Evidence of a broad structure at an invariant mass of 4.32 GeV/c2 in the reaction e+e- --> pi+pi-psi(2S) measured at BABAR

We present a measurement of the cross section of the process e(+)e(-)-->pi(+)pi(-)psi(2S) from threshold up to 8 GeV center-of-mass energy using events containing initial-state radiation, produced at the SLAC PEP-II e(+)e(-) storage rings. The study is based on 298 fb(-1) of data recorded with the BABAR detector. A structure is observed in the cross section not far above threshold, near 4.32 GeV. We also investigate the compatibility of this structure with the Y(4260) previously reported by this experiment.     

Photoproduction of the omega meson on the proton at large momentum transfer

The differential cross section, dsigma/dt, for omega meson exclusive photoproduction on the proton above the resonance region (2.6相似文献   

Observation of the psi(4415)-->DD2*(2460) decay using initial-state radiation

We report measurements of the exclusive cross section for e(+)e(-)-->D(0)D(-)pi(+) over the center-of-mass energy range 4.0 GeV to 5.0 GeV with initial-state radiation and the first observation of the decay psi(4415)-->D(0)D(-)pi(+). From a study of the resonant substructure in psi(4415) decay we conclude that the psi(4415)-->D(0)D(-)pi(+) decay is dominated by psi(4415)-->DD(2)(*)(2460). We obtain B(psi(4415)-->D(0)D(-)pi(nonresonant)(+))/B(psi(4415)-->DD(2)(*)(2460)-->D(0)D(-)pi(+))<0.22 at 90% C.L. The analysis is based on a data sample collected with the Belle detector with an integrated luminosity of 673 fb(-1).     

Measurement of the e+e- -->pi+pi- J/psi cross section via initial-state radiation at Belle

The cross section for e(+)e(-)-->pi(+)pi(-)J/psi between 3.8 and 5.5 GeV/c(2) is measured using a 548 fb(-1) data sample collected on or near the Upsilon(4S) resonance with the Belle detector at KEKB. A peak near 4.25 GeV/c(2), corresponding to the so called Y(4260), is observed. In addition, there is another cluster of events at around 4.05 GeV/c(2). A fit using two interfering Breit-Wigner shapes describes the data better than one that uses only the Y(4260), especially for the lower-mass side of the 4.25 GeV enhancement.     

Double pi(0) Photoproduction on the Proton at GRAAL

The double pi(0) photoproduction off the proton has been measured in the beam energy range of 0.65-1.5 GeV. The total and differential cross sections and the Sigma beam asymmetry were extracted. The total cross section measured for the first time in the third resonance region of the nucleon shows a prominent peak. The interpretation of these results by two independent theoretical models infers mostly the selective excitation of P11- and D13-nucleon resonances.     

Elastic and proton-dissociative \rho^0 photoproduction at HERA

Elastic and proton-dissociative photoproduction (, , respectively, with ) has been studied in interactions at HERA for photon-proton centre-of-mass energies in the range GeV and for GeV, where is the square of the four-momentum transfer at the proton vertex; the results on the proton-dissociative reaction are presented for masses of the dissociated proton system in the range . For the elastic process, the invariant mass spectrum has been investigated as a function of . As in fixed target experiments, the resonance shape is asymmetric; this asymmetry decreases with increasing , as expected in models in which the asymmetry is ascribed to the interference of resonant and non-resonant production. The cross section has been studied as a function of ; a fit to the resonant part with the form gives . The resonant part of the cross section is b at GeV. The dependence of the cross section can be described by a function of the type with (stat.) (syst.) GeV and (stat.) (syst.) GeV. The dependence has also been studied as a function of and a value of the slope of the pomeron trajectory GeV has been deduced. The spin density matrix elements , and have been measured and found to be consistent with expectations based on -channel helicity conservation. For proton-dissociative photoproduction in the mass range, the distributions of the two-pion invariant mass, and the polar and azimuthal angles of the pions in the helicity frame are the same within errors as those for the elastic process. The distribution has been fitted to an exponential function with a slope parameter GeV. The ratio of the elastic to proton-dissociative photoproduction cross section is . Received: 3 December 1997 / Online publication: February 26, 1998     

Rho(0) meson production in the pp-->pppi(+)pi(-) reaction at 3.67 GeV/c

Total and differential cross sections for the exclusive reaction pp-->pp rho observed via the pi(+)pi(-) decay channel have been measured at p(beam)=3.67 GeV/c. The observed total meson production cross section is determined to be (23.4+/-0.8+/-8) mu b 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 (approximately cos(theta(CM)(rho)) in the rho(0) meson production.     

