Narrow Results

The 1992–1995 running of the Fermilab Tevatron (the so-called Run I) ended with many important physics goals accomplished, including the discovery of the top quark, and the anticipation of many further questions to be answered in the future. After many upgrades to the detector and to the accelerator complex, Run II began in April 2001. First results obtained by the Collider Detector at Fermilab (CDF) collaboration from the analysis of early Tevatron Run II data are reported here. They fall into two categories: a number of measurements have been performed with the primary goal of establishing detector performance and physics potential. Another set of measurements make use of completely new capabilities of the upgraded detector, thus allowing for competitive results with a modest amount of integrated luminosity.

The possibility of the existence of multiquark hadrons made of 4-quarks for mesons and 5-quarks for baryons was predicted by Gell-Mann [Phys. Lett. 8, 214 (1964)]. The renewed interest for the search for exotic pentaquark states was initiated by the paper by Diakonov, Petrov, and Polyakov [Z. Phys. A 359, 305 (1997)]. The 2003 experimental reports on the observation of ${\mathrm{\Theta }}^{+}$ pentaquark with $uudd\bar{s}$ quark content created a great excitement and many following experiments have reported its observation [K. H. Hicks, Eur. Phys. J. H 37, 1 (2012)]. After high-statistics experiments at JLab, which did not confirm previous claims by the CLAS collaboration, the community concluded that the ${\mathrm{\Theta }}^{+}$ pentaquark either does not exist at all or has an extremely small cross-section, making it currently unobserved. There were different review papers on this subject, questioning the existence of ${\mathrm{\Theta }}^{+}$ or trying to explain the reasons why reaching a conclusion based on production experiments is challenging [M. Amaryan, Eur. Phys. J. Plus 137, 684 (2022)]. To address the challenge of minimal 3-body final states, a formation experiment with a projectile-kaon beam is proposed. In the following, we discuss how the ${\mathrm{\Theta }}^{+}$ could be observed in the $K_{L}p\to {\mathrm{\Theta }}^{+}\to K^{+}n$ reaction in the KLF experiment at JLab [M. Amaryan et al. [KLF Collaboration], arXiv:2008.08215 [nucl-ex]].

I discuss the recent experimental and theoretical developments following the discovery of the Θ⁺ pentaquark – an exotic baryon resonance observed in the KN channel by several experiments, and an exotic Ξ*^-- (ddssū) reported by NA49 at CERN. I focus on the theoretical interpretation of the data, both in terms of quark and chiral degrees of freedom, on the predictions for related exotic states, and on several unresolved questions raised by the experimental data, such why some experiments observe the pentaquarks and other don't, the apparently extremely narrow width of the Θ⁺ and the determination of its parity. I also describe the likely properties of the proposed heavy-quark pentaquarks – an anticharmed exotic baryon and , , which are expected to be extremely narrow or even stable against strong decays. H1 recently reported observation of a possible Θ_c candidate in D*^-p channel. Pentaquarks are also being searched for in e⁺e^- annihilation and γγ collisions in the LEP data and at B-factories.

Recent lattice QCD results on charmonium properties are reviewed. I comment on molecules and hybrid states as well as on future studies of states near strong decay thresholds.

Fundamental questions concerning the strong interaction are addressed by the PANDA experiment at the future FAIR facility at GSI-Darmstadt. PANDA will be a general purpose detector of modular design optimized to measure the interaction of an antiproton beam with proton and heavy nuclear targets. The physics program at PANDA covers a wide range of topics including gluonic excitations, spectroscopy of strange and charm mesons, Drell-Yan and CP violating processes. This contribution focuses on the part of the physics program dealing with antiproton - proton annihilation.

Monojet events consist in event topologies with a high transverse momentum jet and a large amount of missing transverse energy. They constitute a promising final state that could lead to phenomena beyond the Standard Model. The theoretical models giving rise to such a signature include the pair production of Weakly Interacting Massive Particles, as dark matter candidates, and models of large extra dimensions. Monojet events can even be used to measure the Standard Model properties of Z boson decays, provided that the precision of the analysis is high enough. Such precision can be achieved by using data-driven determinations of the Standard Model contributions to monojet events. Exotics searches for new physics in such a final state have been performed at all high energy hadronic collider experiments since SPS. The ATLAS and CMS analyses with 7 TeV LHC data provide the latest and most useful information obtained from monojet studies. Their results are presented and discussed in this review paper.

