Study of the production of π, K and p in pp collisions at √s = 13 TeV as a function of the Transverse Spherocity and the Relative Transverse Activity

High-energy heavy-ion collisions allow the Quark-Gluon Plasma (QGP) production and study, a state of high-density QCD matter in which quarks and gluons are no longer confined inside hadrons for a very short time. Different observables reveal an enhanced production of strange hadrons, signatures of collective effects and opacity to jets due to the QGP formation. However, collective effects and strangeness enhancement are also observed in pp and p-Pb collisions (small systems) with high charged-particle multiplicity. These observations in small systems are very puzzling since the QGP is not expected to be formed since the small systems are considered too dilute and too short-lived.In this thesis, I present a study on the production of π, K and p in pp collisions at √s = 13 TeV using data recorded by the ALICE experiment. To investigate the origins of collective effects and strangeness enhancement, I measure the particle production as a function of the Relative Transverse Activity (RT) and the Transverse Spherocity (S0). In the RT analysis, particle production is measured in different topological regions (toward, away, and transverse) with respect to the leading charged track per event. The toward and away regions mainly contain the fragmentation products of the jet, while the Underlying Event dominates the transverse. The transverse momentum spectra and K/π and p/π ratios are measured as a function of RT = NT/⟨NT⟩, where NT is the charged-particle multiplicity in the transverse region. It is observed that the K/π and p/π ratios increase with increasing RT in the toward region, while little RT dependence is observed in the transverse. Models tuned to e+e- results describe the low-RT particle ratios qualitatively.The transverse spherocity is an event shape observable that can disentangle jet-like from isotropic topologies. I studied particle production in high-multiplicity events as a function of spherocity. I contrast the results obtained using a forward and a mid-pseudorapidity multiplicity estimator. The results show that the mid-pseudorapidity estimator combined with the spherocity selection allows selecting events with more significant variations in the average transverse momentum (⟨pT⟩) than the forward estimator. I present the pT spectra and particle ratios as a function of S0. Finally, all the data results are contrasted with microscopic models

Production of He-4 and (4) in Pb-Pb collisions at root(NN)-N-S=2.76 TeV at the LHC

Results on the production of He-4 and (4) nuclei in Pb-Pb collisions at root(NN)-N-S = 2.76 TeV in the rapidity range vertical bar y vertical bar <1, using the ALICE detector, are presented in this paper. The rapidity densities corresponding to 0-10% central events are found to be dN/dy4(He) = (0.8 +/- 0.4 (stat) +/- 0.3 (syst)) x 10(-6) and dN/dy4 = (1.1 +/- 0.4 (stat) +/- 0.2 (syst)) x 10(-6), respectively. This is in agreement with the statistical thermal model expectation assuming the same chemical freeze-out temperature (T-chem = 156 MeV) as for light hadrons. The measured ratio of (4)/He-4 is 1.4 +/- 0.8 (stat) +/- 0.5 (syst). (C) 2018 Published by Elsevier B.V.Peer reviewe

Effects of hospital facilities on patient outcomes after cancer surgery: an international, prospective, observational study

Background Early death after cancer surgery is higher in low-income and middle-income countries (LMICs) compared with in high-income countries, yet the impact of facility characteristics on early postoperative outcomes is unknown. The aim of this study was to examine the association between hospital infrastructure, resource availability, and processes on early outcomes after cancer surgery worldwide.Methods A multimethods analysis was performed as part of the GlobalSurg 3 study-a multicentre, international, prospective cohort study of patients who had surgery for breast, colorectal, or gastric cancer. The primary outcomes were 30-day mortality and 30-day major complication rates. Potentially beneficial hospital facilities were identified by variable selection to select those associated with 30-day mortality. Adjusted outcomes were determined using generalised estimating equations to account for patient characteristics and country-income group, with population stratification by hospital.Findings Between April 1, 2018, and April 23, 2019, facility-level data were collected for 9685 patients across 238 hospitals in 66 countries (91 hospitals in 20 high-income countries; 57 hospitals in 19 upper-middle-income countries; and 90 hospitals in 27 low-income to lower-middle-income countries). The availability of five hospital facilities was inversely associated with mortality: ultrasound, CT scanner, critical care unit, opioid analgesia, and oncologist. After adjustment for case-mix and country income group, hospitals with three or fewer of these facilities (62 hospitals, 1294 patients) had higher mortality compared with those with four or five (adjusted odds ratio [OR] 3.85 [95% CI 2.58-5.75]; p&lt;0.0001), with excess mortality predominantly explained by a limited capacity to rescue following the development of major complications (63.0% vs 82.7%; OR 0.35 [0.23-0.53]; p&lt;0.0001). Across LMICs, improvements in hospital facilities would prevent one to three deaths for every 100 patients undergoing surgery for cancer.Interpretation Hospitals with higher levels of infrastructure and resources have better outcomes after cancer surgery, independent of country income. Without urgent strengthening of hospital infrastructure and resources, the reductions in cancer-associated mortality associated with improved access will not be realised

