Willis Lin

This paper describes the conclusions that can be drawn from the data taken thus far with the PHOBOS detector at RHIC. In the most central Au + Au collisions at the highest beam energy, evidence is found for the formation of a very high energy density system whose description in terms of simple hadronic degrees of freedom is inappropriate. Furthermore, the constituents of this novel system are found to undergo a significant level of interaction. The properties of particle production at RHIC energies are shown to follow a number of simple scaling behaviors, some of which continue trends found at lower energies or in simpler systems. As a function of centrality, the total number of charged particles scales with the number of participating nucleons. When comparing Au + Au at different centralities, the dependence of the yield on the number of participants at higher pT (∼4GeV/c) is very similar to that at low transverse momentum. The measured values of charged particle pseudorapidity density and elliptic flow were found to be independent of energy over a broad range of pseudorapidities when effectively viewed in the rest frame of one of the colliding nuclei, a property we describe as “extended longitudinal scaling”. Finally, the centrality and energy dependences of several observables were found to factorize to a surprising degree.

This paper presents measurements of the elliptic flow of charged particles as a function of pseudorapidity and centrality from Cu-Cu collisions at 62.4 and 200 GeV using the PHOBOS detector at the Relativistic Heavy Ion Collider (RHIC).The elliptic flow in Cu-Cu collisions is found to be significant even for the most central events.For comparison with the Au-Au results, it is found that the detailed way in which the collision geometry (eccentricity) is estimated is of critical importance when scaling out system-size effects.A new form of eccentricity, called the participant eccentricity, is introduced which yields a scaled elliptic flow in the Cu-Cu system that has the same relative magnitude and qualitative features as that in the Au-Au system.

Pseudorapidity distributions of charged particles emitted in $Au+Au$, $Cu+Cu$, $d+Au$, and $p+p$ collisions over a wide energy range have been measured using the PHOBOS detector at RHIC. The centrality dependence of both the charged particle distributions and the multiplicity at midrapidity were measured. Pseudorapidity distributions of charged particles emitted with $|\eta|<5.4$, which account for between 95% and 99% of the total charged-particle emission associated with collision participants, are presented for different collision centralities. Both the midrapidity density, $dN_{ch}/d\eta$, and the total charged-particle multiplicity, $N_{ch}$, are found to factorize into a product of independent functions of collision energy, $\sqrt{s_{_{NN}}}$, and centrality given in terms of the number of nucleons participating in the collision, $N_{part}$. The total charged particle multiplicity, observed in these experiments and those at lower energies, assumes a linear dependence of $(\ln s_{_{NN}})^2$ over the full range of collision energy of $\sqrt{s_{_{NN}}}$=2.7-200 GeV.

We present measurements of the pseudorapidity distribution of primary charged particles produced in Au+Au collisions at three energies, √sNN=19.6, 130, and 200 GeV, for a range of collision centralities. The distribution narrows for more central collisions and excess particles are produced at high pseudorapidity in peripheral collisions. For a given centrality, however, the distributions are found to scale with energy according to the "limiting fragmentation" hypothesis. The universal fragmentation region described by this scaling grows in pseudorapidity with increasing collision energy, extending well away from the beam rapidity and covering more than half of the pseudorapidity range over which particles are produced. This approach to a universal limiting curve appears to be a dominant feature of the pseudorapidity distribution and therefore of the total particle production in these collisions.Received 5 October 2002DOI:https://doi.org/10.1103/PhysRevLett.91.052303©2003 American Physical Society

We present the first measurement of pseudorapidity densities of primary charged particles near midrapidity in Au+Au collisions at sqrt[s(NN)] = 56 and 130 GeV. For the most central collisions, we find the charged-particle pseudorapidity density to be dN/deta|(|eta|<1) = 408+/-12(stat)+/-30(syst) at 56 GeV and 555+/-12(stat)+/-35(syst) at 130 GeV, values that are higher than any previously observed in nuclear collisions. Compared to proton-antiproton collisions, our data show an increase in the pseudorapidity density per participant by more than 40% at the higher energy.

The design and construction of the silicon strip microvertex detector (SMD) of the L3 experiment at LEP are described. We present the sensors, readout electronics, data acquisition system, mechanical assembly and support, displacement monitoring systems and radiation monitoring system of the recently installed double-sided, double-layered SMD. This detector utilizes novel and sophisticated techniques for its readout.

We have measured transverse momentum distributions of charged hadrons produced in d+Au collisions at sqrt[s(NN)]=200 GeV. The spectra were obtained for transverse momenta 0.25<p(T)<6.0 GeV/c, in a pseudorapidity range of 0.2<eta<1.4 in the deuteron direction. The evolution of the spectra with collision centrality is presented in comparison to p+pmacr; collisions at the same collision energy. With increasing centrality, the yield at high transverse momenta increases more rapidly than the overall particle density, leading to a strong modification of the spectral shape. This change in spectral shape is qualitatively different from observations in Au+Au collisions at the same energy. The results provide important information for discriminating between different models for the suppression of high-p(T) hadrons observed in Au+Au collisions.

A measurement of two-particle correlations with a high transverse momentum trigger particle (p trig T > 2.5 GeV/c) is presented for Au+Au collisions at √ s N N =200 GeV over the uniquely broad longitudinal acceptance of the PHOBOS detector (-4 < ∆η < 2).A broadening of the away-side azimuthal correlation compared to elementary collisions is observed at all ∆η.As in p+p collisions, the near-side is characterized by a peak of correlated partners at small angle relative to the trigger particle.However, in central Au+Au collisions an additional correlation extended in ∆η and known as the 'ridge' is found to reach at least |∆η| ≈ 4. The ridge yield is largely independent of ∆η over the measured range, and it decreases towards more peripheral collisions.For the chosen p trig T cut, the ridge yield is consistent with zero for events with less than roughly 100 participating nucleons.

This Rapid Communication describes the measurement of elliptic flow for charged particles in Au+Au collisions at √sNN=200 GeV using the PHOBOS detector at the Relativistic Heavy Ion Collider. The measured azimuthal anisotropy is presented over a wide range of pseudorapidity for three broad collision centrality classes for the first time at this energy. Two distinct methods of extracting the flow signal were used to reduce systematic uncertainties. The elliptic flow falls sharply with increasing |η| at 200 GeV for all the centralities studied, as observed for minimum-bias collisions at √sNN=130 GeV.Received 12 July 2004DOI:https://doi.org/10.1103/PhysRevC.72.051901©2005 American Physical Society

The charged-particle pseudorapidity density dNch/deta has been measured for Au+Au collisions at sqrt(sNN)=130 GeV at RHIC, using the PHOBOS apparatus. The total number of charged particles produced for the 3% most central Au+Au collisions for |eta|<=5.4 is found to be 4200+-470. The evolution of dNch/deta with centrality is discussed, and compared to model calculations and to data from proton-induced collisions. The data show an enhancement in charged-particle production at mid-rapidity, while in the fragmentation regions, the results are consistent with expectations from pp and pA scattering.

The PHOBOS experiment has measured the charged particle multiplicity at midrapidity in Au+Au collisions at sNN=200 GeV as a function of the collision centrality. Results on dNch/dη||η|<1 divided by the number of participating nucleon pairs 〈Npart〉/2 are presented as a function of 〈Npart〉. As was found from similar data at sNN=130 GeV, the data can be equally well described by parton saturation models and two-component fits, which include contributions that scale as Npart and the number of binary collisions Ncoll. We compare the data at the two energies by means of the ratio R200/130 of the charged particle multiplicity for the two different energies as a function of 〈Npart〉. For events with 〈Npart〉>100, we find that this ratio is consistent with a constant value of 1.14±0.01(stat)±0.05(syst). Received 10 January 2002DOI:https://doi.org/10.1103/PhysRevC.65.061901©2002 American Physical Society

We present transverse momentum distributions of charged hadrons produced in Au+Au collisions at sNN=200 GeV. The spectra were measured for transverse momenta pT from 0.25 to 4.5 GeV/c in a pseudorapidity range of 0.2<η<1.4. The evolution of the spectra is studied as a function of collision centrality, from 65 to 344 participating nucleons. The results are compared to data from proton–antiproton collisions and Au+Au collisions at lower RHIC energies. We find a significant change of the spectral shape between proton–antiproton and semi-peripheral Au+Au collisions. Comparing semi-peripheral to central Au+Au collisions, we find that the yields at high pT exhibit approximate scaling with the number of participating nucleons, rather than scaling with the number of binary collisions.

