Beauty production in heavy-ion collisions with ALICE at the LHC

In this contribution, the final measurements of the centrality dependence of the nuclear modification factor ($R_{\rm AA}$) of non-prompt $\rm D^0$ in Pb--Pb collisions at $\sqrt{s_{\scriptscriptstyle \rm NN}}$ = 5.02 TeV will be presented. These measurements provide important constraints to the in-medium mass dependent of energy loss and hadronisation of the beauty quark. The $p_{\rm T}$-integrated non-prompt $\rm D^0$ $R_{\rm AA}$ will be presented for the first time and will be compared to the prompt $\rm D^0$ one. This comparison will shed light on possible different shadowing effects between charm and beauty quarks. In addition, the first measurements of non-prompt $\rm D_s$ production in central and semi-central Pb--Pb collisions at $\sqrt{s_{\scriptscriptstyle \rm NN}}$ = 5.02 TeV will be discussed. The non-prompt $\rm D_s$ measurements provide additional information on the production and hadronisation of $\rm B_s$ mesons. Finally, the first measurement of non-prompt D-mesons elliptic flow in Pb--Pb collisions at $\sqrt{s_{\scriptscriptstyle \rm NN}}$ = 5.02 TeV will also be discussed. This measurement can constrain the degree of thermalisation of beauty quarks in the hot and dense QCD medium

Measurement of D^0 production in Pb-Pb collisions at 5.02 TeV with ALICE

The Quark-Gluon Plasma (QGP), a state of strongly-interacting matter in which quarks and gluons are deconfined, is thought to have existed a few micro-seconds after the Big Bang. Ultra-relativistic heavy-ion collisions provide a unique opportunity to study the properties of such deconfined medium. These collisions are realized at the Large Hadron Collider (LHC) and the Relativistic Heavy Ion Collider (RHIC). Jet quenching, the phenomenon in which high transverse momentum partons undergo energy loss by collisions with medium constituents and medium-induced gluon radiation, is widely considered as one of the evidences for QGP formation. Jet quenching can be observed via the measurements of di-hadron angular correlations, the nuclear modification factor ($R_{\rm AA}$), di-jet energy imbalance and via the modification of the jet fragmentation function. Heavy quarks are a powerful probe of the QGP, as they are produced in hard scattering processes on a timescale shorter than the QGP formation time and experience the whole system evolution. This thesis presents the measurements of jet-like correlations with neutral pion triggers in pp and central Pb--Pb collisions at 2.76 TeV, the measurements of prompt $\rm D^0$ production in Pb--Pb collisions at ${\sqrt{s}_{\rm NN}}$ = 5.02 TeV, and the on-going measurements of non-prompt $\rm D^0$ production in p--Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV with the ALICE detector at the LHC. The measurements using two-particle angular correlations between trigger particles and associated particles have been extensively used to search for remnants of the radiated energy and the medium response to the high-$p_{\rm T}$ parton. By varying the transverse momentum for trigger and associated particles one can probe different momentum scales to study the interplay of soft and hard processes. Besides providing access to medium properties, measurements of $\pi^0$-hadron correlations determine the most important background contribution of direct photon-hadron correlation measurements. For this analysis, the neutral pions used as triggers are identified in the di-photon decay channel, with energy deposits are reconstructed with the Electromagnetic Calorimeter (EMCal), avoiding admixtures from changing particle composition of the trigger particle, hence should simplify comparisons with calculations. Associated hadrons are reconstructed with the Inner Tracking System (ITS) and Time Projection Chamber (TPC) down to 0.5 GeV/$c$, and significantly extend the previous measurement that only used charged hadrons above 3 GeV/$c$. After subtracting the dominant background, including the anisotropic flow harmonics $v_{2}$ to $v_{5}$, the per-trigger yields are extracted for Near side with $|\Delta \varphi| 3 GeV/$c$, and increase as the momenta decrease, reaching about$5.2$at lowest$p_{\rm T}$. On the near side, an enhancement of$I_{\rm AA}$from$1.2$to$1.8$at lowest$p_{\rm T}$is observed. The data provides a good constrain to the theoretical models which aim to fully describe jet-medium interactions. The measurements of prompt$\rm D^0$nuclear modification factor ($R_{\rm AA}$) can provide important information about the microscopic interactions of heavy quarks with the medium constituents, in particular on the colour-charge and parton-mass dependence of heavy-quark energy loss. The prompt$\rm D^0$are reconstructed at mid-rapidity via the hadronic decay channel$\rm D^0\to K^-\pi^+$. Selections on the decay topology and particle identification are applied in order to reduce the combinatorial background. The signal is extracted via an invariant-mass analysis. The feed-down from beauty-hadron decays is subtracted according to expectations based on FONLL calculations and assumptions of feed-down nuclear modification factor. The prompt$\rm D^0$nuclear modification factor ($R_{\rm AA}$) has been measured in Pb--Pb collisions at$\sqrt{s_{\rm NN}}$= 5.02 TeV, in the centrality class 0-10\%, 30-50\% and 60-80\%. The results are compatible with those measured at$\sqrt{s_{\rm NN}}$= 2.76 TeV, with better precision and extended$p_{\rm T}$coverage. The data set stringent constraints to theoretical models with different implementations of in-medium energy loss. The cross section of non-prompt$\rm D^0$has been measured in p-Pb collisions at$\sqrt{s_{\rm NN}}$= 5.02 TeV, with the goal to further understanding of beauty hadronisation. A multivariate technique (Boosted Decision Trees) is utilised to improve the separation between non-prompt and prompt$\rm D^0$by optimally combining discriminating variables related to the$\rm D^0$decay topology. This method can significantly improve the statistical precision with which the measurement of non-prompt$\rm D^0$can be made in Pb--Pb collisions with ALICE in the future. At the same time, this technique can be utilised for extracting other physics signal with low signal-to-background ratio. In the first Chapter, the physics of QCD theory and Heavy Ion Collisions will be introduced. The second Chapter describes the role of heavy flavour observables to investigate the QGP. A brief introduction of the ALICE apparatus will be given in Chapter 3. The fourth and fifth Chapters present the main work of the thesis, about$\pi^0$-hadron correlations and prompt$\rm D^0$$R_{\rm AA}$measurements. These results have already been published. The sixth chapter describes an on-going work about non-prompt$\rm D^0$ analysis, which aims to prepare a new measurement in Pb--Pb collisions in the future. Conclusions and Outlook will be drawn in the end

