# Presentation: 530806

## New results from BABAR

- New results from BABAR

- Marie-Hélène Schune
- Laboratoire de l’Accélérateur Linéaire
- Orsay, France

- All numbers are preliminary

- Brookhaven National Laboratory
- Particle Physics Seminar
- May 20, 2002

## New results from BABAR

- I will not talk about
- sin2 in charmonium modes :
- BABAR and PEPII
- Charmless B decays :
- B0, K or KK
- B000
- The “B recoil” physics :
- semileptonic branching fractions
-      of B+ and B0
- D meson production in B decays

- sin20.750.09 0.04

- 56 fb-1

- Winter 2002 conferences

## CKM matrix has 4 real parameters (one phase included)

2 are well known :
 =|Vus|=sin(Cabbibo)=0.22050.0018
A =|Vcb|/2                    =0.83 0.06
unitarity of the CKM matrix leads to constraints that can be tested:

- 2 are well known :
-  =|Vus|=sin(Cabbibo)=0.22050.0018
- A =|Vcb|/2                    =0.83 0.06
- unitarity of the CKM matrix leads to constraints that can be tested:

- CKM matrix for 3 generations

- Unitarity Triangle

- 

- 

## The BABAR detector

**DIRC ****(PID****)**

**1.5T**** ****solenoid**** **

**CsI(Tl)**** ****EMC**

**I****nstrumented**** ****F****lux**** ****R****eturn**

**S****ilicon**** ****V****ertex**** ****T****racker**

**D****rift**** ****C****hamber**

**e****+ ****(3.1GeV)**

**e****- ****(9GeV)**

- SVT: 97% efficiency, 15m z resol. (inner layers, perpendicular tracks)
- Tracking :    pT)/pT = 0.13% PT  0.45%
- DIRC : K- separation >3  for P<3.5GeV/c
- EMC: E/E = 1.33% E-1/4  2.1%

- The BABAR detector

## PEP-II asymmetric B Factory

- 9GeV e- on 3.1GeV e+ :
- s~10.58 GeV
** **** **
- for B0 : coherent neutral B pair production and decay (p-wave)
** **
- boost of (4S) in lab frame : =0.55

## Running at the (4S) 

## May 2nd : 
PEPII delivered : 87 fb-1
BABAR recorded : 83 fb-1 (including 9 fb-1 off peak )

results for 55 fb-1

- PEPII delivered : 87 fb-1
- BABAR recorded : 83 fb-1 (including 9 fb-1 off peak )
- results for 55 fb-1

- B factory performances

- daily integrated luminosity

## 2 - Charmless B decays

- Study of penguins diagrams
- Possible direct CP violation
-  
-  
- B0, K or KK
- Branching fractions (eff , )
- CP violations measurements (eff , )
- B000 (eff )

- (,)

- 

- 

- 

- 

- 

## B0 and CP violation (1)

- BF(B0) << BF(B0K) penguins contributions may be large

- Tree only : =fe2i
- C=0     S=sin(2)

- Tree+Peng.
- C 0 S=sin(2eff)

- mixing e-2i

## B0 and CP violation (2)

**perfect**
- flavour tagging & time resolution

**realistic **
- mis-tagging & finite time resolution

- S=0.7and C=0.

*f*+ : B0 tag

## 

Main variables :
|cosS| : angle between the B0 sphericity axis and the sphericity axis of the rest of the event
F : Fisher discriminant based on “energy flow cones” (CLEO)

- Main variables :
- |cosS| : angle between the B0 sphericity axis and the sphericity axis of the rest of the event
*F* : Fisher discriminant based on “energy flow cones” (CLEO)

- B0, K or KK kinematics

- “Jets”

- Candidate

- Axis of “Rest Event”

- |cosS|

## B0, K or KK : mES and E

- B0, K or KK : mES and E

- Energy substituted mass :
- dominated by the
- beam energy knowledge
-  E : assume  mass
- dominated by the
- tracking resolution
- (E)~26 MeV

- 

- K

- KK

- ~325 MeV

- background

- mES

- 45 MeV

## B0, K or KK : the PID (1)

- B0, K or KK : the PID (1)