This paper describes the measurement of collective flow for charged particles in Au+Au collisions at sqrt[s(NN)]=130 GeV using the PHOBOS detector at the Relativistic Heavy Ion Collider (RHIC). The measured azimuthal hit anisotropy is presented over a wide range of pseudorapidity (-5.0<eta<5.3) for the first time at this energy. The result, averaged over momenta and particle species, is observed to reach 7% for peripheral collisions at midrapidity, falling off with centrality and increasing |eta|. These results call into question the common assumption of longitudinal boost invariance over a large region of rapidity in RHIC collisions.

This paper describes the measurement of the energy dependence of elliptic flow for charged particles in Au+Au collisions using the PHOBOS detector at the Relativistic Heavy Ion Collider (RHIC). Data taken at collision energies of $\sqrt{s_{_{NN}}} =$ 19.6, 62.4, 130 and 200 GeV are shown over a wide range in pseudorapidity. These results, when plotted as a function of $\eta'=|\eta|-y_{beam}$, scale with approximate linearity throughout $\eta'$, implying no sharp changes in the dynamics of particle production as a function of pseudorapidity or increasing beam energy.

The centrality dependence of the midrapidity charged particle multiplicity in $\mathrm{Au}+\mathrm{Au}$ heavy-ion collisions at $\sqrt{{s}_{NN}}=19.6$ and $200\phantom{\rule{0.3em}{0ex}}\mathrm{GeV}$ is presented. Within a simple model, the fraction of hard (scaling with number of binary collisions) to soft (scaling with number of participant pairs) interactions is consistent with a value of $x=0.13\ifmmode\pm\else\textpm\fi{}0.01(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.05(\mathrm{syst})$ at both energies. The experimental results at both energies, scaled by inelastic $p(\overline{p})+p$ collision data, agree within systematic errors. The ratio of the data was found not to depend on centrality over the studied range and yields a simple linear scale factor of ${R}_{200∕19.6}=2.03\ifmmode\pm\else\textpm\fi{}0.02(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.05(\mathrm{syst})$.

We present the first measurement of the pseudorapidity density of primary charged particles in Au+Au collisions at root square[s(NN)] = 200 GeV. For the 6% most central collisions, we obtain dN(ch)/d(eta)/(/eta/<1) = 650+/-35(syst). Compared to collisions at root square[s(NN)] = 130 GeV, the highest energy studied previously, an increase by a factor of 1.14+/-0.05 at 90% confidence level, is found. The energy dependence of the pseudorapidity density is discussed in comparison with data from proton-induced collisions and theoretical predictions.

This manuscript contains a detailed description of the PHOBOS experiment as it is configured for the Year 2001 running period. It is capable of detecting charged particles over the full solid angle using a multiplicity detector and measuring identified charged particles near mid-rapidity in two spectrometer arms with opposite magnetic fields. Both of these components utilize silicon pad detectors for charged particle detection. The minimization of material between the collision vertex and the first layers of silicon detectors allows for the detection of charged particles with very low transverse momenta, which is a unique feature of the PHOBOS experiment. Additional detectors include a time-of-flight wall which extends the particle identification range for one spectrometer arm, as well as sets of scintillator paddle and Cherenkov detector arrays for event triggering and centrality selection.

The measured pseudorapidity distribution of primary charged particles in minimum-bias d+Au collisions at sqrt[s(NN)]=200 GeV is presented for the first time. This distribution falls off less rapidly in the gold direction as compared to the deuteron direction. The average value of the charged particle pseudorapidity density at midrapidity is <dN(ch)/d eta>|eta|< or =0.6)=9.4+/-0.7(syst) and the integrated primary charged particle multiplicity in the measured region is 82+/-6(syst). Estimates of the total charged particle production, based on extrapolations outside the measured pseudorapidity region, are also presented. The pseudorapidity distribution, normalized to the number of participants in d+Au collisions, is compared to those of Au+Au and p+(-)p systems at the same energy. The d+Au distribution is also compared to the predictions of the parton saturation model, as well as microscopic models.

The measured pseudorapidity distributions of primary charged particles over a wide pseudorapidity range of |η|≤5.4 and integrated charged particle multiplicities in d+Au collisions at √sNN=200GeV are presented as a function of collision centrality. The longitudinal features of d+Au collisions at √sNN=200GeV are found to be very similar to those seen in p+A collisions at lower energies. The total multiplicity of charged particles is found to scale with the total number of participants according to NdAuch=12⟨Npart⟩Nppch, and the energy dependence of the density of charged particles produced in the fragmentation region exhibits extended longitudinal scaling.Received 30 September 2004DOI:https://doi.org/10.1103/PhysRevC.72.031901©2005 American Physical Society

The charged-particle pseudorapidity density for Au+Au collisions at √sNN=62.4 GeV has been measured over a wide range of impact parameters and compared to results obtained at other energies. As a function of collision energy, the pseudorapidity distribution grows systematically both in height and width. The midrapidity density is found to grow approximately logarithmically between BNL Alternating Gradient Synchrotron (AGS) energies and the top BNL Relativistic Heavy Ion Collider (RHIC) energy. There is also an approximate factorization of the centrality and energy dependence of the midrapidity yields. The new results at √sNN=62.4 GeV confirm the previously observed phenomenon of “extended longitudinal scaling” in the pseudorapidity distributions when viewed in the rest frame of one of the colliding nuclei. It is also found that the evolution of the shape of the distribution with centrality is energy independent, when viewed in this reference frame. As a function of centrality, the total charged particle multiplicity scales linearly with the number of participant pairs as it was observed at other energies.Received 26 September 2005DOI:https://doi.org/10.1103/PhysRevC.74.021901©2006 American Physical Society

This paper presents results on event-by-event elliptic flow fluctuations in Au+Au collisions at sqrt(s_NN)=200Gev, where the contribution from non-flow correlations has been subtracted. An analysis method is introduced to measure non-flow correlations, relying on the assumption that non-flow correlations are most prominent at short ranges (Delta eta < 2). Assuming that non-flow correlations are of the order that is observed in p+p collisions for long range correlations (Delta eta > 2), relative elliptic flow fluctuations of approximately 30-40% are observed. These results are consistent with predictions based on spatial fluctuations of the participating nucleons in the initial nuclear overlap region. It is found that the long range non-flow correlations in Au+Au collisions would have to be more than an order of magnitude stronger compared to the p+p data to lead to the observed azimuthal anisotropy fluctuations with no intrinsic elliptic flow fluctuations.

This Letter presents the first measurement of event-by-event fluctuations of the elliptic flow parameter v(2) in Au+Au collisions at square root(s(NN))=200 GeV as a function of collision centrality. The relative nonstatistical fluctuations of the v(2) parameter are found to be approximately 40%. The results, including contributions from event-by-event elliptic flow fluctuations and from azimuthal correlations that are unrelated to the reaction plane (nonflow correlations), establish an upper limit on the magnitude of underlying elliptic flow fluctuations. This limit is consistent with predictions based on spatial fluctuations of the participating nucleons in the initial nuclear overlap region. These results provide important constraints on models of the initial state and hydrodynamic evolution of relativistic heavy ion collisions.

We present a measurement of the pseudorapidity density of primary charged particles near mid-rapidity in Au+Au collisions at sqrt(s_NN) = 130 GeV as a function of the number of participating nucleons. These results are compared to models in an attempt to discriminate between competing scenarios of particle production in heavy ion collisions.

We report on measurements of directed flow as a function of pseudorapidity in Au+Au collisions at energies of √ s N N = 19.6,62.4, 130 and 200 GeV as measured by the PHOBOS detector at the Relativistic Heavy Ion Collider (RHIC).These results are particularly valuable because of the extensive, continuous pseudorapidity coverage of the PHOBOS detector.There is no significant indication of structure near midrapidity and the data surprisingly exhibit extended longitudinal scaling similar to that seen for elliptic flow and charged particle pseudorapidity density.

We have measured transverse momentum distributions of charged hadrons produced in Au+Au collisions at sqrt(s_NN) = 62.4 GeV. The spectra are presented for transverse momenta 0.25 < p_T< 4.5 GeV/c, in a pseudo-rapidity range of 0.2 < eta < 1.4. The nuclear modification factor R_AA is calculated relative to p+p data at the same collision energy as a function of collision centrality. For p_T > 2 GeV/c, R_AA is found to be significantly larger than in Au+Au collisions at sqrt(s_NN) =130 and 200 GeV. In contrast, we find that the evolution of the invariant yields per participant pair from peripheral to central collisions is approximately energy independent over this range of collision energies. This observation challenges models of high p_T hadron suppression in terms of parton energy loss.

