babar @ scipp
DESCRIPTION
BaBar @ SCIPP. Part I: Introduction, Service, Radiative Penguin and (3S) Physics. DOE Site Visit June 10, 2008. Bruce Schumm, SCIPP BaBar P.I. BaBar @ SCIPP: Major Highlights. Major physics contributions include: Leading role (Lockman) in BaBar’s discovery of D 0 mixing - PowerPoint PPT PresentationTRANSCRIPT
BaBar @ SCIPP
Part I: Introduction, Service, Radiative Penguin and (3S) Physics
DOE Site VisitJune 10, 2008
Bruce Schumm, SCIPP BaBar P.I.
BaBar @ SCIPP: Major Highlights
Major physics contributions include:
• Leading role (Lockman) in BaBar’s discovery of D0 mixing
•Major role in measurement of |Vtd| and search for new physics in b d transition (very rare!)
• Pioneering work in sub-percent charm-sector CP asymmetries
• Major role in “legacy” measurement of b s transition
Students Post Docs Senior/Faculty
Tim Beck[*] Juergen Kroseberg[1] Al Eisner[2]
Christian Flacco[*] Lei Wang Bill Lockman
Joel Martinez Bruce Schumm
Luke Winstrom Abe Seiden
[*] Graduated this year[1] Now on faculty at U. Bonn[2] Not supported by this grant
Personnel
Final BaBar Data Sample
RUN DURATION ACCUMULATED SAMPLE
RUN I 01/00 10/00 20 fb–1
RUN II 01/01 06/02 61 fb–1
RUN III 11/02 08/03 32 fb–1
RUN IV 09/03 06/04 100 fb–1
RUN V 04/05 08/06 133 fb–1
RUN VI 01/07 – 12/07 79 fb-1
TOTAL Y(4S) 01/00 – 12/07 425 fb-1
(3S) 01/08 – 03/08 30 fb-1
(2S) 03/08 – 04/08 14 fb-1
Off-Peak Interspersed 50 fb-1
GRAND TOTAL 01/00 – 04/08 519 fb-1
Over 7-8 years, BaBar accumulated roughly 0.5 ab-
1 of data, mostly at the Y(4S).
The analyses reported here all incorporated data through at least run V.
SCIPP Service to BaBarTraditionally, involved in SVT, DCH design and construction…
DIRC
SVT
DriftChamber(DCH)
H-Cal/(IFR)
E-Cal(EMC)
Major Service Contributions
Tasks
Wang (Post Doc) Drift Chamber Residuals
Winstrom (Grad) Prompt Reconstruction Manager 6/07-12/07
Martinez (Grad) SVT Commissioner 6/07-11/07
Eisner (Volunteer) SVT Online Data Quality Ongoing
Leadership
Kroseberg (Post Doc) Radiative Penguin Convener To 1/08
Eisner (Volunteer) Trigger/Filter/Luminosity Convener Ongoing
Schumm (Faculty) Speaker’s Bureau 9/06-3/08
Refinement of Drift Chamber Time-to-Distance Relation
DOCA
ANGLE
• Hit position derived from time of signal arrival on wire
• Need position and uncertainty for track fitting
2D distributions shows that error depends on entrance angle as well as “DOCA”
Lei Wang: Characterize residual error (uncertainty) as a function of both DOCA and entrance angle; re-do track reconstruction
Drift Chamber Time-to-Distance Relation Improvements
Number of drift chamber hits per track, improved residual characterization minus
default characterization
Improvements:
• More DCH hits per track (see plot at right)
• Improved by 3% overall and by 15% for pt < 200 MeV/c
• 12% decrease in unused hits
Radiative Penguin Physics
The SM transition is high order (two weak plus one EM vertex…
So new physics can enter at leading order
Also:
• CKM parameters (Vts, Vtd and supports Vub measurement)
• B meson dynamics (input to extraction of Vub from B Xu l
b motionFigure thanks to J Walsh, INFN-Pisa
Fully Inclusive Measurement of (bs)
Winstrom, Eisner, Schumm (with SLAC, Notre Dame, Oregon)
• Find high-energy photon• Use event shapes and lepton tag to suppress continuum background• Look for other 0 () photon, or extended clusters, to suppress
B background• Very challenging!
qq + ττ
BB
XSγ
BB
Cont.
