Pomeron-Odderon interference in production of pi^ + pi^- pairs in ultraperipheral collisions
B. Pire, L. Szymanowski, F. Schwennsen, S. Wallon
备注:
5 pages, 3 figures; To appear in the proceedings of Diffraction 2008: International Workshop on Diffraction in High-Energy Physics, La Londe-les-Maures, France, September 9-14, 2008
In this contribution we discuss the production of two pion pairs in high energy photon collisions as they can be produced in ultraperipheral collisions at hadron colliders such as the Tevatron, RHIC or LHC. We find that charge asymmetries may reveal the existence of the perturbative Odderon.
The heavy quark production in ultraperipheral heavy ion collisions is investigated, in particular we focus on the results from the coherent interactions given by the two-photon process. One addresses the heavy quark total cross sections at photon level considering the saturation model and the BFKL dynamics in the color dipole picture. The corresponding cross sections at nuclear level are presented. It is verified that the QCD dynamics implies an enhancement of the cross section in comparison with previous calculations.
We propose the one-dimensional reggeon theory describing local pomerons and odderons. It generalizes the well-known one-dimensional theory of pomerons (the Gribov model) and includes only triple interaction vertices. The proposed theory is studied by numerical methods: the one-particle pomeron and odderon propagators and the pA amplitude are found as functions of rapidity by integrating the evolution equation.
We calculate the photonuclear production of heavy quarks in ultraperipheral heavy ion collisions. The integrated cross section and the rapidity distribution are computed employing sound high energy QCD formalisms as the collinear and semihard approaches as well as the saturation model. In particular, the color glass condensate (CGC) formalism is also considered using a simple phenomenological parameterization for the color field correlator in the medium, which allow us to obtain more reliable estimates for charm and bottom production at LHC energies.
We predict glueball/oddball resonances lying on the pomeron/odderon trajectories. A simple new form of the trajectories, with threshold and asymptotic behaviour required by analyticity and unitarity, is proposed. The parameters of these (pomeron and odderon) trajectories are fitted to the data on high-energy elastic proton-proton scattering. The fitted trajectories are extrapolated to the resonance region to predict masses and widths of glueballs and oddballs. The (pomeron and odderon) trajectories may be used to calculate processes of central exclusive diffraction (CED).
We study Pomeron-Odderon interference effects giving rise to charge and single-spin asymmetries in diffractive electroproduction of a $π^+ π^-$ pair. We calculate these asymmetries in the Born approximation of QCD in a kinematical domain accessible to HERA experiments.
We suggest to measure Pomeron phase and discover odderon via the measurement of charge asymmetry of pions in the diffractive processes $ep\to eπ^+π^- p$, $eA\to eπ^+π^- A$ and in the processes $AA\to AAπ^+π^-$ with two rapidity gaps.
We review the results of our studies on the charge and the spin asymmetries in the electroproduction of $π^+ π^-$ which are the observables sensitive to the Pomeron-Odderon interference.
In the QCD the small~$x$ evolution of the interacting pomerons and odderons is studied with all angular momenta $l$ taken into account. The resulting system of coupled nonlinear evolution equations is formulated in the momentum space and solved numerically. Excellent convergence in $l$ is observed. Also it is found that states with $l>1$ play an important role and substantially reduce the basic pomeron state at large rapidities
We explore the possibility of observing Odderon exchange in proton--ion collisions at the LHC, via the ultraperipheral photoproduction of C-even mesons. As well as the signal, we consider in detail the principle backgrounds, due to QCD--initiated production (i.e. double Pomeron exchange) and $γγ$ fusion. We find that while the photon--initiated background is dominant at very small momentum transfer, this can be effectively removed by placing a reasonable cut on the transverse momentum of the produced meson. In the case of QCD--initiated production, we show this is in general strongly suppresse…
On March 19-21, 1998, a workshop devoted to questions of the pomeron and the odderon in high energy scattering was held in Heidelberg. This note gives a personal account of some of the issues discussed at this workshop. Of course, misconceptions and misunderstandings are to be blamed on us, not on the other participants of the workshop. A puzzle of odderon physics is identified and a convenient reaction for its experimental study is discussed.
QCD predicts the existence of the perturbative Pomeron and of the Odderon. But both of them appear to be rather difficult to observe experimentally. We describe the experimental status of these two objects, discuss possible reasons for their elusive behavior, and point out promising search strategies.
We study Pomeron-Odderon interference effects giving rise to charge and single-spin asymmetries in diffractive electroproduction of a $π^+ π^-$ pair. The final state interactions and the role of $f_0$ meson are discussed. The absence of $f_0$ signal in the charge asymmetry observed by HERMES may be due to the smalness of its quark component.
