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Otto Nachtmann

Publications and source records attributed to Otto Nachtmann.

At least 37 records · Page 2Linked to original sources
arXiv2021

Exclusive $f_{1}(1285)$ meson production for energy ranges available at the GSI-FAIR with HADES and PANDA

We evaluate the cross section for the $p p \to p p f_{1}(1285)$ and $p \bar{p} \to p \bar{p} f_{1}(1285)$ reactions at near threshold energies relevant for the HADES and PANDA experiments at GSI-FAIR. We assume that at energies close to the threshold the $ωω\to f_{1}(1285)$ and $ρ^{0} ρ^{0} \to f_{1}(1285)$ fusion processes are the dominant production mechanisms. The vertex for the $VV \to f_{1}$ coupling is derived from an effective coupling Lagrangian. The $g_{ρρf_1}$ coupling constant is extracted from the decay rate of $f_{1}(1285) \to ρ^{0} γ$ using the vector-meson-dominance ansatz. We assume $g_{ωωf_1} = g_{ρρf_1}$, equality of these two coupling constants, based on arguments from the naive quark model and vector-meson dominance. The amplitude for the $VV \to f_{1}$ fusion, supplemented by phenomenological vertex form factors for the process, is given. The differential cross sections at energies close to the threshold are calculated. In order to determine the parameters of the model the $γp \to f_{1}(1285) p$ reaction is discussed in addition and results are compared with the CLAS data. The possibility of a measurement by HADES@GSI is presented and discussed. We performed a Monte Carlo feasibility simulations of the $p p \to p p f_1$ reaction for $\sqrt{s}$ = 3.46 GeV in the $π^+ π^- π^+ π^-$ (not shown explicitly) and $π^+ π^- π^+ π^- π^0$ final states using the PLUTO generator. The latter one is especially promising as a peak in the $π^+ π^- η$ should be observable by HADES.

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arXiv2021

The electric dipole moment of the tau lepton revisited

We reconsider the issue of the search for a nonzero electric dipole form factor (EDM) $d_τ(s)$ using optimal observables in $τ^+τ^-$ production by $e^+ e^-$ collisions in the center-of-mass energy range from the $τ$-pair threshold to about $\sqrt{s} \sim 15$ GeV. We discuss the general formalism of optimal observables and apply it to two $CP$-odd observables that are sensitive to the real and imaginary part of $d_τ(s)$, respectively. We compute the expectation values and covariances of these optimal $CP$ observables for $τ$-pair production at $\sqrt{s}=10.58$ GeV with subsequent decays of $τ^\pm$ into major leptonic or semihadronic modes. For the $τ$ decays to two pions and three charged pions we take the full kinematic information of the hadronic system into account. Assuming that the Belle II experiment at the KEKB accelerator will eventually analyze data corresponding to an integrated luminosity of 50 ab$^{-1}$ and applying acceptance cuts on the final-state pions we find that 1~s.d. sensitivities $δ{\rm Re} d_τ= 6.8 \times 10^{-20}$ e cm and $δ{\rm} Im d_τ= 4.0 \times 10^{-20}$ e cm can be obtained with events where both $τ$'s decay semihadronically. In the ideal case where no cuts on the final-state particles are applied we find with 50 ab$^{-1}$ at $\sqrt{s}=10.58$ GeV corresponding to $4.5 \times 10^{10}$ $τ^+ τ^-$ events the 1 s.d. sensitivities $δ{\rm Re} d_τ= 5.8 \times 10^{-20}$ e cm and $δ{\rm} Im d_τ= 3.2 \times 10^{-20}$ e cm, again for events where both $τ$ leptons decay semihadronically. Furthermore, we analyze the potential magnitude of the $τ$ EDM form factor in the type-II two-Higgs doublet extension and in two scalar leptoquark extensions of the Standard Model.

