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J. D. Tapia Takaki

Publications and source records attributed to J. D. Tapia Takaki.

9 recordsLinked to original sources
arXiv2026

Mirror Quantum Tomography Finds Unexpected Polarization Phenomena in Z Boson Production in pp Collisions at the LHC

The ATLAS, CMS and LHCb collaborations have reported data for the inclusive production of lepton pairs with invariant mass 80-100 GeV in pp collisions. We find the ATLAS data from at $\sqrt{s}$ =8 TeV shows an unexpected vortex-like configuration of Z boson spins circulating around the beam axis. Associated with this structure is a local maximum of the entropy of the Z-boson polarization density matrix extracted using quantum tomography. Data from CMS and LHCb at $\sqrt{s}=13$ TeV are broadly consistent. The origin of the observed phenomena is unknown but generally related to observables that are formally odd under charge conjugation, parity and time-reversal. Quantum tomography using Standard Model lepton couplings to the Z boson determines the spin-1 density matrix of the system model-independently, bypassing any model of the hadronic production process.

hep-ph↗
arXiv2022

Snowmass 2021/22 Letter of Interest: A Forward Calorimeter at the LHC

A forward electromagnetic and hadronic calorimeter (FoCal) was proposed as an upgrade to the ALICE experiment, to be installed during LS3 for data-taking in 2027--2029 at the LHC. The FoCal extends the scope of ALICE, which was designed for the comprehensive study of hot and dense partonic matter, by adding new capabilities to explore the small-$x$ parton structure of nucleons and nuclei. The primary objective of the FoCal is high-precision inclusive measurement of direct photons and jets, as well as coincident gamma-jet and jet-jet measurements, in pp and p--Pb collisions. These measurements by FoCal constitute an essential part of a comprehensive small-$x$ program at the LHC down to $x\sim10^{-6}$ and over a large range of $Q^2$ with a broad array of complementary probes, comprising -- in addition to the photon measurements by FoCal and LHCb -- Drell-Yan and open charm measurements planned by LHCb, as well as photon-induced reactions performed by all LHC experiments.

hep-ex↗
arXiv2019

A generator of forward neutrons for ultra-peripheral collisions: $\textbf{n$\mathbf{_O^O}$n}$

The study of photon-induced reactions in collisions of heavy nuclei at RHIC and the LHC has become an important direction of the research program of these facilities in recent years. In particular, the production of vector mesons in ultra-peripheral collisions (UPC) has been intensively studied. Owing to the intense photon fluxes, the two nuclei participating in such processes undergo electromagnetic dissociation producing neutrons at beam rapidities. Here, we introduce the $\textbf{n$\mathbf{_O^O}$n}$ (pronounced noon) Monte Carlo program, which generates events containing such neutrons. $\textbf{n$\mathbf{_O^O}$n}$ is a ROOT based program that can be interfaced with existing generators of vector meson production in UPC or with theoretical calculations of such photonuclear processes. $\textbf{n$\mathbf{_O^O}$n}$ can also be easily integrated with the simulation programs of the experiments at RHIC and the LHC.

nucl-th↗
arXiv2018

Mass dependence of vector meson photoproduction off protons and nuclei within the energy-dependent hot-spot model

We study the photoproduction of vector mesons off proton and off nuclear targets. We work within the colour dipole model in an approach that includes subnucleon degrees of freedom, so-called hot spots, whose positions in the impact-parameter plane change event-by-event. The key feature of our model is that the number of hot spots depends on the energy of the photon--target interaction. Predictions are presented for exclusive and dissociative production of $ρ^{0}$, $\mathrm{J/}ψ$, and $Υ(1S)$ off protons, as well as for coherent and incoherent photoproduction of $ρ^{0}$ off nuclear targets, where Xe, Au, and Pb nuclei are considered. We find that the mass dependence of dissociative production off protons as a function of the energy of the interaction provides a further handle to search for saturation effects at HERA, the LHC and future colliders. We also find that the coherent photonuclear production of $ρ^{0}$ is sensitive to fluctuations in the subnucleon degrees of freedom at RHIC and LHC energies.

hep-ph↗
arXiv2017

Quantum tomography for collider physics: Illustrations with lepton pair production

Quantum tomography is a method to experimentally extract all that is observable about a quantum mechanical system. We introduce quantum tomography to collider physics with the illustration of the angular distribution of lepton pairs. The tomographic method bypasses much of the field-theoretic formalism to concentrate on what can be observed with experimental data, and how to characterize the data. We provide a practical, experimentally-driven guide to model-independent analysis using density matrices at every step. Comparison with traditional methods of analyzing angular correlations of inclusive reactions finds many advantages in the tomographic method, which include manifest Lorentz covariance, direct incorporation of positivity constraints, exhaustively complete polarization information, and new invariants free from frame conventions. For example, experimental data can determine the $entanglement$ $entropy$ of the production process, which is a model-independent invariant that measures the degree of coherence of the subprocess. We give reproducible numerical examples and provide a supplemental standalone computer code that implements the procedure. We also highlight a property of $complex$ $positivity$ that guarantees in a least-squares type fit that a local minimum of a $χ^{2}$ statistic will be a global minimum: There are no isolated local minima. This property with an automated implementation of positivity promises to mitigate issues relating to multiple minima and convention-dependence that have been problematic in previous work on angular distributions.

hep-ph↗
arXiv2017

Energy dependence of dissociative $\mathrm{J/}ψ$ photoproduction as a signature of gluon saturation at the LHC

We have developed a model in which the quantum fluctuations of the proton structure are characterised by hot spots, whose number grows with decreasing Bjorken-$x$. Our model reproduces the $F_2(x,Q^2)$ data from HERA at the relevant scale, as well as the exclusive and dissociative $\mathrm{J/}ψ$ photoproduction data from H1 and ALICE. Our model predicts that for $W_{γ\mathrm{p}} \approx 500$ GeV, the dissociative $\mathrm{J/}ψ$ cross section reaches a maximum and then decreases steeply with energy, which is in qualitatively good agreement to a recent observation that the dissociative $\mathrm{J/}ψ$ background in the exclusive $\mathrm{J/}ψ$ sample measured in photoproduction by ALICE decreases as energy increases. Our prediction provides a clear signature for gluon saturation at LHC energies.

hep-ph↗
arXiv2013

First LHC results on coherent J/psi photoproduction in ultra-peripheral Pb-Pb collisions at sqrt{s_NN} = 2.76 TeV

The first LHC measurement on ultra-peripheral heavy-ion collisions was carried out with the ALICE experiment. In this paper, ALICE results on exclusive J/psi studies in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV, in the rapidity region -3.6 < y < -2.6, are given. The coherent J/psi cross section was found to be dsigma/dy_coh_J/ψ= 1.00 +/- 0.18 (stat) +0.24 -0.26 (syst) mb. These studies favour theoretical models that include strong modifications to the nuclear gluon density, also known as nuclear gluon shadowing.

hep-ex↗
arXiv2008

Prospects for $ϕ$ meson production in pp collisions at the ALICE experiment

The ALICE experiment at the CERN Large Hadron Collider (LHC) will allow the study of resonance production in nucleus-nucleus and proton-proton collisions. This paper presents results based on physics performance studies to discuss prospects in ALICE for $ϕ$(1020) meson production in pp interactions during the LHC startup.

hep-ex↗