Study of the production of π\pi, K\mathrm{K} and p\mathrm{p} in pp\mathrm{pp} collisions at s=13 TeV\sqrt{s}=13~\mathrm{TeV} as a function of the Transverse Spherocity and the Relative Transverse Activity

High-energy heavy-ion collisions allow the Quark-Gluon Plasma (QGP) formation and study. It is a state of high-density QCD matter in which quarks and gluons are free to roam over distances more considerable than the size of the nucleon. Then, the QGP thermalises, cools down, and eventually, hadronisation occurs. Since quarks and gluons can not be directly detected, everything that can be known about the QGP is through the detection of final state hadrons. In some sense, these hadrons are imprinted with information about the QGP properties. For example, the low transverse momentum $(p_{\mathrm{T}})$ identified particles can provide information about radial and anisotropic flow, phenomena associated with collective effects, while high-$p_{\mathrm{T}}$ hadrons can be used as jets proxies for studying parton energy loss in the medium. However, in recent years, signatures of collective effects and strangeness enhancement have also been observed in $\mathrm{pp}$ and $\mathrm{p}-\mathrm{Pb}$ collisions with high charged-particle multiplicity. The systems created in such collisions are commonly called ``small systems'' due to their much smaller size than those of $\mathrm{Pb}-\mathrm{Pb}$ collisions. However, these signatures in small systems are pretty puzzling since QGP formation is not expected, given that they are too dilute and short-lived. The core of this thesis is the results from four physics data analyses performed with the data collected by the ALICE experiment. In chronological order, the first study uses $\mathrm{Pb}-\mathrm{Pb}$ data at $\sqrt{s_{\mathrm{NN}}}=5.02~\mathrm{TeV}$ to measure the $p_{\mathrm{T}}$ spectra of $\pi$, $\mathrm{K}$ and $\mathrm{p}$ as a function of the centrality of the event. The spectra is reported in the $p_{\mathrm{T}}$ interval, $0.1-20~\mathrm{GeV}/c$ and in $|\eta| 120^{\circ} )$. While the toward and away regions contain the fragmentation products of the near-side and the away-side jet, respectively, the UE dominates the transverse. The transverse activity classifier, $R_{\mathrm{T}} = N_{\mathrm{T}} / \langle N_{\mathrm{T}} \rangle$, where $N_{\mathrm{T}}$ is the charged-particle multiplicity measured in the transverse region, is used to control the amount of UE. In this study, I present a method based on the Bayesian unfolding to correct the $R_{\mathrm{T}}$ distribution for detector effects. Furthermore, I describe an extension of the method to obtain the fully corrected $p_{\mathrm{T}}$ spectra of identified particles as a function of $R_{\mathrm{T}}$. It is observed that the relative production of high transverse momentum particles decreases with increasing $R_{\mathrm{T}}$ in both the toward and away regions, indicating a dilution of the jet with increasing UE. Conversely, the spectral shapes in the transverse region harden with increasing $R_{\mathrm{T}}$, i.e., the production of high-$p_{\mathrm{T}}$ particles grows with increasing $R_{\mathrm{T}}$ with respect to the $R_{\mathrm{T}}$-integrated spectrum. These observations suggest a complex interplay in the UE between radiative processes and radial-flow like effects. Finally, it was observed that the $p_{\mathrm{T}}$-differential particle ratios $(\mathrm{K}/\pi$ and $\mathrm{p}/\pi)$ in the low UE limit $(R_{\mathrm{T}} \rightarrow 0)$ approach expectations from fragmentation models tuned to $\mathrm{e}^{+}\mathrm{e}^{-}$ results. The unweighted transverse spherocity is an event shape observable that can disentangle jet-like from isotropic topologies. The topology of an event is characterised by the geometrical distribution of the azimuthal angles of the particles. In this analysis, I study the particle production in $\mathrm{pp}$ collisions at $\sqrt{s}=13~\mathrm{TeV}$ in high-multiplicity events as a function of spherocity. I contrast the results obtained using a forward and a mid-pseudorapidity multiplicity estimator. The results show that the mid-pseudorapidity estimator combined with the spherocity selection allows one to select events based on their hardness. The average transverse momentum $(\langle p_{\mathrm{T}} \rangle)$ measured in events selected with the mid-pseudorapidity estimator showed a clear evolution towards higher values going from isotropic to jet-like topologies. Conversely, the forward estimator showed that the behaviour of the $\langle p_{\mathrm{T}} \rangle$ was a rather tenuous one when plotted as a function of spherocity

