Drell-Yan Model Research Articles

Limits on production of magnetic monopoles utilizing samples from the D0 and CDF detectors at the Fermilab Tevatron

We present 90% confidence level limits on magnetic monopole production at the Fermilab Tevatron from three sets of samples obtained from the D0 and CDF detectors each exposed to a proton-antiproton luminosity of $\ensuremath{\sim}175{\mathrm{pb}}^{\ensuremath{-}1}$ (experiment E-882). Limits are obtained for the production cross sections and masses for low-mass accelerator-produced pointlike Dirac monopoles trapped and bound in material surrounding the D0 and CDF collision regions. In the absence of a complete quantum field theory of magnetic charge, we estimate these limits on the basis of a Drell-Yan model. These results (for magnetic charge values of 1, 2, 3, and 6 times the minimum Dirac charge) extend and improve previously published bounds.

Measurement of Drell-Yan electron and muon pair differential cross sections in p-barp collisions at sqrt s =1.8 TeV.

We measure the Drell-Yan differential cross section [ital d][sup 2][sigma]/[ital dM] d[ital y][vert bar][sub [vert bar][ital y][vert bar][lt]1] over the mass range 11[lt][ital M][lt]150 GeV/[ital c][sup 2] using dielectron and dimuon data from [ital [bar p]p] collisions at a center-of-mass energy of [radical][ital s] =1.8 TeV. Our results show the 1/[ital M][sup 3] dependence that is expected from the naive Drell-Yan model. In comparison to the predictions of recent QCD calculations we find our data favor those parton distribution functions with the largest quark contributions in the [ital x] interval 0.006 to 0.03.

Pion and nucleon structure as probed in the reaction π±N→ μ+μ−X at 253 GeV

New results are presented from Fermilab experiment E615, in which hadroproduction of muon pairs allows a determination of the quark structure of the initial-state hadrons in the context of a Drell-Yan model. 1. ⊎|Comparison of muon-pair production by π + and π − beams shows the cross-section ratio follows Drell-Yan model expectations, except for a dip in σ(π +)/σ(π −) near x π near 1. 2. ⊎|The same data are also used to extract the ratio of the sea to valence quark distributions in the nucleon, with improved accuracy for l N<0.1 compared to deep-inelastic neutrino scattering. 3. ⊎|The Drell-Yan analysis of continuum muon-pair production has been extended down to a mass of 3.2 GeV/c 2 for the π − data sample. This provides stronger evidence of a rise in the nucleon structure function for L N<0.06 compared to that extracted in deep-inelastic lepton scattering. 4. ⊎|The issue is raised of the nonuniqueness of the definition of L π and L N used in the Drell-Yan analysis. A definition proposed by Soper has superior invariance properties to that commonly used. An analysis based on this definition yields generally similar results for the pion and nucleon structure function, compared to use of the common definition, However, the pion structure function shows a larger intercept at L π=1 when the definition of Soper is used.

High-mass dimuon production inp¯Nandπ−N interactions at 125 GeV/c

We have studied muon pairs with an invariant mass between 4 and 9 GeV/${c}^{2}$ produced in p\ifmmode\bar\else\textasciimacron\fi{}N and ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$N interactions at an incident momentum of 125 GeV/c. The experiment was performed at Fermilab using a tungsten target and a special beam enriched to contain 18% antiprotons. We compare differential distributions as functions of the dimuon invariant mass, Feynman x, transverse momentum, and decay angles of the dimuon to the predictions of the Drell-Yan model including QCD corrections. Quark structure functions for the p\ifmmode\bar\else\textasciimacron\fi{} and ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ are extracted. Comparisons of the antiproton data to the Drell-Yan model are significant because the cross sections depend principally on the valence-quark structure functions which are accurately determined by deep-inelastic scattering measurements. The measured absolute cross section (integrated over positive Feynman x and all transverse momenta) is 0.106\ifmmode\pm\else\textpm\fi{}0.005\ifmmode\pm\else\textpm\fi{}0.008 nb/nucleon for the p\ifmmode\bar\else\textasciimacron\fi{}N interaction and 0.107\ifmmode\pm\else\textpm\fi{}0.003\ifmmode\pm\else\textpm\fi{}0.009 nb/nucleon for the ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$N interaction, where the quoted errors are statistical and systematic, respectively. Normalization (K) factors that are required to bring the naive Drell-Yan and first-order QCD predictions into agreement with the measurements are extracted, and the uncertainties involved in such comparisons are examined.

Production of massive muon pairs in pi --nucleus collisions.

We present measurements of the differential cross section for the production of massive muon pairs in 225-GeV/c ${\ensuremath{\pi}}^{\ensuremath{-}}$-nucleus collisions. We have used the data between the $\ensuremath{\psi}$ and $\ensuremath{\Upsilon}$ resonances in the framework of the Drell-Yan quark-antiquark annihilation model to predict the behavior of the cross section in the high-mass (${m}_{\ensuremath{\mu}\ensuremath{\mu}}g11$ GeV/${\mathit{c}}^{2}$) region. The data are consistent with this extrapolation provided that a QCD leading-logarithmic evolution is included in the structure functions.

