Hanbury Brown-Twiss Correlations Research Articles

Identified charged hadron production in Pb-Pb collisions at $$\sqrt {s_{NN} } = 2.76$$ TeV with the ALICE experiment at the LHC

Quark Gluon Plasma (QGP) is an unavoidable consequence of Quantum Chromodynamics (QCD). High-energy heavy-ion collisions offer the unique possibility to reproduce in the laboratory the conditions expected during the very first stages of the evolution of the Universe. The ALICE (A Large Ion Collider Experiment) experiment at the Large Hadron Collider (LHC) allows the study of the dense nuclear environment created in nucleus-nucleus collisions. Particle Identification (PID) is one of the key features of the ALICE experiment. Identified particle spectra represent a crucial tool to understand the behaviour of the matter created in high-energy heavy-ion collisions. The transverse momentum p T distributions of identified hadrons contain information about the transverse expansion of the system and constrain the freeze-out properties of the system. Hydrodynamic models have proved to be very successful reproducing a large number of features of heavy-ion collisions (e.g., particle p T distributions, radial flow, elliptic flow, Hanbury Brown-Twiss correlations, ...). The measurement of the p T distributions of identified π, K and p in Pb-Pb collisions at $$\sqrt {s_{NN} } = 2.76$$ TeV is presented and discussed in terms of hydrodynamics. The V0 detector allows the selection of events based on the eccentricity of the collision (related with the initial geometry). This makes possible the study of the correlation between the p T distribution of hadrons and elliptic flow on an event-by-event basis. Hadron abundances can be obtained from the principle of maximum entropy using statistical concepts. This allows the extrapolation of the chemical freeze-out parameters from the data. Over the last years it has been proved that the chemical freeze-out temperature T ch is connected with the phase transition temperature T C . The measurements of the freeze-out parameters at the LHC energies are described in detail and the results obtained by various groups at lower energies are extended with the inclusion of the LHC measurement. The LHC measurements cast a new light upon the hydrodynamic and thermal behaviour of the hadron production in heavy-ion collisions. The possible scenarios are described and commented.

Fluctuations of pion elliptic flow, triangular flow, and HBT correlation functions in ultrarelativistic heavy ion collisions

We investigate the fluctuations of pion elliptic flow, triangular flow, and Hanbury-Brown–Twiss (HBT) correlation functions for the hydrodynamic sources with fluctuating initial conditions in the heavy ion collisions of Au–Au at GeV and Pb–Pb at TeV. A method based on event-subcollection analysis is used to detect these fluctuations in ultrarelativistic heavy ion collisions. We introduce a granularity length to describe the granular inhomogeneity of the initial sources, and investigate its relationships with the fluctuations of the flow harmonics and HBT correlation functions. Our investigations indicate that the fluctuations of the triangular flow of event subcollections are sensitive to the granularity length of the initial source. This dependence provides a way to investigate the granular inhomogeneity of the initial source through analysing the fluctuations of triangular flow in ultrarelativistic heavy ion collisions.

Twisted emission geometry in noncentral Pb + Pb collisions measurable via azimuthally sensitive Hanbury-Brown–Twiss correlations

We use the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) model to simulate Pb+Pb collisions. In the freeze out geometry of non-central Pb+Pb collisions we observe a tilt of the particle emission zone in the collision plane away from the beam axis. We find that the magnitude of this tilt depends on the scale at which the distribution is measured. We quantify this "twisting" behavior with a parameterization and propose to measure it experimentally via azimuthally sensitive Hanbury-Brown Twiss correlations. Additionally we show that the twist is related to the emission of particles from different times during the evolution of the source. A systematic comparison between the theoretically observed twist in the freeze out position distribution and a mock experimental analysis of the model calculations via HBT correlations is shown.

