arXiv subjects

A. Penzo

Publications and source records attributed to A. Penzo.

15 recordsLinked to original sources

arXiv2025

PREFACE: A search for long-lived particles at the Large Hadron Collider

The Standard Model (SM) fails to explain many problems (neutrino masses, dark matter, and matter-antimatter asymmetry, among others) that may be resolved with new particles beyond the Standard model (BSM). The fact that such new particles are not yet observed may be explained either by their too high mass or by very small coupling to SM particles. The latter case implies long lifetimes. Such long-lived particles (LLPs) would have signatures different from those of SM particles. Searches in the "central region" are covered by the LHC general purpose experiments. The forward small angle region far from the interaction point (IP) is unexplored. Such particles would have large energy $E$ = $\mathcal{O}$(1~TeV) and Lorentz time dilation factor $γ= E/m \approx 10^2 - 10^{3}$, hence long decay distances. A new class of specialized LHC detectors dedicated to LLP searches has been proposed for the forward regions. Among these experiments, FASER is already operational, and FACET is under consideration at a location 100 meters from IP5 (the CMS intersection). However, some features of FACET require a specially enlarged beam pipe, which cannot be implemented for Run 4. In this study, we explore a simplified version of the proposed detector, PREFACE, compatible with the standard LHC beam pipe in the HL-LHC in Run 4. Realistic Geant4 simulations are performed and the background is evaluated. A preliminary analysis of the physics potential with the PREFACE geometry indicates that several significant channels could be accessible with sensitivities comparable to FACET and other LLP searches.

hep-ex↗

arXiv2024

The π^+π^- Coulomb interaction study and its use in the data processing

In this work the Coulomb effects (Coulomb correlations) in $π^+π^-$ pairs produced in p + Ni collisions at 24 GeV/$c$, are studied using experimental $π^+π^-$ pair distributions in $Q$, the relative momentum in the pair center of mass system (c.m.s), and its projections $Q_L$ (longitudinal component) and $Q_t$ (transverse component) relative to the pair direction in the laboratory system (l.s.). The $Q$, $Q_L$, and $Q_t$ distributions of the {\sl Coulomb pairs} in the c.m.s. have been simulated assuming they are described by the phase space modified by the known point-like Coulomb correlation function $A_C(Q)$, corrected for small effects due to the nonpoint-like pair production and the strong two-pion interaction. The same distributions of {\sl non-Coulomb pairs} have been simulated according to the phase space, but without $A_C(Q)$. It is shown that the number of {\sl Coulomb pairs} in all $Q_t$ intervals, including the small $Q_t$ (small opening angles $θ$ in the l.s.) is calculated with the theoretical precision better than 2\%. The comparison of the simulated and experimental numbers of {\sl Coulomb pairs} at small $Q_t$ allows us to check and correct the detection efficiency for the pairs with small $θ$ (0.06 mrad and smaller). It is shown that {\sl Coulomb pairs} can be used as a new physical tool to check and correct the quality of the simulated events. The special property of the {\sl Coulomb pairs} is the possibility of checking and correcting the detection efficiency, especially for the pairs with small opening angles.

hep-ph↗

arXiv2022

FACET: A new long-lived particle detector in the very forward region of the CMS experiment

We describe a proposal to add a set of very forward detectors to the CMS experiment for the high-luminosity era of the Large Hadron Collider to search for beyond the standard model long-lived particles, such as dark photons, heavy neutral leptons, axion-like particles, and dark Higgs bosons. The proposed subsystem is called FACET for Forward-Aperture CMS ExTension, and will be sensitive to any particles that can penetrate at least 50 m of magnetized iron and decay in an 18 m long, 1 m diameter vacuum pipe. The decay products will be measured in detectors using identical technology to the planned CMS Phase-2 upgrade.

