We have investigated the particle production and fragmentation of nuclei participating in the interactions of 10.6 GeV/n gold nuclei in nuclear emulsions. A new criterion has been found to distinguish between the interactions of these gold nuclei with the light (H,C,N,O) and heavy (Ag, Br) target nuclei in the emulsion. This has allowed separate analyses of the multiplicity and pseudo-rapidity distributions of the singly charged particles emitted in Au-(H,C,N,O) and Au-(Ag,Br) interactions, as well as of the modes of breakup of the projectile and target nuclei. The pseudo-rapidity distributions show strong forward asymmetries, particularly for the interactions with the light nuclei. Heavy target nuclei produce a more severe breakup of the projectile gold nucleus than do the lighter targets. A negative correlation between the number of fragments emitted from the target nuclei and the degree of centrality of the collisions has been observed, which can be attributed to the total destruction of the relatively light target nuclei by these very heavy projectile nuclei.
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Charged particle multiplicities from high multiplicity central interactions of 158 GeV/nucleon Pb ions with Pb target nuclei have been measured in the central and far forward projectile spectator regions using emulsion chambers. Multiplicities are significantly lower than predicted by Monte Carlo simulations. We examine the shape of the pseudorapidity distribution and its dependence on centrality in detail.
Q(NAME=B) parameter is the total sum of the individual charges of the projectile fragments.
The Krakow-Louisiana-Minnesota-Moscow Collaboration (KLMM) has exposed a set of emulsion chambers with lead targets to a 158 GeV/c per nucleon beam of Pb208 nuclei, and we report the initial analysis of 40 high-multiplicity Pb-Pb collisions. To test the validity of the superposition model of nucleus-nucleus interactions in this new regime, we compare the shapes of the pseudorapidity distributions with FRITIOF Monte Carlo model calculations, and find close agreement for even the most central events. We characterize head-on collisions as having a mean multiplicity of 1550±120 and a peak pseudorapidity density of 390±30. These estimates are significantly lower than our FRITIOF calculations. © 1996 The American Physical Society.
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Oxygen and sulfur nuclei with energies of 200 GeV/nucleon have been allowed to interact in nuclear emulsions exposed at CERN. These emulsions have been scanned with a minimum bias so that essentially all the interactions occurring were detected. Nearly 1000 interactions of each projectile have been analyzed. We present results on the multiplicity distributions, the pseudorapidity distributions, and the fragmentation of the projectile and target nuclei. It is shown that the mean number of intranuclear collisions in each interaction, calculated from a superposition model, provides a useful parameter for organizing the data. We conclude that there are no significant deviations even at these energies from models, such as the venus model, describing the interactions as being the superposition of individual nucleon-nucleon collisions.
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The degree of excitation of the emulsion target nuclei due to nuclear interactions of oxygen and sulfur projectiles at 200 GeV/nucleon incident energy has been investigated. Using the plausible assumption that the numberNb of slow particles emitted from the struck target nucleus can be interpreted as a measure of the temperatureT of the residual nucleus, we have found that there exists a critical temperatureTc of the excited target nucleus. For Ag and Br target nuclei this temperature corresponds to
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Measurements have been made of inclusive 525 GeV π− interactions in emulsion. The results are compared to proton-emulsion and lower energy pion-emulsion data. Average multiplicities of relativistic shower particles increase with increasing energy, although with a somewhat steeper slope above 60 GeV than at lower energies. The ratio 〈ns〉p/〈ns〉π∼1.1 over the energy range 60–525 GeV. The ratio of the dispersion in the multiplicity distribution to the average multiplicity is the same for proton and pion collisions in emulsion, and is independent of projectile energy. The shape of the shower particle multiplicity distribution does not vary significantly with energy, and KNO scaling appears to hold over the energy range 60–525 GeV. The shower particle pseudorapidity distributions are independent of the beam energy in the target and projectile fragmentation regions, and both the pseudorapidity and multiplicity distributions agree reasonably well with the fritiof model predictions for 525 GeV pions. The dependence of the shower particle multiplicity 〈ns〉 on the number of heavy tracks Nh appraoches saturation as the total shower particle energy becomes a significant fraction of √s , and the pseudorapidity distributions shift toward smaller 〈η〉 with increasing numbers of grey and black tracks at 525 GeV. Neither the average number 〈Nh〉 nor the multiplicity distributions of the heavily ionizing tracks vary significantly with energy, and the normalized angular distributions of grey and black tracks are independent of the type of projectile or projectile energy.
NUCLEUS means average nuclei of BR-2 emulsion.
NUCLEUS means average nuclei of BR-2 emulsion.
NUCLEUS means average nuclei of BR-2 emulsion.
Analyzing powers ( A y ) and spin-rotation-depolarization parameters ( D SS , D SL , D LS , D LL , D NN ) were determined for 500 MeV p + 2 H and p + 12 C inclusive quasielastic scattering at 10°, 15°, and 20° laboratory scattering angles. The p + 2 H data are consistent with the isospin-average of the proton-proton and proton-neutron scattering observables; the p + 12 C data are not. A relativistic plane wave impulse approximation calculation leads to better agreement with the p + 12 C spin-observables.
Inclusive quasielastic p deut measurements.
