1. Mitchell Naisbit Manchester Jan2004 spectral function → a μ, α 1. Motivation Dominant uncertainty comes from experimentally determined hadronic loops:

2. Mitchell Naisbit Manchester Jan2004 2. Motivation cont’d Recent results show discrepancy between and spectral functions Babar ideal to validate τ result.

3. Mitchell Naisbit Manchester Jan2004 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. Mitchell Naisbit Manchester Jan2004 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. Mitchell Naisbit Manchester Jan2004 5. Selection Procedure Selection for data and MC samples: Use 1-1 events and tag to reduce backgrounds Signal side Tag side Truth-match to calculate ε and π : particle ID same mothers

6. Mitchell Naisbit Manchester Jan2004 6. Invariant Mass Spectrum π = 55.1 % ε = 9.6 % τ background dominant, seen to be: mostly a 1 decays where 1 π o is lost improperly reconstructed signal decays

7. Mitchell Naisbit Manchester Jan2004 7. Tag Invariant Mass Spectra μ -tag = no bhabha, low uds e-tag = bhabha background, low uds ρ -tag = uds background, no bhabha

8. Mitchell Naisbit Manchester Jan2004 8. Future Work Running on the entire 124fb -1 sample: Apply cuts to subtract remaining backgrounds and optimise ε and π Unfold detector effects from invariant mass spectrum Perform fits to spectrum to assess contributions from higher ρ resonances.