Production Of Final States Research Articles

Hadronic final states in DIS at NNLO QCD with parton showers

We present a parton-shower matched NNLO QCD calculation for hadronic final state production in Deep Inelastic Scattering. The computation is based on the UNLOPS method and is implemented in the publicly available event generation framework SHERPA. Results are compared to measurements performed by the H1 collaboration.

ϒ(6S)and triangle singularity ine+e−→B1(5721)B¯→Zb(10610)π

We discuss the possibility that production of final states with bottomonium and light mesons at the peak $\Upsilon(6S)$ in the $e^+e^-$ annihilation at approximately 11.00 GeV is in fact due to a triangular singularity at the threshold of the heavy meson pair production $B_1(5721) \bar B + c.c.$ through the process $e^+e^- \to B_1(5721) \bar B \to Z_b(10610) \, \pi$. The presence of the hidden-bottom resonance $Z_b(10610)$ then explains the observed enhanced production of the final channels with both ortho- and para- bottomonium states, $\Upsilon(nS) \pi \pi$ and $h_b(kP) \pi \pi$. The discussed mechanism also predicts a distinct pattern for production of hidden-bottom states at the $\Upsilon(6S)$ energy that can be tested by experiment.

Dynamical approach to MPI in W+dijet and Z+dijet production within the PYTHIA event generator

The new numerical approach that includes 1 to 2 mechanism is applied to double parton scattering (DPS) in W+dijet and Z+dijet final state production in proton-proton collisions at LHC. By using the underlying event (UE) simulation from a pythia 8 tune extracted in hadronic events, we show that, like in the case of a four-jet final state, the inclusion of 1 to 2 mechanism improves the description of experimental data measured at 7 TeV. In addition, predictions for proton-proton collisions at a center-of-mass energy of 14 TeV are shown for DPS- and UE-sensitive observables.

Search for low-scale gravity signatures in multi-jet final states with the ATLAS detector at s = 8 $$ \sqrt{s}=8 $$ TeV

We search for evidence of physics beyond the Standard Model in the production of final states with multiple high transverse momentum jets, using 20.3 fb$^{-1}$ of proton-proton collision data recorded by the ATLAS detector at $\sqrt{s} = 8$ TeV. No excess of events beyond Standard Model expectations is observed, and upper limits on the visible cross-section for non-Standard Model production of multi-jet final states are set. Using a wide variety of models for black hole and string ball production and decay, the limit on the cross-section times acceptance is as low as 0.16 fb at the 95% CL for a minimum scalar sum of jet transverse momentum in the event of about 4.3 TeV. Using models for black hole and string ball production and decay, exclusion contours are determined as a function of the production mass threshold and the gravity scale. These limits can be interpreted in terms of lower-mass limits on black hole and string ball production that range from 4.6 to 6.2 TeV.

The role of finite-size effects on the spectrum of equivalent photons in proton–proton collisions at the LHC

Photon–photon interactions represent an important class of physics processes at the LHC, where quasi-real photons are emitted by both colliding protons. These reactions can result in the exclusive production of a final state X, p+p→p+p+X. When computing such cross sections, it has already been shown that finite size effects of colliding protons are important to consider for a realistic estimate of the cross sections. These first results have been essential in understanding the physics case of heavy-ion collisions in the low invariant mass range, where heavy ions collide to form an exclusive final state like a J/Ψ vector meson. In this paper, our purpose is to present some calculations that are valid also for the exclusive production of high masses final states in proton–proton collisions, like the production of a pair of W bosons or the Higgs boson. Therefore, we propose a complete treatment of the finite size effects of incident protons irrespective of the mass range explored in the collision. Our expectations are shown to be in very good agreement with existing experimental data obtained at the LHC.

Top quark effects in composite vector pair production at the LHC

In the context of strongly coupled Electroweak Symmetry Breaking, composite light scalar singlet and composite triplet of heavy vectors may arise from an unspecified strong dynamics and the interactions among themselves and with the Standard Model gauge bosons and fermions can be described by a SU(2) L ×SU(2) R /SU(2) L+R effective chiral Lagrangian. In this framework, the production of the V + V − and V 0 V 0 final states at the LHC by gluon fusion mechanism is studied in the region of parameter space consistent with the unitarity constraints in the elastic channel of longitudinal gauge boson scattering and in the inelastic scattering of two longitudinal Standard Model gauge bosons into Standard Model fermions pairs. The expected rates of same-sign di-lepton and tri-lepton events from the decay of the V 0 V 0 final state are computed and their corresponding backgrounds are estimated. It is of remarkable relevance that the V 0 V 0 final state can only be produced at the LHC via a gluon fusion mechanism since this state is absent in the Drell–Yan process. It is also found that the V + V − final-state production cross section via gluon fusion mechanism is comparable with the V + V − Drell–Yan production cross section. The comparison of the V 0 V 0 and V + V − total cross sections will be crucial for distinguishing the different models since the vector pair production is sensitive to many couplings. This will also be useful to determine if the heavy vectors are only composite vectors or are gauge vectors of a spontaneously broken gauge symmetry.