Hanbury-Brown–Twiss interferometry relative to the triangular flow plane in heavy-ion collisions

The PHENIX Collaboration has reported third-order harmonic oscillations of the source radius parameters when measuring the Hanbury Brown-Twiss correlation function for charged hadrons relative to the triangular flow angle. We explore possible origins of such third-order oscillations with a simple Gaussian source featuring both a triangular geometric deformation and triangular flow. Third-order oscillations of the HBT radii can arise from a purely geometric triangular deformation superimposed on an azimuthally symmetric radial flow, or from a radially symmetry spatial distribution which expands anisotropically with a triangular component in the flow velocity profile. In both cases the final particle momentum distribution features triangular flow. We show that the two alternatives can be distinguished experimentally through the phase of the azimuthal oscillations of the HBT radii relative to the triangular flow plane.

UrQMD calculations of two-pion HBT correlations in p+p and Pb+Pb collisions at LHC energies

Two-pion Hanbury-Brown-Twiss (HBT) correlations for p+p and central Pb+Pb collisions at the Large-Hadron-Collider (LHC) energies are investigated with the ultrarelativistic quantum molecular dynamics model combined with a correlation afterburner. The transverse momentum dependence of the Pratt-Bertsch HBT radii Rlong, Rout, and Rside is extracted from a three-dimensional Gaussian fit to the correlator in the longitudinal co-moving system. In the p+p case, the dependence of correlations on the charged particle multiplicity and formation time is explored and the data allows to constrain the formation time in the string fragmentation to τf ≤ 0.8 fm/c. In the Pb+Pb case, it is found that Rout is overpredicted by nearly 50%. The LHC results are also compared to data from the STAR experiment at RHIC. For both energies we find that the calculated Rout/Rside ratio is always larger than data, indicating that the emission in the model is less explosive than observed in the data.

SIGNATURES OF NEW PHYSICS FROM HBT CORRELATIONS IN UHECRS

Quantum fields written on noncommutative spacetime (Groenewold–Moyal plane) obey twisted commutation relations. In this paper we show that these twisted commutation relations result in Hanbury–Brown Twiss (HBT) correlations that are distinct from that for ordinary bosonic or fermionic fields, and hence can provide useful information about underlying noncommutative nature of spacetime. The deviation from usual bosonic/fermionic statistics becomes pronounced at high energies, suggesting that a natural place is to look at Ultra High Energy Cosmic Rays (UHECRs). Since the HBT correlations are sensitive only to the statistics of the particles, observations done with UHECRs are capable of providing unambiguous signatures of noncommutativity, without any detailed knowledge of the mechanism and source of origin of UHECRs.

Single-photon emitters based on epitaxial isolated InP/InGaP quantum dots

Quantum dots as single-photon sources have several advantages, such as emitting light over a broad spectral range and being photostable. Quantum dots with densities as low as 1 dot/μm2 have been achieved using ultra-low-rate epitaxy and single-dot emission measured without apertures or post-growth processing. Both excitionic and biexcitonic emissions are observed from single dots created in this way, appearing as doublets with a fine-structure splitting of 320 μeV. The polarization of the split states is also investigated. Hanbury Brown-Twiss correlation measurements for the excitonic emission under cw excitation show anti-bunching behavior with an autocorrelation value of g(2)(0) = 0.2.

Observation of atomic speckle and Hanbury Brown–Twiss correlations in guided matter waves

Speckle patterns produced by multiple independent light sources are a manifestation of the coherence of the light field. Second-order correlations exhibited in phenomena such as photon bunching, termed the Hanbury Brown-Twiss effect, are a measure of quantum coherence. Here we observe for the first time atomic speckle produced by atoms transmitted through an optical waveguide, and link this to second-order correlations of the atomic arrival times. We show that multimode matter-wave guiding, which is directly analogous to multimode light guiding in optical fibres, produces a speckled transverse intensity pattern and atom bunching, whereas single-mode guiding of atoms that are output-coupled from a Bose-Einstein condensate yields a smooth intensity profile and a second-order correlation value of unity. Both first- and second-order coherence are important for applications requiring a fully coherent atomic source, such as squeezed-atom interferometry.

Quantum and Classical Correlations in Waveguide Lattices

We study quantum and classical Hanbury Brown-Twiss correlations in waveguide lattices. We develop a theory for the propagation of photon pairs in the lattice, predicting the emergence of nontrivial quantum interferences unique to lattice systems. Experimentally, we observe the classical counterpart of these interferences using intensity-correlation measurements. We discuss the correspondence between the classical and quantum correlations, and consider path-entangled input states which do not have a classical analogue. Our results demonstrate that waveguide lattices can be used as a robust and highly controllable tool for manipulating quantum states, and offer new ways of studying the quantum properties of light.