hep-ex↗

arXiv2022

Investigation of $K^+K^-$ pairs in the effective mass region near $2m_K$

The DIRAC experiment at CERN investigated in the reaction $\rm{p}(24~\rm{GeV}/c) + Ni$ the particle pairs $K^+K^-, π^+ π^-$ and $p \bar{p}$ with relative momentum $Q$ in the pair system less than 100 MeV/c. Because of background influence studies, DIRAC explored three subsamples of $K^+K^-$ pairs, obtained by subtracting -- using time-of-flight (TOF) technique -- background from initial $Q$ distributions with $K^+K^-$ sample fractions more than 70\%, 50\% and 30\%. The corresponding pair distributions in $Q$ and in its longitudinal projection $Q_L$ were analyzed first in a Coulomb model, which takes into account only Coulomb final state interaction (FSI) and assuming point-like pair production. This Coulomb model analysis leads to a $K^+K^-$ yield increase of about four at $Q_L=0.5$ MeV/c compared to 100 MeV/c. In order to study contributions from strong interaction, a second more sophisticated model was applied, considering besides Coulomb FSI also strong FSI via the resonances $f_0(980)$ and $a_0(980)$ and a variable distance $r^*$ between the produced $K$ mesons. This analysis was based on three different parameter sets for the pair production. For the 70\% subsample and with best parameters, $3680\pm 370$ $K^+K^-$ pairs was found to be compared to $3900\pm 410$ $K^+K^-$ extracted by means of the Coulomb model. Knowing the efficiency of the TOF cut for background suppression, the total number of detected $K^+K^-$ pairs was evaluated to be around $40000\pm 10\%$, which agrees with the result from the 30\% subsample. The $K^+K^-$ pair number in the 50\% subsample differs from the two other values by about three standard deviations, confirming -- as discussed in the paper -- that experimental data in this subsample is less reliable.

hep-ex↗

arXiv2018

First measurement of a long-lived $π^+ π^-$ atom lifetime

The adapted DIRAC experiment at the CERN PS accelerator observed for the first time long-lived hydrogen-like $π^+π^-$ atoms, produced by protons hitting a beryllium target. A part of these atoms crossed the gap of 96~mm and got broken up in the 2.1~\textmu{}m thick platinum foil. Analysing the observed number of atomic pairs, $n_A^L= \left.436^{+157}_{-61}\right|_\mathrm{tot}$, the lifetime of the 2$p$ state is found to be ${τ_{2p}=(\left.0.45^{+1.08}_{-0.30}\right|_\mathrm{tot}) \cdot10^{-11}}$s, not contradicting the corresponding QED $2p$ state lifetime ${τ_{2p}^\mathrm{QED}=1.17 \cdot 10^{-11}}$s. This lifetime value is three orders of magnitude larger than our previously measured value of the $π^+π^-$ atom ground state lifetime $τ=(\left.3.15^{+0.28}_{-0.26}\right|_\mathrm{tot})\cdot 10^{-15}$s. Further studies of long-lived $π^+π^-$ atoms will allow to measure energy differences between $p$ and $s$ atomic states and so to determine $ππ$ scattering lengths with the aim to check QCD predictions.

hep-ex↗

arXiv2017

Measurement of the $πK$ atom lifetime and the $πK$ scattering length

After having announced the statistically significant observation (5.6~$σ$) of the new exotic $πK$ atom, the DIRAC experiment at the CERN proton synchrotron presents the measurement of the corresponding atom lifetime, based on the full $πK$ data sample: $τ= (5.5^{+5.0}_{-2.8}) \cdot 10^{-15}s$. By means of a precise relation ($<1\%$) between atom lifetime and scattering length, the following value for the S-wave isospin-odd $πK$ scattering length $a_0^{-}~=~\frac{1}{3}(a_{1/2}-a_{3/2})$ has been derived: $\left|a_0^-\right| = (0.072^{+0.031}_{-0.020}) M_π^{-1}$.

hep-ex↗

arXiv2015

The transverse momentum dependence of charged kaon Bose-Einstein correlations in the SELEX experiment

We report on the measurement of the one-dimensional charged kaon correlation functions using 600~GeV/{\it c} $Σ^-$, $π^-$ and 540~GeV/{\it c} $p$ beams from the SELEX~(E781) experiment at the Fermilab Tevatron. $K^{\pm}K^{\pm}$ correlation functions are studied for three transverse pair momentum, $k_T$, ranges and parameterized by a Gaussian form. The emission source radii, $R$, and the correlation strength, $λ$, are extracted. The analysis shows a decrease of the source radii with increasing kaon transverse pair momentum for all beam types.

hep-ex↗

arXiv2014

Measurement of Charged Pion Production Yields off the NuMI Target

The fixed-target MIPP experiment, Fermilab E907, was designed to measure the production of hadrons from the collisions of hadrons of momenta ranging from 5 to 120 GeV/c on a variety of nuclei. These data will generally improve the simulation of particle detectors and predictions of particle beam fluxes at accelerators. The spectrometer momentum resolution is between 3 and 4%, and particle identification is performed for particles ranging between 0.3 and 80 GeV/c using $dE/dx$, time-of-flight and Cherenkov radiation measurements. MIPP collected $1.42 \times10^6$ events of 120 GeV Main Injector protons striking a target used in the NuMI facility at Fermilab. The data have been analyzed and we present here charged pion yields per proton-on-target determined in bins of longitudinal and transverse momentum between 0.5 and 80 GeV/c, with combined statistical and systematic relative uncertainties between 5 and 10%.

