A closer look to the H dibaryon Teresa Fernández Caramés (U. Salamanca) poster2.jpg [T.F.C and A. Valcarce, Physical Review C 85, (2012)]

The H dibaryon SU(3) exact Compact 6q object No multiquarks in nature Promising candidate Two-baryon configuration Deuteron is the only dibaryon known so far Promising candidate

Experimental status - No experimental evidence yet - Hypernuclear data constrain the binding energy of H

Theoretical status - Many different calculations and results (bag models, Skyrme, NRQM, QCDSR,…) - They agree for baryon spectrum or interaction. CMI: 6q cluster :  24 Two baryons: 2  16 Sakai, Shimizu and Yazaki, Pr. Th. Phys. Suppl. 137, 121 (2000)] QM’s assume a two-baryon configuration - Study interaction - Search for a bound state

Recent Lattice QCD results NPLQCD: m  = 390 MeV, B H = 13.2 ± 1.8 ± 4.0 MeV HALQCD: m  = 837 MeV, B H = 37.4 ± 4.4 ± 7.3 MeV B H (m  ) = B 0 ’ + c 1 m  B H (m  ) = B 0 + c 1 m   [arXiV: v2] B H = 7.4 ± 2.1 ± 5.8 MeV B H = -0.2 ± 3.3 ± 7.3 MeV

The Chiral Constituent Quark Model (  CQM) Nonrelativistic potential model Semiphenomenological: Phenomenology QCD Asymptotic freedom Confinement Chiral symmetry S  SB: Massive Goldstone bosons Constituent Quarks   SB  CON   g     Two different scales: PERTURBATIVE ONE-GLUON EXCHANGE Interaction potential: LINEAR CONFINEMENT Unified treatment of the 1, 2 and 3-body systems with a reduced and unique set of parameters.

The Chiral Constituent Quark Model (  CQM) Model I: V ch = V  + V  + V K + V  Parameters fitted from a fine tuning of the meson spectra. Scalar singlet Pseudoscalar octet Model II: V ch = V  + V K + V  + V  0 + V a 0 + V  + V  8 Pseudoscalar octet Scalar singlet Scalar octet Extend to SU(3) x SU(3) symmetry Model 0: V ch = V  + V  Parameters fitted from NN data. Successfully described: Interactions among nonstrange baryons Baryon spectra NN phase shifts Deuteron and triton properties

S = -1 cross sections S = -2 cross sections V = V CON + V OGE + V  + V K + V  + V  0 + V a 0 + V  + V  8 Pseudoscalar octet, scalar singlet and scalar octet The Chiral Constituent Quark Model (  CQM) Hypertriton S = -1, -2 cross sections [A. Valcarce, H. Garcilazo, T.F.C., Phys. Lett. B. 693, 305 (2010)][H. Garcilazo, T.F.C., A. Valcarce, Phys. Rev. C75, (2007)]

Coupled-channel calculation D k =  SU(3) EXACT ONE-CHANNEL BINDING ENERGIES Diagonal potentials are attractive Born-Oppenheimer approach

The H dibaryon: results V SCE = V a 0 + V  + V  8 Repulsive OGE in all channels of our model Repulsive PS interaction (common feature) OSE is the only attractive piece Transitions mediated by K and  exchanges Scalar octet contrib: weak by itself but extremely important to connect channels and redistribute probabilities of the physical channels V K, V 

Parameter dependence The binding of the H particle depends most on   and  exchange potentials Large variation of BE in terms of g ch Allows a very loosely bound dibaryon Opposite dependence with masses. The H dibaryon is bound for any reasonable choice of the parameters

Flavor symmetry breaking: Expected to be important (two strange quarks) Our model assumes broken SU(3) Several sources: quark masses and orbital FSB through b s FSB lowers the attraction. General result (Oka et al, Shimizu et al, …) N  gains a lot of attraction for exact SU(3) SU(3) B H (MeV)

Spatial configurations of H: - Six-quark cluster - Two-baryon molecule Original work found a tightly bound H (-81MeV) for a 6 quark cluster However Shen et al. never found a bound H in the (0s) 6 configuration Shimizu et al. needed to include less compact configurations. When enlarging the size of the wave function, H becomes more attractive In our model no initial wave function is postulated Probabilities are quantitatively similar to those of the flavor singlet. SU(3) at first approximation, FSB explaining differences. Other channels in S = -2 A complete analysis of all (S,T) channels should be performed Very attractive 1 S 0 (T = 1) channel Binding energy smaller than B H Need of exp. confirmation, different models do not agree

Conclusions  We have studied the H dibaryon in a model constrained by the elastic and inelastic  and  cross sections.  Obtained a bound H, with B H = 7 MeV, compatible with the Nagara event and with a plausible extrapolation of the recent lattice results.  To learn about the structure of the dibaryon, an analysis of the different contributions has been performed, the scalar octet exchange playing a key role in the binding.  Probabilities of the  and  channels are similar to those of the flavor singlet.  Another bound state, with smaller B.E, was found in the strangeness -2, T=1, S=0 channel.  The abundance of events foreseen in a near future will help us learn the right mechanisms taking part in the H dynamics.