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arXiv2020

Searching for odderon exchange in exclusive $pp \to pp ϕ$ and $pp \to pp ϕϕ$ reactions at the LHC

The possibility to use the exclusive $pp \to pp ϕ$ and $pp \to pp ϕϕ$ reactions in identifying the odderon exchange is discussed. So far there is no unambiguous experimental evidence for the odderon, the charge conjugation $C = -1$ counterpart of the $C = +1$ pomeron. Recently proposed tensor-pomeron and vector-odderon model for soft high-energy reactions is applied. For the $p p \to p p ϕ$ reaction at high energies the photon-pomeron fusion is the dominant process and the odderon-pomeron fusion is an interesting alternative. Adding odderon exchange improves considerably description of the proton-proton angular correlations measured by the WA102 collaboration. The $p p \to p p ϕϕ$ process via pomeron-pomeron fusion is advantageous one as here the odderon does not couple to protons. The observation of large $M_{ϕϕ}$ and the rapidity difference $Y_{ϕϕ}$ seems well suited to identify odderon exchange. Comparisons with data from the WA102 experiment are made and predictions for LHC experiments are given.

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arXiv2020

Central exclusive diffractive production of axial-vector $f_{1}(1285)$ and $f_{1}(1420)$ mesons in proton-proton collisions

We present a study of the central exclusive diffractive production of the $f_{1}(1285)$ and $f_{1}(1420)$ resonances in proton-proton collisions. The theoretical results are calculated within the tensor-pomeron approach. Two pomeron-pomeron-$f_{1}$ tensorial couplings labeled by $(l,S) = (2,2)$ and $(4,4)$ are derived. We adjust the model parameters (coupling constants, cutoff constant) to the WA102 experimental data taking into account absorption effects. Both the $(l,S) = (2,2)$ and $(4,4)$ couplings separately allow one to describe the WA102 differential distributions. We compare these predictions with those of the Sakai-Sugimoto model, where the pomeron-pomeron-$f_{1}$ couplings are determined by the mixed axial-gravitational anomaly of QCD. We derive an approximate relation between the pomeron-pomeron-$f_{1}$ coupling constants of this approach and the $(l,S) = (2,2)$ and $(4,4)$ couplings. Then we present our predictions for the energies available at the RHIC and LHC. The total cross sections and several differential distributions are presented. Analysis of the distributions in the azimuthal angle $ϕ_{pp}$ between the transverse momenta of the outgoing protons may be used to disentangle $f_{1}$- and $η$-type resonances contributing to the same final channel. We find for the $f_{1}(1285)$ a total cross section $\sim 38$ $μ$b for $\sqrt{s} = 13$ TeV and a rapidity cut on the $f_{1}$ of $|{\rm y_{M}}| < 2.5$. We predict a much larger cross section for production of $f_{1}(1285)$ than for production of $f_{2}(1270)$ in the $π^{+}π^{-}π^{+}π^{-}$ decay channel for the LHC energies. This opens a possibility to study the $f_{1}(1285)$ meson in experiments planned at the LHC.

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arXiv2020

Searching for the odderon in $pp \to pp K^{+}K^{-}$ and $pp \to pp μ^{+}μ^{-}$ reactions in the $ϕ(1020)$ resonance region at the LHC