Naked Mole-Rat Social Phenotypes Vary in Investigative and Aggressive Behavior in a Laboratory Partner Preference Paradigm

Here we employed the partner preference test (PPT) to examine how naked mole-rat non-breeding individuals of different behavioral phenotypes make social decisions. Naked mole-rats from six colonies were classified into three behavioral phenotypes (soldiers, dispersers, and workers) using a battery of behavioral tests. They then participated in a 3 h long PPT, where they could freely interact with a tethered familiar or tethered unfamiliar conspecific. By comparing the three behavioral phenotypes, we tested the hypothesis that the PPT can be used to interrogate social decision-making in this species, revealing individual differences in behavior that are consistent with discrete social phenotypes. We also tested whether a shorter, 10 min version of the paradigm is sufficient to capture group differences in behavior. Overall, soldiers had higher aggression scores toward unfamiliar conspecifics than both workers and dispersers at the 10 min and 3 h comparison times. At the 10 min comparison time, workers showed a stronger preference for the familiar animal’s chamber, as well as for investigating the familiar conspecific, compared to both dispersers and soldiers. At the 3 h time point, no phenotype differences were seen with chamber or investigation preference scores. Overall, all phenotypes spent more time in chambers with another animal vs. being alone. Use of the PPT in a comparative context has demonstrated that the test identifies species and group differences in affiliative and aggressive behavior toward familiar and unfamiliar animals, revealing individual differences in social decision-making and, importantly, capturing aspects of species-specific social organization seen in nature

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

Household, community, sub-national and country-level predictors of primary cooking fuel switching in nine countries from the PURE study