Low Mass Dimuons Produced in Relativistic Nuclear Collisions

The NA60 experiment has measured low mass muon pair production in In-In collisions at 158A GeV with unprecedented precision. We show that these data are reproduced very well by a dynamical model with parameters scaled from fits to measurements of hadronic transverse mass spectra and Hanbury Brown-Twiss correlations in Pb-Pb and Pb-Au collisions at the same energy. The data are consistent with in-medium properties of rho and omega mesons at finite temperature and density as deduced from empirical forward-scattering amplitudes. Inclusion of the vacuum decay of the rho meson after freeze-out is necessary for an understanding of the mass and transverse momentum spectrum of dimuons with M less similar 0.9 GeV/c(2).

Observation of Atom Pairs in Spontaneous Four-Wave Mixing of Two Colliding Bose-Einstein Condensates

We study atom scattering from two colliding Bose-Einstein condensates using a position sensitive, time resolved, single atom detector. In analogy to quantum optics, the process can also be thought of as spontaneous, degenerate four-wave mixing of de Broglie waves. We find a clear correlation between atoms with opposite momenta, demonstrating pair production in the scattering process. We also observe a Hanbury Brown-Twiss correlation for collinear momenta, which permits an independent measurement of the size of the pair production source and thus the size of the spatial mode. The back-to-back pairs occupy very nearly two oppositely directed spatial modes, a promising feature for future quantum optics experiments.

Hanbury Brown–Twiss Correlations and Noise in the Charge Transfer Statistics through a Multiterminal Kondo Dot

We analyze the charge transfer statistics through a quantum dot in the Kondo regime, when coupled to an arbitrary number of terminals N. Special attention is paid to current cross correlations between concurring transport channels, which show distinct Hanbury Brown-Twiss antibunching for N>2 reflecting the fermionic nature of charge carriers. While this effect weakens as one moves away from the Kondo fixed point, a new type of correlations between nonconcurring channels emerges which are due entirely to the virtual polarization of the Kondo singlet. As these are not obscured by the background from fixed-point correlations they provide a promising means for extracting information on the parameters of the underlying Fermi-liquid model from the experimental data.

Hanbury Brown-Twiss correlations to probe the population statistics of GHz photons emitted by conductors.

We present the first study of the statistics of GHz photons in quantum circuits, using Hanbury Brown and Twiss correlations. The super-Poissonian and Poissonian photon statistics of thermal and coherent sources, respectively, made of a resistor and a radio frequency generator, are measured down to the quantum regime at milli-Kelvin temperatures. As photon correlations are linked to the second and fourth moments of current fluctuations, this experiment, which is based on current cryogenic electronics, may become a standard for probing electron/photon statistics in quantum conductors.

Observation of Antinormally Ordered Hanbury Brown–Twiss Correlations

We have measured antinormally ordered Hanbury Brown-Twiss correlations for coherent states of the electromagnetic field by using a stimulated parametric down-conversion process. Photons were detected by stimulated emission, rather than by absorption, so that the detection responded not only to actual photons but also to zero-point fluctuations via spontaneous emission. The observed correlations were distinct from normally ordered ones as they showed excess positive correlations, i.e., photon bunching effects, which arose from the thermal nature of zero-point fluctuations.

Three-pion Hanbury Brown-Twiss correlations in relativistic heavy-ion collisions from the STAR experiment.

Data from the first physics run at the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory, Au+Au collisions at sqrt[s(NN)]=130 GeV, have been analyzed by the STAR Collaboration using three-pion correlations with charged pions to study whether pions are emitted independently at freeze-out. We have made a high-statistics measurement of the three-pion correlation function and calculated the normalized three-particle correlator to obtain a quantitative measurement of the degree of chaoticity of the pion source. It is found that the degree of chaoticity seems to increase with increasing particle multiplicity.

