1. Observation of non-BBar decays of (4S)p+p- (1S, 2S)
Bryan Fulsom
For the BaBar Collaboration
APS-DPF JPS 2006
October 31, 2006.

2. Presentation Outline Motivation for search
Event reconstruction and discriminating variables
Fit method
Validation on ISR (initial state radiation) data
Calculation of systematics
Results and interpretation
Observation of non-BBar decays of U(4S)p+p-U(1S, 2S)
Bryan Fulsom, DPF 2006, October 31, 2006.

3. Motivation (4S) decays nearly 100% to BBar
Predict decay to other bottomonium states with branching fraction O(10-4)
Hadronic transitions in other heavy quarkonia are well known:
ie: y(2S)p+p- J/y, (mS) p+p- (nS) for m=2, 3
Theory from QCD multipole expansion makes predictions for the partial widths and dipion spectrum but fails to describe dipion spectrum in 3S1S
Experimental results for (4S) p+p- (1S)
CLEO:
B((4S) p+p- (1S)) < 1.2 x 10-4
B((4S) p+p- (2S)) < 3.9 x 10-4
Belle (conference result):
B((4S) p+p- (1S)) = (1.1+/-0.2+/-0.4) x 10-4
BaBar:
Observation of both decay modes!
Observation of non-BBar decays of U(4S)p+p-U(1S, 2S)
Bryan Fulsom, DPF 2006, October 31, 2006.

4. Bottomonium Spectrum
Observation of non-BBar decays of U(4S)p+p-U(1S, 2S)
Bryan Fulsom, DPF 2006, October 31, 2006.

5. Analysis Outline
Search for (mS) p+p- (nS), reconstructing (nS)l+l-
Kinematic quantities of interest:
Invariant mass M(l+l-), equal to M(nS)
DM=M(p+p-l+l-) – M(l+l-), equal to M(mS) – M(nS)
Fit to DM in regions of M(l+l-) to extract number of signal events
Use Monte Carlo to simulate signal events of (mS) p+p- (nS)
Includes ISR events with m = 2, 3
ISR (2S) p+p- (1S) and (3S) p+p- (1S, 2S) events from data for validation of MC, event yields, dipion distribution, and determining systematics
DM  20MeV M(m+m-)  200 MeV
Background events taken from data sidebands:
DM  60 MeV M(m+m-)  300 MeV
Observation of non-BBar decays of U(4S)p+p-U(1S, 2S)
Bryan Fulsom, DPF 2006, October 31, 2006.

6. Event Reconstruction BaBar dataset:
211 fb-1 “on-peak”, 230M (4S) events
22 fb-1 “off-peak”, approximately 40 MeV below (4S) resonance
Reconstruct (mS)  p+p- (nS), (nS)  l+l-
Require at least four charged tracks originating from same vertex
Discard candidates with small opening angle between charged tracks
9.0<M(l+l-)<10.5 GeV, 9.0<M(p+p- l+l-)<11.2 GeV
In cases of multiple candidates, retain best reconstructed vertex c2 probability
Focus mainly on (nS)m+m-
(nS)e+e- has poor efficiency and higher backgrounds
Dominant background is m+m-g
Lesser contributions from e+e-g and ISR 4p
Select cuts to discriminate between signal and background events, avoid any bias in angular and dipion invariant mass distributions
Observation of non-BBar decays of U(4S)p+p-U(1S, 2S)
Bryan Fulsom, DPF 2006, October 31, 2006.

7. Discriminating Variables
cosqp+p-: Opening angle between the two pions
Strongly correlated to dipion invariant mass
Loose cut to avoid biasing M(p+p-)
Mee: Invariant mass of pion candidates assuming electron hypothesis
Correlated to cosqp+p-, hence M(p+p-)
Loose cut to avoid bias
Nveto: Number of pion candidates vetoed as electrons
Pions that also pass PID as electrons
Strictly require pion candidates to not be electrons
p*expected: Centre of mass momentum of (mS) candidate
Defined as:
For ISR events, use
Expected to have a value of 0 for signal events
Observation of non-BBar decays of U(4S)p+p-U(1S, 2S)
Bryan Fulsom, DPF 2006, October 31, 2006.

8. Summary of Cuts Observation of non-BBar decays of U(4S)p+p-U(1S, 2S)
Bryan Fulsom, DPF 2006, October 31, 2006.

9. Data Distribution
Observation of non-BBar decays of U(4S)p+p-U(1S, 2S)
Bryan Fulsom, DPF 2006, October 31, 2006.

10. Data Distribution
Observation of non-BBar decays of U(4S)p+p-U(1S, 2S)
Bryan Fulsom, DPF 2006, October 31, 2006.

11. Data Distribution
Observation of non-BBar decays of U(4S)p+p-U(1S, 2S)
Bryan Fulsom, DPF 2006, October 31, 2006.

12. Fit Method Perform 1D unbinned extended maximum likelihood fit to DM
Fit region:
|M(m+m-) – (nS)| < 200 MeV/c2 (1S), < 150 MeV/c2 (2S)
DM  40 MeV
Parameterize the signal PDF on signal MC
Attempt Gaussian, double-Gaussian, Breit-Wigner, Voigtian (B-W & Gaussian)
Voigtian has best c2/d.o.f. for (4S)p+p- (1S, 2S) and ISR MC modes
Use linear background, allow Nsig and DMsig to float
Observation of non-BBar decays of U(4S)p+p-U(1S, 2S)
Bryan Fulsom, DPF 2006, October 31, 2006.