Inclusive quasielastic p c measurements.
An updated analysis using about 1.5 million events recorded at $\sqrt{s} = M_Z$ with the DELPHI detector in 1994 is presented. Eighteen infrared and collinear safe event shape observables are measured as a function of the polar angle of the thrust axis. The data are compared to theoretical calculations in ${\cal O} (\alpha_s^2)$ including the event orientation. A combined fit of $\alpha_s$ and of the renormalization scale $x_{\mu}$ in $\cal O(\alpha_s^2$) yields an excellent description of the high statistics data. The weighted average from 18 observables including quark mass effects and correlations is $\alpha_s(M_Z^2) = 0.1174 \pm 0.0026$. The final result, derived from the jet cone energy fraction, the observable with the smallest theoretical and experimental uncertainty, is $\alpha_s(M_Z^2) = 0.1180 \pm 0.0006 (exp.) \pm 0.0013 (hadr.) \pm 0.0008 (scale) \pm 0.0007 (mass)$. Further studies include an $\alpha_s$ determination using theoretical predictions in the next-to-leading log approximation (NLLA), matched NLLA and $\cal O(\alpha_s^2$) predictions as well as theoretically motivated optimized scale setting methods. The influence of higher order contributions was also investigated by using the method of Pad\'{e} approximants. Average $\alpha_s$ values derived from the different approaches are in good agreement.
The weighted value of ALPHA-S from all the measured observables using experimentally optimized renormalization scale values and corrected for the b-mass toleading order.
The value of ALPHA-S derived from the JCEF and corrected for heavy quark mass effects. The quoted errors are respectively due to experimental error, hadronization, renormalization scale and heavy quark mass correction uncertainties.
Energy Energy Correlation EEC.
We report charged-particle pair correlation analyses in the space of Delta -phi (azimuth) and Delta -eta (pseudo-rapidity), for central Au + Au collisions at sqrt{s_{NN}} = 200 GeV in the STAR detector. The analysis involves unlike-sign charge pairs and like-sign charge pairs, which are transformed into charge-dependent (CD) signals and charge-independent (CI) signals. We present detailed parameterizations of the data. A model featuring dense gluonic hot spots as first proposed by van Hove predicts that the observables under investigation would have sensitivity to such a substructure should it occur, and the model also motivates selection of transverse momenta in the range 0.8 < p_t < 2.0$ GeV/c. Both CD and CI correlations of high statistical significance are observed and possible interpretations are discussed.
FIG. 1: a) left side: The $\Delta\phi$ - $\Delta\eta$ correlation data for unlike-sign charge particle pairs from the Star central trigger dataset shown in a 2-dimensional (2-D) perspective plot. The particle tracks have 0.8 GeV/c < $p_t$ < 2.0 GeV/c and |$\eta$| < 1.0. The structure that looks like tiles on a roof is due to the readout boundary effects of the 12 sector TPC. b) right side: The similar correlation data for like-sign charge particle pairs is shown.
FIG. 1: a) left side: The $\Delta\phi$ - $\Delta\eta$ correlation data for unlike-sign charge particle pairs from the Star central trigger dataset shown in a 2-dimensional (2-D) perspective plot. The particle tracks have 0.8 GeV/c < $p_t$ < 2.0 GeV/c and |$\eta$| < 1.0. The structure that looks like tiles on a roof is due to the readout boundary effects of the 12 sector TPC. b) right side: The similar correlation data for like-sign charge particle pairs is shown.
FIG. 2: a) left side: The correlation data for the ratio of the histograms of same-event-pairs to mixed-event-pairs for unlike-sign charged pairs, shown in a two-dimensional (2-D) perspective plot $\Delta\phi$ - $\Delta\eta$. The plot was normalized to a mean of 1. b) right side: The similar correlation data for like-sign charge pairs.
The STAR collaboration presents jet substructure measurements related to both the momentum fraction and the opening angle within jets in \pp and \AuAu collisions at \sqrtsn $= 200$ GeV. The substructure observables include SoftDrop groomed momentum fraction (\zg), groomed jet radius (\rg), and subjet momentum fraction (\zsj) and opening angle (\tsj). The latter observable is introduced for the first time. Fully corrected subjet measurements are presented for \pp collisions and are compared to leading order Monte Carlo models. The subjet \tsj~distributions reflect the jets leading opening angle and are utilized as a proxy for the resolution scale of the medium in \AuAu collisions. We compare data from \AuAu collisions to those from \pp which are embedded in minimum-bias \AuAu events in order to include the effects of detector smearing and the heavy-ion collision underlying event. The subjet observables are shown to be more robust to the background than \zg~and \rg. We observe no significant modifications of the subjet observables within the two highest-energy, back-to-back jets, resulting in a distribution of opening angles and the splittings that are vacuum-like. We also report measurements of the differential di-jet momentum imbalance ($A_{\rm{J}}$) for jets of varying \tsj. We find no qualitative differences in energy loss signatures for varying angular scales in the range $0.1 < $\tsj $ < 0.3$, leading to the possible interpretation that energy loss in this population of high momentum di-jet pairs, is due to soft medium-induced gluon radiation from a single color-charge as it traverses the medium.
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