Scintillation light detection techniques in a 750-ton liquid argon TPC for the Deep Underground Neutrino Experiment

The experimental confirmation of the neutrino oscillations, and therefore the non-zero neutrino mass, opened a new era of physics beyond the Standard Model of particle physics. Neutrinos do have mass, and their flavour change when propagating. Thanks to the huge effort of the neutrino physics community, many neutrino properties have been measured in the last decades, including most of the neutrino oscillation parameters. However, other properties remain unknown, such as the absolute scale of the neutrino masses, or the nature itself of their masses. The Deep Underground Neutrino Experiment (DUNE) will bring neutrino physics to a new era, measuring the oscillation parameters with unprecedented precision that will allow determining the CP violation phase in the leptonic sector and the neutrino mass ordering. It also aims at detecting neutrinos from a core-collapsing supernova within the galaxy if it occurs during the running of the experiment and performing beyond standard model searches. DUNE is a long-baseline neutrino oscillation experiment designed by an international collaboration of around 1,300 scientists. It will consist of the most powerful neutrino beam installed at Fermilab (US), a Near Detector placed downstream the beam, and a Far Detector located 1.5 km underground at the Sandford Underground Research Facility (SURF), around 1,300 km away from the beam. The Far Detector of DUNE will consist of four liquid-argon time projection chambers (LAr-TPCs) of 17 kton each. DUNE will bring the LAr-TPC technology to an unprecedented large scale. A LAr-TPC is a kind of particle detector that allows the particle-track reconstruction with millimetre precision. In a LAr-TPC, the interacting particles ionize the liquid argon along their tracks. This charge is drifted by a uniform electric field and readout. Additionally, scintillation light is produced, providing a fast signal used as a trigger and also to reconstruct the particle interaction time. The excellent imaging capabilities of the LAr-TPC technology, and the advantages of using liquid argon as a detector medium for neutrino physics, will allow DUNE to fulfil its physics goals. A full prototyping effort is being carried out by the DUNE collaboration to validate the LAr-TPC technology at the kiloton scale. In particular, two prototypes have been assembled and operated at the CERN neutrino platform: ProtoDUNE Single-Phase and ProtoDUNE Dual-Phase, of 300 ton of active mass each, and which took data from 2018 to 2020. While ProtoDUNE Single-Phase is based on a more traditional approach of a LAr-TPC based on wire readout planes, the innovative Dual-Phase approach includes a gas layer at the top, with an extraction layer and Large Electron Multipliers (LEMs) to amplify the signal. The work presented in this thesis has been carried out in the framework of this prototyping work, specifically it has been focused on the operation and performance measurement of the photon detection system of ProtoDUNE Dual-Phase. The obtained results are of interest for any liquid argon experiment. The first chapters of this thesis introduce the status of neutrino physics, the operating principles of the LAr-TPC technology and the DUNE experiment. Then, ProtoDUNE Dual-Phase and its different systems are explained with a particular focus on the photon detection system. The photon detection system is a crucial part of any LAr-TPC, since it provides the interaction time, which is needed to reconstruct the event in three dimensions and contributes to the particle calorimetric recontruction. The photon detection system can also provide a trigger for non-beam events. The ProtoDUNE Dual-Phase photon detection system consists of 36 photomultiplier tubes (PMTs) placed below the TPC active volume. Due to the monolithic design of the detector, the photon detection system must detect scintillation light from more than six meters away, being the longest light detection distance in any liquid argon TPC up to date. A good characterization of the photon detection system is crucial in order to demonstrate its capabilities. The ProtoDUNE Dual-Phase photon detection system performance is studied in detail in chapter 5. Additionally, a good understanding of the light production, propagation and detection processes is key in order to extrapolate the performance of the detector at larger scales. In this sense, the development of a Monte Carlo simulation allows identifying the main parameters affecting the detector performance. A dedicated Monte Carlo simulation of the scintillation light production, propagation and detection has been developed, including the light production from cosmic muons and low energy radiological backgrounds, and compared with data. The understanding of the radiological backgrounds is critical to correctly evaluate the physics performance of DUNE at low energies. The simulation is explained in chapter 6 and the comparison with ProtoDUNE Dual-Phase data can be found in chapter 7. Since scintillation light in liquid argon is produced at 127 nm, at which most photosensors are not sensitive, fluorescent materials are introduced in order to shift the light wavelength towards the visible range, where PMTs have maximal detection efficiency. ProtoDUNE Dual-Phase has carried out an innovative photon detection program, by testing several wavelength shifting techniques at the multi-ton scale which are the object of analysis in this thesis. ProtoDUNE Dual-Phase has been the first detector deploying the novel polyethylene naphthalate (PEN) together with the more traditional tetraphenyl butadiene (TPB) as a wavelength-shifter. Although TPB has proven its good performance in many liquid argon experiments, its deployment requires sophisticated coating setups that are difficult to scale to large surfaces. TPB coatings are also very delicate, making its handling difficult. In this sense, PEN appears as a promising alternative, since it is a thermoplastic similar to PET, very stable and easy to handle. However its wavelength-shifting efficiency is not well known, and it has been never studied in real operating conditions in large scale LAr-TPC. The PEN wavelength efficiency is measured and its performance is evaluated and compared with TPB in chapter 8. This study is critical to understand if PEN represents an effective alternative to TPB for DUNE. Xenon doping is another alternative light detection technique for large scale LAr-TPCs. The presence of xenon at the level of a few ppm (parts-per-million) in the liquid argon acts as a wavelength shifter, shifting part of the scintillation light to longer wavelengths and reducing the light attenuation with the propagation distance. The simplicity of just adding a small quantity of xenon makes it an attractive alternative for large-scale LAr-TPC that is being considered for one of the DUNE Far Detector modules. However, the light production mechanisms in xenon-doped liquid argon have not been characterized yet, and their effects in the detected light in a several-meter-drift LAr-TPC have never been measured. In this sense, a deep study is needed in order to validate the xenon-doping technique for DUNE. ProtoDUNE Dual-Phase took data with xenon-doped liquid argon contaminated with a small amount of nitrogen. The performance of the photon detection system using xenon-doped liquid argon and its comparison with pure liquid argon using ProtoDUNE Dual-Phase data is explained in chapter 9. This analysis represents a unique opportunity to study the performance of a LAr-TPC using xenon-doped liquid argon, as the ProtoDUNE Dual-Phase is the largest monolithic LAr-TPC ever operated. The observation of the proton decay is a process beyond the Standard Model that it has never been observed. Proton decay is one of the requirements of many Gran Unification Theories (GUT), and it would also help to explain the matter-antimatter asymmetry in the universe. Placed deeply underground to mitigate backgrounds and thanks to the good imaging capabilities that allow to identify the interacting particles, DUNE has a promising potential to perform proton decay searches. However, the imaging capabilities rely strongly on having a good and efficient light detection system providing the interaction time of the event. In chapter 10, the performance of a light detection system based on TPB-coated PMTs, as in ProtoDUNE Dual-Phase, is studied. The goal is to validate its capability to provide the event time of proton decay events in the presence of background events in a 10 kton Far Detector of DUNE. This is a key study since the capability to perform proton decay searches is one of the primary physics goals of DUNE