13. Validation (ISR & Off-Peak)
ISR event yield from data compares well with
expected from known BFs and MC efficiency
Ratio of (3S) (2S) / (3S) (1S)
compatible with CLEO
Ratio of ISR yield for e+e- / m+m- modes
equal to 1 within error
ISR dipion distribution matches previous
measurements (see plots)
Perform fit to off-peak data
Number of (4S) events
consistent with zero
Size of background from on-peak fit
consistent with yield in off-peak
Observation of non-BBar decays of U(4S)p+p-U(1S, 2S)
Bryan Fulsom, DPF 2006, October 31, 2006.

14. Systematics Number of (4S) events / luminosity
BaBar B counting uncertainty 1.2%, (4S) should be equivalent
Tracking
Reconstruction efficiency uncertainty in BaBar estimated at 1.3% per track
Muon PID
Compare efficiency of particle ID selector in MC sample to ISR data control sample, find 0.7% systematic error per muon
Acceptance (Uncertainty in angular distribution)
Unknown dipion invariant mass distribution
Estimate by comparing yield assuming phase space distribution (in MC)
to yield using m(p+p-) dependent efficiency from multipole expansion
As large as 10% based on ISR control samples
Observation of non-BBar decays of U(4S)p+p-U(1S, 2S)
Bryan Fulsom, DPF 2006, October 31, 2006.

15. Systematics (continued)
Event Selection
Vary the cut selection and measure the stability of the yield
Release cut on p*, release all cuts but p*, widen dimuon mass window, impose helicity and angular cuts
Test on ISR control sample, take maximum discrepancy in yield for each test in quadrature (total of ~4.3%)
Signal Parametrization
Allow PDF parameters to float individually, or try other parameterizations
Compare yield with background subtracted “cut and count” number of events in 20 MeV window
Negligible effect
Background Parametrization
Compare yield using linear versus quadratic function for background
Systematic less than 2%
Observation of non-BBar decays of U(4S)p+p-U(1S, 2S)
Bryan Fulsom, DPF 2006, October 31, 2006.

16. Summary of Systematics
Observation of non-BBar decays of U(4S)p+p-U(1S, 2S)
Bryan Fulsom, DPF 2006, October 31, 2006.

17. Signal Fit Results
Observation of non-BBar decays of U(4S)p+p-U(1S, 2S)
Bryan Fulsom, DPF 2006, October 31, 2006.

18. Results Significance determined by:
Efficiency is percentage of events returned by fit from total generated in MC
Branching fraction derived from:
Significant observation in m+m- mode, e+e- less compelling
Observation of non-BBar decays of U(4S)p+p-U(1S, 2S)
Bryan Fulsom, DPF 2006, October 31, 2006.

19. Results (continued)
Use experimental values of B((nS)m+m-) to calculate B((4S)p+p- (nS))
Experimental values for B((nS)m+m-) from PDG
G derived from BaBar measurement of G((4S))
Branching fraction for 4S1S compatible with preliminary result from Belle
Partial widths are comparable to other bottomonium dipion transitions, O(keV)
Observation of non-BBar decays of U(4S)p+p-U(1S, 2S)
Bryan Fulsom, DPF 2006, October 31, 2006.

20. Dipion Invariant Mass Spectrum
Shape of 4S1S distribution close to expected from theory
4S2S transition has a low M(p+p-) enhancement...unexpected!
Observation of non-BBar decays of U(4S)p+p-U(1S, 2S)
Bryan Fulsom, DPF 2006, October 31, 2006.

21. Summary Search for non-BBbar decays of (4S)
Observe bottomonium decays (4S) p+p- (nS), (nS)m+m-, where n = 1, 2
Significance: 10.0s for 4S1S, 7.3s for 4S2S
Measure product of branching fractions:
Branching ratios and partial widths are compatible with theoretical predictions and previous experimental limits and results in the bottomonium system
Dipion spectrum for 4S2S is incompatible with QCD multipole expansion
Results published in:
Observation of non-BBar decays of U(4S)p+p-U(1S, 2S)
Bryan Fulsom, DPF 2006, October 31, 2006.

22. Backup Slides Observation of non-BBar decays of U(4S)p+p-U(1S, 2S)
Bryan Fulsom, DPF 2006, October 31, 2006.

23. The BaBar Detector
Observation of non-BBar decays of U(4S)p+p-U(1S, 2S)
Bryan Fulsom, DPF 2006, October 31, 2006.