Entangled Hanbury Brown Twiss effects with edge states

Electronic Hanbury Brown Twiss correlations are discussed for geometries in which transport is along adiabatically guided edge channels. We briefly discuss partition noise experiments and discuss the effect of inelastic scattering and dephasing on current correlations. We then consider a two-source Hanbury Brown Twiss experiment which demonstrates strikingly that even in geometries without an Aharonov–Bohm effect in the conductance matrix (second-order interference), correlation functions can (due to fourth-order interference) be sensitive to a flux. Interestingly, we find that this fourth-order interference effect is closely related to orbital entanglement. The entanglement can be detected via violation of a Bell Inequality in this geometry even so particles emanate from uncorrelated sources.

Intensity interferometry for a chaotic source with a collective flow and multiple scattering

We study the effects of a collective flow and multiple scattering on two-particle correlation measurements in Hanbury-Brown–Twiss (HBT) intensity interferometry. While the derivation in this paper is not rigorous, we propose a semi-quantitative derivation to shed further light on the interesting RHIC HBT puzzle. We find that under a collective flow the effective source distribution in a two-particle correlation measurement depends on the initial source distribution. In addition, it depends on a collective flow phase function which consists of terms that tend to cancel each other. As the detected particles traverse from the source point to the freeze-out point, they are subject to multiple scattering with medium particles. We examine the effects of multiple scattering on HBT correlations. Applying the Glauber theory to multiple scattering at high energies and the optical model at intermediate energies, we find that multiple scattering leads to an absorption and an effective density distribution that depends on the initial source distribution.

Hanbury Brown–Twiss interferometry of direct photons in heavy ion collisions

We explore the possibility of measurements of Hanbury Brown–Twiss correlations in gg channels in the high multiplicity environment of heavy ion collisions. We consider all possible sources of photon-photon correlations and show that one can separate correlations of photons produced directly in the hot zone and residual correlations of decay photons: the former contribute to the region of small invariant relative momentum qinv&50 MeV, while the latter contribute to larger relative momentum and, negligibly, to the small qinv region. We make predictions of the photon correlation functions at SPS and RHIC energies.

Hanbury Brown–Twiss correlation functions from event generators: A reliable approach to determine the size of the emitting source in ultrarelativistic heavy ion collisions?

Employing NEXUS, one of the most recent simulation programs for heavy ion collisions, we investigate in detail the Hanbury Brown--Twiss correlation function of charged pions and kaons for central reactions 158-A GeV $\mathrm{P}\mathrm{b}+\mathrm{P}\mathrm{b}.$ For this study we supplement the standard simulation program by electromagnetic interactions. We find a wide distribution of freeze-out times which corresponds to a broad distribution of source sizes. Strong space-momentum space correlations as well as the electromagnetic interaction between the correlated pairs and the environment, which is of the same size as that between the hadrons of the correlated pair, strongly modify the correlation function. It can still be well parametrized by $C(\mathbf{k})=1+\ensuremath{\lambda}{e}^{\ensuremath{-}4{\mathbf{k}}^{2}{R}^{2}},$ where k is the relative momentum. R, however, is not a simple function of the source radius; the complicated space-time structure of the source as well as the space-momentum space correlations and the final-state Coulomb interactions are encoded. The true source radius, as given by the rms radius of the emission points, and R differ by up to 30%.

Elliptic flow and Hanbury-Brown–Twiss correlations in noncentral nuclear collisions

Elliptic flow and Hanbury-Brown--Twiss correlations (HBT) are studied for noncentral relativistic nuclear collisions. Azimuthal asymmetries show up in both elliptic flow and HBT radii and are calculated in both collisionless and hydrodynamic limits relevant for peripheral and central collisions, respectively. Determining the reaction plane and measuring the HBT radii as a function of the angle between the reaction plane and the particle momenta can determine the physical quantities as source sizes, deformations, emission times, duration of emission, and opacities. Comparison to SPS data and predictions for RHIC and LHC energies are given. The centrality dependence with and without a phase transition to a quark-gluon plasma is discussed---in particular, how the physical quantities are expected to display a qualitative different behavior in the case of a phase transition.