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.