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Proposal to join the BaBar experiment. Oct 1 st 2002. Gerhard Raven, On Behalf of the B-physics group . Current Knowledge of r - h plane (Y.Nir, ICHEP02). =. The possible effects of New Physics. In this example, a clean measurement of g could provide evidence for new physics.

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Proposal to join the babar experiment

Proposal to join the BaBar experiment

Oct 1st 2002

Gerhard Raven,

On Behalf of the B-physics group

Gerhard Raven

Current knowledge of r h plane y nir ichep02
Current Knowledge of r-h plane (Y.Nir, ICHEP02)


Gerhard Raven

The possible effects of new physics
The possible effects of New Physics

In this example, a clean measurement

of g could provide evidence for new physics

Gerhard Raven

Lhcb and babar detectors
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

Lhcb and babar physics programs
LHCb and BaBar: Physics Programs

Marcel Merk SAC April 2002

Gerhard Raven

Lhcb and babar physics programs1
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

Can we measure sin 2 b g at babar
Can we measure sin(2b+g) at BaBar?





































  • |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

Current sample of d r and d a 1
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*-/+r +/-

Could have the equivalent of 5K

“perfectly tagged” D*r

with 300/fb


Gerhard Raven

Expected sensitivity
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

Impact on the r h plane
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

Integrated luminosity projections
Integrated Luminosity Projections

Expect ~15K reconstructed D*r by summer ‘05

Gerhard Raven

Reliability of pep ii predictions run 2
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

Service tasks
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


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

Backup slides

Gerhard Raven

A few words about j k 0 k s p 0
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

J y k 0 and cos 2 b
J/yK*0 and cos(2b)



  • 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

Example of a fully reconstructed event
Example of a Fully Reconstructed Event

(2S) Ks

m+m- p+p-

D*+ p-

 Dp+


Gerhard Raven

Cp violating observables for b mesons
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 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

Sin 2 b statistical error vs time
Sin 2b statistical error vs. time

Still improving faster

than statistics:

improved resolution,

improved efficiency,

additional modes,


Winter 01


Winter 02

Gerhard Raven

What about belle
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

Impact with small group
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

Isn t babar done
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

Why not d0
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