We explore the possibility of observing odderon exchange in the $pp \to pp K^{+}K^{-}$ and $pp \to pp μ^{+}μ^{-}$ reactions at the LHC. We consider the central exclusive production (CEP) of the $ϕ(1020)$ resonance decaying into $K^{+} K^{-}$ and $μ^{+}μ^{-}$. We compare the purely diffractive contribution (odderon-pomeron fusion) to the photoproduction contribution (photon-pomeron fusion). The theoretical results are calculated within the tensor-pomeron and vector-odderon model for soft reactions. We include absorptive corrections at the amplitude level. In order to fix the coupling constants for the photon-pomeron fusion contribution we discuss the reactions $γp \to ωp$ and $γp \to ϕp$ including $ϕ$-$ω$ mixing. We compare our results for these reactions with the available data, especially those from HERA. Our coupling constants for the pomeron-odderon-$ϕ$ vertex are taken from an analysis of the WA102 data for the $p p \to p p ϕ$ reaction. We show that the odderon-exchange contribution significantly improves the description of the $pp$ azimuthal correlations and the $dP_{t}$ "glueball-filter variable" dependence of $ϕ$ CEP measured by WA102. To describe the low-energy data more accurately we consider also subleading processes with reggeized vector-meson exchanges. However, they do not play a significant role at the LHC. We present predictions for two possible types of measurements: at midrapidity and with forward measurement of protons (relevant for ATLAS-ALFA or CMS-TOTEM), and at forward rapidities and without measurement of protons (relevant for LHCb). We discuss the influence of experimental cuts on the integrated cross sections and on various differential distributions. With the corresponding LHC data one should be able to get a decisive answer concerning the presence of an odderon-pomeron fusion contribution in single $ϕ$ CEP.

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arXiv2019

The Tensor Pomeron and Small-x Deep Inelastic Scattering

We apply the tensor-pomeron model to small-$x$ deep-inelastic lepton-proton scattering and photoproduction. Our model includes a soft and a hard tensor pomeron as well as a reggeon contribution. Data with c.m. energies $6 < \sqrt{s} < 318$ GeV and virtualities $Q^2 < 50 \,\mbox{GeV}^2$ are considered. Our fit gives a very good description of the available data in this kinematic region, including the latest HERA data for $x < 0.01$. In particular, the transition region from low to high $Q^2$ is well described. Within the errors, the hard pomeron is absent in photoproduction. The intercepts of the soft and hard pomeron in the two-tensor-pomeron model are found to be $1.0935\, ({}^{+76}_{-64})$ and $1.3008 \,({}^{+73}_{-84})$, respectively. We argue that a vector pomeron would not give any contribution to photoproduction.

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arXiv2019

Extracting the pomeron-pomeron-$f_{2}(1270)$ coupling in the $p p \to p p π^{+} π^{-}$ reaction through angular distributions of the pions

We discuss how to extract the pomeron-pomeron-$f_2(1270)$ ($\mathbb{P} \mathbb{P} f_2(1270)$) coupling within the tensor-pomeron model. The general $\mathbb{P} \mathbb{P} f_2(1270)$ coupling is a combination of seven basic couplings (tensorial structures). To study these tensorial structures we propose to measure the central-exclusive production of a $π^+ π^-$ pair in the invariant mass region of the $f_2(1270)$ meson. An analysis of angular distributions in the $π^+ π^-$ rest system, using the Collins-Soper (CS) and the Gottfried-Jackson (GJ) frames, turns out to be particularly relevant for our purpose. For both frames the $\cosθ_{π^{+}}$ and $ϕ_{π^{+}}$ distributions are discussed. We find that the azimuthal angle distributions in these frames are fairly sensitive to the choice of the $\mathbb{P} \mathbb{P} f_2$ coupling. We show results for the resonance case alone as well as when the dipion continuum is included. We show the influence of the experimental cuts on the angular distributions in the context of dedicated experimental studies at RHIC and LHC energies. Absorption corrections are included for our final distributions.

