Do p+p Collisions Flow at RHIC? Understanding One-Particle Distributions, Multiplicity Evolution, and Conservation Laws

Collective, explosive flow in central heavy ion collisions manifests itself in the mass dependence of $p_T$ distributions and femtoscopic length scales, measured in the soft sector ($p_T\lesssim 1$ GeV/c). Measured $p_T$ distributions from proton-proton collisions differ significantly from those from heavy ion collisions. This has been taken as evidence that p+p collisions generate little collective flow, a conclusion in line with naive expectations. We point out possible hazards of ignoring phase-space restrictions due to conservation laws when comparing high- and low-multiplicity final states. Already in two-particle correlation functions, we see clear signals of such phase-space restrictions in low-multiplicity collisions at RHIC. We discuss how these same effects, then, {\it must} appear in the single particle spectra. We argue that the effects of energy and momentum conservation actually dominate the observed systematics, and that $p+p$ collisions may be much more similar to heavy ion collisions than generally thought.Comment: 4 pages, 3 figures - To appear in the conference proceedings for Quark Matter 2009, March 30 - April 4, Knoxville, Tennesse

Global Conservation Laws and Femtoscopy of Small Systems

It is increasingly important to understand, in detail, two-pion correlations measured in p+p and d+A collisions. In particular, one wishes to understand the femtoscopic correlations, in order to compare to similar measurements in heavy ion collisions. However, in the low-multiplicity final states of these systems, global conservation laws generate significant N-body correlations which project onto the two-pion space in non-trivial ways and complicate the femtoscopic analysis. We discuss a model-independent formalism to calculate and account for these correlations in measurements.Comment: 7 pages; 10 figures; Invited talk at the Second Workshop on Particle Correlations and Femtoscopy (WPCF06), Sept 9-11 2006, Sao Paulo, Brazi

Pion Interferemetry from p+p to Au+Au in STAR

The geometric substructure of the particle-emitting source has been characterized via two-particle interferometry by the STAR collaboration for all energies and colliding systems at RHIC. We present systematic studies of charged pion interferometry. The collective nature of the source is revealed through the $m_T$ dependence of HBT radii for all particle types. Preliminary results suggest a scaling in the pion HBT radii with overall system size, as central Au+Au collisions are compared to peripheral collisions as well as with Cu+Cu and even with d+Au and p+p collisions, naively suggesting comparable flow strength in all systems. To probe this issue in greater detail, multidimensional correlation functions are studied using a spherical decomposition method. This allows clear identification of source anisotropy and, for the light systems, the presence of significant long-range non-femtoscopic correlations.Comment: Proceedings for WPCF, Kromeriz, Czech Republic, August 200

Recent HBT results in Au+Au and p+p collisions from PHENIX

We present Hanbury-Brown Twiss measurements from the PHENIX experiment at RHIC for final results for charged kaon pairs from sqrt{s_{NN}} = 200 GeV Au+Au collisions and preliminary results for charged pion pairs from sqrt{s} = 200 GeV p+p collisions. We find that for kaon pairs from Au+Au, each traditional 3D Gaussian radius shows approximately the same linear increase as a function of N^{1/3}_{part}. An imaging analysis reveals a significant non-Gaussian tail for r \gtrsim 10 fm. The presence of a tail for kaon pairs demonstrates that similar non-Gaussian tails observed in earlier pion measurements cannot be fully explained by decays of long-lived resonances. The preliminary analysis of pions from sqrt{s} = 200 GeV p+p minimum biased collisions show correlations which are well suited to traditional 3D HBT radii extraction via the Bowler-Sinyukov method, and we present R_out, R_side, and R_long as a function of mean transverse pair mass.Comment: 4 pages, 3 figures - To appear in the conference proceedings for Quark Matter 2009, March 30 - April 4, Knoxville, Tennesse

On Determining Dead Layer and Detector Thicknesses for a Position-Sensitive Silicon Detector

