Ρ0 Production Research Articles

Exclusive ϱ0 production in polarized DIS at SMC

Preliminary spin cross section asymmetries for exclusive ϱ 0 lepto-production, μ+ N→μ′+N+ϱ 0(ϱ 0→π +π −) , are reported. These asymmetries have been determined for the first time by the Spin Muon Collaboration (SMC) at low Q 2 (photoproduction) and at large Q 2 (DIS) for different p T 2 intervals in the kinematic range 0.01 < Q 2 < 60 GeV 2 and 140 < W 2 < 310 GeV 2 (< W >≅ 15 GeV) for the full SMC data set. About 100 K ϱ 0's have been selected for 0.62 < m( π + π −) < 1.07 GeV/ c 2 and | I| < 0.05. Within the statist precision, no significant asymmetries have been observed at low Q 2 in the preliminary results.

Diffractive production of $\rho^0 (770)$ mesons in muon-proton interactions at 470 GeV

The diffractive production of ρ0(770 @#@) mesons in muon-proton interactions is studied in the kinematic region 0.15 GeV2 < Q2 < 20 GeV2 and 20 GeV < ? < 420 GeV. The data were obtained in the Fermilab fixed-target experiment E665 with primary muons of 470 GeV energy. Results are presented on the Q2, x and ? dependence of the cross section, on the shape of the ρ+ρt - mass spectrum, on the slope of the diffraction peak and on the production and decay angular distributions of the ρ0(770). The cross section for diffractive production of ρ0 by virtual photons on protons depends mainly on Q2. At fixed Q2, no significant dependence on x or ? is observed. The extrapolation to Q2 = 0 yields a photoproduction cross section of (10.30 ± 0.33) μb. The slope of the t′ distribution has a value of (7.0 ± 0.2) GeV−2, with a tendency to decrease as Q2 increases. The production and decay angular distributions of the ρ0 depend strongly on Q2 and are consistent with s-channel helicity conservation. The ratio R = σ l /σ t deduced from the decay angular distributions rises strongly with Q2, passing the value of 1 at Q2 ≈ 2 GeV2.

Spin alignment and parity violation effects inρ 0 production in neutrino and antineutrino charged-current interactions

Most of the measured events on hydrogen, deuterium and neon targets from BEBC at CERN and the 15-foot Bubble Chamber at Fermilab are combined to measure spin-density matrix elements for ρ0 production in the current-fragmentation region in neutrino and antineutrino charged-current interactions. The spin-alignment parameter η is found to be 0.08±0.11 for neutrino and 0.41±0.11 for antineutrino interactions. The parity-odd density matrix element Im(ρ10+ρ−10) is consistent with zero in both reactions. In the combined neutrino and antineutrino data an indication of parity violation is observed: Im ρ1−1=0.38±0.16 atxB>0.2,Q2>8 GeV2 andz>0.6.

Diffractive production of vector mesons in muon scattering on nucleons and nuclei

Recent results from the NMC on diffractive vector meson muoproduction are presented. The selected topics include the cross-sections and kinematical distributions for exclusive ϱ0 production on deuterons, the comparison of the cross-sections for exclusive ϕ and ϱ0 production, and nuclear effects in quasi-elastic photoproduction of J/ψ.

Exclusive ϱ0 production in deep inelastic electron-proton scattering at HERA

The exclusive production of ϱ 0 mesons in deep inelastic electron-proton scattering has been studied using the ZEUS detector. Cross sections have been measured in the range 7 < Q 2 < 25 GeV 2 for λ ∗p centre of mass (c.m.) energies 40 to 130 GeV. The λ ∗p → ϱ 0p cross section exhibits a Q −(4.2±0.8 −0.5 +1.4) dependence and both longitudinally and transversely polarised ϱ 0's are observed. The λ ∗p → ϱ 0p cross section rises strongly with increasing c.m. energy, when compared with NMC data at lower energy, which cannot be explained by production through soft pomeron exchange. The data are compared with perturbative QCD calculations where the rise in the cross section reflects the increase in the gluon density at low x.

Comparison of photon and hadron induced production of ρ0 mesons in the energy range of 65 to 175 GeV

The inclusive production of ρ0 mesons was measured in γp andh ± p collisions at beam energies of 65 GeV≦E γ≦175 GeV andE h =80, 140 GeV, respectively, whereh is π orK. Cross sections were determined for all beams and energies as functions ofx F (−0.1≦x F≦1.0),p T (0≦p T≦3.5 GeV/c) and the polar decay angle of the ρ0 by fitting the ρ0 signal in π+π- mass distributions. The ρ0 line shape is found to be distorted from a pure Breit-Wigner distribution throughout most of thex F−p T plane for both photon and hadron beams and a simple explanation is suggested. Throughout the paper emphasis is put on the comparison of photon and hadron beam data. The comparison of cross sections of γp andhp data provides a measure of the Vector Meson Dominance factor throughout thex F−p T range of the ρ0. The ρ0 production at lowp T can be described for both photon and hadron beams by a triple regge model at largex F. Similarly central production is well described by the quark-antiquark fusion model. At largep T there is an excess of ρ0 photoproduction which is consistent with the expected onset of pointlike photon interactions.

