An LHCb Vertex Locator (VELO) for 2030s

The Upgrade II of the LHCb detector, foreseen for 2031, will operate at an instantaneous luminosity of 1.5 x 10$^{34}$ cm$^{-2}$s$^{-1}$, accumulating a sample of more than 300 fb$^{-1}$. To cope with the estimated pile-up of 42 and 200 charged particle tracks per event, precise timing will be added to the tracking and vertexing sub-systems. A new Vertex Locator (VELO), capable to manage the expected 7.5-fold increase in data rate, occupancy, and radiation fluence is needed. Based on a 4D hybrid silicon pixel technology, with enhanced rate and timing capabilities on the ASIC, the new VELO will allow for precise beauty & charm hadron identification and real time pattern recognition. Through detailed simulations, the fluence, inner radius, material budget and pixel size phase space are explored, while constraining the Impact Parameter (IP) resolution to the Upgrade I value. Two distinct scenarios emerge as starting points for further optimizations, with inner radii and end of life fluence of 5.1 mm at 6 x 10$^{16}$ n$_{eq}$/cm$^{2}$ and 12.5 mm at 8 x 10$^{15}$ n$_{eq}$/cm$^{2}$ respectively. Advances and current R&D on sensor technologies, including LGADs, 3Ds and planar pixels are reviewed, focusing on radiation hard designs and defect engineering. ASIC related requirements with respect to sensor capacitance and power budget are taken into consideration for achieving the 30 ps per hit timing target towards the future 28 nm protype submission. Improvements in cooling, mechanics and vacuum implementations are examined with respect to each layout scenario. The use of bi-phasic Krypton cooling is evaluated as an option for the case of above 1.5 W/cm$^{2}$ power dissipation. Replaceable sensor modules, coupled with 3D printed titanium supports are also under consideration. Finally, a comprehensive R&D schedule towards final design optimization within a six-year period is discussed.Comment: Proceedings of 31st International Workshop on Vertex Detectors (VERTEX 2022

Overview of CNM LGAD results: Boron Si-on-Si and epitaxial wafers

Low Gain Avalanche Detectors (LGADs) are n-on-p silicon sensors with an extra p-layer below the collection electrode which provides signal amplification. When the primary electrons reach the amplification region new electron-hole pairs are created that enhance the generated signal. The moderate gain of these sensors, together with the relatively thin active region, provide precise time information for minimum ionizing particles. To mitigate the effect of pile-up at the HL-LHC the ATLAS and CMS experiments have chosen the LGAD technology for the High Granularity Timing Detector (HGTD) and for the End-Cap Timing Layer (ETL), respectively. A full characterization of recent productions of LGAD sensors fabricated at CNM has been carried out before and after neutron irradiation up to 2.5 $\times$ 10$^{15}$ n$_{eq}$/cm$^{2}$ . Boron-doped sensors produced in epitaxial and Si-on-Si wafers have been studied. The results include their electrically characterization (IV and bias voltage stability) and performance studies (charge and time resolution) for single pad devices with a Sr-90 radioactive source set-up. The behaviour of the Inter-Pad region for irradiated 2 $\times$ 2 LGAD arrays, using the Transient Current Technique (TCT), is shown. The results indicate that the Si-on-Si devices with higher resistivity perform better than the epitaxial ones

Multidifferential study of identified charged hadron distributions in ZZ-tagged jets in proton-proton collisions at s=\sqrt{s}=13 TeV

Jet fragmentation functions are measured for the first time in proton-proton collisions for charged pions, kaons, and protons within jets recoiling against a $Z$ boson. The charged-hadron distributions are studied longitudinally and transversely to the jet direction for jets with transverse momentum 20 $< p_{\textrm{T}} < 100$ GeV and in the pseudorapidity range $2.5 < \eta < 4$. The data sample was collected with the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 1.64 fb$^{-1}$. Triple differential distributions as a function of the hadron longitudinal momentum fraction, hadron transverse momentum, and jet transverse momentum are also measured for the first time. This helps constrain transverse-momentum-dependent fragmentation functions. Differences in the shapes and magnitudes of the measured distributions for the different hadron species provide insights into the hadronization process for jets predominantly initiated by light quarks.Comment: All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-013.html (LHCb public pages

Study of the B−→Λc+Λˉc−K−B^{-} \to \Lambda_{c}^{+} \bar{\Lambda}_{c}^{-} K^{-} decay

