Azimuthal Angle Correlations Research Articles

High Transverse Momentum Correlations in STAR

Azimuthal correlations of charged hadrons with transverse momenta above 2 GeV/c are measured relative to ≥ GeV/c trigger particle in p+p and Au+Au at \(\sqrt {s_{NN} } = 200\) GeV in STAR. The correlations exhibit small relative azimuthal angle correlations characteristic of jets. The p+p and peripheral Au+Au data exhibit a peak on the opposite side of the jet indicating the presence of hard scattering in the form of di-jets. The away-side jet disappears for the most central Au+Au collisions, suggesting jet quenching in a dense medium.

QCD corrections to jet correlations in weak boson fusion

Higgs boson production via weak boson fusion is sensitive to the tensor structure of the HVV (V=W,Z) couplings, which distinguishes loop induced vertices from SM expectations. At the CERN large hadron collider this information shows up most clearly in the azimuthal angle correlations of the two forward and backward quark jets which are typical for weak boson fusion. We calculate the next-to-leading order QCD corrections to this process, in the presence of anomalous HVV couplings. Gluon emission does not significantly change the azimuthal jet correlations.

AZIMUTHAL CORRELATION OF SECONDARY PARTICLES FROM 24Mg-NUCLEI COLLISIONS WITH EMULSION AT 4.5A GeV/c

A systematic study and statistically significant results of the different types of correlations, for angles, rapidity and rapidity intervals, between various charged secondary particles and projectile fragments produced in the inelastic interactions of 24 Mg with emulsion at 4.5 A GeV/c have been investigated. All types of particles are found to be emitted asymmetrically in the azimuthal plane. This asymmetry increases with decreasing the impact parameter. The two-particle correlation function is found to be positive except in the extreme projectile fragmentation region. It has also been observed that the particles belonging to the different kinematical regions of the nucleus-nucleus interactions (intergroup correlation) have a tendency to be emitted from opposite sides of the azimuthal plane. The azimuthal angle correlations for pairs of charged secondary particles are also studied.

Medium effects in the production and π0γ decay of ω-mesons in pA collisions in the GeV region

The omega-resonance production and its pi0 gamma decay in p-A reactions close to threshold is considered within the Intranuclear Cascade (INC) Model. The pi0 gamma invariant mass distribution shows two components which correspond to the omega decay 'inside' and 'outside' the nucleus, respectively. The 'inside' component is distorted by medium effects, which introduce a mass shift as well as collisional broadening for the omega-meson and its decaying pion. The relative contribution of the 'inside' component is analyzed in detail for different kinematical conditions and nuclear targets. It is demonstrated that a measurement of the correlation in azimuthal angle between the pi0 and gamma momenta allows to separate events related to the 'inside' omega decay from different sources of background when uncorrelated pi0's and gamma's are produced.

Continuous Evolution from Ferroelectric to Antiferroelectric State in Chiral Smectics

Continuous evolution of polar properties from ferro- to antiferro- has been observed in binary mixtures. Pure components exhibit antiferroelectric or ferroelectric smectic phases. The static dielectric constant in antiferroelectric-like smectic phase increases continuously upon increasing the ferroelectric component concentration. This behavior could be attributed to changes of the strength of azimuthal tilt angle correlations leading to a frustrated state. In materials with frustrated phase ferroelectricity can be enforced by strong boundary conditions in thin cell. The switching behavior found in thin cells was similar to that observed in thresholdless antiferroelectrics.

Formation and deexcitation of the composite nucleus in the Ni + Al reaction at 28 A·MeV

The formation and the deexcitation of the composite nucleus formed during the Ni + Al reaction at 28 A·MeV has been studied with the 4 π multidetector AMPHORA. A rigourous selection of the experimental data is described in order to extract a central collision sample. Then different models are compared to the data. The incomplete fusion process is in agreement with the data. The azimuthal angle correlations of He-Li and Li-Li pairs have been used to discriminate sequential or instantaneous emission. The sequential deexcitation is more consistent with all the data. The different analyses allow to describe all the characteristics of the compound nucleus and finally a fusion cross section of 300 ± 100 mbarn has been measured.

Observation of a Frustrated Phase in Mixtures of Ferroelectric and Antiferroelectric Liquid Crystals

Continuous evolution of polar properties from ferro- to antiferro- has been observed in binary mixtures of compounds having antiferroelectric and ferroelectric phases. The dielectric constant in the antiferroelectriclike smectic phase increases continuously upon increasing the ferroelectric component concentration. The variations of antiferroelectric phase properties could be attributed to changes of the azimuthal tilt angle correlations, which result in frustration between antiferroelectric and ferroelectric interactions and formation of clusters of both phases. A strong difference between dielectric susceptibilities of zero-field-cooled and field-cooled samples was observed in a frustrated phase.

