{"id":7317,"date":"2020-07-13T18:29:21","date_gmt":"2020-07-13T18:29:21","guid":{"rendered":"https:\/\/www.particlebites.com\/?p=7317"},"modified":"2020-07-13T18:29:22","modified_gmt":"2020-07-13T18:29:22","slug":"charmonium-onium-a-fully-charmed-tetraquark","status":"publish","type":"post","link":"https:\/\/www.particlebites.com\/?p=7317","title":{"rendered":"Charmonium-onium: A fully charmed tetraquark"},"content":{"rendered":"

Paper Title:<\/strong> Observation of structure in the $latex J\/\\psi$-pair mass spectrum<\/p>\n

Authors:<\/strong> LHCb Collaboration<\/p>\n

Reference:<\/strong> https:\/\/arxiv.org\/pdf\/2006.16957.pdf<\/p>\n

\"\"<\/a>
My (artistic) rendition of a tetraquark. The blue and orange balls represent charm and anticharm quarks with gluons connecting all of them.<\/figcaption><\/figure>\n

The Announcement<\/u><\/p>\n

The LHCb collaboration reports a 5-sigma resonance at 6.9 GeV, consistent with predictions of a fully-charmed tetraquark state.<\/p>\n

The Background<\/u><\/p>\n

One of the ways quarks interact with each other is the strong nuclear force. This force is unlike the electroweak or gravitational forces in that the interaction strength increases with the separation between quarks, until it sharply falls off at roughly $latex 10^{-15}$m. We say that the strong force is \u201cconfined\u201d due to this sharp drop off. It is also dissimilar to the other forces in that the Strong force is non-perturbative. For perturbation theory to work well, the more complex a Feynman diagram becomes, the less it should contribute to the process. In the strong interaction though, each successive diagram contributes more than the previous one. Despite these challenges, physicists have still made sense organizing the zoo of quarks and bound states that come from particle collisions.<\/p>\n

The quark ($latex q$) model [1,2] classifies hadrons into Mesons ($latex q \\bar{q}$) and Baryons ($latex qqq$ or $latex \\bar{q}\\bar{q}\\bar{q}$). It also allows for the existence of exotic hadrons like the tetraquark ($latex qq\\bar{q}\\bar{q}$) or pentaquark ($latex qqq\\bar{q}\\bar{q}\\bar{q}$). The first evidence for an exotic hardon of this nature came in 2003 from the Belle Collaboration [1]. According to the LHCb collaboration, \u201call hadrons observed to date, including those of exotic nature, contain at most two heavy charm ($latex c$) or bottom ($latex b$) quarks, whereas many QCD-motivated phenomenological models also predict the existence of states consisting of four heavy quarks.\u201d In this paper, the LHCb reports evidence of a $latex cc\\bar{c}\\bar{c}$ state, the first fully charmed tetraquark state.<\/p>\n

The Method<\/u><\/p>\n

Perhaps the simplest way to form a fully charmed tetraquark state, $latex T_{ cc \\bar{c}\\bar{c}}$ from now on, is to form two charmonium states ($latex \u00a0J\/\\psi$) which then themselves form a bound state. This search focuses on pairs of charmonium that are produced from two separate interactions, as opposed to resonant production through a single interaction. This is advantageous because \u201cthe distribution of any di-$latex J\/\\psi$ observable can be constructed using the kinematics from single $latex J\/\\psi$ production.\u201d In other words, independent $latex J\/\\psi$ production reduces the amount of work it takes to construct observables.<\/p>\n

Once $latex J\/\\psi$ is formed, the most useful decay it undergoes is into pairs of muons with about a 6% branching ratio [2]. To form $latex J\/\\psi$ candidates, the di-muon invariant mass must be between $latex 3.0 – 3.2$GeV. To form a di-$latex J\/\\psi$ candidate, the $latex T_{ cc \\bar{c}\\bar{c}}$, all four muons are required to have originated from the same proton-proton collision point. This eliminates the possibility of associating two $latex J\/\\psi$s from two different proton collisions.<\/p>\n

The Findings<\/u><\/p>\n

When the dust settles, the LHCb finds a $latex 5-\\sigma$ resonance at $latex m_{\\text{di}- J\/\\psi} = 6905 \\pm 11 \\pm 7$ MeV with a width of $latex \\Gamma = 80 \\pm 19 \\pm 33 $ MeV. This resonance is just above twice the $latex J\/\\psi$ mass.<\/p>\n

References<\/u><\/p>\n

[1] – An $latex SU3$<\/span><\/span><\/span><\/span><\/span> model for strong interaction symmetry and its breaking<\/a>.<\/p>\n

[2] – A schematic model of baryons and mesons<\/span><\/a>.<\/p>\n

[3] –\u00a0Observation of a narrow charmonium-like state in exclusive $latex B^+ \\rightarrow K^+ \\pi^+ \\pi^- J\/\\psi$ decays<\/a>.<\/p>\n

[4] – http:\/\/pdg.lbl.gov\/2010\/listings\/rpp2010-list-J-psi-1S.pdf<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"

Paper Title: Observation of structure in the $latex J\/\\psi$-pair mass spectrum Authors: LHCb Collaboration Reference: https:\/\/arxiv.org\/pdf\/2006.16957.pdf The Announcement The LHCb collaboration reports a 5-sigma resonance at 6.9 GeV, consistent with predictions of a fully-charmed tetraquark state. The Background One of the ways quarks interact with each other is the strong nuclear force. This force is … <\/p>\n

Continue reading “Charmonium-onium: A fully charmed tetraquark”<\/span><\/a><\/p>\n","protected":false},"author":28,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-7317","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/www.particlebites.com\/index.php?rest_route=\/wp\/v2\/posts\/7317","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.particlebites.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.particlebites.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.particlebites.com\/index.php?rest_route=\/wp\/v2\/users\/28"}],"replies":[{"embeddable":true,"href":"https:\/\/www.particlebites.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=7317"}],"version-history":[{"count":11,"href":"https:\/\/www.particlebites.com\/index.php?rest_route=\/wp\/v2\/posts\/7317\/revisions"}],"predecessor-version":[{"id":7329,"href":"https:\/\/www.particlebites.com\/index.php?rest_route=\/wp\/v2\/posts\/7317\/revisions\/7329"}],"wp:attachment":[{"href":"https:\/\/www.particlebites.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=7317"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.particlebites.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=7317"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.particlebites.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=7317"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}