D s + f 0 (980) e + n and Implications for B s J/ y f 0 (980)
1
D D s s + + f f 0 0 (980) e (980) e + + and Implications for and Implications for B B s s J/ J/ f f 0 0 (980) (980) Liming Zhang (Syracuse University) Liming Zhang (Syracuse University) on behalf of the CLEO Collaboration on behalf of the CLEO Collaboration Introduction Introduction “B s -B s mixing phase” -2 s : a place to look for New Physics Measurements of CP violation in the B meson system are sensitive to the presence of heavy, as yet undiscovered, particles. The SM value sin(2 s ) = 0.037 0.002 is small, where 2 s 2arg[ − V ts V tb * /V cs V cb * ] Both CDF and D0 have investigated -2 s using B s J/ decays. The central value has been found far from the expected SM value, but the error is large and the significance of the possible discrepancy is in the 2-3 range. B s J/ f 0 (980) The ss quarks not only can form a , but also , ' and f 0 (980) mesons. The scalar f 0 state, however, has not been previously considered. From BESII, we know f 0 (980) decay is dominated by + - , which is more useful than the , ' modes because of poor photon efficiency at current hadron collider experiments. 0 -eigenstates, and thus an angular analysis is unnecessary. Since the final state J/ is not a CP-eigenstate, an angular analysis is necessary, which requires large statistics compared to CP eigenstates. Estimate using D s + semileptonic decays Stone and Zhang [1] argued that the branching ratio B s J/ f 0 (980), f 0 + - to J/ could be estimated by the ratio of decay widths at q 2 = 0, where q 2 is the e + and neutrino invariant mass squared ) 0 , , ( ) 0 , , ) 980 ( ( ) , / ( ) ), 980 ( / ( 2 2 0 0 0 0 q K K e D q f e f D K K J B f f J B s s s s The Feynman diagrams in B s and D s + are analogous: J/ in B s and virtual W + in D s + are both spin-1 objects. The available energy in B s , m Bs -m J/ =2.27 GeV, is comparable to m Ds =1.97 GeV, so q 2 = 0 in the D s + semileptonic decays give good estimation for the B s case. FIG. 2: Diagrams for B s J/ (f 0 ) and D s + (f 0 ) e + FIG. 1: -2 s from B s J/ CLEO-c Technique CLEO-c Technique Tag Method: We use e + e D s D s * at 4170 MeV with 600 pb 1 of data. We fully reconstruct one D s and also the from D s * as a “tag”, then examine the properties of the other D s + . The D s tags we reconstructed can come from either directly produced D s mesons or those that result from the decay of a D s * mesons. Tag Reconstruction: We first reconstruct D s from 9 decay modes and require the beam constrained mass of candidates in the interval of [2.015, 2.067] GeV to pre-select D s D s * events. We then detect the photon from the D s * decay by looking for an additional photon candidate in the event that satisfies our shower shape requirement. We calculate the missing mass squared MM* 2 recoiling against the photon and the D s tag, Single Tag Yields: To obtain number of D s tags, we simultaneously fit to the invariant mass ) and MM* 2 . We obtain the total number of single tags 30848±695±925 in the invariant mass signal region ( 17.5 MeV from the D s mass) and MM [3.782, 4.0] GeV 2 CM 2 CM 2 * ) ( ) ( MM p p p Ds Ds E E E Mass Projection MM* 2 Projection Sideband bkgrnd Multi bkgrnd FIG. 3: D s invariant mass and MM* 2 distributions from 9 tag modes (for detail see PRD 79, 052001 (2009)) Signal Reconstruction & Data Distribution Signal Reconstruction & Data Distribution Candidate events are selected that contain only or K + K and a track with opposite charge to the tag, which we identify as an electron. The electron identification requires the track makes an angle >25.8 with respect to the beam line and momentum >200 MeV. In addition we require that there not be any photon detected in the calorimeter