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Charm Threshold Running and Rare Decays

This report discusses the benefits of running experiments at the charm threshold, including improved precision in mixing parameters and the study of rare decays. The analysis focuses on the potential of a run at the ψ(3770) energy and the impact it could have on CKM γ measurements and D0 mixing studies. The report also highlights the importance of measuring strong phases and quantum correlations in multi-body channels. Data from the DD threshold is used as a basis for projections, with the expectation of reduced uncertainties in Dalitz plot models.

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Charm Threshold Running and Rare Decays

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  1. Report from Charm WG(White Paper  TDR) Running at “Charm Threshold” and Rare Decays B. Meadows U. Cincinnati for the charm team D. Asner, Carleton U, I. Bigi, U. Notre Dame, R. Andreassen, M. Sokoloff U. Cincinnati Brian Meadows, U. Cincinnati Super B, Elba, Italy, 5/30-6/05/2010

  2. 2 Outline • Running at charm threshold • General • Improved precision in mixing parameters • Semi-leptonic asymmetries – aSL • Time-Dependent Quantum Correlations (TDQC)? • Rare decays • D0+- • D0hl+l- • Summary Brian Meadows, U. Cincinnati Super B, Elba, Italy, 5/30-6/05/2010

  3. Threshold Running Scenario The run envisaged here is a 500 fb-1 exposure at (3770) About 600 x CLEO-c and (50-100) x BES III Just above DD threshold At one-tenth nominal luminosity, Super B can complete this in a few months Set up and tuning of final focus may take another few months  Perhaps a year altogether – maybe less? Possible schedules (in order of preference) Plan this in as a run after 25 ab-1 at (4S) Run because of a discovery at (4S) Start-up Super B with this run Do this only at the end of 10 years at (4S)

  4. General Reasons for a (3770) Run It is possible (likely?) that an unusual effect – perhaps due to NP – will be found in the charm sector from (4S) running A true confirmation in the entirely different charm scenario at (3770) will trump a simple repeat performance with more luminosity at (4S) A 500 fb-1 run will improve both our own, and also LHCb’s CKM  measurement by a factor ~ 3. Decays of (3770)  D0D0 produce coherent (C=-1) pairs of D0’s. Quantum correlations in their subsequent decays allow measurements of strong phases Required for improved measurement of CKM  Also required for D0 mixing studies

  5. General Reasons for a (3770) Run A record exists of several cases where CLEO-c, sometimes with just 281 pb-1 of their 818 pb-1 sample at (3770), has successfully competed with BaBar’s ~0.5 ab-1 and Belle’s ~1 ab-1 at (4S). Examples: Measurement of decay constants – fD and fDs Studies of leptonic and semi-leptonic decays, Measurements of absolute hadronic branching fractions Other runs for CLEO-c at other CM masses have produced useful and novel results for Ds as well as D decays from (3770).  Is a program at (4S) complete without the “service” of one at (3770), etc.?

  6. CLEO-c Hadronic Charm Decays at (3770) Single Tags Only E ~ 0 in signal E sidebands in yellow

  7. Semi-Leptonic Decays Example of D0 K-e+e decay from CLEO-c’s 818 pb-1 exposure at (3770). Quantity plotted is U = Emiss – c Pmiss (Note background level ~0)

  8. 8 Quantum-Correlations (QC) • Running at (3770) CLEO c were able to measure K-+ strong phase: from 281 pb-1 • Including other D mixing results: • ALSO, they were able to measure bin-by-bin strong phase variations in, for example, the Ks+- Dalitz plot • Of value to improved (model-independent) measurement of CKM  • Also of value in D0 mixing measurements Brian Meadows, U. Cincinnati Super B, Elba, Italy, 5/30-6/05/2010

  9. 9 m-2 (GeV2/c4) m02 (GeV2/c4) Time-Integrated QC in Multi-body Channels • Relative phases “bin-by-bin” in multi-body phase-space. Quantum correlations remove necessity for model describing phase space. Probably ONLY way to obtain a true PWA fit. X X For higher multiplicities, we could measure “coherence” and a single strong phase. For 3-body final states this provides model-independent measurement of strong phase variation over the Dalitz plot Brian Meadows, U. Cincinnati Super B, Elba, Italy, 5/30-6/05/2010

  10. 10 “Double-Dalitz” Plot Fit: An example from CLEO c e+e-(3770)  (Ks+-) (Ks+-) • There are two Dalitz plots correlated in a time-dependent way: • If you select CP-odd Ks0 in one, you see “no”Ks0 in the other. • If you select RS K*-+ in one, you see only (opp. sign) RS K*+- in the other. EXCEPT: • There will be a small signal arising from MIXING. • This has a definite time-dependence, making it more identifiable above background. • Backgrounds at (3770) are small ! CLEO data: - It works !! J. Napolitano http://indico.ihep.ac.cn/conferenceDisplay.py?confId=176 Brian Meadows, U. Cincinnati Super B, Elba, Italy, 5/30-6/05/2010

  11. DD Threshold Measurements • Data from DD threshold provide measurement of strong phases such as K and <K¼0 >. • They also provide measured values of  in Dalitz plot bins This can be used (with a model for the values forr) to significantly reduce uncertainties in the Dalitz plot model used in the golden channel analyses. • As a basis for projection, we take results from CLEO-c: N. Lowrey et al, PRD80, 031105 (2009), 0903.4853 • We assume that new data from threshold will reduce the uncertainties in model uncertainty: • BES III – ~factor 3 improvement in model uncertainty • Super B 500 fb-1DD threshold run – ~factor 10 improvement.