Introduction. Switchingfrom polluting (e.g. wood, crop waste, coal)to clean (e.g. gas, electricity) cooking fuels can reduce household air pollution exposures and climate-forcing emissions.While studies have evaluated specific interventions and assessed fuel-switching in repeated cross-sectional surveys, the role of different multilevel factors in household fuel switching, outside of interventions and across diverse community settings, is not well understood. Methods.We examined longitudinal survey data from 24 172 households in 177 rural communities across nine countries within the Prospective Urban and Rural Epidemiology study.We assessed household-level primary cooking fuel switching during a median of 10 years offollow up (∼2005–2015).We used hierarchical logistic regression models to examine the relative importance of household, community, sub-national and national-level factors contributing to primary fuel switching. Results. One-half of study households(12 369)reported changing their primary cookingfuels between baseline andfollow up surveys. Of these, 61% (7582) switchedfrom polluting (wood, dung, agricultural waste, charcoal, coal, kerosene)to clean (gas, electricity)fuels, 26% (3109)switched between different polluting fuels, 10% (1164)switched from clean to polluting fuels and 3% (522)switched between different clean fuels

π0\pi^0-hadron correlations in pp and Pb–Pb collisions and π0\pi^0 elliptic flow in Pb–Pb collisions measured at the ALICE experiment

The study of the azimuthal correlation and anisotropy with π0 offers a powerful way to investigate the properties of strongly-interacting matter created in ultra-relativistic heavy-ion collisions. In this talk, we present the measurement of two-particle correlations of π0 trigger particles with associated charged particles versus azimuthal angle difference (Δ φ ) in pp and central Pb–Pb collisions at sNN=2.76 TeV , as well as the measurement of the elliptic flow (v2) of π0 in Pb-Pb collisions at sNN=2.76 TeV at the ALICE experiment. π0 are detected by the ALICE electromagnetic calorimeter EMCal for transverse momenta 8<pT<16 GeV/c , and charged particles are measured by the ALICE main tracking detectors ITS and TPC for 0.5<pT<10 GeV/c , both at mid-rapidity. For π0 -hadron correlations, the per-trigger yield modification factors ( I AA ) are extracted on the near and away side and are compared with results from models and other experiments. For π0v2 , the current status of measurement will be presented. Both measurements serve as important investigations of the medium modified fragmentation pattern and the path-length dependence of energy loss in QGP, as well as the corresponding physics interpretation

Non-strange and strange D-meson and charm-baryon production in heavy-ion collisions measured with ALICE at the LHC

We present recent results on strange and non-strange D-meson production measured with ALICE in Pb–Pb collisions at the LHC. In addition, the measurements of the Λc+ -baryon production and of the Λc+/D0 ratio in pp, p–Pb, and, for the first time ever, Pb–Pb collisions are reported.We present recent result on strange and non-strange D-meson production measured with ALICE in Pb--Pb collisions at the LHC. In addition, the measurements of the $\Lambda_{{\rm c}}^+$-baryon production and of the $\Lambda_{{\rm c}}^+/{\rm D^0}$ ratio in pp, p--Pb, and, for the first time ever, Pb--Pb collisions are reported

