Bent monolithic active pixel sensors are the basis for the planned fully cylindrical ultra low material budget tracking detector ITS3 of the ALICE experiment. This paper presents results from testbeam campaigns using high-energy particles to verify the performance of 50 mu m thick bent ALPIDE chips in terms of efficiency and spatial resolution. The sensors were bent to radii of 18, 24 and 30 mm, slightly smaller than the foreseen bending radii of the future ALICE ITS3 layers. An efficiency larger than 99.9% and a spatial resolution of approximately 5 mu m, in line with the nominal operation of flat ALPIDE sensors, is obtained at nominal operating conditions. These values are found to be independent of the bending radius and thus constitute an additional milestone in the demonstration of the feasibility of the planned ITS3 detector. In addition, a special geometry in which the beam particles graze the chip and traverse it laterally over distances of up to 3 mm is investigated.

The production of ${K}^{*}{(892)}^{\ifmmode\pm\else\textpm\fi{}}$ meson resonance is measured at midrapidity ($|y|<0.5$) in $\mathrm{Pb}\text{\ensuremath{-}}\mathrm{Pb}$ collisions at $\sqrt{{s}_{NN}}=5.02$ TeV using the ALICE detector at the CERN Large Hadron Collider. The resonance is reconstructed via its hadronic decay channel ${K}^{*}{(892)}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{K}_{\mathrm{S}}^{0}{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$. The transverse momentum distributions are obtained for various centrality intervals in the ${p}_{\mathrm{T}}$ range of $0.4\text{\ensuremath{-}}16 \mathrm{GeV}/c$. Measurements of integrated yields, mean transverse momenta, and particle yield ratios are reported and found to be consistent with previous ALICE measurements for ${K}^{*}{(892)}^{0}$ within uncertainties. The ${p}_{\mathrm{T}}$-integrated yield ratio $2\phantom{\rule{0.16em}{0ex}}{K}^{*}{(892)}^{\ifmmode\pm\else\textpm\fi{}}/({K}^{+}+{K}^{\ensuremath{-}}$) in central $\mathrm{Pb}\text{\ensuremath{-}}\mathrm{Pb}$ collisions shows a significant suppression at a level of $9.3\ensuremath{\sigma}$ relative to $pp$ collisions. Thermal model calculations result in an overprediction of the particle yield ratio. Although both hadron resonance gas in partial chemical equilibrium (HRG-PCE) and music $+$ smash simulations consider the hadronic phase, only HRG-PCE accurately represents the measurements, whereas music $+$ smash simulations tend to overpredict the particle yield ratio. These observations, along with the kinetic freeze-out temperatures extracted from the yields measured for light-flavored hadrons using the HRG-PCE model, indicate a finite hadronic phase lifetime, which decreases with increasing collision centrality percentile. The ${p}_{\mathrm{T}}$-differential yield ratios $2\phantom{\rule{0.16em}{0ex}}{K}^{*}{(892)}^{\ifmmode\pm\else\textpm\fi{}}/({K}^{+}+{K}^{\ensuremath{-}}$) and $2\phantom{\rule{0.16em}{0ex}}{K}^{*}{(892)}^{\ifmmode\pm\else\textpm\fi{}}/({\ensuremath{\pi}}^{+}+{\ensuremath{\pi}}^{\ensuremath{-}}$) are presented and compared with measurements in pp collisions at $\sqrt{s}=5.02$ TeV. Both particle ratios are found to be suppressed by up to a factor of five at ${p}_{\mathrm{T}}<2.0 \mathrm{GeV}/c$ in central $\mathrm{Pb}\text{\ensuremath{-}}\mathrm{Pb}$ collisions and are qualitatively consistent with expectations for rescattering effects in the hadronic phase. The nuclear modification factor (${R}_{\mathrm{AA}}$) shows a smooth evolution with centrality and is found to be below unity at ${p}_{\mathrm{T}}>8 \mathrm{GeV}/c$, consistent with measurements for other light-flavored hadrons. The smallest values are observed in most central collisions, indicating larger energy loss of partons traversing the dense medium.