- _The DIRC_

- Measure Angle of Cherenkov Cone in quartz
- Transmitted by internal reflection
- Detected by PMTs

- Particle

- Quartz bar

- Cherenkov light

- Active Detector Surface

## DIRC PMT +light catchers

- DIRC stand-off box, magnetic shielding and electronic crates

## B0, K or KK : the PID (2)

- DIRC performances measured on data using D*D0 and D0 K

- (***c*)  2.2 mrad

- K/ separation

- 2.5

- p range of 2-body B decays at BABAR

## B0, K or KK : analysis strategy

- B0, K or KK : analysis strategy

- Start with a B0h+h- (no PID)

- ~17600 events for ~56 fb-1

- unbinned max* L *with
- E, mES, *F*, 1c, 2c

- measure N NK NKK and

- add t and tagging information (as for sin2), fix the yields extract S and C

- B0, K or KK :branching fractions results

| Mode | Yield | Branching Fraction (10-6) | KAsymmetry (AK |
| --- | --- | --- | --- |
| B0+- |  |  |  |
| B0K-+ |  |  |  |
| B0 K+K- |  |  |  |

- Likelihood projections : remove one 1 variable from fit ; cut on *L* proba

-       mES                                     E

-               mES                                     E

- small cross-feed

- small cross-feed

- ~356 B0K

## B0, K or KK : BF comparison

|  | CLEO 9 fb-1 | BABAR 56 fb-1
 | BELLE 31fb-1 |
| --- | --- | --- | --- |
| BF(B0+-)(10-6) | 4.31.60.5
 | 5.40.70.4 | 5.11.10.4
 |
| BF(B0K-+)(10-6)
 | 17.22.51.2
 | 17.81.10.8
 | 21.81.81.5
 |
| BF(B0K-K+)(10-6)
 | <1.9 at 90%CL
 | <1.1 at 90%CL | <0.5 at 90%CL
 |
| AK | -0.040.16 | -0.060.050.01 | -0.060.080.01 |

- BF(B0) << BF(B0K)

## B0, K or KK : CP analyses t

- Time information t :
- resolution dominated by Btag vtx ((z) ~ 180 m)
- extracted from data Breco sample (D(*),D(*),D(*)a1...)
- Background shape : side bands

- Similar to sin(2) analyses

## B Flavour tagging methods

- For electrons, muons and kaons use the charge correlation

- b

- c

- l-

- 

- D, D*

- W-

- Lepton Tag

- b

- W-

- W+

- c

- s

- K*0

- Kaon Tag

- Each category is characterized by the probability of giving the wrong answer (mistag fraction *w*)

- Multivariate analysis exploiting the other kinematic information of the event, e.g.,

-  Momentum spectrum of the charged particles
-  Information from non-identified leptons and kaons
-  Soft  from D* decay

- Neural
- Network

- Hierarchical, mutually exclusive, tagging categories

## B0, K or KK : CP analyses tagging

- Split the events into 4 tagging categories :
- leptons
- kaons
- NT1
- NT2
- Performances obtained
- on data (Breco sample)

- Similar to sin(2) analyses

- NN type
- tagging

-  leptons

-  kaons

-  NT1

-  NT2

- mES

## B0, K or KK : CP analyses validation

- B0, K or KK : CP analyses validation

- Validation : measure B on /K sample :
- Validation : measure md

- B=1.66 0.09 ps

- md=0.517 0.062 ps-1

- Select the Kevents and plot Amix

## B0, K or KK : CP analyses results

- S =-0.010.370.07 S[-0.66,+0.62] at 90 % CL
- C =-0.020.290.07 C[-0.54,+0.48] at 90 % CL

- ~27 B0

- ~9 Background

- ~25 B0

- ~9 Background

- Select the B0 events
- Plot the asymmetry between B0 tag and B0tag  events

## (,) constraints from S and C

- M. Beneke, G. Buchalla, M. Neubert and C.T. Sachrajda Nucl.Phys.B606 (2001) 245

