Measurement of sin(2) in the decays B0 D()D()

Douglas Roberts

University of Maryland

Physics Motivation

Prediction of Standard Model: The CP asymmetries in all Bd decays that do not

involve direct b u or b d transitions have to be the same.

This implies that CP asymmetries in B D()D(), which is bc(cd), should be the same as seen in BJ/KS, which is bc(cs) Both measurements related to sin(2)

Any difference in measurements would indicate non-Standard Model contributions

Physics Motivation (cont.) SUSY with gluino masses of ~100-300 GeV can

lead to deviations from SM asymmetry prediction in B D()D() measurable by BABAR†. Looking for ~10% difference in asymmetry measurement

(Standard Model uncertainty). Depends on ratio of tree and penguin matrix elements in

B D()D(), so would need good calculation of hadronic matrix elements

One can also potentially measure the angle g in these decays via the interference of the tree and penguin‡

†for example, Y. Grossman and M. Worah, Phys. Lett. B 395, 241 (1997)‡A. Datta, D. London, Phys. Lett. B 584, 81 (2004)

DD Analysis Group

University of Maryland Vincent Lillard (Graduate Student, graduated Spring 2004) Chung Khim Lae (Graduate Student) Jacob Anderson (Graduate Student) Chunhui Chen (Postdoc) Douglas Roberts (Faculty)

UC Irvine Maarten Bruinsma (Postdoc)

Caltech Justin Albert (Postdoc) Tim Pietenko (Graduate Student)

Reconstruction of B0DD

We reconstruct B0 mesons exclusively using a number of D* and D decay modes: DD0, DD0

D0K, K0, K, KS

D+K, KS, K-K+

Total of 22 mode combinations used Results based on 1999-2004 data

210 fb-1, about 200 million BB pairs

Signal Observation, B0DD

270 ± 19 events in the signal region

Purity of ~75% Branching Fraction:

(8.1±0.6±1.0)×10-4

Preliminary Also see signals in:

DD

DD

DD

DD

DD

DD

B0DD Data Event

BABAR B0 D*+ D*-

D0 + D0 -

K _+

K+ - + -

1 2

3 4

5 6 7

1

2

3

4

5

76

8

Transversity Amplitudes in B0DD

The vector-vector final state of B0DD is not a pure CP eigenstate.

Assuming factorization CP-odd P-wave component could be of the order 5%.

We can measure this directly, however

RT is fraction of CP-odd component, given by:

Will present preliminary result at Heavy Flavor 9 conference

2 21 3 3(1 )sin cos

cos 4 2T tr T trtr

dR R

d

Angular DistributionAngular Distribution

4

2 2 21 0

1 d 9 1

d cos d cos d d 32 | | | | | |tr tr t A A A

2 2 2 20 1{4 | | cos sin costr trA

2 2 2 212 | | sin sin sintr trA

2 2 212 | | sin cos trA

* 20 12 ( )sin 2 sin sin 2tr trA A

*0 12 ( )sin 2 sin 2 costr trA A * 2

12 ( )sin sin 2 sin }tr trA A

Time dependent full angular distribution for B0 D*+ D*

(A┴ A┴ for B0 decay)trttrttr

RR

22 cos2

3sin)1(

4

3

cos d

d1

Integrating over time, B flavor, 1, tr

get one dimensional pdf in terms of Rt:

The above pdf does NOT take detector acceptance into account!The above pdf does NOT take detector acceptance into account! (previous measurements measured bias in MC and added to final result) We choose to put efficiency directly into PDF….

CP-evenCP-evencomponentcomponent

CP-oddCP-oddcomponentcomponent

Results - RResults - Rtt

RRtt = 0.125 = 0.125 0.044 0.044(stat)(stat)

0.0070.007(syst)(syst)

B0 D*+ D* is found to be mostly CP-even

Shown is the projectionprojection of events with mES > 5.27 GeV/c2

Background parameter consistent with fits to sideband events: bb22 = -0.16 = -0.16 ± 0.17± 0.17

500 toy experiments show goodness of fit:

Angular DistributionAngular Distribution4

2 2 21 0

1 d 9 1

d cos d cos d d 32 | | | | | |tr tr t A A A

2 2 2 20 1{4 | | cos sin costr trA

2 2 2 212 | | sin sin sintr trA

2 2 212 | | sin cos trA

* 20 12 ( )sin 2 sin sin 2tr trA A

*0 12 ( )sin 2 sin 2 costr trA A * 2

12 ( )sin sin 2 sin }tr trA A

Time dependent full angular distribution for B0 D*+ D*

Time dependent amplitudes:

00,|| / 2

0,|| 2 22

2( ) cos sin

(1 | | )

imt t mt mtA

A t e e i

0

/ 22 22

2( ) cos sin

(1 | | )

imt t mt mtAA t e e i

Generalized comparison: let’s assume penguin contributions are negligable let’s assume penguin contributions are negligable (only one )(only one ) (and |q/p| = 1 so that |A|2 = ||2 ) Now, integrating over all three angles…

