Mitja Rosina POSSIBILITIES OF THE SEARCH for the DD and BB DIMESONS Faculty of Mathematics and Physics, University of Ljubljana and Institute Jožef Stefan, Ljubljana, Slovenia Talk presented at the Mini-Workshop BLED 2016: QUARKS, HADRONS, MATTER 3 – 10 July 2016

ABSTRACT I shall present an interesting comparison between the “molecule“ of two mesons and the hydogen molecule. Especially interesting are dimesons made of two heavy (charmed) mesons. At short distance, the two protons in the hydrogen molecule are repelled by the electrostatic interaction, while the two heavy (charm) quarks in the mesonic molecule are attracted by the chromodynamic interaction because they can recouple their colour charges. The BB* dimeson (tetraquark) is expected to be strongly bound (>100 MeV) while the DD* dimeson is weakly bound (~2 MeV) or a low resonance. AIM: Effective quark-quark interaction (Is Vuu = Vcu = Vcc = Vcc = Vbu = Vbb?) Interesting 4-body problem CHALLENGE: Old theory, but a new chance for measurement of DD*=(cu,cd) at the future upgraded Belle-2 at KEK, Tsukuba (Japan); and BB*=(bu,bd) at LHC .

(is Vuu = Vcu = Vcc = Vcc = Vbb ?) OUTLINE Comparison between charmed dimesons and hydrogen molecule 2. Test of the effective quark-quark interaction (is Vuu = Vcu = Vcc = Vcc = Vbb ?) 3. The production of tetraquarks 4. The decay of the dimeson DD* detection

1. Comparison between charmed . dimesons and hydrogen molecule He u c c d d He atom Meson π+ Atom-like tetraquark c u p e e p u u d d c Molecule H+H Baryon (nucleon) Dimeson D+D*

PHENOMENOLOGICAL ESTIMATE OF BINDING u u b u bb b b d b d d Dimeson B+B* (5279+5325=10604)MeV like Λb antibaryon (5620 10476)MeV Tetraquark u u c u c c cc d c d d like Λ c antibaryon (2286 3967)MeV Dimeson D+D* (1867+2008=3875)MeV Tetraquark

COMPARISON BETWEEN DIMESON AND HYDROGEN MOLECULE POTENTIAL V rcc u cc c c c D + D* d

(is Vuu = Vcu = Vcc = Vcc = Vbb ?) 2. Test of the effective quark-quark interaction (is Vuu = Vcu = Vcc = Vcc = Vbb ?) A. One-gluon exchange + confinement (color.color) [GRENOBLE] B.One-Goldstone boson exch.+ confinement (flavor.flavor) [GRAZ ]

The „Vqq = Vqq rule“ , cc ud = cud + c + cc - cc 12 , cc ud = cud + c + cc - cc [A]: (color.color)=4/3 for cc =2/3 for cc [B]: Flux tube model c   c c c c

3. The production of tetraquarks 1.step: double two-gluon fusion (g + g) + (g + g) (c + c) + (c + c) 2.step: two c fly close enough in phase space (c + c) cc [colour antisymmetric diquark] 3.step: the diquark cc gets dressed, cc ccud. 4.step: dimeson forms, cc u d cu cd = D D* The upper bound for LHCb (@ a luminosity 1033/cm2s) was estimated to be 104 events/hour (or 5 events per hour for bbud) The alternative process that first two D mesons form and later they find each other and merge, is less probable.

The estimate of the diquark formation (Del Fabro, Janc, Rosina Treleani 2005) We make an impulse approximation that this two- quark state is instantaneously transformed in any of the 27 nb (LHCb) ; 58 nb (ALICE)

b B- = bu ….. 0.375+0.015 B0 = bd Bs = bs 0.160+0.025 Λb = bud The dressing (fragmentation) of the b quark b B- = bu ….. 0.375+0.015 B0 = bd Bs = bs 0.160+0.025 Λb = bud 0.090+0.028 Fermilab CDF 2000 The dressing (fragmentation) of the cc diquark cc cc++ = ccu ….. 37 % cc+ = ccd Ω cc+ = ccs 16 % T cc+ =ccud 9 %

If SELEX has really seen 15 , + If SELEX has really seen 15 , then it could have seen 4 T+cc --- too few! There are much better chances at Belle2 ! cc +

4. The decay of the dimeson DD* detection         or: D* D + γ + 143 MeV DD* D + D + γ + ~140 MeV

WHY DO WE PREFER Tcc to Tbb ? It is more abundant (perhaps 10000 : 5) It is easier to detect, Tcc D+ + K- + π+ (in analogy to + Λ c+ + K- + π+ ) It is more delicate, barely bound or barely unbound, . would distinguish between different models. Might help to understand the mechanism of high . production rate of double cc + cc pairs @ Belle.

THANKS FOR YOUR ATTENTION! YOUR CRITICISM AND SUGGESTIONS I SHALL APPRECIATE YOUR CRITICISM AND SUGGESTIONS

Interpretation of the X(3872) as a The X(3872) puzzle Interpretation of the X(3872) as a charmonium state (c c) plus an extra component due to the coupling to the meson - meson continuum (D D*) & (D D*) E. Santopinto (INFN),J. Ferretti (INFN) , G. Galatà (UNAM) We only know thanks to LHCb that it is 1++ 16

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