Search for long-lived stopped R-hadrons decaying out of time with pp collisions using the ATLAS detector
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
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Hadronic production of W and Z bosons at large transverse momentum
We propose a modified factorization formalism in quantum chromodynamics for hadronic production of W and Z bosons at large transverse momentum p T . When p T is much larger than the invariant mass Q of the vector boson, this new factorization formalism systematically resums the large fragmentation logarithms, α s m ln m ( p T 2 / Q 2 ) , to all orders in the strong coupling α s . Using our modified factorization formalism, we present the next-to-leading-order (NLO) predictions for W and Z boson production at high p T at the CERN Large Hadron Collider and at a future 100 TeV proton-proton collider. Our NLO results are about 5% larger in normalization, and they reflect improved convergence and moderate reduction of the scale variation compared to the NLO predictions derived in a conventional fixed-order perturbative expansion.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Probing Strangeness Hadronization with Event-by-Event Production of Multistrange Hadrons
This Letter presents the first measurement of event-by-event fluctuations of the net number (difference between the particle and antiparticle multiplicities) of multistrange hadrons Ξ − and $\overline{Ξ}$ + and its correlation with the net-kaon number using the data collected by the ALICE Collaboration in pp, p-Pb, and Pb-Pb collisions at a center-of-mass energy per nucleon pair $\sqrt{s_{NN}}$ = 5.02 TeV. The statistical hadronization model with a correlation over three units of rapidity between hadrons having the same and opposite strangeness content successfully describes the results. On the other hand, string-fragmentation models that mainly correlate strange hadrons with opposite strange quark content over a small rapidity range fail to describe the data.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for invisible decays of the Higgs boson produced in association with a hadronically decaying vector boson in pp collisions at √s = 8 with the ATLAS detector
A search for Higgs boson decays to invisible particles is performed using 20.3 fb⁻¹ of pp collision data at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the Large Hadron Collider. The process considered is Higgs boson production in association with a vector boson (V = W or Z) that decays hadronically, resulting in events with two or more jets and large missing transverse momentum. No excess of candidates is observed in the data over the background expectation. The results are used to constrain V H production followed by H decaying to invisible particles for the Higgs boson mass range 115 < m H < 300 GeV. The 95 % confidence-level observed upper limit on σ VH × BR(H → inv.) varies from 1.6 pb at 115 GeV to 0.13 pb at 300 GeV. Assuming Standard Model production and including the gg → H contribution as signal, the results also lead to an observed upper limit of 78% at 95% confidence level on the branching ratio of Higgs bosons decays to invisible particles at a mass of 125 GeV.
43 PARTICLE ACCELERATORS↗
Searches for Dijet Resonances at Hadron Colliders
We review the experimental searches for new particles in the dijet mass spectrum conducted at the CERN SppS, the Fermilab Tevatron Collider, and the CERN Large Hadron Collider. The theory of the QCD background and new particle signals is reviewed, with emphasis on the choices made by the experiments to model the background and signal. The experimental techniques, data, and results of dijet resonance searches at hadron colliders over the last quarter century are described and compared. Model independent and model specific limits on new particles decaying to dijets are reviewed, and a detailed comparison is made of the recently published limits from the ATLAS and CMS experiments.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Color Confinement, Hadron Dynamics, and Hadron Spectroscopy from Light-Front Holography and Superconformal Algebra
