Sticky Hadrons

Hadrons are beautiful - their structure remains mysterious and enigmatic !

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Hadron Physics in a Nutshell ! . Almost everybody knows electric charge, but what the hell is hypercharge? This is not a new energy for alien ships or an additional mode for your e-car. It was invented to have some handy order parameter for the many hadrons which have been discovered until the 1960s. . It started with the Gell-Mann-Nishijima formula, which related the charge of the object (like proton and neutron) to other observed quantum numbers like strangeness, thus the electric charge was Q = I3+½(B+S) ⚡️with B being the baryon number (counts how many baryons are present) and S the strangeness of the object and I3 its Isospin-parameter. To make this formula simpler, the hypercharge 🔗 Y=B+S accounts for everything except Isospin and Q became I3+½Y. . Over the years the quark model was invented and other quarks have been discovered with respective quantum numbers like charmness (C), bottomness (B') or topness (T'). Thus the formula for the hypercharge evolved to 🔗 Y=B+S+C+B'+T'. But since e.g. strangeness was identified with the respective number of (anti-)strangequarks, the full formula can also be written in terms of the number of quarks of each species 🔗 Y=1/3u+1/3d-2/3s+4/3c-2/3b+4/3t (with anti-quarks being counted antipodal). 👍🏻 . But beware! This refers to the strong hypercharge, don't mess it up with the weak hypercharge which includes also lepton numbers ! 😉

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The Bag Model was one of the first models for hadrons to incorporate basic features of the field theory of strong interactions and not only constituents within a certain potential. A design feature of the model was to implement confinement as a construction element from the start. . To understand the concept of the Bag Model one has to go back to the theory of electric and magnetic fields. These phenomena have been elegantly condensed in 4 simple formulae, Maxwell's equations. This has been generalized to the subatomic world and electro dynamics evolved to quantum electro dynamics (QED). . The scientists at MIT went the other way round: starting with quantum chromo dynamics (QCD) of quarks and gluons, they formulated a model with color electric and color magnetic fields. Maxwell's electro magnetic fields cannot escape from a closed cavity if the cavity is surrounded by a perfect conductor. Using this analogy, the vacuum of QCD outside of the hadron is designed in the bag model in a similar way like the electro magnetic conductor and you get confinement for free, while the quarks move freely within the bag. An elegant solution. . Within this model, many low lying states and also glueballs have been calculated. While the mesons came out quite ok, the calculation of the mass of glueballs seems to be way off. . References and further reading: . A. Chodos et al., Phys.Rev.D 9 (1974) 3471-3495

Nathan Isgur was one of the most influential hadron scientists and apart from his great original work, his legacy ais the crowd if many excellent PhD students from his time in Toronto, which are now shaping the field of theoretical hadronic physics all over the world: Simon Capstick, Kevin Dooley, Paul Geiger, Stephen Godfrey, Gregory Grondin, Richard Kokoski, Roman Koniuk, David Kotchan, Kim Maltman, Colin Morningstar, Catherine Reader, Eric Swanson, and John Weinstein. . Very early he embarked on the properties of hadrons and the consequences of quarks and gluons as kind of constituents of the very hadrons. Already 1975 he published on the mixing angle of pseudo-scalar mesons due to annihilation into gluons and explained why the pseudoscalar mixing angle should be -10 degrees, like we see it in nature. . He was always full of ideas and visions. For many he his well known for the flux-tube model, a kind of model which is inspired by Lattice Gauge Theory, but much simpler which led to "simple" formulas for the excitation spectra of exotic particles like hybrids (1985 with J. Paton). The predictions from this model triggered a lot of new experiments. Others may know him because of his invention of the heavy quark symmetry of QCD (1989 with M. Wise). . Something many people don't know is that originally he started in Caltech by studying biology but changed later and made his BSc in physics. He had to leave the US after denying the draft notice for the Vietnam war and made his PhD in Toronto and became a Canadian citizen eventually. . 1990 he returned to the US and became chief scientist of Jefferson Lab and unfortunately died in 2001 prematurely at the age of 54. . References and further reading: . Wikipedia (english) Jefferson Lab archives University of Toronto archives

