arXiv subjects

Cristian Baldenegro

Publications and source records attributed to Cristian Baldenegro.

14 recordsLinked to original sources

arXiv2026

Analysis note: one-point charge correlator with DELPHI Open Data

We present the first measurement of the one-point charge correlator, the angular flux of electric charge in hadronic final states, using DELPHI Open Data collected at LEP-1 at $\sqrt{s} = 91.2$~GeV during 1994 and 1995. The data, corrected for detector effects, exhibit a clear $\sin(2θ)$ modulation, consistent with the parity-violating hadronic charge flow that the chiral structure of the $Z$ couplings imprints on the final state. The measurement demonstrates the experimental feasibility of the observable and establishes strategies for controlling associated detector effects, thereby motivating a new program to measure charge-flux observables. This note documents the experimental details supporting the companion experimental paper and the joint theory--experiment Letter.

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arXiv2026

First measurement of the one-point charge correlator in $e^+e^-$ collisions at $\sqrt{s} = 91.2$ GeV with DELPHI Open Data

The chiral structure of the $Z$ couplings imprints a parity-odd flow of electric charge on hadronic $Z$ decays. The related forward-backward asymmetries, a key set of observables in the electroweak precision program, were measured at LEP and SLC using the jet charge. The one-point charge correlator offers a complementary route, measuring the hadronic charge flow directly as a function of polar angle relative to the incoming electron-beam axis, without reference to jets or a reconstructed quark direction, following the formalism developed in a companion paper. We report its first measurement, using $61~\mathrm{pb}^{-1}$ of archival DELPHI Open Data recorded at $\sqrt{s} = 91.2$~GeV in 1994 and 1995. Detector effects are corrected in two stages. The first is derived from fully simulated samples, and the second bounds the residual charge-misreconstruction difference between data and simulation using a measurement in $e^+e^-\toτ^+τ^-$ events. The measured charge correlator exhibits the characteristic parity-odd $\sin(2θ)$ modulation and agrees with the \textsc{PYTHIA}~8.3 prediction. The measurement demonstrates the experimental feasibility of the observable and establishes strategies for controlling associated detector effects, paving the way for a new program of charge-flux measurements, both in archival $e^+e^-$ data and at future colliders.

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arXiv2025

Scaling of the elastic proton-proton cross-section

We discuss scaling properties of the elastic $pp$ cross-section both at the ISR and the LHC. We observe that the ratio of bump to dip positions of the differential cross-section $dσ_{\rm el}/dt$ is constant over a wide energy range. We next study the consequences of this property, including geometric scaling at the ISR and new scaling laws at the LHC.

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arXiv2024

Secondary Lund jet plane as a gluon enriched sample

We propose a new strategy to obtain a high-purity sample of gluon-initiated jets at the LHC. Our approach, inspired by the Lund jet plane picture, is to perform a dijet selection where the two jets are collinear to each other and their momentum fraction share is highly asymmetric, and to measure the primary Lund plane density of emissions of the subleading jet. The subleading jet in this topology is practically equivalent to a secondary Lund jet plane. We demonstrate by means of fixed-order calculations that such a simple setup yields gluon jet fractions of around 90% for the subleading jet for both quark- and gluon-initiated jets. This observation is confirmed using hadron-level Monte Carlo generated events. We also show that the extracted gluon purities are highly resilient to the overall colour structure of the event, to the flavour of the hard-scattering process, and to the parton distribution functions. This strategy is well-suited for constraining the radiation pattern of gluon-initiated jets using a set of fiducial cuts that can readily be tested at the LHC, without relying on taggers or statistical demixing.

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arXiv2024

Scaling properties of elastic pp cross-section

We show that the elastic differential $pp$ cross-section has a unique universal property that the ratio of bump-to-dip position is constant from the energies of the ISR to the LHC. We explore this property to compare Geometric Scaling present at the ISR with the recently proposed scaling law at the LHC. We argue that at the LHC, within present experimental uncertainties, there is fact a family of scaling laws.

