Particle misidentification in the invariant mass spectrum of the delta resonance

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Grounds, Alexander

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The quark-gluon plasma is a new phase of matter and is the focus of much research in particle physics today. One of the main purposes of the famous Large Hadron Collider (LHC) at CERN is to create quark-gluon plasma by colliding lead nuclei at high energies. The plasma can only exist for extremely short amounts of time, so our only method of investigating it is to analyze the particles it produces. This is one of the goals of A Large Ion Collider Experiment(ALICE) and the construction of the ALICE detectors at the LHC. Of particular importance are so-called resonance particles. Like the quark-gluon plasma, these particles only live for very short amounts of time be- fore decaying. Therefore, they can be created and even re-created while the plasma exists. For this reason, they are extremely important to our analysis of the quark-gluon plasma. However, since they are so short-lived, we cannot directly see these resonance particles either. Rather, we look at the longer-lived particles which they decay into. We determine facts about the resonances from the information we have about their decay products. However, identifying these decay products can be difficult as well, especially in high- energy experiments such as those in ALICE. It is often the case that we think that a particle is a pion, for instance, when indeed it was a proton. This is called a misidentification. By misidentifying decay products, we then misidentify the particle from which those products decayed. To account for this phenomenon, we simulate particle misidentification. The simulation gives us expectations for the shape of distributions of misidentified particles. Knowing the shape, we can then attempt to locate these distributions in experimental data and subtract them out to produce a cleaner distribution of our resonance particle. In this paper, we analyze the invariant mass distribution of the [delta] resonance. We look at four other particles which can by misidentified as the [delta] and analyze their misidentified invariant mass distributions. We then investigate the dependence of these distributions upon the particle's momentum. The analysis gives us information about when it is possible to find a misidentified particle's distribution inside an experimental distribution of the [delta] mass and what shape we should expect the misidentified distribution to take. This analysis will be useful for further studies of the [delta] in high-energy collisions.



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