E852 was an experiment at @brookhavenlab to search for hybrid particles. . What does hybrid particle mean? Hybrid comes from the greek work ὕβρις (hýbris) which means e.g., arrogance or presumption. The modern meaning is a little different and means something which is mixed. This is unfortunately misleading. Hadrons contain a bunch of quarks (the constituents, like bricks) which are held together by gluons (like cement). In hadron spectroscopy a hybrid is a hadron where the gluons behave differently than in conventional hadrons. If we compare it to the cement in a wall, it's like if the cement hardened with some tension and this internal stress alters the properties of the wall. . E852 was the successor of E818 which has had a similar focus and already some interesting findings. Both experiments have been performed at the Multi Particle Spectrometer (MPS-II) (see photo and sketch), but E852 aimed also at neutral particles as well. . One of the important results was the observation of the so called pi1(1600) (see graph, denoted with P+ in the original paper). It appears as a peak (like a resonance curve similar to a damped electric circuit) in one drawing and as an interference pattern in another (like interfering sound waves). . Up to know it's still unclear what the nature of the pi1(1600) is. A lot of speculations have been made and being a hybrid is one of them, but there are many more. Only by finding more similar particles, it will be possible to make an undoubted assignment. . References and further reading: . E852 Collaboration: E.I.Ivanov et al., Phys.Rev.Lett.86(2001)3977 E852 Collaboration: G.S. Adams et al., J.Phys.Conf.Ser.9(2005)

💡Did you know? . It's common knowledge in the particle physics community that the J/psi - a bound state of a charm and an anti-charm quark - has been discovered by the groups of Sam Ting and Burton Richter in 1974 in different experiments at BNL and SLAC respectively. They both received the Nobel Prize for this in 1976 🏅. This you'll find in any text book. Also the story about the strange naming is an anecdote which is appearing frequently. . What you rarely find and only as a side remark is that the the J/psi could have been discovered much earlier. This would have pretty much avoided the quarrel about the name 😉. . A team around Jim Christenson and Leon Lederman performed an experiment aiming at neutral vector bosons and Drell-Yan processes in the 1960s looking for massive muon-pair production in the collision of protons and heavy atomic nuclei. They found a "shoulder" in the mass distribution at the J/psi position already in 1968 which was interpreted by theorists differently than being a new particle. A misinterpretation and a truely missed opportunity 😢. . The second picture shows the apparatus which measured the muon pairs coming out of the p+Uranium collision. The experiment was performed at the Alternate Gradient Synchrotron (AGS) of the Brookhaven National Laboratory (BNL). . 📓 References and further reading : . J.H. Christenson, G.S. Hicks, L.M. Lederman, P.J. Limon, and B.G. Pope, Phys.Rev.Lett. 25(1970)1523 and Phys.Rev.D 8 (1972) 2016-2034. FNAL E-288: S. Herb et al., Phys.Rev.Lett. 39(1977)252 . #hadronphysics #hadronsspectroscopy #experimentalphysics #missedopportunity #brookhavennationallaboratory

1977: DESY (Deutsches Elektronensynchrotron), Hamburg, Germany - The DASP (DESY Double Arm Spectrometer, see fig.) reports the evidence for something which they believe is the bound state of a charm and an anti-strange quark (charge conjugates included 😉). . In the inclusive eta-production (that means, that you sum up everything where an eta-meson is present) in the annihilation of electrons and positrons at DORIS, an excess was seen for particular energies. From this they concluded the evidence for the F-meson at about (2,030±60) MeV/c^2 and the F*-Meson at about (2,140±60) MeV/c^2. . It took a while for a really convincing observation, since the F-meson was difficult to detect: Finally, the CLEO experiment at the Cornell Electron Storage Ring (CESR) (see fig.) found a doubtless excess in the decay of it to a phi-meson and a pion at about 1970 MeV/c^2. . After exhausting the greek alphabet, a lot of mesons got capital latin letters like A, B, D, E ... thus F seemed to be a natural choice. In 1985 the whole naming scheme was revisited and names have been changed to reflect more the basic structure and properties of the particle. . Thus, these particles are known today as Ds± and Ds*± and their mass is pretty well known. They are listed as (1,968.34±0.07) MeV/c^2 and (2,112.2±0.4) MeV/c^2 respectively. . References and further reading . R.Brandelik et al., Phys.Lett 70B(1977)132 J.L. Rosner, "New Particles", A.Ass.of Physics Teachers, Stony Brook (1981)74 J.M.Yelton, Nature, 306(1983)223