The decay $B^{-} \to \Lambda_{c}^{+} \bar{\Lambda}_{c}^{-} K^{-}$ is studied in proton-proton collisions at a center-of-mass energy of $\sqrt{s}=13$ TeV using data corresponding to an integrated luminosity of 5 $\mathrm{fb}^{-1}$ collected by the LHCb experiment. In the $\Lambda_{c}^+ K^{-}$ system, the $\Xi_{c}(2930)^{0}$ state observed at the BaBar and Belle experiments is resolved into two narrower states, $\Xi_{c}(2923)^{0}$ and $\Xi_{c}(2939)^{0}$, whose masses and widths are measured to be $$m(\Xi_{c}(2923)^{0}) = 2924.5 \pm 0.4 \pm 1.1 \,\mathrm{MeV}, \\ m(\Xi_{c}(2939)^{0}) = 2938.5 \pm 0.9 \pm 2.3 \,\mathrm{MeV}, \\ \Gamma(\Xi_{c}(2923)^{0}) = \phantom{000}4.8 \pm 0.9 \pm 1.5 \,\mathrm{MeV},\\ \Gamma(\Xi_{c}(2939)^{0}) = \phantom{00}11.0 \pm 1.9 \pm 7.5 \,\mathrm{MeV},$$ where the first uncertainties are statistical and the second systematic. The results are consistent with a previous LHCb measurement using a prompt $\Lambda_{c}^{+} K^{-}$ sample. Evidence of a new $\Xi_{c}(2880)^{0}$ state is found with a local significance of $3.8\,\sigma$, whose mass and width are measured to be $2881.8 \pm 3.1 \pm 8.5\,\mathrm{MeV}$ and $12.4 \pm 5.3 \pm 5.8 \,\mathrm{MeV}$, respectively. In addition, evidence of a new decay mode $\Xi_{c}(2790)^{0} \to \Lambda_{c}^{+} K^{-}$ is found with a significance of $3.7\,\sigma$. The relative branching fraction of $B^{-} \to \Lambda_{c}^{+} \bar{\Lambda}_{c}^{-} K^{-}$ with respect to the $B^{-} \to D^{+} D^{-} K^{-}$ decay is measured to be $2.36 \pm 0.11 \pm 0.22 \pm 0.25$, where the first uncertainty is statistical, the second systematic and the third originates from the branching fractions of charm hadron decays.Comment: All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-028.html (LHCb public pages

Measurement of the ratios of branching fractions R(D∗)\mathcal{R}(D^{*}) and R(D0)\mathcal{R}(D^{0})

The ratios of branching fractions $\mathcal{R}(D^{*})\equiv\mathcal{B}(\bar{B}\to D^{*}\tau^{-}\bar{\nu}_{\tau})/\mathcal{B}(\bar{B}\to D^{*}\mu^{-}\bar{\nu}_{\mu})$ and $\mathcal{R}(D^{0})\equiv\mathcal{B}(B^{-}\to D^{0}\tau^{-}\bar{\nu}_{\tau})/\mathcal{B}(B^{-}\to D^{0}\mu^{-}\bar{\nu}_{\mu})$ are measured, assuming isospin symmetry, using a sample of proton-proton collision data corresponding to 3.0 fb${ }^{-1}$ of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode $\tau^{-}\to\mu^{-}\nu_{\tau}\bar{\nu}_{\mu}$. The measured values are $\mathcal{R}(D^{*})=0.281\pm0.018\pm0.024$ and $\mathcal{R}(D^{0})=0.441\pm0.060\pm0.066$, where the first uncertainty is statistical and the second is systematic. The correlation between these measurements is $\rho=-0.43$. Results are consistent with the current average of these quantities and are at a combined 1.9 standard deviations from the predictions based on lepton flavor universality in the Standard Model.Comment: All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-039.html (LHCb public pages

Recent achievements of the ATLAS upgrade Planar Pixel Sensors R&D; project

In the context of the HL-LHC upgrade of the ATLAS experiment, the introduction of a highly segmented radiation hard siliconized inner tracker is envisaged to cope with highly granularity. The Planar Pixel Sensors (PPS) collaboration, comprising of institutes from 16 countries, was established to investigate the transposability of already proven planar pixel technology to those harsh requirements. Introducing a comprehensive approach, state-of-the-art achievements in several scopes are presented: novice designs, including bias rail rerouting, active edge technologies and enlarged pixel implementations, 3D TCAD doping profile simulations in conjunction with secondary ion mass spectroscopy measurements, slim sensor productions eliminating support wafers as well as large area devices, Ni-Au under-bump metallisation effects as well as hybridization efforts, data acquisition systems developments and irradiation results from recent test beams. Presented results form a synthetic approach, providing insight in contemporary developments and open subjects with respect to silicon particle detectors

