FNAL Tevatron Research Articles

Double prompt J/ψ production at hadron colliders

In this paper, we give a brief review of recent theoretical studies of double prompt [Formula: see text] production at the FNAL Tevatron and the CERN LHC, to which both single- and double-parton-scattering processes contribute. In single parton scattering, we mainly present the results computed within the framework of non-relativistic quantum chromodynamics factorization combined with one of the two approaches to describe the parton inside the (anti)proton, the collinear parton model and the parton Reggeization approach. The contributions from double parton scattering calculated with different values of [Formula: see text] are also discussed. We conclude that, in double prompt [Formula: see text] hadroproduction, there remain some differences between theoretical predictions and experimental measurements.

Search for Multi-quark Exotic States with Heavy Flavor at D0 Experiment

We present the results for multi-quark exotic states search from D0 Collaboration at the FNAL Tevatron. This includes an evidence for a state (X(5568)) with hadronic decays of Bs meson, a confirmation of the X(5568) state with semileptonic decays of Bs meson, and a search for exotic baryons decaying to J/ψΛ pairs.

The Drell–Yan process as a testing ground for parton distributions up to LHC

The Drell–Yan massive dilepton production in hadron–hadron collisions provides a unique tool, complementary to Deep Inelastic Scattering, for improving our understanding of hadronic substructure and in particular for testing parton distributions. We will consider measurements of the differential and double-differential Drell–Yan cross sections from FNAL Tevatron up to CERN LHC energies and they will be compared to the predictions of perturbative QCD calculations using most recent sets (CT14 and MMHT14) of parton distribution functions, as well as those provided by the statistical approach.

NEXT-TO-LEADING ORDER TESTS OF NON-RELATIVISTIC-QCD FACTORIZATION WITH J/ψ YIELD AND POLARIZATION

We report on recent progress in testing the factorization formalism of non-relativistic quantum chromodynamics (NRQCD) at next-to-leading order (NLO) for J/ψ yield and polarization. We demonstrate that it is possible to unambiguously determine the leading color-octet (CO) long-distance matrix elements (LDMEs) in compliance with the velocity scaling rules through a global fit to experimental data of unpolarized J/ψ production in pp, [Formula: see text], ep, γγ, and e+e-collisions. Three data sets not included in the fit, from hadro-production and from photo-production in the fixed-target and colliding-beam modes, are nicely reproduced. The polarization observables measured in different frames at DESY HERA and CERN LHC reasonably agree with NLO NRQCD predictions obtained using the LDMEs extracted from the global fit, while measurements at the FNAL Tevatron exhibit severe disagreement. We demonstrate that the alternative LDME sets recently obtained, with different philosophies, in two other NLO NRQCD analyses of J/ψ yield and polarization also fail to reconcile the Tevatron polarization data with the other available world data.

Drell-Yan lepton pair production at high energies in the parton Reggeization approach

According to extensive theoretical studies of the high-energy limit of QCD, inelastic interactions are dominated by the multi-Regge final states. The appropriate gauge-invariant objects, which simultaneously incorporate the transverse momentum degrees of freedom, are Reggeized gluons, quarks and antiquarks. In the present communication we extend parton Reggeization approach to Drell-Yan production of massive lepton pairs. The basic ingredient is a process of Reggeized quark-antiquark annihilation, $\mathcal{Q}\overline{\mathcal{Q}}\ensuremath{\rightarrow}{\ensuremath{\gamma}}^{\ensuremath{\star}}\ensuremath{\rightarrow}{l}^{+}{l}^{\ensuremath{-}}$, which is described by the Reggeon-Reggeon-photon effective vertex ${\ensuremath{\Gamma}}_{\mathcal{Q}\overline{\mathcal{Q}}}^{\ensuremath{\gamma}}$. We calculate transverse-momentum and invariant-mass distributions of Drell-Yan lepton pairs measured at the CERN SPS, FNAL Tevatron and CERN LHC in the different ranges of energy and rapidity. We focus on angular distributions of Drell-Yan leptons in different kinematical ranges. The obtained results are compared with the existing data and a good agreement is found. The predictions for future experiments for Drell-Yan lepton pair production at the CERN LHC have been made.