In this work, two particular properties of the position-sensitive, thick silicon detectors (known as the "E" detectors) in the High Resolution Array (HiRA) are investigated: the thickness of the dead layer on the front of the detector, and the overall thickness of the detector itself. The dead layer thickness for each E detector in HiRA is extracted using a measurement of alpha particles emitted from a $^{212}$Pb pin source placed close to the detector surface. This procedure also allows for energy calibrations of the E detectors, which are otherwise inaccessible for alpha source calibration as each one is sandwiched between two other detectors. The E detector thickness is obtained from a combination of elastically scattered protons and an energy-loss calculation method. Results from these analyses agree with values provided by the manufacturer.Comment: Accepted for publication in Nuclear Instruments and Methods in Physics Researc

Probing elastic and inelastic breakup contributions to intermediate-energy two-proton removal reactions

The two-proton removal reaction from 28Mg projectiles has been studied at 93 MeV/u at the NSCL. First coincidence measurements of the heavy 26Ne projectile residues, the removed protons and other light charged particles enabled the relative cross sections from each of the three possible elastic and inelastic proton removal mechanisms to be determined. These more final-state-exclusive measurements are key for further interrogation of these reaction mechanisms and use of the reaction channel for quantitative spectroscopy of very neutron-rich nuclei. The relative and absolute yields of the three contributing mechanisms are compared to reaction model expectations - based on the use of eikonal dynamics and sd-shell-model structure amplitudes.Comment: Accepted for publication in Physical Review C (Rapid Communication

Elastic breakup cross sections of well-bound nucleons

The 9Be(28Mg,27Na) one-proton removal reaction with a large proton separation energy of Sp(28Mg)=16.79 MeV is studied at intermediate beam energy. Coincidences of the bound 27Na residues with protons and other light charged particles are measured. These data are analyzed to determine the percentage contributions to the proton removal cross section from the elastic and inelastic nucleon removal mechanisms. These deduced contributions are compared with the eikonal reaction model predictions and with the previously measured data for reactions involving the re- moval of more weakly-bound protons from lighter nuclei. The role of transitions of the proton between different bound single-particle configurations upon the elastic breakup cross section is also quantified in this well-bound case. The measured and calculated elastic breakup fractions are found to be in good agreement.Comment: Phys. Rev. C 2014 (accepted

Transport model analysis of the transverse momentum and rapidity dependence of pion interferometry at SPS energies

Based on the UrQMD transport model, the transverse momentum and the rapidity dependence of the Hanbury-Brown-Twiss (HBT) radii $R_L$, $R_O$, $R_S$ as well as the cross term $R_{OL}$ at SPS energies are investigated and compared with the experimental NA49 and CERES data. The rapidity dependence of the $R_L$, $R_O$, $R_S$ is weak while the $R_{OL}$ is significantly increased at large rapidities and small transverse momenta. The HBT "life-time" issue (the phenomenon that the calculated $\sqrt{R_O^{2}-R_S^{2}}$ value is larger than the correspondingly extracted experimental data) is also present at SPS energies.Comment: 17 pages, 11 figure

Investigations of three, four, and five-particle exit channels of levels in light nuclei created using a 9C beam

The interactions of a E/A=70-MeV 9C beam with a Be target was used to populate levels in Be, B, and C isotopes which undergo decay into many-particle exit channels. The decay products were detected in the HiRA array and the level energies were identified from their invariant mass. Correlations between the decay products were examined to deduce the nature of the decays, specifically to what extent all the fragments were created in one prompt step or whether the disintegration proceeded in a sequential fashion through long-lived intermediate states. In the latter case, information on the spin of the level was also obtained. Of particular interest is the 5-body decay of the 8C ground state which was found to disintegrate in two steps of two-proton decay passing through the 6Beg.s. intermediate state. The isobaric analog of 8Cg.s. in 8B was also found to undergo two-proton decay to the isobaric analog of 6Beg.s. in 6Li. A 9.69-MeV state in 10C was found to undergo prompt 4-body decay to the 2p+2alpha exit channel. The two protons were found to have a strong enhancementin the diproton region and the relative energies of all four p-alpha pairs were consistent with the 5Lig.s. resonance