D0 Experiment Research Articles

SU(3) Gauge Symmetry: An Experimental Review of Diffractive Physics in e+p, p+p, p+A, and A+A Collision Systems

This review focuses on diffractive physics, which involves the long-range interactions of strong nuclear force at high energies described by SU(3) gauge symmetry. It is expected that diffractive processes account for nearly 40% of the total cross-section at LHC energies. These processes consist of soft-scale physics where perturbation theory cannot be applied. Although highly successful and often described as a perfect theory, quantum chromodynamics relies heavily on perturbation theory, a model best suited for hard-scale physics. The study of pomerons could help bridge the soft and hard processes and provide a complete description of the theory of the strong interaction across the full momentum spectrum. Here, we will discuss some of the features of diffractive physics, experimental results from SPS, HERA, and the LHC, and where the field could potentially lead. With the recent publication of the odderon discovery in 2021 by the D0 and TOTEM collaborations and the new horizon of physics that lies ahead with the upcoming Electron-Ion Collider at Brookhaven National Laboratory, interest is seemingly piquing in high energy diffractive physics.

Model-Independent Odderon Results Based on New TOTEM Data on Elastic Proton–Proton Collisions at 8 TeV

Evaluating the H(x,s|pp) scaling function of elastic proton–proton (pp) collisions from recent TOTEM data at s=8 TeV and comparing it with the same function of elastic proton–antiproton (pp¯) data of the D0 collaboration at s=1.96 TeV, we find, from this comparison alone, an at least 3.79 σ signal of odderon exchange. If we combine this model-independently obtained result with that of a similar analysis but using TOTEM elastic pp scattering data at s=7 TeV, which resulted in an at least 6.26 σ signal, the combined significance of odderon exchange increases to at least 7.08 σ. Further combinations of various datasets in the TeV energy range are detailed in the manuscript.

Compatibility and combination of world W-boson mass measurements

The compatibility of W-boson mass measurements performed by the ATLAS, LHCb, CDF, and D0 experiments is studied using a coherent framework with theory uncertainty correlations. The measurements are combined using a number of recent sets of parton distribution functions (PDF), and are further combined with the average value of measurements from the Large Electron–Positron collider. The considered PDF sets generally have a low compatibility with a suite of global rapidity-sensitive Drell–Yan measurements. The most compatible set is CT18 due to its larger uncertainties. A combination of all mW\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$m_W$$\\end{document} measurements yields a value of mW=80,394.6±11.5\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$m_W = 80{,}394.6 \\pm 11.5$$\\end{document} MeV with the CT18 set, but has a probability of compatibility of 0.5% and is therefore disfavoured. Combinations are performed removing each measurement individually, and a 91% probability of compatibility is obtained when the CDF measurement is removed. The corresponding value of the W boson mass is 80,369.2±13.3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$80{,}369.2 \\pm 13.3$$\\end{document} MeV, which differs by 3.6σ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$3.6\\sigma $$\\end{document} from the CDF value determined using the same PDF set.

Effects of odderon spin on helicity amplitudes in pp elastic scattering

In recent years, the discovery of the odderon, a colorless C-odd gluonic compound, has been confirmed in the TOTEM and D0 collaborations. However, the spin quantum number of the odderon remains unidentified. In this work, we aim to attribute a spin of J=3 to the odderon in pp elastic scattering by calculating the helicity amplitudes and the corresponding complex parameter r_5, the ratio of helicity’s single-flip to non-flip amplitudes, for the spin-3 tensor odderon with the standard spin-2 tensor pomeron exchanges. Then, we apply these results to the constraints obtained from the STAR experiment at RHIC. By comparing to the contributions of the spin-1 vector odderon and spin-2 tensor pomeron, we demonstrate that the spin-3 tensor odderon, i.e. J=3, provides a better explanation for the observable in pp elastic scattering.

Recent results from the TOTEM collaboration and the discovery of the odderon

We describe the most recent results from the TOTEM collaboration on elastic, inelastic and total cross sections as well as the odderon discovery by the D0 and TOTEM collaborations.

Physics with intact protons at the LHC: from the odderon discovery to the sensitivity to beyond standard model physics

We describe the discovery of the colorless C-odd gluonic compound, the odderon, by the D0 and TOTEM Collaborations by comparing elastic differential cross sections measured in pp and pp¯ interactions at high energies. We also discuss the reach on quartic anomalous couplings and the sensitivity to axion like particle production by using the LHC as a γγ collider and detecting the intact protons at high luminosity.