Two-photon processes at Belle

We review recent measurements of pure neutral final state production in the two-photon processes, γγ → π0π0 and ηπ0 at the Belle experiment. In the lower invariant mass region, properties of light scalar mesons are measured by partial wave analysis. In the higher energy region the total and differential cross section are compared with QCD models.

Collider implications of Kaluza-Klein excitations of the gluons

We consider an asymmetric string compactification scenario in which the SM gauge bosons can propagate into one TeV$^{-1}$-size extra compact dimension. These gauge bosons have associated KK excitations that present additional contributions to the SM processes. We calculate the effects that the KK excitations of the gluons, $g^{\star}$'s, have on multijet final state production in proton-proton collisions at the Large Hadron Collider energy. In the case of dijet final states with very high $p_{{}_T}$, the KK signal due to the exchanges of the $g^{\star}$'s is several factors greater than the SM background for compactification scales as high as about 7 TeV. The high-$p_{{}_T}$ effect is not as dramatic for the direct production of a single on-shell $g^{\star}$, which subsequently decays into $q$-$\bar{q}$ pairs, where the KK signal significantly exceeds the SM three-jet background for compactification scales up to about 3 TeV. We also present our results for the four-jet final state signal from the direct production of two on-shell $g^{\star}$'s.

Single- and multi-photon production in e+e− collisions at a centre-of-mass energy of 183 GeV

Abstract The production of final states involving one or more energetic photons from e+e− collisions is studied in a sample of 58.5 pb −1 of data recorded at a centre-of-mass energy of 183 GeV by the ALEPH detector at LEP. The e + e − → ν ν γ(γ) and e + e − → γγ(γ) cross sections are measured. The data are in good agreement with predictions based on the Standard Model and are used to set upper limits on the cross sections for anomalous photon production in the context of two supersymmetric models and for various extensions to QED. In particular, in the context of a super-light gravitino model a cross section upper limit of 0.38 pb is placed on the process e + e − → G G γ , allowing a lower limit to be set on the mass of the gravitino. Limits are also set on the mass of the lightest neutralino in Gauge Mediated Supersymmetry Breaking models. In the case of equal ee ∗ γ and eeγ couplings a 95% C.L. lower limit on M e ∗ of 250 GeV /c 2 is obtained.

Four-jet final state production in e+e− collisions at centre-of-mass energies ranging from 130 to 184 GeV

The four jet topology is analysed in the ALEPH data taken between November 1995 and November 1997, at centre-of-mass energies ranging from 130 to 184 GeV. While an unexpected accumulation of events with a dijet mas sum around 105 GeV/c**2 had been observed during the first run in 1995 at 130/136 GeV, corresponding to an integrated luminosity of 5.7 pb-1, no significant differences between data and standard model prediction is noticed, either in the high energy runs (81.1 pb-1 taken at centre-of-mass energies from 161 to 184 GeV) or in the 7.1 pb-1 recorded during a new short run at 130/136 GeV in 1997. We have found no other explanation for the earlier reported ``four jet anomaly'' than a statistical fluctuation.

A study of single and multi-photon production in e+e− collisions at centre-of-mass energies of 130 and 136 GeV

The production of final states involving one or more energetic photons from e+e− collisions at high energies is studied using data collected by the ALEPH detector at LEP. The data consist of two samples of 2.9 pb−1 each, recorded at centre-of-mass energies of 130 GeV and 136 GeV. The data are in agreement with the predictions of the Standard Model. From an analysis of two-photon final states new limits are placed on the parameters of models involving e+e−γγ contact interactions and excited electrons. The 95% confidence level lower limits on the QED cut-off parameters Λ+ and Λ− are found to be 169 and 132 GeV respectively.

Four-jet final state production in e+e− collisions at centre-of-mass energies of 130 and 136 GeV

Four-jet final state production in e+e− collisions at centre-of-mass energies of 130 and 136 GeV

Four-jet final state production in ${\rm e^+e^-}$ collisions at centre-of-mass energies of 130 and 136 GeV

The four-jet final state is analyzed to search for hadronic decays of pair-produced heavy particles. The analysis uses the ALEPH data collected at LEP in November 1995 at centre-of-mass energies of 130 and 136 GeV, corresponding to a total integrated luminosity of 5.7 pb(-1). An excess of four-jet events is observed with respect to the standard model predictions. In addition, these events exhibit an enhancement in the sum of the two di-jet masses around 105 GeV/c(2). The properties of these events are studied and compared to the expectations from standard processes and to pair production hypotheses.