hep-ph↗
arXiv2019

Searching for odderon exchange in exclusive $pp \to pp ϕϕ$ reaction

We discuss the possibility to use the $pp \to pp ϕϕ$ process in identifying the odderon exchange. So far there is no unambiguous experimental evidence for the odderon, the charge conjugation $C = -1$ counterpart of the $C= +1$ pomeron. Last year results of the TOTEM collaboration suggest that the odderon exchange can be responsible for a disagreement of theoretical calculations and the TOTEM data for elastic proton-proton scattering. Here we present recent studies for central exclusive production (CEP) of $ϕϕ$ pairs in proton-proton collisions. We consider the pomeron-pomeron fusion to $ϕϕ$ ($\mathbb{P}\mathbb{P} \to ϕϕ$) through the continuum processes, due to the $\hat{t}$- and $\hat{u}$-channel reggeized $ϕ$-meson, photon, and odderon exchanges, as well as through the $s$-channel resonance process ($\mathbb{P}\mathbb{P} \to f_{2}(2340) \to ϕϕ$). This $f_{2}$ state is a candidate for a tensor glueball. The amplitudes for the processes are formulated within the tensor-pomeron and vector-odderon approach. Some model parameters are determined from the comparison to the WA102 experimental data. The odderon exchange is not excluded by the WA102 data for high $ϕϕ$ invariant masses. The measurement of large $M_{ϕϕ}$ or $\rm{Y_{diff}}$ events at the LHC would therefore suggest presence of the odderon exchange.

hep-ph↗
arXiv2019

Central exclusive diffractive production of $K^{+} K^{-} K^{+} K^{-}$ via the intermediate $ϕϕ$ state in proton-proton collisions

We present a study of the exclusive $pp \to pp K^{+} K^{-} K^{+} K^{-}$ reaction at high energies. We consider diffractive mechanisms with the intermediate $ϕϕ$ state with its decay into the $K^{+} K^{-} K^{+} K^{-}$ system. We include the $ϕ(1020)$ $\hat{t}/\hat{u}$-channel exchanges and the $f_{2}(2340)$ $s$-channel exchange mechanism. This $f_{2}$ state is a candidate for a tensor glueball. We discuss the possibility to use the $pp \to pp ϕϕ$ process in identifying the odderon exchange. An upper limit for the $\mathbb{P} \mathbb{O} ϕ$ coupling is extracted from the WA102 experimental data. The amplitudes for the processes are formulated within the tensor-pomeron and vector-odderon approach. We adjust parameters of our model to the WA102 data and present several predictions for the ALICE, ATLAS, CMS and LHCb experiments. Integrated cross sections of order of a few nb are obtained including the experimental cuts relevant for the LHC experiments. The distributions in the four-kaon invariant mass, rapidity distance between the two $ϕ$ mesons, special ``glueball filter variable'', proton-proton relative azimuthal angle are presented. The distribution in rapidity difference of both $ϕ$-mesons could shed light on the $f_{2}(2340) \to ϕϕ$ coupling, not known at present. We discuss the possible role of the $f_{0}(2100)$, $η(2225)$, and $X(2500)$ resonances observed in the $ϕϕ$ channel in radiative decays of $J/ψ$. Using typical kinematic cuts for LHC experiments we find from our model that the odderon-exchange contribution should be distinguishable from other contributions for large rapidity distance between the $ϕ$ mesons and in the region of large four-kaon invariant masses. At least, it should be possible to derive an upper limit on the odderon contribution in this reaction.

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arXiv2019

The Tensor Pomeron and Low-x Deep Inelastic Scattering

The tensor-pomeron model is applied to low-x deep-inelastic lepton-nucleon scattering and photoproduction. We consider c.m. energies in the range 6 - 318 GeV and Q^2 < 50 GeV^2. In addition to the soft tensor pomeron, which has proven quite successful for the description of soft hadronic high-energy reactions, we include a hard tensor pomeron. We also include f_2-reggeon exchange which turns out to be particularly relevant for real-photon-proton scattering at c.m. energies in the range up to 30 GeV. The combination of these exchanges permits a description of the absorption cross sections of real and virtual photons on the proton in the same framework. In particular, a detailed comparison of this two-tensor-pomeron model with the latest HERA data for x < 0.01 is made. Our model gives a very good description of the transition from the small-Q^2 regime where the real or virtual photon behaves hadron-like to the large-Q^2 regime where hard scattering dominates. Our fit allows us, for instance, a determination of the intercepts of the hard pomeron as 1.3008(+73,-84), of the soft pomeron as 1.0935(+76,-64), and of the f_2 reggeon. We find that in photoproduction the hard pomeron does not contribute within the errors of the fit. We show that assuming a vector instead of a tensor character for the pomeron leads to the conclusion that it must decouple in real photoproduction.