Production off 2(1270) andf 0(975) mesons by photons and hadrons of energy 65?175 GeV

Measurements are reported of inclusivef 2(1270) andf 0(975) production in γp, π± p andK ± p collisions at photon beam energies of 65 to 175 GeV and hadron beam energies of 80 and 140 GeV. Thef 2 andf 0 mesons were found at masses of 1.250 GeV and 0.961 GeV respectively. Inclusivef 2 production at lowx F was found to have a similarp T dependence for each beam type, whereas an additional pion-exchange contribution was found for production by pions at highx F. Cross sections are compared with those for ρ0 production and give no indication of a non-q\(\bar q\) component in eitherf-meson state.

Observation of meson central production in baryon exchange processes

The central production of ρ0,f2 and ρ30 mesons is observed for the first time in processes which are originated by π+p reactions proceeding via baryon exchange mechanism. The data come from the CERN WA56 experiment designed to separate the baryon exchange reactions in π+p-collisions at 20 GeV/c. We report on the measured integral and differential cross sections and also give the density matrix elements of the meson resonances observed.

Evidence for higher twist mechanisms in highp ⊥π− p events with prompt ρ0 production at 38 GeV/c

The π−p interactions with at least one charged secondary produced at polar angle ∼90° in c.m.s. and having the transverse momentum above 1 GeV/c were investigated. The data were obtained using streamer chamber magnetic spectrometer RISK at 38 GeV/c π beam from Serpukhov accelerator. The analyzis of associated production in reconstructed events suggests, that if the transverse momentum of a pair of oppositely charged secondaries compensates the trigger particlep⊥ practically completely, this pair is the product of the ρ0 decay in marked fraction of such events. We observed a large spin-alignment for the ρ0-mesons selected as described above: the probability of zero spin projection onto the normal to the ρ0 production plane is equal to ρ00T=0.86±0.23. The enhancement of the number of events, in which the ρ0 picks up practically full momentum transfer carrying by the exchange, and also the enlarged tensor polarization for the ρ0-mesons in these events could be qualitatively explained as manifestation of direct ρ0-production via the QCD higher twist processes in the highp⊥π−p collisions. At the same time, the observed effects are markedly larger than the values predicted with QCD model in which the higher twist corrections were included.

ρ0 production the reaction ξξ→3π+3π−ξξ→ρ0ρ0(1700)

We have studied the ρ0 production rate in the reaction ξξ→3π+3π− in the energy range 1.6≦Wγγ≦7.5 GeV with the CELLO detector at PETRA. Our analysis points to a substantial yield of ρ0ρ0π+π− events in particular atWγγ>4.0 GeV. We give cross sections for the ρ02π+2π− and ρ0ρ0π+π− final states and calculate upper limits for the reaction γγ→ρ0ρ0 (1700) →ρ0ρ0π+π−.

Inclusive meson resonance production inK + p interactions at 250 GeV/c

A detailed analysis of the inclusive production of the vector mesonsφ,K*+,0(892)\(\bar K*^0 (892),\rho ^{ + ,0} ,\omega \) and the tensor mesonsK 2 *0 )(1430) andf2(1270) inK+p interactions at 250 GeV/c is presented The data are compared with results at lower energies and with various quark-parton models. The production ofρ0,K*0(892) and\(\bar K*^0 (892)\) increases at the same rate as a function ofs, is concentrated in the central region and is not reproduced by the models. Production of the tensor mesonsf2(1270) andK 2 *0 (1340) is suppressed relative toρ0 andK*0(892) by a factor of about 3.

Helicity flip in exclusive deep-inelastic ϱ0 production

The European Muon Collaboration reports that in exclusive ϱ 0 production in deep-inelastic muon scattering from hydrogen and nitrogen targets, the ϱ 0 is found predominately in a longitudinally polarised state. The t-dependence is typical of a hard scattering process. The ϱ 0's are claimed to be mainly produced by transverse photons. The cross section decreases as ( Q 2) −2. While the latter is expected in a vector dominance model, the dominance of helicity flip is inconsistent with such a model. We show that it is possible to reconcile these experimental results in a simple hard scattering model. However, we must suppose the photons mainly longitudinal, in agreement with Donnachie and Landshoff.

Exclusive ρ0 and Φ production in deep inelastic muon scattering

Data are presented on exclusive ρ0 and ϕ production in deep inelastic muon scattering from a target consisting mainly of nitrogen. The ratio of the total cross sections for ρ0 and ϕ production is found to be 9∶(1.6±0.4) at 〈Q2〉=7.5 GeV2, consistent with theSU(3) prediction of 9∶2. Thet dependence for exclusive ρ0 production is found to become shallover asQ2 increases and, for largeQ2, thet dependence is typical of that for a hard scattering process. Furthermore, the ratio of the cross sections for coherent: incoherent production from nitrogen is found to decrease rapidly withQ2. Such behaviour indicates that even for exclusive vector meson production the virtual photon behaves predominantly as an electromagnetic probe.

