We present strange particle spectra and yields measured at mid-rapidity in $\sqrt{\text{s}}=200$ GeV proton-proton ($p+p$) collisions at RHIC. We find that the previously observed universal transverse mass ($\mathrm{m_{T}}\equiv\sqrt{\mathrm{p_{T}}^{2}+\mathrm{m}^{2}}$) scaling of hadron production in $p+p$ collisions seems to break down at higher \mt and that there is a difference in the shape of the \mt spectrum between baryons and mesons. We observe mid-rapidity anti-baryon to baryon ratios near unity for $\Lambda$ and $\Xi$ baryons and no dependence of the ratio on transverse momentum, indicating that our data do not yet reach the quark-jet dominated region. We show the dependence of the mean transverse momentum (\mpt) on measured charged particle multiplicity and on particle mass and infer that these trends are consistent with gluon-jet dominated particle production. The data are compared to previous measurements from CERN-SPS, ISR and FNAL experiments and to Leading Order (LO) and Next to Leading order (NLO) string fragmentation model predictions. We infer from these comparisons that the spectral shapes and particle yields from $p+p$ collisions at RHIC energies have large contributions from gluon jets rather than quark jets.
Corrected mid-rapidity (|y| < 0.5) pT spectra for $K^{+}$, $K^{−}$, $K^{0}_{S}$, Λ, Ξ, and Ω. Λ spectra that have been corrected for feed-down are shown as open symbols in the Λ panel. The dashed lines are fits using Equation 11 except for the $\Omega+\overline{\Omega}$ where the fit uses Equation 9. The error bars displayed include systematic errors while the fits were done using statistical errors only for all species except the charged kaons.
Corrected mid-rapidity (|y| < 0.5) pT spectra for $K^{+}$, $K^{−}$, $K^{0}_{S}$, Λ, Ξ, and Ω. Λ spectra that have been corrected for feed-down are shown as open symbols in the Λ panel. The dashed lines are fits using Equation 11 except for the $\Omega+\overline{\Omega}$ where the fit uses Equation 9. The error bars displayed include systematic errors while the fits were done using statistical errors only for all species except the charged kaons.
Corrected mid-rapidity (|y| < 0.5) pT spectra for $K^{+}$, $K^{−}$, $K^{0}_{S}$, Λ, Ξ, and Ω. Λ spectra that have been corrected for feed-down are shown as open symbols in the Λ panel. The dashed lines are fits using Equation 11 except for the $\Omega+\overline{\Omega}$ where the fit uses Equation 9. The error bars displayed include systematic errors while the fits were done using statistical errors only for all species except the charged kaons.
We present the scaling properties of Lambda, Xi, Omega and their anti-particles produced at mid-rapidity in Au+Au collisions at RHIC at sqrt(s_NN) = 200 GeV. The yield of multi-strange baryons per participant nucleon increases from peripheral to central collisions more rapidly than the Lambda yield, which appears to correspond to an increasing strange quark density of matter produced. The value of the strange phase space occupancy factor gamma_s, obtained from a thermal model fit to the data, approaches unity for the most central collisions. We also show that the nuclear modification factors, R_CP, of Lambda and Xi are consistent with each other and with that of protons in the transverse momentum range 2.0 < p_T < 5.0 GeV/c. This scaling behaviour is consistent with a scenario of hadron formation from constituent quark degrees of freedom through quark recombination or coalescence.
Transverse momentum distributions of (a) $\Lambda(\overline{\Lambda})$ for $|y|<1.0$, (b) $\Xi^{-}(\overline{\Xi}^{+})$ for $|y|<0.75$ and (c) $\Omega^{-}+\overline{\Omega}^{+}$ for $|y|<0.75$ in Au+Au collisions at $\sqrt{s_{NN}}$ as a function of centrality. The $\Lambda$ spectra were corrected for weak decay of $\Xi$, $\Xi^{0}$ and $\Omega$. Scale factors were applied to the spectra for clarity. Only statistical errors are shown. The dashed curves show a Boltzmann fit to the $\Lambda$, $\Xi^{-}$ and $\Omega^{-}+\overline{\Omega}^{+}$ data, the fits to the $\overline{\Lambda}$ and $\overline{\Xi}^{+}$ are omitted for clarity.
Transverse momentum distributions of (a) $\Lambda(\overline{\Lambda})$ for $|y|<1.0$, (b) $\Xi^{-}(\overline{\Xi}^{+})$ for $|y|<0.75$ and (c) $\Omega^{-}+\overline{\Omega}^{+}$ for $|y|<0.75$ in Au+Au collisions at $\sqrt{s_{NN}}$ as a function of centrality. The $\Lambda$ spectra were corrected for weak decay of $\Xi$, $\Xi^{0}$ and $\Omega$. Scale factors were applied to the spectra for clarity. Only statistical errors are shown. The dashed curves show a Boltzmann fit to the $\Lambda$, $\Xi^{-}$ and $\Omega^{-}+\overline{\Omega}^{+}$ data, the fits to the $\overline{\Lambda}$ and $\overline{\Xi}^{+}$ are omitted for clarity.
