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Capstone Presentation Department of Physics 09 June 2010

Measurement of D* + Natural Line Width Carol Fabby Rolf Andreassen, Mikhail Dubrovin, Zach Huard, Brian Meadows, Mike Sokoloff University of Cincinnati. Capstone Presentation Department of Physics 09 June 2010. What is Particle Physics?.

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Capstone Presentation Department of Physics 09 June 2010

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  1. Measurement ofD*+ Natural Line WidthCarol Fabby Rolf Andreassen, Mikhail Dubrovin,Zach Huard, Brian Meadows,Mike Sokoloff University of Cincinnati Capstone Presentation Department of Physics 09 June 2010

  2. What is Particle Physics? • Study of elementary building blocks of matter • Interactions of particles • Forces that hold particles together and act on particles • What gives particles their mass? • Why an imbalance between matter and antimatter • Physicists want to find limits of TheStandardModelofFundamentalParticlesandInteractions and see what is beyond Carol Fabby Capstone Presentation University of Cincinnati 09 June 2010

  3. BABAR Experiment(1999-2008, Stanford Linear Accelerator Center, SLAC) • Set up to analyze collisions between electrons and their equal/opposite antiparticles, positrons • To understand differences between matter and antimatter PEP-II Storage Rings of Accelerator Carol Fabby Capstone Presentation University of Cincinnati 09 June 2010 BABAR Detector Graphics provided by BABAR Collaboration www.slac.stanford.edu/BFROOT

  4. Decay being studied (for D*+ natural line width): D*+ D0πs+ D0 K-π+ These particles reach layers of the detector πs+ π+ D0 K- D*+ Signal Side e + e - Tag Side Carol Fabby Capstone Presentation University of Cincinnati 09 June 2010

  5. What is Known About D* Width? • Previous studies • ACCMOR 1: • 90% CL upper limit to Γ of 131 keV • Poor statistics • CLEO 2: • 1st measurement Γ = [96 ± 4 (stat) ± 22 (syst)] keV • Good resolution, poor statistics 1. S. Barlag, et al. Measurement of the mass and width of the charmed meson D*+ (2010), Phys. Let. B 279, 4 (1992); 480-484 2. A Anastassov, et. al. First Measurement of Γ(D*+) , Phys. Rev. Lett. 87, 25 (2001) Carol Fabby Capstone Presentation University of Cincinnati 09 June 2010

  6. Event Selection • For high quality tracks, good track resolution and to remove background: • Slow Pion DCH Hits > 12 • Kaon DCH Hits > 20 • Pion DCH Hits > 20 • Make requirements on number of hits to have well measured tracks: • Pion SVT OK • Kaon SVT OK • Slow Pion SVT OK Carol Fabby Capstone Presentation University of Cincinnati 09 June 2010

  7. Event Selection • To eliminate electron mis-identification from D*0→ D0π0π0 →γ γ , γ e+ e- • πs , veto on IsGammaConversion • πs , veto on IsDalitzConversion • Overall general cut, to eliminate e- • -3 < πs Pull for dE/dx (DCH) < 2 • -3 < πs Pull for dE/dx (SVT) < 2 Carol Fabby Capstone Presentation University of Cincinnati 09 June 2010

  8. Carol Fabby Capstone Presentation University of Cincinnati 09 June 2010

  9. Fitting Models We use a Monte Carlo simulation to determine the resolution function. Signal (peak) is modeled with: • Sum of 3 Gaussians with independent means (central values) and widths Background (red dotted line) is modeled with: • Threshold function Pull Distribution (σ) MONTE CARLO (MC) We look at pull distributions centered around zero to check for systematic variation Carol Fabby Capstone Presentation University of Cincinnati 09 June 2010

  10. REAL DATA BW Convo with [(Res Fct) x (1+ε)] Fitting Models Δm signal (peak) is modeled with: • Non-relativistic Breit-Wigner convolved with resolution function extracted from MC and includes: • Offset parameters • Allows for differences in mean (central) values in MC and RD • Parameter ε • Scales overall MC resolution function Background (red dotted line) is modeled with: • Threshold function Pull Distribution (σ) REAL DATA (RD) Carol Fabby Capstone Presentation University of Cincinnati 09 June 2010