Observation of exclusive electron-positron production in hadron-hadron collisions

We present the first observation of exclusive e(+)e(-) production in hadron-hadron collisions, using pp[over] collision data at (square root) s = 1.96 TeV taken by the run II Collider Detector at Fermilab, and corresponding to an integrated luminosity of 532 pb(-1). We require the absence of any particle signatures in the detector except for an electron and a positron candidate, each with transverse energy E(T) > 5 GeV and pseudorapidity |eta| < 2. With these criteria, 16 events are observed compared to a background expectation of 1.9+/-0.3 events. These events are consistent in cross section and properties with the QED process pp[over] --> p + e(+)e(-) + p[over] through two-photon exchange. The measured cross section is 1.6(-0.3)(+0.5)(stat) +/- 0.3(syst) pb. This agrees with the theoretical prediction of 1.71+/-0.01 pb.     

The photoproduction of neutral pions from protons at forward angles in the resonance region

Differential cross sections for the photoproduction of pi-zero mesons from protons have been measured at angles between 10° and 70° c.m. in the energy range 0.85 GeV to 1.30 GeV. The values are compared with the fits to pion photoproduction data from three recent partial-wave analyses.     

Photoproduction of the 1.6 GeV ρ0ρ0 state

We calculate the photoproduction cross section for the 1.6 GeV state recently observed in γγ collisions. The integrated cross section forx _F >0 could be 500nb at 50 GeV, and therefore the state should be detectable in existing photoproduction experiments.     

Evidence for nucleon-resonance excitation in omega-meson photoproduction

The photoproduction of the omega meson has been studied at GRAAL from threshold up to a photon energy of 1.5 GeV. The differential cross sections and beam asymmetries have been measured precisely at all angles. The total cross section is also obtained. Systematic enhancements of the differential cross section at large angles and nonzero beam asymmetries at intermediate angles provide clear evidence for s- and u-channel resonant processes. The data are compared to the results of hadron and quark models.     

Observing the odderon: tensor meson photoproduction

We calculate high-energy photoproduction of the tensor meson by odderon and photon exchange in the reaction , where X is either the nucleon or the sum of the N(1520) and N(1535) baryon resonances. Odderon exchange dominates except at very small transverse momentum, and we find a cross section of about 20 nb at a centre-of-mass energy of 20 GeV. This result is compared with what is currently known experimentally about photoproduction. We conclude that odderon exchange is not ruled out by present data. On the contrary, an odderon-induced cross section of the above magnitude may help to explain a puzzling result observed by the E687 experiment. Received: 16 February 2000 / Published online: 8 May 2000     

Neutral-pion photoproduction off protons in the energy range 0.3 GeV<E(gamma)<3 GeV

Single pi(0) photoproduction has been studied with the CB-ELSA experiment at Bonn using tagged photon energies between 0.3 and 3.0 GeV. The experimental setup covers a very large solid angle of approximately 98% of 4pi. Differential cross sections dsigma/dOmega have been measured. Complicated structures in the angular distributions indicate a variety of different resonances being produced in the s channel intermediate state gammap-->N(*)(Delta(*))-->ppi(0). A combined analysis including the data presented in this letter along with other data sets reveals contributions from known resonances and evidence for a new resonance N(2070)D15.     

The photoproduction of neutral pions from protons between 0.7 GeV and 1.7 GeV

Measurements of differential cross sections for pi-zero photoproduction from protons have been made at angles between 60° and 140° c.m. in the photon energy range 0.7 GeV to 1.7 GeV. The data are compared with the rits provided by three recent partial-wave analyses of pion photoproduction and some significant discrepancies observed.     