Measurement of the proton structure parameters in the forward-backward charge asymmetry

The forward-backward asymmetry ($A_{FB}$) in the Drell-Yan process $pp/p\bar p \to Z/\gamma^* \to \ell^+\ell^-$ is sensitive to the proton structure information. Such information has been factorized into well-defined proton structure parameters which can be regarded as experimental observables. In this paper, we extract the structure parameters from the $A_{FB}$ distributions reported by the CMS collaboration in $pp$ collisions at $\sqrt{s} = 8$ TeV, and by the D0 collaboration in $p\bar p$ collisions at $\sqrt{s} = 1.96$ TeV. It is the first time that the unique parton information in the $A_{FB}$ spectrum can be decoupled from the electroweak calculation and measured as standalone observables, which can be used as new data constraints in the global quantum chromodynamics analysis of the parton distribution functions (PDFs). Although the parton information in the $pp$ and $p\bar p$ collisions are different, and the precisions of the measured structure parameters are statistically limited, the results from both the hadron colliders indicate that the down quark contribution might be higher than the theoretical predictions with the current PDFs at the relevant momentum fraction range.

Fresh look at experimental evidence for odderon exchange

Theory suggests that in high-energy elastic hadron+hadron scattering, t-channel exchange of a family of colourless crossing-odd states – the odderon – may generate differences between pp¯ and pp cross-sections in the neighbourhood of the diffractive minimum. Using a mathematical approach based on interpolation via continued fractions enhanced by statistical sampling, we develop robust comparisons between pp¯ elastic differential cross-sections measured at √s=1.96 TeV by the D0 Collaboration at the Tevatron and function-form-unbiased extrapolations to this energy of kindred pp measurements at √s/TeV=2.76,7,8,13 by the TOTEM Collaboration at the LHC and a combination of these data with earlier cross-section measurements at √s/GeV=23.5,30.7,44.7,52.8,62.5 made at the intersecting storage rings. Focusing on a domain that straddles the diffractive minimum in the pp¯ and pp cross-sections, we find that these two cross-sections differ at the (2.2−2.6)σ level; hence, supply evidence with this level of significance for the existence of the odderon. If combined with evidence obtained through different experiment-theory comparisons, whose significance is reported to lie in the range (3.4−4.6)σ, one arrives at a (4.0−5.2)σ signal for the odderon.

Jets separated by a large pseudorapidity gap at the Tevatron and at the LHC

We present a phenomenological analysis of events with two high transverse momentum (pT) jets separated by a large (pseudo-)rapidity interval void of particle activity, also known as jet-gap-jet events. In the limit where the collision energy sqrt{s} is much larger than any other momentum scale, the jet-gap-jet process is described in terms of perturbative pomeron exchange between partons within the Balitsky-Fadin-Kuraev-Lipatov (BFKL) limit of perturbative quantum chromodynamics (QCD). The BFKL pomeron exchange amplitudes, with resummation at the next-to-leading logarithmic approximation, have been embedded in the PYTHIA8 Monte Carlo event generator. Standard QCD dijet events are simulated at next-to-leading order in αs matched to parton showers with POWHEG+PYTHIA8. We compare our calculations to measurements by the CDF, D0, and CMS experiments at center-of-mass energies of 1.8, 7 and 13 TeV. The impact of the theoretical scales, the parton densities, final- and initial-state radiation effects, multiple parton interactions, and pT thresholds and multiplicities of the particles in the rapidity gap on the jet-gap-jet signature is studied in detail. With a strict gap definition (no particle allowed in the gap), the shapes of most distributions are well described except for the CMS azimuthal-angle distribution at 13 TeV. The survival probability is surprisingly well modelled by multiparton interactions in PYTHIA8. Without multiparton interactions, theoretical predictions based on two-channel eikonal models agree qualitatively with fits to the experimental data.

Comparison of $pp$ and $p \bar{p}$ differential elastic cross sections and observation of the exchange of a Colorless $C$-odd gluonic compound

We describe the discovery of the colorless CC-odd gluonic compound, the odderon, by the D0 and TOTEM Collaborations by comparing elastic differential cross sections measured in pppp and p \bar{p}pp‾ interactions at high energies.