Recent achievements of the ATLAS upgrade Planar Pixel Sensors R&D project

International audienceIn the context of the HL-LHC upgrade of the ATLAS experiment, the introduction of a highly segmented radiation hard siliconized inner tracker is envisaged to cope with highly granularity. The Planar Pixel Sensors (PPS) collaboration, comprising of institutes from 16 countries, was established to investigate the transposability of already proven planar pixel technology to those harsh requirements. Introducing a comprehensive approach, state-of-the-art achievements in several scopes are presented: novice designs, including bias rail rerouting, active edge technologies and enlarged pixel implementations, 3D TCAD doping profile simulations in conjunction with secondary ion mass spectroscopy measurements, slim sensor productions eliminating support wafers as well as large area devices, Ni-Au under-bump metallisation effects as well as hybridization efforts, data acquisition systems developments and irradiation results from recent test beams. Presented results form a synthetic approach, providing insight in contemporary developments and open subjects with respect to silicon particle detectors

High-Granularity Timing Detector for the Phase-II up-grade of the ATLAS Calorimeter system

The expected increase of the particle flux at the high luminosity phase of the LHC (HL-LHC) with instantaneous luminosities up to L ≃ 7.5×1034 cm−2s−1 will have a severe impact on pile-up. The pile-up is expected to increase on average to 200 interactions per bunch crossing. The reconstruction and trigger performance for electrons, photons as well as jets and transverse missing energy will be severely degraded in the end-cap and forward region, where the liquid Argon based electromagnetic calorimeter has coarser granularity compared to the central region. A High Granular Timing Detector (HGTD) is proposed in front of the liquid Argon end-cap calorimeters for pile-up mitigation at Level-0 (L0) trigger level and in offline reconstruction. This device should cover the pseudo-rapidity range of 2.4 to about 4.2. Four layers of Silicon sensors, possibly interleaved with Tungsten, are foreseen to provide precision timing information for charged and neutral particles with a time resolution of the order of 50 pico-seconds per readout cell in order to assign the energy deposits in the calorimeter to different proton-proton collision vertices. Each readout cell has a transverse size of only a few mm, leading to a highly granular detector with several hundred thousand readout cells. Using the information provided by the detector, the contribution from pile-up jets can be reduced significantly while preserving high efficiency for hard-scatter jets. The expected improvements in performance are in particular relevant for physics processes with forward jets, like vector-boson fusion and vector-boson scattering processes, and for physics signatures with large missing transverse energy. Silicon sensor technologies under investigation are Low Gain Avalanche Detectors (LGAD), pin diodes, and HV-CMOS sensors. The physics motivations and expected performance of the High Granular Timing Detector at the HL-LHC are summarized. The proposed detector layout and Front End readout, laboratory and beam test characterization of sensors and the results of radiation tests are presented

Characterization of Irradiated Boron, Carbon-Enriched and Gallium Si-on-Si Wafer Low Gain Avalanche Detectors

Low Gain Avalanche Detectors (LGADs) are n-on-p silicon sensors with an extra doped p-layer below the n-p junction which provides signal amplification. The moderate gain of these sensors, together with the relatively thin active region, provides excellent timing performance for Minimum Ionizing Particles (MIPs). To mitigate the effect of pile-up during the High-Luminosity Large Hadron Collider (HL-LHC) era, both ATLAS and CMS experiments will install new detectors, the High-Granularity Timing Detector (HGTD) and the End-Cap Timing Layer (ETL), that rely on the LGAD technology. A full characterization of LGAD sensors fabricated by Centro Nacional de Microelectrónica (CNM), before and after neutron irradiation up to 1015 neq/cm2, is presented. Sensors produced in 100 mm Si-on-Si wafers and doped with boron and gallium, and also enriched with carbon, are studied. The results include their electrical characterization (I-V, C-V), bias voltage stability and performance studies with the Transient Current Technique (TCT) and a Sr-90 radioactive source setup

Characterization and simulation of radiation effects on active edges n-on-p technology planar pixel sensors

International audienceThe ATLAS inner tracker has to be upgraded to meet the requirements for radiation hardness and geometrical acceptance in order to withstand the harsh conditions of High Luminosity LHC (HL-LHC). This requires segmented silicon sensors of increased geometrical efficiency. The active edge technology allows to reduce the inactive area at the border of the sensor. The main objective of this work is to evaluate by TCAD simulation, conducted using Silvaco™ TCAD software, the performance of planar n-on-p technology sensors with active edges exposed to high level of radiation for fluences up to 1×1016neq/cm2, using a three-level trap model for ptype FZ silicon material. By using the secondary ion mass spectrometry (SIMS) technique, an accurate representation of the sensor structure was obtained in terms of doping concentration profile. Charge collection efficiency (CCE) is studied as a function of radiation fluence. •Secondary Ion Mass Spectrometry method (SIMS) is used to investigate the doping profile.•The charge collection efficiency (CCE) are simulated a function of radiation fluence.•An ADVACaM edgless sensor matrix is implemented in a full TCAD simulation