CP dilution factor: K = 1 – 2Rt

2

2 2

0 * *(1 | | ) 2 ( )

(1 | | ) (1 | | )

1 d ( )1 cos sin

dtB D D

e mt K mtt

q Ap A

Time dependent asymmetry:Time dependent asymmetry:2

2 2

2 ( ) (1 | | )

(1 | | ) (1 | | )sin cosCPA K mt mt

S =K sin2 C

(–)(–) (+ )

Allowing Penguins…Allowing Penguins…

If penguin diagrams are non-negligible, this leads to different ||, 0, ┴

00,|| / 2

0,|| 0,||2 22

2( ) cos sin

(1 | | )

imt t mt mtA

A t e e i

0

/ 22 22

2( ) cos sin

(1 | | )

imt t mt mtAA t e e i

2 0 * *34

tr

2 2+

2 2

2

1 d ( ){

dcos d

[ sin 2cos ]

+ [ sin 2cos ]cos

+ [ sin

t

tr tr

tr tr

tr

B D De

t

O O

C C mt

S

22cos ]sin }trS mt

Now the decay rate can be written as a function of tr and time:

Note: a common value of || or Im() cannot be factored!

Mixture of CP-evenCP-even(+) and CP-odd(CP-odd())contributions dilute sin(mt) coeff.!

2 2|| 0

2 2|| 0

2

2

|| 02 2

|| 0

2

12

12

(1 | | ) (1 | | )0 2 0 2|| 0(1 | | ) (1 | | )

(1 | | ) 0 2

(1 | | )

2 ( ) 2 ( )0 2 0 2|| 0(1 | | ) (1 | | )

2 ( ) 0 2

(1 | | )

(1 ) 1

(1 )

| | | |

| |

| | | |

| |

t

t

O K R

O K R

C A A

C A

S A A

S A

(–)

(–)

(–)

Results – CP fitResults – CP fit

C = 0.06 ±0.06 ± 0.170.17(stat)(stat) ± 0.030.03(syst)(syst)

sin2 = 0.75 ±0.75 ± 0.250.25(stat)(stat) ± 0.030.03(syst)(syst)

Charmonium sin2 = 0.685 ± 0.032World AverageWorld Average

Summary

CP asymmetries consistent with charmonium results Assuming no

penguin contribution

Future Prospects

Measurement of CP asymmetries and RT submitted to PRL(hep-ex/0505092)

Have seen evidence for other B0DD decay modes useful for CP studies

We are beginning a more comprehensive program to measure all decays of the type BDD

Both charged and neutral B Will help get a handle on penguin contributions Look at color-suppressed decays Currently working on a paper draft that included branching ratio

measurements (or limits) for all 10 modes of the type B DD

This will be an excellent compliment to our measurement of sin2 in B0J/KS!

Dr. Chen has started looking at BDDK decays Potential to measure cos2

The BaBar Silicon Vertex Tracker

Maryland Involvement in the BABAR Silicon Vertex Tracker (SVT) The Maryland group has had continued involvement

in the calibration and maintenance of the SVT D. Roberts, V. Lillard, C.K. Lae, together with a

group from LBL and UC Santa Cruz, have been working on the internal, in situ, alignment of the SVT Involves measuring location and orientation of 340 silicon

wafer with an accuracy < 5 m Improvements in vertex resolution seen during past year

have improved many analyses, including CP measurements and lifetimes

SVT Local Alignment

We have developed a fitting tool used for alignment that fits ee events as a single track using the know beam boost parameters.

This provides very accurate measurements of the track orbit, and allows tracks to be fit in the SVT alone.

Reduces errors on alignment parameters by close to factor of 10 for same statistical sample of events

With about 100,000 -pair events together with some cosmic tracks, we are able to measure alignment to a few microns Position resolution is >10m

SVT Operations

Graduate students V. Lillard and C.K. Lae and postdoc C. Chen have all served as SVT Operations Managers C. Chen in early part of 2004 C.K. Lae currently serving

Operations Managers are responsible for the day-to-day operations of the SVT Check data quality First ones to get paged when something goes wrong Serve for a 3 month term

C. Chen is currently serving as the Operations Coordinator Responsible for training the Op. Managers Expected to be more of an expert than the managers and should

be able to deal with more serious problems

SVT System Management

Since May of 2003, D. Roberts has been acting as one of the two SVT system managers Responsible for current operation of SVT Coordinating software and hardware development Planning for future detector upgrades

Recently pushed through a successful plan to upgrade to the radiation monitoring and protection system System was installed summer of 2004, and has been functioning as expected

During the 2006 shutdown, we could have the opportunity for an intervention of the SVT (i.e. take it apart and fix/replace any problem components) Over past year or so, we have done a risk/benefit analysis of performing an

intervention. Conclusion was that the SVT is functioning fine as is, risk of damage not outweighed

by benefit. Actively involved in understanding performance of the SVT in the upcoming

high-luminosity runs of PEP-II Impact of radiation to lifetime of SVT Impact on physics of higher detector occupancy Integration with redesigned interaction region