Proposal to join the BaBar experiment

1. Proposal to join the BaBar experiment Oct 1st 2002 Gerhard Raven, On Behalf of the B-physics group Gerhard Raven

2. Current Knowledge of r-h plane (Y.Nir, ICHEP02) = Gerhard Raven

3. The possible effects of New Physics In this example, a clean measurement of g could provide evidence for new physics Gerhard Raven

4. LHCb and BaBar: Detectors • Dedicated B physics experiments • Physics programs based on exclusive reconstructed B events • Triggers for purely hadronic B decays • (trivial in the case of BaBar ;-) • Momentum resolution • Vertex resolution • Excellent particle ID: • K/pi separation crucial for many topics in B physics • Dedicated Cherenkov detectors for K/pi separation Gerhard Raven

5. LHCb and BaBar: Physics Programs Marcel Merk SAC April 2002 Gerhard Raven

6. LHCb and BaBar: Physics Programs • Measure Bs lifetime • Requires B reconstruction in Ds pi, J/psi phi • Requires some particle ID • Requires vertexing, time resolution • Measure Bs mixing • Requires flavour tagging • Requires particle ID • (lepton, K) • Measure sin(-2dg) (“Bs mixing phase”) • Requires all the above • Requires reconstruction of (easy) CP modes (J/yf) • Requires angular analysis • Measure sin(-2dg+g) • Requires excellent particle ID • Bs->DsK vs. Bs->Dsp, Bd->Ds*p • Measure Bd lifetime • Requires B reconstruction in copious modes • Requires some particle ID • Requires vertexing, time resolution • Measure Bd mixing • Requires flavour tagging • Requires Particle ID • (lepton, K, slow pion) • Measure sin(2b) (“Bd mixing phase”) • Requires all the above • Requires reconstruction of (rare) CP modes (J/p Ks and similar) • What next? • Sin(2b+g)?? Measurement of g using Bd mixing Measurement of g using Bs mixing Gerhard Raven

7. Can we measure sin(2b+g) at BaBar? r+ u d u d D*- B0 b d b d c d c d D*- B0 r+ c d c d r- b d b d u d u d D*+ B0 D*+ B0 r- • |VubVcd*/Vcb*Vud|~2% • As for Bs-> Ds-K+, can make 2 asymmetries • B0 vs. B0 • D*-r+ vs. D*+r- • As in Bs->J/yf, need to make an angular decomposition • six components: {0,||,} x { 0,||,} • In J/yf , J/y K* 3 out of 6 vanish • The combination of these creates enough observables (6*2 asymmetries!) to extract • the relative strong phases, • the relative magnitudes of the amplitudes • the weak phase (2b+g), There are no penguin b->s (qq) , b->d(qq) contributions to these decays Gerhard Raven

8. Current Sample of D*r (and D*a1) 4748 signal 3624 signal As of ICHEP02, BaBar has recorded 89/fb on the (4S) resonance D*-/+a1+/- D*-/+r +/- Could have the equivalent of 5K “perfectly tagged” D*r with 300/fb Q=e(1-2w)230% Gerhard Raven

9. Expected Sensitivity This is the limiting factor! • Generate time and angular distributions (4D) • Use suppressed amplitude which is 2% of the allowed amplitude • |VubVcd*/Vcb*Vud|~2% • Include strong phases • 5000 events generated, with perfect tagging • Not taken into account: • acceptance corrections, • angular and Dt resolution • Expect O(10%) effects on the final error • assumes the resolution/acceptance is well known • can be measured on control samples: D(*)p • Perform full 4D fit • extract sin(2b+g) + 5 strong phases + 5 amplitudes • Plot distribution of errors on sin(2b+g) Warning: the expected precision does depend on the values of the strong phases! Extremely Preliminary! Gerhard Raven

10. Impact on the r-h plane Using todays most likely value of sin(2b+g) from indirect measurements Or a completely different value due to new physics… Gerhard Raven

11. PEP-II Luminosity Planning Gerhard Raven

12. Integrated Luminosity Projections Expect ~15K reconstructed D*r by summer ‘05 Gerhard Raven

13. Reliability of PEP-II predictions (“Run 2”) “Seeman scenario” expectation was first shown March, 2001 Deviation towards end of 17 month run mainly due to worse than expected running efficiency of PEP-II, Mainly due to postponed maintenance… Gerhard Raven

14. Service Tasks • In LHCb, one of our main responsibilities is the tracking software • In BaBar, we also want to focus on tracking • Have the required experience/history in this area • G.R. used to be BaBar Tracking Coordinator • DCH-SVT Alignment • Initially developed by G.R. + Wouter Verkerke • Beamspot determination • Utilize the D(*)(pi/rho/a1) sample for data quality checks • Absolute momentum scale • Mass resolution • Validation of new software releases/improvements • Can be extended to monitoring of K/pi performance of DIRC • Same sample also needed for vertex resolution and mistag rates… • The LHCb and BaBar tracking reconstruction (and simulation) software are surprisingly similar… • And so is (less surprising) the analysis software and model! • So even from the service tasks we can learn for LHCb! The BaBar senior management agrees that the above is a reasonable and relevant proposal, beneficial for the experiment Gerhard Raven