Standard-model dimuon sources in pp-bar collisions.

Dimuon events observed at the CERN pp\ifmmode\bar\else\textasciimacron\fi{} collider offer an opportunity to check the QCD fusion mechanism for heavy-quark production at high ${p}_{T}$, along with the Drell-Yan mechanism. We present predicted dimuon rates and distributions from these standard-model sources at \ensuremath{\surd}s =630 GeV, for comparison with the forthcoming collider data. The like-sign/unlike-sign dimuon ratio from heavy quarks is sensitive to the details of fragmentation, as well as possible ${B}^{0\mathrm{\ensuremath{-}}}$B\ifmmode\bar\else\textasciimacron\fi{} $^{0}$ mixing. The number of isolated dimuons to be expected from heavy-quark sources is a related question that we discuss. Preliminary data agree well with Drell-Yan predictions for isolated unlike-sign dimuons. For non-isolated dimuons the data lie about a factor 2 below our initial heavy-quark predictions, but this discrepancy is within theoretical uncertainties and can be removed by specific parameter choices. The reported like-sign isolated dimuons cannot be consistently interpreted as heavy-flavor decays without destroying agreement with the Drell-Yan model.

Continuum dimuon production in p-bar-W collisions at 125 GeV/c.

The cross section for the reaction p-barN..--> mu../sup +/..mu../sup -/X with muon pairs in the mass range 40 was measured to be sigma = 0.104 +- 0.005 +- 0.008 nb/nucleon. The distributions dsigma/dx/sub F/ and M/sup 3/dsigma/dM were compared to the QCD-improved Drell-Yan model and to calculations including first-order QCD corrections using deep-inelastic structure functions. Excellent agreement with the data was obtained if the calculations were multiplied by factors of 2.45 and 1.41, respectively.

Observation of anomalous scaling violation in muon pair production by 194 GeV/c π−-tungsten interactions

The differential cross-section for dimuon production by 194 GeV/c π− onW, as measured by the NA10 Collaboration, is compared with theoretical models. The wide kinematical range of the data, extending well above the ϒ resonances, provides the opportunity of a comparison with ‘realistic’ Drell-Yan models, i.e. with those allowing for scaling violation in the hadronic structure functions. The data in fact clearly indicate the failure of the ‘naïve’ Drell-Yan model, while the available ‘realistic’ versions (leading logarithm approximation and next-to-leading logarithm approximation in first order QCD), although giving a better description of the data, still disagree in thex F and\(\sqrt \tau \) dependences of the cross-section at high dimuon masses. This disagreement is referred to here as ‘anomalous’ scaling violation. The dependence of the results on external inputs (nucleon and pion-sea structure functions) is analysed; it is shown that in the next-to-leading logarithm approximation the value 〈K〉=1.03±0.03 (stat.) can be obtained for the ratio experimental/theoretical cross-section.

Spin asymmetries for W and Z production in [formula omitted] collisions

Using a realistic set of spin dependent structure functions and going beyond the naive Drell-Yan model, we calculate the spin asymmetries for the leptonic decays of W and Z produced in p p collisions with longitudinally polarized protons one expects from the SU(2) × U(1) electroweak gauge theory. The results are of direct interest for future experiments, at the CERN p p collider and at the Fermilab Tevatron.

Study of the low mass dimuon continuum produced in hadronic interactions

We present here the analysis of low mass dimuon events (1.8 < M μμ < 2.6 GeV/ c 2 ) produced by positive and negative pion and proton beams at 200 GeV/ c. Using the difference between the π - and the π + cross sections, and comparing to the Drell-Yan model, we find a K-factor of 2.47 ± 0.5. Only about 1 2 of the events can be attributed to the Drell-Yan mechanism. If the remaining events are attributed to muonic decays of D mesons we findan upper limit for the cross section of charmed meson production.

Angular distributions of Drell Yan pairs in the leading twist approximation

We compute the angular decay distribution of lepton pairs, integrated over the transverse momentum within the soft gluons resummation procedure. The deviations from the naive Drell-Yan model are found very small. Therefore, the phase space boundary region should provide a clear signal for higher twist contributions.