Signal
selection
But also rewarding…
Direct searches (LEP)
B s constraints
MSSMConstraints
Extra DimensionsSUSY
Leading indirect constraint on several new physics scenarios
% of total Error
Statistitical
Systematic
Model
Run I-II Result (Phys.Rev.Lett.97:171803,2006 )
Br (BXs) = (3.67 0.29 0.34 0.29) x 10-4
Run I-V analysis projecting 3.4% statistical error (run I-II is 7.9%)
Must work hard to reduce systematic and model errors!
Update to Runs I-V Sample
Fate of “Other” (Low-Energy) Photon
Below 30 MeV (lost) 13.9%
Interact before DIRC (lost) 5.0%
Pass through CAL (lost) 0.8%
Interact in DIRC, and lost 5.0%
Interact in DIRC, and found 8.0%
Convert in CAL, and lost 6.1%
Conver in CAL, and found 61.2%
TOTAL 100%
Reduce B backgrounds (blue) by finding “other” photon and reconstructing 0() decay
How often is “other” (low-energy) photon missed?
Answer: About 2/3 of time. Need to understand 1/3 loss with great precision!
0 that fakes signal
“other” B/Bbar Backgrounds
Working with Calorimeter group to understand losses in DIRC, and in CAL (cracks, overlap with other clusters, etc.)
Also working on smaller but significant background from anti-neutrons (how to constrain with antiprotons from p?)
Also doing basic coding and general infrastructure support for analysis…
Group targeting late summer for result (updated branching fraction plus first and second photon energy moments).
Fully Inclusive Measurement of (bs): Contributions and Target
bd and the CKM Parameter Vtd
Measurement of the bd transition provides direct sensitivity to Vtd
Vtd
Accurate measurement of Vtd provided by Bd mixing rate; normalize to Bs mixing rate to minimize hadronic uncertainties (CDF, D0; Phys.Rev.Lett. 97 (2006) 242003 )
(d) (d)(d)
(d)
(d)
(d)
(d) (d)(d)
(d)
Vtd
Penguin physics accesses Vtd via independent diagram…
MIXING: Xd ~ 0.2 SM rate of order 10-1 x B
PENGUINS: Overall suppression of 10-5 SM rate of order 10-5 x B
New physics likely much more visible in bd width
Comparison of Penguin and Mixing measurements of |Vtd/Vts| is a sensitive testbed for new physics
bd and New Physics
(d)
(d)
Two approaches; both avoid hadronic uncertainties by normalizing to corresponding bs process:
Exclusive measurement of Br(B [/])/Br(BK*)
Martinez, Kroseberg, Schumm (with CalTech)
Semi-Inclusive measurement of (bd)/(bs)
Beck (thesis), Schumm (with Imperial College and Edinburgh)
As for Bd/Bs mixing, ratio of d and s observables directly sensitive to |Vtd/Vts|2 0.04
bd Measurements
B (/) (a.k.a. b d “exclusive”)(and )
Current Results (x106)
BaBar (Run I-V) BELLEPRL 98, 151802 PRL 96, 221601
B+ + 1.1 0.3 0.1 0.6 0.4 0.1
B0 0 0.8 0.2 0.1 1.3 0.4 0.1
B0 0 < 0.8 <1.0
Since 0 has yet to be found, optimize Run I-VI analysis for this mode.
