The p/π ratio pT dependence in the RHIC range of baryo-chemical potential

The BRAHMS measurement of proton-to-pion ratios in Au+Au and p+p collisions at $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 62.4 GeV and $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 200 GeV is presented as a function of transverse momentum and collision centrality within the pseudorapidity range 0 ≤ η ≤ 3. The baryo-chemical potential, μ _B , for the indicated data spans from μ _B ≈ 26 MeV ($ \sqrt {s_{NN} } $ \sqrt {s_{NN} } 200 GeV, η ≈ 0) to μ _B ∼ 260 MeV ($ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 62.4 GeV, η ≈ 3) [1]. The p/πratio measured for Au+Au system at $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } 62.4 GeV, η ≈ 3 reaches astounding value of 8–10 at p _T > 1.5 GeV/c. For these energy and pseudorapidity interval no centrality dependency of p/π ratio is observed. Moreover, the baryon-to-meson ratio of nucleus-nucleus data are consistent with results obtained for p+p interactions.     

Systematic study of photon production at forward rapidity in STAR

We present the measurement of multiplicity and pseudorapidity distributions of photons production at forward rapidity (−2.3 ≤ η ≤ −3.8) for Cu + Cu collisions at $ \sqrt {S_{NN} } $ \sqrt {S_{NN} } = 62.4 and 200 GeV. Photons are measured using the Photon Multiplicity Detector (PMD) in STAR experiment at RHIC. The distributions of (η−η _beam), where η _beam is beam rapidity is presented. Pseudorapidity distributions of photons at forward rapidities, when ob-served in the frame of one of the colliding particles show the signature of energy independent scaling at forward rapidities known as Limiting Fragmentation. Measurement of inclusive photons reflect the distribution for π ⁰ as most of the photons come from π ⁰ decay. Gluon saturation at initial conditions of the collisions is one of the possible explanations for this scaling. Study of system-size and incident energy dependence of this phenomenon help us understand the mechanisms better. The system-size and energy dependence of the widths of scaling in pseudorapidity and comparison with model predictions are presented.     

η′q¯q and η′NN vertex suppression in effective theories

In an effective theory containing only quark degrees of freedom, such as the extended Nambu–Jona–Lasinio model, the influence of the axial anomaly can be incorporated by a self-interaction of the 't Hooft determinant type. I will show that despite the threshold problem related to the η′ meson this leads to a significant suppression of the η′ coupling g _η′qˉq to dynamical quarks which suggests a suppression of the η′NN vertex as compared to the ηNN vertex. Received: 8 January 1999     

First measurement of J/ψ anisotropy by PHENIX experiment at RHIC

Understanding the J/ψ suppression and possible recombination mechanisms at RHIC is one of the outstanding challenges for theorists and experimentalists. Recent results provided by PHENIX showed a stronger suppression at forward rapidity, while at mid-rapidity the suppression is similar to lower energy collision experiments. A large sample of Au + Au collisions at $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 200 GeV was collected in 2007 with the PHENIX experiment at RHIC. Using this sample, J/ψs were identified in the di-electron decay channel. In order to probe the charm coalescence as an additional J/ψ production mechanism at RHIC, we studied the first determination of its v ₂ elliptic flow parameter at mid-rapidity.     

Baryon to meson ratios in jets and ridges

We present an analysis of relative baryon to meson production for intermediate transverse momentum hadrons associated with a high-p _T trigger. The results of pion and (anti)proton spectra and ratios are presented for the “jet” and “ridge” components of the two-dimensional Δν − Δϕ triggered correlations in central Au+Au collisions at ?{s_NN }\sqrt {s_{NN} } = 200 GeV. We compare these results with the inclusive (non-triggered) measurements for the same data, and discuss our observations in conjunction with the results from d+Au, and pp data.     

Charged kaon spectra from Au+Au collisions at ?{sNN }\sqrt {s_{NN} } = 200 GeV

The Time-of-Flight detector, based on MRPC technology, has greatly enhanced particle identification capability in STAR. By combining dE/dx measured by the TPC and velocity information from the TOF, we have extended the charged kaon transverse momentum spectra measurements up to ρ _T − 5 GeV/c at mid-rapidity for Au+Au collisions at ?{s_NN }\sqrt {s_{NN} } = 200 GeV. Estimation of charged kaon’s contribution factors from K* and ϕ is also made.     