Estudio de la contribución de flujo elíptico V2 para sistemas pequeños en colisiones de protón-protón a las energías de LHC en el modelo SPM

"El presente manuscrito es el resultado del estudio enmarcado en la fenomenología de colisiones de iones pesados en el Modelo de Percolación de Cuerdas de Color (SPM) que estudia la interacción y los efectos colectivos que ocurren en la región de bajo momento transverso (pT ) e intermedio (pT ) en las colisiones hadrónicas ultrarrelativistas. Dado que en este modelo se describen los efectos colectivos que llevan a la multiproducción de partículas en colisiones Núcleo-Núcleo (N-N) exitosamente, en este trabajo se utiliza el modelo (SPM) para el estudio de la contribución de flujo elíptico (v2) para sistemas pequeños como lo son las colisiones de protón-protón, esto en búsqueda de una posible señal del cambio de fase para los eventos de alta multiplicidad en estos sistemas pequeños es decir la posible formación del medio Quark Gluon Plasma.

Measurement of jet radial profiles in Pb–Pb collisions at sNN=2.76 TeV

The jet radial structure and particle transverse momentum (pT) composition within jets are presented in centrality-selected Pb–Pb collisions at sNN=2.76 TeV. Track-based jets, which are also called charged jets, were reconstructed with a resolution parameter of R=0.3 at midrapidity |ηch jet|<0.6 for transverse momenta pT,ch jet=30–120 GeV/c. Jet–hadron correlations in relative azimuth and pseudorapidity space (Δφ,Δη) are measured to study the distribution of the associated particles around the jet axis for different pT,assoc-ranges between 1 and 20 GeV/c. The data in Pb–Pb collisions are compared to reference distributions for pp collisions, obtained using embedded PYTHIA simulations. The number of high-pT associate particles (4<pT,assoc<20 GeV/c) in Pb–Pb collisions is found to be suppressed compared to the reference by 30 to 10%, depending on centrality. The radial particle distribution relative to the jet axis shows a moderate modification in Pb–Pb collisions with respect to PYTHIA. High-pT associate particles are slightly more collimated in Pb–Pb collisions compared to the reference, while low-pT associate particles tend to be broadened. The results, which are presented for the first time down to pT,ch jet=30 GeV/c in Pb–Pb collisions, are compatible with both previous jet–hadron-related measurements from the CMS Collaboration and jet shape measurements from the ALICE Collaboration at higher pT, and add further support for the established picture of in-medium parton energy loss. © 2019 The Author(s

Measurement of Λ (1520) production in pp collisions at √s=7TeV and p–Pb collisions at √sNN=5.02TeV

The production of the Λ (1520) baryonic resonance has been measured at midrapidity in inelastic pp collisions at s=7TeV and in p–Pb collisions at sNN=5.02TeV for non-single diffractive events and in multiplicity classes. The resonance is reconstructed through its hadronic decay channel Λ (1520) → pK - and the charge conjugate with the ALICE detector. The integrated yields and mean transverse momenta are calculated from the measured transverse momentum distributions in pp and p–Pb collisions. The mean transverse momenta follow mass ordering as previously observed for other hyperons in the same collision systems. A Blast-Wave function constrained by other light hadrons (π, K, KS0, p, Λ) describes the shape of the Λ (1520) transverse momentum distribution up to 3.5GeV/c in p–Pb collisions. In the framework of this model, this observation suggests that the Λ (1520) resonance participates in the same collective radial flow as other light hadrons. The ratio of the yield of Λ (1520) to the yield of the ground state particle Λ remains constant as a function of charged-particle multiplicity, suggesting that there is no net effect of the hadronic phase in p–Pb collisions on the Λ (1520) yield. © 2020, CERN for the benefit of the ALICE collaboration

Inclusive J/ψ production at mid-rapidity in pp collisions at √s = 5.02 TeV

Inclusive J/ψ production is studied in minimum-bias proton-proton collisions at a centre-of-mass energy of s = 5.02 TeV by ALICE at the CERN LHC. The measurement is performed at mid-rapidity (|y| < 0.9) in the dielectron decay channel down to zero transverse momentum pT, using a data sample corresponding to an integrated luminosity of Lint = 19.4 ± 0.4 nb−1. The measured pT-integrated inclusive J/ψ production cross sec- tion is dσ/dy = 5.64 ± 0.22(stat.) ± 0.33(syst.) ± 0.12(lumi.) μb. The pT-differential cross section d2σ/dpTdy is measured in the pT range 0–10 GeV/c and compared with state-of- the-art QCD calculations. The J/ψ 〈pT〉 and 〈pT2〉 are extracted and compared with results obtained at other collision energies. [Figure not available: see fulltext.]. © 2019, The Author(s)