True muonium resonant production at lepton colliders with standard crossing angle

What is it about?

True muonium is the one of the heaviest and smallest atoms, composed oa a muon and an anti-muon. Several of new physics discovery potential is hidden in the atomic spectroscopy of leptonic bound states. Among these interesting objects, one of the most sensible ones, is the so-called TM, a μ+ μ− bound state. TM can be produced on resonance with a 67 nb cross-section at e+ e− collider running at a 2mμ = 211.4 MeV center-of-mass energy. In real-world scenarios, due to the smallness of its B.E. with respect to the beam's energy spread σE , the cross-section is smaller by a factor proportional to σE . In this paper, the DAΦNE collider at the Frascati National Laboratory of INFN is used, which now runs at 1020 MeV c.o.m. energy, as the benchmark of machine requirements for TM research. For this reason, its beam and collision parameters were studied to assess whether there is a potential for discovery of TM excited states, in the hypothesis to run at the proper c.o.m. energy. The TM decay vertex to an electron pair can indeed be reconstructed and employed to discriminate signal over background. It was therefore shown that TM excited states can be observed in a data-taking of the order of one month using a detector with a polar acceptance angle of θ = 60°, made of a multi-layer silicon tracker with 10 μm spatial resolution, a calorimeter with a resolution better than 6% at 100 MeV and a hermetic cosmic ray veto. Previous proposals for TM discovery involved the construction of e+ e− colliders with large collision crossing angles (θ ∼ 30°), in order to provide TM with enough boost to observe its fundamental state. On the contrary, it was proved that also the small crossing angle of already existing colliders like DAΦNE is sufficient to discover TM, by observing its excited states.

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Why is it important?

Previous proposals for TM discovery involved the construction of e+ e− colliders with large collision crossing angles (θ ∼ 30°), in order to provide TM with enough boost to observe its fundamental state. On the contrary, it was proved that also the small crossing angle of already existing colliders like DAΦNE is sufficient to discover TM, by observing its excited states.