Comparison of $pp$ and $p \bar{p}$ differential elastic cross sections and observation of the exchange of a colorless $C$-odd gluonic compound

We describe the discovery of the colorless CC-odd gluonic compound, the odderon, by the D0 and TOTEM Collaborations by comparing elastic differential cross sections in pppp and p \bar{p}pp‾ interactions at high energies.

The Odderon Discovery by the D0 and TOTEM Collaborations

We describe the discovery of the colorless $C$-odd gluonic compound, the odderon, by the D0 and TOTEM Collaborations by comparing elastic differential cross sections measured in $pp$ and $p \bar{p}$ interactions at high energies.

The odderon discovery by the D0 and TOTEM collaborations

We describe the discovery of the colorless $C$-odd gluonic compound, the odderon, by the D0 and TOTEM Collaborations by comparing elastic differential cross sections measured in $pp$ and $p \bar{p}$ interactions at high energies.

Mass spectra and decays of open-heavy tetraquark states

The observation of the exotic states ${X}_{0,1}(2900)$ with four open flavors by the LHCb Collaboration has promoted great interest in searching for the open-charm and open-bottom tetraquark states. In this work, we perform a systematic study of the open-heavy tetraquark systems $qq\overline{q}\overline{Q}$ ($q=u$, $d$, $s$ and $Q=c$, $b$) within the improved chromomagnetic interaction model. The mass spectra and color-spin wave functions of $S$-wave open-heavy tetraquark states with quantum numbers ${J}^{P}={0}^{+}$, ${1}^{+}$, and ${2}^{+}$ are calculated. A number of compact tetraquark states are predicted in both open-charm and open-bottom systems. The two-body decay properties of these tetraquark states are phenomenologically analyzed. Our results suggest that the exotic open-charm state ${X}_{0}(2900)$ observed by the LHCb Collaboration is likely a compact tetraquark state with quantum number $I{J}^{P}=0{0}^{+}$ (isospin singlet). For the open-bottom systems, our results also suggest a candidate for the exotic state ${X}^{\ifmmode\pm\else\textpm\fi{}}(5568)$ reported by the D0 Collaboration. The other tetraquark states predicted in this work may also be examined in future experiments.

TOTEM, recent experimental review

The TOTEM (TOTal cross section, Elastic scattering and diffraction dissociation Measurement at the LHC) experiment, located at the interaction point 5 of the LHC, has measured the total, elastic and inelastic proton-proton crosssections, using a luminosity independent method, based on the optical theorem, in a center-of-mass energy range from 2.76 to 13 TeV. The elastic scattering was investigated in a wide range of the squared four-momentum transfer |t| allowing study of the Coulomb-nuclear interference region down to |t| ∼ 8 × 10−4 GeV2. This made possible the first measurement of the ρ parameter at √s = 13 TeV, ρ being the ratio between the real and the imaginary part of the nuclear elastic scattering amplitude at t = 0. This measurement, combined with the total crosssection results, led to the exclusion of all the models classified and published by the COMPETE Collaboration. The results obtained by TOTEM are indeed compatible with predictions of a colourless 3-gluon bound state exchange in the t-channel of proton-proton elastic scattering, as postulated by alternative theoretical models both in the Regge-like framework and in the modern QCD framework. This result has been confirmed, with a significance of 5.4σ, also by the comparison with the pp data measured by the D0 collaboration at Fermilab. In this contribution the TOTEM experiment results will be described, along with the actual experiment status, the future physics program for the LHC Run 3.

Odderon Exchange from Elastic Scattering Differences between pp and pp[over ¯] Data at 1.96TeV and from pp Forward Scattering Measurements.

We describe an analysis comparing the pp[over ¯] elastic cross section as measured by the D0 Collaboration at a center-of-mass energy of 1.96TeV to that in pp collisions as measured by the TOTEM Collaboration at 2.76, 7, 8, and 13TeV using a model-independent approach. The TOTEM cross sections, extrapolated to a center-of-mass energy of sqrt[s]=1.96 TeV, are compared with the D0 measurement in the region of the diffractive minimum and the second maximum of the pp cross section. The two data sets disagree at the 3.4σ level and thus provide evidence for the t-channel exchange of a colorless, C-odd gluonic compound, also known as the odderon. We combine these results with a TOTEM analysis of the same C-odd exchange based on the total cross section and the ratio of the real to imaginary parts of the forward elastic strong interaction scattering amplitude in pp scattering for which the significance is between 3.4σ and 4.6σ. The combined significance is larger than 5σ and is interpreted as the first observation of the exchange of a colorless, C-odd gluonic compound.