  11. ε Carol Fabby Capstone Presentation University of Cincinnati 09 June 2010

  12. Summary • Using this non-relativistic Breit-Wigner model for the line shape, we find the D*+ natural line width to be: Γ = [101 ± 1 ] keV Systematic error is still being investigated • This measurement will constrain models used to describe interactions of charm mesons • Providing a model with correct Breit-Wigner tails will permit better Monte Carlo simulations of D*+ in the future. Carol Fabby Capstone Presentation University of Cincinnati 09 June 2010

  13. Future Analysis • We will: • Try different Breit-Wigner shapes • Study variation of results as a function of such variables as: • Lab momentum of the sample • Track quality • Evaluate cause of systematic variation observed in pull distribution plots Carol Fabby Capstone Presentation University of Cincinnati 09 June 2010

  14. Acknowledgements Advisors Mike Sokoloff Brian Meadows Post Doctorates Graduate Students Mikhail Dubrovin Rolf Andreassen Zach Huard Carol Fabby Capstone Presentation University of Cincinnati 09 June 2010

  15. BACK-UP SLIDES Carol Fabby Capstone Presentation University of Cincinnati 09 June 2010

  16. Building Blocks: Elementary Particles • The strong force is responsible for quarks “sticking” together to form protons, neutrons and related particles. • The electromagnetic force binds electrons to atomic nuclei (clusters of protons and neutrons) to form atoms. • The weak force facilitates the decay of heavy particles into smaller siblings. • The gravitational force acts between massive objects. Although it plays no role at the microscopic level, it is the dominant force in our everyday life and throughout the universe. • The gluon mediates the strong force; it “glues” quarks together. • The photon carries the electromagnetic force; it also transmits light. • The W and Z bosons represent the weak force; they introduce different types of decays Carol Fabby Capstone Presentation University of Cincinnati 09 June 2010

  17. Graphics provided by BABAR Collaboration www.slac.stanford.edu/BFROOT

  18. BABAR Detector • Silicon Vertex Detector: • Provides precise position information on charged tracks • Drift Chamber: • Provides main momentum measurements for charged particles; helps with particle ID through dE/dx measurements • CSF Calorimeter • A calorimeter is a device that measures the energy and position of a particle by absorbing it. • Detector of Internally Reflected Cerenkov radiation: DIRC • A Cerenkov detector is a particle identification device. It uses the Cerenkov angle of a charged track to determine the track velocity. • The primary task of the DIRC is to distinguish between charged pions and charged kaons at high momentum. (At low momentum, pion/kaon separation is based on dE/dx measurements in the SVT and DCH.) • Instrumented Flux Return: IRF • The IFR is BaBar's outermost subdetector. It is used to detect muons and long-lived neutral hadrons. Carol Fabby Capstone Presentation University of Cincinnati 09 June 2010 Descriptions provided by BABAR Collaboration www.slac.stanford.edu/BFROOT

  19. SVTOK • Bitmask • >2 hits in r/phi-view (at least 1 hit in layer 1-3) • >2 hits in z-view (at least 1 hit in layer 1-3) • >6 hits total (r/phi + z view) Carol Fabby Capstone Presentation University of Cincinnati 09 June 2010

  20. Variables Carol Fabby Capstone Presentation University of Cincinnati 09 June 2010

  21. Why? Short Answer The lifetime of a D*+ is so quick we can’t resolve it, but we can find the width and from that we can find the lifetime: τ = 1/ Γ Longer Answer The underlying mechanics are revealed at / hinted by the lifetime. For example: Φ which is a ssbar state [See diagram] This is a strong decay Φ → K-K+ (1.02 GeV)→ (0.99 GeV) in terms of mass So only a small amount of energy goes to the kinematics of K-K+. On the other hand there is a light mode Φ→ π+ π- π0 (1.02 GeV)→(0.415 GeV) Much more energy (phase space) for this mode [See diagram] But if you can ‘cut’ the gluon lines in a diagram the ‘fast’ 3π decay mode is suppressed and the 2K mode is slower, since it needs specific kinematics to happen.

  22. Why? On the other hand there is a light mode Φ→π+ π- π0 (1.02 GeV)→(0.415 GeV) Much more energy (phase space) for this mode But if you can ‘cut’ the gluon lines in a diagram the ‘fast’ 3π decay mode is suppressed and the 2K mode is slower, since it needs specific kinematics to happen. Carol Fabby

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