Recently the CMS and ATLAS collaborations have found evidence for an unexpectedly large ttbar cross section in the threshold region, with an excess of the order of 5-10 pb relative to continuum perturbative calculations. A convenient approach to the theoretical study of this region, unifying the above- and below-threshold behaviour, is the non-relativistic Green's function formalism. It was first applied to top production more than 35 years ago, well before the discovery of the top. We therefore revive and dissect the old formalism, and put it back together in a more consistent form, suited for Monte Carlo event generation. Combined with some practical prescriptions, it can be applied to current conditions. As an example, the below-threshold cross section comes out to be of the order of 6.5 pb, i.e. comparable with the CMS and ATLAS numbers. The new code is publicly available in the Pythia event generator so can be used for more detailed comparisons.

The odderon is the C-odd amplitude that does not fall (or decrease very slowly) with energy. The expected amplitude is small and mainly real. Therefore, extracting it from the data on top of a much larger Ceven contribution is challenging. The only chance is to consider the very low-tregion of the Coulomb nuclear interference or the diffractive dip region. Here, we perform the analysis of elastic scattering pp and pp data at low momentum transfer t < 0.1 GeV2 within large collider energy interval \/s = 50 GeV-13 TeV in order to evaluate quantitatively the possible odderon contribution. We use the two-channel eikonal model, which naturally accounts for the screening of the odderon amplitude by the C-even (Pomeron) exchanges.

It is shown that contrary to claims of Ref. [1] the formulated in the proper physical variables Low theorem [2] for soft photon emission does not require any modification. We also reject the criticism in Ref. [1] of the papers [3,4]. At the same time, we identify some inaccuracies in Ref. [3] in the presentation of the soft-photon theorem for the case of spin-one-half particles. We also point out shortcomings in consideration of the Low theorem in the classic textbooks [5,6].

We perform the analysis of elastic scattering pp and p¯p data at low momentum transfer |t|<0.1 GeV2 within large collider energy interval s=50 GeV–13 TeV in order to evaluate quantitatively the possible Odderon contribution. We use the two-channel eikonal model, which naturally accounts for the screening of the Odderon amplitude by C-even (Pomeron) exchanges. Published by the American Physical Society 2024

It is shown that contrary to claims of Lebiedowicz et al. (Phys Rev D 105(1):014022, 2022) the formulated in the proper physical variables Low theorem (Low in Phys Rev 110(4):974–977, 1958) for soft photon emission does not require any modification. We also reject the criticism in Lebiedowicz et al. (2022) of the papers (Bell and Van Royen in Nuovo Cim A 60:62–68, 1969; Lipatov in Nucl Phys B 307:705–720, 1988). At the same time, we identify some inaccuracies in Bell and Van Royen (1969) in the presentation of the soft-photon theorem for the case of spin-one-half particles. We also point out shortcomings in consideration of the Low theorem in the classic textbooks (Berestetskii et al. in Quantum electrodynamics. Pergamon Press, Oxford, 1982; Lifshitz and Pitaevsky in Relativistic quantum theory, part 2, Fizmatlit, 2002).

We analyse the cross-section of events with Large Rapidity Gaps observed in proton–lead collisions by the CMS Collaboration ( arXiv:2301.07630 ). The role of the transverse size of elementary pN amplitude is discussed. We emphasize that the cross-section of incoming proton dissociation caused by the photon radiated off the lead ion is close to the value of dσ /dΔη ^F measured by the CMS, and it is not clear why there is no room in the data for the Pomeron-induced contribution

The goal of this whitepaper is to give a comprehensive overview of the rich field of forward physics. We discuss the occurrences of BFKL resummation effects in special final states, such as Mueller-Navelet jets, jet gap jets, and heavy quarkonium production. It further addresses TMD factorization at low x and the manifestation of a semi-hard saturation scale in (generalized) TMD PDFs. More theoretical aspects of low x physics, probes of the quark gluon plasma, as well as the possibility to use photon-hadron collisions at the LHC to constrain hadronic structure at low x, and the resulting complementarity between LHC and the EIC are also presented. We also briefly discuss diffraction at colliders as well as the possibility to explore further the electroweak theory in central exclusive events using the LHC as a photon-photon collider.