Azimuthal correlation of multifragments of nuclei at GeV

The azimuthal angle correlations in pairs of projectile fragments (PFs) of charge Z = 2 and Z > 2 are studied in the Pb-emulsion interactions at GeV, as a function of their transverse momentum . The correlation strength increases with the centrality of the collision (except at b = 0), and is much larger than the Au data at GeV.

Origin of complex fragments from32S+natAg reaction at 37.5 A·MeV

Fragment emission from collisions of32S withnatAg at 37.5 A·MeV has been studied with the 4π multi-detector AMPHORA. Production of intermediate mass and heavy fragments as well as of light charged particles has been measured. The total charged particle multiplicity and polar angular distributions have been used to select various classes of collisions. Analysis of angular and energy distributions of fragments and light particles in central collisions indicates the formation of a hot source (excitation energy of≈4.4 A·MeV) with an additional contribution from a preequilibrium process at more forward angles. Azimuthal angle correlations of He-Li, Li-Li, B-B, and C-C pairs have been used as a tool to study the origin of complex fragments. Data at backward angles are well described by considering a thermalized emitter with an angular momentum around 70ℏ and a fragment emission time of the order of 200 fm/c. A microscopic approach of BNV type confirms these emission times and angular momenta indicating the persistence of an incomplete fusion process responsible for the emission of complex fragments at backward angles.

Collective-flow correlations in 197Au-emulsion interactions at 10.6 A GeV

We have studied the azimuthal angle correlations in pairs of alpha particles, in Intermediate Mass Fragments (IMFs), and in higher order multiplets observed in 197Au-emulsion interactions at 10.6 A GeV. The correlation functions for higher fragment multiplets (greater than three or more fragments) exhibit characteristic signatures which are enhanced compared to those of two-fragment correlation functions. The pure multiplet contribution is extracted from the observed higher-order correlation functions. The measurements of collective flow correlations in heavy-ion collisions are best obtained by studying several fragments with mixed charges including He fragments.

Study of inclusive baryon-antibaryon pair production ofp orΛ in two-photon processes

Inclusive baryon-antibaryon pair production was studied in two-photon events which were collected at thee + e − collider TRISTAN, and correspond to an integrated luminosity of 303 pb−1. Correlations between a baryon and an antibaryon were studied for their flavors (p orΛ) and their momentum vectors. The experimental results were compared with the expectations from a jet-fragmentation Monte Carlo simulation. We have found that although the ratios of the cross sections of different baryon-flavor combinations are consistent with the Monte Carlo expectations, the cross section shows an excess over the Monte Carlo expectation in a low invariant-mass region of final-state particles at large angles, that indicates a significant contribution from higher-order QCD or non-perturbative effects. The experimental data show no narrow azimuthal-angle correlation, which is expected from a jet-fragmentation Monte Carlo. A search for exclusiveΛ pair production has also been made. We have no candidates and have obtained the upper limit for the cross section.

Dijet production at large rapidity intervals.

We examine dijet production at large rapidity intervals at Tevatron energies, by using the theory of Lipatov and collaborators which resums the leading powers of the rapidity interval. We analyze the growth of the Mueller-Navelet $K$-factor in this context and find it to be negligible. However, we do find a considerable enhancement of jet production at large transverse momenta. In addition, we show that the correlation in transverse momentum and azimuthal angle of the tagging jets fades away as the rapidity interval is increased.

Collective bounce-off phenomenon in139La+Ag(Br) reaction at 1.1 A GeV energy

Out of a total statistics of 896139La+Ag(Br) interactions, 128 interactions having multiplicity of target fragments (Z⩾1)⩾8 and projectile fragments (Z⩾2)⩾4 have been selected. They correspond to quasi-peripheral interactions. Azimuthal angle correlation between sources of target fragments (TFs) and projectile fragments (PFs) shows the existence of bounce-off effect. Using data of La+Ag(Br) and84Kr+Ag(Br) reactions it is shown that individual helium [Z=2, PFs] and heavier fragment [Z⩾3, PFs] show different emission characteristics. Further, a two prong correlation functionT(Φ ij ) plotted for heavier fragments and helium fragments separately, indicates the possibility of existence of different physical conditions. This observation is supported by the different momentum widths of helium fragments and heavier fragments. From the momentum width data of Kr+Ag(Br) reactions normalized density comes out to be ≈4.7. Using quasi-elastic kinematics for the bounce-off nuclei, the excitation energy has been computed from the experimental data of flow angles. The strength of bounce-off seems to decrease with the increase of excitation energy or temperature.

Li-Li azimuthal angular correlations: A test for emission from a rotating source versus instantaneous multifragmentation.