The QCD light-front Hamiltonian equation H L F Ψ = M 2 Ψ derived from quantization at fixed LF time τ = t + z / c provides a causal, frame-independent method for computing hadron spectroscopy as well as dynamical observables such as structure functions, transverse momentum distributions, and distribution amplitudes. The QCD Lagrangian with zero quark mass has no explicit mass scale. de Alfaro, Fubini, and Furlan (dAFF) have made an important observation that a mass scale can appear in the equations of motion without affecting the conformal invariance of the action if one adds a term to the Hamiltonian proportional to the dilatation operator or the special conformal operator. If one applies the dAFF procedure to the QCD light-front Hamiltonian, it leads to a color-confining potential κ 4 ζ 2 for mesons, where ζ 2 is the LF radial variable conjugate to the q q ¯ invariant mass squared. The same result, including spin terms, is obtained using light-front holography, the duality between light-front dynamics and A d S 5 , if one modifies the A d S 5 action by the dilaton e κ 2 z 2 in the fifth dimension z . When one generalizes this procedure using superconformal algebra, the resulting light-front eigensolutions provide a unified Regge spectroscopy of meson, baryon, and tetraquarks, including remarkable supersymmetric relations between the masses of mesons and baryons and a universal Regge slope. The pion q q ¯ eigenstate has zero mass at m q = 0 . The superconformal relations also can be extended to heavy-light quark mesons and baryons. This approach also leads to insights into the physics underlying hadronization at the amplitude level. I will also discuss the remarkable features of the Poincaré invariant, causal vacuum defined by light-front quantization and its impact on the interpretation of the cosmological constant. AdS/QCD also predicts the analytic form of the nonperturbative running coupling α s ( Q 2 ) ∝ e - Q 2 / 4 κ 2 . The mass scale κ underlying hadron masses can be connected to the parameter Λ M S ¯ in the QCD running coupling by matching the nonperturbative dynamics to the perturbative QCD regime. The result is an effective coupling α s ( Q 2 ) defined at all momenta. One obtains empirically viable predictions for spacelike and timelike hadronic form factors, structure functions, distribution amplitudes, and transverse momentum distributions. Finally, I address the interesting question of whether the momentum sum rule is valid for nuclear structure functions.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Hadron Spectroscopy at Jefferson Lab: Search for new States of Hadronic Matter
Hadrons are complex systems of confined quarks and gluons and exhibit the characteristic spectra of excited states. Quantum Chromodynamics (QCD) is only poorly understood in this non-perturbative regime. It is one of the key issues in hadronic physics to identify the relevant degrees of freedom giving rise to the observed mass spectra and the effective forces between them. Current efforts of the CLAS Collaboration at Jefferson Lab focus on the search for new baryon resonances utilizing polarized beams and targets. A further particular interesting question in hadron spectrosocpy concerns the role of glue and how this is related to the confinement in QCD. I will briefly discuss the efforts of the GlueX Collaboration to search for new forms of hadronic matter beyond simple quark-antiquark systems.
Crede, Volker↗
Search for charged Higgs bosons decaying via H ± → τ ± ν in fully hadronic final states using pp collision data at s $$ \sqrt{s} $$ = 8 TeV with the ATLAS detector
The results of a search for charged Higgs bosons decaying to a τ lepton and a neutrino, H ± → τ ± ν, are presented. The analysis is based on 19.5 fb –1 of proton-proton collision data at √s = 8 TeV collected by the ATLAS experiment at the Large Hadron Collider. Charged Higgs bosons are searched for in events consistent with top-quark pair production or in associated production with a top quark, depending on the considered H ± mass. The final state is characterized by the presence of a hadronic τ decay, missing transverse momentum, b-tagged jets, a hadronically decaying W boson, and the absence of any isolated electrons or muons with high transverse momenta. The data are consistent with the expected background from Standard Model processes. A statistical analysis leads to 95% confidence-level upper limits on the product of branching ratios Β(t → bH ± ) × Β(H ± → τ ± ν), between 0.23% and 1.3% for charged Higgs boson masses in the range 80-160GeV. It also leads to 95% confidence-level upper limits on the production cross section times branching ratio, σ(pp → tH ± + X) × Β(H ± → τ ± ν), between 0.76 pb and 4.5 fb, for charged Higgs boson masses ranging from 180 GeV to 1000 GeV. In the context of different scenarios of the Minimal Supersymmetric Standard Model, these results exclude nearly all values of tan β above one for charged Higgs boson masses between 80 GeV and 160 GeV, and exclude a region of parameter space with high tan β for H ± masses between 200 GeV and 250 GeV.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Suppression of high-p{sub T} hadrons in Pb+Pb collisions at energies available at the CERN Large Hadron Collider