Constraints on jet quenching in p-Pb collisions at sNN\mathbf{\sqrt{s_{NN}}} = 5.02 TeV measured by the event-activity dependence of semi-inclusive hadron-jet distributions

The ALICE Collaboration reports the measurement of semi-inclusive distributions of charged-particle jets recoiling from a high-transverse momentum trigger hadron in p–Pb collisions at sNN=5.02 TeV. Jets are reconstructed from charged-particle tracks using the anti- kT algorithm with resolution parameter R=0.2 and 0.4. A data-driven statistical approach is used to correct the uncorrelated background jet yield. Recoil jet distributions are reported for jet transverse momentum 15<pT,jetch<50GeV/c and are compared in various intervals of p–Pb event activity, based on charged-particle multiplicity and zero-degree neutral energy in the forward (Pb-going) direction. The semi-inclusive observable is self-normalized and such comparisons do not require the interpretation of p–Pb event activity in terms of collision geometry, in contrast to inclusive jet observables. These measurements provide new constraints on the magnitude of jet quenching in small systems at the LHC. In p–Pb collisions with high event activity, the average medium-induced out-of-cone energy transport for jets with R=0.4 and 15<pT,jetch<50GeV/c is measured to be less than 0.4 GeV/c at 90% confidence, which is over an order of magnitude smaller than a similar measurement for central Pb–Pb collisions at sNN=2.76TeV . Comparison is made to theoretical calculations of jet quenching in small systems, and to inclusive jet measurements in p–Pb collisions selected by event activity at the LHC and in d–Au collisions at RHIC

Neutral pion and η\eta meson production at mid-rapidity in Pb-Pb collisions at sNN\sqrt{s_{NN}} = 2.76 TeV

