η production in nuclei by protons at Tp≦ 1 GeV

The reactionpA →η X has been measured on⁶Li, C and Cu targets at a proton energy of 0.9 GeV at the SATURNE accelerator. The doubly differential cross sections at T_p=0.9 GeV together with data at T_p=1 GeV, previously presented [1], are analysed in the frame of a recent folding model [3].     

Particle composition at high transverse momenta in p-p-collisions in the central region at the CERN ISR

Preliminary measurements have been made at centre of mass energies √s = 31 and 44 GeV of the π, K and p production ratios at 90° for p_T between 2.0 and 3.5 GeV/c. The (K+p)/π ratio is given down to p_T = 1.4 GeV/c. No strong energy dependence is observed for these transverse momenta.     

Nuclear mass number dependence of inclusive pion production by pions and protons at 4.3GeV/c

The inclusive production of π⁺ for 0.4≤p_T<1.0 GeV/c in pion-nucleus and proton-nucleus collisions at 4.3 GeV/c was measured. A strong A-dependence of the cross sections at high p_T is observed to be persistent in the low energy region. The ratio of the cross sections for proton-nucleus and pion-nucleus collisions is also observed to be compatible with the quark-parton picture, for p_T>0.6 GeV/c.     

Search for direct single-photon production at large pT in photon-proton collisions at √s = 62.4 GeV

As part of a study of large p_T phenomena in photon-proton collisions at the CERN ISR, a search for direct single photon production has been performed. A statistical division of the data sample into the fraction consistent with single photon and the fraction due to multiphoton decays of neutral hadrons is accomplished by measuring the average conversion probability for the sample in a one radiation length thick converter. The fraction of the sample attributable to direct single photon production is 〈γ/all〉 = 0.074 ± 0.012 for 6 GeV/c < p_T 10 GeV/c, and 〈γ/all〉 = 0.26 ± 0.04 for p_T > 10 GeV/c, with an additional systematic uncertainty of ±0.05 for both values.     

Large transverse momentum particle production in αα and pp collisions at the CERN ISR

The production of charged hadrons with high p_T in αα collisions at √s=126 GeV and pp collisions at √s=31 and 63 GeV is compared, and the structure of the events associated with the high-pT particles is studied. The probability of finding associated particles close to the trigger particle increases strongly between √s=31 and 63 GeV for pp collisions. For p_T>2.5GeV/c the αα/pp cross section ratio at the same energy per nucleon is measured to be 18.7 ± 2.0, to be compared with A² = 16, and a higher associated multiplicity is observed for αα.     

Double prompt photon production at high transverse momentum byπ − on protons at 280 GeV/c

A search for pairs of highp _T prompt photons produced in hydrogen by a 280 GeV/c incidentπ ^- beam has been carried out using a fine-grained electromagnetic calorimeter and the Omega spectrometer at the CERN SPS. Clear evidence for the existence of such events is found with a six standard deviation signal forp _T >3.0 GeV/c. The cross-sections are consistent with beyond leading order QCD calculations. A discussion on the determination of α _s is also presented.     

Measurement of large transverse momentum positive particles produced at medium angles at √s = 52.5 GeV

The inclusive spectrum of positive particles has been measured at the ISR energy √s = 52.5 GeV as function of transverse momentum, p_T for large p_T values using the Split Field Magnet facility. The angular dependence of the distribution is observed and discussed in the range $\text{9° ? θ}{}^1\text{? 21°}$. An upper limit for the production of ? meson with p_T ? 3 GeV/c is derived from the same sample of data.     

Transverse momentum distribution in Pomeron-Pomeron collisions at the CERN ISR

Proton-proton interactions which result in a central cluster of massM _x and two quasi-elastically scattered protons are generally described by Pomeron-Pomeron scattering. A study of this process at ISR energies with the Split Field Magnet detector is carried out in terms of transverse momentum behaviour for the centrally produced system of particles. The inclusivep _T distribution for central hadrons is measured up to 3 GeV/c. Forp _T <1.2 GeV/c, thep _T distribution is exponential. Using a subsample of exclusive events, this exponential shape is shown to originate from a phase-space-like decay ofM _x when convoluted with a transverse component of the pomeron momentum. In the highp _T range, the shape of thep _T distribution strongly depends on Feynman-x of the scattered protons in a way that can be described by hard parton scattering.     

Charged hadron suppression in Au+Au collisions at high p T from STAR

We report high statistics measurements of inclusive charged hadron production in Au+Au collisions at $\sqrt {s_{NN} } = 200$ GeV and 130 GeV. A large, approximately constant hadron suppression is observed in central Au+Au collisions for 5 ‖p _T ‖ 12 GeV/c. The collision energy dependence of the yields and the centrality and p _T dependence of the suppression provide stringent constraints on theoretical models of suppression. Models incorporating initial-state gluon saturation or partonic energy loss in dense matter are largely consistent with observations. The p _T -dependent suppression expected from models incorporating jet attenuation in cold nuclear matter or absorption of fragmentation hadrons is not observed.     