15. Conclusion We have the opportunity to participate with a cutting edge, dedicated, well-running B physics experiment Predictable performance, low risk Timescale good match to current LHC startup With a limited but coherent effort, we can make an impact on the r-h plane Measurement(s) of g at BaBar are a good match to our established LHCb plans We can gain a lot of B-physics experience which will help improve our readiness to analyze LHCb data at the startup of LHC Exclusive B reconstruction/selection, time dependent & angular fits, analysis logistics, … Gerhard Raven

16. BACKUP SLIDES Gerhard Raven

17. A few words about J/K*0(KSp0) J/ K*0(KSp0) angular components: • A|| ,A0 : CP = +1 • A : CP = -1 (define R = |A|2 ) CP asymmetry diluted by D = (1 - 2R) R = (16.0 ± 3.2 ± 1.4) % (BABAR, to appear in PRL) • Last year, just used R as an additional dilution • Now, perform full angular analysis instead: O 1D: Treat R as dilution  2D: Use qtr 4D: Full angular analysis Gerhard Raven

18. J/yK*0 and cos(2b) rad rad • The time and angle dependent decay rate is given by • The angular terms depend on the transversity angles w and amplitudes Ax • These amplitudes are functions of the strong phases • D(w, Ax) suffers from the sign ambiguity under • Floating cos(2b) does not change the value of sin(2b): fit is not very sensitive to cos(2b) • The effect seems large, but it is statistical: ±0.7 (syst) ±0.7 (syst) Gerhard Raven

19. Example of a Fully Reconstructed Event (2S) Ks m+m- p+p- D*+ p-  Dp+ K-p+ Gerhard Raven

20. CP violating observables for B mesons u,c,t d B0 B0 W- W- d b u,c,t d p- u b W- u b B0 p+ d d • Need at least two amplitudes with different phases • In B decays, we can consider two different types of amplitudes: • Those responsible fordecay • Those responsible formixing • This gives rise to three possiblemanifestations of CP violation: • Direct CP violation • (interference between two decay amplitudes) • Indirect CP violation • (interference between two mixing amplitudes) • CP violation in the interferencebetween mixed and unmixed decays Gerhard Raven

21. Sin 2b statistical error vs. time Still improving faster than statistics: improved resolution, improved efficiency, additional modes, … ICHEP00 Winter 01 LP01 Winter 02 Gerhard Raven

22. What about Belle? • KEK performance looks better right now than PEP • But PEP, after 3 years, is still ahead on integrated luminosity • My expectation: both machines will remain within O(10%) over the next 4 years (with Belle maybe with a slight lead) • Detectors have both their strong and weak points: • Belle: better m-ID, calorimeter resolution, easier trigger (no beams bending just before IR!) • Babar: better K-p separation, low momentum tracking (5 layer SVT!), DAQ with more headroom, more advanced analysis • Example: s(sin 2b ): • BaBar 0.741 +- 0.067+-0.033 (88M BB events) • Belle 0.719 +-0.074+-0.035 (85M BB events) • BaBar statistical error includes items which are in the Belle systematic error (uncertainties due to control sample size!), BaBar systematic includes things which Belle hasn’t considered yet… (choice of resolution model, tagging-vertexing correlations, phases of tag side ‘wrong sign’ decays). • 74/63 = sqrt(1.4)  sqrt(1.04) = sqrt(88/85) • LHCb analysis software strongly modeled on BaBar • ~50% of BaBar is in Europe (UK, France, Italy, Germany) • good infrastructure for phone meetings: most meetings are at 8 AM PST (i.e. 5 PM EST) Gerhard Raven

23. Impact with small group? • Builds on previous experience in BaBar • Pick closely related analysis, which benefit from each other and existing experience • Focus on service tasks closely related to analysis and/or where we have experience • Strategic relations with a few other institutes • UCSD (V. Sharma, D. MacFarlane), • Iowa (S. Prell -- formerly UCSD), • UCSB (C. Campagniari, W. Verkerke) • By BaBar standards, the group isn’t even small! • small compared to say SLAC, Berkeley, Saclay, • but not to Harvard, Princeton, Stanford,… • UCSD was 2 faculty (part-time), 3 postdoc, 1 grad student, and had/has major contributions to the physics results, tracking, calibrations, running of the experiment Gerhard Raven

24. Isn’t BaBar ‘done’? • Far from it! Current Hot Topics: • Sin(2aeff) with pp and g with Kpi/pipi • Sin(2a) with rp • Sin(2b) with other modes • b -> ccd: D(*)D(*) • penguin modes: fKs, h(‘)Ks • Direct CP in rare (charmless) modes • Vub with ‘semi exclusive’ reconstruction • Part of a set of so-called ‘recoil side’ studies • Rare decays: K*g, K*l+l- • Tests of B decay models (factorization) • New round of lifetime and mixing measurements • Including dG and CP/T tests • Next round: prepare for measurements with a few 100/fb • Towards gamma! Gerhard Raven

25. Why not D0? • Not a dedicated B physics experiment • Limited K/p ID, trigger, … • It is not clear that we could learn more for LHCb from D0 than from BaBar… • Expect a measurement of xs • But there must be many people working on that already • Is there more B physics than J/y X • and Bs -> Dsp? • Eg. will D0 be able to measure g? • Can D0 keep up with CDF in B(s) • physics? • Perceived higher risk than BaBar: • Can do B physics today at BaBar • Learning curve much easier in • BaBar Gerhard Raven