with energy greater than 300 MeV. The missing mass squared, MM 2 , evaluated by taking into account the observed f 0 () meson, e D S and should peak at zero; We use a set of kinematical constraints and fit each event to two hypotheses one of which is that the D s tag is the daughter of a D s * and the other that the D s * + decays into D s + , with the D s + subsequently decaying into signal. In addition, we constrain the invariant mass of the D s to the known D s mass. This gives us a total of 7 constraints. The missing neutrino four-vector needs to be determined, so we are left with a three-constraint fit. We perform a standard iterative fit minimizing . We choose the fitted MM 2 from the hypothesis giving the smaller 2 . We simultaneously fit the D s invariant mass, MM 2 and or K + K invariant mass. A large mass window for dipion is chosen to measure the f (980) mass and width. Here a relativistic Breit-Wigner function ) is used to fit the data distribution, where The fit gives = 92 2 ) ( CM 2 ) ( CM 2 ) ( ) ( MM 0 0 f e Ds f e Ds E E E E E p p p p p Results (Preliminary) Results (Preliminary) D s + f 0 e + form factors The decay rate can be written in terms of as + - invariant mass (m) and q 2 where G F is the Fermi constant, p f 0 is the momentum of the f 0 in the D s + rest frame, |V cs | is a CKM matrix element, f + (q 2 ) is function called form-factor, and P(m 2 ) is the PDF of the f 0 mass distribution. The q 2 distribution and branching fractions We separate data into 5 q 2 bins, and perform similar fits as used before but fix the f 0 mass and width to the observed values. The yields, efficiencies and efficiency corrected yields in the 5 q 2 bins are shown in Table 1. The branching fractions can be extracted by dividing the efficiency corrected yields sums in each mode by the number of tags. We find B(D s f 0 e + f 0 + 0.200.03 0.01 and B(D s e + 2.360.23 0.13 We fit the efficiency corrected q 2 distribution. For the f 0 e + , the fit function is Eq. (1) integrated over m, and a simple pole model f + (q 2 )=1/(1q 2 /m A 2 ) is used. For the e + , we use the BABAR measured shape [2]. We obtain a preliminary value of the pole mass and preliminary ratio ) ( | ) ( | ) , ( 192 | | ) ( 2 2 2 2 3 3 4 2 2 2 2 0 0 m P q f q m p m V G dq dm e f D d f D cs F s s FIG. 4: Distributions of (a) MM 2 and (b) m + - for f 0 e + and (c) MM 2 and (d) m K + K - for e + , superimposed with the total fitting function and each of its components in colors. , )) ( ( ) ( ) ( ) ( 2 2 0 2 2 0 2 2 0 2 m m m m m m m BW m m m m m m m 0 2 2 0 2 2 0 2 4 / 4 / ) ( Non-D S backgroun d signal ( 0 )e + '()e + (a) (b) (c) (d) Non-D S backgroun d (1) GeV 2 . 0 7 . 1 5 . 4 7 . 0 A m )% 11 42 ( ) 0 , , ( ) 0 , , ) 980 ( ( 2 2 0 0 q K K e D q f e f D s s We study D s + f 0 (980)e + , f 0 (980) + - and D s + e + , K + K using e + e D S D S * interactions at 4170 MeV collected with the CLEO-c detector. By examining the rate as a function of the four-momentum transfer, q 2 , we measure the ratio of f 0 / rates at q 2 = 0 to be (4211)%, thus indicating that the decay B s J/f 0 (980), could be useful for measuring the “B s -B s mixing phase” -2 s . Properties of the f 0 (980) are also studied. Table 1: Preliminary number of events and efficiency e in q2 intervals. (The errors on e are ab FIG. 5: Preliminary q 2 distributions with fit functions superimposed. MeV ) 3 91 ( MeV ) 1 977 ( 30 22 0 11 9 0 m Systemic errors obtained by varying m A In the earlier + - invariant mass fit, we did not take into account the fact that the phase space for the larger f 0 masses is somewhat smaller than that for smaller f 0 masses, due to the finite D s mass. To take into account this effect, we need integrate Eq. (1) over q 2 in the