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Joakim Nystrand

Publications and source records attributed to Joakim Nystrand.

At least 19 recordsLinked to original sources
arXiv2023

Bremsstrahlung as a probe of baryon stopping in heavy-ion collisions

In collisions between heavy ions at ultra-relativistic energies the participating protons lose energy, which is converted into new particles. As the protons slow down, they emit bremsstrahlung radiation. The yield and angular distribution of the emitted radiation are sensitive probes of how much energy the incoming protons have lost. In this paper, the spectrum of bremsstrahlung radiation is calculated for different stopping scenarios, and the results are compared with the expected yield of photons from hadronic interactions.

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arXiv2022

Vector meson photoproduction in UPCs with FoCal

We discuss the physics prospects of photon-induced measurements using the high-granularity FoCal detector to be installed at the ALICE experiment, covering the pseudorapidity interval $3.4 \leq η\leq 5.8$. This new detector, scheduled to be in operation from Run 4, will explore the small Bjorken-$x$ physics region in an unprecedented way. In this region the gluon saturation phenomenon is expected to be dominant. Combined with the rest of the ALICE subdetectors, including the zero degree calorimenters, FoCal will serve to reconstruct in a model-independent way the measured photoproduction cross sections for vectors mesons in a wide range of photon-target energies, down to $x$ values of about $7\times 10^{-6}$ and $2\times 10^{-6}$ in ultra-peripheral photon--proton and photon--lead collisions, respectively.

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arXiv2020

New opportunities at the photon energy frontier

Ultra-peripheral collisions (UPCs) involving heavy ions and protons are the energy frontier for photon-mediated interactions. UPC photons can be used for many purposes, including probing low-$x$ gluons via photoproduction of dijets and vector mesons, probes of beyond-standard-model processes, such as those enabled by light-by-light scattering, and studies of two-photon production of the Higgs.

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arXiv2016

STARlight: A Monte Carlo simulation program for ultra-peripheral collisions of relativistic ions

Ultra-peripheral collisions (UPCs) have been a significant source of study at RHIC and the LHC. In these collisions, the two colliding nuclei interact electromagnetically, via two-photon or photonuclear interactions, but not hadronically; they effectively miss each other. Photonuclear interactions produce vector meson states or more general photonuclear final states, while two-photon interactions can produce lepton or meson pairs, or single mesons. In these interactions, the collision geometry plays a major role. We present a program, STARlight, that calculates the cross-sections for a variety of UPC final states and also creates, via Monte Carlo simulation, events for use in determining detector efficiency.

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arXiv2014

Photonuclear production of vector mesons in ultra-peripheral Pb-Pb collisions at the LHC

Vector mesons are copiously produced in ultra-peripheral nucleus-nucleus collisions. In these collisions, the nuclei are separated by impact parameters larger than the sum of the nuclear radii, and the interaction is mediated by the electromagnetic field. The interaction effectively corresponds to a photonuclear interaction between a photon, generated from the electromagnetic field of one of the nuclei, and the target nucleus. The ALICE Collaboration has previously published results on exclusive J/psi photoproduction at mid and forward rapidities in Pb-Pb collisions. The cross section for this process is a particularly good measure of the nuclear gluon distribution. In this talk, the latest results on exclusive production of light and heavy vector mesons from ALICE in Pb-Pb collisions will be presented.

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arXiv2013

Photonuclear vector meson production in ultra-peripheral Pb-Pb collisions studied by the ALICE experiment at the LHC

The strong electromagnetic fields surrounding the Pb-ions accelerated at the CERN Large Hadron Collider (LHC) allow two-photon and photonuclear interactions to be studied in a so far unexplored kinematic regime. Exclusive photoproduction of vector mesons can be studied in ultra-peripheral collisions, where the impact parameters are larger than the sum of the nuclear radii and hadronic interactions are strongly suppressed. During the heavy-ion runs at the LHC in 2010 and 2011, the ALICE collaboration used special triggers to select ultra-peripheral collisions. These triggers were based on the Muon spectrometer, the Time-of-Flight detector, the Silicon Pixel detector, and the VZERO scintillator array. Information from other detectors was also used in the analysis. The cross section for coherent photoproduction of J/Psi mesons at forward rapidities will be presented. The result will be compared to model calculations and its implications for nuclear gluon shadowing will be discussed.

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arXiv2011

Single and Double Photonuclear Excitations in Pb+Pb Collisions at sqrt(s_NN) = 2.76 TeV at the CERN Large Hadron Collider

Cross sections are calculated for single and double photon exchange in ultraperipheral Pb+Pb collisions at the LHC. The particle production is simulated with the DPMJET event generator. Large cross sections are found for particle production around mid-rapidity making these processes an important background to hadronic nuclear interactions at both the trigger and analysis levels.