This paper presents a review of the study of Exclusive Central Production at a center-of-mass energy of at the Fermilab Fixed Target program. In all reactions reviewed in this paper, protons with an energy of 800 GeV were extracted from the Tevatron accelerator at Fermilab and directed to a Liquid Hydrogen target. The states reviewed include , ϕϕ and D*^±. Partial Wave Analysis results will be presented on the light states but only the cross-section will be reviewed in the diffractive production of D*^±.

The present status and future plans of the physics program of Central Exclusive Production (CEP) at RHIC are described. The measurements are based on the detection of the forward protons from the Double Pomeron Exchange (DPE) process in the Roman Pot system and of the recoil system of charged particles from the DPE process measured in the STAR experiment's Time Projection Chamber (TPC). The data described here were taken using polarized proton–proton collisions at . The preliminary spectra of two-pion mass reconstructed by STAR TPC in central region of pseudorapidity |η| < 1, are presented. Near future plans to take data with the current system at center-of-mass energy and plans to upgrade the forward proton tagging system are presented. Also a possible addition of the RPs to the sPHENIX detector is discussed.

In this talk we review the vector-vector and vector-baryon interaction within the hidden gauge formalism in a coupled channel unitary approach. The vector-vector interaction is studied for all the sectors not studied before: C = 0; S = 1 (hidden-charm), C = 1, S = 1, and the flavor exotic sectors C = 1; S = -1, 2 and C = 2; S = 0, 1, 2. We find nine states, four of them in the C = 1; S = 1 sector, where one can be identified with the and it is interpreted as a D* K* molecular state. The other five resonances are found in the flavor exotic sectors C = 1; S = -1, C = 2; S = 0, 1 and can be considered as , D* D* and molecular states. In the case of the vector-baryon interaction we generate hidden charm resonances around 4.3 GeV, without or with strangeness, N*, Λ*. Nevertheless, there is not experimental evidence of such states yet.

Doubly charmed mesons are studied within a quark model framework. We solve the four-quark Schordinger equation by means of a variational approach by using different interacting potentials. Our results point to the existence of a stable isoscalar doubly charmed four-quark meson with quantum numbers J^P = 1⁺.

During the last three years strong experimental evidence from B and charm factories has been accumulating for the existence of exotic hadronic quarkonia, narrow resonances which cannot be made from a quark and an antiquark. Their masses and decay modes show that they contain a heavy quark-antiquark pair, but their quantum numbers are such that they must also contain a light quark-antiquark pair. The main theoretical challenge has been to determine the nature of these resonances. The main possibilities are that they are either "genuine tetraquarks", i.e. two quarks and two antiquarks within one confinement volume, or "hadronic molecules" of two heavy-light mesons. In the last few months there is more and more evidence in favor of the latter. I discuss the experimental data and its interpretation and provide fairly precise predictions for masses and quantum numbers of the additional exotic states which are naturally expected in the molecular picture but have yet to be observed. I also provide arguments in favor of the existence of an even more exotic state – a hypothetical deuteron-like bound state of two heavy baryons.

The inclusive reaction was studied at IHEP accelerator with 70 GeV proton beam using SVD-2 detector. Two different samples of , statistically independent and belonging to different phase space regions were used in the analyses and a narrow baryon resonance with the mass M = 1523 ± 2(stat.) ± 3(syst.) MeV/c² was observed in both samples of the data.

Questions to discuss:

• In which case experiment could unambiguously (dis)prove the existence of Quark-Gluon Plasma?
• If the investigations of HI collisions can clarify the confinement problem?
• Is there time enough for establishing the local thermodynamic equilibrium in the course of the HI collision?
• Can HI collisions imitate the early instants of the Universe evolution?
• Can we observe magnetic chiral effects in HI collisions?