Measurements of the kinematic distributions of $J/\psi$ mesons produced in $p-$C, $p-$Ti and $p-$W collisions at $\sqrt{s}=41.6 \mathrm{GeV}$ in the Feynman-$x$ region $-0.34 < x_{F} < 0.14$ and for transverse momentum up to $p_T = 5.4 \mathrm{GeV}/c$ are presented. The $x_F$ and $p_T$ dependencies of the nuclear suppression parameter, $\alpha$, are also given. The results are based on $2.4 \cdot 10^{5}$ $J/\psi$ mesons in both the $e^+ e^-$ and $\mu^{+}\mu^{-}$ decay channels. The data have been collected by the HERA-B experiment at the HERA proton ring of the DESY laboratory. The measurement explores the negative region of $x_{F}$ for the first time. The average value of $\alpha$ in the measured $x_{F}$ region is $0.981 \pm 0.015$. The data suggest that the strong nuclear suppression of $J/\psi$ production previously observed at high $x_F$ turns into an enhancement at negative $x_F$.
J/PSI distributions (dN/dp_T, normalized to their integrals over the measured range) for three targets materials with statistical and systematics uncertainties.
J/PSI distributions (dN/dx_F, normalized to their integrals over the measured range) for three targets materials with statistical and systematics uncertainties.
The parameter Alpha as a function of p_T. Statistical and systematic uncertainties are indicated separately.
A study of the angular distributions of leptons from decays of J/psi's produced in p-C and p-W collisions at sqrt{s}=41.6 GeV has been performed in the Feynman-x region -0.34 < x_F < 0.14 and for transverse momentum up to 5.4 GeV/c. The data were collected by the HERA-B experiment at the HERA proton ring of the DESY laboratory. The results, based on a clean selection of 2.3 x 10^5 J/psi's reconstructed in both the e^+ e^- and mu^+ mu^- decay channels, indicate that J/psi's are produced with longitudinal polarization. The magnitude of the effect is maximal at low p_T. For p_T >1 GeV/c a significant dependence on the reference frame is found: the polar anisotropy is more pronounced in the Collins-Soper frame and almost vanishes in the helicity frame, where, instead, a significant azimuthal anisotropy arises.
Output parameters obtained by fitting the distributions.
Values of the parameters Lambda_theta, Lambda_phi et Lambda_theta_phi measured in the Collins-Soper frame as functions of the average reconstructed p_T for combined carbon and tungsten data.
Values of the parameters Lambda_theta, Lambda_phi et Lambda_theta_phi measured in the Collins-Soper frame as functions of the average reconstructed x_F for combined carbon and tungsten data.
A measurement of the ratio R_chic = (chic -> Jpsi + gam)/ Jpsi in pC, pTi and pW interactions at 920 GeV/c (sqrt{s}=41.6 GeV) in the Feynman-x range -0.35 < x_F(Jpsi) < 0.15 is presented. Both mu+mu- and e+e- Jpsi decay channels are observed with an overall statistics of about 15000 chic events, which is by far the largest available sample in pA collisions. The result is R_chic = 0.188+-0.013(st)(+0.024)(-0.022)(sys) averaged over the different materials, when no Jpsi and chic polarisations are considered. The chic_1 to chic_2 production ratio R_12 = R_chic1/R_chic2 is measured to be 1.02+-0.40, leading to a cross section ratio sigma(chic_1)/sigma(chic_2)=0.57+-0.23. The dependence of R_chic on the Feynman-x of the Jpsi, x_F(Jpsi), and its transverse momentum, p_T(Jpsi), is studied, as well as its dependence on the atomic number, A, of the target. For the first time, an extensive study of possible biases on R_chic and R_12 due to the dependence of acceptance on the polarization states of Jpsi and chic is performed. By varying the polarisation parameter, lambda(obs), of all produced Jpsi's by two sigma around the value measured by HERA-B, and considering the maximum variation due to the possible chic_1 and chic_2 polarisations, it is shown that R_chic could change by a factor between 1.02 and 1.21 and R_12 by a factor between 0.89 and 1.16.
Measurement of R_CHI/C in <E+ E->, <MU+ MU-> and combined channel.
Measurement of R_12 in <E+ E->, <MU+ MU-> and combined channel.
Measurement of SIG(C1)/SIG(C2) in <E+ E->, <MU+ MU-> and combined channel.
We present the xF and pT differential cross sections of J/ψ and ψ′, respectively, in the ranges −0.05<xF<0.25 and pT<3.5 GeV/c. The data samples are constituted by about 12 000 J/ψ and 200 ψ′ produced in proton-silicon interactions at 800 GeV/c and decaying into opposite sign muons. The xF and pT distributions are compared with recent results from experiments E789 at the same energy and to leading order QCD predictions using the MRS D0 parametrization for the parton structure function. The measured shapes of the differential cross sections, except for the dσ/dxF at small xF, agree very well with the prediction, even though their value is quite a bit larger than the prediction. We also present the cosθ differential cross section of the J/ψ which indicates unpolarized production in contrast with color octet models predictions.
Additional systematic error given above.
Additional systematic error given above.
Additional systematic error given above.
The differential cross sections dσ/dxF for J/ψ produced inclusively in 800 GeV/c p-Cu and p-Be collisions have been measured in the kinematic range 0.30≤xF≤0.95 through the decay mode J/ψ→μ+μ−. They are compared with the predictions of the semilocal duality model for several sets of parton density functions. No evidence for a suggested intrinsic charm contribution to the cross section is observed. The ratio of the differential cross sections for Cu and Be targets confirms the suppression of J/ψ production in heavy nuclei at large xF.
No description provided.
No description provided.
Hadroproduction of the Jψ and ψ′ states has been studied in 300-GeV/c proton, antiproton, and π±Li interactions. Both total and differential cross sections in xF and pT have been measured for the Jψ for the π±, proton, and antiproton interactions. The ratio of ψ′ to Jψ production has been determined for the four types of beam particles.
No description provided.
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A detailed study ofJ/ψ hadronic production has been performed in a high statistics experiment (more than 1.5 106J/ψ observed in their dimuon decay mode). Data have been taken with incident π±,K±,p±, on hydrogen and platinum targets, at 150, 200 and 280 GeV/c. We find from the observed nuclear dependance of the cross sections, that about 18% of theJ/ψ are produced diffractively. Using known structure functions of the quarks in the nucleon and in the pion, we derive estimations for the gluon structure functions.
No description provided.
No description provided.
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We report the measurements of the inclusive μ-pair production by 150-GeV protons and π+ mesons on beryllium. Absolute cross sections as well as the Feynman-x and PT dependence are presented in the mass region between 0.211 and 3.5 GeV/c2. Upper limits are also given for the inclusive production of η and ρ′(1600) mesons.
DATA OBTAINED FROM FIGURE BY A.A. LEBEDEV.
DATA OBTAINED FROM FIGURE BY A.A. LEBEDEV.
No description provided.
Invariant mass spectrum of μ + μ − pairs produced by 70 GeV/ c protons in Be target are presented. Distinct enhancements in the mass regions of ϱ, ω mesons, φ meson and J/ψ particle are observed. For J/ψ production x and p ⊥ 2 distributions are given. The total cross section for the reaction p + Be → ( J ψ → μ + μ − ) + … is equal to 9.5 ± 2.5 nb/nucleus .
No description provided.
ASSUME B.R.(MU+MU-) = 0.069.
ASSUME A**(2/3) DEPENDENCE FOR SIGMA.
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