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arXiv2010

Higher order QED in high mass e+ e- pairs production at RHIC

Lowest order and higher order QED calculations have been carried out for the RHIC high mass e+ e- pairs observed by PHENIX with single ZDC triggers. The lowest order QED results for the experimental acceptance are about two standard deviations larger than the PHENIX data. Corresponding higher order QED calculations are within one standard deviation of the data.

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arXiv2010

Photons and Exclusive Processes at Hadron Colliders

The theoretical and experimental aspects of particle production from the strong equivalent photon fluxes present at high energy hadron colliders are reviewed. The goal is to show how photons at hadron colliders can improve what we have learnt from experiments with lepton beams. Experiments during the last 5-10 years have shown the feasibility of studying photoproduction in proton-proton and heavy-ion collisions. The experimental and theoretical development has revealed new opportunities as well as challenges.

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arXiv2009

Two-Photon Interactions with Nuclear Breakup in Relativistic Heavy Ion Collisions

Highly charged relativistic heavy ions have high cross-sections for two-photon interactions. The photon flux is high enough that two-photon interactions may be accompanied by additional photonuclear interactions. Except for the shared impact parameter, these interactions are independent. Additional interactions like mutual Coulomb excitation are of experimental interest, since the neutrons from the nuclear dissociation provide a simple, relatively unbiased trigger. We calculate the cross sections, rapidity, mass and transverse momentum ($p_T)$ distributions for exclusive $γγ$ production of mesons and lepton pairs, and for $γγ$ reactions accompanied by mutual Coulomb dissociation. The cross-sections for $γγ$ interactions accompanied by multiple neutron emission ($XnXn$) and single neutron emission ($1n1n$) are about 1/10 and 1/100 of that for the unaccompanied $γγ$ interactions. We discuss the accuracy with which these cross-sections may be calculated. The typical $p_T$ of $γγ$ final states is several times smaller than for comparable coherent photonuclear interactions, so $p_T$ may be an effective tool for separating the two classes of interactions.

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arXiv2008

Photoproduction in Ultra-Peripheral Heavy-Ion Collisions

The strong electromagnetic fields present in ultra-peripheral collisions of heavy-ions offer a possibility to study two-photon and photonuclear collisions complementary to similar studies with lepton beams but over an increased photon energy range. This presentation will give an overview of photoproduction at hadron colliders.

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arXiv2008

Ultra-Peripheral Collisions at RHIC

This presentation summarizes the results on ultra-peripheral collisions obtained at RHIC. It also discusses some aspects of the corresponding electromagnetic interactions in pp and pbarp collisions.

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arXiv2006

Ultra-peripheral collisions of heavy ions at RHIC and the LHC

This paper deals with so-called Ultra-Peripheral Collisions (UPCs) of heavy ions. These can be defined as collisions in which no hadronic interactions occur because of the large spatial separation between the projectile and target. The interactions are instead mediated by the electromagnetic field. Two types of ultra-peripheral collisions can be distinguished: purely electro-magnetic interactions (two-photon interactions) and photonuclear interactions, in which a photon from the projectile interacts with the hadronic component of the target.

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arXiv2005

Physics of Ultra-Peripheral Nuclear Collisions

Moving highly-charged ions carry strong electromagnetic fields that act as a field of photons. In collisions at large impact parameters, hadronic interactions are not possible, and the ions interact through photon-ion and photon-photon collisions known as {\it ultra-peripheral collisions} (UPC). Hadron colliders like the Relativistic Heavy Ion Collider (RHIC), the Tevatron and the Large Hadron Collider (LHC) produce photonuclear and two-photon interactions at luminosities and energies beyond that accessible elsewhere; the LHC will reach a $γp$ energy ten times that of the Hadron-Electron Ring Accelerator (HERA). Reactions as diverse as the production of anti-hydrogen, photoproduction of the $ρ^0$, transmutation of lead into bismuth and excitation of collective nuclear resonances have already been studied. At the LHC, UPCs can study many types of `new physics.'

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arXiv2005

Photoproduction of Heavy Vector Mesons at the LHC

The strong electromagnetic fields associated with high energy protons and nuclei may lead to exclusive photoproduction of vector mesons in proton-proton and nucleus-nucleus collisions at the LHC. This paper will discuss the expected cross sections and rapidity and transverse momentum distributions.

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arXiv2003

Photoproduction of Quarkonium in Proton-Proton and Nucleus-Nucleus Collisions

We discuss the photoproduction of $Υ$ and $J/ψ$ at high energy $\bar{p}p$, $pp$ and heavy ion colliders. We predict large rates in $\bar{p}p$ interactions at the Fermilab Tevatron %and in heavy-ion interactions at the CERN LHC. These reactions can be and in $pp$ and heavy-ion interactions at the CERN LHC. The $J/ψ$ is also produced copiously at RHIC. These reactions can be used to study the gluon distribution in protons and heavy nuclei. We also show that the different CP symmetries of the initial states lead to large differences in the transverse momentum spectra of mesons

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