International audienceNeutral pion and η meson production in the transverse momentum range 1 <pT< 20 GeV/c have been measured at midrapidity by the ALICE experiment at the Large Hadron Collider (LHC) in central and semicentral Pb-Pb collisions at sNN  = 2.76 TeV. These results were obtained using the photon conversion method as well as the Photon Spectrometer (PHOS) and Electromagnetic Calorimeter detectors. The results extend the upper pT reach of the previous ALICE π0 measurements from 12 to 20 GeV/c and present the first measurement of η meson production in heavy-ion collisions at the LHC. The η/π0 ratio is similar for the two centralities and reaches at high pT a plateau value of 0.457 ± 0.013stat ± 0.018syst. A suppression of similar magnitude for π0 and η meson production is observed in Pb-Pb collisions with respect to their production in pp collisions scaled by the number of binary nucleon-nucleon collisions. We discuss the results in terms of Next to Leading Order (NLO) pQCD predictions and hydrodynamic models. The measurements show a stronger suppression than observed at lower center-of-mass energies in the pT range 6 <pT< 10 GeV/c. For pT< 3 GeV/c, hadronization models describe the π0 results while for the η some tension is observed

Neutral pion and η\eta meson production in p-Pb collisions at sNN=5.02\sqrt{s_\mathrm{NN}} = 5.02 TeV

Neutral pion and $\eta$ meson invariant differential yields were measured in non-single diffractive p–Pb collisions at $\sqrt{s_{\mathrm{NN}}}$  = 5.02 TeV with the ALICE experiment at the CERN LHC. The analysis combines results from three complementary photon measurements, utilizing the PHOS and EMCal calorimeters and the Photon Conversion Method. The invariant differential yields of $\pi ^{0}$ and $\eta$ meson inclusive production are measured near mid-rapidity in a broad transverse momentum range of $0.3 4$\hbox {GeV}/c$at$0.483 \pm 0.015_{\mathrm{stat}} \pm 0.015_{\mathrm{sys}}$. A deviation from$m_{\mathrm{T}}$scaling is observed for$p_{\mathrm{T}}<$2$\hbox {GeV}/c$. The measured$\eta /\pi ^{0}$ratio is consistent with previous measurements from proton-nucleus and pp collisions over the full$p_{\mathrm{T}}$range. The measured$\eta /\pi ^{0}$ratio at high$p_{\mathrm{T}}$also agrees within uncertainties with measurements from nucleus–nucleus collisions. The$\pi ^{0}$and$\eta $yields in p–Pb relative to the scaled pp interpolated reference,$R_{{\mathrm{pPb}}}$, are presented for$0.3 < p_{\mathrm{T}}<$20$\hbox {GeV}/c$and$0.7 < p_{\mathrm{T}}<$20$\hbox {GeV}/c$, respectively. The results are compared with theoretical model calculations. The values of$R_{{\mathrm{pPb}}}$are consistent with unity for transverse momenta above 2$\hbox {GeV}/c$ . These results support the interpretation that the suppressed yield of neutral mesons measured in Pb–Pb collisions at LHC energies is due to parton energy loss in the hot QCD medium

ϕ\phi meson production at forward rapidity in Pb-Pb collisions at sNN=2.76\sqrt{s_\mathrm{NN}}=2.76 TeV

$\phi$ meson measurements provide insight into strangeness production, which is one of the key observables for the hot medium formed in high-energy heavy-ion collisions. ALICE measured $\phi$ production through its decay in muon pairs in Pb–Pb collisions at $\sqrt{s_\mathrm {NN}} = 2.76$ TeV in the intermediate transverse momentum range $2< p_\mathrm {T}< 5$  GeV/c and in the rapidity interval $2.5<y<4$ . The $\phi$ yield was measured as a function of the transverse momentum and collision centrality. The nuclear modification factor was obtained as a function of the average number of participating nucleons. Results were compared with the ones obtained via the kaon decay channel in the same $p_\mathrm {T}$ range at midrapidity. The values of the nuclear modification factor in the two rapidity regions are in agreement within uncertainties

Prompt and non-prompt J/ψ\hbox {J}/\psi production and nuclear modification at mid-rapidity in p–Pb collisions at sNN=5.02\mathbf{\sqrt{{ s}_{\text {NN}}}= 5.02} TeV

A measurement of beauty hadron production at mid-rapidity in proton-lead collisions at a nucleon–nucleon centre-of-mass energy $\sqrt{s_\text {NN}}=5.02$ TeV is presented. The semi-inclusive decay channel of beauty hadrons into $\hbox {J}/\psi$ is considered, where the $\hbox {J}/\psi$ mesons are reconstructed in the dielectron decay channel at mid-rapidity down to transverse momenta of 1.3 GeV/c. The $\hbox {b}\bar{\hbox {b}}$ production cross section at mid-rapidity, $\hbox {d}\sigma _{\hbox {b}\bar{\hbox {b}}}/\hbox {d}y$ , and the total cross section extrapolated over full phase space, $\sigma _{\text {b}\bar{\text {b}}}$ , are obtained. This measurement is combined with results on inclusive $\hbox {J}/\psi$ production to determine the prompt $\hbox {J}/\psi$ cross sections. The results in p–Pb collisions are then scaled to expectations from pp collisions at the same centre-of-mass energy to derive the nuclear modification factor $R_{\text {pPb}}$ , and compared to models to study possible nuclear modifications of the production induced by cold nuclear matter effects. $R_{\text {pPb}}$ is found to be smaller than unity at low $p_{\mathrm{T}}$ for both $\hbox {J}/\psi$ coming from beauty hadron decays and prompt $\hbox {J}/\psi$