  12. Dalitz plot model uncertainty shrinks • Information on overall strong phase is added Uncertainty inxDimproves more than that of yD Value of Strong Phase Measurements • Two improvements in mixing precision come from threshold data:

  13. Origin of CPV from aSL • Wrong Sign (WS) lepton asymmetry measures CPV that can arise ONLY from mixing: No CPV See Talk by I. Bigi here ? If measurement lies on curve, CPV is ALL in MIXING aSL |q/p| Current Measurement !

  14. Precision of aSL Uncertainty from a signal S over background B is

  15. 0.82 fb-1 492 fb-1 344 fb-1 Another D In event Measurement of aSL – Needs (3770) Data! • Decays to wrong-sign (WS) leptons proceed through mixing • Rate is very small RM=(x2+y2)/2x10-4~ 5x 10-5 and not yet observed: Right-sign (RS) Decays D0K-e+e+ c.c. RM< 6x10-4 RM< 13x10-4 (3770): D0tagged 4S): D0 tagged by D*+D0 + fully reconstructed not reconstructed Include Hadronic decays* Background limits WS data asl) for 500 fb-1 ~ 0.20 asl) for 75 ab-1 ~ 0.80 asl) for 75 ab-1 ~ 0.20 *At (3770). We need CLEO-c data to refine our knowledge of backgrounds we can expect.

  16. 16 aSL from (3770) Data(Needs evaluation from simulation) • Two un-ambiguous possibilities. • One ambiguous possibility. • Ambiguity should be resolved using difference and interference in time-dependence of mixing vs. direct DCS decay. (3770) (3770) K+e-e  K+e-e  Bose statistics requires that one D0 had to mix (3770)  K+e-e D0K+-5 x more likely to beDCSthanD0->K+e-eis from mixing Brian Meadows, U. Cincinnati Super B, Elba, Italy, 5/30-6/05/2010

  17. 17 Summary of CPV Sensitivity from Mixing Brian Meadows, U. Cincinnati Super B, Elba, Italy, 5/30-6/05/2010

  18. 18 m-2 (GeV2/c4) m02 (GeV2/c4) Time-dependent QC Decays – “Super D” ? • The moving CMS means we could measure time-dependent (TD) strong phases resulting from D0 mixing. Samples are large. E.g. Ks+- (on both sides) will have about 500K events. X X Boost is ~same as for Y(4S) but D0 ~ 0.4B0 Is this possible or useful ? Brian Meadows, U. Cincinnati Super B, Elba, Italy, 5/30-6/05/2010

  19. 19 “Super D” ? • The time-dependent “Double-Dalitz” analysis can be made on a wide variety of double-tagged events: • (Ks+-) - (Ks+-) • (Ks+-) – (Ks K+K-) • (Ks+-) – (K-+0) • (Ks+-) – (K-+) • (Ks+-) – (K-K+) • … etc. • We need a simulation to learn how well this might work in face of reduced time-resolution wrt “Super B”.. • Large samples. • Highly constrained (model-dependent) • Measure |q/p| and =Arg{q/p} direct CPV, … Brian Meadows, U. Cincinnati Super B, Elba, Italy, 5/30-6/05/2010

  20. 20 Rare Decay D0+- Brian Meadows, U. Cincinnati Super B, Elba, Italy, 5/30-6/05/2010

  21. 21 Search for D0+- • There is considerable theoretical interest in the FCNC decay D0+-(see I. Bigi’s talk, Perugia, Friday am) • The SM estimates a lower limit BF > 4 x 10-13 • Estimates would be improved by measurement of D0 • Only estimate so far - BF[D0] < 1.5 x 10-5 [Recall that, for KL+-, SMBF = 6.4 x 10-8 – right on the money!] Long-range mechanism (Dominant in KL+- - NOT necessarily so in D0 case) Brian Meadows, U. Cincinnati Super B, Elba, Italy, 5/30-6/05/2010

  22. 22 12k + c qk - u 22k Interest in D0+- • R-parity SUSY could increase the decay rate by up to to 7 orders to BF~3.5x10-6 • Current experimental limits are: • Super B should be able to arrive at upper limits much better than this and also measure BF[D0] to better understand the SM limit. Opens a 7 orders of magnitude search window for NP Brian Meadows, U. Cincinnati Super B, Elba, Italy, 5/30-6/05/2010

  23. 23 Interest in D0+- • Ikaros: “10-8 would be an interesting goal” • At D threshold, the +- (or ) are “back-to-back” in transverse momentum and should present an excellent signal-to-noise ratio. [BESIII claim they will use 20 fb-1 to give them a 90% limit at 3 x 10-8 – apparently a mistake] http://arXiv.org/pdf/0801.1833 and Eur.Phys.J.C57:309-492,2008. • Further study of CLEO-c data at threshold will show if a better limit can be reached. Brian Meadows, U. Cincinnati Super B, Elba, Italy, 5/30-6/05/2010

  24. D0 A recent CLEO-c study (private communication from D. Asner) has shown that an efficiency of 5% has been achieved with no background events in the full 818 pb-1 sample.

  25. Summary A strong case for a 500 fb-1 run at (3770), based upon a single study of NP is not difficult to make. One candidate may be a clean search for D0+- decays with a limit near or below 10-8. This requires study of CLEO-c data and a better idea of PID performance at Super B A great breadth of excellent results to support other findings at Super B related to charm physics or spectroscopy could also be made. Very precise measurements of fDs will be possible. Rare decays to D0“nothing”, a sure sign of NP, will be possible only at charm threshold.

  26. 26 David Asner … our young man, heading West. Expert at running at DD threshold. Ikaros Bigi … willing to grow a beard if CPV is not observed in D decays by 2017! Get well soon, Ikaros !! Brian Meadows, U. Cincinnati Super B, Elba, Italy, 5/30-6/05/2010

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