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Upgrade of Belle II vertex detector with CMOS pixel technology
No full textThe Belle II experiment at KEK in Japan considers upgrading its vertex detector system toaddress the challenges posed by high background levels caused by the increased luminosity of theSuperKEKB collider. One proposal for upgrading the vertex detector aims to install a 5-layer allmonolithic pixel vertex detector based on fully depleted CMOS sensors in 2027. The new system willuse the OBELIX MAPS chips to improve background robustness and reduce occupancy levels throughsmall and fast pixels. This causes better track finding, especially for low transverse momentatracks. This text will focus on the predecessor of the OBELIX sensor, the TJ-Monopix2, presentinglaboratory and test beam results on pixel response, efficiency, and spatial resolution
First observation of <math display="inline"><msubsup><mi mathvariant="normal">Λ</mi><mi>c</mi><mo>+</mo></msubsup><mo stretchy="false">→</mo><mi mathvariant="normal">Λ</mi><msup><mi>K</mi><mo>+</mo></msup><msup><mi>π</mi><mn>0</mn></msup></math> and evidence of <math display="inline"><msubsup><mi mathvariant="normal">Λ</mi><mi>c</mi><mo>+</mo></msubsup><mo stretchy="false">→</mo><mi mathvariant="normal">Λ</mi><msup><mi>K</mi><mo>+</mo></msup><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>-</mo></msup></math>
No full textWe present the first observation of the singly Cabibbo-suppressed decay Λc+→ΛK+π0 with a significance of 5.7σ and the first evidence of Λc+→ΛK+π+π- decay with a significance of 3.1σ, based on e+e- annihilation data recorded by the BESIII detector at the BEPCII collider. The data correspond to an integrated luminosity of 6.4 fb-1, in the center-of-mass energy range from 4.600 to 4.950 GeV. We determine the branching fractions of Λc+→ΛK+π0 and Λc+→ΛK+π+π- relative to their Cabibbo-favored counterparts to be B(Λc+→ΛK+π0)B(Λc+→Λπ+π0)=(2.09±0.39stat±0.07syst)×10-2 and B(Λc+→ΛK+π+π-)B(Λc+→Λπ+π+π-)=(1.13±0.41stat±0.06syst)×10-2, respectively. Moreover, by combining our measured result with the world average of B(Λc+→Λπ+π0), we obtain the branching fraction B(Λc+→ΛK+π0)=(1.49±0.27stat±0.05syst±0.08ref)×10-3. This result significantly departs from theoretical predictions based on quark SU(3) flavor symmetry, which is underpinned by the presumption of meson pair S-wave amplitude dominance
Technical Design Report for the LUXE experiment
No full textThis Technical Design Report presents a detailed description of all aspects of the LUXE (Laser Und XFEL Experiment), an experiment that will combine the high-quality and high-energy electron beam of the European XFEL with a high-intensity laser, to explore the uncharted terrain of strong-field quantum electrodynamics characterised by both high energy and high intensity, reaching the Schwinger field and beyond. The further implications for the search of physics beyond the Standard Model are also discussed
Operation and performance of the MEG II detector
No full textThe MEG II experiment, located at the Paul Scherrer Institut (PSI) in Switzerland, is the successor to the MEG experiment, which completed data taking in 2013. MEG II started fully operational data taking in 2021, with the goal of improving the sensitivity of the \upmu ^+ \rightarrow {\textrm{e}}^+ \upgamma decay down to almost an order of magnitude better than the current limit. In this paper, we describe the operation and performance of the experiment and give a new estimate of its sensitivity versus data acquisition time
Performance and calibration of quark/gluon-jet taggers using 140 fb of pp collisions at TeV with the ATLAS detector*
No full textThe identification of jets originating from quarks and gluons, often referred to as quark/gluon tagging, plays an important role in various analyses performed at the Large Hadron Collider, as Standard Model measurements and searches for new particles decaying to quarks often rely on suppressing a large gluon-induced background. This paper describes the measurement of the efficiencies of quark/gluon taggers developed within the ATLAS Collaboration, using TeV proton–proton collision data with an integrated luminosity of 140 fb collected by the ATLAS experiment. Two taggers with high performances in rejecting jets from gluon over jets from quarks are studied: one tagger is based on requirements on the number of inner-detector tracks associated with the jet, and the other combines several jet substructure observables using a boosted decision tree. A method is established to determine the quark/gluon fraction in data, by using quark/gluon-enriched subsamples defined by the jet pseudorapidity. Differences in tagging efficiency between data and simulation are provided for jets with transverse momentum between 500 GeV and 2 TeV and for multiple tagger working points
Double-pion electroproduction off protons in deuterium: Quasifree cross sections and final-state interactions