Forward-backward correlations of charged-particle multiplicities in symmetric bins in pseudorapidity are studied to gain insight into the underlying correlation structure of particle production in Au+Au collisions. The PHOBOS detector is used to measure integrated multiplicities in bins centered at \ensuremath{\eta}, defined within $|\ensuremath{\eta}|&lt;3$, and covering intervals $\ensuremath{\Delta}\ensuremath{\eta}$. The variance ${\ensuremath{\sigma}}_{C}^{2}$ of a suitably defined forward-backward asymmetry variable $C$ is calculated as a function of $\ensuremath{\eta},\ensuremath{\Delta}\ensuremath{\eta}$, and centrality. It is found to be sensitive to short-range correlations, and the concept of ``clustering'' is used to interpret comparisons to phenomenological models.

We present results on two-particle angular correlations in proton-proton collisions at center-of-mass energies of 200 and 410 GeV. The PHOBOS experiment at the BNL Relativistic Heavy Ion Collider has a uniquely large coverage for charged particles, giving the opportunity to explore the correlations at both short- and long-range scales. At both energies, a complex two-dimensional correlation structure in Δη and Δϕ is observed. In the context of an independent cluster model of short-range correlations, the cluster size and its decay width are extracted from the two-particle pseudorapidity correlation function and compared with previous measurements in proton-proton and proton-antiproton collisions, as well as PYTHIA and HIJING predictions.3 MoreReceived 6 April 2007DOI:https://doi.org/10.1103/PhysRevC.75.054913©2007 American Physical Society

We have measured the ratios of antiparticles to particles for charged pions, kaons, and protons near mid-rapidity in central Au+Au collisions at sqrt[s(NN)] = 130 GeV. We observe <pi(-)>/<pi(+)> = 1.00+/-0.01(stat)+/-0.02(syst), <K->/<K+> = 0.91+/-0.07(stat)+/-0.06(syst), and / = 0.60+/-0.04(stat)+/-0.06(syst). The <K->/<K+> and / ratios give a consistent estimate of the baryo-chemical potential mu(B) of 45 MeV, a factor of 5-6 smaller than in central Pb+Pb collisions at sqrt[s(NN)] = 17.2 GeV.

We present transverse momentum distributions of charged hadrons produced in Cu + Cu collisions at square root of SNN = 62.4 and 200 GeV. The spectra are measured for transverse momenta of 0.25 < pT < 5.0 GeV/c at square root of SNN = 62.4 GeV and 0.25 < pT < 7.0 GeV/c at square root of SNN = 200 GeV, in a pseudorapidity range of 0.2 < eta < 1.4. The nuclear modification factor R(AA) is calculated relative to p + p data at both collision energies as a function of collision centrality. At a given collision energy and fractional cross section, R(AA) is observed to be systematically larger in Cu + Cu collisions compared to Au + Au. However, for the same number of participating nucleons, R(AA) is essentially the same in both systems over the measured range of pT, in spite of the significantly different geometries of the Cu + Cu and Au + Au systems.

The PHOBOS experiment at the BNL Relativistic Heavy Ion Collider has measured the total multiplicity of primary charged particles as a function of collision centrality in Au+Au collisions at √sNN= 19.6, 130, and 200 GeV. An approximate independence of ⟨Nch⟩/⟨Npart/2⟩ on the number of participating nucleons is observed, reminiscent of "wounded nucleon" scaling (Nch∝Npart) observed in proton-nucleus collisions. Unlike p+A, the constant of proportionality does not seem to be set by the pp/¯pp data at the same energy. Rather, there seems to be a surprising correspondence with the total multiplicity measured in e+e− annihilations, as well as the rapidity shape measured over a large range. The energy dependence of the integrated multiplicity per participant pair shows that e+e− and A+A data agree over a large range of center-of-mass energies (√s>20 GeV), and pp/¯pp data can be brought to agree approximately with the e+e− data by correcting for the typical energy taken away by leading particles. This is suggestive of a mechanism for soft particle production that depends mainly on the amount of available energy. It is conjectured that the dominant distinction between A+A and p+p collisions is the multiple collisions per participant, which appears to be sufficient to substantially reduce the energy taken away by leading particles.Received 11 January 2005DOI:https://doi.org/10.1103/PhysRevC.74.021902©2006 American Physical Society

We have measured the transverse momentum distributions of charged hadrons in d+Au collisions at sqrt sNN = 200 GeV in the range of 0.5 < p_T < 4.0 GeV/c. The total range of pseudorapidity, eta, is 0.2 < eta < 1.4, where positive eta is in the deuteron direction. The data has been divided into three regions of pseudorapidity, covering 0.2 < eta < 0.6, 0.6 < \eta < 1.0, and 1.0 < eta < 1.4 and has been compared to charged hadron spectra from p+pbar collisions at the same energy. There is a significant change in the spectral shape as a function of pseudorapidity. As eta increases we see a decrease in the nuclear modification factor RdAu.

Two-particle correlations of identical charged pion pairs from Au+Au collisions at √sNN=62.4 and 200 GeV were measured by the PHOBOS experiment at BNL Relativistic Heavy Ion Collider (RHIC). Data for the 15% most central events were analyzed with Bertsch-Pratt and Yano-Koonin-Podgoretskii parametrizations using pairs with rapidities of 0.4<yππ<1.3 and transverse momenta 0.1<kT<1.4 GeV/c. The Bertsch-Pratt radii Ro and Rℓ decrease as a function of pair transverse momentum. Ro and Rs are independent of collision energy, while Rℓ shows a slight increase. The source rapidity yYKP scales roughly with the pair rapidity yππ, indicating strong dynamical correlations.Received 1 September 2004DOI:https://doi.org/10.1103/PhysRevC.73.031901©2006 American Physical Society

Transverse momentum spectra of pions, kaons, protons, and antiprotons from Au+Au collisions at √sNN = 62.4 GeV have been measured by the PHOBOS experiment at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. The identification of particles relies on three different methods: low momentum particles stopping in the first detector layers; the specific energy loss (dE/dx) in the silicon spectrometer, and time-of-flight measurement. These methods cover the transverse momentum ranges 0.03–0.2, 0.2–1.0, and 0.5–3.0 GeV/c, respectively. Baryons are found to have substantially harder transverse momentum spectra than mesons. The pT region in which the proton to pion ratio reaches unity in central Au+Au collisions at √sNN = 62.4 GeV fits into a smooth trend as a function of collision energy. At low transverse mass, the spectra of various species exhibit a significant deviation from transverse mass scaling. The observed particle yields at very low pT are comparable to extrapolations from higher pT for kaons, protons and antiprotons. By comparing our results to Au+Au collisions at √sNN = 200 GeV, we conclude that the net proton yield at midrapidity is proportional to the number of participant nucleons in the collision.5 MoreReceived 27 September 2006DOI:https://doi.org/10.1103/PhysRevC.75.024910©2007 American Physical Society

The Muon Scattering Experiment at the Paul Scherrer Institute uses a mixed beam of electrons, muons, and pions, necessitating precise timing to identify the beam particles and reactions they cause. We describe the design and performance of three timing detectors using plastic scintillator read out with silicon photomultipliers that have been built for the experiment. The Beam Hodoscope, upstream of the scattering target, counts the beam flux and precisely times beam particles both to identify species and provide a starting time for time-of-flight measurements. The Beam Monitor, downstream of the scattering target, counts the unscattered beam flux, helps identify background in scattering events, and precisely times beam particles for time-of-flight measurements. The Beam Focus Monitor, mounted on the target ladder under the liquid hydrogen target inside the target vacuum chamber, is used in dedicated runs to sample the beam spot at three points near the target center, where the beam should be focused.

We present results on charged particle production at very low transverse momenta in the 15% most central Au+Au collisions at sqrt(s_NN) = 200 GeV obtained with the PHOBOS detector at RHIC. The invariant yields were measured at mid-rapidity in the transverse momentum ranges from 30 to 50 MeV/c for charged pions, 90 to 130 MeV/c for charged kaons and 140 to 210 MeV/c for protons and antiprotons. No significant enhancement in low transverse momentum particle production is observed as compared to extrapolations of identified particle spectra measured at an intermediate pT range. The spectra tend to flatten at low pT, consistent with the expectations of transverse expansion of the system.

