Continuous Monitoring of STAR's Main Time Projection Chamber

Journal of the Arkansas Academy of Science Volume 52 Article 6 1998 Continuous Monitoring of STAR's Main Time Projection Chamber Wilfred J. Braithwaite University of Arkansas at Little Rock Edwin S. Braithwaite Cedarville University Follow this and additional works at: http://scholarworks.uark.edu/jaas Part of the Elementary Particles and Fields and String Theory Commons Recommended Citation Braithwaite, Wilfred J. and Braithwaite, Edwin S. (1998) "Continuous Monitoring of STAR's Main Time Projection Chamber," Journal of the Arkansas Academy of Science: Vol. 52 , Article 6. Available at: http://scholarworks.uark.edu/jaas/vol52/iss1/6 This article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able to read, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking prior permission from the publisher or the author. This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academy of Science by an authorized editor of ScholarWorks@UARK. For more information, please contact , . Journal of the Arkansas Academy of Science, Vol. 52 [1998], Art. 6 Continuous Monitoring of STAR's Main Time Projection Chamber Wilfred J. Braithwaite* Department of Physics and Astronomy, University of Arkansas at Little Rock Little Rock, AR 72204 and Edwin S. Braithwaite Department of Science and Mathematics Cedarville College, Cedarville, OH 45314 *Corresponding Author Abstract STAR refers to the Solenoidal Tracking instrument At RHIC (the Relativistic Heavy Ion Collider). For momenta above 500 MeV/c charged kaons are not separated from pions within STAR's Main TPC (Time Projection Chamber) by track density alone and they are poorly separated below 500 MeW c, even when using information from other sources like the vertex tracker. Within the TPC large numbers of kaons and pions decay into muons (and undetected neutrinos). Earlier work has shown parent pions and kaons whose decays are detected within a TPC may be distinguished uniquely from each other in a two-dimensional plot of muon-emission angle versus momentum difference (between each parent meson and its decay muon). Since pions and kaons have zero spin, each muon decay-product emerges isotropically in its parent meson's rest frame. Identification of particle type provides the parent meson's rest mass and, thus, its total energy. This means the measurement of each decay event is kinematically complete. Thus, Lorentz Transformations may be used to transform each component of the decaying muon's laboratory four-momentum into the "rest frame" of its parent meson, where the muon decay is isotropic. An aggregated plot of muon directions from many "parent rest frames" willbe isotropic in each (selected) sub-volume of the TPC unless there is a problem within the TPC or in its tracking algorithms. Continuous monitoring of a TPC is possible using this subset of detected charged particles. Introduction Previous work using muon decays of pions and kaons (Braithwaite and Braithwaite, 1997b) has shown that by using relativistic kinematics alone (Braithwaite, 1972) parent pions and kaons whose decays are detected within a TPC (Time Projection Chamber) may be distinguished uniquely from each other. This separation is accomplished using a 2Dplot of observables within the TPC: muon-emission angle versus momentum difference (between parent meson and muon). This previous work was predicated on even earlier work (Climer et al., 1996) where mapping STAR's TPC for acceptance and efficiency was suggested using parent kaons. What was missing from this earlier work was a feasibility study of the expected quality of the separation ofkaons from the much more prevalent pions using the relativistic kinematics of muon decays. Uniquely identifying kaons and counting them measures the amount of strangeness production occurring in each central collision between two ultrarelativistic nuclei; kaon production is a direct measure of strangeness production as kaons are singly strange. This method for measuring strangeness production using charged kaon decay complements measurements of neutral kaon decay within a microTPC designed to be the component detector located closest to the collider vertex for ultra-relativistic nucleus-nucleus collisions (Braithwaite and Braithwaite, 1997a). Despite the importance of measuring strangeness production as one signature of the onset of the Quark Gluon Plasma (Harris and Miiller,1996), the present work concentrates on a new approach to mapping STAR's Main TPC (Sauli, 1987) for acceptance and efficiency as a function of position within the TPC, using both kaons and pions. For each parent meson, the spin = 0 description of the quantum ground state requires the direction of each muon decay to be isotropic in its parent meson's rest frame. As outlined below, this feature of isotropic decay, due to the decaying pions and kaons being spin = 0 mesons, provides a new dimension in the monitoring of STAR's Main TPC. Materials and Methods "Kinematic trajectories" for meson decays cluster into Journal of the Arkansas Academy of Science, Vol. 52, 1998 Published by Arkansas Academy of Science, 1998 28 28 Journal of the Arkansas Academy of Science, Vol. 52 [1998], Art. 6 Continuous Monitoring of STAR's Main Time Projection Chamber Fig. 1. Both pions and kaons decay isotropically in their respective rest frames. Each muon and unobserved neutrino has an equal but opposite 3 momentum value in the COM (center of momentum) frame, which is also the parent's rest frame. Results and Discussion Journal of the Arkansas Academy of Science, Vol. 52, 1998 http://scholarworks.uark.edu/jaas/vol52/iss1/6 29 29 Journal of the Arkansas Academy of Science, Vol. 52 [1998], Art. 6 Wilfred J. Braithwaite and Edwin S. Braithwaite Fig. 2. Conservation of total-energy in the COM Frame predicts a constant "length" for the muon's 3-momentum. This 3momentum vector points with equal probability in all (6, ty) directions in the COM Frame. Journal of the Arkansas Academy of Science, Vol. 52, 1998 Published by Arkansas Academy of Science, 1998 30 30 Journal of the Arkansas Academy of Science, Vol. 52 [1998], Art. 6 Continuous Monitoring of STAR's Main Time Projection Chamber Acknowledgments. —This research was supported in part by the U. S. Department of Energy through Grant DE-FG05-92ER-40753. The first author wishes to thank Miss Amber Climer, a Donaghey Scholar at UALR, and Dr. Iwona Sakrejda, a permanent Staff Member of Lawrence Berkeley National Laboratory, for their suggestion of using the decays of charged kaons as a vehicle for an accepseparating kaons from pions in order to carry out + tance and efficiency study for the detection of K and K' within the Main Time Projection Chamber of STAR. Also, both aut (...truncated)