Λc+\Lambda_{\rm c}^+ production in pp collisions at s=7\sqrt{s} = 7 TeV and in p-Pb collisions at sNN=5.02\sqrt{s_{\rm NN}} = 5.02 TeV

The p$_{T}$-differential production cross section of prompt Λ$_{c}^{+}$ charmed baryons was measured with the ALICE detector at the Large Hadron Collider (LHC) in pp collisions at $\sqrt{s}=7$ TeV and in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV at midrapidity. The Λ$_{c}^{+}$ and ${\overline{\varLambda}}_{\overline{\mathrm{c}}}$ were reconstructed in the hadronic decay modes Λ$_{c}^{+}$ → pK$^{−}$π$^{+}$, Λ$_{c}^{+}$ → pK$_{S}^{0}$ and in the semileptonic channel Λ$_{c}^{+}$ → e$^{+}$ν$_{e}$Λ (and charge conjugates). The measured values of the Λ$_{c}^{+}$ /D$^{0}$ ratio, which is sensitive to the c-quark hadronisation mechanism, and in particular to the production of baryons, are presented and are larger than those measured previously in different colliding systems, centre-of-mass energies, rapidity and p$_{T}$ intervals, where the Λ$_{c}^{+}$ production process may differ. The results are compared with the expectations obtained from perturbative Quantum Chromodynamics calculations and Monte Carlo event generators. Neither perturbative QCD calculations nor Monte Carlo models reproduce the data, indicating that the fragmentation of heavy-flavour baryons is not well understood. The first measurement at the LHC of the Λ$_{c}^{+}$ nuclear modification factor, R$_{pPb}$, is also presented. The R$_{pPb}$ is found to be consistent with unity and with that of D mesons within the uncertainties, and consistent with a theoretical calculation that includes cold nuclear matter effects and a calculation that includes charm quark interactions with a deconfined medium

Measurement of beauty production via non-prompt D0{\rm D}^{0} mesons in Pb-Pb collisions at sNN\sqrt{s_{\rm NN}} = 5.02 TeV

The production of non-prompt ${\rm D}^{0}$ mesons from beauty-hadron decays was measured at midrapidity ($\left| y \right| 5~\mathrm{GeV}/c$ in the $0-10$% central Pb-Pb collisions. The data are described by models that include both collisional and radiative processes in the calculation of beauty-quark energy loss in the quark-gluon plasma, and quark recombination in addition to fragmentation as a hadronization mechanism. The ratio of the non-prompt to prompt ${\rm D}^{0}$-meson $R_{\rm AA}$ is larger than unity for $p_{\rm T} > 4~\mathrm{GeV}/c$ in the $0-10$% central Pb-Pb collisions, as predicted by models in which beauty quarks lose less energy than charm quarks in the quark-gluon plasma because of their larger mass

First measurement of the absorption of 3He‾^{3}\overline{\rm He} nuclei in matter and impact on their propagation in the galaxy

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

First study of the two-body scattering involving charm hadrons

This Letter presents the first measurement of the interaction between charm hadrons and nucleons. The two-particle momentum correlations of $\mathrm{pD^-}$ and $\mathrm{\overline{p}D}^+$ pairs are measured by the ALICE Collaboration in high-multiplicity pp collisions at $\sqrt{s} = 13~\mathrm{TeV}$. The data are compatible with the Coulomb-only interaction hypothesis within (1.1-1.5)$\sigma$. Considering an attractive nucleon(N)$\overline{\mathrm{D}}$ strong interaction, in contrast to most model predictions which suggest an overall repulsive interaction, slightly improves the level of agreement. This measurement allows for the first time an estimation of the 68% confidence level interval for the isospin $\mathrm{I}=0$ inverse scattering length of the $\mathrm{N\overline{D}}$ state ${f_{0,~\mathrm{I}=0}^{-1} \in [-0.4,0.9]~\mathrm{fm^{-1}}}$, assuming negligible interaction for the isospin $\mathrm{I}=1$ channel