The nuclear modification factor R{sub AA}(p{sub T}) for large transverse momentum pion spectra in Pb+Pb collisions at {radical}(s)=2.76 TeV is predicted within the next-to-leading order perturbative QCD parton model. The effect of jet quenching is incorporated through medium-modified fragmentation functions within the higher-twist approach. The jet transport parameter that controls medium modification is proportional to the initial parton density, and the coefficient is fixed by data on the suppression of large-p{sub T} hadron spectra obtained at the BNL Relativistic Heavy Ion Collider. Data on charged hadron multiplicity dN{sub ch}/d{eta}=1584{+-}80 in central Pb+Pb collisions from the ALICE experiment at the CERN Large Hadron Collider are used to constrain the initial parton density both for determining the jet transport parameter and the 3 + 1 dimensional (3 + 1D) ideal hydrodynamic evolution of the bulk matter that is employed for the calculation of R{sub PbPb}(p{sub T}) for neutral pions.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Quark-hadron duality in structure functions
We review recent progress in the study of quark-hadron duality in electron-nucleon structure functions. New developments include insights into the local aspects of duality obtained using truncated moments of structure functions, which allow duality-violating higher-twist contributions to be identified in individual resonance regions. Preliminary studies of pion electropro-duction have also showed the first glimpses of duality in semi-inclusive cross sections, which if confirmed would greatly expand the scope of constraining the flavor and spin dependence of parton distributions.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Quark-hadron duality in proton and neutron F{sub 2} structure functions
I present a summary of recent studies of quark-hadron duality in the proton and neutron F{sub 2} structure functions which highlight the possibility of using averaged resonance region data to constrain parton distribution functions in the kinematic region of high Bjorken x where, presently, few experimental constraints exist. A recent extraction of the neutron F{sub 2}{sup n} structure function from proton and deuterium data in the resonance region is also discussed.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Strong longitudinal color-field effects in pp collisions at energies available at the CERN Large Hadron Collider
We study the effect of strong longitudinal color fields (SCF) in p + p reactions up to Large Hadron Collider (LHC) energies in the framework of the hijing/BB (v2.0) model that combines (collinear factorized) perturbative quantum chromodynamics multiple minijet production with soft longitudinal string excitation and hadronization. The default vacuum string tension, {kappa}{sub 0} = 1 GeV/fm, is replaced by an effective energy-dependent string tension, {kappa}(s)={kappa}{sub 0}(s/s{sub 0}){sup 0.06} that increases monotonically with center-of-mass energy. The exponent {lambda}=0.06 is found sufficient to reproduce well the energy dependence of multiparticle observables in the Relativistic Heavy Ion Collider, Tevatron, as well as recent LHC data. This exponent is half of that predicted by the color glass saturation (CGC) model, {lambda}{sub CGC}=0.115, where gluon fusion multiparticle production mechanisms are assumed. In hijing/BB (v2.0), the rapid growth of dN{sub ch}/d{eta} with energy is due to the interplay of copious minijet production with increasing SCF contributions. The large (strange) baryon-to-meson ratios measured at Tevatron energies are well described. A significant enhancement of these ratios is predicted up to the highest LHC energy (14 TeV). The effect of JJ loops and SCF on baryon-antibaryon asymmetry, and its relation to baryon number transport, is also discussed.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurements of branching fractions of leptonic and hadronic $ D_s^{+} $ meson decays and extraction of the $ D_s^{+} $ meson decay constant