The ratios of the yields of primary charged antiparticles to particles have been obtained for pions, kaons, and protons near midrapidity for p+p collisions at sNN=200GeV. Ratios of 〈π−/π+〉=1.000±0.012 (stat.) ±0.019 (syst.), 〈K−/K+〉=0.93±0.05 (stat.) ±0.03 (syst.), and 〈p¯/p〉=0.85±0.04 (stat.) ±0.03 (syst.) have been measured. The reported values represent the ratio of the yields averaged over the rapidity range of 0.1<yπ<1.3 and 0<yK,p<0.8, and for transverse momenta of 0.1<pTπ,K<1.0GeV/c and 0.3<pTp<1.0GeV/c. Within the uncertainties, all three ratios are consistent with the values measured in d+Au collisions at the same energy. The data are compared to results from other collision systems and energies.Received 2 September 2004DOI:https://doi.org/10.1103/PhysRevC.71.021901©2005 American Physical Society

The ratios of charged antiparticles to particles have been obtained for pions, kaons and protons near midrapidity in central Au+Au collisions at sqrt(s_NN) = 200 GeV. Ratios of / = 1.025 +/- 0.006 (stat.) +/- 0.018 (syst.), / = 0.95 +/- 0.03 (stat.) +/- 0.03 (syst.) and / = 0.73 +/- 0.02 (stat.) +/- 0.03 (syst.) have been observed. The / and / ratios are consistent with a baryochemical potential mu_B of 27 MeV, roughly a factor of 2 smaller than in sqrt(s_NN) = 130 GeV collisions. The data are compared to results from lower energies and model calculations. Our accurate measurements of the particle ratios impose stringent constraints on current and future models dealing with baryon production and transport.

The centrality dependence of the midrapidity charged-particle multiplicity density ($|\ensuremath{\eta}|&lt;1$) is presented for $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Cu}+\mathrm{Cu}$ collisions at RHIC over a broad range of collision energies. The multiplicity measured in the $\mathrm{Cu}+\mathrm{Cu}$ system is found to be similar to that measured in the $\mathrm{Au}+\mathrm{Au}$ system, for an equivalent ${N}_{\mathrm{part}}$, with the observed factorization in energy and centrality still persistent in the smaller $\mathrm{Cu}+\mathrm{Cu}$ system. The extent of the similarities observed for bulk particle production is tested by a comparative analysis of the inclusive transverse momentum distributions for $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Cu}+\mathrm{Cu}$ collisions near midrapidity. It is found that, within the uncertainties of the data, the ratio of yields between the various energies for both $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Cu}+\mathrm{Cu}$ systems are similar and constant with centrality, both in the bulk yields and as a function of ${p}_{T}$, up to at least 4 GeV/$c$. The effects of multiple nucleon collisions that strongly increase with centrality and energy appear to only play a minor role in bulk and intermediate transverse momentum particle production.

The ratios of the yields of charged antiparticles to particles have been obtained for pions, kaons, and protons near midrapidity for $d+\mathrm{Au}$ collisions at $\sqrt{{s}_{NN}}=200\phantom{\rule{0.3em}{0ex}}\mathrm{GeV}$ as a function of centrality. The reported values represent the ratio of the yields averaged over the rapidity range of $0.1&lt;{y}_{\ensuremath{\pi}}&lt;1.3$ and $0&lt;{y}_{K,p}&lt;0.8$, where positive rapidity is in the deuteron direction, and for transverse momenta $0.1&lt;{p}_{T}^{\ensuremath{\pi},K}&lt;1\phantom{\rule{0.3em}{0ex}}\mathrm{GeV}∕c$ and $0.3&lt;{p}_{T}^{p}&lt;1\phantom{\rule{0.3em}{0ex}}\mathrm{GeV}∕c$. Within the uncertainties, a lack of centrality dependence is observed in all three ratios. The data are compared to results from other systems and model calculations.

This paper presents the analysis of the dynamic fluctuations in the inclusive charged particle multiplicity measured by PHOBOS for Au+Au collisions at √sNN = 200GeV within the pseudo-rapidity range of −3 < η < 3. First the definition of the fluctuations observables used in this analysis is presented, together with the discussion of their physics meaning. Then the procedure for the extraction of dynamic fluctuations is described. Some preliminary results are included to illustrate the correlation features of the fluctuation observable. New dynamic fluctuations results will be available in a later publication.

Antiparticle to particle ratios for identified protons, kaons, and pions at $\sqrt{{s}_{\mathit{NN}}}=62.4$ and 200 GeV in Cu+Cu collisions are presented as a function of centrality for the midrapidity region of $0.2&lt;\ensuremath{\eta}&lt;1.4$. No strong dependence on centrality is observed. For the $\ensuremath{\langle}\overline{p}\ensuremath{\rangle}/\ensuremath{\langle}p\ensuremath{\rangle}$ ratio at $\ensuremath{\langle}{p}_{T}\ensuremath{\rangle}\ensuremath{\approx}0.51$ GeV/$c$, we observe an average value of $0.50\ifmmode\pm\else\textpm\fi{}0.{003}_{(\mathrm{stat})}\ifmmode\pm\else\textpm\fi{}0.{04}_{(\mathrm{syst})}$ and $0.77\ifmmode\pm\else\textpm\fi{}0.{008}_{(\mathrm{stat})}\ifmmode\pm\else\textpm\fi{}0.{05}_{(\mathrm{syst})}$ for the 10% most central collisions of 62.4 and 200 GeV $\mathrm{Cu}+\mathrm{Cu}$, respectively. The values for all three particle species measured at $\sqrt{{s}_{\mathit{NN}}}=200$ GeV are in agreement within systematic uncertainties with that seen in both heavier and lighter systems measured at the same RHIC energy. This indicates that system size does not appear to play a strong role in determining the midrapidity chemical freeze-out properties affecting the antiparticle to particle ratios of the three most abundant particle species produced in these collisions.

Particle production in Au+Au collisions has been measured in the PHOBOS experiment at RHIC for a range of collision energies. Three empirical observations have emerged from this dataset which require theoretical examination. First, there is clear evidence of limiting fragmentation. Namely, particle production in central Au+Au collisions, when expressed as $dN/dη'$ ($η' \equiv η-y_{beam}$), becomes energy independent at high energy for a broad region of $η'$ around $η'=0$. This energy-independent region grows with energy, allowing only a limited region (if any) of longitudinal boost-invariance. Second, there is a striking similarity between particle production in e+e- and Au+Au collisions (scaled by the number of participating nucleon pairs). Both the total number of produced particles and the longitudinal distribution of produced particles are approximately the same in e+e- and in scaled Au+Au. This observation was not predicted and has not been explained. Finally, particle production has been found to scale approximately with the number of participating nucleon pairs for $N_{part}&gt;65$. This scaling occurs both for the total multiplicity and for high $\pT$ particles (3 $

A large area radial silicon pad detector has been produced, tested, and installed for the WA98 experiment at CERN. This paper describes the structure and the first test results of the silicon sensors used in this detector. Double metal technology has been used to lead the signals from the inner pads to the edge of the sensitive region. The capacitance for each pad has been measured and is shown to vary according to the pad size. Signals from 90Sr radiation have been analysed, and a signal-to-noise ratio of over 30 has been achieved. The RMS noise varies with the capacitance of each pad, and the variation agrees with the specification of the preamplifier. No evidence of cross talk due to the capacitance coupling between two metal layers has been observed.

The PHOBOS experiment at RHIC has measured the multiplicity of primary charged particles as a function of centrality and pseudorapidity in Au+Au collisions at sqrt(s_NN) = 19.6, 130 and 200 GeV. Two kinds of universal behavior are observed in charged particle production in heavy ion collisions. The first is that forward particle production, over a range of energies, follows a universal limiting curve with a non-trivial centrality dependence. The second arises from comparisons with pp/pbar-p and e+e- data. N_tot/(N_part/2) in nuclear collisions at high energy scales with sqrt(s) in a similar way as N_tot in e+e- collisions and has a very weak centrality dependence. This feature may be related to a reduction in the leading particle effect due to the multiple collisions suffered per participant in heavy ion collisions.

This paper presents the first PHOBOS results on charged particle multiplicity fluctuations measured for Au+Au collisions at the highest RHIC energy within a wide pseudorapidity range of |η| < 3. The dependence on collision geometry is removed in the analysis by using the normalized difference between the number of particles in separate η bins. We compare our data to HIJING model predictions.

The MUon Scattering Experiment, MUSE, at the Paul Scherrer Institute, Switzerland, investigates the proton charge radius puzzle, lepton universality, and two-photon exchange, via simultaneous measurements of elastic muon-proton and electron-proton scattering. The experiment uses the PiM1 secondary beam channel, which was designed for high precision pion scattering measurements. We review the properties of the beam line established for pions. We discuss the production processes that generate the electron and muon beams, and the simulations of these processes. Simulations of the $\pi$/$\mu$/$e$ beams through the channel using TURTLE and G4beamline are compared. The G4beamline simulation is then compared to several experimental measurements of the channel, including the momentum dispersion at the IFP and target, the shape of the beam spot at the target, and timing measurements that allow the beam momenta to be determined. We conclude that the PiM1 channel can be used for high precision $\pi$, $\mu$, and $e$ scattering.

