proposal to join the babar experiment

WAR, October 1st, 2002 Gerhard Raven 1

Proposal to join the BaBar experimentProposal to join the BaBar experiment

Oct 1st 2002

Gerhard Raven,On Behalf of the B-physics group


Current Knowledge of Current Knowledge of -- plane (Y.Nir, plane (Y.Nir, ICHEP02)ICHEP02)

=


The possible effects of New PhysicsThe possible effects of New Physics

In this example, a clean measurement of could provide evidence for new physics


LHCb and BaBar: DetectorsLHCb 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


LHCb and BaBar: Physics ProgramsLHCb and BaBar: Physics Programs

Marcel Merk SAC April 2002


LHCb and BaBar: Physics ProgramsLHCb and BaBar: Physics ProgramsMeasure Bd lifetime

Requires B reconstruction in copious modes

Requires some particle IDRequires vertexing, time resolution

Measure Bd mixingRequires flavour tagging

Requires Particle ID(lepton, K, slow pion)

Measure sin(2) (“Bd mixing phase”)

Requires all the aboveRequires reconstruction of (rare) CP modes (J/p Ks and similar)

What next? Sin(2+)??

Measure Bs lifetimeRequires B reconstruction in Ds pi, J/psi phi

Requires some particle IDRequires vertexing, time resolution

Measure Bs mixingRequires flavour tagging

Requires particle ID (lepton, K)

Measure sin(-2) (“Bs mixing phase”)

Requires all the aboveRequires reconstruction of (easy) CP modes (J/)Requires angular analysis

Measure sin(-2+)Requires excellent particle ID

Bs->DsK vs. Bs->Ds, Bd->Ds*Measurement of

using Bs mixingMeasurement of using Bd mixing


Can we measure sin(2Can we measure sin(2++) at BaBar?) at BaBar?

•As for Bs-> Ds-K+, can make 2

asymmetries•B0 vs. B0 •D*-+ vs. D*+-

•As in Bs->J/, need to make an angular decomposition

•six components: {0,||,} x { 0,||,}•In J/ , J/ K* 3 out of 6 vanishThere are no penguin b->s (qq) , b->d(qq) contributions

to these decays

B0 bd

ud

cd

+D*-

bd

cd

ud

+

D*-B0

bd

cd

ud

bd

ud

cd

-

-D*+

D*+

B0

B0

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+),

|Vubub

V cd* /V

cb* V

ud|~

2%


Current Sample of D*Current Sample of D* (and D*a (and D*a11))

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*-/+a1+/-

Q=(1-2w)230%


Expected SensitivityExpected Sensitivity•Generate time and angular distributions (4D)•Use suppressed amplitude which is 2% of the allowed amplitude

•|VububVcd*/Vcb

*Vud|~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!


Impact on the Impact on the -- plane planeUsing todays most likely value of sin(2+) from indirect measurements

Or a completely different value due to new physics…


PEP-II Luminosity PlanningPEP-II Luminosity Planning


Integrated Luminosity ProjectionsIntegrated Luminosity Projections

0

200

400

600

800

yearly luminosity 39 65 68 124 156 185integrated luminosity(/ f b)

106 171 239 363 519 704

2002 2003 2004 2005 2006 2007

Expect ~15K reconstructed D* by summer ‘05


Reliability of PEP-II predictions (“Run 2”)Reliability of PEP-II predictions (“Run 2”)

“Seeman scenario”

expectationwas first shown

March, 2001Deviation towards end of 17 month run mainly due to worsethan expected running efficiency of PEP-II, Mainly due to postponed maintenance…


Service TasksService 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


ConclusionConclusion• 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, …


BACKUP SLIDESBACKUP SLIDES


A few words about J/A few words about J/K*K*00(K(KSS00))

J/ K*0(KS0) 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 tr 4D: Full angular analysis


• The time and angle dependent decay rate is given by

• The angular terms depend on the transversity angles and amplitudes Ax

• These amplitudes are functions of the strong phases• D(, Ax) 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/J/K*K*00 and cos(2 and cos(2))

φ ,φ

rad

rad

)2(cos2.22sin12cos 2

±0.7 (syst)

±0.7 (syst)


Example of a Fully Reconstructed Example of a Fully Reconstructed EventEvent

(2S) Ks +- +-

• D*+ -

D +

K-+


CPCP violating observables for B mesons 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 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

d

bW

d

uu

d

B0

B0 B0

b

b d

du,c,t

u,c,t

W W


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

ICHEP00

Winter 01

LP01

Winter 02

Still improving fasterthan statistics:

improved resolution,improved efficiency,additional modes,…


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 -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 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)


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


Isn’t BaBar ‘done’?Isn’t BaBar ‘done’?Far from it! Current Hot Topics: •Sin(2eff) with and with Kpi/pipi•Sin(2) with •Sin(2) with other modes

•b -> ccd: D(*)D(*)•penguin modes: Ks, (‘)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*, K*l+l-•Tests of B decay models (factorization)•New round of lifetime and mixing measurements

•Including dand CP/T tests

•Next round: prepare for measurements with a few 100/fb•Towards gamma!


Why not D0?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 xs•But there must be many people working on that already

•Is there more B physics than J/ X and Bs -> Ds

•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

proposal to join the babar experiment

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