Benchmark cross sections forp \bar p collisions at 1.8 TeV

High-energyp \(\bar p\) collisions provide many quantitative tests of the standard model. Of particular interest are “hard scattering” processes, which test not only standard model matrix elements and higher order perturbative corrections, but also the distributions of quarks and gluons in the colliding hadrons. We present detailed comparisons of data from the CERNSp \(\bar p\) S collider with theory, incorporating up-to-date parton distributions derived from recent deep inelastic scattering data. Encouraged by the excellent agreement between data and theory at \(\sqrt s \) =630GeV, we present a complete set of “benchmark” predictions for the FNALp \(\bar p\) collider at \(\sqrt s \) =1.8TeV.     

Wino and zino production inp\bar p collisions: first order supersymmetric QCD corrections

We compute the first order supersymmetric QCD correction to wino \((\tilde W)\) and zino \((\tilde Z)\) production in \(p\bar p\) collisions via subprocesses involving two massless partons inside the nucleon or one massless parton and a massive SUSY parton (squark or gluino). The first order SQCD corrections to the rapidity dependence at CERN collider and Tevatron energies are found large (K～2). The rates are important (～10^?2 nb at \(\sqrt s = 630\) GeV and ～10^?1 nb at \(\sqrt s = 2\) TeV), as soon as the \((\tilde W)\) and \((\tilde Z)\) production by squarks is allowed. Transverse momentum distributions are also given and their shape is found very sensitive to the presence of SUSY partons inside the nucleon.     

Mirror fermion production inep collisions

The phenomenology of mirror fermions is studied in a model with three heavy mirror fermion families. The tree unitarity bounds on the mirror masses are determined. The production cross-sections and decay characteristics of mirror fermions are calculated in high energy electron-proton collisions. For mirror mixing angles of the order of the present upper limits mirror fermion production at HERA ( \(\sqrt s = 314 GeV\) ) is observable up to masses near 200 GeV. For a possible HERA upgrade ( \(\sqrt s = 566 GeV\) ) this limit goes up to about 350 GeV and anep collider in the LEP tunnel ( \(\sqrt s = 1.4 TeV\) ) could cover the range below 500 GeV.     

Searching for new heavy vector bosons inp \bar p colliders

Production and detection of new heavy vector bosons is studied at present (or near future)p \(\bar p\) collider experiments. Application to CERN and Tevatron experiments is considered in detail, but some results for the UNKp \(\bar p\) collider, at \(\sqrt s \) = 6TeV, are also presented. Rather than considering a number of detailed models, we prefer to discuss some general, although necessarily schematic, classes of new vector bosons ranging from strongly interacting Higgs sector models to extended gauge models. We study in particular signals and backgrounds in the \(\ell \overline \ell jj\) channels, where ? are leptons andj are hadron jets.     

Reggeon calculus at collider energies

The phenomenology of the perturbative reggeon calculus at collider energies is studied. It is found that the graphs which were neglected at ISR energies are still negligeable at \(\sqrt s = 540 GeV\) . The pertubative series for the total cross section still converges reasonably fast. The values of the different parameters which describe rightly the data up to ISR energies give rise to a total cross section of around 60 mb at \(\sqrt s = 540 GeV\) . For these values, the corresponding low mass and high mass eikonal series converges much more slowly. The non perturbative reggeon calculus gives rise to a total cross section less than 60 mb.     

Minijets as a further test of QCD

Perturbative QCD is shown to be in quantitative agreement with one-and two-jet production data in the range \(27 \lesssim \sqrt s \lesssim 900GeV\) GeV forP _T(jet)?5 GeV. The integrated jet yield above a fixedP _T(parton)?3 GeV accounts for the \(\bar pp\) inelastic cross section rise in the same range. QCD predictions for jet yields up to \(\sqrt s = 40TeV\) are presented and the role of non-perturbative corrections, ultimately saving unitarity, is briefly discussed.     

Multiplicity dependence of the average transverse momentum and of the particle source size inp−p interactions at\sqrt s =62, 44 and 31 GeV

The average transverse momentum and the size of the particle emitting source (measured via Bose-Einstein correlations) have been studied as functions of the charged particle density in the central region inp-p interactions at \(\sqrt s \) =62, 44 and 31 GeV. Both the average transverse momentum and the source size increase with increasing density at all three energies. This effect, very weak at \(\sqrt s \) =31 GeV, becomes stronger with increasing energy.     

