Hanbury Brown-Twiss Correlations Research Articles

Resonance contributions to Hanbury-Brown–Twiss correlation radii

We study the effect of resonance decays on intensity interferometry for heavy ion collisions. Collective expansion of the source leads to a dependence of the two-particle correlation function on the pair momentum {bold K}. This opens the possibility to reconstruct the dynamics of the source from the {bold K} dependence of the measured Hanburg-Brown{endash}Twiss (HBT) radii. Here we address the question to what extent resonance decays can fake such a flow signal. Within a simple parametrization for the emission function we present a comprehensive analysis of the interplay of flow and resonance decays on the one- and two-particle spectra. We discuss in detail the non-Gaussian features of the correlation function introduced by long-lived resonances and the resulting problems in extracting meaningful HBT radii. We propose to define them in terms of the second-order q moments of the correlator C({bold q},{bold K}). We show that this yields a more reliable characterisation of the correlator in terms of its width and the correlation strength {lambda} than other commonly used fit procedures. The normalized fourth-order q moments (kurtosis) provide a quantitative measure for the non-Gaussian features of the correlator. At least for the class of models studied here, the kurtosis helps separating effectsmore » from expansion flow and resonance decays, and provides the cleanest signal to distinguish between scenarios with and without transverse flow. {copyright} {ital 1997} {ital The American Physical Society}« less

New cross term in the two-particle Hanbury-Brown-Twiss correlation function in ultrarelativistic heavy-ion collisions.

Using two specific models and a model-independent formalism, we show that in addition to the usual quadratic ``side,`` ``out,`` and ``longitudinal`` terms, a previously neglected ``out-longitudinal`` cross term arises naturally in the exponent of the two-particle correlator. Since its effects can be easily observed, such a term should be included in any experimental fits to correlation data. We also suggest a method of organizing correlation data using rapidity rather than longitudinal momentum differences, since in the former every relevant quantity is longitudinally boost invariant.

Isospin recoupling and Bose-Einstein pion correlations in N-barN annihilations.

We study the effect of isospin projections on a two source picture of coherent pions coming from nucleon-antinucleon annihilation. We show that important Hanbury-Brown Twiss correlations among like charge pion pairs compared with unlike arise from these isospin projections.

Model independent features of the two-particle correlation function

The Hanbury-Brown Twiss correlation function for two identical particles is studied for systems with cylindrical symmetry. Its shape for small values of the relative momentum is derived in a model independent way. In addition to the usual quadratic “side”, “out” and “longitudinal” terms in the exponent of the correlator, a previously neglected “out-longitudinal” cross term is found and discussed. The model-independent expressions for the size parameters of the HBT correlation function are interpreted as lengths of homogeneity of the source, in distinction to its purely geometrical size. They are evaluated analytically and numerically for two specific thermal models featuring collective transverse and longitudinal flow. The analytic expressions derived allow one to establish qualitatively important connections between the space-time features of the source and the shape of the correlation function. New ways of parametrizing the correlation function and a new approach to the measurement of the duration of the emission process are suggested.

Bose-Einstein pion correlations in [formula omitted] annihilations

We study intensity correlations for pions from NN annihilation at rest. Pions coming from a coherent source with local isospin show strong Hanbury-Brown Twiss correlations for like charged pairs. Isospin projections, integration over the source and experimental binning leads to the emergence of these correlations without any thermal or related random phase assumptions.