Study of depth-dependent charge collection profiles in irradiated pad diodes

In this work, charge collection profiles of non-irradiated and irradiated 150 $\mu$m $p$-type pad diodes were measured using a 5.2 GeV electron beam traversing the diode parallel to the readout electrode. Four diodes were irradiated to 1 MeV neutron equivalent fluences of 2, 4, 8, and 12E15 {cm}^{-2} with 23 MeV protons. The Charge Collection Efficiency profiles as a function of depth are extracted by unfolding the data. The results of the measurements are compared to the simulation using three radiation damage models from literature which were tuned to different irradiation types and fluences

Search for new particles in events with energetic jets and large missing transverse momentum in proton-proton collisions at root s=13 TeV

A search is presented for new particles produced at the LHC in proton-proton collisions at root s = 13 TeV, using events with energetic jets and large missing transverse momentum. The analysis is based on a data sample corresponding to an integrated luminosity of 101 fb(-1), collected in 2017-2018 with the CMS detector. Machine learning techniques are used to define separate categories for events with narrow jets from initial-state radiation and events with large-radius jets consistent with a hadronic decay of a W or Z boson. A statistical combination is made with an earlier search based on a data sample of 36 fb(-1), collected in 2016. No significant excess of events is observed with respect to the standard model background expectation determined from control samples in data. The results are interpreted in terms of limits on the branching fraction of an invisible decay of the Higgs boson, as well as constraints on simplified models of dark matter, on first-generation scalar leptoquarks decaying to quarks and neutrinos, and on models with large extra dimensions. Several of the new limits, specifically for spin-1 dark matter mediators, pseudoscalar mediators, colored mediators, and leptoquarks, are the most restrictive to date.Peer reviewe

Probing effective field theory operators in the associated production of top quarks with a Z boson in multilepton final states at root s=13 TeV

Peer reviewe

Charge collection of irradiated silicon pad diodes and characterization of pixel sensor for the CMS experiment

Silicon sensors are considered for the Phase-2 upgrade of the Inner Tracker of the Compact Muon Solenoid (CMS) detector. The high radiation environment changes the properties of the sensors and degrades their performance. In this regard, two types of sensors are studied: pad diodes and hybrid pixel sensors. Both types of sensors are p-type with a thickness of 150 µm produced by Hamamatsu Photonics K.K on the same wafer. Sensors are irradiated with 23 MeV protons at the same irradiation facility. Using Transient Current Technique with α-particles and red-light laser, Charge Collection Efficiency (CCE) of two irradiated pad diodes are measured close to their n^+ and p^+ implants. Irradiation is done at 1 MeV neutron-equivalent fluences of 2 and 8E15 cm^-2. For the n^+ implant, CCE measured by α-particles shows a higher value than measurements with a red-light laser for all bias voltage. By reducing the energy of α-particles, CCE results became similar to the CCE measured by a red-light laser. The results can be understood by assuming a "non-active region" with a reduced CCE. A model is developed to extract the width and CCE of this region. Next, charge collection profiles of non-irradiated and irradiated pad diodes are measured using a 5.2 GeV electron beam traversing the diode parallel to the readout electrode. The CCE profiles as a function of depth are extracted by unfolding the measured charge collection profiles. The results of the measurements are compared to the simulation using three radiation damage models from the literature. The second half of the work is related to the characterisation of hybrid pixel modules in the test-beam and lab. Planar sensors with various designs and pixel sizes of 25 x 100 µm^2 and 50 x 50 µm^2 are bump bonded to the RD53A readout chip. To extract parameters such as hit efficiency, spatial resolution, and cluster size, the irradiated and non-irradiated modules are tested at Deutsches Elektronen-Synchrotron (DESY) with a 5.2 GeV electron beam. Irradiation is done up to the 1 MeV neutron-equivalent fluence of 2.0E16 cm^-2. All irradiated modules, except one with a bias-dot, reach a hit efficiency of 0.98 at a bias voltage below 800 V. The estimated spatial resolution degrades after irradiation due to the reduction of cluster size. The RD53A readout chip has a non-staggered bump-bond pattern. Therefore, the opening for passivation of the sensor pixel is not directly above its implant and routing is needed. This routing increases the cross-talk effect between neighbouring pixels in adjacent rows. Cross-talk biases the hit reconstruction by the sensor and deteriorates spatial resolution. In this work, cross-talk of three non-irradiated sensors with different designs is characterised using the charge injection method

Characterisation of planar sensors for the inner tracker of the CMS experiment

The Compact Muon Solenoid (CMS) experiment is expected to collect an integrated luminosity of $3000 \, \text{fb}^{-1}$ during the High Luminosity phase of the Large Hadron Collider (HL-LHC). This scenario comes with a high number of collisions per bunch crossing, and in turn, a high level of radiation for the innermost layer of the CMS tracker. Simulations estimate a $1 \, \text{MeV}$ neutron equivalent fluence, $\Phi_\text{eq}$, of $2.3\times 10^{16} \, \text{cm}^{-2}$ at a distance of $2.8 \, \text{cm}$ from the collision point. The inner tracker of the CMS detector is required to withstand this range of fluence and maintain tracking performance. Planar pixel sensors with an active thickness of $150 \, \mu \text{m}$ and pixel sizes of $25 \times 100 \, \mu \text{m}^2$ or $50 \times 50 \, \mu \text{m}^2$ have been produced by Hamamatsu Photonics (HPK) and Fondazione Bruno Kessler (FBK). The sensors were bumped bonded to the RD53A readout chip prototype. The sensor-chip modules were irradiated with $23 \, \text{MeV}$ protons to the $1 \, \text{MeV}$ neutron equivalent fluence of up to $2.4 \times 10^{16} \, \text{cm}^{-2}$ at the Zyklotron AG (ZAG). Non-irradiated and irradiated modules were tested in the DESY II beam test facility. The spatial resolution as a function of the incidence angle and hit efficiency as a function of the bias voltage of the sensors were determined from these measurements. It is shown that for the highest fluence, the planar modules still reach $98 \, \%$ hit efficiency at bias voltages below $800 \, \text{V}$