Strange hadron production in Σ-A interactions in the SELEX experiment

We report our observations on the resonance signals of masses of 1520, 1670, 1810 (1 820), and 2100 MeV c−2, produced inclusively in the reaction Σ− + C(Cu) → p + K− + X, and the signals of masses of 1020 and 1525 MeV c−2, produced inclusively in the reaction Σ− + C(Cu) → K+ + K− + X, with a 600-GeV c−1- momentum hyperon beam in the SELEX experiment at the Fermilab. The masses, widths, and branching ratios were measured. The resonance signal of mass of 1520 MeV c−2 correspond to the known Λ(1520) hyperon. The signals of masses of 1020 and 1525 MeV c−2 in the K+K− system correspond to the φ0(1020)- and f2′(1525) mesons, respectively. The branching ratio of the resonance of mass of 1670 MeV c−2 relative to Λ(1520) is (24.92 ± 0.45 ± 0.48)%, while that of the resonance of mass of 1810 (or 1 820) MeV c−2 relative to Λ(1520) is (16.13 ± 0.38 ± 0.45)%. The branching ratio of the f2′(1525) resonance relative to φ0(1020) is (10.75 ± 0.25 ± 0.45)%. Data analysis was performed over 6 × 107 trigger events registered by the SELEX setup on the FNAL Tevatron.

Parametrization of the driven betatron oscillation

An AC dipole is a magnet which produces a sinusoidally oscillating dipole field and excites coherent transverse beam oscillations in a synchrotron. By observing this driven coherent oscillation, the linear optical parameters can be directly measured at locations of the beam position monitors. The driven oscillations induced by an AC dipole will generate a phase space ellipse which differs from that of free oscillations. If not properly accounted for, this difference can lead to misinterpretations of the actual optical parameters, for instance, 6% or more in the cases of the Tevatron, RHIC, or LHC. This paper shows that the effect of an AC dipole on the observed linear optics is identical to that of a thin lens quadrupole. By introducing a new amplitude function to describe this new phase space ellipse, the motion produced by an AC dipole becomes easier to interpret. The introduction of this new amplitude function also helps measurements of the normal Courant-Snyder parameters based on beam position data taken under the influence of an AC dipole. This new parametrization of driven oscillations is presented and is used to interpret data taken in the FNAL Tevatron using an AC dipole.

W → τν at the Tevatron

We present resultsfrom the CDF and DØ detectors on the production of W-bosons decaying to τν τ at the FNAL Tevatron from data taken between 1992 and 1996. From CDF comes the first observation of W charge asymmetry in W → τν final states, and from DØ a new measurement of g W τ / g W e , 1.003 ± 0.032.

Maximizing spin correlations in top quark pair production at the Tevatron

A comparison is made between the off-diagonal and helicity spin bases for top quark pair production at the FNAL Tevatron. In the off-diagonal basis, 92% of the top quark pairs are in the spin configuration up-down plus down-up, whereas in the helicity basis only 70% are left-right plus right-left. The off-diagonal basis maximizes the spin asymmetry and hence the measured angular correlations between the decay products, which are more than twice as big in this basis as compared to the helicity basis. In addition, for the process q qbar --> t tbar, we give a very simple analytic expression for the matrix element squared which includes all spin correlations between the production and subsequent decay of the top quarks.

Global analysis of precision electroweak data within the minimal supersymmetric extension of the standard model

We present detailed results of a global analysis of precision electroweak data within the context of the Minimal Supersymmetric Extension of the Standard Model (MSSM). We present constraints on the parameters of the MSSM in 3 planes that are commonly used in phenomenological analyses, namely the ( m A, tan β) plane describing the supersymmetric Higgs sector, the ( μ, m g ) plane describing the chargino/neutralino sector, and the ( m 0, m g ) plane describing sfermions. In each case, we compare the indirect limits that we derive with the results of direct searches and the prospects for future experiments. We find that the indirect constraints are not yet very significant in the supersymmetric Higgs sector, although they may have the potential to become so, particularly if the top-quark mass is relatively light. The indirect constraints also give only modest extensions of direct bounds on charginos and neutralinos. However, the indirect constraints already give interesting improvements of existing direct searches for sfermions, and may even pre-empt some of the physics reach of LEP II and the FNAL Tevatron Collider.

A silicon active target for charm particle identification

A silicon active target has been realized to reconstruct with high efficiency the primary vertex of heavy flavour photoproduction events in experiment E687 at the FNAL tevatron. The target is a telescope of 48 layers divided in 4 elements each, giving a total of 192 electronic channels read out with a preamplifier, an amplifier and a charge integrating ADC. The efficiency of the detector in identifying primary vertices has been measured to be ≅ 80%, while the longitudinal resolution turned out to be σ ≅ 340 μm. Its level of performance allowed the use of the target as a powerful tool to select heavy quark events.