- (,) constraints from S and C

**CKM Fitter**
- H. Höcker, H. Lacker, S. Laplace
-  and F. Le Diberder
- Eur. Phys. J. C21 225-259 (2001)
- http://ckmfitter.in2p3.fr/

## B0, K or KK : CP comparisons

- Belle (K Trabelsi Moriond):

- -C (BABAR)

- 2(SC

- A

## Search for B000

- BF(B000) :
- measured   isospin analysis to get  from B0+-
- 					(M. Gronau, D. London Phys Rev Lett. 65 3381-3384 (1990))
- upper bound  still a useful constraint:
- (Y. Grossman, H. Quinn  Phys Rev D 58 017504 (1998))
- Experimentally challenging :
- low BF expected (th. predictions : 10-7 - few 10-6)
- purely neutral final state
- Recent results :

|  | Yield | limit (10-6) (90% CL) |
| --- | --- | --- |
| CLEO (9 fb-1) | 6.2+4.8-3.7 | 5.7 |
| BELLE (30 fb-1) | 126 | 5.6 |

## 

Main variables :
|cosS| : angle between the B0 sphericity axis and the sphericity axis of the rest of the event
F : Fisher discriminant based on the “energy flow cones”
mEC : energy constrained mass
 E = E*B –s/2 in the CMS

- Main variables :
- |cosS| : angle between the B0 sphericity axis and the sphericity axis of the rest of the event
*F* : Fisher discriminant based on the “energy flow cones”
- mEC : energy constrained mass
-  E = E*B –s/2 in the CMS

- Search for B000 : analysis (1)

- “Jets”

- Candidate

- Axis of “Rest Event”

*F*

## Search for B000 : analysis (2)

- The B 0 background :
- event shape similar to the signal one
- mEC only slightly wider (small  missing)
-  E is the only discriminating variable
- in the fit : fix BF(B 0)=2.410-5 (from CLEO upper limit)

## Unbinned maximum L fit using F PDF and (mEC , E ) PDF
Compare with an optimized cut and count analysis :

Fit yield : 

- Unbinned maximum* L* fit using *F *PDF* *and* *(mEC , E ) PDF
- Compare with an optimized cut and count analysis :
- Fit yield :

- Search for B000 : results

- BF(B000) < 3.4 10-6 at 90 % CL

- Main systematics :
- neutral efficiency
- continuum mEC param.
*F* param.
- B 0 yield

- 54 fb-1

## 3 - The “B recoil” physics

- generic B decay
- B type known
- should allow (in principle !) to measure all B BF
- Will show :  leptonic studies
- 		D0 and D production

## The “B recoil” physics

- B factories : the world’s largest sample of reconstructed B mesons

- 56 fb-1

- B0 sample

- Nsignal=13743125

- B+ sample

- Nsignal=12909120

- Reconstruct the Cabibbo-favored hadronic decays :

## Inclusive semileptonic B decays

- Inclusive rate is large
- Sides of the unitarity triangle |Vcb| and |Vub|
- BXce is large
- BXueis an experimental challenge

- (0,0)

- ()

- 

- 

- 

- (1,0)

## Compare b+/b0 with (B+)/(B0) :

Extract the prompt and cascade lepton spectrum from the charge correlation with the Breco :
B-Xce-
B+Xce+
B0 : correct for mixing

CLEO results (2.4 fb-1) using B0 tagged sample and (4S) l :
b0 = (10.78 0.600.69)%
b+ = (10.25 0.570.65)%
b+/b0 =  

- Extract the prompt and cascade lepton spectrum from the charge correlation with the Breco :
- B-Xce-
- B+Xce+
- B0 : correct for mixing
- _CLEO results (2.4 fb__-1__) using B__0__ tagged sample and ____(4S) ____*l*_* *:
- b0 = (10.78 0.600.69)%
- b+ = (10.25 0.570.65)%
- b+/b0 =

- Inclusive semileptonic B decays

## Electron identification

- Variables :
- E/p
- Shower shapes
- DCH and DIRC
- Performances measured on data:

- 90%

- Backgrounds :
-  conversions
- 0 dalitz decays
- J/ decays

- 10-3

- p (GeV)