Transverse momentum distributions of (a) $\Lambda(\overline{\Lambda})$ for $|y|<1.0$, (b) $\Xi^{-}(\overline{\Xi}^{+})$ for $|y|<0.75$ and (c) $\Omega^{-}+\overline{\Omega}^{+}$ for $|y|<0.75$ in Au+Au collisions at $\sqrt{s_{NN}}$ as a function of centrality. The $\Lambda$ spectra were corrected for weak decay of $\Xi$, $\Xi^{0}$ and $\Omega$. Scale factors were applied to the spectra for clarity. Only statistical errors are shown. The dashed curves show a Boltzmann fit to the $\Lambda$, $\Xi^{-}$ and $\Omega^{-}+\overline{\Omega}^{+}$ data, the fits to the $\overline{\Lambda}$ and $\overline{\Xi}^{+}$ are omitted for clarity.
We report measurements of transverse momentum $p_t$ spectra for ten event multiplicity classes of p-p collisions at $\sqrt{s} = 200$ GeV. By analyzing the multiplicity dependence we find that the spectrum shape can be decomposed into a part with amplitude proportional to multiplicity and described by a L\'evy distribution on transverse mass $m_t$, and a part with amplitude proportional to multiplicity squared and described by a gaussian distribution on transverse rapidity $y_t$. The functional forms of the two parts are nearly independent of event multiplicity. The two parts can be identified with the soft and hard components of a two-component model of p-p collisions. This analysis then provides the first isolation of the hard component of the $p_t$ spectrum as a distribution of simple form on $y_t$.
FIG. 1: Corrected and normalized charged-particle spectra on transverse momentum $p_t$ (left) and transverse rapidity $y_t$ (right) for 10 event multiplicity classes, displaced upward by successive factors 40 relative to $\hat{n}_{ch}$ = 1 at bottom. Solid curves represent reference function $n_s/n_{ch} · S_0(y_t)$ (cf.Sec. IV C). Dotted curves are spline fits to guide the eye.
FIG. 1: Corrected and normalized charged-particle spectra on transverse momentum $p_t$ (left) and transverse rapidity $y_t$ (right) for 10 event multiplicity classes, displaced upward by successive factors 40 relative to $\hat{n}_{ch}$ = 1 at bottom. Solid curves represent reference function $n_s/n_{ch} · S_0(y_t)$ (cf.Sec. IV C). Dotted curves are spline fits to guide the eye.
FIG. 2. Left: Relative residuals from power-law fits to $p_{t}$ spectra in Fig. 1. The hatched band represents the expected statistical errors for STAR data. Right: Exponents $n$ from power-law fits to data (solid points) and to corresponding twocomponent fixed-model functions (open circles, see Sec. VI) compared to the two-component fixed-model Lévy exponent $12.8 \pm 0.15$ (hatched band). NOTE 1: For points with invisible error bars, the point size was considered as an absolute upper limit for the uncertainty. NOTE 2: The "data_stat" uncertainty corresponds to the expected statistical error (hatched band).
We present the first data on $e^+e^-$ pair production accompanied by nuclear breakup in ultra-peripheral gold-gold collisions at a center of mass energy of 200 GeV per nucleon pair. The nuclear breakup requirement selects events at small impact parameters, where higher-order corrections to the pair production cross section should be enhanced. We compare the pair kinematic distributions with two calculations: one based on the equivalent photon approximation, and the other using lowest-order quantum electrodynamics (QED): the latter includes the photon virtuality. The cross section, pair mass, rapidity and angular distributions are in good agreement with both calculations. The pair transverse momentum, $p_T$, spectrum agrees with the QED calculation, but not with the equivalent photon approach. We set limits on higher-order contributions to the cross section. The $e^+$ and $e^-$ $p_T$ spectra are similar, with no evidence for interference effects due to higher-order diagrams.
(a) The pair mass distribution, (b) pair $p){T}$ , (c) pair rapidity and (d) pair cos($\theta′$) distributions. The data (points) are compared with predictions from the EPA (solid histogram) and lowest-order QED (dashed histogram) calculations. The error bars include both statistical and systematic errors.
(a) The pair mass distribution, (b) pair $p){T}$ , (c) pair rapidity and (d) pair cos($\theta′$) distributions. The data (points) are compared with predictions from the EPA (solid histogram) and lowest-order QED (dashed histogram) calculations. The error bars include both statistical and systematic errors.
(a) The pair mass distribution, (b) pair $p){T}$ , (c) pair rapidity and (d) pair cos($\theta′$) distributions. The data (points) are compared with predictions from the EPA (solid histogram) and lowest-order QED (dashed histogram) calculations. The error bars include both statistical and systematic errors.
