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Upsilon Cross Section Status Matthew Jones B Analysis Status Subgroup Meeting May 29 , 2012

Upsilon Cross Section Status Matthew Jones B Analysis Status Subgroup Meeting May 29 , 2012. Upsilon Cross Section. is the number of ϒ signal events obtained by fitting the mass distribution. is the acceptance, calculated using Monte Carlo.

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Upsilon Cross Section Status Matthew Jones B Analysis Status Subgroup Meeting May 29 , 2012

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  1. Upsilon Cross Section StatusMatthew JonesB Analysis Status Subgroup MeetingMay 29, 2012

  2. Upsilon Cross Section • is the number of ϒ signal events obtained by fitting the mass distribution. • is the acceptance, calculated using Monte Carlo. • is the product of trigger and selection efficiencies. • is the integrated luminosity.

  3. Fit to di-muonmass distribution • No explicit silicon hit requirement. • Binned likelihood fit: • Three Gaussian functions for the ϒ(nS) signals • Fixed mass splitting • Floating Gaussian resolution • Polynomial background • Fit CMUP_CMU and CMUP_CMX samples separately. • Probably biased slightly by the radiative tail, but this should not change with time. • Plot the yield of ϒ(1S) divided by integrated luminosity as a function of time…

  4. CDF Note 10628 • The only reason we did not pursue a cross section measurement was figure 66: A “luminosity period” contains approximately 250 pb-1 of equivalent integrated luminosity. Why isn’t it constant?

  5. Table of run ranges Period 0 Period 10 Period 29 CMUP_CMU CMUP_CMX

  6. Update with the full data sample Things did not remain stable after luminosity period 20. The apparent cross section continued to drop.

  7. Comparison of fits Lumi period 4 Lumi period 24 Obvious difference in normalization…

  8. Comparison of Fits Lumi period 4 (histogram) Lumi period 24 (error bars) Normalizing lumi period 24 to the number of events in lumi period 4 – the background shape is only slightly different.

  9. Gaussian Resolution • Possibly a 10% change at lumi period 20 • start of offline period 29 • beginning of 0p dataset • Should not affect yield to first order CMUP_CMU CMUP_CMX

  10. What was checked? • Acceptance calculated using Monte Carlo: This was done using 500 pb-1 integrated luminosity periods. Lower CMX acceptance in early data understood as due to incremental additions CMX coverage. The important thing is that the CMUP_CMU acceptance is completely flat. CMUP_CMU CMUP_CMX

  11. Absolute Track Reconstruction Efficiency • Checked using : The statistical precision of this test is limited. Analysis of the (almost) complete J/ψ sample still does not suggest that there is a loss of tracking efficiency. We asked for a much higher statistics test to be performed using the yields to rule out a degradation of the tracking efficiency…

  12. XFT Track Finding Efficiency • Also checked using : • XFT acceptance cuts: • Efficiency for K+ to be matched with an XFT track:

  13. Vertex Cut Efficiency • Checked using J/ψ sample and a simple model for the XFT+CMU acceptance. Consistent with the estimate that is usually used, which was based on the analysis of minimum bias events. If anything, the efficiency seems to increase in the later data, but only by about 1%. Changes in do not line up with jumps in the cross section. 250 pb-1

  14. Integrated Luminosity • Cross checked DPS luminosity accounting but did not find any systematic problem. • Similar time dependence observed for triggers. Offline period 18

  15. Comparison with Upsilon Yield Offline period 18 Integrated luminosity period 10

  16. Luminosity Measurement • Could there be changes in the CLC efficiency that have not been taken into account? • Since (we hope), we can consider only the first term.

  17. Luminosity Measurement • Keeping only the first term, with • We observe NØ empty bunch crossings out of N total bunch crossings, solve for and calculate . If δ was larger than the assumed value (ie, ε or A was smaller), then the estimate for μ and hence ℒ would be biased low.  We see fewer inelastic collisions than expected, so we think the luminosity is lower than it really is. But then we would expect to see more ϒsignal per calculated pb-1, not less… P(Ø)=NØ/N μ

  18. Luminosity Measurement • If thresholds were set too low and the CLC was triggering on noise then effectively, δ would be larger than expected. • Bottom line: it would be nice to cross check the luminosity calculation by some other method, like counting vertices in zero bias data.

  19. Conclusions • So far, no obvious time dependence has been found in any trigger, tracking or reconstruction efficiencies. • Other completely unrelated triggers see similar time dependence of cross sections. • The luminosity measurement remains one input that has not been carefully checked. • Discussion to follow…

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