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arXiv2024

Scaling laws of elastic proton-proton scattering differential cross sections

We show that elastic scattering $pp \to pp $ differential cross sections as function of the four-momentum transfer square $|t|$ have a universal property, such that the ratio of bump-to-dip positions is constant from the energies of the ISR to the LHC, from tens of GeV and up to the TeV scale. We explore this property to compare the geometrical scaling observed at the ISR with the recently proposed scaling law at the LHC. We argue that, at the LHC, within present experimental uncertainties, there is in fact a family of scaling laws. We discuss the constraints that the scaling laws impose on the parametrization of the elastic $pp\to pp$ scattering amplitude.

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arXiv2022

Searching for anomalous top quark interactions with proton tagging and timing detectors at the LHC

We study the LHC sensitivity to new broad neutral resonances produced in two-photon fusion and decaying to a top quark pair, $γγ\to t\bar{t}$. This is probed in central exclusive $t\bar{t}$ production in proton-proton collisions, $pp \to p t\bar{t} p$. We use the tagging of the intact protons by PPS (CMS) and AFP (ATLAS) and consider the semi-leptonic $t\bar t$ channel. The sensitivity is also mapped onto a set of dimension-8 $γγt\bar{t}$ operators in the large mass limit. Using the kinematical correlations between the intact protons and the reconstructed $t\bar{t}$ system, we obtain a sensitivity to the couplings of the dimension-8 operators of $1.4 \cdot 10^{-11}~\mathrm{GeV}^{-4}$ at 95% CL. The sensitivity to the anomalous couplings is significantly improved down to about $7\cdot 10^{-12}~\mathrm{GeV}^{-4}$ if the proton time-of-flight is known with a precision of 20 ps in future measurements. The 95% CL sensitivity to broad neutral resonances reaches masses of order $ 1500~\mathrm{GeV} $ when using timing information.

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arXiv2022

White Paper on Forward Physics, BFKL, Saturation Physics and Diffraction

The goal of this whitepaper is to give a comprehensive overview of the rich field of forward physics. We discuss the occurrences of BFKL resummation effects in special final states, such as Mueller-Navelet jets, jet gap jets, and heavy quarkonium production. It further addresses TMD factorization at low x and the manifestation of a semi-hard saturation scale in (generalized) TMD PDFs. More theoretical aspects of low x physics, probes of the quark gluon plasma, as well as the possibility to use photon-hadron collisions at the LHC to constrain hadronic structure at low x, and the resulting complementarity between LHC and the EIC are also presented. We also briefly discuss diffraction at colliders as well as the possibility to explore further the electroweak theory in central exclusive events using the LHC as a photon-photon collider.

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arXiv2020

Jet measurements at CMS

Recent measurements based on jet production in high energy pp collisions at the CERN LHC with the CMS detector are reported. Specifically, the measurement of the inclusive jet production cross section as a function of the anti-$k_t$ distance parameter $R$ divided by the jet cross section at $R = 0.4$, is discussed. The cross section ratio is sensitive to various perturbative and non-perturbative treatments of the jet formation process in quantum chromodynamics (QCD). In the second study, the regimes of validity of the parton shower and matrix element approaches are tested on multijet events in pp collisions at $\sqrt{s} = 8$ and $13$ TeV. Special attention is given to the second and third leading $p_\text{T}$ jets and their momenta and rapidity-azimuth correlations. Finally, studies of dijet production where the two leading $p_T$ jets are separated by a large pseudorapidity interval void of charged particles is presented. This signature is expected from hard color singlet exchange (two-gluon exchange in perturbative QCD). The latter can be treated with perturbative QCD techniques based on the Balitsky-Fadin-Kuraev-Lipatov (BFKL) evolution equations.