allowed region [0, (m Ds -m) 2 ]. Here we use P(m 2 )=BW(m 2 ). We used our fitted form-factor shape for f + (q 2 ). We obtain m 0 = (977 1) MeV and 0 = (91 3) MeV. The systematic errors are determined by varying the form-factor by one error width. FIG 6: Invariant mass distribution for + . The signal shape is a relativistic Breit-Wigner modified by phase space and form-factor effects. For the meanings of the curves, see FIG 4 (a). f f 0 0 (980) Properties (980) Properties f f 0 0 (980) in (980) in D D s s Hadronic Decays Hadronic Decays Stone and Zhang [1] also use branching fractions of D s + K + K and + from CLEO and the BABAR Dalitz analysis of the 3 mode [3] (Fig. 7) to derive where the mass is within 90 MeV of the f 0 (980) mass. Fig. 8 shows the diagram for D s decay into plus an ss system. )%, 30 ~ 20 ( ) , ( ) , ( 0 0 0 K K D f f D s s BABAR FIG. 7: Dalitz plot projections (dots with error bars) and fit results (solid histogram). The hatched histograms show the background contribution. From the BABAR Collaboration [3]. f 0 (980) FIG. 8: Diagram for a D s + decay into plus an ss system. References References [1] S. Stone and L. Zhang “S-waves and the measurement of CP violation phases in B s decays,” Phy. Rev. D 79, 074024 (2009). [2] B. Aubert et. al. (BABAR) , “Study of the decay D s + K + K e + ” Phy. Rev. D 78, 051101 (R) (2008). [3] B. Aubert et. al. (BABAR) , “Dalitz plot analysis of D s + + ,” arXiv:0808.0971 Conclusions (Preliminary) Conclusions (Preliminary) We present an updated result for the first measurement of Assuming a simple pole model for the form-factor, |f + (q 2 )|, we estimate the pole mass as In the final state the only hadron present is the f 0 . This provides a particular clean environment that allows us to measure the mass and width as We update our measurement of We measure the ratio of decay rates at q 2 = 0 of This ratio has been predicted by Stone and Zhang [1] to equal Our measurement indicates that the B s J/ f 0 may indeed be a useful place to measure CP violation in the B s system since the rate can be ~ 40% that of the J/ mode, especially since an angular analysis is not necessary as the J/ f 0 mode is a CP-eigenstate. )%. 01 . 0 03 . 0 20 . 0 ( ) , ) 980 ( ( 0 0 f e f D s B . GeV 2 . 0 7 . 1 5 . 4 7 . 0 . ly respectiv MeV, ) 3 91 ( and MeV ) 1 977 ( 30 22 11 9 )%. 13 . 0 23 . 0 36 . 2 ( ) ( e D s B )%. 11 42 ( ) 0 , , ( ) 0 , , ) 980 ( ( 2 2 0 0 q K K e D q f e f D s s . ) , / ( ) ), 980 ( / ( 0 0 K K J B f f J B s s Y f0 (q 2 =0) = 39 9 2 f 0 e + Use pole model 2 2 2 / 1 ) 0 ( ) ( A m q f q f e + Y (q 2 =0) = 93 9 +30 - 22 +11 - 9 +28 -21
description
Non- D S background. Systemic errors obtained by varying m A. Multi g bkgrnd. Sideband bkgrnd. Mass Projection. MM* 2 Projection. D s + f 0 (980) e + n and Implications for B s J/ y f 0 (980). Liming Zhang (Syracuse University) on behalf of the CLEO Collaboration. - PowerPoint PPT Presentation
Transcript of D s + f 0 (980) e + n and Implications for B s J/ y f 0 (980)
DDss++ f f00(980) e(980) e++and Implications forand Implications for BBss J/ J/ f f00(980)(980)
Liming Zhang (Syracuse University)Liming Zhang (Syracuse University)on behalf of the CLEO Collaborationon behalf of the CLEO Collaboration
IntroductionIntroduction
“Bs-Bs mixing phase” -2s: a place to look for New Physics
Measurements of CP violation in the B meson system are sensitive to the presence of heavy, as yet undiscovered, particles. The SM value sin(2s) = 0.037 0.002 is small, where 2s 2arg[ − VtsVtb
*/VcsVcb*
] Both CDF and D0 have investigated -2s using Bs J/ decays. The central value has been found far from the expected SM value, but the error is large and the significance of the possible discrepancy is in the 2-3 range.
