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TOPIC: Quarkonium

Blobrana

L

Posts: 131433

Date: Dec 22 14:34 2011

RE: Quarkonium	Permalink

LHC reports discovery of its first new particle The Large Hadron Collider (LHC) on the Franco-Swiss border has made its first clear observation of a new particle since opening in 2009. It is called Chi_b (3P) and will help scientists understand better the forces that hold matter together. Read more __________________

Blobrana

L

Posts: 131433

Date: Dec 22 14:25 2011

chi_b(nP) quarkonium states	Permalink

Title: Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS Authors: ATLAS Collaboration The chi_b(nP) quarkonium states are produced in proton-proton collisions at the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS detector. Using a data sample corresponding to an integrated luminosity of 4.4 fb^-1, these states are reconstructed through their radiative decays to Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new structure centred at a mass of 10.539±0.004 (stat.)±0.008 (syst.) GeV is also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes. This is interpreted as the chi_b(3P) system. Read more (172kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: May 27 09:37 2011

Quarkonia	Permalink

CMS observes hints of melting of Upsilon particles in lead-nuclei collisions One of the predicted characteristics of the QGP is that its high temperature causes the "melting" of quarkonia - bound states of a quark and its anti-quark. This melting manifests itself as the suppression of quarkonia production in heavy-ion collisions, compared to the number of quarkonia produced in collisions between protons. The (Upsilon) particle, a quarkonium consisting of a bottom and an anti-bottom quark, exists in three states known as 1S, 2S and 3S, in decreasing order of how tightly the quarks are bound. (1S is the ground state of the , while the others are excited states.) Because they are more loosely bound, the 2S and 3S states will melt more readily in the QGP. This means that the number of (2S) and (3S) particles produced relative to (1S) in heavy-ion collisions should be less than corresponding numbers from proton collisions. Read more __________________

Blobrana

L

Posts: 131433

Date: Apr 12 17:22 2011

Bottomonium	Permalink

A new bottomonium particle makes its debut Data collected by the BaBar experiment during its final months of operation in 2008 point to a new member of the "bottomonium" family of subatomic particles. BaBar collaboration member and SLAC physicist Valentina Santoro presented the results on behalf of the collaboration last month at the Lake Louise Winter Institute, a yearly conference held at Lake Louise, Alberta, Canada. The discovery adds another piece to physicists' model of the so-called "strong" force, which binds subatomic particles into larger chunks of matter. In 2008, members of the BaBar collaboration announced they'd discovered the lowest-energy bottomonium particle, called b (pronounced eta-sub-b). A subsequent BaBar study confirmed the finding in 2009. Continued examination of the final BaBar data set has now revealed another particle of the bottomonium family, called the hb (h sub b). Read more __________________

Blobrana

L

Posts: 131433

Date: Jan 26 14:22 2011

Quarkonium	Permalink

Title: Quarkonium states in a complex-valued potential Authors: Matthew Margotta, Kyle McCarty, Christina McGahan, Michael Strickland, David Yager-Elorriaga We calculate quarkonium binding energies using a realistic complex-valued potential for both an isotropic and anisotropic quark-gluon plasma. We determine the disassociation temperatures of the ground and first excited states considering both the real and imaginary parts of the binding energy. We show that the effect of momentum-space anisotropy is smaller on the imaginary part of the binding energy than on the real part of the binding energy. In the case that one assumes an isotropic plasma, we find disassociation temperatures for the J/psi, Upsilon and chi_b of 2.3 T_c, 2.9 T_c, and 1.8 T_c, respectively. We find that a finite oblate momentum-space anisotropy increases the disassociation temperature for all states considered and results in a splitting of the p-wave states associated with the chi_b first excited state of bottomonium. Read more (83kb, PDF) __________________

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