Depth-dependent charge collection profile of pad diodes

The collected charge of two pad diodes is measured along the diode width using a 5.2GeV electron beam at the DESY II beam test facility. The electron beam enters parallel to the readout electrode plane and perpendicular to the edge of the diode. The position of the electron beam is reconstructed by three planes of an EUDET-type telescope. An in-situ procedure is developed to align the diode surface parallel to the electron beam. The result of these measurements is the charge collection efficiency profile as a function of depth for each diode. For a non-irradiated diode, the charge profile is uniform as a function of the beam position for bias voltages above the full-depletion, as expected. For the irradiated diode, the charge profile is non-uniform and changes as a function of bias voltage

Annual Report 2023 and Phase-I Closeout

This report summarises the activities of the CERN strategic R&D programme on technologies for future experiments during the year 2023, and highlights the achievements of the programme during its first phase 2020-2023

Search for Bc+→π+μ+μ−B_c^+\to\pi^+\mu^+\mu^- decays and measurement of the branching fraction ratio B(Bc+→ψ(2S)π+)/B(Bc+→J/ψπ+){\cal B}(B_c^+\to\psi(2S)\pi^+)/{\cal B}(B_c^+\to J/\psi \pi^+)

International audienceThe first search for nonresonant $B_c^+\to\pi^+\mu^+\mu^-$ decays is reported. The analysis uses proton-proton collision data collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of 9 fb$^{-1}$. No evidence for an excess of signal events over background is observed and an upper limit is set on the branching fraction ratio ${\cal B}(B_c^+\to\pi^+\mu^+\mu^-)/{\cal B}(B_c^+\to J/\psi \pi^+) < 2.1\times 10^{-4}$ at $90\%$ confidence level. Additionally, an updated measurement of the ratio of the $B_c^+\to\psi(2S)\pi^+$ and $B_c^+\to J/\psi \pi^+$ branching fractions is reported. The ratio ${\cal B}(B_c^+\to\psi(2S)\pi^+)/{\cal B}(B_c^+\to J/\psi \pi^+)$ is measured to be $0.254\pm 0.018 \pm 0.003 \pm 0.005$, where the first uncertainty is statistical, the second systematic, and the third is due to the uncertainties on the branching fractions of the leptonic $J/\psi$ and $\psi(2S)$ decays. This measurement is the most precise to date and is consistent with previous LHCb results

Observation of the Bc+→J/ψπ+π0B_c^+ \to J/\psi \pi^+ \pi^0 decay

International audienceThe first observation of the $B_c^+ \to J/\psi \pi^+ \pi^0$ decay is reported with high significance using proton-proton collision data, corresponding to an integrated luminosity of 9fb$^{-1}$, collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13 TeV. The ratio of its branching fraction relative to the $B_c^+ \to J/\psi \pi^+$ channel is measured to be $$\frac{ {\cal{B}}( B_c^+ \to J/\psi \pi^+\pi^0 ) } { {\cal{B}}( B_c^+ \to J/\psi \pi^+ ) } = 2.80 \pm 0.15 \pm 0.11 \pm 0.16 \,,$$ where the first uncertainty is statistical, the second systematic and the third related to imprecise knowledge of the branching fractions for $B^+ \to J/\psi K^{*+}$ and $B^+ \to J/\psi K^+$ decays, which are used to determine the $\pi^0$ detection efficiency. The $\pi^+\pi^0$ mass spectrum is found to be consistent with the dominance of an intermediate $\rho^+$ contribution in accordance with a model based on QCD factorisation

Measurement of ZZ boson production cross-section in pppp collisions at s=5.02\sqrt{s} = 5.02 TeV

International audienceThe first measurement of the $Z$ boson production cross-section at centre-of-mass energy $\sqrt{s} = 5.02\,$TeV in the forward region is reported, using $pp$ collision data collected by the LHCb experiment in year 2017, corresponding to an integrated luminosity of $100 \pm 2\,\rm{pb^{-1}}$. The production cross-section is measured for final-state muons in the pseudorapidity range $2.0 20\,\rm{GeV/}\it{c}$. The integrated cross-section is determined to be $$\sigma_{Z \rightarrow \mu^{+}\mu^{-}} = 39.6 \pm 0.7\,(\rm{stat}) \pm 0.6\,(\rm{syst}) \pm 0.8\,(\rm{lumi}) \ \rm{pb}$$ for the di-muon invariant mass in the range $60<M_{\mu\mu}<120\,\rm{GeV/}\it{c^{2}}$. This result and the differential cross-section results are in good agreement with theoretical predictions at next-to-next-to-leading order in the strong coupling. Based on a previous LHCb measurement of the $Z$ boson production cross-section in $p$Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV, the nuclear modification factor $R_{p\rm{Pb}}$ is measured for the first time at this energy. The measured values are $1.2^{+0.5}_{-0.3}\,(\rm{stat}) \pm 0.1\,(\rm{syst})$ in the forward region ($1.53<y^*_{\mu}<4.03$) and $3.6^{+1.6}_{-0.9}\,(\rm{stat}) \pm 0.2\,(\rm{syst})$ in the backward region ($-4.97<y^*_{\mu}<-2.47$), where $y^*_{\mu}$ represents the muon rapidity in the centre-of-mass frame