In the second half of the last century an incredible number of new subatomic particles have been discovered which almost exhausted the greek alphabet 😉 ... δ ε η θ ι λ π ρ σ τ φ χ ψ ω Δ Λ Ω Σ became sisters and brothers of the already known proton and neutron. This triggered a gold stampede to understand the structure and dynamics of these particles which were now called HADRONS. Finally, constituents - the quarks - have been postulated and a corresponding theory has been formulated. In this framework protons and similar particles are made out of three quarks, while pions and pion-like particles are made out of a quark and an antiquark ⚛️. . An important consequence in order to get this all together, was to invent something similar to photons which glues the constituents together - the GLUONS 🪡. At a conference in 1972 in Chicago 🏙, Harald Fritzsch and Murray Gell-Mann speculated in a side-remark, that quarks may also be arranged in other configurations than the most simple ones and that one even could imagine particles which do not contain quarks at all, thus consisting entirely of gluons. . This is like removing bricks 🧱 in a wall and you are left just with the cement. It's not as stable as before, but it's possible 😉. . This was the starting signal 💥 for the search for the so called GLUEBALLS 👽. A lot of models have been formulated and a many experiments have been performed. But even 50 years later, the original speculation is neither proved nor disproved and the quest remains a driving force for hadron physics. . References: . H.Fritzsch and M.Gell-Mann proposed at XVI International Conference on High Energy Physics, (Proc. Vol. 2, p.135, Chicago, 1972) . Graphics taken from: . C.Yuan and S.Olsen on the BES3 physics programme arXiv:2001.01164v1 C.Morningstar and M.Pearden, Phys.Rev.D60:034509,1999

Today I want to talk about a scientist which inspired me most in my PhD years and who can be regarded as one of the fathers of our field of hadron physics: Lucien Montanet (1930-2003). I remember one famous sentence of this extremely cordial and modest person: "may be I talk too much". Everybody who knew him, knew this sentence 😉. But in contrast to his statement, he was so full of knowledge and memories, that everybody hang on his lips and was eager to hear and learn from him and he never could speak too much. As a young graduate from the Arts et Métiers engineering school in Paris, Lucien Montanet extended his knowledge of physics at Paris University 🇫🇷. Coming from the nuclear reactor ZOE in France, Lucien was one of the first physicists to settle at CERN, as early as 1957, even before any offices had been built on the site. He co-signed the discovery of the first meson resonance found at CERN and in Europe 🇪🇺, the E meson. This was the start of a long career devoted to meson and baryon spectroscopy, a field in which he became one of the leading specialists. In his experimental activities, he initiated and coordinated several experiments of central importance at @cern . One of the most illustrious was the EHS (European Hybrid Spectrometer). He was a key member of the Particle Data Group 🌍, organising and leading numerous workshops and conferences on hadron spectroscopy. In 1973 he became the editor of 'Physics Letters' and continued playing this role competently and efficiently even after his retirement in 1995. This enabled him to remain in close contact with the high-energy physics community and made him a well-known figure for the younger generations. He was adept at attracting young physicists and infusing them with his enthusiasm and experience. Apart from the many skills he had, this enthusiasm was probably the most influential and remains a lasting memory to a whole generation of hadron scientists who is now building up on his inheritance by creating new infrastructures, breaking new frontiers and finding new insights in the subatomic world.

ASTERIX was an experiment at LEAR at @cern in the mid 1980s. The name is a funny but superb acronym since it stands for "Antiproton STop Experiment with tRigger on Initial X-rays" 😉 . Designed to study the annihilation of protons and antiprotons, it was constructed in a similar fashion as many other detectors for central kinematics at this time. Based on a solenoidal magnet setup with mostly gaseous and scintillating elements, the unique selling point was a central low-density drift-chamber (XDC, see fig.) to trigger on atomic X-rays ⚡️ from the atomic protonium cascade for a particular pre-selection of data 📀. . The most important result was the discovery of a new state, the AX(1565) (see fig. 📈📉) nowadays listed as the f2(1565) in the review of particle properties of the particle data group. Albeit discovered in 1989, the nature and internal structure of this object remains unresolved 🔮. . References and further reading: . B.May et al. ZPhys. 1990(C46)191 S.Ahmad et al., NIM 1989(A286)76 Proposal CERN/PSCC/80-101 CERN Photo Archive . #cern #lear #asterix #axparticle #f2 #tensor #isoscalar #hadronspectroscopy #hadronphysics #hadronexperiment #physics #particlephysics #hadron #baryonium #protonium #quarks #gluons #baryon #meson #exotichadrons #exotics #cern #lear

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