We study the possibility to observe heavy (M-inst > 60 GeV) QCD instantons at the LHC in events with one or two tagged leading protons including fast simulation of detector and pile-up effects. We show that the expected instanton signal in a single-tagged configuration is strongly affected by central detector and pile-up effects. For double-tagged approach, where larger integrated luminosities and hence larger pile-up contaminations need to be considered, the combinatorial background overwhelms the expected signal. We suggest that additional time information about tracks at central and forward rapidities would be crucial for potential improvements.

This is the Snowmass2021 Energy Frontier (EF) Beyond the Standard Model (BSM) report. It combines the EF topical group reports of EF08 (Model-specific explorations), EF09 (More general explorations), and EF10 (Dark Matter at Colliders). The report includes a general introduction to BSM motivations and the comparative prospects for proposed future experiments for a broad range of potential BSM models and signatures, including compositeness, SUSY, leptoquarks, more general new bosons and fermions, long-lived particles, dark matter, charged-lepton flavor violation, and anomaly detection.

We study the central production of QCD instantons at hadron colliders in events with two large rapidity gaps. These gaps in rapidity are formed by either Pomeron or photon exchanges or a combination of the two. The kT-factorization formalism is used to reduce the factorization scale dependence. We compute for the first time the relevant differential cross-sections for a complete set of central instanton production processes at the LHC, including gluon-induced and quark-induced amplitudes, and also show that the largest contribution comes from processes with Pomeron exchanges where a single gluon from each Pomeron couples to the instanton.

We analyse in detail the role of additional hadron–hadron interactions in elastic photon–initiated (PI) production at the LHC, both in pp and heavy ion collisions. We first demonstrate that the source of difference between our predictions and other results in the literature for PI muon pair production is dominantly due to an unphysical cut that is imposed in these latter results on the dimuon–hadron impact parameter. We in addition show that this is experimentally disfavoured by the shape of the muon kinematic distributions measured by ATLAS in ultraperipheral PbPb collisions. We then consider the theoretical uncertainty due to the survival probability for no additional hadron–hadron interactions, and in particular the role this may play in the tendency for the predicted cross sections to lie somewhat above ATLAS data on PI muon pair production, in both pp and PbPb collisions. This difference is relatively mild, at the \sim 10\% ∼10% level, and hence a very good control over the theory is clearly required. We show that this uncertainty is very small, and it is only by taking very extreme and rather unphysical variations in the modelling of the survival factor that this tension can be removed. This underlines the basic, rather model independent, point that a significant fraction of elastic PI scattering occurs for hadron–hadron impact parameters that are simply outside the range of QCD interactions, and hence this sets a lower bound on the survival factor in any physically reasonable approach. Finally, other possible origins for this discrepancy are discussed.

We outline a strategy of how to search for QCD instantons of invariant mass 20 -- 60 GeV in diffractive events in low luminosity runs at the LHC. We show that by imposing appropriate selection criteria on the final states, one can select the kinematic regime where the instanton signal exceeds the background by a factor of at least 8. In spite of the relatively strong cuts that we impose on the total transverse energy and the number of charged tracks, $\sum_i E_{T,i}>15$ GeV, $N_{\rm ch}>20$ measured within the $0<\eta<2$ interval and excluding events with high $p_{T}$ particles, the expected cross-section is sufficiently large to study the instanton production in the events with Large Rapidity Gaps at low luminosities, thus avoiding problems with pile-up. The paper also includes an updated computation of instanton cross-sections and other parameters relevant for the ongoing studies.

