Infrared and collinear safe event shape distributions and their mean values are determined in e+e- collisions at centre-of-mass energies between 45 and 202 GeV. A phenomenological analysis based on power correction models including hadron mass effects for both differential distributions and mean values is presented. Using power corrections, alpha_s is extracted from the mean values and shapes. In an alternative approach, renormalisation group invariance (RGI) is used as an explicit constraint, leading to a consistent description of mean values without the need for sizeable power corrections. The QCD beta-function is precisely measured using this approach. From the DELPHI data on Thrust, including data from low energy experiments, one finds beta_0 = 7.86 +/- 0.32 for the one loop coefficient of the beta-function or, assuming QCD, n_f = 4.75 +/- 0.44 for the number of active flavours. These values agree well with the QCD expectation of beta_0=7.67 and n_f=5. A direct measurement of the full logarithmic energy slope excludes light gluinos with a mass below 5 GeV.
1-THRUST distribution.
THRUST-MAJOR distribution.
THRUST-MINOR distribution.
The Fermilab E866/NuSea Collaboration has measured the Drell-Yan dimuon cross sections in 800 GeV/$c$ $pp$ and $pd$ collisions. This represents the first measurement of the Drell-Yan cross section in $pp$ collisions over a broad kinematic region and the most extensive study to date of the Drell-Yan cross section in $pd$ collisions. The results indicate that recent global parton distribution fits provide a good description of the light antiquark sea in the nucleon over the Bjorken-$x$ range $0.03 \lesssim x < 0.15$, but overestimate the valence quark distributions as $x \to 1$.
Measurment of the scaling form of the MU+ MU- cross section in the XL range-0.05 to 0.05 from the hydrogen target.
Measurment of the scaling form of the MU+ MU- cross section in the XL range0.05 to 0.10 from the hydrogen target.
Measurment of the scaling form of the MU+ MU- cross section in the XL range0.10 to 0.15 from the hydrogen target.
The balance function is a new observable based on the principle that charge is locally conserved when particles are pair produced. Balance functions have been measured for charged particle pairs and identified charged pion pairs in Au+Au collisions at $\sqrt{s_{NN}}$ = 130 GeV at the Relativistic Heavy Ion Collider using STAR. Balance functions for peripheral collisions have widths consistent with model predictions based on a superposition of nucleon-nucleon scattering. Widths in central collisions are smaller, consistent with trends predicted by models incorporating late hadronization.
The balance function versus ∆η for charged particle pairs from a) central and peripheral Au+Au collisions at $\sqrt{s_{NN}}$ = 130 GeV and mixed events from central and peripheral Au+Au collisions, and b) HIJING events filtered with GEANT [16] and shuffled pseudorapidity events from central and peripheral Au+Au collisions. To guide the eye, Gaussian fits excluding the lowest bin in ∆η are shown. The error bars shown are statistical. The balance function for HIJING events is independent of centrality.
The balance function versus ∆η for charged particle pairs from a) central and peripheral Au+Au collisions at $\sqrt{s_{NN}}$ = 130 GeV and mixed events from central and peripheral Au+Au collisions, and b) HIJING events filtered with GEANT [16] and shuffled pseudorapidity events from central and peripheral Au+Au collisions. To guide the eye, Gaussian fits excluding the lowest bin in ∆η are shown. The error bars shown are statistical. The balance function for HIJING events is independent of centrality.
The width of the balance function for charged particles, $⟨\Delta \eta⟩$, as a function of normalized impact parameter $(b/b_{max})$. Error bars shown are statistical. The width of the balance function from HIJING events is shown as a band whose height reflects the statistical uncertainty. Also shown are the widths from the shuffled pseudorapidity events.
The inclusive cross section for J/ψ production times the branching ratio B(J/ψ→μ+μ−) has been measured in the forward pseudorapidity region: B×dσ[p¯+p→J/ψ(pT>10GeV/c,2.1<|η|<2.6)+X]/dη=192±9(stat)±29(syst)pb. The results are based on 74.1±5.2pb−1 of data collected by the CDF Collaboration at the Fermilab Tevatron Collider. The measurements extend earlier measurements of the D0 Collaboration to higher pTJ/ψ. In the kinematic range where the experiments partially overlap, these data are in good agreement with previous measurements.
The integrated cross section for J/PSI --> MU+ MU- decay.
Cross section as a function of PT. Statistical errors only.
Values of the ratios in the mid-rapidity yields of anti-Lambda/Lambda = 0.71 +/- 0.01(stat.) +/- 0.04(sys.), anti-Xi+/Xi- = 0.83 +/- 0.04(stat.) +/- 0.05 (sys.), anti-Omega+/Omega- = 0.95 +/- 0.15(stat) +/- 0.05(sys.) and K+/K- 1.092 +/- 0.023(combined) were obtained in central sqrt(s_NN) = 130 GeV Au+Au collisions using the STAR detector. The ratios indicate that a fraction of the net-baryon number from the initial system is present in the excess of hyperons over anti-hyperons at mid-rapidity. The trend in the progression of the baryon ratios, with increasing strange quark content, is similar to that observed in heavy-ion collisions at lower energies. The value of these ratios may be related to the charged kaon ratio in the framework of simple quark-counting and thermal models.
