Cleven, Martin: Systematic Study of Hadronic Molecules in the Heavy Quark Sector. - Bonn, 2014. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
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author = {{Martin Cleven}},
title = {Systematic Study of Hadronic Molecules in the Heavy Quark Sector},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2014,
month = jan,

note = {In this work we have studied properties of hadronic molecules in the heavy quark sector. These have become increasingly important since from the beginning of this century a large number of states have been measured that for different reasons do not fit the predictions of simple quark models. Theorists have proposed different explanations for these states including tetraquarks, hybrids, hadro-quarkonia and, subject of this work, hadronic molecules. The study of these new states promises to provide insights in an important field of modern physics, the formation of matter by the strong force. Hadronic molecules are bound systems of hadrons in the same way two nucleons form the deuteron. For this the molecular states need to be located close to S-wave thresholds of their constituents. The dynamics of their constituents will have a significant impact on the molecules which allows us to make predictions that are unique features of the molecular assignement.
Here we focus on two candidates in the open charm sector, D s0*(2317) and D s1(2460), and two candidates in the bottomonium sector, Zb(10610) and Zb(10650). The DsJ are located similarly far below the open charm thresholds DK and D*K. Since the spin dependent interactions of the pseudoscalar and vector charmed mesons are suppressed in the heavy quark limit the interpretation of these two states as mainly DK and D*K bound states naturally explains their similarities.
The more recently discovered states Zb(10610) and Zb(10650), located very close to the open bottom thresholds B* B‾+c.c. and B* B‾*, respectively, are manifestly non-conventional. Being electromagnetically charged bottomonia these states necessarily have at least four valence quarks. We can explain that together with the fact that they decay similarly into final states with S- and P-wave bottomonia if we assume they are B* B‾+c.c. and B* B‾* molecules, respectively. Since the current experimental situation in both cases does not allow for final conclusions we try to point out quantities that, once measured, can help to pin down the nature of these states.
For the DsJ we can make use of the fact that the interactions between charmed mesons and Goldstone bosons are dictated by chiral symmetry. This means that we can calculate the coupled channel scattering amplitudes for DK and Dsη and their counterparts with charmed vector mesons. D s0*(2317) and D s1(2460) can be found as poles in the unitarized scattering amplitudes. We can calculate the dependence of these poles on the the strange quark mass and the averaged mass of up and down quark. This makes the result comparable to lattice calculations. Solving QCD exactly on the lattice can help us to understand the nature of the DsJ states while in the meantime it possibly takes one more decade until the PANDA experiment at FAIR will be able to judge if the molecular assignement is correct.
Furthermore we calculate the radiative and hadronic two-body decays. Here we find that in the molecular picture the isospin symmetry violating decays D s0*(2317)Ds*π and D s1(2460)→ Ds*π are about one order of magnitude larger than the radiative decays. This is a unique feature of the molecular interpretation --- compact c‾ s states have extremely suppressed hadronic decay rates. At the same time the radiative decays have comparable rates regardless of the interpretation. In conclusion the hadronic decay widths are the most promising quantities to experimentally determine the nature of D s0*(2317) and D s1(2460).
The methods we used in the open charm sector cannot be applied to the bottomonia one-to-one. Since we do not know the interaction strength between open bottom mesons we cannot obtain the state as a pole in a unitarized scattering matrix. We therefore need different quantities to explore the possible molecular nature. In a first attempt we show that the invariant mass spectra provided by the Belle group can be reproduced by assuming the Zb(*) are bound states located below the B* B‾+c.c. and B* B‾* thresholds, respectively.
Furthermore we present the dependence of the lineshape on the exact pole position. An important conclusion here is that for near threshold states like the Zb(*) a simple Breit Wigner parametrization as it is commonly used by experimental analyses is not the appropriate choice. Instead we suggest to use a Flatté parametrization in the proximity of open thresholds.
The second part of the discussion of the ZB states includes calculations of two-body decays. In particular we present the final states Υ π and hbπ which have already been seen by experiment and make predictions for a new final state χ bγ. The rates into this new final state are large enough to be seen at the next-generation B-factories.},

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