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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;
19 May 2006 G.Boirssov, Dzero Results on CP violation phase in Bs system 3
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;
19 May 2006 G.Boirssov, Dzero Results on CP violation phase in Bs system 4
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
19 May 2006 G.Boirssov, Dzero Results on CP violation phase in Bs system 5
• 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
19 May 2006 G.Boirssov, Dzero Results on CP violation phase in Bs system 6
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
19 May 2006 G.Boirssov, Dzero Results on CP violation phase in Bs system 7
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)()()()(
19 May 2006 G.Boirssov, Dzero Results on CP violation phase in Bs system 8
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;
19 May 2006 G.Boirssov, Dzero Results on CP violation phase in Bs system 9
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
19 May 2006 G.Boirssov, Dzero Results on CP violation phase in Bs system 10
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
19 May 2006 G.Boirssov, Dzero Results on CP violation phase in Bs system 11
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
19 May 2006 G.Boirssov, Dzero Results on CP violation phase in Bs system 12
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
19 May 2006 G.Boirssov, Dzero Results on CP violation phase in Bs system 13
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
19 May 2006 G.Boirssov, Dzero Results on CP violation phase in Bs system 14
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
19 May 2006 G.Boirssov, Dzero Results on CP violation phase in Bs system 15
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
19 May 2006 G.Boirssov, Dzero Results on CP violation phase in Bs system 16
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
19 May 2006 G.Boirssov, Dzero Results on CP violation phase in Bs system 17
BACKUP SLIDES
19 May 2006 G.Boirssov, Dzero Results on CP violation phase in Bs system 18
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;
19 May 2006 G.Boirssov, Dzero Results on CP violation phase in Bs system 19
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
ssdd
sSLss
dSLdd
SL ;1; 2
2 (Grossman, Nir, Raz, hep-ph/0605028,
assuming G/G
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