Invariant mass distributions for $\Lambda$ and Anti-$\Lambda$
Invariant mass distributions for $\Xi$ and Anti-$\Xi$
Invariant mass distributions for $\Omega$ and Anti-$\Omega$
Azimuthal correlations for large transverse momentum charged hadrons have been measured over a wide pseudo-rapidity range and full azimuth in Au+Au and p+p collisions at $\sqrt{s_{NN}}$ = 200 GeV. The small-angle correlations observed in p+p collisions and at all centralities of Au+Au collisions are characteristic of hard-scattering processes already observed in elementary collisions. A strong back-to-back correlation exists for p+p and peripheral Au + Au. In contrast, the back-to-back correlations are reduced considerably in the most central Au+Au collisions, indicating substantial interaction as the hard-scattered partons or their fragmentation products traverse the medium.
Azimuthal distributions of opposite-sign pairs in p+p collisions. All correlation functions require a trigger particle with $4<p_T^{\rm trig}<6$ GeV/$c$ and associated particles with $2<p_T<p_T^{\rm trig}$ GeV/$c$.
Azimuthal distributions of same-sign pairs in p+p collisions. All correlation functions require a trigger particle with $4<p_T^{\rm trig}<6$ GeV/$c$ and associated particles with $2<p_T<p_T^{\rm trig}$ GeV/$c$.
Azimuthal distributions of same-sign and opposite-sign pairs in minimum bias and background-subtracted 0-10% central Au+Au collisions. All correlation functions require a trigger particle with $4<p_T^{\rm trig}<6$ GeV/$c$ and associated particles with $2<p_T<p_T^{\rm trig}$ GeV/$c$.
Total and differential cross sections for the exclusive reaction pp->pp rho^0 observed via the pi+pi- decay channel have been measured at beam momentum=3.67 GeV/c. The observed total meson production cross section is determined to be 23.4 +- 0.8 +-8 microb and is significantly lower than typical cross sections used in model calculations for heavy ion collisions. The differential cross sections measured indicate a strong anisotropy cos^2(theta^{CM}) in the rho^0 meson production.
Total cross section determined by normalising to the simultaneously measured ETA yield to the known cross section of 135 +- 35 MUB.
PHENIX has measured the centrality dependence of charged hadron p_T spectra from central Au+Au collisions at sqrt(s_NN)=130 GeV. The truncated mean p_T decreases with centrality for p_T > 2 GeV/c, indicating an apparent reduction of the contribution from hard scattering to high p_T hadron production. For central collisions the yield at high p_T is shown to be suppressed compared to binary nucleon-nucleon collision scaling of p+p data. This suppression is monotonically increasing with centrality, but most of the change occurs below 30% centrality, i.e. for collisions with less than about 140 participating nucleons. The observed p_T and centrality dependence is consistent with the particle production predicted by models including hard scattering and subsequent energy loss of the scattered partons in the dense matter created in the collisions.
Number of participants and binary collisions and their systematic errors for the individual centrality selections used in this analysis. Also given is the ratio of the number of binary collisions for the most central sample relative to the one for each sample. The last column quantifies the ratio of binary collisions to participant pairs.
The ratio $p/h$ represents the proton plus anti-proton yield relative to the total charged hadron multiplicity. This shows the $p_T$ dependence of $p/h$ for minimum bias events.
The ratio $p/h$ represents the proton plus anti-proton yield relative to the total charged hadron multiplicity. This shows the centrality dependence of $p/h$ for $p_T >$ 1.8 GeV/$c$.
We report on measurements of the branching ratios of the decays B+→χc10(1P)K+ and B+→J/ψK+π+π−, where χc10(1P)→J/ψγ and J/ψ→μ+μ− in pp¯ collisions at s=1.8TeV. Using a data sample from an integrated luminosity of 110pb−1 collected by the Collider Detector at Fermilab we measure the branching ratios to be BR(B+→χc10(1P)K+)=15.5±5.4(stat)±1.5(syst)±1.3(br)×10−4 and BR(B+→J/ψK+π+π−)=6.9±1.8(stat)±1.1(syst)±0.4(br)×10−4 where (br) is due to the finite precision on BR(B+→J/ψK+), BR(χc10(1P)→J/ψγ) is used to normalize the signal yield, and (syst) encompasses all other systematic uncertainties.
Branching ratio for B+ decay in chi_c1(1P) and K+ Last error is due to finite precision on the branching ratio for chi_c1(1P) --> J/psi photon.
Branching ratio for B+ decay in J/psi K+ pi+ pi- Last error is due to finite precision on the branching ratio for B+ --> J/psi K+.
Inclusive transverse momentum distributions of charged hadrons within 0.2<pT<6.0 GeV/c have been measured over a broad range of centrality for Au+Au collisions at sqrt(sNN)=130 GeV. Hadron yields are suppressed at high pT in central collisions relative to peripheral collisions and to a nucleon-nucleon reference scaled for collision geometry. Peripheral collisions are not suppressed relative to the nucleon-nucleon reference. The suppression varies continuously at intermediate centralities. The results indicate significant nuclear medium effects on high pT hadron production in heavy ion collisions at high energy.
Inclusive $p_T$ distributions of ($h^+ + h^−)/2$. Non-central bins are scaled down by the indicated factors. The combined statistical and systematic errors are shown. Curves are fits to Eq. (2). Hash marks at the top indicate bin boundaries for $p_T>1.5$ GeV/c.
Ratio of charged hadron yields within $|\eta| < 0.5$ for central over peripheral collisions, normalized to $\langle Nbin\rangle$.
$R_{AA}$($p_T$) for various centrality bins, for Au+Au relative to an NN reference spectrum. Error bars are described in the text. Errors between different $p_T$ and centrality bins are highly correlated.
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