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arXiv2018

Tensor pomeron, vector odderon and diffractive production of meson and baryon pairs in proton-proton collisions

We review some selected results of the tensor-pomeron and vector-odderon model of soft high-energy proton-proton scattering and central exclusive production of meson and baryon pairs in proton-proton collisions. We discuss the theoretical aspects of this approach and consider the phenomenological implications in a variety of processes at high energies, comparing to existing experimental data. We consider the diffractive dipion and dikaon production including the continuum and the dominant scalar and tensor resonance contributions as well as the photoproduction processes. The theoretical results are compared with existing CDF experimental data and predictions for planned or current LHC experiments, ALICE, ATLAS, CMS, LHCb are presented.

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arXiv2018

Production of $p\bar{p}$ pairs in UPC at the LHC

We discuss production of $p\bar{p}$ pairs in two-photon interactions in heavy-ion collisions. We present predictions for the ultraperipheral, ultrarelativistic, heavy-ion collisions (UPC) $^{208}\!Pb \, ^{208}\!Pb \to$ $^{208}\!Pb \, ^{208}\!Pb \,p \bar{p}$. The parameters of vertex form factors are adjusted to the Belle data for the $γγ\to p \bar{p}$ reaction. To described the Belle data we include the proton-exchange, the $f_2(1270)$ and $f_2(1950)$ $s$-channel exchanges, as well as the hand-bag mechanism. Then, the total cross section and several differential distributions for experimental cuts corresponding to the LHC experiments are presented. The distribution in $\mathrm{y}_{diff}$, the rapidity distance between the proton and antiproton, is particularly interesting. We find the total cross sections: 100 $μ$b for the ALICE cuts, 160 $μ$b for the ATLAS cuts, 500 $μ$b for the CMS cuts, and 104 $μ$b taking into account the LHCb cuts. This opens a possibility to study the $γγ\to p \bar{p}$ process in UPC at the LHC.

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arXiv2018

Central exclusive production of $K^{+}K^{-}$ pairs in proton-proton collisions

We discuss central exclusive diffractive production of light mesons in the reactions $pp \to ppπ^{+}π^{-}$ and $pp \to ppK^{+}K^{-}$. The calculation is based on a tensor-pomeron approach. We include a purely diffractive dipion continuum, and the scalar $f_{0}(980)$, $f_{0}(1500)$, $f_{0}(1710)$ and tensor $f_{2}(1270)$, $f'_{2}(1525)$ resonances decaying into pseudoscalar meson pairs. We include also photoproduction mechanisms for the nonresonant (Drell-Söding) and the $ϕ(1020)$ resonance contributions. The theoretical results are compared with existing CDF experimental data and predictions for being carried out LHC experiments are presented. The distributions in dimeson invariant mass and in a special "glueball filter variable" including the interference effects of resonance and dimeson continuum are presented.

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arXiv2018

Towards a complete study of central exclusive production of $K^{+}K^{-}$ pairs in proton-proton collisions within the tensor Pomeron approach