015.0200.0 021.0020.0
ts
td
V
V
~8% “theory” error from annihlation, form factor
Reject continuum with “Boosted Decision Tree” multivariate discriminator with 55 input variables (validate with B K* sample)
Reconstruct
B0 0 0 + -
B+ + + + 0
B0 0 0 + - 0
(rejection of kaons from B K*; K* K is critical)Use the two largely uncorrelated “fit” discriminating variables:
E event energy sum
MES event momentum balance
**
beamBEEE 22*
BbeamESpEm
Boosted Decision Tree selection much cleaner:
B0 0 analysis; old (Run I-V)
analysis
B0 0 analysis; new (Run I-VI)
analysis
But luck is not with us…
Current and New Results (x106) Comparison
PRELIMINARY; NOT PUBLIC
BaBar Run I-V BaBar Run I-VI PRL 98, 151802 PRD to come…
B+ + 1.10 0.34 0.09 1.20 0.42 0.25
B0 0 0.79 0.21 0.06 1.03 0.23 0.11
B0 0 0.40 0.22 0.05 0.49 0.26 0.07Restricting new analysis to Run I-V shows that:
• Significance improved for B0 0
• Run VI data has unlucky background fluctuation in B+
Collaboration needs to decide whether to use these or stay with old numbers (probable: these will supplant old numbers via a PRD article)
Fit to B Sample
b d “semi-inclusive” measurement
Reconstruct 7 b d final states, along with corresponding b s states.
Restrict to mass range 0 < Mhad < 1.8 GeV/c2 (S/N issues)
More signal, but no explicit use of intermediate resonance structure higher backgrounds
Measure more of partial width lower (?) and independent systematics
First time ever tried for b d
Breakdown of Measured/Unmeasured WidthNominal Signal MC
Mhad
# 0
# bodies
MEASURED
UNMEASURED
(,,K*)
1.0 < Mhad < 1.8 1.8 < Mhad
XS
Xd
Increase measured fraction of bd width from ~10% to ~30%
FIT…
Fit to seven bd modes in high-mass region (most challenging of four fitting
regions)
Preliminary – Not Yet Public
Continuum background
bs + MisID background
(Statistical errors only, but dominated by bd statistics)
Correct for unmeasured modes, mhad < 1.8 GeV/c2
= 1.2 0.2
Ratio of (bd) to (bs) in rangeMhad < 1.8 GeV/c2
Extraction of |Vtd|/|Vts|
Rsb
db
V
V
had
had
M
M
ts
td
8.1
8.1
2
)(
)(
where 1 corrects for
• Possible differences in d and s spectrum above Mhad = 1.8 GeV/c
2 (should be small)
• Annihilation diagrams effects (as for / )
• Quark/hadron duality assumption
But: once theorists have done their work, should provide a better-than 20% measurement of |Vtd|/|Vts| (global / constraint is about 13%)
Search for Dark Matter Candidates at the (3S)
Using 30 fb-1 of e+e- (3S)
Luke Winstrom (thesis topic), Al Eisner, Bruce Schumm; with Steve Sekula (Ohio State postdoc)
• Develop tagged sample of (1S) decays through decay chain (3S) (1S) + + + -
• Look for (1S) invisible; possible sources include SUSY, generic light dark matter
• Limit with 30 fb-1 of e+e- (3S) expected to be better than 5x10-4 (Belle limit with 3 fb-1 is 2.5x10-3)
Irreducible Background:
(3S) (1S) + + + -
with leptons outside of fiducial volume.
l+ + l-
Luke Winstrom:
Asymmetric detector allows geometrical inefficiency to be constrained by looking at difference between one- and two-lepton cos distributions
BOTH MUONS FOUND
ONE MUON FOUND
Goal: Preliminary result by late summer
BaBar @ SCIPP
On to charm physics…
Initial plans:
1) Xs fragmentation has been measured well, and correction factors derived. We can apply those correction factors to Xd and see how K changes.
2) Alternative Xs model based on RS for ~10 resonances developed; simulate corresponding Rd and see how K changes.