The small x evolution of the QCD pomeron and the QCD odderon is investigated in the mean field limit of the Color Glass Condensate. The resulting system of coupled nonlinear evolution equations is transformed to the momentum space and analyzed at a very small momentum transfer. The main properties of the C-even and C-odd dipole densities in momentum space are obtained analytically. The critical scaling dimension is found for the odderon and the universal asymptotic behavior of the solutions is determined for small and large gluon momenta. We find that the same saturation scale characterizes bo…
We consider the first LHC data for pp collisions in the framework of Regge theory. The integral cross sections and inclusive densities of secondaries are determined by the Pomeron exchange, and we present the corresponding predictions for them. The first measurements of inclusive densities in midrapidity region are in agreement with these predictions. The possible contribution of Odderon (Reggeon with alpha(Odd)(0) ~ 1 and negative signature) exchange to the differences in the inclusive spectra of particle and antiparticle in the central region could be significant at LHC energies. The first d…
We discuss the production of two pion pairs in photon collisions at high energies as it can take place in ultraperipheral collisions at hadron colliders such as the LHC. We calculate the according matrix elements in kT factorization and discuss the possibility to reveal the existence of the perturbative Odderon by charge asymmetries.
We show that the asymmetry in the fractional energy of charm versus anticharm jets produced in high energy diffractive photoproduction is sensitive to the interference of the Odderon $(C = -)$ and Pomeron $(C = +)$ exchange amplitudes in QCD. We predict the dynamical shape of the asymmetry in a simple model and estimate its magnitude to be of the order 15% using an Odderon coupling to the proton which saturates constraints from proton-proton vs. proton-antiproton elastic scattering. Measurements of this asymmetry at HERA could provide firm experimental evidence for the presence of Odderon exch…
We introduce a new model of near-forward elastic proton-(anti)proton scattering at high energy based on the modern formulation of Pomeron and Odderon in terms of Wilson lines and generalized TMDs (GTMDs). We compute the helicity-dependent elastic amplitudes $ϕ_{1,2,3,4,5}$ in this model and study their energy dependence from the nonlinear small-$x$ evolution equations. While both Pomeron and Odderon contribute to helicity-flip processes in general, in the forward limit $t=0$ only the double helicity-flip amplitude $ϕ_2$, dominated by the spin-dependent Odderon, survives. This may affect the ex…
In the quest for an effective field theory which could help to understand some non perturbative feature of the QCD in the Regge limit, we consider a Reggeon Field Theory (RFT) for both Pomeron and Odderon interactions and perform an analysys of the critical theory using functional renormalization group techniques, unveiling a novel symmetry structure.
We calculate the contribution arising from nonperturbative quark-gluon chromomagnetic interaction to the high energy total quark-quark cross section and to gluon distributions in nucleon. The estimation obtained within the instanton model of QCD vacuum leads to the conclusion that this type of interaction gives the dominating contribution to the Pomeron coupling with the light quarks and to gluon distribution in light hadrons at small virtualities of quarks and gluons. We argue that the Odderon, which is the $P=C=-1$ partner of Pomeron, is governed by the spin-flip component related to nonpert…
The contribution of the QCD Pomeron to the process AA -> AA J/Psi J/Psi is discussed. We focus on the photon-photon collision, with the quasi-real photon coming from the Weizsacker - Williams spectrum of the nuclei. We calculate the cross section for this process considering the solution of the LLA BFKL equation at zero momentum transfer using a small-t approximation for the differential cross section of the subprocess. Furthermore, the impact of non-leading corrections to the BFKL equation is also analyzed. In both cases the cross section is found to increase with the energy, predicting consi…
The interference of Pomeron and Odderon amplitudes gives rise to a charge asymmetry in the diffractive electroproduction of a pi+pi- -pair. We calculate this charge asymmetry in perturbative QCD in the Born approximation and on the leading Q^2-level. The numerical evaluation shows a sizeable asymmetry in an experimentally accessible kinematical region. We find a characteristic m_{pi+pi} -dependence mainly dictated by the relevant Breit-Wigner-amplitudes and the corresponding phase-shifts.
A model for soft high-energy scattering is developed. The model is formulated in terms of effective propagators and vertices for the exchange objects: the pomeron, the odderon, and the reggeons. The vertices are required to respect standard rules of QFT. The propagators are constructed taking into account the crossing properties of amplitudes in QFT and the power-law ansaetze from the Regge model. We propose to describe the pomeron as an effective spin 2 exchange. This tensor pomeron gives, at high energies, the same results for the p-p and p-pbar elastic amplitudes as the standard Donnachie-L…
We discuss how exact conformal invariance in the strong coupling leads naturally through AdS/CFT correspondence to a systematic expansion for the Pomeron and Odderon intercepts in power of $λ^{-1/2}$, with $λ=g^2N_c$ the 't Hooft coupling. We also point out the importance of confinement for a realistic treatment of DIS in the HERA energy range.