Azimuthal angle correlations have been measured for Li-Li pairs from $^{40}\mathrm{Ar}$ + $^{197}\mathrm{Au}$, $^{\mathrm{nat}}\mathrm{Ag}$, $^{\mathrm{nat}}\mathrm{Cu}$, $^{27}\mathrm{Al}$ (17A, 27A, and 34A MeV). Many of these correlations exhibit enhancements at \ensuremath{\Delta}cphi of 0\ifmmode^\circ\else\textdegree\fi{} and 180\ifmmode^\circ\else\textdegree\fi{}, the classical pattern for evaporation from a hot, high-spin source. A very different pattern is predicted by a simple multifragmentation model, i.e., a peak at \ensuremath{\Delta}cphi\ensuremath{\approxeq}60\ifmmode^\circ\else\textdegree\fi{}. This peak is driven by the rapid Coulomb explosion of a nonrotating nucleus. The latter pattern is not observed experimentally, however, if collective rotation is included in the multifragmentation model, its predictions are more consistent with the observations. Such comparisons can give a promising test for sequential emission from a rotating source versus instantaneous explosive multifragmentation, but one needs a very good selection of collision centrality to reduce the role of the collective rotation. For most of these data the dominant driving forces seem to be rotational motion perturbed by final-state Coulomb repulsions for time delays of the order of ${10}^{\mathrm{\ensuremath{-}}22}$ s between successive emissions of Li fragments.

Resolving minijets in the minimum-biased events of hadronic interactions.

We propose and demonstrate that the ${p}_{T}$ dependence of two-particle correlation functions can be utilized to study the minijet contribution to particle production in minimum-biased events of high-energy hadronic interactions, especially when the transverse momenta of these minijets are lower than allowed by the current cluster-finding method of identifying minijets. Two-particle correlations both in azimuthal angle $\ensuremath{\varphi}$ and pseudorapidity $\ensuremath{\eta}$ are studied and the effects of a limited rapidity cut are investigated.

Azimuthal correlations between charmed particles produced in 230 GeV/ c π −Cu interactions

In the CERN NA32 experiment a high-resolution silicon vertex detector and a purely topological approach were used to collect 642 events with two or more secondary vertices. They are consistent with double production of charm. Azimuthal angle correlations are studied for D 0, D +, D s + and Λ c +; we also investigate these correlations as a function of the number of leading D mesons.

First observation of correlations between high transverse momentum charged particles in events from the CERN proton-antiproton collider

In events at centre of mass energy 540 GeV from the CERN p p collider, we have found clear evidence for correlations in rapidity and azimuthal angle between high transverse momentum charged particles. These correlations increase with transverse momentum and are much stronger than the general two-particle correlations in minimum bias events. By analogy to ISR results, a qualitative interpretation in terms of hard scattering and fragmentation of partons is discussed.

Comment on the CERN ISRπ0−π0azimuthal correlation data

The ..pi../sup 0/-..pi../sup 0/ azimuthal-angle distributions measured at CERN ISR are described in terms of standard large-p/sub perpendicular/ two-jet and three-jet contributions in combination with a background obtained by superimposing two uncorrelated ..pi../sup 0/ spectra (one at high p/sub perpendicular/, the other at low p/sub perpendicular/). The main characteristics of the data can be fitted surprisingly well by a simple analytic expression. We emphasize the importance of having azimuthal-angle correlation data at higher values of the transverse-momentum cut.

Signals for Tau neutrino interactions in a beam dump experiment

We propose a test which can be used in beam dump experiments to observe, for the first time, the sequential neutrino ν τ associated with the tau; lepton. The test relies on the ability of new detectors to measure the direction of the hadron spray and hence test for missing transverse momentum and determine certain azimuthal angle correlations.

Characteristics of possible neutral-heavy-lepton production in muon reactions

We study the production of a neutral heavy lepton by an incident muon via the reaction ${\ensuremath{\mu}}^{\ifmmode\pm\else\textpm\fi{}}+N\ensuremath{\rightarrow}{\stackrel{(\ifmmode\bar\else\textasciimacron\fi{})}{M}}^{0}+X$ followed by the decay ${\stackrel{(\ifmmode\bar\else\textasciimacron\fi{})}{M}}^{0}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{\ensuremath{-}}{\ensuremath{\mu}}^{+}\ensuremath{\cdots}$. We analyze the experimentally observable characteristics of the resulting dimuon pair and present distributions in final-muon energy, hadron energy, total visible energy, muon transverse momenta, and dimuon invariant-mass and azimuthal-angle correlations. On the basis of this study we formulate a set of cuts and tests which can be used to search for the dimuon signal from the ${\stackrel{(\ifmmode\bar\else\textasciimacron\fi{})}{M}}^{0}$. The main features of various backgrounds are briefly discussed from the viewpoint of discriminating between them and the ${\stackrel{(\ifmmode\bar\else\textasciimacron\fi{})}{M}}^{0}$ signal. Our analysis is directly applicable to a current muon experiment being conducted by a Berkeley-Fermilab-Princeton collaboration.