Crossing-odd effects in soft nucleon collisions

A complete set of the data onpp andp \(\bar p\) scattering including measurements in the Coulomb interference region are analised to discover crossingodd effects in soft collisions. It is shown that the odderon is unable to produce a significant increase in ReA/ImA at \(\sqrt s = 546\) GeV. Moreover, the data give preference to that odderon which makes negative contribution to Re \(A_{p\bar p} \) and ceases the decrease of difference inp \(\bar p\) andpp total cross-sections.     

Collider monojets ofW→τv origin

Within the standard model it is found that the most copious source of events with a single hadronic jet balanced by large missing transverse momentum \((\mathop {p_T }\limits^/ )\) is the decay process \(W \to \tau \bar v \to (n\pi )v\bar v\) . A detailed calculation of the monojet cross-section predicts a lower limit ofO(2) events with \(\mathop {p_T }\limits^/ > 35\) GeV per 100 nb^?1 of integrated luminosity at presently available \(\bar pp\) collider energies.     

Rules of thumb for theZ line shape

In this paper the theoretical parameters of theZ line shape, such asM _Z andΓ _Z, and the one photon exchange diagram are related to a set of parameters characterizing the experimental line shape. The latter are the peak height σ_max, peak position \(\sqrt {s_{\max } } \) and half peak positions \(\sqrt {s_ \pm } \) . The rules of thumb are accurate within 10 MeV. As a result we obtain approximate formulae which expressM _Z and Γ_Z in the measured \(\sqrt {s_{\max } } \) and \(\sqrt {s_ + } - \sqrt {s_ - } \) .     

Partition temperature and fireballs of hadron-proton collisions

A geometric property is considered to relate the impact parameterb ofhh collision at a given \(\sqrt s \) to the partition temperatureT _p of producedn _ch pions. It is based on the overlapping of two Lorentz contracted fireballs (FB) associated to the primary hadrons, as is described in the partition temperature model (PTM), assuming for the FB radiusR=r(3n _ch/2)^1/3. For \(\bar p\) p collisions at \(\sqrt s \) = 540 GeV analyzed by the authors of the PTM,r=0.70±0.03 fm consistent with the pion radius, the computedT _p agree with their results for variousn _ch. The energy dependence ofT _p for \(\bar p\) p from \(\sqrt s \) = 13.8 to 900 GeV is accounted for by assuming the FB velocity with respect to the c.m.s., to behave likepp, i.e., β _F =1?λ with λ=2 〈P _⊥〉/λ〈P _∥〉 and \(\bar b = 0.98fm\) . Remarks are made on the relationship betweenT _p and the conventional temperature determined by 〈P _⊥〉 in terms of the Lorentz factor of the FB.     

Heavy gluino and squark decays atp \bar p collider

The recent limits, \(m_{\tilde g} , m_{\tilde q} \gtrsim 40\) , GeV for gluino and squark masses obtained from experiments at the collider are based on jet +p _T analysis, in the hypothesis that the gluino or the squark decays into photino+quarks with a branching ratio near to one. We show that this hypothesis is generally not justified for higher masses of the gluino and the squarks, 50 GeV \( \lesssim m_{\tilde g,\tilde q} \lesssim \) 150 GeV, relevant to present and future \(\bar p\) colliders. In an interesting range of the parameters we study the different decay modes and the related signatures, among which isolated leptons or photons in the final states.     

High-p T direct photon production inpp collisions

Direct photon and neutral-pion production have been measured inpp collisions at the CERN ISR for 30< \(\sqrt s \) <63 GeV and transverse momenta up to 12 GeV/c. The direct photon signal relative to neutral-pion production increases withp _T and shows little \(\sqrt s \) -dependence. Results are reported from a variety of running conditions, and details are given on the method of analysis and on the evaluation of systematic errors for the inclusive cross-section of single-photon and neutral-pion production.     

Very high energy nucleus-nucleus collisions and multi-chain model

Inclusive and semi-inclusive production of Λ and \(\bar \Lambda\) inK ⁺ p interactions is studied at an incident momentum of 70 GeV/c. Cross sections and single particle distributions are presented and compared with data at lower energies. Scaling is observed between 32 and 70 GeV/c in the Feynmanx variable in the target and the beam fragmentation regions for Λ and \(\bar \Lambda\) inclusive production respectively. An increase of Λ ( \(\bar \Lambda\) ) production is observed in the beam (target) fragmentation regions, whereas the data at 70 and 32 GeV/c are reasonably close in the central region. The dependence of the Λ( \(\bar \Lambda\) ) polarization as a function ofx is measured and found to be in general agreement with the results at 32 GeV/c. The (Λ \(\bar \Lambda\) ) pair production cross section increases significantly from 32 to 70 GeV/c. The Λ and \(\bar \Lambda\) production associated with an identified proton is also studied.     