AbstractThe transverse-momentum $$(p_{\textrm{T}})$$ ( p T ) spectra of K$$^{*}(892)^{0}~$$ ∗ ( 892 ) 0 and $$\mathrm {\phi (1020)}~$$ ϕ ( 1020 ) measured with the ALICE detector up to $$p_{\textrm{T}} $$ p T = 16 GeV/c in the rapidity range $$-1.2< y < 0.3,$$ - 1.2 < y < 0.3 , in p–Pb collisions at the center-of-mass energy per nucleon–nucleon collision $$\sqrt{s_{\textrm{NN}}} = 5.02$$ s NN = 5.02 TeV are presented as a function of charged particle multiplicity and rapidity. The measured $$p_{\textrm{T}} $$ p T distributions show a dependence on both multiplicity and rapidity at low $$p_{\textrm{T}} $$ p T whereas no significant dependence is observed at high $$p_{\textrm{T}} $$ p T . A rapidity dependence is observed in the $$p_{\textrm{T}} $$ p T -integrated yield (dN/dy), whereas the mean transverse momentum $$\left( \langle p_{\textrm{T}} \rangle \right) $$ ⟨ p T ⟩ shows a flat behavior as a function of rapidity. The rapidity asymmetry ($$Y_{\textrm{asym}}$$ Y asym ) at low $$p_{\textrm{T}} $$ p T (< 5 GeV/c) is more significant for higher multiplicity classes. At high $$p_{\textrm{T}} $$ p T , no significant rapidity asymmetry is observed in any of the multiplicity classes. Both K$$^{*}(892)^{0}~$$ ∗ ( 892 ) 0 and $$\mathrm {\phi (1020)}~$$ ϕ ( 1020 ) show similar $$Y_{\textrm{asym}}$$ Y asym . The nuclear modification factor $$(Q_{\textrm{CP}})$$ ( Q CP ) as a function of $$p_{\textrm{T}} $$ p T shows a Cronin-like enhancement at intermediate $$p_{\textrm{T}} $$ p T , which is more prominent at higher rapidities (Pb-going direction) and in higher multiplicity classes. At high $$p_{\textrm{T}}$$ p T (> 5 GeV/$$c$$ c ), the $$Q_{\textrm{CP}}$$ Q CP values are greater than unity and no significant rapidity dependence is observed.

The ALICE ITS3 (Inner Tracking System 3) upgrade project and the CERN EP R&D on monolithic pixel sensors are investigating the feasibility of the Tower Partners Semiconductor Co. 65 nm process for use in the next generation of vertex detectors. The ITS3 aims to employ wafer-scale Monolithic Active Pixel Sensors thinned down to 20 to 40 um and bent to form truly cylindrical half barrels. Among the first critical steps towards the realisation of this detector is to validate the sensor technology through extensive characterisation both in the laboratory and with in-beam measurements. The Digital Pixel Test Structure (DPTS) is one of the prototypes produced in the first sensor submission in this technology and has undergone a systematic measurement campaign whose details are presented in this article. The results confirm the goals of detection efficiency and non-ionising and ionising radiation hardness up to the expected levels for ALICE ITS3 and also demonstrate operation at +20 C and a detection efficiency of 99% for a DPTS irradiated with a dose of $10^{15}$ 1 MeV n$_{\mathrm{eq}}/$cm$^2$. Furthermore, spatial, timing and energy resolutions were measured at various settings and irradiation levels.

AbstractA newly developed observable for correlations between symmetry planes, which characterize the direction of the anisotropic emission of produced particles, is measured in Pb–Pb collisions at $$\sqrt{s_\text {NN}}$$ s NN = 2.76 TeV with ALICE. This so-called Gaussian Estimator allows for the first time the study of these quantities without the influence of correlations between different flow amplitudes. The centrality dependence of various correlations between two, three and four symmetry planes is presented. The ordering of magnitude between these symmetry plane correlations is discussed and the results of the Gaussian Estimator are compared with measurements of previously used estimators. The results utilizing the new estimator lead to significantly smaller correlations than reported by studies using the Scalar Product method. Furthermore, the obtained symmetry plane correlations are compared to state-of-the-art hydrodynamic model calculations for the evolution of heavy-ion collisions. While the model predictions provide a qualitative description of the data, quantitative agreement is not always observed, particularly for correlators with significant non-linear response of the medium to initial state anisotropies of the collision system. As these results provide unique and independent information, their usage in future Bayesian analysis can further constrain our knowledge on the properties of the QCD matter produced in ultrarelativistic heavy-ion collisions.

