ions (HI) requires a different tracking setup as compared to pp collisions. This is dictated by the difference in experimental conditions, where instead of a huge pile-up of 200 parasitic interactions per crossing in pp collisions, the HI physics expects only one collision per bunch crossing. Despite this, a central lead ion collision produces a comparable number of tracks as to pp collisions. The single vertex of the collision allows for optimizations and in other aspects makes the task more challenging. The talk the progress in setting up the ACTS based track reconstruction for HI in the ITk, shows a comparison between pp and HI tracking performances, and presents the predicted performance of ACTS compared to the existing tracking algorithms used by ATLAS
System testing of the CMS Endcap MIP Timing Layer
No full textThe high luminosity phase of the LHC (HL-LHC) opens up new windows for exciting discoveries but also brings about new challenges due to the high pileup environment of approximately 200 simultaneous interactions per collision. Precise measurements of track and vertex timing can efficiently mitigate these pileup effects. Therefore, the CMS detector will be upgraded with a MIP timing detector (MTD) capable of providing ultra-fast timing information of trajectories of charged particles. With a time resolution of below 50 ps per hit the MTD will be a key ingredient to discover new physics at the HL-LHC. The endcap region of the MTD () has to endure high fluences, motivating the use of thin radiation tolerant silicon sensors with fast charge collection. Tests and developments of these low gain avalanche diodes (LGADs) by CMS together with manufacturers have resulted in a robust design of 16x16 pixel sensors. A custom readout chip for ETL sensors (ETROC) containing clock trees, preamplifier, discriminator, and TDC is being developed in parallel. Several testing campaigns were carried out in the last year, from test beams to characterize the performance of the ETROC2 prototypes together with bump bonded LGAD sensors, to initial tests of the full system, including front end electronics and back end prototypes
Hadron spectroscopy and hadron-hardon interactions
No full textThese proceedings present a selection of results on behalf of all the experiments at LHC. This contribution covers a selection of results appeared after the 2024 winter conferences and before ICHEP2024. Highlights include the observation of new charmonium(-like) states in decays and exotic resonances produced in central exclusive production collisions. Additionally, the Elliptic anisotropy measurement of the f0(980) hadron in proton-lead collisions at CMS is described, along with a similar analysis by the ALICE experiment on the observation of abnormal suppression of f0(980) production in p-Pb collisions
Triggerless Readout System and High-Level Trigger System for AMBER Experiment at CERN
No full textThe available triggering methods limit traditional data acquisition systems. This work presents a novel approach that entirely eliminates the hardware trigger and its logic, replacing it with a streaming mode that offers unprecedented flexibility for physics experiments. Such a system is currently being developed for the AMBER experiment at CERN. It relies on an intelligent data acquisition framework that includes FPGA modules and advanced software processing. By implementing a triggerless mode, the system allows more time for data filtering and applying complex algorithms. Additionally, it uses a custom data protocol optimized to meet the specific requirements of the streaming system. The filtering process takes place on a server farm, which acts as a high-level trigger. I have designed and implemented a high-performance filtering framework that uses optimized algorithms and load balancing to handle high data rates. This work also covers the filter pipeline and the simulation chain used to generate synthetic data for testing and validation of the filtering system
The LSPE-Strip Pointing Reconstruction and Star Tracker
No full textThis paper aims to describe the Pointing Reconstruction Model (PRM) and the prototype Star Tracker, which will be mounted on LSPE-Strip, a microwave Q- and W-band CMB telescope planned for installation at the "Observatorio del Teide" in Tenerife. The PRM integrates information on the instantaneous attitude provided by the telescope control system to determine the actual pointing direction and focal plane orientation of the telescope. It accounts for various non-idealities in the telescope setup, represented by eight configuration angles, which will be calibrated using the Star Tracker. Following the derivation of the PRM formalism and its implementation, we investigate the pointing errors caused by incorrect calibration of these configuration angles to validate the required 1 arcminute maximum systematic pointing error for the LSPE-Strip survey. This paper also describes the main structure and operations of the Star Tracker and presents the results of a campaign of actual sky observations conducted with a prototype. The results demonstrate a Star Tracker RMS accuracy of approximately 3 arcseconds, while systematic errors remain below 10 arcseconds. Based on these results, we analyzed the problem of reconstructing the PRM configuration angles. Two methods for intercalibrating the Star Tracker's pointing direction with respect to the focal plane's pointing direction were examined: (1) observations of planets and (2) observations of a drone carrying both an optical beacon and a radio beacon. In the first case, an intercalibration accuracy between 1/3 arcminute and 1 arcminute is achievable. In the second case, the expected intercalibration accuracy ranges from 0.25 arcminute to 1 arcminute