We present a study of the central exclusive production of the $K^{+} K^{-}$ pairs in proton-proton collisions at high energies. We consider diffractive mechanisms including the $K^{+} K^{-}$ continuum, the dominant scalar $f_{0}(980)$, $f_{0}(1500)$, $f_{0}(1710)$ and tensor $f_{2}(1270)$, $f'_{2}(1525)$ resonances decaying into the $K^{+} K^{-}$ pairs. We include also photoproduction mechanisms for the non-resonant (Drell-Söding) and the $ϕ(1020)$ resonance contributions. The theoretical results are calculated within the tensor-pomeron approach including both pomeron and reggeon exchanges. Predictions for planned or current experiments at RHIC and LHC are presented. We discuss the influence of the experimental cuts on the integrated cross section and on various differential distributions for outgoing particles. The distributions in two-kaon invariant mass, in a special `glueball filter variable', as well as examples of angular distributions in the $K^{+}K^{-}$ rest frame are presented. We compare the $ϕ(1020)$ and continuum photoproduction contributions to the $f_{0}(980)$ and continuum diffractive contributions and discuss whether the $ϕ(1020)$ resonance could be extracted experimentally. For the determination of some model parameters we also include a discussion of $K$-nucleon scattering, in particular total cross sections, and of $ϕ(1020)$ photoproduction.

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arXiv2018

Central exclusive diffractive production of $p \bar{p}$ pairs in proton-proton collisions at high energies

We consider the central exclusive production of the $p\bar{p}$ in the continuum and via resonances in proton-proton collisions at high energies. We discuss the diffractive mechanism calculated within the tensor-pomeron approach including pomeron, odderon, and reggeon exchanges. The theoretical results are discussed in the context of existing WA102 and ISR experimental data and predictions for planned or current experiments at the RHIC and the LHC are presented. The distribution in ${\rm y}_{diff}$, the rapidity distance between proton and antiproton, is particularly interesting. We find a dip at ${\rm y}_{diff} = 0$ for the $p \bar{p}$ production, in contrast to the $π^{+}π^{-}$ and $K^{+}K^{-}$ production. We predict also the $p \bar{p}$ invariant mass distribution to be less steep than for the pairs of pseudoscalar mesons. We argue that these specific differences for the $p \bar{p}$ production with respect to the pseudoscalar meson pair production can be attributed to the proper treatment of the spin of produced particles. We discuss asymmetries that are due to the interference of $C=+1$ and $C=-1$ amplitudes of $p \bar{p}$ production. We have also calculated the cross section for the $pp \to pp Λ\overlineΛ$ reaction. Here, the cross section is smaller but the characteristic feature for $dσ/d{\rm y}_{diff}$ is predicted to be similar to $p \bar{p}$ production. The presence of resonances in the $p \bar p$ channel may destroy the dip at ${\rm y}_{diff} = 0$. This opens the possibility to study diffractively produced resonances. We discuss the observables suited for this purpose.

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arXiv2017

From the $γγ\to p \bar{p}$ reaction to the production of $p \bar{p}$ pairs in ultraperipheral ultrarelativistic heavy-ion collisions at the LHC

In this paper we consider the production of proton-antiproton pairs in two-photon interactions in electron-positron and heavy-ion collisions. We try to understand the dependence of the total cross section on the photon-photon c.m. energy as well as corresponding angular distributions measured by the Belle Collaboration for the $γγ\to p \bar{p}$ process. To understand the Belle data we include the proton-exchange, the $f_2(1270)$ and $f_2(1950)$ $s$-channel exchanges, as well as the hand-bag mechanism. The helicity amplitudes for the $γγ\to f_{2} \to p \bar{p}$ process are written explicitly based on a Lagrangian approach. The parameters of vertex form factors are adjusted to the Belle data. Having described the angular distributions for the $γγ\to p \bar{p}$ process we present first predictions for the ultraperipheral, ultrarelativistic, heavy-ion reaction $^{208}\!Pb \, ^{208}\!Pb \to$ $^{208}\!Pb \, ^{208}\!Pb \,p \bar{p}$. Both, the total cross section and several differential distributions for experimental cuts corresponding to the ALICE, ATLAS, CMS, and LHCb experiments are presented. We find the total cross section 100 $μ$b for the ALICE cuts, 160 $μ$b for the ATLAS cuts, 500 $μ$b for the CMS cuts, and 104 $μ$b taking into account the LHCb cuts. This opens a possibility to study the $γγ\to p \bar{p}$ process at the LHC.

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