Entanglement in the Extended XY Spin Model with Three Spin Interaction and External Field

We investigate the pairwise thermal entanglement of the extended XY model with three spin interactions and external filed on zig-zag lattice. The influences of three spin interactions J ₂ and external field λ on the thermal entanglement of the nearest neighbor (NN) and next nearest neighbor (NNN) spins are considered. It is found that J ₂ and λ suppress both the maximal value and the critical temperature of the NN entanglement C ₁₂. However, when it comes to the NNN entanglement C ₁₃, there exists a critical value of J ₂ above which both the maximal entanglement and the critical temperature can be enhanced by J ₂ for a fixed external field. With J ₂ fixed, the effect of λ on C ₁₃ are different for different values of J ₂. For J ₂<1, λ suppresses both T _C and the maximal values of C ₁₃. For J ₂≥1, λ enhances the maximal values of C ₁₃ while decreases the critical temperature. These results show that one is able to get the entanglement wanted by properly controlling the values of the three spin interactions J ₂ and the external field λ.     

Beam-energy and system-size dependence of dynamical net charge fluctuations

We present measurements of net charge fluctuations in Au + Au collisions at ?{s_NN }\sqrt {s_{NN} } = 19.6, 62.4, 130, and 200 GeV, Cu + Cu collisions at ?{s_NN }\sqrt {s_{NN} } = 62.4, 200 GeV, and p + p collisions at ?s\sqrt s = 200 GeV using the net charge dynamical fluctuations measure ν+ −,dyn. The dynamical fluctuations are non-zero at all energies and exhibit a rather modest dependence on beam energy. We find that at a given energy and collision system, net charge dynamical fluctuations violate 1/N _ch scaling, but display approximate 1/N _part scaling. We observe strong dependence of dynamical fluctuations on the azimuthal angular range and pseudorapidity widths.     

Directed flow of identified particles from Au+Au collisions at RHIC

We present the measurement of directed flow (v ₁) for the identified particles, namely, Λ, $ \bar \Lambda $ \bar \Lambda and K _s ⁰, as a function of rapidity and centrality in Au+Au collisions at $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 200 GeV and 62.4 GeV. The measurement is based on the run IV data obtained by the STAR experiment at RHIC. In order to enhance event plane resolution, we use tracks reconstructed from the Forward Time Projection Chambers (FTPCs), together with the sideward deflection of spectator neutrons measured by the STAR’s Shower Maximum Detector at Zero Degree Calorimeters (ZDC-SMDs). We find that for 200 GeV, proton and antiproton v ₁ is less than 1%, the K _s ⁰ Λ, $ \bar \Lambda $ \bar \Lambda v ₁ is less than 2%; for 62 GeV, proton v ₁ is less than 1% and antiproton is less than 2%, v ₁ for K _s ⁰, Λ, $ \bar \Lambda $ \bar \Lambda is less than 2% in Au+Au collisions at 200 GeV.     

Azimuthal correlations with high-pT multi-hadron cluster triggers in Au+Au collisions at ?{sNN } \sqrt {s_{NN} } = 200 GeV from STAR

Di-hadron correlation measurements have been used to probe di-jet production in heavy ion collisions at RHIC. A strong suppression of the away-side high-p _T yield in these measurements is direct evidence that high-p _T partons lose energy as they traverse the strongly interacting medium. However, since the momentum of the trigger particle is not a good measure of the jet energy, azimuthal di-hadron correlations have limited sensitivity to the shape of the fragmentation function. We explore the possibility to better constrain the initial parton energy by using clusters of multiple high-p _T hadrons in a narrow cone as the ‘trigger particle’ in the azimuthal correlation analysis. We present first results from this analysis of multi-hadron triggered correlated yields in Au+Au collisions at $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 200 GeV from STAR. The results are compared with measurements in d + Au collisions and Pythia calculations, and the implications for energy loss and jet fragmentation are discussed.     

