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Baryon spectrum from 2+1 flavours of DWF QCD

Baryon spectrum from 2+1 flavours of DWF QCD. RBC and UKQCD collaborations. Chris Maynard. Chris Allton, Tom Blum, Paul Cooney , Luigi del Debbio, Meifeng Lin , Aurora Trivini , Takeshi Yamazaki, James Zanotti. Outline. Motivation Why baryons Ensemble details What has been measured

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Baryon spectrum from 2+1 flavours of DWF QCD

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  1. Baryon spectrum from 2+1 flavours of DWF QCD RBC and UKQCD collaborations Chris Maynard Chris Allton, Tom Blum, Paul Cooney, Luigi del Debbio, Meifeng Lin, Aurora Trivini, Takeshi Yamazaki, James Zanotti DWF@10 : BNL, NY : 15-17 March 2007

  2. Outline • Motivation • Why baryons • Ensemble details • What has been measured • Baryon spectrum (degenerate) • Nucleons • Decuplet baryons • Outlook and conclusions DWF@10 : BNL, NY : 15-17 March 2007

  3. Why baryons are important • N. Isgur 1947-2001nucl-th/0007008 • Why N*'s are Important" • Nucleons are the stuff of which world is made • Simplest system in which the quintessentially nonabelian character of QCD is manifest • Nc quarks in proton because there are Nc colours • Baryons are sufficiently complex to reveal physics hidden from us in Mesons • Non-analytic chiral behaviour DWF@10 : BNL, NY : 15-17 March 2007

  4. Spectrum not completely understood Excited states do not fit “naturally” in Quark Model e.g. the Roper resonance N(1440) JP=1/2+ Lattice QCD can give definitive answer Excited states are hard Is Roper radial excitation of nucleon, or something else QM HO potential Roper Resonance DWF@10 : BNL, NY : 15-17 March 2007

  5. Matrix elements • Diverse phenomenology • Structure functions • Collider physics • Strangeness content of nucleon • Cold Dark Matter • Neutron electro-dipole moment • SUSY phenomenology • Proton decay • GUT and SUSY GUT models DWF@10 : BNL, NY : 15-17 March 2007

  6. Ensembles L= 2fm L= 3fm Not complete Iwasaki gauge action b=2.13, 2+1 flavours (ms=0.04) LS=16 mres=0.003 a-1=1.60(3) (rho,r0, method of planes) 243 is still running and more measurements to come Results are preliminary DWF@10 : BNL, NY : 15-17 March 2007

  7. Nucleons • RBC and UKQCD separate measurement datasets for matrix elements • Combined analysis for m=0.01 V=243 • 60 configurations • 5 Smearing combinations (6 for N*) • Local-local LL • Gaussian-local (R=4) GL • Gaussian-Gaussian GG • Box (L=16) (extra N* operator) BL • Gaussian-local (R=7) G2L (4 tps) DWF@10 : BNL, NY : 15-17 March 2007

  8. Nucleon mass • Fit effective mass • 1 fit parameter • No fit-range systematic error • Only for m=0.01 DWF@10 : BNL, NY : 15-17 March 2007

  9. Nstar mass • 3-6 timeslices per correlator • Result is fit-range sensitive for individual correlators • Uber-fit is fit-range insensitive DWF@10 : BNL, NY : 15-17 March 2007

  10. Finite size effects DWF@10 : BNL, NY : 15-17 March 2007

  11. Nucleon FSE • No obvious FSE for Nucleon • 2 and 3 fm box • mP ~ 390Mev • mPL ~ 3.9 and 5.8 • mP/mV ~ 0.45 • No FSE expected • m=0.005 mPL ~ 4.6 DWF@10 : BNL, NY : 15-17 March 2007

  12. Nstar FSE • No obvious FSE for Nstar • No expectation • N* Uber fit for 243 • N* noisey for 163 • No FSE • Statistics limited DWF@10 : BNL, NY : 15-17 March 2007

  13. Edinburgh plot • Displays all 2+1 flavour DWF data • Apparently lies on universal curve • LS, gauge coupling, volume • Lightest data noisy due to vector correlator DWF@10 : BNL, NY : 15-17 March 2007

  14. Chiral extrapolation • Linear extrap. vs mP2 • m=0.01 uberfit • No fit systematic • m=0.005 datum low? • Chiral effect? • mP ~ 310MeV DWF@10 : BNL, NY : 15-17 March 2007

  15. Chiral extrapolation II • NLO cPT term • mP3 • Radius of convergence? • Maybe lightest • Definitely not heaviest • Just for fun! DWF@10 : BNL, NY : 15-17 March 2007

  16. Decuplet baryons • Valence degenerate • D mV=mu=mSea • W mV=mstrange • Effective mass plot for D m=0.01 • Not fitting Meff DWF@10 : BNL, NY : 15-17 March 2007

  17. Chiral extrapolation • Data consistent with linear extrapolation DWF@10 : BNL, NY : 15-17 March 2007

  18. Baryon Spectrum • Three lowest lying valence degenerate states • Negative parity partners • Reasonable agreement with experiment • a-1=1.60(3) GeV DWF@10 : BNL, NY : 15-17 March 2007

  19. Baryon spectrum • Ultimately expect non-linear chiral behaviour • Can’t get spectrum right with linear • NLO cPT fit not realistic • goes in right direction • maybe just statistics • Require lighter quarks and better statistics DWF@10 : BNL, NY : 15-17 March 2007

  20. Conclusions • Preliminary results for Baryon spectrum • Broadly agrees with experiment • starting to reach interesting regime • mu/ms < 1/5, mP/mV ~ 0.38, mP ~ 310 MeV • Measurements still running • Complex chiral behaviour must be explored to get spectrum right • Finer lattice spacing simulation under way • control lattice artefacts DWF@10 : BNL, NY : 15-17 March 2007

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