PHOBOS is one of the four experiments at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. PHOBOS utilizes silicon sensors to measure charged particle multiplicity distributions and to track particles in a 2-arm spectrometer. The detector consists of 450 silicon pad sensors. Nine different pad geometries are used to match the different physics needs of the experiment. A relatively high granularity, of up to 1536 channels per sensor, is used in the spectrometer. The multiplicity detector uses 128 and 64 channel sensors and the charge deposition per pad is measured to determine the multiplicity of single events. All sensors are of the double-metal silicon pad type with pad sizes from 1 up to 4cm2. They are produced in Taiwan by the ERSO foundry under supervision of Miracle Co. and National Central University. An extensive testing procedure makes it possible to select sensors suited for use in PHOBOS. Detector modules consisting of up to 5 sensors are read out with integrated chips of either 64 or 128 channels. The test results of the sensors and the performance of the assembled detector modules are discussed.

The PHOBOS experiment is well positioned to obtain crucial information about relativistic heavy ion collisions at RHIC, combining a multiplicity counter with a multi-particle spectrometer.The multiplicity arrays will measure the charged particle multiplicity over the full solid angle.The spectrometer will be able to identify particles at mid-rapidity.The experiment is constructed almost exclusively of silicon pad detectors.Detectors of nine different types are configured in the multiplicity and vertex detector (22,000 channels) and two multi-particle spectrometers (120,000 channels).The overall layout of the experiment, testing of the silicon sensors and the performance of the detectors during the engineering run at RHIC in 1999 are discussed.

Spectator fragments resulting from relativistic heavy ion collisions, consisting of single protons and neutrons along with groups of stable nuclear fragments up to Nitrogen (Z=7), are measured in PHOBOS. These fragments are observed in Au+Au (sqrt(sNN)=19.6 GeV) and Cu+Cu (22.4 GeV) collisions at high pseudorapidity ($\eta$). The dominant multiply-charged fragment is the tightly bound Helium ($\alpha$), with Lithium, Beryllium, and Boron all clearly seen as a function of collision centrality and pseudorapidity. We observe that in Cu+Cu collisions, it becomes much more favorable for the $\alpha$ fragments to be released than Lithium. The yields of fragments approximately scale with the number of spectator nucleons, independent of the colliding ion. The shapes of the pseudorapidity distributions of fragments indicate that the average deflection of the fragments away from the beam direction increases for more central collisions. A detailed comparison of the shapes for $\alpha$ and Lithium fragments indicates that the centrality dependence of the deflections favors a scaling with the number of participants in the collision.

The status of the Silicon Microvertex Detector (SMD) and its installation into the LEP-I.3experiment are presented, highiighting novel features and sophisticated techniques.Preliminary results based on 1993 data are given and compared with Monte Carlo predictions, to understand the detector performances and its tracking capabilities.

Abstract A single-sided silicon sensor with capacitors coupling and polysilicon bias resistors has been designed and fabricated. A proposed process with ONO (Oxide-Nitride-Oxide) replacing the usual SiO 2 layer as the dielectric of coupling capacitor, in conjunction with a reordering of sequence for layer formations, is to produce sensors with self-moisture-protection and free from the effect of pin holes. A comparison of presented data of IV, CV and RV measurements for the sensors with ONO and with SiO 2 dielectrics revealed that the ONO processes could lead to an excellent voltage-handling capability of the coupling capacitor. One sensor has been successfully tested twice in the beam at CERN in the past two years, yielding an S/N ratio of 20 and an efficiency above 95%, also demonstrating its excellent stability with respect to lengthy exposure to atmosphere.

The PHOBOS experiment at RHIC has measured the total multiplicity of primary charged particles as a function of collision centrality in Au+Au collisions at sqrt(s_NN) = 19.6, 130 and 200 GeV. Above sqrt(s_NN) ~ 20 GeV, the total multiplicity per participating nucleon pair ( / ) in central events scales with sqrt(s) in the same way as in e+e- data. This is suggestive of a universal mechanism of particle production in strongly-interacting systems, controlled mainly by the amount of energy available for particle production (per participant pair for heavy ion collisions). The same effect has been observed in pp/pbar-p data after correcting for the energy taken away by leading particles. An approximate independence of / on the number of participating nucleons is also observed, reminiscent of ``wounded nucleon'' scaling ( proportional to ), but with the constant of proportionality set by the multiplicity measured in e+e- data rather than by pp/pbar-p data.

We present transverse momentum distributions of charged hadrons produced in Au+Au collisions at sqrt(s_NN) = 200 GeV. The evolution of the spectra for transverse momenta p_T from 0.25 to 5GeV/c is studied as a function of collision centrality over a range from 65 to 344 participating nucleons. We find a significant change of the spectral shape between proton-antiproton and peripheral Au+Au collisions. Comparing peripheral to central Au+Au collisions, we find that the yields at the highest p_T exhibit approximate scaling with the number of participating nucleons, rather than scaling with the number of binary collisions.

Transverse momentum spectra of pions, kaons and protons, as well as antiparticle to particle ratios near mid-rapidity from d+Au collisions at have been measured by the PHOBOS experiment at RHIC. The transverse momentum range of particle identification was extended to beyond 3 GeV/c using the TOF detector and a new trigger system. The pseudorapidity dependence of the nuclear modification factor for charged hadrons in d+Au collisions is presented.

Abstract The analysis on test beam data of a large silicon microstrip detector is presented. The spatial resolution has been studied with full GEANT simulation to calculate the systematic uncertainty due to multiple scattering. Several cluster position-finding algorithms have been applied for inclined tracks. The cluster profile and spatial resolution have the predicted geometrical correlation to the track angle.

High-precision tracking and charge selection with silicon strip detectors for relativistic ions has been investigated using a 12C beam of 1.5GeV/u at GSI with prototype modules developed for the AMS tracker. The ionization energy loss is measured and compared to the Landau–Vavilov theory for ions of charge number up to Z=6. The linearity in Z2 is examined. The capability to distinguish different Z values based on the ionization energy loss is evaluated. The spatial resolution of the silicon strip detectors is investigated for carbon ions. The angular distribution of multiple Coulomb scattering is studied with lead absorbers. The results are compared to the Molière theory and the Gaussian approximation of GEANT calculations.

Some of the latest results of the PHOBOS experiment from the Au+Au data are discussed. Those relevant to strangeness production are emphasized. These observations relate to the nature of the matter created when heavy ions collide at the highest achieved energy.

Collision centrality is a valuable parameter used in relativistic nuclear physics which relates to geometrical quantities such as the number of participating nucleons. PHOBOS utilizes a multiplicity measurement as a means to estimate fractional cross-section of a collision event-by-event. From this, the centrality of this collision can be deduced. The details of the centrality determination depend both on the collision system and collision energy. Presented here are the techniques developed over the course of the RHIC program that are used by PHOBOS to extract the centrality. Possible biases that have to be overcome before a final measurement can be interpreted are discussed.

Two-particle correlations of identical charged pion pairs from Au+Au collisions at sqrt(s_NN) = 200 GeV were measured by the PHOBOS experiment at RHIC. Data for the most central (0--15%) events were analyzed with Bertsch-Pratt (BP) and Yano-Koonin-Podgoretskii (YKP) parameterizations using pairs with rapidities of 0.4 < y < 1.3 and transverse momenta 0.1 < k_T < 1.4 GeV/c. The Bertsch-Pratt radii decrease as a function of pair transverse momentum. The pair rapidity Y_pipi roughly scales with the source rapidity Y_YKP, indicating strong dynamical correlations.

An overview of results for interactions of Au+Au ions at centre-of-mass energies of √sNN = 56, 130 and 200 GeV obtained by the PHOBOS collaboration at RHIC is given. Measurements of primary charged particle density near mid-rapidity indicate that particle production grows logarithmically with collision energy and faster than linearly with the number of interacting nucleons. Elliptic flow is found to be much stronger at RHIC than at SPS energy. The effect is strongest in peripheral events and decreases for more central collisions and emission angles |η| > 1. The measured anti-particle to particle ratios of production rates for pions, kaons and protons in central Au+Au interactions at √sNN = 130 GeV are compatible with the statistical model of particle production, showing an increasingly baryon-free region in mid-rapidity with the increase of collision energy.

We present new results from the PHOBOS experiment at RHIC on event‐by‐event fluctuations of particle multiplicities and angular distributions in nucleus‐nucleus collisions at RHIC. Our data for Au+Au collisions at sNN = 200 GeV show that at a level of 10−4 or less, no rare, large‐amplitude fluctuations in the total multiplicity distributions or the shape of the pseudorapidity distributions are observed. We however find significant short‐range multiplicity correlations in these data, that can be described as particle production in clusters. In Cu+Cu collisions, we observe large final‐state azimuthal anisotropies ν2. A common scaling behavior for Cu+Cu and Au+Au for these anisotropies emerges when fluctuations in the initial state geometry are taken into account.