hep-ex↗

arXiv2014

First $πK$ atom lifetime and $πK$ scattering length measurements

The results of a search for hydrogen-like atoms consisting of $π^{\mp}K^{\pm}$ mesons are presented. Evidence for $πK$ atom production by 24 GeV/c protons from CERN PS interacting with a nickel target has been seen in terms of characteristic $πK$ pairs from their breakup in the same target ($178 \pm 49$) and from Coulomb final state interaction ($653 \pm 42$). Using these results the analysis yields a first value for the $πK$ atom lifetime of $τ=(2.5_{-1.8}^{+3.0})$ fs and a first model-independent measurement of the S-wave isospin-odd $πK$ scattering length $\left|a_0^-\right|=\frac{1}{3}\left|a_{1/2}-a_{3/2}\right|= \left(0.11_{-0.04}^{+0.09} \right)M_π^{-1}$ ($a_I$ for isospin $I$).

nucl-ex↗

arXiv2011

Determination of $ππ$ scattering lengths from measurement of $π^+π^-$ atom lifetime

The DIRAC experiment at CERN has achieved a sizeable production of $π^+π^-$ atoms and has significantly improved the precision on its lifetime determination. From a sample of 21227 atomic pairs, a 4% measurement of the S-wave $ππ$ scattering length difference $|a_0-a_2| = (.0.2533^{+0.0080}_{-0.0078}|_\mathrm{stat}.{}^{+0.0078}_{-0.0073}|_\mathrm{syst})M_{π^+}^{-1}$ has been attained, providing an important test of Chiral Perturbation Theory.

hep-ex↗

arXiv2010

Forward Neutron Production at the Fermilab Main Injector

We have measured cross sections for forward neutron production from a variety of targets using proton beams from the Fermilab Main Injector. Measurements were performed for proton beam momenta of 58 GeV/c, 84 GeV/c, and 120 GeV/c. The cross section dependence on the atomic weight (A) of the targets was found to vary as $A^(alpha)$ where $α$ is $0.46\pm0.06$ for a beam momentum of 58 GeV/c and 0.54$\pm$0.05 for 120 GeV/c. The cross sections show reasonable agreement with FLUKA and DPMJET Monte Carlos. Comparisons have also been made with the LAQGSM Monte Carlo.

hep-ex↗

arXiv2010

Charged Kaon Mass Measurement using the Cherenkov Effect

The two most recent and precise measurements of the charged kaon mass use X-rays from kaonic atoms and report uncertainties of 14 ppm and 22 ppm yet differ from each other by 122 ppm. We describe the possibility of an independent mass measurement using the measurement of Cherenkov light from a narrow-band beam of kaons, pions, and protons. This technique was demonstrated using data taken opportunistically by the Main Injector Particle Production experiment at Fermi National Accelerator Laboratory which recorded beams of protons, kaons, and pions ranging in momentum from +37 GeV/c to +63 GeV/c. The measured value is 491.3 +/- 1.7 MeV/c^2, which is within 1.4 sigma of the world average. An improvement of two orders of magnitude in precision would make this technique useful for resolving the ambiguity in the X-ray data and may be achievable in a dedicated experiment.

hep-ex↗

arXiv2009

Evidence for $πK$-atoms with DIRAC

We present evidence for the first observation of electromagnetically bound $π^\pm K^\mp$-pairs ($πK$-atoms) with the DIRAC experiment at the CERN-PS. The $πK$-atoms are produced by the 24 GeV/c proton beam in a thin Pt-target and the $π^\pm$ and $K^\mp$-mesons from the atom dissociation are analyzed in a two-arm magnetic spectrometer. The observed enhancement at low relative momentum corresponds to the production of 173 $\pm$ 54 $πK$-atoms. The mean life of $πK$-atoms is related to the s-wave $πK$-scattering lengths, the measurement of which is the goal of the experiment. From these first data we derive a lower limit for the mean life of 0.8 fs at 90% confidence level.

hep-ex↗

arXiv2002

The "miniskirt" counter array at CDF-II

As a part of the CDF Upgrade for Run-II of the Tevatron collider, the azimuthal coverage of the muon detectors between pseudorapidities of 0.6 and 1.2 was completed by the insertion of stacks of drift chambers and scintillation counters, which came to be known as the "miniskirts" because they cover lower 90^o in azimuth. The design and construction of the miniskirts was rather complex and posed special problems because of its interference with the floor and the supports of the central detector. The original design parameters of the "miniskirt" scintillator counters for the CDF Muon System are presented and the modifications, testing and installation of these counters in the course of the CDF Upgrade Project are described in detail

hep-ex↗

arXiv1998

Perspectives for Direct CP Violation Tests in Hyperon Decays

We discuss the perspectives of measuring direct CP violation parameters in hyperon decays by measurements with proton and/or antiproton beams, to be carried out at various facilities, and in particular we propose new experiments at the Tevatron and at the LHC.

hep-ph↗