nucleon spin
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2020 ◽  
Vol 1643 (1) ◽  
pp. 012197
Author(s):  
Qinghua Xu

Abstract The contribution from the sea quark polarization to the nucleon spin is an important piece for the complete understanding of the nucleon spin structure. The production of W ± bosons in longitudinally polarized p+p collisions at the RHIC collider at Brookhaven National Laboratory provides a unique probe of the sea quark polarization, through the parity-violating single-spin asymmetry, AL . At the STAR experiment, the W bosons that decay through the W → ev channel at mid-rapidity (|η <1.3) can be effectively determined with the Electromagnetic Calorimeters and Time Projection Chamber. The STAR measurements of AL for W boson from datasets taken in 2011 and 2012 at s =510 GeV have been included in the global analysis of polarized parton distribution functions, and provided significant constraints on the helicity distribution functions of u ¯ and d ¯ quarks. The final AL results from 2013 STAR data sample are reported, which is about three times larger than the total integrated luminosity of previous years. The combined results of AL for 2011-2013 data are also given. A flavor asymmetry of light sea quark helicity distribution, Δ u ¯ ( x )   −   Δ d ¯ ( x ) > 0 , is confirmed from a re-weighting of global analysis NNPDFpol1.1 after including the new AL results. In addition, results on the double-spin asymmetries ALL for W ±, and AL for Z/γ* production are also reported.


2019 ◽  
Vol 35 (08) ◽  
pp. 2050048 ◽  
Author(s):  
Silas R. Beane ◽  
Peter J. Ehlers

The nucleon is naturally viewed as a bipartite system of valence spin — defined by its non-vanishing chiral charge — and non-valence or sea spin. The sea spin can be traced over to give a reduced density matrix, and it is shown that the resulting entanglement entropy acts as an order parameter of chiral symmetry breaking in the nucleon. In the large-[Formula: see text] limit, the entanglement entropy vanishes and the valence spin accounts for all of the nucleon spin, while in the limit of maximal entanglement entropy, the nucleon loses memory of the valence spin and consequently has spin dominated by the sea. The nucleon state vector in the chiral basis, fit to low-energy data, gives a valence spin content consistent with experiment and lattice QCD determinations, and has large entanglement entropy.


Universe ◽  
2019 ◽  
Vol 5 (3) ◽  
pp. 73
Author(s):  
Vitaly Kudryavtsev for the LUX and LZ Collaborations

Weakly Interacting Massive Particle (WIMP) remains one of the most promising dark matter candidates. Many experiments around the world are searching for WIMPs and the best current sensitivity to WIMP-nucleon spin-independent cross-section is about 10 − 10 pb. LUX has been one of the world-leading experiments in the search for dark matter WIMPs. Results from the LUX experiment on WIMP searches for different WIMP masses are summarised in this paper. The LUX detector will be replaced by its successor, the LUX-ZEPLIN (LZ) detector. With 50 times larger fiducial mass and an increased background rejection power due to specially-designed veto systems, the LZ experiment (due to take first data in 2020) will achieve a sensitivity to WIMPs exceeding the current best limits by more than an order of magnitude (for spin-independent interactions and for WIMP masses exceeding a few GeV). An overview of the LZ experiment is presented and LZ sensitivity is discussed based on the accurately modelled background and the high-sensitivity material screening campaign.


2019 ◽  
Vol 12 (4) ◽  
pp. 861
Author(s):  
C. Alexandrou ◽  
M. Constantinou ◽  
K. Hadjiyiannakou ◽  
K. Jansen ◽  
C. Kallidonis ◽  
...  

2018 ◽  
Author(s):  
Kyriakos Hadjiyiannakou ◽  
Constantia Alexandrou ◽  
Martha Constantinou ◽  
Karl Jansen ◽  
Christos Kallidonis ◽  
...  

2018 ◽  
Vol 98 (3) ◽  
Author(s):  
Michael C. Birse ◽  
Judith A. McGovern
Keyword(s):  

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