An upgrade of the L3 central tracking system, a silicon muvertex detector (SMD), is described. The detector consists of two layers of silicon, each equipped for rφ and z readout with resolution ≈ 6 μm and ≈ 20 μm respectively. The SMD will provide full azimuthal coverage over the polar angular range 22°≤θ≤158°. The total thickness is ≈0.9% of one radiation length.

Two modules of the L3 Silicon Microvertex Detector (SMD) have been tested on beam. The active area of the modules consists of double sided silicon microstrip detectors; the implantation pitch is 25 μm and 50 μm in the junction and ohmic side, respectively. The detectors are read out by a VLSI radiation hard amplifier (SVX-H). The position resolution, with a readout pitch of 50 μm and 200 μm for the two sides, is determined to be 7.0 μm and 14.3 μm. A signal to noise ratio ⩾ 16 and a detection efficiency ⩾ 99% are measured for both sides.

The Phobos experiment concluded its first year of operation at RHIC taking data in Au–Au nucleus collisions at snn=65GeV and 130GeV/nucleon pair. First preliminary results of the performances of our silicon detectors in the experiment are summarized. The Phobos experiment uses silicon pad detectors for both tracking and multiplicity measurements. The silicon sensors vary strongly in their pad geometry. In this paper, we compare the signal response, the signal uniformity and signal-to-noise performance as measured in the experiment for the different geometries. Additionally, we investigate effects of very high channel occupancy on the signal response.

Recent results from the PHOBOS experiment at RHIC are presented, both from Au+Au collisions from the 2001 run and p+p and d+Au collisions from 2003. The centrality dependence of the total charged particle multiplicity in p+p and d+Au show features, such as Npart-scaling and limiting fragmentation, similar to p+A collisions at lower energies. Multiparticle physics in Au+Au is found to be local in (pseudo)rapidity, both when observed by HBT correlations and by forward-backward pseudorapidity correlations. The shape of elliptic flow in Au+Au, measured over the full range of pseudorapidity, appears to have a very weak centrality dependence. Identified particle ratios in d+Au reactions show little difference between the shape of proton and anti-proton spectra, while the absolute yields show an approximate m_T scaling.

PHOBOS is one of the four heavy ion experiments currently running at the Relativistic Heavy Ion Collider (RHIC). In this paper we will present some of the current results from PHOBOS: the study of charged multiplicity distribution as function of pseudorapidity and centrality at <IMG SRC="/img/revistas/bjp/v34n3a/a32img01.gif" > or = 19.6, 130 and 200 GeV, a discussion of multiplicity scaling, and a measurement of transverse momentum spectra (pT) of charged hadrons produced in d+Au and Au+Au interactions at <IMG SRC="/img/revistas/bjp/v34n3a/a32img01.gif" > or = 200 GeV. The dependence of the Au+Au yields as function of centrality is found to be independent of pT. A strong suppression in the Au+Au hadron spectra relative to p<IMG SRC="/img/revistas/bjp/v34n3a/a32img05.gif"> at high pT is observed. The spectral shape for d+Au collisions is significantly different from the observations in Au+Au, the yield suppression is not observed in d+Au.

Elliptic flow is an interesting probe of the dynamical evolution of the dense system formed in the ultrarelativistic heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC).The elliptic flow dependences on transverse momentum, centrality, and pseudorapidity were measured using data collected by the PHOBOS detector, which offers a unique opportunity to study the azimuthal anisotropies of charged particles over a wide range of pseudorapidity.These measurements are presented, together with an overview of the analysis methods and a discussion of the results.Collisions of Au nuclei at the Relativistic Heavy Ion Collider (RHIC) are the most energetic nucleus-nucleus collisions ever achieved in a laboratory, allowing for the study of the properties of nuclear matter under extreme conditions.In order to characterize the medium created in the Au+Au collisions at RHIC, it is necessary to establish that the particles in the system undergo enough reinteractions to reach a state of thermal equilibrium.Only in such a state may the evolution of the medium be described in terms of thermodynamical quantities.Elliptic flow is one of the experimental observables than can help resolve this question.

We report test beam results on the overall system performance of two modules of the L3 Silicon Microvertex Detector exposed to a 50 GeV pion beam. Each module consists of two AC coupled double-sided silicon strip detectors equipped with VLSI readout electronics. The associated data acquisition system comprises an 8 bit FADC, an optical data transmission circuit, a specialized data reduction processor and a synchronization module. A spatial resolution of 7.5 mu;m and 14 mu;m for the two coordinates and a detection efficiency in excess of 99% are measured.

Abstract A report on the status of the construction of the L3 Silicon Microvertex Detector is presented here. The detector will consist of two double sided AC coupled silicon layers equipped with rφ and z readout with an expected intrinsic resolution of ≈ 6 μ m and ≈ 25 μ m respectively. A description of the detector with its mechanical support, alignment system and readout electronics is presented.

The new technologies used in the construction of the L3 Silicon Microvertex Detector (SMD) at LEP are presented. The SMD consists of two cylindrical layers of double sided silicon sensors to provide very precise measurements of both rφ and z coordinates. In order to minimize the amount of material in the central region, a Kapton fanout has been developed to bring the signals of the z strips (transverse coordinate) to the end of the mechanical structure. To get rid of the leakage currents a new capacitor chip, with diode protection against overvoltages, has been designed and used. In addition, a solution based on optodecoupling has been adopted to read the silicon n-side strips operating at the bias voltage.

We present a test beam study of energy straggling and multiple scattering in silicon strip detectors using electrons and pions of momenta up to 50 GeV. Results are compared with GEANT simulation using a simple algorithm to parameterize energy loss distribution. The deflection due to multiple scattering in crystalline structure was investigated by placing a GaAs wafer at various angles.

PHOBOS is one of the four experiments at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. PHOBOS almost exclusively utilizes silicon sensors to measure charged particle multiplicity distributions and to track particles in a 2-arm spectrometer. The detector consists of about 450 silicon pad sensors. Nine different pad geometries are used to match the different physics needs of the experiment. A relatively high granularity, of up to 1536 channels per sensor, is used in the spectrometer. The multiplicity detector uses 128 and 64 channel sensors and the charge deposition per pad is measured to determine the multiplicity of single events. All sensors are of the double-metal silicon pad type with pad sizes from 1 cm2 up to 4 cm2. They are produced in Taiwan by the ERSO foundry under supervision of Miracle Co. and National Central University. An extensive testing procedure makes it possible to select sensors suited for use in PHOBOS. Detector modules consisting of up to five sensors are read out with integrated chips of either 64 or 128 channels. The testing of the sensors and the performance of assembled detector modules is discussed.

Transverse momentum spectra of charged hadrons with p T < 6 GeV/c have been measured near mid-rapidity (0.2 < η < 1.4) by the PHOBOS experiment at RHIC in Au + Au and d + Au collisions at ${\sqrt{s_{_{NN}}}~= \rm {200~GeV}}$ . The spectra for different collision centralities are compared to ${p + \bar{p}}$ collisions at the same energy. The resulting nuclear modification factor for central Au + Au collisions shows evidence of strong suppression of charged hadrons in the high-p T region (>2 GeV/c). In contrast, the d + Au nuclear modification factor exhibits no suppression of the high-p T yields. These measurements suggest a large energy loss of the high-p T particles in the highly interacting medium created in the central Au + Au collisions. The lack of suppression in d + Au collisions suggests that it is unlikely that initial state effects can explain the suppression in the central Au + Au collisions. PACS: 25.75.-q

United States Department of Energy (grants DE-AC02-98CH10886, DE-FG02-93ER40802, DEFG02- 94ER40818, DE-FG02-94ER40865, DE-FG02- 99ER41099, and DE-AC02-06CH11357)

high-pT trigger particle, elliptic flow fluctuations and two particle correlations. ∗the PHOBOS Collaboration: B.Alver4, B.B.Back1, M.D.Baker2, M.Ballintijn4, D.S.Barton2, R.R.Betts6, A.A.Bickley7, R.Bindel7, W.Busza4, A.Carroll2, Z.Chai2, V.Chetluru6, M.P.Decowski4, E.Garcia6, T.Gburek3, N.George2, K.Gulbrandsen4, C.Halliwell6, J.Hamblen8, I.Harnarine6, M.Hauer2, C.Henderson4, D.J.Hofman6, R.S.Hollis6, R.HoAlynski3, B.Holzman2, A.Iordanova6, E.Johnson8, J.L.Kane4, N.Khan8, P.Kulinich4, C.M.Kuo5, W.Li4, W.T.Lin5, C.Loizides4, S.Manly8, A.C.Mignerey7, R.Nouicer2, A.Olszewski3, R.Pak2, C.Reed4, E.Richardson7, C.Roland4, G.Roland4, J.Sagerer6, H.Seals2, I.Sedykh2, C.E.Smith6, M.A.Stankiewicz2, P.Steinberg2, G.S.F.Stephans4, A.Sukhanov2, A.Szostak2, M.B.Tonjes7, A.Trzupek3, C.Vale4, G.J.van Nieuwenhuizen4, S.S.Vaurynovich4, R.Verdier4, G.I.Veres4, P.Walters8, E.Wenger4, D.Willhelm7, F.L.H.Wolfs8, B.Wosiek3, K.Woźniak3, S.Wyngaardt2, B.WysAlouch4 1 Argonne National Laboratory, Argonne, IL 60439-4843, USA 2 Brookhaven National Laboratory, Upton, NY 11973-5000, USA 3 Institute of Nuclear Physics PAN, Krakow, Poland 4 Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA 5 National Central University, Chung-Li, Taiwan 6 University of Illinois at Chicago, Chicago, IL 60607-7059, USA 7 University of Maryland, College Park, MD 20742, USA 8 University of Rochester, Rochester, NY 14627, USA