The ATLAS RPC Phase II ugrade for High Luminosity LHC era
No full textRPC detectors play a crucial role in triggering events containing muons in the central region of the ATLAS experiment. In view of the High-Luminosity LHC program, the existing RPC system, consisting of six independent concentric cylindrical detector layers each providing a full space time localization of hits, is currently facing a significant upgrade. In the next few years, 306 triplets of new generation RPCs will be installed in the innermost region of the ATLAS Muon Barrel Spectrometer, increasing from 6 to 9 the number of tracking layers, doubling the trigger lever arm. This allows a substantial enhancement of the present trigger redundancy, increasing the coverage from 76\% to 96\% approximately. The new chamber design is based on a very efficient integration of an innovative front-end electronics within the detector Faraday cage, allowing to operate the RPCs with an order of magnitude less of average charge per count, correspondingly increasing rate capability and longevity. Fitting new chambers in the narrow space left in ATLAS inner barrel was a challenge,achieved by optimizing RPC materials and thickness, featuring a 1 mm gas gap (instead of 2 mm), and 1.4 mm resistive electrodes (instead of 1.8 mm). Both sides of RPCs are readout by strip panels oriented to measure the bending coordinate of the muon spectrometer, while the second coordinate is reconstructed from the time difference of signal drift at opposite detector's ends. To achieve such results, a 100 ps precise TDC has been integrated in the front-end electronics ASIC. The expected time resolution of a single 1 mm RPC gas gap is approximately 300 ps, and the possibility of a stand-alone Time-of-Flight measurement will have a huge impact on ATLAS searches for massive long-lived particles. An overview and the present status of the ATLAS RPC Phase II project will be presented
Mechanical Design of a ReBCO Non/Metal-Insulated 40 T Solenoid for the Muon Collider
No full textIn the framework of the design studies of a Muon Collider (MuC), the design of Ultra-High-Field (UHF) magnets is a crucial part, particularly for the MuC's final cooling stage. To address this, CERN has recently introduced a conceptual design for a 40 T solenoid characterized by very compact pancake coils. Due to the high magnetic field and operating current density (approximately 600 A/mm2), the Lorentz forces acting on the winding are extremely large. Consequently, the mechanical design, along with quench protection, represents a significant challenge in the development of this magnet. An additional mechanical complexity is constituted by the strong anisotropy and low strength of ReBCO tapes. This article focuses on the proposed mechanical design of the 40 T solenoid. The primary objective of this design is to keep the stresses induced in the coils by Lorentz forces below materials admissible limits. Initially, the paper presents a conceptual design based on analytical calculations relying on the application of a radial pre-compression (approximately 200 MPa) to the pancake coils by shrink-fitting, prior to energization. Subsequently, a finite element analysis is performed, introducing various nonlinearities (material, geometric, plasticity) to optimize the magnet's design. The study also investigates a hybrid solution, in which the initial coil loading is obtained by a combination of shrink fitting and mechanical compression by a clamped conical connection based on shrink discs. The highly anisotropic mechanical properties of the tape, which are not extensively documented in current literature, were investigated by a series of dedicated tests relying on specially designed tooling. This design and experimental testing complement the simulation efforts by allowing to derive and implement in the models more accurate material properties. In conclusion, the proposed magnet design exemplifies a synergistic integration of experimental work and simulation efforts, advancing the development of UHF magnets for the Muon Collider
Online track reconstruction with graph neural networks on FPGAs for the ATLAS experiment
No full textFor the HL-LHC upgrade of the ATLAS TDAQ system, a heterogeneous computing farm deploying GPUs and/or FPGAs is considered to be used for the Event Filter system, together with the use of modern machine learning algorithms such as Graph Neural Networks (GNNs) to solve computationally complex tasks within that system. In this study, the development of a GNN based track finding pipeline on FPGAs for the ATLAS Inner Tracker is presented as part of the Event Filter system. Each step in the GNN-based tracking pipeline is explored: graph construction, edge classification using an interaction network, and segmentation of the graph into track candidates. Optimizations of the GNN approach are investigated to minimize FPGA resource utilization and maximize throughput while maintaining high track reconstruction efficiency and low fake rates required for the ATLAS Event Filter tracking system. These optimizations include model hyperparameter tuning, model pruning, quantization-aware training, and sequential processing of sub-graphs across the detector