No full textThe single-differential and fully integrated cross sections for quasifree π+π− electroproduction off protons bound in deuterium have been extracted for the first time. The experimental data were collected at Jefferson Laboratory with the CLAS detector. The measurements were performed in the kinematic region of the invariant mass W from 1.3 to 1.825 GeV and the photon virtuality Q2 from 0.4 to 1.0 GeV2. Sufficient experimental statistics allowed for narrow binning in all kinematic variables, while maintaining a small statistical uncertainty. The extracted cross sections were compared with the corresponding cross sections off free protons, which allowed us to obtain an estimate of the contribution from events in which interactions between the final-state hadrons and the spectator neutron took place
Search for dark matter particles in WW events with transverse momentum imbalance in proton-proton collisions at = 13 TeV
No full textA search for dark matter particles is performed using events with a pair of W bosons and large missing transverse momentum. Candidate events are selected by requiring one or two leptons (ℓ = electrons or muons). The analysis is based on proton-proton collision data collected at a center-of-mass energy of 13 TeV by the CMS experiment at the LHC and corresponding to an integrated luminosity of 138 fb. No significant excess over the expected standard model background is observed in the ℓνqq and 2ℓ2ν final states of the WW boson pair. Limits are set on dark matter production in the context of a simplified dark Higgs model, with a dark Higgs boson mass above the WW mass threshold. The dark matter phase space is probed in the mass range 100–300 GeV, extending the scope of previous searches. Current exclusion limits are improved in the range of dark Higgs masses from 160 to 250 GeV, for a dark matter mass of 200 GeV.[graphic not available: see fulltext
Prompt and non-prompt J production at midrapidity in Pb–Pb collisions at = 5.02 TeV
No full textThe transverse momentum (p) and centrality dependence of the nuclear modification factor R of prompt and non-prompt J/ψ, the latter originating from the weak decays of beauty hadrons, have been measured by the ALICE collaboration in Pb–Pb collisions at = 5.02 TeV. The measurements are carried out through the ee decay channel at midrapidity (|y| < 0.9) in the transverse momentum region 1.5 < p < 10 GeV/c. Both prompt and non-prompt J/ψ measurements indicate a significant suppression for p > 5 GeV/c, which becomes stronger with increasing collision centrality. The results are consistent with similar LHC measurements in the overlapping p intervals, and cover the kinematic region down to p = 1.5 GeV/c at midrapidity, not accessible by other LHC experiments. The suppression of prompt J/ψ in central and semicentral collisions exhibits a decreasing trend towards lower transverse momentum, described within uncertainties by models implementing J/ψ production from recombination of c and quarks produced independently in different partonic scatterings. At high transverse momentum, transport models including quarkonium dissociation are able to describe the suppression for prompt J/ψ. For non-prompt J/ψ, the suppression predicted by models including both collisional and radiative processes for the computation of the beauty-quark energy loss inside the quark-gluon plasma is consistent with measurements within uncertainties.[graphic not available: see fulltext
Measurement of associated J/ψ-ψ(2S) production cross-section in pp collisions at = 13 TeV
No full textThe cross-section of associated J/ψ-ψ(2S) production in proton-proton collisions at a centre-of-mass energy of = 13 TeV is measured using a data sample corresponding to an integrated luminosity of 4.2 fb, collected by the LHCb experiment. The measurement is performed for both J/ψ and ψ(2S) mesons having transverse momentum p< 14 GeV/c and rapidity 2.0 < y < 4.5, assuming negligible polarisation of the J/ψ and ψ(2S) mesons. The production cross-section is measured to be 4.5 ± 0.7 ± 0.3 nb, where the first uncertainty is statistical and the second systematic. The differential cross-sections are measured as functions of several kinematic variables of the J/ψ-ψ(2S) candidates. The results are combined with a measurement of J/ψ-J/ψ production, giving a cross-section ratio between J/ψ-ψ(2S) and J/ψ-J/ψ production of 0.274 ± 0.044 ± 0.008, where the first uncertainty is statistical and the second systematic.[graphic not available: see fulltext
Muon identification using multivariate techniques in the CMS experiment in proton-proton collisions at sqrt(s) = 13 TeV
No full textThe identification of prompt and isolated muons, as well asmuons from heavy-flavour hadron decays, is an important task. Wedeveloped two multivariate techniques to provide highly efficientidentification for muons with transverse momentum greater than10 GeV. One provides a continuous variable as an alternative to acut-based identification selection and offers a betterdiscrimination power against misidentified muons. The other oneselects prompt and isolated muons by using isolation requirements toreduce the contamination from nonprompt muons arising inheavy-flavour hadron decays. Both algorithms are developed using59.7 fb of proton-proton collisions data at a centre-of-massenergy of √(s)=13 TeV collected in 2018 with the CMSexperiment at the CERN LHC