ΛN Space-exchange effects in thes-shell hypernuclei and Λ 9 Be

Variational Monte Carlo calculations of the ground state separation energiesB _Λ of thes-shell hypernuclei and also of _Λ ⁹ Be have been made for an Urbana-type central space-exchange ΛN potential consistent with Λp scattering, and also including three-body ΛNN forces. Thes-shell hypernuclei are treated asA-body systems (A = baryon number), and _Λ ⁹ Be is analysed as a partially nine-body problem in the Λ — 2α model. The reduction ofB _Λ due to the space-exchange ΛN potential has been calculated for thes-shell hypernuclei for a range of interactions: both ΛN and ΛN + ΛNN forces. ForA = 3,4,5 the exchange energy is approximately, 0.04, 0.15 and 0.50 MeV, respectively. For _Λ ⁹ Be a much more limited study gives ≅ 1.3 MeV. These values are much larger than that for ‘soft’ ΛN +NN potentials when the correlations are weak. Preliminary results were presented at the DAE Symp. on ‘Nuclear Physics’ Vol. 32B (1989).     

Heavy quarkonia production in p+p, d+Au and Cu+Cu collisions by PHENIX experiment at ?{sNN }\sqrt {s_{NN} } = 200 GeV

The PHENIX experiment has measured, J/ψ, ψ′ and γ productions for different collision systems in the forward rapidities 1.2 < | η | < 2.2 at ?{S_NN }\sqrt {S_{NN} } = 200 GeV. We have observed significant suppressions of J/ψ production in both Cu+Cu and Au+Au collisions relative to the yield in p+p system. The measurements of higher mass heavy quarkonia states (ψ′ and γ) will help us to constrain various quarkonium suppression models in heavy ion collisions. A first hint of ψ′ and γ productions in 200GeV p+p collisions has been observed at forward and backward rapidities at PHENIX.     

Tensor A yy and vector A y analyzing powers in the 1H(d, d′)X and 12C(d, d′)X reactions at initial deuteron momenta of 9 GeV/c in the region of baryonic resonance excitation

The angular dependence of the tensor A _yy and vector A _y analyzing powers in the inelastic scattering of deuterons with a momentum of 9.0 GeV/c on hydrogen and carbon has been measured. The range of measurements corresponds to the baryonic resonance excitation with masses of ∼2.2–2.6 GeV/c ². The A _yy data, being in good agreement with the previous results, demonstrate an approximate t scaling up to −1.5 (GeV/c)². The large values of A _y show a significant role of the spin-dependent part of the elementary amplitude of the NN → NN* reaction. The results of the experiment are compared with model predictions of the plane-wave impulse approximation. The text was submitted by the authors in English.     

πNN Dynamics in pp → pp,pp →πd and πd →πd Processes Below 1 GeV

pp and πd scattering and pp →πd reaction processes at incident proton laboratory energies T _L ≤ 1 GeV are studied in the framework of πNN dynamics. For this purpose three-body calculations are performed with the πN interaction in the P ₁₁, P ₃₃, S ₁₁ and S ₃₁ states and NN forces in the ³ S ₁ -³ D ₁, ¹ S ₀, and ³ P ₂ states. In addition, the backward-going pion contribution at the πNΔ vertex, the πN-ρN coupling, the heavy-meson exchanges in the NN → NN driving term, and the effect of the off-shell structure in the πN-ρN P ₃₃ interaction are taken into account. Received March 28, 1994; revised July 29, 1994; accepted for publication August 31, 1994     

Cosmic-ray Monte Carlo predictions for forward particle production in p-p, p-Pb, and Pb-Pb collisions at the LHC

We present and compare the predictions of various cosmic-ray Monte Carlo models for the energy (dE/dη) and particle (dN/dη) flows in p-p, p-Pb and Pb-Pb collisions at $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 14, 8.8, and 5.5 TeV respectively, in the range covered by forward LHC detectors like CASTOR or TOTEM (5.2 < |η|<6.6) and ZDC or LHCf (|η| ≥ 8.1 for neutrals).     