Top search at fermilab: Multijet signals and backgrounds

We investigate the possibilities of finding the top quark at the FNAL Tevatron p p collider (√ s = 1.8 TeV). For a top-quark mass greater than O( M W) top quark will be predominantly produced through direct QCD t t production. The decay channel into a lepton, neutrino and a number of jets together with the dominant background signal is examined. We first study the standard way of finding the top-quark mass using invariant mass distributions. We then introduce and study the quantity R 3 2 (m top ) , defined as the ratio of the number of “3 jet + lepton” events to the number of “2 jet + lepton” events. Through the strong dependence on the top-quark mass of this simple ratio it should be possible to detect the presence of a top quark for a large range of possible top-quark mass values.

Limits on the mass of a superstring Z′ from the CERN pp̄ collider

We illustrate how recent CERN pp̄ collider data can be used to bound the mass of a possible Z′ in superstring-inspired models. We take into account the fact that the Z′ couplings to quarks and leptons are smaller than those of the conventional Z, and the possibility that the Z′ may be able to decay into exotic particles, thereby suppressing the Z′→ℓ +ℓ − branching ratio. In the minimal rank-five model we find m Z′ > 167GeV if the Z′ can only decay into conventional quarks and leptons and m Z′ > 118 GeV for the least favourable spectrum of three E 6 27 generations of particles and sparticles which is allowed by other experiments. When combined with a global analysis of neutral current data, the latter conservative limit can be increased to m Z′ > 156 GeV. We derive analogous limits for two other superstring-inspired models. We show how these limits can be improved using future FNAL Tevatron and SLC data.

The microstrip vertex detector for the E687 experiment at tevatron

A vertex detector has been realized to reconstruct with high efficiency the decay vertices of heavy flavours in the E687 photoproduction experiment at the FNAL Tevatron. The vertex detector consists of 12 microstrip planes with a strip-by-strip readout. The readout electronics consists of a low noise preamplifier, an amplifier and a fast integrating ADC. All these units were developed by the INFN Milano and taylored to the actual vertex detector in order to fully exploit its intrinsic capabilities. A test of a part of the microvertex detector has been carried out in the real experimental conditions at Fermilab during summer 1985. Detection efficiency, charge collection and charge sharing between adjacent strips, signal to noise ratio, spurious hits, cross-talk and correlations have been extensively investigated. A simulation program, which makes use of a purposely developed pattern recognition and of the measured performances of the microvertex, gives for the experiment a total sensitivity of ∼ 600 events/nb for beauty and ∼2×10 6 for charm in ∼2000 hours of data taking.

Statistics of Dipole Steering in the Tevatron

Methods of calculating the expected rms orbit distortion and the expected peak orbit distortion for a large FODO synchrotron are described. An expression for the expected rms correction element dipole strength necessary to correct the closed orbit of a large FODO synchrotron is derived. The uncorrected closed orbit of the FNAL Tevatron accelerator is determined from beam position data and operational settings of the correction element dipole magnets. The uncorrected orbit and correction element dipole strengths are compared to the results of the Tevatron design study. Use of these expressions for SSC lattices is discussed.

The determination of theW anomalous magnetic moment in $$p\bar p \to W\gamma X$$

We investigate the possibilities of measuring theW anomalous magnetic moment parameter, κ, in the reaction\(p\bar p \to W\gamma X\). We present a calculation of the κ dependence of the total cross-section, the lab frame angular differential cross-section, the invariant mass distribution and the angular distribution of the decay lepton. We conclude that it will be extremely difficult to measure κ at the CERN collider (even after an upgrade to 700 GeV total cm energy) but that it may be feasible at the FNAL Tevatron.

A vertex detector to search for beauty

This paper describes a high resolution vertex detector designed to study heavy quarks and other rare phenomena at the FNAL Tevatron machine. Its performance is examined and discussed. This vertex detector will be used in the frame of experiment E-687, being set up at Fermilab.

Detecting a heavy colored object at the FNAL tevatron

We investigate the possibility of detecting a heavy colored scalar or pseudoscalar object at FNAL tevatron energies ( $$\sqrt s = 2000$$ GeV). As our model for the calculation we take the techni-eta of extended technicolor models, with a mass of 250 GeV. We find that if one detects a final state photon, accompanied by a gluon jet, the signal can reach 10% of the background due to highp ⊥ events.