Nuclear dynamics of several decaying overlapping electronic states: A time-dependent formulation

The nuclear dynamics accompanying the excitation of a polyatomic target to a manifold of decaying overlapping electronic states and the subsequent decay to final electronic states are discussed. Nonadiabatic interactions within the manifold of decaying states as well as of final states are included. The cross sections for the excitation and for the production of final states are derived. The wave packet dynamics are investigated for both the excitation and the decay and related to the corresponding cross sections. Particular attention is paid to core levels of systems with equivalent atoms. The time-dependent formulation is also used to compute the gross features of the observed spectra via a spectral moment expansion. An interesting example is investigated where the decaying as well as the final states have extremely localized electron vacancies.

Nuclear dynamics of decaying states: A time-dependent formulation

The wave packet dynamics accompanying the excitation to a decaying electronic state and the subsequent decay to final electronic states are discussed. The cross sections for the excitation and for the production of final states are related to the corresponding wave packets. The time-dependent formulation adds insight into the process and is amenable to semiclassical approximations and interpretations. It can also be used to compute the gross features of the observed spectra via a spectral moment expansion. An illustrative application demonstrates the usefulness of the expansion.

Two-photon production of final states with ap $$\bar p$$ pair

Two-photon production of the exclusive final statesp\(\bar p\)+nπ (n=0, 1, 2, and 3) has been investigated using the ARGUS detector at thee+e− storage ring DORIS II at DESY. The reactionsγγ→p\(\bar p\)π andγγ→p\(\bar p\)π+π−π0 have been observed for the first time, as have theΔ++ and\(\overline {\Delta ^{ + + } } \) baryons in the final statep\(\bar p\)π+π−. No evidence was found forΔ++\(\overline {\Delta ^{ + + } } \) production. Topological cross sections for two-photon production ofp\(\bar p\),p\(\bar p\)π0,p\(\bar p\)π+π− andp\(\bar p\)π+π−π0, as well as the crosssection forγγ→Δ++\(\bar p\)π+π−+c.c., have been measured. Upper limits are given for the cross section forγγ→Δ0\(\overline {\Delta ^0 } \),γγ→Δ++\(\overline {\Delta ^{ + + } } \) andγγ→Λ\(\bar \Lambda \).

Production of four-prong final states in photon-photon collisions.

Results are presented on the exclusive production of four-prong final states in photon-photon collisions from the TPC/Two-Gamma detector at the SLAC e+e− storage ring PEP. Measurement of dE/dx and momentum in the time-projection chamber (TPC) provides identification of the final states 2π+2π−, K+K−π+π−, and 2K+2K−. For two quasireal incident photons, both the 2π+2π− and K+K−π+π− cross sections show a steep rise from threshold to a peak value, followed by a decrease at higher mass. Cross sections for the production of the final states ρ0ρ0, ρ0π+π−, and φπ+π− are presented, together with upper limits for φρ0, φφ, and K*0K¯ *0. The ρ0ρ0 contribution dominates the four-pion cross section at low masses, but falls to nearly zero above 2 GeV. Such behavior is inconsistent with expectations from vector dominance but can be accommodated by four-quark resonance models or by t-channel factorization. Angular distributions for the part of the data dominated by ρ0ρ0 final states are consistent with the production of JP=2+ or 0+ resonances but also with isotropic (nonresonant) production. When one of the virtual photons has mass (mγ2=-Q2≠0), the four-pion cross section is still dominated by ρ0ρ0 at low final-state masses Wγγ and by 2π+2π− at higher mass. Further, the dependence of the cross section on Q2 becomes increasingly flat as Wγγ increases.Received 27 February 1987DOI:https://doi.org/10.1103/PhysRevD.37.28©1988 American Physical Society

Investigation of the doubly coherent production ofπ−byHe3ions of 910 MeV on the Li isotopes

Doubly coherent production of ${\ensuremath{\pi}}^{\ensuremath{-}}$ on $^{6}\mathrm{Li}$ and $^{7}\mathrm{Li}$ at 0\ifmmode^\circ\else\textdegree\fi{} was measured with $^{3}\mathrm{He}$ ions of 910 MeV. The cross sections for the production of discrete nuclear states are of the order of pb/sr. The spectra show a preferential production of final states in the continuum.

Multinucleon captures of slow antiprotons in complex nuclei and a search for the H dibaryon

From a sample of 80 000 antiproton annihilations in complex nuclei, a search has been made for those multinucleon reactions which would result in the production of two units of strangeness. No example of such processes has been found, leading to upper limits for the frequencies of production of final states containing 2Λ 0, 2K +, K −Λ 0, or the H dibaryon of (1−5)×10 −4 per p̄ annihilation.

Strange-particle cross sections fromπ+pinteractions at 10.3 GeV/c

Cross sections are presented for production of final states with two strange particles from ${\ensuremath{\pi}}^{+}p$ interactions at 10.3 GeV/c in a 31.1-event/\ensuremath{\mu}b bubble-chamber experiment.