This letter reports measurements which characterize the underlying event associated with hard scatterings at mid-pseudorapidity ($|\eta|<0.8$) in pp, p$-$Pb and Pb$-$Pb collisions at centre-of-mass energy per nucleon pair, $\sqrt{s_{\rm NN}}=5.02$ TeV. The measurements are performed with ALICE at the LHC. Different multiplicity classes are defined based on the event activity measured at forward rapidities. The hard scatterings are identified by the leading particle defined as the charged particle with the largest transverse momentum ($p_{\rm T}$) in the collision and having $8 < p_{\rm T} < 15$ GeV/$c$. The $p_{\rm T}$ spectra of associated particles ($0.5 \leq p_{\rm T}<6$ GeV/$c$) are measured in different azimuthal regions defined with respect to the leading particle direction: toward, transverse, and away. The associated charged particle yields in the transverse region are subtracted from those of the away and toward regions. The remaining jet-like yields are reported as a function of the multiplicity measured in the transverse region. The measurements show a suppression of the jet-like yield in the away region and an enhancement of high-$p_{\rm T}$ associated particles in the toward region in central Pb$-$Pb collisions, as compared to minimum-bias pp collisions. These observations are consistent with previous measurements that used two-particle correlations, and with an interpretation in terms of parton energy loss in a high-density quark gluon plasma. These yield modifications vanish in peripheral Pb$-$Pb collisions and are not observed in either high-multiplicity pp or p$-$Pb collisions.

This letter reports measurements which characterize the underlying event associated with hard scatterings at mid-pseudorapidity (|eta| < 0.8) in pp, p-Pband Pb-Pb collisions at centre-of-mass energy per nucleon pair, root sNN= 5.02TeV. The measurements are performed with ALICE at the LHC. Different multiplicity classes are defined based on the event activity measured at forward rapidities. The hard scatterings are identified by the leading particle defined as the charged particle with the largest transverse momentum (pT) in the collision and having 8< pT< 15GeV/c. The p(T) spectra of associated particles (0.5= pT< 6GeV/c) are measured in different azimuthal regions defined with respect to the leading particle direction: toward, transverse, and away. The associated charged particle yields in the transverse region are subtracted from those of the away and toward regions. The remaining jet-like yields are reported as a function of the multiplicity measured in the transverse region. The measurements show a suppression of the jet-like yield in the away region and an enhancement of high-p(T) associated particles in the toward region in central Pb-Pb collisions, as compared to minimum-bias pp collisions. These observations are consistent with previous measurements that used two-particle correlations, and with an interpretation in terms of parton energy loss in a high-density quark gluon plasma. These yield modifications vanish in peripheral Pb-Pb collisions and are not observed in either high-multiplicity pp or p-Pb collisions. (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).

The long term goal of the CERN Experimental Physics Department R&D on monolithic sensors is the development of sub-100nm CMOS sensors for high energy physics. The first technology selected is the TPSCo 65nm CMOS imaging technology. A first submission MLR1 included several small test chips with sensor and circuit prototypes and transistor test structures. One of the main questions to be addressed was how to optimize the sensor in the presence of significant in-pixel circuitry. In this paper this optimization is described as well as the experimental results from the MLR1 run confirming its effectiveness. A second submission investigating wafer-scale stitching has just been completed. This work has been carried out in strong synergy with the ITS3 upgrade of the ALICE experiment.