We propose to look for the Odderon through the production of two pion pairs in photon collisions at high energies. We calculate the corresponding matrix elements in kT-factorization and discuss the possibility to reveal the existence of the perturbative Odderon by charge asymmetries, relying on models for the generalized distribution amplitudes of pi+ pi-. The application of this strategy to ultraperipheral collisions at the LHC suffers from the difficulty to trigger on interesting events and is plagued with severe background problems in p-p mode. Electron - positron colliders like ILC seem to…
In this paper one presents a naive parametrization to $pp$ and $\bar{p}p$ total cross sections. The main goal of this parametrization is to study the possible fractal structure present in the total cross section. The result of the fitting procedure shows two different fractal dimensions: a negative (low-energies) and a positive (high-energies). The negative fractal dimension represents the emptiness of the total cross section structure and the positive represents the filling up process with the energy increase. Hence, the total cross section presents a multifractal behavior. At low-energies, t…
In this work the double vector meson production in ultraperipheral heavy ion collisions is investigated within the BFKL approach. The integrated cross sections and event rates for the processes AA --> V1 V2 AA (V_i = rho, omega, phi, J/Psi, Upsilon) are computed and theoretical estimates for scattering on both light and heavy nuclei are given for energies of RHIC and LHC.
The model of elastic scattering amplitudes dominated by the triple (at $t=0$) pomeron pole suggested earlier is modified to confront to existing experimental data on $pp$ and $\bar pp$ total and differential cross sections at $\sqrt{s}\geq 19$ GeV and $|t|\leq 14.2$ GeV$^{2}$ including the newest TOTEM data. Predictions for the future TOTEM measurements at 13 and 14 TeV are given.
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 result…
In this paper we extend our recent non perturbative functional renormalization group analysis of Reggeon Field Theory to the interactions of Pomeron and Odderon fields. We establish the existence of a fixed point and its universal properties, which exhibits a novel symmetry structure in the space of Odderon-Pomeron interactions. As in our previous analysis, this part of our program aims at the investigation of the IR limit of reggeon field theory (the limit of high energies and large transverse distances). It should be seen in the broader context of trying to connect the nonperturbative infrar…
The photonuclear production of vector mesons in ultraperipheral heavy ion collisions is investigated within the QCD color dipole picture, with particular emphasis on the saturation model. The integrated cross section and the rapidity distribution for the A + A --> V + A + A (V = rho, omega, phi, J/Psi) process are computed and theoretical estimates for scattering on both light and heavy nuclei are given for energies of RHIC and LHC. A comparison with the recent STAR data on coherent production of rho mesons is also presented. Furthermore, we calculate the photoproduction of vector mesons in pr…
We study the rapidity dependence of the cross section on the rapidity of the central exclusive production cross sections of C-even mesons in $pA$ and $AA$ collisions, where $A$ is a heavy ion. We observe qualitatively different behaviour of the contributions arising from $γ$-Odderon and Pomeron-Pomeron fusion mechanisms. This can be used to extract the Odderon signal from the events of $f_2$ mesons exclusively produced in the forward region. Estimates, obtained using expected values of the Odderon cross section, indicate that the $γ$-Odderon contribution may exceed by a few times the Pomeron-i…
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 pro…
Glueball masses with J<=7 are computed both for C=+1 and C=-1 using the string Hamiltonian derived in the framework of the Vacuum Correlator Method. No fitting parameters are used, and masses are expressed in terms of string tension $σ$ and effective value of $α_s$. We extend the calculations done for J<=3 using the same Hamiltonian, which provided glueball masses in good agreement with existing lattice data, to higher mass states. It is shown that 3^{--}, 5^{--} and 7^{--} states lie on the odderon trajectories with the intercept around or below 0.14. Another odderon trajectory with 3g glueba…
From the perspective of AdS/CFT the Pomeron is identified with a Reggeized Graviton, while the Odderons correspond to Reggeized anti-symmetric $AdS_5$ Kalb-Ramond tensor-fields. In this paper, we consider the strong coupling expansion of the dimension of the leading twist operators dual to these Regge trajectories, $Δ(j)$, to determine its analytic continuation in $j$ beyond the diffusion limit. In particular, we compute the strong coupling expansion of the intercept to order $λ^{-3}$, where $λ$ is the t'Hooft coupling, for both the Pomeron, which is $C=+1$ crossing-even, and the "Odderons", w…
We consider the reaction (gamma p) to (pi+ pi- p) at high energies. Our description includes dipion production via the resonances rho, omega, rho-prime and f2, and via non-resonant mechanisms. The calculation is based on a model of high energy scattering with the exchanges of photon, pomeron, odderon and reggeons. The pomeron and the C=+1 reggeons are described as effective tensor exchanges, the odderon and the C=-1 reggeons as effective vector exchanges. We obtain a gauge-invariant version of the Drell-Soeding mechanism which produces the skewing of the rho-meson shape. Starting from the expl…
Phenomenological studies of odderon effects are shortly reviewed. Special emphasis is devoted to a recent study of the exclusive production of J/psi or Upsilon in pp and bar p p collisions, where the meson emerges from the pomeron--odderon and the pomeron--photon fusion.