Inclusive ϱ0 production in [formula omitted] charged current interactions

Inclusive ϱ 0 production has been studied in antineutrino-proton charged current interactions, using a sample of 3340 events obtained in BEBC filled with hydrogen and exposed to the CERN wideband antineutrino beam. An average multiplicity of 0.11 ± 0.02 ϱ 0 per event at a mean hadronic mass W of 4.2 GeV is observed. The ϱ 0 production characteristics are determined as functions of p T, x F, and z. The ratio ϱ 0/“π 0” is found to be low at small z values consistent with centrally produced pions coming mainly from resonances. At large z values this ratio approaches 0.45 ± 0.15 which is compatible with a vector/pseudoscalar meson direct production ratio of one. The results are compared with those obtained from neutrino-proton interactions in the same experimental set-up.

Inclusive ϱ0 production in [formula omitted] D charged current interactions

Inclusive production of the meson resonance ϱ 0 in high-energy neutrino and antineutrino charged current (CC) interactions in deuterium was studied using the bubble chamber BEBC exposed to the CERN-SPS wide band neutrino and antineutrino beams. In a sample of 10693 charged current ν μ D and 13 758 ν μ D interactions we found 0.222 ± 0.014 ϱ 0 per charged current event. Thr production of f mesons is smaller than 0.03 per CC event (90% confidence level). The ϱ 0 production properties are studied in terms of charged hadron multiplicity, of the mass of the hadronic system and of various kinematical variables. The experimental results are compared with the predictions of the Lund fragmentation model, whose predictions are about 50% higher than the experimental values.

The effect of resonance production and diffraction on the inclusive spectra of pions and protons in 19 GeV/c pn interactions

Bubble chamber data on pn interactions at 19 GeV/c are used to investigate the effects of nucleon diffraction and resonance production on the inclusivex- andpT2-distributions of protons and pions. We determine the differential distributions of p, π− and π+ due to neutron and proton diffraction and similarly the distributions from the decay of the strong resonances Δ++(1232) and Δ−(1232) and from ρ0(770). Thex-distributions of the protons in the two c.m. hemispheres become quite similar when the effect of diffraction and Δ++ is subtracted. ThepT2-distributions can then be described by a single exponential in the whole kinematic region. The net effect on the shapes of thex-distributions of the pions due to diffraction, Δ++/Δ− and ρ0 production is rather small. The separate effects of these processes on the particle ratio π−/π+ is investigated. By excluding the diffraction and Δ++/Δ− production, the strength of the low-pT2 component of thepT2-distributions of the pions is reduced, but it seems that diffraction and resonance production cannot account for all oft hislow-pT2 enhancement.

ϱ0 production in deep inelastic μ-p interactions

Inclusive ϱ 0 meson production has been measured in 120 GeV and 280 GeV muon-proton interactions. Distributions of z and p T 2 are presented. Primary ϱ 0 production is found to be equal to that of π 0 production within errors.

Inclusive ϱ0 production in e +e − annihilation at high energy

We have observed ϱ 0 production in e +e − annihilation to hadrons at high energies. The differential cross section at a centre of mass energy W, of 34 GeV, is presented. In the range 0.2< x < 0.7, we measure 0.33 ± 0.06 (stat.) ± 0.07 (syst.), 0.22 ± 0.06 ± 0.05 and 0.22 ± 0.02 ± 0.05 ϱ 0/event at W = 14, 22 and 34 GeV respectively.

Elastic scattering and particle production in two-prongπ−pinteractions at 8 GeV/c

Results of a high-statistics study of elastic scattering and meson resonances produced by π−p interactions at 8 GeV/c are presented. Large statistics and small systematic errors permit examination of the complete kinematic region. Total differential cross sections are given for ρ0,−, f0, g0,−, Δ±, Δ0, and N* resonances. Spin-density matrix elements and Legendre-polynomial moments are given for ρ, f, and Δ resonances. The results for ρ0 and f0 resonances are compared with the predictions of a Regge-pole-exchange model. Properties of the above resonances are compared and discussed. In particular, we present evidence that the ρ0 and f0 production mechanisms are similar. The similarity of the g0 t distribution to that of the ρ0 and f0 suggests a common production mechanism for all three resonances.Received 11 January 1982DOI:https://doi.org/10.1103/PhysRevD.26.1572©1982 American Physical Society

Inclusive resonance production in 7.3 GeV/c $$\bar pp$$ interactions

We present results on inclusive baryon and meson resonance production in\(\bar pp\) interactions at 7.3 GeV/c. Total inclusive and semi-inclusive cross sections are given for Δ(1232),∑*(1385), ϱ0,f andK*±(892) production. For the meson resonances separation into annihilation and non-annihilation components has been made, the annihilation component being dominant at this energy. We find that the energy dependence of inclusive cross sections for ϱ0 production inpp interactions and\(\bar pp\) non-annihilations shows a type of scaling behaviour previously reported for ϕ, ψ, ψ′ and ϒ production inpp interactions.Δ++, ϱ0 andK*± production are studied in terms of Feynmanx,y* andpT2. For the vector mesons we compare they* andx dependences with the predictions of simple quark models.