Proposal to join the BaBar experiment

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Proposal to join the BaBar experiment
Gerhard Raven, On Behalf of the B-physics group

• Oct 1st 2002

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Current Knowledge of r-h plane (Y.Nir, ICHEP02)
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The possible effects of New Physics
In this example, a clean measurement of g could
provide evidence for new physics
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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

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LHCb and BaBar Physics Programs
Marcel Merk SAC April 2002
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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(-2dgg)
• Requires excellent particle ID
• Bs-gtDsK vs. Bs-gtDsp, Bd-gtDsp

• 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(2bg)??

Measurement of g using Bd mixing
Measurement of g using Bs mixing
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Can we measure sin(2bg) at BaBar?
VubVcd/VcbVud2

• As for Bs-gt Ds-K, can make 2 asymmetries
• B0 vs. B0
• D-r vs. Dr-
• As in Bs-gtJ/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 (62 asymmetries!) to extract
• the relative strong phases,
• the relative magnitudes of the amplitudes
• the weak phase (2bg),

There are no penguin b-gts (qq) , b-gtd(qq)
contributions to these decays
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Current Sample of Dr (and Da1)
As of ICHEP02, BaBar has recorded 89/fb on the
?(4S) resonance
D-/a1/-
D-/r /-
Could have the equivalent of 5K perfectly
tagged Dr with 300/fb
Qe(1-2w)2?30
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Expected Sensitivity
This is the limiting factor!

• Generate time and angular distributions (4D)
• Use suppressed amplitude which is 2 of the
  allowed amplitude
• VubVcd/VcbVud2
• 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(2bg) 5 strong phases 5
  amplitudes
• Plot distribution of errors on sin(2bg)

Warning the expected precision does depend on
the values of the strong phases!
Extremely Preliminary!
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Impact on the r-h plane
Using todays most likely value of sin(2bg)
from indirect measurements
Or a completely different value due to new
physics
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PEP-II Luminosity Planning
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Integrated Luminosity Projections
Expect 15K reconstructed Dr by summer 05
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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
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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
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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,

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BACKUP SLIDES
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A few words about J/?K0(KSp0)

• J/? K0(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
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J/yK0 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)
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Example of a Fully Reconstructed Event

• ?(2S) Ks
• ? mm- ? pp-
• D p-
• ? D p
• ?K-p

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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 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

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Sin 2b statistical error vs. time
Still improving faster than statistics improved
resolution, improved efficiency, additional
modes,
ICHEP00
Winter 01
LP01
Winter 02
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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 hasnt 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)

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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 isnt 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

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Isnt 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 -gt 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 Kg, Kll-
• 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!

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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 -gt 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