We estimate the production of two meson pairs in high energy photon photon collisions produced in ultraperipheral collisions at LHC. We show that the study of charge asymmetries may reveal the existence of the perturbative Odderon and discuss the concrete event rates expected at the LHC. Sizable rates and asymmetries are expected in the case of proton-proton collisions and medium values of gamma-gamma energies \sqrt{s_{γγ}} \approx 20GeV. Proton-proton collisions will benefit from a high rate due to a large effective gamma-gamma luminosity and ion-ion collisions with a somewhat lower rate from…
The transverse single-spin asymmetry A_N observed in high energy proton-proton collisions p^\uparrow p \to pi X has been found to increase with the momentum fraction x_F of the pion up to the largest measured x_F \sim 0.8, where A_N \simeq 40%. We consider the possibility that the asymmetry is due to a non-perturbatively generated spin-flip coupling in soft rescattering on the target proton. We demonstrate using perturbation theory that a non-vanishing asymmetry can be generated through interference between exchanges of even and odd charge conjugation provided both helicity flip and non-flip c…
We study Pomeron-Odderon interference effects giving rise to charge and single-spin asymmetries in diffractive electroproduction of a pi+ pi- pair. We calculate these asymmetries originating from both longitudinal and transverse polarizations of the virtual photon in the framework of QCD and in the Born approximation, in a kinematical domain accessible to HERA experiments. We predict a sizable charge asymmetry with a characteristic dependence on the invariant mass of the pi+ pi- pair, which makes this observable very important for establishing the magnitude of the Odderon exchange in hard proc…
We study the exclusive production of J/psi or Upsilon in pp and bar pp collisions, where the meson emerges from the pomeron--odderon and the pomeron--photon fusion. We estimate the cross sections for these processes for the kinematical conditions of the Tevatron and of the LHC.
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 $ϕϕ$ ($…
In this work we use the holographic softwall AdS/QCD model with anomalous dimension contributions coming from two different QCD beta functions to calculate the masses of higher spin glueball states for both even and odd spins and its respective Regge trajectories, related to the pomeron and the odderon, respectively. We further investigate this model taking into account dynamical corrections due to a dilaton potential consistent with Einstein equations in 5 dimensions. The results found in this work for the Regge trajectories within the anomalous softwall model with dynamical corrections are c…
In the paper we propose and solve analytically the non-linear evolution equation in the leading twist approximation for the Odderon contribution. We found three qualitative features of this solution, which differs the Odderon contribution from the Pomeron one :(i) the behaviour in the vicinity of the saturation scale cannot be derived from the linear evolution in a dramatic difference with the Pomeron case; (ii) a substantial decrease of the Odderon contribution with the energy; and (iii) the lack of geometric scaling behaviour. The two last features have been seen in numerical attempts to sol…
In diffractive hadronic scattering processes, the Pomeron trajectory, originating from Regge theory, significantly contributes to the behavior of the total and differential cross sections; the same holds for the description of the proton structure function in deep inelastic scattering. So far, the Odderon as the odd-parity partner of the Pomeron has only been observed in differences between differential cross sections for p p and p pbar scattering at low t. We investigate exclusive photoproduction of two neutral pion final states at e+e- colliders; in this reaction, Pomeron exchange is forbidd…
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 …
We study pp and p\bar p collisions which lead to the exclusive production of J/psi or Upsilon from the pomeron-odderon and the pomeron-photon fusion. We calculate scattering amplitudes of these processes in the lowest order approximation and in the framework of k_T factorization. We present estimates of cross sections for the kinematic conditions of the Tevatron and of the LHC.