A Condensed Matter Interpretation of SM Fermions and Gauge Fields

We present the bundle (Aff(3)⊗ℂ⊗Λ)(ℝ³), with a geometric Dirac equation on it, as a three-dimensional geometric interpretation of the SM fermions. Each (ℂ⊗Λ)(ℝ³) describes an electroweak doublet. The Dirac equation has a doubler-free staggered spatial discretization on the lattice space (Aff(3)⊗ℂ)(ℤ³). This space allows a simple physical interpretation as a phase space of a lattice of cells. We find the SM SU(3) _c ×SU(2) _L ×U(1) _Y action on (Aff(3)⊗ℂ⊗Λ)(ℝ³) to be a maximal anomaly-free gauge action preserving E(3) symmetry and symplectic structure, which can be constructed using two simple types of gauge-like lattice fields: Wilson gauge fields and correction terms for lattice deformations. The lattice fermion fields we propose to quantize as low energy states of a canonical quantum theory with ℤ₂-degenerated vacuum state. We construct anticommuting fermion operators for the resulting ℤ₂-valued (spin) field theory. A metric theory of gravity compatible with this model is presented too.     

Energy Dependence of the πN Amplitude and the Three-Nucleon Interaction

By calculating the contribution of the ππ three-body force to the three-nucleon binding energy in terms of the πN amplitude using perturbation theory, we are able to determine the importance of the energy dependence and the contribution of the different partial waves of the πN amplitude to the three-nucleon force. A separable representation of the non-pole πN amplitude allows us to write the three-nucleon force in terms of the amplitude for NN → NN*, propagation of the NNN* system, and the amplitude for NN* → NN , with N* being the πN quasi-particle amplitude in a given state. The division of the πN amplitude into a pole and non-pole part gives a procedure for the determination of the πNN form factor within the model. The total contribution of the three-body force to the binding energy of the triton for the separable approximation to the Paris nucleon-nucleon potential (PEST) is found to be very small mainly as a result of the energy dependence of the πN amplitude, the cancellation between the S- and P-wave πN amplitudes, and the soft πNN form factor. Received April 12, 1994; revised November 11, 1994; accepted for publication December 1, 1994     

Searching for the color glass condensate with the STAR Forward Meson Spectrometer

Early results from the Solenoidal Tracker At RHIC (STAR) using prototype forward calorimeters (FPD/FPD++) have shown that in d+Au collisions at $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 200 GeV a stronger suppression of forward π ⁰ yield is observed than would be expected from shadowing effects. Exploratory measurements and observations can be qualitatively interpreted using the Color Glass Condensate (CGC) model to describe the colliding nucleus. A new detector, the Forward Meson Spectrometer (FMS), has been built to measure forward pion and photon production to quantify gluon suppression at low x in heavy nuclei over a large range in x and p _T .     

Azimuthal anisotropy of electrons from heavy flavor decays in \sqrt{s_{NN}} =200 GeV Au-Au collisions at PHENIX

The PHENIX experiment has measured the azimuthal anisotropy parameter v₂, the second harmonic of the azimuthal distribution, for electrons at mid-rapidity (|η|<0.35) as a function of transverse momentum (0.5<p_T (GeV/c)<5.0) in Au+Au collisions at  =200 GeV. From the result we have calculated the non-photonic electron v₂, which is expected to reflect charm quark azimuthal anisotropy, by subtracting the v₂ of electrons from other sources such as photon conversions and Dalitz decays.     

Centrality dependence of v 2 in Au + Au at \sqrt{s_{NN}}=200 GeV

One of the most striking results is the large elliptic flow (v ₂) at RHIC. Detailed mass and transverse momentum dependence of elliptic flow are well described by ideal hydrodynamic calculations for p _T<1 GeV/c, and by parton coalescence/recombination picture for p _T=2–6 GeV/c. The systematic error on v ₂ is dominated by so-called “non-flow effects”, which are correlations other than flow, such as resonance decays and jets. It is crucial to understand and reduce the systematic error from non-flow effects in order to understand the underlying collision dynamics. In this paper, we present the centrality dependence of v ₂ with respect to the first harmonic event plane at ZDC-SMD (v ₂{ZDC-SMD}) in Au + Au collisions at  GeV. A large rapidity gap (|Δη|>6) between midrapidity and the ZDC-SMD could enable us to minimize possible non-flow contributions. We compare the results of v ₂{ZDC-SMD} with v ₂{BBC}, which is measured by event plane determined at |η|=3.1–3.9. Possible non-flow contributions in those results will be discussed.