Cross sections and transverse single-spin asymmetries in forward neutral-pion production from proton collisions at sqrt[s]=200 GeV

Measurements of the production of forward high-energy pi(0) mesons from transversely polarized proton collisions at sqrt[s]=200 GeV are reported. The cross section is generally consistent with next-to-leading order perturbative QCD calculations. The analyzing power is small at x(F) below about 0.3, and becomes positive and large at higher x(F), similar to the trend in data at sqrt[s]< or =20 GeV. The analyzing power is in qualitative agreement with perturbative QCD model expectations. This is the first significant spin result seen for particles produced with p(T)>1 GeV/c at a polarized proton collider.     

Measurement of open beauty production in photoproduction at HERA

The production and semi-leptonic decay of heavy quarks have been studied in the photoproduction process with the ZEUS detector at HERA using an integrated luminosity of 38.5 pb. Events with photon-proton centre-of-mass energies, , between 134 and 269 GeV and a photon virtuality, , less than 1 GeV were selected requiring at least two jets of transverse energy GeV and an electron in the final state. The electrons were identified by employing the ionisation energy loss measurement. The contribution of beauty quarks was determined using the transverse momentum of the electron relative to the axis of the closest jet, . The data, after background subtraction, were fit with a Monte Carlo simulation including beauty and charm decays. The measured beauty cross section was extrapolated to the parton level with the b quark restricted to the region of transverse momentum 5 GeV and pseudorapidity 2. The extrapolated cross section is . The result is compared to a perturbative QCD calculation performed to next-to-leading order. Received: 22 November 2000 / Published online: 5 February 2001     

Identified baryon and meson distributions at large transverse momenta from Au + Au collisions at square root sNN=200 GeV

Transverse momentum spectra of pi+/-, p, and p up to 12 GeV/c at midrapidity in centrality selected Au + Au collisions at square root sNN=200 GeV are presented. In central Au + Au collisions, both pi +/- and p(p) show significant suppression with respect to binary scaling at pT approximately >4 GeV/c. Protons and antiprotons are less suppressed than pi+/-, in the range 1.5 approximately < pT approximately < 6 GeV/c. The pi-/pi+ and p/p ratios show at most a weak pT dependence and no significant centrality dependence. The p/pi ratios in central Au + Au collisions approach the values in p + p and d + Au collisions at pT approximately >5 GeV/c. The results at high pT indicate that the partonic sources of pi+/-, p, and p have similar energy loss when traversing the nuclear medium.     

Dijet photoproduction at HERA and the structure of the photon

The dijet cross section in photoproduction has been measured with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb. The events were required to have a virtuality of the incoming photon, , of less than 1 GeV and a photon-proton centre-of-mass energy in the range GeV. Each event contains at least two jets satisfying transverse-energy requirements of GeV and GeV and pseudorapidity requirements of \mbox{}. The measurements are compared to next-to-leading-order QCD predictions. The data show particular sensitivity to the density of partons in the photon, allowing the validity of the current parameterisations to be tested. Received: 21 December 2001 / Published online: 5 April 2002     

Observation of e(+)e(-) annihilation into the C = +1 hadronic final states rho(0)rho(0) and phirho(0)

We report the first observation of e(+)e(-) annihilation into states of positive C parity, namely, rho(0)rho(0) and phirho(0). The two states are observed in the pi(+)pi(-)pi(+)pi(-) and K(+)K(-)pi(+)pi(-) final states, respectively, in a data sample of 225 fb(-1) collected by the BABAR experiment at the Positron-Electron Project II e(+)e(-) storage rings at energies near sqrt[s]=10.58 GeV. The distributions of costheta(*), where theta(*) is the center-of-mass polar angle of the phi meson or the forward rho(0) meson, suggest production by two-virtual-photon annihilation. We measure cross sections within the range |costheta(*)|<0.8 of sigma(e(+)e(-)-->rho(0)rho(0))=20.7+/-0.7(stat)+/-2.7(syst) fb and sigma(e(+)e(-)-->phirho(0))=5.7+/-0.5(stat)+/-0.8(syst) fb.