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

2 WAR, October 1 st, 2002Gerhard Raven Current Knowledge of  -  plane (Y.Nir, ICHEP02) =

3 WAR, October 1 st, 2002Gerhard Raven The possible effects of New Physics In this example, a clean measurement of  could provide evidence for new physics

4 WAR, October 1 st, 2002Gerhard Raven 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

5 WAR, October 1 st, 2002Gerhard Raven LHCb and BaBar: Physics Programs Marcel Merk SAC April 2002

6 WAR, October 1 st, 2002Gerhard Raven LHCb and BaBar: Physics Programs Measure B d lifetime Requires B reconstruction in copious modes Requires some particle ID Requires vertexing, time resolution Measure B d mixing Requires flavour tagging Requires Particle ID (lepton, K, slow pion) Measure sin(2  ) (“B d mixing phase”) Requires all the above Requires reconstruction of (rare) CP modes (J/p Ks and similar)  What next?  Sin(2  +  )??  Measure B s lifetime  Requires B reconstruction in Ds pi, J/psi phi  Requires some particle ID  Requires vertexing, time resolution  Measure B s mixing  Requires flavour tagging  Requires particle ID  (lepton, K)  Measure sin(-2  ) (“B s mixing phase”)  Requires all the above  Requires reconstruction of (easy) CP modes (J/  )  Requires angular analysis  Measure sin(-2  +  )  Requires excellent particle ID  B s ->D s K vs. B s ->D s , B d ->D s *  Measurement of  using B s mixing Measurement of  using B d mixing

7 WAR, October 1 st, 2002Gerhard Raven Can we measure sin(2  +  ) at BaBar? As for B s -> D s - K +, can make 2 asymmetries B 0 vs. B 0 D* -  + vs. D* +  - As in B s ->J/ , need to make an angular decomposition six components: {0,||,  } x { 0,||,  } In J/ , J/  K* 3 out of 6 vanish There are no penguin b->s (qq), b->d(qq) contributions to these decays B0B0 bdbd udud cdcd ++ D* - bdbd cdcd udud ++ B0B0 bdbd cdcd udud bdbd udud cdcd -- -- D* + B0B0 B0B0 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 (2  +  ), ub |V ub V cd * /V cb * V ud |~2%

8 WAR, October 1 st, 2002Gerhard Raven Current Sample of D*  (and D*a 1 ) 4748 signal 3624 signal As of ICHEP02, BaBar has recorded 89/fb on the  (4S) resonance Could have the equivalent of 5K “perfectly tagged” D*  with 300/fb D* -/+  +/- D* -/+ a 1 +/- Q=  (1-2w) 2  30%

9 WAR, October 1 st, 2002Gerhard Raven Expected Sensitivity Generate time and angular distributions (4D) Use suppressed amplitude which is 2% of the allowed amplitude ub|V ub V cd * /V cb * V ud |~2% Include strong phases 5000 events generated, with perfect tagging Not taken into account: acceptance corrections, angular and  t resolution Expect O(10%) effects on the final error assumes the resolution/acceptance is well known can be measured on control samples: D (*)  Perform full 4D fit extract sin(2  +  ) + 5 strong phases + 5 amplitudes Plot distribution of errors on sin(2  +  ) This is the limiting factor! Warning: the expected precision does depend on the values of the strong phases! Extremely Preliminary!

10 WAR, October 1 st, 2002Gerhard Raven Impact on the  -  plane Using todays most likely value of sin(2  +  ) from indirect measurements Or a completely different value due to new physics…

11 WAR, October 1 st, 2002Gerhard Raven PEP-II Luminosity Planning

12 WAR, October 1 st, 2002Gerhard Raven Integrated Luminosity Projections Expect ~15K reconstructed D*  by summer ‘05

13 WAR, October 1 st, 2002Gerhard Raven 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…

14 WAR, October 1 st, 2002Gerhard Raven 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

15 WAR, October 1 st, 2002Gerhard RavenConclusion 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  -  plane –Measurement(s) of  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, …

16 WAR, October 1 st, 2002Gerhard Raven BACKUP SLIDES

17 WAR, October 1 st, 2002Gerhard Raven A few words about J/  K* 0 (K S  0 ) J/  K* 0 (K S  0 ) angular components: A ||,A 0 : CP = +1 A  : CP = -1 (define R  = |A  | 2 )  CP asymmetry diluted by D  = (1 - 2R  )  R  = (16.0 ± 3.2 ± 1.4) % (B A B AR, 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  tr  4D: Full angular analysis

18 WAR, October 1 st, 2002Gerhard Raven The time and angle dependent decay rate is given by The angular terms depend on the transversity angles  and amplitudes A x These amplitudes are functions of the strong phases D( , A x ) suffers from the sign ambiguity under Floating cos(2  ) does not change the value of sin(2  ): fit is not very sensitive to cos(2  ) The effect seems large, but it is statistical: J/  K* 0 and cos(2  ) rad ±0.7 (syst)

19 WAR, October 1 st, 2002Gerhard Raven Example of a Fully Reconstructed Event  (2S) K s   +  -   +  - D* +  -  D  +  K -  +

20 WAR, October 1 st, 2002Gerhard Raven CP violating observables for B mesons Need at least two amplitudes with different phases In B decays, we can consider two different types of amplitudes: –Those responsible for decay –Those responsible for mixing This gives rise to three possible manifestations of CP violation: –Direct CP violation (interference between two decay amplitudes) –Indirect CP violation (interference between two mixing amplitudes) –CP violation in the interference between mixed and unmixed decays d b WW d u u d   B0B0 B0B0 B0B0 b bd d u,c,tu,c,t u,c,tu,c,t WW WW

21 WAR, October 1 st, 2002Gerhard Raven Sin 2  statistical error vs. time ICHEP00 Winter 01 LP01 Winter 02 Still improving faster than statistics: improved resolution, improved efficiency, additional modes, …

22 WAR, October 1 st, 2002Gerhard Raven 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  -ID, calorimeter resolution, easier trigger (no beams bending just before IR!) Babar: better K-  separation, low momentum tracking (5 layer SVT!), DAQ with more headroom, more advanced analysis Example:  (sin 2  ): BaBar (88M BB events) Belle (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)

23 WAR, October 1 st, 2002Gerhard Raven 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

24 WAR, October 1 st, 2002Gerhard Raven Isn’t BaBar ‘done’? Far from it! Current Hot Topics: Sin(2  eff ) with  and  with Kpi/pipi Sin(2  ) with  Sin(2  ) with other modes b -> ccd: D(*)D(*) penguin modes:  K s,  ( ‘ ) K s Direct CP in rare (charmless) modes V ub with ‘semi exclusive’ reconstruction Part of a set of so-called ‘recoil side’ studies Rare decays: K* , K*l + l - Tests of B decay models (factorization) New round of lifetime and mixing measurements Including d  and CP/T tests Next round: prepare for measurements with a few 100/fb Towards gamma!

25 WAR, October 1 st, 2002Gerhard Raven Why not D0? Not a dedicated B physics experiment Limited K/  ID, trigger, … It is not clear that we could learn more for LHCb from D0 than from BaBar… Expect a measurement of x s But there must be many people working on that already Is there more B physics than J/  X and B s -> D s  Eg. will D0 be able to measure  ? 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