8/spl times/4 cm/sup 2/ single-sided p/sup +/-i (or v)-n/sup +/ silicon microstrip sensors with coupling capacitors and polysilicon bias resistors were fabricated with the planar technology, and various techniques used to reduce the leakage currents of sensors and their results are presented. Different gettering processes have been employed to remove the impurities and defects from the sensor active regions, and the Electronic Research and Service Organization (ERSOs) Charge-Coupled Device (CCD) gettering technique, combined with backside polysilicon and oxide-nitride-oxide (ONO) deposition process, was found to be the most effective and suitable one. From the measurement results of the special p/sup +/-i (or v)-n/sup +/ junction test structures, it was found that the sensor leakage current mainly came from the side-wall leakage of its p/sup +/-strip. A modified LOCal Oxidation of Silicon (LOGOS) isolation process has been used to reduce this side-wall leakage. Also, the Sirtl-etch analysis of the sensor revealed that the side-wall leakage current has been caused by residual boron-implantation defects after annealing. These defects would concentrate along the edge of p/sup +/-strip and be enhanced to cause dislocations by the film-edge-induced stress effect. Several annealing techniques have also been studied to remove the boron-implantation damages. The fabricated prototype sensors have been tested in a beam at the CERN Super Proton Synchrotron area. The test results showed that the sensor concept under study is feasible.

The early summer of 2000 saw the start of the RHIC experimental programme. The PHOBOS collaboration used data from the beginning of the running period to extract the first physics information about this exciting new regime. This first measurement consisted of pseudorapidity densities of primary charged particles near mid-rapidity in central Au + Au collisions at beam energies which gave centre-of-mass energies per pair of colliding nucleons of √snn = 56 and 130 GeV. The observed densities are higher than those observed previously in any collisions in the laboratory. In addition, the rate of increase in density between the two energies is significantly larger than that for nucleon-nucleon collisions at comparable beam energies. This paper will briefly describe the PHOBOS experiment (including the subset of the full detector installed for the early period of the RHIC beam), discuss the results of the first physics measurement and conclude with the prospects for the future, especially in the area of strangeness production.

Research regarding patient awareness of osteopathic manipulative medicine (OMM) can help identify barriers and factors limiting patient knowledge. Levels of knowledge about OMM and osteopathic physicians have been studied in New York's Chinese and Korean populations, but have not previously been investigated in the South Asian population.To assess the knowledge of OMM and osteopathic physicians within a South Asian community of New York.A cross-sectional study was designed in which a culturally appropriate survey, provided in both English and Hindi, was administered to study participants in order to measure knowledge of osteopathic medicine. The study utilized convenience sampling and distributed surveys to individuals who identified themselves of South Asian descent at high traffic sites in Hicksville, New York. The survey contained 10 questions, assessing the individual's knowledge of osteopathic medicine. The Kruskal-Wallis and Chi-Square tests were employed to determine statistical significance of the data obtained from the surveys.The survey was conducted on 100 participants in Hicksville, New York. The respondent demographics included 53 males and 47 females with an average age of 41.2 ± 16.3 years old. There were 34 (34%) participants who had heard of osteopathic manipulative medicine (OMM) and 26 (26%) participants who had knowledge of doctor of osteopathic medicine (DO) physicians. Respondents were found more likely to have knowledge of DOs if they were born in the United States (US) vs. other countries (US, 8 of 14 [57.1%] vs. others, 18 of 86 [20.9%]; p=0.006) or lived longer in the US (11 of 26 [42.3%], p=0.039). Participants who spoke a non-English primary language were also found less likely to have knowledge of DOs as they made up 46 of the 58 respondents who indicated no knowledge (79.3%, p=0.042).A general lack of knowledge of DOs and OMM exists within the South Asian community of Hicksville, New York and lower levels of awareness were found among participants who were male, born outside the US, had a language other than English as their primary language, and had spent less time in the US. Additional educational resources may be implemented to increase awareness of DOs and OMM among this and similar communities.

PHOBOS is one of the four experiments at the Relativistic Heavy Ion Collider measuringp + p, d + Au, andAu + Au collisions over a broad range of energies. PHOBOS is a silicon-pad based detector with a 4π multiplicity detector and a high resolution mid-rapidity spectrometer, along with other detectors (time-of-flight walls, proton and zero degree calorimeters). PHOBOS is able to measure particles at low transverse momentum, spectra, flow, particle ratios, and multiplicity over a large region of phase space. A comparison of results forAu + Au andd + Au collisions at√SNN = 220GeV will be discussed.

The production of δ-ray electrons in silicon strip tracking systems is measured for electrons in the energy range of 2–50 GeV. The results are compared to GEANT calculations. The production cutoff threshold is calibrated, and a value of Tcut=500keV is chosen. The δ-ray angular distribution is measured for electrons transmitting through a 320μm silicon wafer. The δ-ray production rate is approximately 1.3% within an angular region of 1–50 mrad.

Forward calorimetry in the PHOBOS detector has been used to study charged hadron production in d+Au, p+Au, and n+Au collisions at sNN=200GeV. The forward proton calorimeter detectors are described and a procedure for determining collision centrality with these detectors is detailed. The deposition of energy by deuteron spectator nucleons in the forward calorimeters is used to identify p+Au and n+Au collisions in the data. A weighted combination of the yield of p+Au and n+Au is constructed to build a reference for Au+Au collisions that better matches the isospin composition of the gold nucleus. The pT and centrality dependence of the yield of this improved reference system is found to match that of d+Au. The shape of the charged-particle transverse momentum distribution is observed to extrapolate smoothly from p+p¯ to central d+Au as a function of the charged-particle pseudorapidity density. The asymmetry of positively and negatively charged hadron production in p+Au is compared to that of n+Au. No significant asymmetry is observed at midrapidity. These studies augment recent results from experiments at the CERN Large Hadron Collider and BNL Relativistic Heavy Ion Collider facilities to give a more complete description of particle production in p+A and d+A collisions, essential for the understanding the medium produced in high-energy nucleus-nucleus collisions.11 MoreReceived 25 May 2015DOI:https://doi.org/10.1103/PhysRevC.92.034915©2015 American Physical Society

We have studied the spatial resolution of a preshower system with aluminum as absorber and silicon strips as the active sampling detector. The test beam was performed at X3 of the CERN SPS using an electron beam with energies between 4 and 50 GeV. The shower profiles of different beam momenta and absorber thicknesses are compared to full GEANT simulations.

An 8×4 cm 2 single-sided silicon microstrip sensor with coupling capacitors and polysilicon bias resistors has been fabricated with planar technology. The oxide-nitride-oxide (ONO) films have been chosen to replace the usual SiO 2 layer as the dielectric of the coupling capacitor. In conjunction with a reordering of the process sequence for layer formations, the proposed process could be used to fabricate sensors with self-moisture protection and free from the effect of pinholes. From the measurement results of special p-n junction test structures, we found that their leakage current was dominated by that of the sidewall one. Stress measurement and Sirtl-etch analysis revealed that the sidewall leakage current was increased by the dielectric stress and implantation damage. A boron solid-source predeposition process was employed to reduce this leakage current. From the results of electrical measurement and beam test on sensors, it was shown that the proposed process was able to produce sensors having very good performance.

In order to separate K and  with momenta up to 1.1 GeV/c using Time-of-Flight (TOF) over a distance of about 100 cm in the magnet, we will use Multi-Gap Resistive Plate Chamber (MRPC) due to the need of large area, high efficiency and overall time resolution in the range of 50-100 ps.We built a 260 μm × 10 gaps MRPC with an active area of 10 × 50 cm 2 and a pad size of 2.5 × 40 cm 2 .We studied the trigger rate dependence and the gas mixture of this MRPC.It was found that high enough voltage is necessary to achieve a good time resolution and high efficiency at large trigger rates.The gas mixture composed of R134a : SF6 : Iso-Butane at 90% : 5% : 5% is our optimized choice.

