dresults on cp violation phase in bs system...

D results on CP violation phase in Bs system

G.BorissovLancaster University

19 May 2006 G.Boirssov, Dzero Results on CP violation phase in Bs system 2

CP violation in Bs system

• Contrary to any other system, Bs is strongly mixed;

• Two physical states BsH (heavy) and BsL (light) have distinct masses and lifetimes:

;arg

;cos2

;2

12

12

12

12

M

Mmmm

s

sHLs

LHs M12 and 12 are elements of complex mass matrix (M-i /2)of Bs system;

s- CP violating phase;


Open window for New Physics

• SM model predicts very small value for CP phase s:

s(SM)= O(|Vus|2 mc2/mb2) ~ 5·10-3 = 0.3º– GIM suppression factor (mc2/mb2);– Additional suppression by |Vus|2 ~ 2 ( =0.22 - Wolfenstein

parameter);

• New physics contributions can lift these suppressions;

• Small SM value of s simplifies detection of NP contributions;


First measurement of s

• DØ experiment performs the first measurement of s in different processes:– From the time dependence of polarization amplitudes in

– From the time-integrated di-muon charge asymmetry:

– From time-integrated charge asymmetry of Bs µ D s decay:

NNNN

ASL

)()()()(

XDBNXDBNXDBNXDBN

Assss

ssssuntSL

/JBs


• Clean signal selection;• Final state is mostly CP-even state

with small CP-odd contribution;• They produce different angular

distributions of polarization amplitudes A0, A|| (CP-even) and A(CP-odd);

• Time evolution of these amplitudes depends on lifetime difference sand CP-violation phase s

sDØ preliminary

1 fb-1


Results from Bs J/

• Dzero Conference note 5144

• Most precise direct measurement of s;

• First measurement of s• Consistent with the SM

prediction:

s=0.10±0.03 ps-1

s 0.005

s

01.056.079.0

ps03.009.017.0 -1

s

s1-s contour


Dimuon Charge Asymmetry

• Charge asymmetry of muons from B decays depends on the CP violation phase:

• Non-zero Asl corresponds to CP violation in mixing;• The only type of CP violation not observed yet in B

decays;• At Tevatron, the dimuon charge asymmetry is

measured - better control of systematics:

)tan()()()()(

mXlBNXlBNXlBNXlBN

ASL

SLAllbbNXllbbNllbbNXllbbN

A)()()()(


Dimuon events in DØ

• ~5 Mln of same sign dimuon events collected (1 fb-1) ;

• Excellent muon system with very low punch-through;

• Strong suppression of cosmic background;

• Regular reversal of magnets polarities - reduced detector systematics;


Results

• The most precise measurement of Asl obtained (DØconference note 5042):

• To be compared with Asld results from B-factories:

• Both Bd and Bs contribute to the measured ASL(Dzero);• Combination of these results provides important

information on CP violation in Bs system;

3

3

10)(8.3)(4.56.1)Babar(

10)(0.7)(9.71.1)Belle(

syststatA

syststatAdSL

dSL

310))(8.2)(0.44.4()Dzero( syststatASL


Asymmetry in semileptonicBs decays

• ASLs can also be obtained from time-integrated charge asymmetry in semileptonic decays Bs µ D s:

(U.Nierste hep-ph/0406300)• Large sample of decays Bs µ D s

with D s was collected by DØ;

1/

;21

121

)()()()(

2

2

sss

sSL

sSL

s

s

ssss

ssssuntSL

mx

AAx

x

DBNDBNDBNDBN

A

DØ Preliminary

~27K (µDs) events

1.2 fb-1


Results

• Analysis is similar to the measurement of ASL in same sign dimuon events;

• Exploits the reversal of magnet polarities, which cancels the detector effects;

• First measurement of ASLs for Bs meson (DØ conference note 5143):

210)35.093.145.2(sSLA


Combined value of ASLs

• Both DØ results on ASL can be combined together:– (DØ Conference note 5189);– ASLd value from b-factories is used;

)CDF ,ps 3.03.17 (assuming

ps16.001.0)tan(

0091.00007.0)tan(

-1

-1

s

ssSLss

ss

ssSL

m

mA

mA


Constraints on s and s• We have two constraints (both from DØ) on s and s:• From charge asymmetry:

• From analysis of Bs J/ :

-1ps16.001.0)tan( ssSLss mA

01.056.079.0

ps03.009.017.0 -1

s

s

1-s contour

s


s versus s• Combination of results from ASL and from Bs J/

improves the precision of s :

44.041.0

109.008.0 56.0;15.0 ss ps

s

s


Conclusions

• DØ delivered first ever results on CP violation phase in Bssystem;

• First measurement of CP phase in Bs J/ :

• Most precise measurement of charge dimuon asymmetry:

• First measurement of ASLs :

01.056.079.0

ps03.009.017.0 -1

s

s

310))(8.2)(0.44.4()Dzero( syststatASL

210)35.093.145.2(sSLA


Conclusions

• Results on ASLd from B-factories (Babar, Belle, Cleo) can be combined with Dzero results giving:

• Combining all results together we get:

• Result on CP phase consistent with SM prediction;

10)1.97.0()tan( 3ss

ssSL m

A

44.041.0

109.008.0 56.0;15.0 ss ps


BACKUP SLIDES


µ–

Toroid+

p p

µ+

Toroid+

p p

µ–

Toroid–

p p

µ+

Toroid–

p p

EffEff

Change polarities

EffEff

• Changing magnet polarities cancel detector effects in chrge asymmetry of muon reconstruction;

• Significant reduction in systematics achieved;


Combination of DØ results• ASL in dimuon events at Tevatron can be expressed as:

• DØ extracted ASLd assuming ASLs=0;

• Rewriting it in general form:

• Using ASLd measured at b-factories (Babar, Belle, Cleo) we get:

• Combining it with ASLs from semileptonic decays

• we get:

Mx

x

xZ

ZfZfAZfAZf

A qq

qq

ssdd

sSLss

dSLdd

SL ;1; 2

2 (Grossman, Nir, Raz, hep-ph/0605028,

assuming G/G

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