Neutral strange particle production in proton-proton collisions at\sqrt s = 63 GeV

The inclusive cross section for the production ofK _s ⁰ mesons, Λ and \(\bar \Lambda\) particles in proton-proton interactions at \(\sqrt s = 63\) GeV is presented. The produced particles have been detected in the full phase space. Behaviour of the longitudinal and transversal depandences of the cross sections are discussed. The total production cross sections for _s ⁰ mesons and Λ particles was determined to \(\sigma _{{\rm K}_S^0 } = (25.5 \pm 1.4)\) mb andσ _Λ =(7.8±1.2) mb respectively. A strong energy dependence of the production cross sections is observed.     

\bar \Lambda Production inK − p interactions at 32 GeV/c

Antilambda production is studied inK ^? p interactions at 32 GeV/c. Both total and differential cross sections are presented. The inclusive \(\bar \Lambda \) production cross section amounts to 109±7 μb. A remarkable energy dependence is observed, σ( \(\bar \Lambda \) ) increasing by a factor of four between 14.3 and 32 GeV/c. Thep _⊥ ² distribution exhibits an exponential fall-off with a slope of 3.3±0.2 (GeV/c)^?2. Most of the \(\bar \Lambda \) 's are emitted in the forward hemisphere. The invariantx distribution increases between 14.3 and 32 GeV/c. Data are presented for \(\bar \Lambda \) production inK ^- p→Λ \(\bar \Lambda \) +X K ^- p→ \(\bar \Lambda \) K ⁿ +X, andK ^- p→ \(\bar \Lambda \) p+X.     

Strong decays ofΨ(4.03) andΨ(4.16) as radial excitations of charmonium

Considering the signals detected at 4.03 and 4.16 GeV as radial excitations of charmonium, we study their relative decay rates intoD \(\bar D\) ,D \(\bar D^* \) ,D ^* \(\bar D\) ,D ^* \(\bar D^* \) . We point out that one can understand these two peaks as ac \(\bar c\) 3S?2D wave state system with a large mixing angle in a Coulomb+linear interquark potential. We also examine the possibility that these two signals are respectively 3S and 4S wave excitations by studying a logarithmic charmonium potential model. We show that both these interpretations lead to drastically different predictions for the Ψ (4.16) decay rates (eitherD \(\bar D^* \) +D ^* \(\bar D\) orD \(\bar D\) mode is strongly suppressed) which would be very instructive to test experimentally.     

\bar K K and\bar p p off-shell annihilations fromK − +p → Λ + pions at 4.2 GeV/c

We have investigated the properties of off-shell \(\bar K\) K and \(\bar p\) p annihilations into pions by using the interactionsK ^? p → Λ + pions at 4.2 GeV/c. The properties considered are multiplicities, hadronic temperatures and angular distributions. These properties appear more akin to those of \(\bar p\) p annihilations in flight than to that of \(\bar p\) p annihilation at rest despite the fact that the annihilation energy is small.     

Quark-diagram estimates ofCP violation in two-body baryonicB_d^0 - \bar B_d^0 decays

CP violation in partial-decay-rate asymmetries are examined for some two-body baryonic decays of \(B_d^0 - \bar B_d^0 \) system. We discuss two feasible experimental circumstances: the symmetrice ⁺ e ^? collisions (i) on theZ ⁰ resonance to produce incoherent \(B_d^0 \bar B_d^0 \) states, and (ii) just above the ?(4S) resonance to produceC=even \(B_d^0 \bar B_d^0 \) states. Using the quark-diagram scheme, we estimate the branching ratios of those decays, and the numbers ofb \(\bar b\) pairs needed for testing theCP-violating effects for 3σ signature. We find that the promising channels may beB _d ⁰ , \(\bar B_d^0 \to p\bar p\) , \(\Delta ^ + \bar \Delta ^ - \) , \(p\bar \Delta ^ - \) , \(\Delta ^ + \bar p\) , \(n\bar n\) , \(\Delta ^0 \bar \Delta ^0 \) , \(n\bar \Delta ^0 \) , \(\Delta ^0 \bar n\) , \(\Sigma _c^ + \bar \Sigma _c^ - \) , \(\Lambda _c^ + \bar \Lambda _c^ - \) , \(\Sigma _c^ + \bar \Lambda _c^ - \) , \(\Lambda _c^ + \bar \Sigma _c^ - \) , \(\Sigma _c^0 \bar \Sigma _c^0 \) , \(\Xi _c^0 \bar \Xi _c^0 \) , which should be interesting for experimental observation.