Searcharxiv⌕ Search

arXiv subjects

Joakim Nystrand

Publications and source records attributed to Joakim Nystrand.

29 records · Page 2Linked to original sources
arXiv2003

Photoproduction of $J/ψ$ and $Υ$ in pp and $\bar{p}p$ Collisions

Exclusive vector meson photoproduction, $pp\to ppV$ and $\bar pp\to\bar ppV$ occurs with significant rates at hadron colliders. The reaction can be used to study the gluon distribution of protons. Vector mesons may be produced with either proton as a target; because of interference between the two production channels, the $p_T$ spectra of vector mesons produced in $pp$ and $\bar pp$ collisions are quite different. Because of the unique event signature, vector meson photoproduction can be separated from hadroproduction events, despite the small ratio of cross sections. We consider production of $J/ψ$ and $Υ$ at RHIC, the Tevatron and the LHC.

hep-ph↗
arXiv2003

Does particle decay cause wave function collapse: An experimental test

We describe an experimental test of whether particle decay causes wave function collapse. The test uses interference between two well separated, but coherent, sources of vector mesons. The short-lived mesons decay before their wave functions can overlap, so any interference must involve identical final states. Unlike previous tests of nonlocality, the interference involves continuous variables, momentum and position. Interference can only occur if the wave function retains amplitudes for all possible decays. The interference can be studied through the transverse momentum spectrum of the reconstructed mesons.

quant-ph↗
arXiv2002

Heavy Quark Photoproduction in Ultra-peripheral Heavy Ion Collisions

Heavy quarks are copiously produced in ultra-peripheral heavy ion collisions. In the strong electromagnetic fields, c c-bar and b b-bar are produced by photonuclear and two-photon interactions; hadroproduction can occur in grazing interactions. We present the total cross sections, quark transverse momentum and rapidity distributions, as well as the Q Q-bar invariant mass spectra from the three production channels. We consider AA and pA collisions at the Relativistic Heavy Ion Collider and Large Hadron Collider. We discuss techniques for separating the three processes and describe how the AA to pA production ratios might be measured accurately enough to study nuclear shadowing.

hep-ph↗
arXiv2002

Coherent Vector Meson Photoproduction with Nuclear Breakup in Relativistic Heavy Ion Collisions

Relativistic heavy ions are copious sources of virtual photons. The large photon flux gives rise to a substantial photonuclear interaction probability at impact parameters where no hadronic interactions can occur. Multiple photonuclear interactions in a single collision are possible. In this letter, we use mutual Coulomb excitation of both nuclei as a tag for moderate impact parameter collisions. We calculate the cross section for coherent vector meson production accompanied by mutual excitation, and show that the median impact parameter is much smaller than for untagged production. The vector meson rapidity and transverse momentum distribution are very different from untagged exclusive vector meson production.

nucl-th↗
arXiv2002

Aspects of Coulomb Dissociation and Interference in Peripheral Nucleus-Nucleus Collisions

Coherent vector meson production in peripheral nucleus-nucleus collisions is discussed. These interactions may occur for impact parameters much larger than the sum of the nuclear radii. Since the vector meson production is always localized to one of the nuclei, the system acts as a two-source interferometer in the transverse plane. By tagging the outgoing nuclei for Coulomb dissociation it is possible to obtain a measure of the impact parameter and thus the source separation in the interferometer. This is of particular interest since the life-time of the vector mesons are generally much shorter than the impact parameters of the collisions.

nucl-th↗
arXiv2001

Coherent Interactions in Nucleus-Nucleus Collisions

At the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory and at the Large Hadron Collider (LHC) at CERN, particles will be produced in coherent and diffractive nuclear interactions. In extremely peripheral nuclear collisions (b$>$2R), coherent interactions occur at very high rates and are dominated by photon-Pomeron or photon-meson processes. In these reactions, the photon and the Pomeron/meson from the electromagnetic and nuclear fields couple coherently to all nucleons. The rates for photonuclear interactions are roughly two orders of magnitude larger than for two-photon interactions at comparable center-of-mass energies.

nucl-th↗
arXiv2001

Photoproduction of top in peripheral heavy ion collisions

In relativistic heavy ion collisions, top quarks can be produced by photon-gluon fusion when a photon from the Weizsäcker-Williams virtual photon field of one nucleus interacts with a gluon in the other nucleus. Photoproduction with heavy ions at the Large Hadron Collider (LHC) will be the first accessible non-hadronic top production channel. We calculate the $t \bar t$ photoproduction cross sections, pair mass and top quark rapidity distributions in peripheral heavy ion collisions. The cross sections are sensitive to the top quark charge and the large-$Q^2$ gluon distribution in the nucleus. We find a cross section of 94 pb in calcium-calcium collisions, leading to 190 pairs in a one month ($10^6$ sec) LHC run. We also find $p$Pb and $p$Ca cross sections of 5.8 and 3.4 pb respectively, resulting in 6 and 34 $t\bar t$ pairs per month.

hep-ph↗
arXiv1999

Interference in Exclusive Vector Meson Production in Heavy Ion Collisions

Photons emitted from the electromagnetic fields of relativistic heavy ions can fluctuate into quark anti-quark pairs and scatter from a target nucleus, emerging as vector mesons. These coherent interactions are identifiable by final states consisting of the two nuclei and a vector meson with a small transverse momentum. The emitters and targets can switch roles, and the two possibilities are indistinguishable, so interference may occur. Vector mesons are negative parity so the amplitudes have opposite signs. When the meson transverse wavelength is larger than the impact parameter, the interference is large and destructive. The short-lived vector mesons decay before amplitudes from the two sources can overlap, and so cannot interfere directly. However, the decay products are emitted in an entangled state, and the interference depends on observing the complete final state. The non-local wave function is an example of the Einstein-Podolsky-Rosen paradox.

hep-ph↗
arXiv1999

Exclusive Vector Meson Production in Relativistic Heavy Ion Collisions

Exclusive vector meson production reactions such as $Au + Au \to Au + Au + V$, where $V=ρ, ω, ϕ$ or $J/ψ$ can proceed through photon-Pomeron and photon-meson interactions. Photons from the electromagnetic field of one nucleus interact coherently with the other nucleus. Photonuclear cross sections are scaled from $γp$ data, and convoluted with the photon spectrum to find the exclusive rates. The cross sections at the RHIC and LHC heavy ion colliders are huge, 10% of the total hadronic cross section at RHIC, and 50% at LHC. These accelerators may be useful as vector meson factories. With iodine beams at RHIC, 640 $ρ$ are produced each second (10^{10}/year); with calcium at the LHC the rate is 240 kHz. The $ϕ$ rates are 39 Hz at RHIC and 15 kHz at LHC, while the $J/ψ$ rate is 0.3 Hz at RHIC and 780 Hz at the LHC. Because of the coherent couplings, the reactions kinematics are similar to coherent two-photon interactions; we discuss the interplay between the two reactions.

hep-ph↗
arXiv1998

Two-Photon Physics in Nucleus-Nucleus Collisions at RHIC

Ultra-relativistic heavy-ions carry strong electromagnetic and nuclear fields. Interactions between these fields in peripheral nucleus-nucleus collisions can probe many interesting physics topics. This presentation will focus on coherent two-photon and photonuclear processes at RHIC. The rates for these interactions will be high. The coherent coupling of all the protons in the nucleus enhances the equivalent photon flux by a factor Z^2 up to an energy of ~3 GeV. The plans for studying coherent interactions with the STAR experiment will be discussed. Experimental techniques for separating signal from background will be presented.

nucl-ex↗