Gribov-90 Memorial Volume, pp. 25-28 (2021) No AccessVLADIMIR NAUMOVICH — INCREDIBLE INTUITIONM.G. RYSKIN and V.A. KHOZEM.G. RYSKINPetersburg Nuclear Physics Institute, NRC Kurchatov Institute, Gatchina, St. Petersburg, 188300, Russia and V.A. KHOZEPetersburg Nuclear Physics Institute, NRC Kurchatov Institute, Gatchina, St. Petersburg, 188300, RussiaInstitute for Particle Physics Phenomenology, University of Durham, Durham, DH1 3LE, Englandhttps://doi.org/10.1142/9789811238406_0010Cited by:0 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail Abstract: 1. It was a great privilege and luck for both of us to be the members of Gribov's theory group, to participate in his seminars and to observe how he was working and leading the discussion. Gribov felt physics as nobody else. He had an outstanding intuition not only in the field of his own interest but in any physics subject. Just two examples among many other — both on the Nobel Prize level… FiguresReferencesRelatedDetails Gribov-90 Memorial VolumeMetrics History PDF download

We consider the absorptive corrections and the rapidity gap survival factor which are necessary to provide the unitarization of the BFKL Pomeron. In particular we discuss the role of the enhanced screening diagrams.

Ultra-peripheral collisions (UPCs) involving heavy ions and protons are the energy frontier for photon-mediated interactions. UPC photons can be used for many purposes, including probing low-$x$ gluons via photoproduction of dijets and vector mesons, probes of beyond-standard-model processes, such as those enabled by light-by-light scattering, and studies of two-photon production of the Higgs.

Abstract We study the rapidity dependence 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 $$\gamma $$ γ -Odderon and Pomeron–Pomeron fusion mechanisms. This can be used to extract the Odderon signal from the events of $$f_2$$ f2 mesons exclusively produced in the forward region. Estimates, obtained using expected values of the Odderon cross section, indicate that the $$\gamma $$ γ -Odderon contribution may exceed by a few times the Pomeron-induced background in Pb–Pb collisions. Moreover, the Odderon effect can be clearly seen in terms of the asymmetry in pA and AA collisions with the beam and target reversed. It is particularly interesting to note that the asymmetry for $$\gamma $$ γ -Odderon fusion reaches its maximum value close to 1 in the forward direction, whereas the asymmetry for the Pomeron–Pomeron fusion contribution is small. The role of additional interactions of the $$f_2$$ f2 meson with nucleons in the heavy ion, and also the contributions from secondary Reggeons, are estimated. The photon–Odderon contribution has a large normalisation uncertainty but the enhanced cross-section in the forward region combined with a large asymmetry increases the chance of experimentally detecting the Odderon.

We evaluate the contribution of inelastic intermediate states (such as p → N excitations) to the phase between the one-photon-exchange and the “nuclear” high energy pp scattering amplitudes as t → 0, caused by multiphoton diagrams. It turns out to be rather small—much smaller than to have any influence on the experimental accuracy of the measurements of ρ, defined to be the ratio of the real to imaginary parts of the forward nuclear amplitude.

We present results of the updated SuperChic 3 Monte Carlo event generator for central exclusive production. This extends the previous treatment of proton-proton collisions to include heavy ion (pA and AA) beams, for both photon and QCD-initiated production, the first time such a unified treatment of exclusive processes has been presented in a single generator. To achieve this we have developed a theory of the gap survival factor in heavy ion collisions, which allows us to derive some straightforward results about the A scaling of the corresponding cross sections. We compare against the recent ATLAS and CMS measurements of light-by-light scattering at the LHC, in lead-lead collisions. We find that the background from QCD-initiated production is expected to be very small, in contrast to some earlier estimates. We also present results from new photon-initiated processes that can now be generated, namely the production of axion-like particles, monopole pairs and monopolium, top quark pair production, and the inclusion of W loops in light-by-light scattering.