Perturbative QCD and weak asymmetries in lepton pair production

The interference of electromagnetic and weak production mechanisms for lepton pair production may give rise to several effects which violate parity and charge symmetry. These effects are generally of the order of 1% for dilepton masses of 10 GeV. The theoretical calculations presented here show that experimental studies of these asymmetries may be useful. In particular, measurements of these asymmetries in collisions of pions with polarized protons may lead to a greatly enhanced understanding of the polarization distribution of quarks in a polarized proton. The polarization structure of the d quark is shown to be of special interest. Measurement of the parity-violating asymmetries in proton-polarized proton collisions may prove to be a sensitive probe of the flavor symmetry of the proton antiquark sea. Analysis of the parity conserving charge asymmetry (which is predicted to occur in collisions of unpolarized hadrons) allows a unique further test of the Drell-Yan model for lepton pair production, as well as of our understanding of weak interactions. The above asymmetries mentioned are computed within the framework of the parton model. The focus of this work is on the asymmetries calculated with the inclusion of first-order perturbative QCD effects. The asymmetries are calculated in a differential form for values of the dilepton transverse momentum large compared with the typical (∼1 GeV) scale of nonperturbative effects, and also in a form in which this transverse momentum has been integrated over. Corrections to the parton model results, which can be large, show rather different structure for the various asymmetries. A parity-violating asymmetry which may occur in collisions of unpolarized hadrons is also discussed. This asymmetry is very sensitive to the nonperturbative structure of hadrons, and is estimated to be approximately 0.01% for dilepton masses of 10 GeV.

Counting neutrinos in collider experiments

Abstract The production of neutrino-antineutrino pairs in proton-antiproton collisions is studied theoretically using the Drell-Yan model. The signal for this process is missing energy or transverse momentum in the hadronic part of the final state. The total cross section is proportional to the number of neutrino species coupling to weak currents in the usual way. This number is an important quantity both in the study of the problem of fermion generations and in the big bang model of cosmogenesis. The sizes of the experimental signals are estimated using various phenomenological assumptions.

Quark sea in nuclei and its effects in Drell-Yan processes

The sea of quark-antiquark pairs arising from the interactions between the nucleons within the target nucleus leads to important consequences in a hard-scattering process. We have investigated the implications of such a quark sea for inclusive reactions involving massive dimuons initiated by hadrons off nuclei, assuming the validity of the Drell-Yan model. Besides the dependence on the variables ${x}_{F}$ and ($\frac{{m}^{2}}{s}$), the exponent $\ensuremath{\alpha}$ is expected to depend on the beam type and also on the specific nuclei used as targets.

DIMUON PRODUCTION IN HADRONIC INTERACTIONS

This report summarizes the new data submitted to the XXI International Conference on High Energy Physics on high mass dimuon production in ..pi../sup -/N and anti pN interactions by Fermilab Experiment E-537, CERN Experiment NA3 and Fermilab Experiment E-326. Successes and failures of the Drell-Yan model and low order QCD are reviewed. New results on the production of the J/psi from E-537, NA3 and CERN experiment WAll are also reported.

A-dependence of muon pair production in π-nucleus interactions at 280 GeV/c

We have measured the relative cross sections for muon pair production by 280 GeV/ c negative pions on three different targets: carbon, copper, and tungsten. The value of α obtained from the parametrization σ = constant × A α is 0.94 ± 0.02 ± 0.02, whereas the parametrization σ≈σ 0( Z A ) A α′ , where σ 0( Z A ) is given by the Drell-Yan model, leads to α′ = 0.97 ±0.02±0.02. This last result is in agreement with the quark additivity rule which is inherent in the Drell-Yan model, no dependence is observed on the transverse momentum of the muon pair.

Test of nuclear effects in hadronic dimuon production

We present the final analysis of the nuclear effects on the cross section of dimuon production, using simultaneously a hydrogen and a platinum target in a 150, 200 and 280 GeV pion beam. For the dimuon mass interval 4.1 to 8.5 GeV, the ratio of the cross sections is in agreement with the Drell-Yan model within a 10% error, mainly due to systematics. The variation of this ratio with the dimuon mass, x 1 and x 2 is also in good agreement, and no variation with the transverse momentum is observed.

Comparison of angular distributions in π −N→μ +μ − + … with lowest order QCD

Recent measurements of angular distributions in π −N→μ +μ − + … are compared with theoretical expectations based on the naive Drell-Yan model including transverse momentum for the constituents and lowest order QCD corrections.

Dilepton production in hadronic collisions

Dilepton data have provided decisive lests of the basic hypothesis of the quark-parton model on the presence of constituents within a hadron. To first order, the predictions of the Drell-Yan model have been found to be correct. The recent data on the dilepton transverse momentum and on the absolute value of the production cross-section represent a rather severe, and at present successful, test of the quark-gluon interaction, as described by the QCD theory. In addition, careful analyses of dilepton data have been able to provide us with knowledge of the pion and kaon structure functions, which cannot be studied in deep-inelastic-scattering experiments.

Where does the Drell-Yan picture really break down?

Recently, Duke and Teper have claimed that the Drell-Yan picture is not applicable in a large kinematic domain where it was applied previously. We point out an error in their arguments, and show that the Drell-Yan model can be applied in a much larger domain.