Azimuthal anisotropy ($v_2$) and two-particle angular correlations of high $p_T$ charged hadrons have been measured in Au+Au collisions at $\sqrt{s_{NN}}$=130 GeV for transverse momenta up to 6 GeV/c, where hard processes are expected to contribute significantly. The two-particle angular correlations exhibit elliptic flow and a structure suggestive of fragmentation of high $p_T$ partons. The monotonic rise of $v_2(p_T)$ for $p_T<2$ GeV/c is consistent with collective hydrodynamical flow calculations. At $\pT>3$ GeV/c a saturation of $v_2$ is observed which persists up to $p_T=6$ GeV/c.
$v_{2}$($p_{T}$) for different collision centralities. The errors are statistical only. The systematic uncertainties, which are highly correlated point-to-point, are $^{+5}_{-20}%$.
$v_{2}$($p_{T}$) for minimum-bias events (circles). The error bars represent the statistical errors and the caps show the systematic uncertainty. The data are compared with hydro+pQCD calculations [9] assuming the initial gluon density $dN^{g}/dy$ = 1000 (dashed line), 500 (dotted line), and 200 (dashed-dotted line). Also shown are pure hydrodynamical calculations [16] (solid line).
High $p_{T}$ azimuthal correlation functions for central events. Upper panel: Correlation function for $|\Delta\eta|$ < 0.5 (solid circles) and scaled correlation function for 0.5 < $|\Delta\eta|$ < 1.4 (open squares). Lower panel: Difference of the two correlation functions. Also shown are the fits to the data (described in the text).
Identified pi^[+/-] K^[+/-], p and p-bar transverse momentum spectra at mid-rapidity in sqrt(s_NN)=130 GeV Au-Au collisions were measured by the PHENIX experiment at RHIC as a function of collision centrality. Average transverse momenta increase with the number of participating nucleons in a similar way for all particle species. The multiplicity densities scale faster than the number of participating nucleons. Kaon and nucleon yields per participant increase faster than the pion yields. In central collisions at high transverse momenta (p_T greater than 2 GeV/c), anti-proton and proton yields are comparable to the pion yields.
Transverse momentum spectra for PI+ in the midrapidity range for the centrality region 0 to 5 PCT. Errors are combined statistical and systematics.
Transverse momentum spectra for PI- in the midrapidity range for the centrality region 0 to 5 PCT. Errors are combined statistical and systematics.
Transverse momentum spectra for K+ in the midrapidity range for the centrality region 0 to 5 PCT. Errors are combined statistical and systematics.
Characteristics of the hadronic final state of diffractive deep inelastic scattering events, ep -> eXp, were studied in the kinematic range 4 < M_X < 35 GeV, 4 < Q^2 < 150 GeV^2, 70 < W < 250 GeV and 0.0003 < x_pom < 0.03 with the ZEUS detector at HERA using an integrated luminosity of 13.8 pb^{-1}. The events were tagged by identifying the diffractively scattered proton using the leading proton spectrometer. The properties of the hadronic final state, X, were studied in its center-of-mass frame using thrust, thrust angle, sphericity, energy flow, transverse energy flow and ``seagull'' distributions. As the invariant mass of the system increases, the final state becomes more collimated, more aligned and more asymmetric in the average transverse momentum with respect to the direction of the virtual photon. Comparisons of the properties of the hadronic final state with predictions from various Monte Carlo model generators suggest that the final state is dominated by qqg states at the parton level.
Thrust distribution for a DIS hadronic final state mass between 11 and 17.8GeV.
Thrust distribution for a DIS hadronic final state mass between 17.8 and 27.7 GeV.
Sphericity distribution for a DIS hadronic final state mass between 11 and 17.8 GeV.
Event shape and charged particle inclusive distributions are measured using 750000 decays of the Z to hadrons from the DELPHI detector at LEP. These precise data allow a decisive confrontation with models of the hadronization process. Improved tunings of the JETSET, ARIADNE and HERWIG parton shower models and the JETSET matrix element model are obtained by fitting the models to these DELPHI data as well as to identified particle distributions from all LEP experiments. The description of the data distributions by the models is critically reviewed with special importance attributed to identified particles.
Transverse momentum PTIN w.r.t. the Thrust axis. For the first table Thrust axis definition is from seen charged particles corrected to final state particles. For the second table Thrust axis definition is from seen charged plus neutral particles corrected to final state charged plus neutral particles.
Transverse momentum PTOUT w.r.t. the Thrust axis. For the first table Thrust axis definition is from seen charged particles corrected to final state particles. For the second table Thrust axis definition is from seen charged plus neutral particles corrected to final state charged plus neutral particles.
Transverse momentum PTIN w.r.t. the Sphericity axis. For the first table Sphericity axis definition is from seen charged particles corrected to final state particles. For the second table Sphericity axis definition is from seen charged plus neutral particles corrected to final state charged plus neutral particles.
None
No description provided.
ALL NEGATIVE PARTICLES WAS CONSIDERED AS PI-.
ALL NEGATIVE PARTICLES WAS CONSIDERED AS PI-.
None
No description provided.
No description provided.
No description provided.
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