## Background subtracted electrons spectra

- 		Right	sign				      Wrong sign

- B
- N right sign= N+p

- B0
- Nright sign=N0p(1-d)+N0cd
- Nwrong sign=N0pd+N0c(1-d)

- results on 21 fb-1

##   b0 and b+ results

-   b0 and b+ results

- BF results :				ratio :

- B+

- B0

## Inclusive branching fractions of B0 and B+ to charmed hadrons
Enters in the nc (= mean charm per B decay ) computation 

For each B specie two measurements are performed :
The absolute BF : BF(BDX) with D = D0 or D+ 
“large statistics”
Need (D) from MC
The wrong D ratio : 
Wrong D sample statistically limited 
Need to correct for mixing for the B0
More MC independant

- Enters in the *n**c* (= mean charm per *B* decay ) computation
- For each B specie two measurements are performed :
- The absolute BF : BF(BDX) with D = D0 or D+
- “large statistics”
- Need (D) from MC
- The wrong D ratio :
- Wrong D sample statistically limited
- Need to correct for mixing for the B0
- More MC independant

- D production in B decays

## D production in B decays reconstruction

-  Hadronic :
- B0 D*D*D*a1

- Semileptonic*:** B*0  *D**l ***
- fit to cos*B-D*l  *variable
**

- mES

- cos*B-D*l*

- D reconstruction : D0 Kand D K

- 50 fb-1

## BF(BDX) 

- BF(BDX)

- Fit N(*D*) and correct for *B*rec background  BF(BDX)

- Brec : B0 D*l

- M(K)

- M(K)

- Brec : B0 D*D*D*a1

|  | BF(B0D0X)(%) |
| --- | --- |
| Semilep. | 57.1  3.3  4.6 |
| Hadronic | 59.3  5.9  3.9 |
| Combined | 57.9  2.9  2.1(*)  3.5(**) |

|  | BF(B0DX)(%) |
| --- | --- |
| Semilep. | 35.7  2.8  3.9 |
| Hadronic | 35.3  4.3  3.8 |
| Combined | 35.6  2.3  1.1(*)  3.6(**) |

- (*)  Correlated syst.
- (**) Uncorrelated syst.

## w(D) for neutral B mesons

*w*(D) for neutral B mesons

- Correlate the D and the B flavours :
- For B0 : should correct for mixing
- done on an optimized time interval (|t|<2.5 ps)  reduced statistical uncertainty, md dependance

- obs =

- Mix

- Mix+Unmix

- = d + *w* (1 2 d)

- Unmix

- Mix

- Brec : B0 D*l

- Brec : B0 D*D*D*a1

- M(K)

- 	*w*( *B*0  *D* X) (%)
- Semilept.  7.3  3.7  1.9
- Hadronic  8.9  7.1  1.8
- Combined 7.7  3.3  1.4  0.8

- 	*w*( *B*0  *D *0X ) (%)
- Semilept. 15.9  3.5  2.4
- Hadronic  9.6  4.7  1.1
- Combined 13.1  2.8  1.5  0.6

## Results suggest B0 spectator quark effect negligible in wrong D production
Results consistent with world data (“B admixture”)

In the future : 
Add the B sample 
100 fb-1 
 start to look for Ds and c (looser Breco selection ?)

- Results consistent with world data (“*B* admixture”)
- In the future :
- Add the B sample
- 100 fb-1
-  start to look for Ds and c (looser Breco selection ?)

- D production in B decays

- Better understanding of the overall picture of the B decays

- Compare BF( *B*0  *D*0 + *D*+ X) =  (83.1  6.4) % with
- world data: BF( *B*admixt  *D*0 + *D*+ X) =  (78.5  3.4) %

- 30 or 51 fb-1

## Summary

- A true factory of B mesons :
- BF(B0 +-) = (5.40.70.4) 10-6
- BF(B0 K+-) = (17.81.10.8) 10-6
- Unfortunately not enough to get B000
- BF(B000) < 3.4 10-6 at 90 % CL
- CP violation results :
- S =-0.010.370.07
- C =-0.020.290.07
- “B recoil” physics is starting :
- Semi leptonic measurements
- D mesons production in B
-     decays