ϒ production at large transverse momentum as a probe of axigluons

Large-p_T production of J/Ψ and ϒ particles is suggested as a sensitive probe of axigluons of mass less than 40 GeV at the CERN collider and 80 GeV at the Tevatron. It is shown that existing CERN collider data on large-p_T ϒ production exclude axigluon masses less than around 20 GeV. At the projected SSC, ϒ and vector toponium production at large p_T through axigluon exchange by far outweighs the QCD contribution over a vast range of axigluon and toponium masses.     

Spin dependence of the inclusive reaction p + p (polarized) → π0 + X at 24 GeV/c for high-pTπ0 produced in the central region

The spin dependence of π⁰ inclusive production by 24 GeV/c protons has been measured using a polarized target for Fhe Feynman x near 0 in the transverse momentum range 1.0 < p_T < 2.5 GeV/c. The results indicate a negative updown asymmetry growing strongly with p_T and greater than 50% in absolute value for p_T greater than 2 GeV/c.     

Measurement of Neutral pions in √NN=200 GeV and 62.4 GeV Au+Au collisions at RHIC-PHENIX

Neutral pions (π⁰) in √_NN=200 GeV and 62.4 GeV Au+Au collisions were measured at RHIC-PHENIX Year-4 Run. In √_NN=200 GeV, π⁰ spectra are measured up to p _T=20 GeV/c. A strong suppression by a factor of ～5 is observed and stays almost constant up to 20 GeV/c.     

Low p T phenomena in A+A and p+A collisions at mid-rapidity

CERN experiment NA44 measures pion and kaon distributions at p _T = 0–320 MeV/c at midrapidity in p+A and A+A collisions at 450 and 200A GeV/c, respectively. Pion production from p+Pb and A+A is slightly enhanced at low p _T relative to p+Be, but less than observed at target rapidity. The low p _T behavior can be understood in the context of the RQMD model as arising from baryonic resonance decays.     

Photon production in √s NN =200 GeV Au+Au collisions measured by the PHENIX experiment at RHIC

Direct photon production in Au+Au collisions at √s _NN =200 GeV has been measured in the p _Trange of 1<p _T<5 GeV/c. The yield as a function of centrality is in agreement with published data of the RHIC 2002 run, and with results from a new method that explores very low mass dileptons. The result is compared to several theoretical calculations, and it is found that the measurement is not inconsistent with calculations including thermal photon contributions.     

Analysis of transverse momentum distributions forpp interactions at 360 GeV/c in the framework of a quark-diquark fragmentation model

Using a quark-diquark fragmentation model, in which either the Field-Feynman or the Lund model is coupled with a quark-diquark distribution function, we study transverse momentum distributions,p _T, for the inclusive reactionspp→hadron +anything at 360 GeV/c. We find that a primordial mean transverse momentum 〈k _T〉?0.4 GeV/c can well reproduce thep _T ² distributions of charged hadrons, π⁰,K _s ⁰ , Λ⁰,K ^* and Σ^* and the Feynmanx?p _T correlations. We confirm that a diquark in a proton plays an important rôle in reproducing thex?p _T correlation of Λ⁰.     

Transverse momentum distributions of hadrons produced in αα and αp collisions at the CERN intersecting storage rings

The inclusive production of charged hadrons has been measured in αα and αp collisions at nucleon-nucleon c.m. energies (√s_nn)of 31 and 44 GeV, respectively, for transverse momenta p_T up to 5 GeV/c in the central rapidity (y) region. at high p_T the yields are consistent with being 4 times and 16 times highere than the ones in pp interactions at y=0, for αp and αα interactions, respectively. However, an enhancement over these factors, as expected from an earlier FNAL experiment, cannot be ruled out.     

A measurement of direct photon production at large pT at the CERN ISR

We have measured direct photon production in pp collisions at the CERN intersecting storage rings for c.m. energies 31 < √s < 63 GeV and transverse momenta up to 9GeV/c, using segmented lead/liquid-argon calorimeters. The ratio of direct photon to π⁰ production is significantly larger than zero, starting at p_T ≈ 4 GeV/c and increasing to values of about 0.4 at 9GeV/c. No significant √s dependence is seen.     

Inclusive neutron and lambda production in proton-proton interactions at 12 and 24 GeV/c

A method for the determination of neutron spectra in a bubble chamber experiment is developed. Double differential cross sections for inclusive neutron and lambda production are presented. The n/Λ particle ratios are determined as functions of x and p_T; at p_T = 0 GeV/c they are compatible with the ratios measured in pCu interactions at 24 GeV/c. Our neutron spectra are compared with spectra for protons produced near the direction of the incident neutron in pn interactions at FNAL and with neutron spectra measured in pp interactions at the ISR. Exchange mechanisms are studied in the framework of single diffraction dissociation and the triple-Regge model. The scattering of virtual pions and kaons on real protons is investigated.     

Inclusive η production at high pT at the ISR

The inclusive η production cross section at the CERN ISR has been measured for p_T values of up to 11 GeV/c. We find that the $\text{η}\text{π}{}^0$ cross-section ratio has an average value of 0.55 ± 0.07 and varies little with p_T.