AbstractThe elliptic flow $$(v_2)$$ ( v 2 ) of $${\textrm{D}}^{0}$$ D 0 mesons from beauty-hadron decays (non-prompt $${\textrm{D}}^{0})$$ D 0 ) was measured in midcentral (30–50%) Pb–Pb collisions at a centre-of-mass energy per nucleon pair $$\sqrt{s_{\textrm{NN}}} = 5.02$$ s NN = 5.02 TeV with the ALICE detector at the LHC. The $${\textrm{D}}^{0}$$ D 0 mesons were reconstructed at midrapidity $$(|y|<0.8)$$ ( | y | < 0.8 ) from their hadronic decay $$\mathrm {D^0 \rightarrow K^-\uppi ^+}$$ D 0 → K - π + , in the transverse momentum interval $$2< p_{\textrm{T}} < 12$$ 2 < p T < 12 GeV/c. The result indicates a positive $$v_2$$ v 2 for non-prompt $${{\textrm{D}}^{0}}$$ D 0 mesons with a significance of 2.7$$\sigma $$ σ . The non-prompt $${{\textrm{D}}^{0}}$$ D 0 -meson $$v_2$$ v 2 is lower than that of prompt non-strange D mesons with 3.2$$\sigma $$ σ significance in $$2< p_\textrm{T} < 8~\textrm{GeV}/c$$ 2 < p T < 8 GeV / c , and compatible with the $$v_2$$ v 2 of beauty-decay electrons. Theoretical calculations of beauty-quark transport in a hydrodynamically expanding medium describe the measurement within uncertainties.

The production of prompt $\rm \Lambda_{\rm c}^{+}$ baryons at midrapidity ($|y|<0.5$) was measured in central (0-10%) and mid-central (30-50%) Pb-Pb collisions at the center-of-mass energy per nucleon-nucleon pair $\sqrt{s_{\rm NN}} = 5.02$ TeV with the ALICE detector. The $\rm \Lambda_{\rm c}^{+}$ production yield, the $\rm \Lambda_{\rm c}^{+}$/D$^0$ production ratio, and the $\rm \Lambda_{\rm c}^{+}$ nuclear modification factor $R_{\rm AA}$ are reported. The results are more precise and more differential in transverse momentum ($p_{\rm T}$) and centrality with respect to previous measurements. The $\rm \Lambda_{\rm c}^{+}$/D$^0$ ratio, which is enhanced with respect to the pp measurement for $4< p_{\rm T} < 8$ GeV/$c$, is described by theoretical calculations that model the charm-quark transport in the quark-gluon plasma and include hadronization via both coalescence and fragmentation mechanisms.

Antimatter particles such as positrons and antiprotons abound in the cosmos. Much less common are light antinuclei, composed of antiprotons and antineutrons, which can be produced in our galaxy via high-energy cosmic-ray collisions with the interstellar medium or could also originate from the annihilation of the still undiscovered dark-matter particles. On Earth, the only way to produce and study antinuclei with high precision is to create them at high-energy particle accelerators like the Large Hadron Collider (LHC). Though the properties of elementary antiparticles have been studied in detail, knowledge of the interaction of light antinuclei with matter is rather limited. This work focuses on the determination of the disappearance probability of \ahe\ when it encounters matter particles and annihilates or disintegrates. The material of the ALICE detector at the LHC serves as a target to extract the inelastic cross section for \ahe\ in the momentum range of $1.17 \leq p < 10$ GeV/$c$. This inelastic cross section is measured for the first time and is used as an essential input to calculations of the transparency of our galaxy to the propagation of $^{3}\overline{\rm He}$ stemming from dark-matter decays and cosmic-ray interactions within the interstellar medium. A transparency of about 50% is estimated using the GALPROP program for a specific dark-matter profile and a standard set of propagation parameters. For cosmic-ray sources, the obtained transparency with the same propagation scheme varies with increasing $^{3}\overline{\rm He}$ momentum from 25% to 90%. The absolute uncertainties associated to the $^{3}\overline{\rm He}$ inelastic cross section measurements are of the order of 10%$-$15%. The reported results indicate that $^{3}\overline{\rm He}$ nuclei can travel long distances in the galaxy, and can be used to study cosmic-ray interactions and dark-matter decays.