This study is aimed at exploring the details of various aspects of building long microstrip ladders for future particle physics collider experiments. Several configurations of silicon microstrip detectors (up to 64 cm in length) and two GaAs detectors were constructed and beam tested using the Viking front end chip and a PC-based data acquisition system allowing easy comparison and understanding of the results. Results on cluster charge, signal-to-noise, resolutions, and efficiencies for different configurations are presented and compared here.

United States. Department of Energy (Grants DE-AC02-98CH10886, DE-FG02-93ER40802, DE-FG02- 94ER40818, DE-FG02-94ER40865, DE-FG02-99ER41099, and DE-AC02-06CH11357)

Author(s): Alston-Garnjost, M.; Avery, R.E.; Barker, A.R.; Bauer, D.A.; Bay, A.; Buijs, A.; Belcinski, R.; Bingham, H.H.; Bloom, E.D.; Buchanan, C.D.; Caldwell, D.O.; Chao, H-Y.; Chun, S-B.; Clark, A.R.; Crane, D.A.; Dahl, O.I.; Daoudi, M.; Eastman, J.J.; Eberhard, P.H.; Edberg, T.K.; Eisner, A.M.; Erne, F.C.; Fairfield, K.H.; Godfrey, G.; Hauptman, J.M.; Hofmann, W.; Kenney, R.W.; Khacheryan, S.; Knopfle, K.T.; Kofler, R.R.; Lambert, D.J.; Langeveld, W.G.J.; Layter, J.G.; Lin, W.T.; Linde, F.L.; Loken, S.C.; Lu, A.; Lynch, G.R.; Lys, J.E.; Madaras, R.J.; Marsiske, H.; Masek, G.E.; Loken, S.C.; Lu, A.; Lynch, G.R.; Lys, J.E.; Madaras, R.J.; Marsiske, H.; Masek, G.E.; Mathis, L.G.; Miller, E.S.; Nicol, N.A.; Nygren, D.R.; Oddone, P.J.; Oyang, Y.-T.; Paar, H.P.; Palounek, A.P.T.; Park, S.K.; Pellett, D.E.; Pripstein, M.; Ronan, M.T.; Ross, R.R.; Sens, J.C.; Shapiro, G.; Shen, B.C.; Steinman, J.S.; Stephens, R.W.; Stevenson, M.L.; Stork, D.H.; Strauss, M.G.; Sullivan, M.K.; Toutounchi, S.; Vernon, W.; Wang, E.M.; Wang, Y.-X.; Wenzel, W.A.; Yamamoto, H.; Yellin, S.J.; Yost, G.P.; Zapalac, G.; Zeitlin, C.

A selection of experimental results from the PHOBOS Collaboration relevant for probing high-energy nuclear collisions with high transverse momentum particles is presented. The inclusive yields of charged particles and comparisons between nuclear and elementary collisions already reveal a large amount of parton energy loss in the hot and dense medium created in heavy ion collisions. Remarkable scaling and factorization features are observed, unifying the data taken at various collision energies, centralities and nuclear sizes. To further analyze the nature of the energy loss, a measurement of pseudorapidity (Δη) and azimuthal angle (Δφ) correlations between high transverse momentum charged hadrons (p T >2.5 GeV/c) and all associated charged particles is presented at both short-range (small Δη) and long-range (large Δη) over a continuous detector acceptance covering −4<Δη<2. Various near- and away-side features of the correlation structure are discussed as a function of centrality in Au + Au collisions at $\sqrt{s_{NN}}=200$ GeV. The results provide new information about the longitudinal (Δη) extent of the near-side ‘ridge’ structure, first observed by the STAR Collaboration over a narrower η range. In central Au + Au collisions the ridge structure extends to at least Δη=4, and its strength completely diminishes as collisions become more peripheral.

Author(s): Wosiek, B; Alver, B; Back, BB; Baker, MD; Ballintijn, M; Barton, DS; Betts, RR; Bickley, AA; Bindel, R; Busza, W; Carroll, A; Chai, Z; Chetluru, V; Decowski, MP; Garcia, E; Gburek, T; George, N; Gulbrandsen, K; Halliwell, C; Hamblen, J; Harnarine, I; Hauer, M; Henderson, C; Hofman, DJ; Hollis, RS; Holynski, R; Holzman, B; Iordanova, A; Johnson, E; Kane, JL; Khan, N; Kulinich, P; Kuo, CM; Li, W; Lin, WT; Loizides, C; Manly, S; Mignerey, AC; Nouicer, R; Olszewski, A; Pak, R; Reed, C; Richardson, E; Roland, C; Roland, G; Sagerer, J; Seals, H; Sedykh, I; Smith, CE; Stankiewicz, MA; Steinberg, P; Stephans, GSF; Sukhanov, A; Szostak, A; Tonjes, MB; Trzupek, A; Vale, C; van Nieuwenhuizen, GJ; Vaurynovich, SS; Verdier, R; Veres, GI; Walters, P; Wenger, E; Willhelm, D; Wolfs, FLH; Woźniak, K; Wyngaardt, S; Wyslouch, B | Abstract: Recently PHOBOS has focused on the study of fluctuations and correlations in particle production in heavy-ion collisions at the highest energies delivered by the Relativistic Heavy Ion Collider (RHIC). In this report, we present results on event-by-event elliptic flow fluctuations in Au + Au collisions at √sNN =200 GeV. A data-driven method was used to estimate the dominant contribution from non-flow correlations. Over the broad range of collision centralities, the observed large elliptic flow fluctuations are in agreement with the fluctuations in the initial source eccentricity.

Loeys–Dietz syndrome (LDS) is caused by connective tissue mutations; the resulting defective connective tissue in organs such as the eye may be related to ocular symptoms in patients with LDS. The aim of this study was to review different ocular manifestations in LDS. A literature review of articles published within the past 5 years was performed using Web of Science™ and PubMed to search for ‘Loeys–Dietz’ with the terms ‘ocular’ and ‘ophthalmology.’ Additional search terms were generated from the initial literature assessment, and 32 articles were ultimately reviewed. Reported ocular symptoms in LDS included hypertelorism, ocular misalignment, refractive errors, and more. For LDS, the most reported findings were hypertelorism (n=111), astigmatism (n=25), down slanting palpebral fissures (n=20), myopia (n=9), and strabismus (n=8). However, more research on ocular symptoms in LDS is needed.

We present a study of lateral shower profiles using granular silicon microstrip detectors for electrons of momenta from 2 to 50 GeV. The absorbers used are lead, copper and tungsten from 0.5 to 4X0. The measurements of lateral shower spectra and shower multiplicities are compared to full GEANT simulations.

The PHOBOS experiment has measured the properties of particle production in heavy ion collisions between sqrt(s_NN) of 20 and 200 GeV. The dependencies of charged particle yield on energy, system size, and both longitudinal and transverse momentum have been determined over close to the full kinematic range. Identified charged particles emitted near mid-rapidity have been studied over about 2 orders of magnitude in transverse momentum. This broad data set was found to be characterized by a small number of simple scalings which factorize to a surprising degree. This study has recently been extended by the addition of new data for Cu+Cu as well as new analyses of Au+Au data, including more peripheral collisions. In addition, the exploration of global properties has been expanded with the use of new techniques, including two-particle correlations, more sensitive searches for rare events, and more detailed studies of particles emitted at very forward rapidity. The characteristics of particle production which are revealed by this extensive data set will be described along with the implications for future data from the LHC.

We present measurements of elliptic flow and event-by-event fluctuations established by the PHOBOS experiment. Elliptic flow scaled by participant eccentricity is found to be similar for both systems when collisions with the same number of participants or the same particle area density are compared. The agreement of elliptic flow between Au+Au and Cu+Cu collisions provides evidence that the matter is created in the initial stage of relativistic heavy ion collisions with transverse granularity similar to that of the participant nucleons. The event-by-event fluctuation results reveal that the initial collision geometry is translated into the final state azimuthal particle distribution, leading to an event-by-event proportionality between the observed elliptic flow and initial eccentricity.

We introduce an analysis method to measure elliptic flow (v 2 ) fluctuations using the PHOBOS detector for Au+Au collisions at √ s NN = 200 GeV.In this method, v 2 is determined event-by-event by a maximum likelihood fit.The non-statistical fluctuations are determined by unfolding the contribution of statistical fluctuations and detector effects using Monte Carlo simulations(MC).Application of this method to measure dynamical fluctuations embedded in special MC are presented.It is shown that the input fluctuations are reconstructed successfully for v 2 ≥ 0.03.