Measurement of D0\rm D^0 production in Pb-Pb collisions at 5.02 TeV with ALICE

The Quark-Gluon Plasma (QGP), a state of strongly-interacting matter in which quarks and gluons are deconfined, is thought to have existed a few micro-seconds after the Big Bang. Ultra-relativistic heavy-ion collisions provide a unique opportunity to study the properties of such deconfined medium. These collisions are realized at the Large Hadron Collider (LHC) and the Relativistic Heavy Ion Collider (RHIC). Jet quenching, the phenomenon in which high transverse momentum partons undergo energy loss by collisions with medium constituents and medium-induced gluon radiation, is widely considered as one of the evidences for QGP formation. Jet quenching can be observed via the measurements of di-hadron angular correlations, the nuclear modification factor ($R_{\rm AA}$), di-jet energy imbalance and via the modification of the jet fragmentation function. Heavy quarks are a powerful probe of the QGP, as they are produced in hard scattering processes on a timescale shorter than the QGP formation time and experience the whole system evolution. This thesis presents the measurements of jet-like correlations with neutral pion triggers in pp and central Pb--Pb collisions at 2.76 TeV, the measurements of prompt $\rm D^0$ production in Pb--Pb collisions at ${\sqrt{s}_{\rm NN}}$ = 5.02 TeV, and the on-going measurements of non-prompt $\rm D^0$ production in p--Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV with the ALICE detector at the LHC. The measurements using two-particle angular correlations between trigger particles and associated particles have been extensively used to search for remnants of the radiated energy and the medium response to the high-$p_{\rm T}$ parton. By varying the transverse momentum for trigger and associated particles one can probe different momentum scales to study the interplay of soft and hard processes. Besides providing access to medium properties, measurements of $\pi^0$-hadron correlations determine the most important background contribution of direct photon-hadron correlation measurements. For this analysis, the neutral pions used as triggers are identified in the di-photon decay channel, with energy deposits are reconstructed with the Electromagnetic Calorimeter (EMCal), avoiding admixtures from changing particle composition of the trigger particle, hence should simplify comparisons with calculations. Associated hadrons are reconstructed with the Inner Tracking System (ITS) and Time Projection Chamber (TPC) down to 0.5 GeV/$c$, and significantly extend the previous measurement that only used charged hadrons above 3 GeV/$c$. After subtracting the dominant background, including the anisotropic flow harmonics $v_{2}$ to $v_{5}$, the per-trigger yields are extracted for Near side with $|\Delta \varphi| 3 GeV/$c$, and increase as the momenta decrease, reaching about$5.2$at lowest$p_{\rm T}$. On the near side, an enhancement of$I_{\rm AA}$from$1.2$to$1.8$at lowest$p_{\rm T}$is observed. The data provides a good constrain to the theoretical models which aim to fully describe jet-medium interactions. The measurements of prompt$\rm D^0$nuclear modification factor ($R_{\rm AA}$) can provide important information about the microscopic interactions of heavy quarks with the medium constituents, in particular on the colour-charge and parton-mass dependence of heavy-quark energy loss. The prompt$\rm D^0$are reconstructed at mid-rapidity via the hadronic decay channel$\rm D^0\to K^-\pi^+$. Selections on the decay topology and particle identification are applied in order to reduce the combinatorial background. The signal is extracted via an invariant-mass analysis. The feed-down from beauty-hadron decays is subtracted according to expectations based on FONLL calculations and assumptions of feed-down nuclear modification factor. The prompt$\rm D^0$nuclear modification factor ($R_{\rm AA}$) has been measured in Pb--Pb collisions at$\sqrt{s_{\rm NN}}$= 5.02 TeV, in the centrality class 0-10\%, 30-50\% and 60-80\%. The results are compatible with those measured at$\sqrt{s_{\rm NN}}$= 2.76 TeV, with better precision and extended$p_{\rm T}$coverage. The data set stringent constraints to theoretical models with different implementations of in-medium energy loss. The cross section of non-prompt$\rm D^0$has been measured in p-Pb collisions at$\sqrt{s_{\rm NN}}$= 5.02 TeV, with the goal to further understanding of beauty hadronisation. A multivariate technique (Boosted Decision Trees) is utilised to improve the separation between non-prompt and prompt$\rm D^0$by optimally combining discriminating variables related to the$\rm D^0$decay topology. This method can significantly improve the statistical precision with which the measurement of non-prompt$\rm D^0$can be made in Pb--Pb collisions with ALICE in the future. At the same time, this technique can be utilised for extracting other physics signal with low signal-to-background ratio. In the first Chapter, the physics of QCD theory and Heavy Ion Collisions will be introduced. The second Chapter describes the role of heavy flavour observables to investigate the QGP. A brief introduction of the ALICE apparatus will be given in Chapter 3. The fourth and fifth Chapters present the main work of the thesis, about$\pi^0$-hadron correlations and prompt$\rm D^0$$R_{\rm AA}$measurements. These results have already been published. The sixth chapter describes an on-going work about non-prompt$\rm D^0$ analysis, which aims to prepare a new measurement in Pb--Pb collisions in the future. Conclusions and Outlook will be drawn in the end. \vspace{0.5cm} {\large\textbf{Keywords:}} LHC, ALICE experiment, Pb--Pb collisions, ultra-relativistic heavy-ion collisions, D mesons, heavy flavour production, nuclear modification factor, Quark-Gluon Plasma (QGP), two-particle correlation