1. 媒體來源： CERN 2.完整新聞標題： The LHCb experiment is charmed to announce observation of a new particle with two heavy quarks 3. 完整新聞內容： Geneva,6 July 2017. Today at EPS Conference on High Energy Physics in Venice, the LHCb experiment at CERN's Large Hadron Collider has reported the ++ ++ observation of Ξcc (Xicc ) a new particle containing two charm quarks and one up quark. The existence of this particle from the baryon family was expected by current theories, but physicists have been looking for such baryons with two heavy quarks for many years. The mass of the newly identified particle is about 3621 Mev,which is almost four times heavier than the most familiar baryon,the proton,a property that arises from its doubly charmed quark content. It is the first time that such a particle has been unambigulusly detected. Nearly all the matter that we see around us is made of baryons, which are common particles composed of three quarks, the best-known being protons and neutrons. But there are six types of existing quarks, and theoretically many different potential combinations could form other kinds of baryons. Baryons so far observed are all made of,at most,one heavy quark. "Finding a doubly heavy-quark baryon is of great interest as it will provide a unique tool to further probe quantum chromodynamics,the theory that describes the strong interaction,one of the four fundamental forces,"said Giovanni Passaleva,new Spokesperson of the LHCb collaboration."Such particles will thus help us improve the predictive power of our theories." "In contrast to other baryons,in which the three quarks perform an elaborate dance around each other,a doubly heavy baryon is expected to act like a planetary system,where the two heavy quarks play the role of heavy stars orbiring one around the other,with the lighter quark orbiting around this binary system,"added Guy Wilkinson,former Spokesperson of the collaboration, ++ Measuring the properties of theΞcc will help to establish how a system of two heavy quarks and a light quark behaves.Important insights can be obtained by precisely measuring production and decay mechanisms,and the lifetime of this new particle. The observation of this new baryon proved to be challenging and has been made possible owing to high production rate of heavy quarks at the LHC and to the unique capabilities of the LHCb experiment,which can identify the decay ++ products with excellent efficiency.TheΞcc baryon was identified via + - its decay into a Λc baryon and three lighter mesons K + + ,π and π. ++ The obserbation of the Ξcc in LHCb raises the expectations to detect other representatives of the family of doubly-heavy baryons. They will now be serched for at the LHC. This result is based on 13TeV recorded during run 2 at the Large Hadron Collider,and confirmed using 8TeV data from run 1. The collaboration has submitted a paper reporting these findings to the journal Physical Review Letters. 4.完整新聞連結(或短網址) https://goo.gl/svkcke 5.備註 昨天台灣半夜突然公布，看沒有人發就貼過來。 PRL：https://goo.gl/cr7vUe --

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