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arXiv2020

Review of results on forward physics and diffraction by CMS

Results by the CMS Collaboration on forward physics, diffraction, and physics in the small-$x$ limit of quantum chromodynamics (QCD), are presented. In particular, results on azimuthal angle decorrelations between two jets in events where two outermost jets are separated by a large rapidity interval are discussed. In addition, results based on the production of two jets separated by a large rapidity gap (interval void of radiation) are presented. These dijet production processes are expected to be sensitive to Balitsky-Fadin-Kuraev-Lipatov (BFKL) evolution effects. We highlight results on inclusive forward jet production and on exclusive vector meson production in proton-lead collisions, which access gluon densities in the small-$x$ and $Q^2$ where saturation effects may play a role. A summary of results on underlying event activity studies based on inclusive $Z$ boson production, charged particle spectra in minimum bias events, and energy density in forward pseudorapidities is presented. These studies provide valuable inputs for Monte Carlo event generator tuning, and test predictions based on perturbative and non-perturbative QCD techniques.

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arXiv2018

PHOTON-2017 conference proceedings

This document collects the proceedings of the PHOTON 2017 conference ("International Conference on the Structure and the Interactions of the Photon", including the 22th "International Workshop on Photon-Photon Collisions", and the "International Workshop on High Energy Photon Colliders") held at CERN (Geneva) in May 2017. The latest experimental and theoretical developments on the topics of the PHOTON conference series are covered: (i) $γ\,γ$ processes in e$^+$e$^-$, proton-proton (pp) and nucleus-nucleus (AA) collisions at current and future colliders, (ii) $γ$-hadron interactions in e$^\pm$p, pp, and AA collisions, (iii) final-state photon production (including Standard Model studies and searches beyond it) in pp and AA collisions, and (iv) high-energy $γ$-ray astrophysics. These proceedings are dedicated to the memory of Maria Krawczyk.

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arXiv2018

Searching for axion-like particles with proton tagging at the LHC

The existence of an axion-like particle (ALP) would induce anomalous scattering of light by light. This process can be probed at the Large Hadron Collider in central exclusive production of photon pairs in proton-proton collisions by tagging the surviving protons using forward proton detectors. Using a detailed simulation, we estimate the expected bounds on the ALP--photon coupling for a wide range of masses. We show that the proposed search is competitive and complementary to other collider bounds for masses above 600 GeV, especially for resonant ALP production between 600 GeV and 2 TeV. Our results are also valid for a CP-even scalar, and the efficiency of the search is independent of the width of the ALP.

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arXiv2017

Anomalous gauge interactions in photon collisions at the LHC and the FCC

The forward proton detectors recently installed and operating at the LHC open the possibility to observe photon collisions with high precision, providing a novel window on physics beyond the Standard Model. We review recent simulations and theoretical developments about the measurement of anomalous $γγγγ$ and $Zγγγ$ interactions. The searches for these anomalous gauge interactions are expected to set bounds on a wide range of particles including generic electroweak particles, neutral particles with dimension-5 coupling to gauge bosons, polarizable dark particles, and are typically complementary from new physics searches in other channels.

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arXiv2017

Probing the anomalous $γγγZ$ coupling at the LHC with proton tagging

The sensitivities to the anomalous quartic gauge boson coupling $γγγZ$ are estimated via $γZ$ production with intact protons in the forward region at the LHC. Proton tagging proves to be a powerful tool to suppress the background, which allows consideration of the hadronic decays of the $Z$ boson in addition to the leptonic ones. We discuss the discovery potential for an integrated luminosity of $300\,\mathrm{fb}^{-1}$ and $3000\,\mathrm{fb}^{-1}$. The sensitivity we obtain at $300\,\mathrm{fb}^{-1}$ goes beyond the one expected from LHC bounds on the $Z\rightarrow γγγ$ decay by about three orders of magnitude. The $γZ$ channel provides important discriminatory information with respect to the exclusive $γγ$ channel, as many particles beyond the Standard Model (such as a radion or Kaluza Klein gravitons) predict a signal in the latter but not the former.

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