By using a Regge-pole model for vector meson production (VMP), successfully describing the HERA data, we analyse the correlation between VMP cross sections in photon-induced reactions at HERA and those in ultra-peripheral collisions at the Large Hadron Collider (LHC). The rapidity distributions of proton-proton collisions at 13~TeV and lead-lead collisions at 2.76 and 5.02 TeV are investigated. The transverse momentum distribution in nuclear coherent vector meson production is also addressed. Predictions for future experiments on production of $J/ψ$ and $ψ(2S)$ are presented.
In this work we use gauge/string dualities and a dynamical model that takes into account dynamical corrections to the metric of the anti de Sitter space due to a quadratic dilaton field and calculate the masses of even and odd spin glueball states with $P=C=+1$, and $P=C=-1$, respectively. Then we construct the corresponding Regge trajectories which are associated with the pomeron for even states with $P=C=+1$, and with the odderon for odd states with $P=C=-1$. We compare our results with those coming from experimental data as well as other models.
The rates of inclusive photo- and electroproduction of the eta_c meson: gamma* + p -> eta_c + X are calculated in the triple Regge region, integrated over the diffractive mass X. For the Regge exchanges we use the hard Pomeron and Odderon, both being calculated in the framework of perturbative QCD. The integrated cross-section depends upon the coupling of the BFKL pomeron to two $C=-1$ odderons, and it is found to be of the order 60 pb for photoproduction and 1.5 pb at Q^2=25 GeV^2.
A new production mechanism for the Standard Model Higgs boson in Ultraperipheral Collisions at LHC, which allows Central Exclusive Diffractive production by Double Pomeron Exchange in photon-proton processes, is presented. The Higgs boson is centrally produced by gluon fusion with two Large Rapidity Gaps emerging in the final state, being the main experimental signature for this process. As already studied for Pomeron-Pomeron and two-photon processes, the Higgs boson photoproduction is studied within this new mechanism in proton-proton ($pp$) and proton-nucleus ($pA$) collisions, where each sy…
The Real Compton Scattering in ultraperipheral $pPb$ collisions at RHIC and LHC energies is investigated and predictions for the squared transverse momentum ($t$) and rapidity ($Y$) distributions are presented. The scattering amplitude is assumed to be given by the sum of the Reggeon and Pomeron contributions and the Pomeron one is described by the Color Dipole formalism taking into account the non - linear (saturation) effects in the QCD dynamics. We demonstrate that the behaviour of the cross sections at large -- $t$ and/or $Y$ is dominated by the Pomeron contribution and is strongly affecte…
The double meson production in ultraperipheral heavy ions collisions is addressed, focusing on the particular case of rho-J/Psi from two-photon reactions. The cross section at photon level is obtained using distinct parameterizations for the gluon distribution on the light meson. The resulting estimates for the nuclear case are presented and discussed. As a by product, we estimate the double rho production cross section using the Pomeron-exchange factorization relations.
We analyse the momentum space triple Pomeron vertex in perturbative QCD. In addition to the standard form of this vertex which is used in the context of total cross-sections at high energies and in the QCD reggeon field theory, there exists an alternative form which has to be used in the study of high-mass diffraction. We review and analyse the relation between these two versions. We discuss some implications for the BK-equation. In the second part of our paper we extend this analysis to the Pomeron-Odderon-Odderon vertex.
We reinterpret the JIMWLK/KLWMIJ evolution equation as the QCD Reggeon field theory (RFT). The basic "quantum Reggeon field" in this theory is the unitary matrix $R$ which represents the single gluon scattering matrix. We discuss the peculiarities of the Hilbert space on which the RFT Hamiltonian acts. We develop a perturbative expansion in the RFT framework, and find several eigenstates of the zeroth order Hamiltonian. The zeroth order of this perturbation preserves the number of $s$ - channel gluons. The eigenstates have a natural interpretation in terms of the $t$ - channel exchanges. Study…
One-point charge correlator as a probe for the odderon
Northwestern University(西北大学);Stony Brook University(石溪大学);University of California, Los Angeles(加州大学洛杉矶分校);Mani L. Bhaumik Institute for Theoretical Physics, University of California, Los Angeles(加州大学洛杉矶分校马尼·L·巴乌米克理论物理研究所);Center for Frontiers in Nuclear Science, Stony Brook University(石溪大学核科学前沿中心);Université Paris-Saclay(巴黎萨克雷大学);CNRS/IN2P3, IJCLab(法国国家科学研究中心/法国原子能和替代能源委员会,IJCLab);Department of Physics and Astronomy, University of California, Los Angeles(加州大学洛杉矶分校物理与天文学系)