We present measurements of absolute branching fractions of hadronic and lep-tonic \( D_s^{+} \) decays to K - K + π + , \( {{\overline{K}}^0} \) K + , ηπ + , μ + ν μ and τ + ν τ and report a search for the leptonic \( D_s^{+} \) → e + ν e decays. The results are obtained from a data sample of 913 fb -1 collected at or near the \( \varUpsilon \) (4 S ) and \( \varUpsilon \) (5 S ) resonances with the Belle detector at the KEKB asymmetric-energy e + e - collider. The branching fractions of hadronic decays are measured to be $$ \begin{array}{*{20}{c}} {\mathcal{B}\left( {D_s^{+}\ \to\ {K^{-}}{K^{+}}{\pi^{+}}} \right) = \left( {5.06\pm 0.15\pm 0.21} \right)\%,} \\ {\mathcal{B}\left( {D_s^{+}\ \to\ {{\overline{K}}^0}{K^{+}}} \right) = \left( {2.95\pm 0.11\pm 0.09} \right)\%,} \\ {\mathcal{B}\left( {D_s^{+}\ \to\ \eta {\pi^{+}}} \right) = \left( {1.82\pm 0.14\pm 0.07} \right)\%,} \\ \end{array} $$ where the first and second uncertainties are statistical and systematic, respectively. The branching fractions of leptonic decays are measured to be $$ \begin{array}{*{20}{c}} {\mathcal{B}\left( {D_s^{+}\ \to\ {\mu^{+}}{\nu_{\mu }}} \right)=\left( {0.531\pm 0.028\pm 0.020} \right)\%,} \\ {\mathcal{B}\left( {D_s^{+}\to {\tau^{+}}{\nu_{\tau }}} \right)=\left( {5.70\pm 0.21_{-0.30}^{-0.31 }} \right)\%,} \\ \end{array} $$ which are combined to determine the \( D_s^{+} \) meson decay constant $$ {f_{{{D_s}}}}=\left( {255.5\pm 4.2\pm 5.1} \right)\ \mathrm{MeV}. $$ We find no significant signal for \( D_s^{+} \) → e + ν e decays and set an upper limit of \( \mathcal{B}\left( {D_s^{+}\ \to\ {e^{+}}{\nu_e}} \right) \) < 1 . 0(0 . 83) × 10 -4 at 95% (90%) confidence level.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Searches for heavy long-lived sleptons and R-hadrons with the ATLAS detector in pp collisions at s = 7 TeV
Not Available
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Elliptic flow of muons from heavy-flavour hadron decays at forward rapidity in Pb–Pb collisions at s NN = 2.76 TeV
Not Available
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Elastic and resonance structures of the nucleon from the hadronic tensor in lattice QCD: Implications for neutrino-nucleon scattering and hadron physics
We compute the Euclidean hadronic tensor from charge density operators and extract elastic and resonance structures by employing exponential fits to the four-point function correlator, as well as a Bayesian reconstruction inverse algorithm to obtain the corresponding spectral density for qualitative comparison. We present the determination of the nucleon’s Sachs electric form factor using the hadronic tensor formalism and verify that it is consistent with that from the conventional three-point function calculation. Beyond the elastic peak, we observe a structure located approximately 0.5–0.7 GeV above the nucleon mass in the Bayesian reconstruction. This structure is interpreted as a mixture of the Roper resonance [𝑁(1440)], and states with both positive and negative parities in this mass region, as well as multihadron states. Assuming the observed structure is dominated by 𝐽 𝑃 = 1/2 ± states, we extract the transition electric form factor 𝐺$^*_𝐸$(𝑄 2 ) and the corresponding longitudinal helicity amplitude 𝑆 1/2 (𝑄 2 ), and compare them with those determined from the CLAS experimental data of nucleon-to-Roper transition. Although fitting to the four-point correlation function or using the inverse algorithm does not resolve individual resonances, it nevertheless enables the determination of total inclusive lepton–nucleon scattering cross sections in appropriate energy bins. This lattice QCD calculation presents the first major step toward studying the inclusive 𝑁 → 𝑋 contributions within the hadronic tensor formalism.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Charged-hadron and identified-hadron (𝐾$^{0}_{𝑆}$, Λ, $Ξ$ − ) yield measurements in photonuclear Pb + Pb and 𝑝 + Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV with ATLAS
This paper presents the measurement of charged-hadron and identified-hadron (𝐾$^{0}_{𝑆}$, Λ, $Ξ$ − ) yields in photonuclear collisions using 1.7nb −1 of $\sqrt{s_{NN}}$ = 5.02 TeV Pb + Pb data collected in 2018 with the ATLAS detector at the Large Hadron Collider. Candidate photonuclear events are selected using a combination of tracking and calorimeter information, including the zero-degree calorimeter. The yields as a function of transverse momentum and rapidity are measured in these photonuclear collisions as a function of charged-particle multiplicity. These photonuclear results are compared with 0.1 nb −1 of $\sqrt{s_{NN}}$ = 5.02 TeV p + Pb data collected in 2016 by ATLAS using similar charged-particle multiplicity selections. These photonuclear measurements shed light on potential quark-gluon plasma formation in photonuclear collisions via observables sensitive to radial flow, enhanced baryon-to-meson ratios, and strangeness enhancement. The results are also compared with the Monte Carlo generator and hydrodynamic calculations to test whether such photonuclear collisions may produce small droplets of quark-gluon plasma that flow collectively.
H & He induced nuclear reactions↗