Bs J/ f0(980)
The ss quarks not only can form a , but also , ' and f0(980) mesons. The scalar f0 state, however, has not been previously considered. From BESII, we know f0(980) decay is dominated by +-, which is more useful than the , ' modes because of poor photon efficiency at current hadron collider experiments. The f0 (& , ') modes are pure CP-eigenstates, and thus an angular analysis is unnecessary. Since the final state J/ is not a CP-eigenstate, an angular analysis is necessary, which requires large statistics compared to CP eigenstates.
Estimate using Ds+ semileptonic decays
Stone and Zhang [1] argued that the branching ratio Bs J/ f0(980), f0 +- to J/ could be estimated by the ratio of decay widths at q2 = 0, where q2 is the e+ and neutrino invariant mass squared )0,,(
)0,,)980((
),/(
)),980(/(2
20000
qKKeD
qfefD
KKJB
ffJB
s
s
s
s
The Feynman diagrams in Bs and Ds+ are analogous: J/ in Bs and virtual W+ in Ds
+ are both spin-1 objects. The available energy in Bs, mBs-mJ/=2.27 GeV, is comparable to mDs=1.97 GeV, so q2 = 0 in the Ds
+ semileptonic decays give good estimation for the Bs case.
FIG. 2: Diagrams for Bs J/(f0) and Ds
+ (f0) e+
FIG. 1: -2s from Bs J/
CLEO-c TechniqueCLEO-c Technique
Tag Method: We use e+eDsDs* at 4170 MeV with 600 pb1 of data. We fully reconstruct one Ds and also the
from Ds* as a “tag”, then examine the properties of the other Ds+.The Ds
tags we reconstructed can come from
either directly produced Ds mesons or those that result from the decay of a Ds* mesons.
Tag Reconstruction: We first reconstruct Ds from 9 decay modes and require the beam constrained mass of
candidates in the interval of [2.015, 2.067] GeV to pre-select DsDs* events. We then detect the photon from the Ds* decay by looking for an additional photon candidate in the event that satisfies our shower shape requirement.
We calculate the missing mass squared MM*2 recoiling against the photon and the Ds tag,
Single Tag Yields: To obtain number of Ds with tags, we simultaneously fit to the invariant mass (MDs) and
MM*2. We obtain the total number of single tags 30848±695±925 in the invariant mass signal region ( 17.5 MeV from the Ds mass) and MM2 [3.782, 4.0] GeV2.
2CM
2CM
2* )()(MM ppp DsDs EEE
Mass Projection MM*2 Projection
Sideband bkgrnd
Multi bkgrnd
FIG. 3: Ds invariant mass and MM*2 distributions from 9 tag modes (for detail see PRD 79, 052001 (2009))
Signal Reconstruction & Data Distribution Signal Reconstruction & Data Distribution
Candidate events are selected that contain only or K+K and a track with opposite charge to the tag, which we identify as an electron. The electron identification requires the track makes an angle >25.8 with respect to the beam line and momentum >200 MeV. In addition we require that there not be any photon detected in the calorimeter with energy greater than 300 MeV. The missing mass squared, MM2, evaluated by taking into account the observed f0 () meson, eDS
and should peak at zero;
We use a set of kinematical constraints and fit each event to two hypotheses one of which is that the Ds tag is the
daughter of a Ds* and the other that the Ds*
+ decays into Ds+, with the Ds
+ subsequently decaying into signal. In
addition, we constrain the invariant mass of the Ds to the known Ds mass. This gives us a total of 7 constraints.
The missing neutrino four-vector needs to be determined, so we are left with a three-constraint fit. We perform a standard iterative fit minimizing 2. We choose the fitted MM2 from the hypothesis giving the smaller 2.
We simultaneously fit the Ds invariant mass, MM2 and or K+K invariant mass. A large mass window for dipion is chosen to measure the f0(980) mass and width. Here a relativistic Breit-Wigner function BW(m2) is used to fit the data distribution, where
The fit gives m0 = 968 9 MeV and 0 = 92 MeV (Preliminary) .
2)(CM
2)(CM
2 )()(MM00 feDsfeDs EEEEE ppppp
Results (Preliminary)Results (Preliminary)
Ds+f0 e+ form factors
The decay rate can be written in terms of as +- invariant mass (m) and q2
where GF is the Fermi constant, pf0 is the momentum of the f0 in the Ds+ rest frame, |Vcs| is a CKM matrix element,
f+(q2) is function called form-factor, and P(m2) is the PDF of the f0 mass distribution.