Toward the existence of the odderon as a three-gluon bound state

Inspired by the evidence of the odderon exchange recently observed by the D0 and TOTEM Collaborations, a QCD sum rule investigation is performed to study the odderon as a three-gluon bound state. There may exist six lowest-lying three-gluon odderons with the quantum numbers $J^{PC} = 1/2/3^{\pm-}$. We systematically construct their interpolating currents, and calculate their mass spectra. To verify their existence, we propose to search for the spin-3 odderons in their $VVV$ and $VVP$ decay channels directly at LHC, with $V$ and $P$ light vector and pseudoscalar mesons respectively.

Відкриття зв’язаного стану трьох глюонів – оддерона

The TOTEM collaboration at the Large Hadron Collider, together with the D0 collaboration at the Tevatron collider at Fermilab, have announced the discovery of the odderon – a bound state of three gluons that was predicted about 50 years ago. The result was presented at CERN on March 5 and follows the joint submission in December 2020 of a CERN and Fermilab preprints by TOTEM and D0 reporting this observation. States comprising several gluons are usually called “glueballs”, and are peculiar objects made only of the carriers of the strong force. The advent of quantum chromodynamics led theorists to predict the existence of the odderon, C-odd gluonic compound. Proving its existence in high-energy collisions at Tevatron and LHC has been a major experimental challenge. The work is based on a model-independent analysis of data at medium-range momentum transfer. The TOTEM and D0 teams compared proton-proton data (recorded at collision energies of 2.76, 7, 8, and 13 TeV and extrapolated to 1.96 TeV), with Tevatron proton-antiproton data measured at 1.96 TeV. In agreement with theoretical predictions, the proton-proton cross-section exhibits a deeper dip and stays below the proton-antiproton cross-section until the bump region, thus evidence of odderon was found.

Spin-Orbit Coupling Changes the Identity of the Hyper-Open-Shell Ground State of Ce+, and the Bond Dissociation Energy of CeH+ Proves to Be Challenging for Theory.

Cerium (Ce) plays important roles in catalysis. Its position in the sixth period of the periodic table leads to spin-orbit coupling (SOC) and other open-shell effects that make the quantum mechanical calculation of cerium compounds challenging. In this work, we investigated the low-lying spin states of Ce+ and the bond energy of CeH+, both by multiconfigurational methods, in particular, SA-CASSCF, MC-PDFT, CASPT2, XMS-PDFT, and XMS-CASPT2, and by single-configurational methods, namely, Hartree-Fock theory and unrestricted Kohn-Sham density functional theory with 34 choices of the exchange-correlation functional. We found that only CASPT2, XMS-CASPT2, and SA-CASSCF (among the five multiconfigurational methods) and GAM, HCTH, SOGGA11, and OreLYP (among the 35 single-configuration methods) successfully predict that the SOC-free ground spin state of Ce+ is a doublet state, and CASPT2 and GAM give the most accurate multireference and single-reference calculations, respectively, of the excitation energy of the first SOC-free excited state for Ce+. We calculated that the ground doublet state of Ce+ is an intra-atomic hyper-open-shell state. We calculated the spin-orbit energy (ESO) of Ce+ by the five multiconfigurational methods and found that ESO calculated by CASPT2 is the closest to the experimental value. Taking advantage of the availability of an experimental D0 for CeH+ as a way to provide a unique test of theory, we showed that all the multiconfigurational methods overestimate D0 by at least 246 meV (5.7 kcal/mol), and only three functionals, namely, SOGGA, MN15, and GAM, have an error of D0 that is less than 200 meV (5 kcal/mol).

Discovery potential for the LHCb fully charm tetraquark X(6900) state via p¯p annihilation reaction

Inspired by the observation of the fully-charm tetraquark $X(6900)$ state at LHCb, the production of $X(6900)$ in $\bar{p}p\rightarrow J/\psi J/\psi $ reaction is studied within an effective Lagrangian approach and Breit-Wigner formula. The numerical results show that the cross section of $X(6900)$ at the c.m. energy of 6.9 GeV is much larger than that from the background contribution. Moreover, we estimate dozens of signal events can be detected by D0 experiment, which indicates that searching for the $X(6900)$ via antiproton-proton scattering may be a very important and promising way. Therefore, related experiments are suggested to be carried out.