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1. Motivation • spectral function → aμ , α Dominant uncertainty comes from experimentally determined hadronic loops: Mitchell Naisbit Manchester Jan2004
2. Motivation cont’d Recent results show discrepancy between and spectral functions Babar ideal to validate τ result.
3. Aim • Study ρ line shape → Assess contribution from ρ(1450) and ρ(1700) • Make a selection of signal events, maximising the efficiency and purity • Form invariant mass spectrum of the system.
4. Samples Produced using TauUser package 19 fb-1 of run 1, 2 and 3 data (124 fb-1) 60 M τ Events 130 M uds events small bhabha samples
5. Selection Procedure Selection for data and MC samples: Use 1-1 events and tag to reduce backgrounds Signal sideTag side • Truth-match to calculate ε and π: • particle ID • same mothers
6. Invariant Mass Spectrum ε = 9.6 % π = 55.1 % • τ background dominant, seen to be: • mostly a1 decays where 1 πo is lost • improperly reconstructed signal decays
7. Tag Invariant Mass Spectra e-tag = bhabha background, low uds μ-tag = no bhabha, low uds ρ-tag = uds background, no bhabha
8. Future Work • Running on the entire 124fb-1 sample: • Apply cuts to subtract remaining backgrounds and optimiseε and π • Unfold detector effects from invariant mass spectrum • Perform fits to spectrum to assess contributions from higher ρ resonances.