The q2 distribution and branching fractions
We separate data into 5 q2 bins, and perform similar fits as used before but fix the f0 mass and width to the observed values. The yields, efficiencies and efficiency corrected yields in the 5 q2 bins are shown in Table 1. The branching fractions can be extracted by dividing the efficiency corrected yields sums in each mode by the number of tags. We find B(Dsf0 e+f0 +0.200.03 0.01andB(Ds e+2.360.23 0.13
We fit the efficiency corrected q2 distribution. For the f0e+, the fit function is Eq. (1) integrated over m, and a simple pole model f+(q2)=1/(1q2/mA
2) is used. For the e+, we use the BABAR measured shape [2].
We obtain a preliminary value of the pole mass and preliminary ratio
)(|)(|),(192
||)( 2222334
22
220
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m
VG
dqdm
efDdf
D
csFs
s
FIG. 4: Distributions of (a) MM2 and (b) m+
- for f0e+ and (c) MM2 and (d) mK+K
- for e+, superimposed with the total fitting function and each of its components in colors.
,))(()(
)()(
220
220
2
202
mmmm
mmmBW
m
m
mm
mmm 0
220
22
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Non-DS
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signal (0)e+
'()e+
(a) (b)
(c) (d)
Non-DS
background
(1)
GeV2.07.1 5.47.0
Am
)%1142()0,,(
)0,,)980((2
200
qKKeD
qfefD
s
s
We study Ds+f0(980)e+, f0(980)+- and Ds
+e+, K+K using e+eDSDS* interactions at 4170 MeV collected with the CLEO-c detector. By examining the rate as a function of the four-momentum transfer, q2, we measure the ratio of f0/ rates at q2 = 0 to be (4211)%, thus indicating that the decay BsJ/f0(980), could be useful for measuring the “Bs-Bs mixing phase” -2s. Properties of the f0(980) are also studied.
Table 1: Preliminary number of events and efficiency e in q2 intervals. (The errors on e are about 1%.)
FIG. 5: Preliminary q2 distributions with fit functions superimposed.
MeV)391(
MeV)1977(30220
1190
m
Systemic errors obtained by varying mA
In the earlier +- invariant mass fit, we did not take into account the fact that the phase space for the larger f0 masses is somewhat smaller than that for smaller f0 masses, due to the finite Ds mass.
To take into account this effect, we need integrate Eq. (1) over q2 in the allowed region [0, (mDs-m)2]. Here we use P(m2)=BW(m2).
We used our fitted form-factor shape for f+(q2).
We obtain m0 = (977 1) MeV and 0 = (91 3) MeV. The systematic errors are determined by varying
the form-factor by one error width.
FIG 6: Invariant mass distribution for +. The signal shape is a relativistic Breit-Wigner modified by phase space and form-factor effects. For the meanings of the
curves, see FIG 4 (a).
ff00(980) Properties(980) Properties
ff00(980) in (980) in DDss Hadronic Decays Hadronic Decays
Stone and Zhang [1] also use branching fractions of Ds
+ K+K and + from CLEO and the BABAR Dalitz analysis of the 3 mode [3] (Fig. 7) to derive
where the mass is within 90 MeV of the f0(980) mass.
Fig. 8 shows the diagram for Ds decay into plus an ss system.
)%,30~20(),(
),(
0
00
KKD
ffD
s
s
BABAR
FIG. 7: Dalitz plot projections (dots with error bars) and fit results (solid histogram). The hatched histograms show the background contribution. From the BABAR Collaboration [3].
f0(980)
FIG. 8: Diagram for a Ds+ decay into plus
an ss system.
ReferencesReferences[1] S. Stone and L. Zhang “S-waves and the measurement of CP violation phases in Bs decays,” Phy. Rev. D 79, 074024 (2009). [2] B. Aubert et. al. (BABAR) , “Study of the decay Ds
+ K+ K e+ ” Phy. Rev. D 78, 051101 (R) (2008). [3] B. Aubert et. al. (BABAR) , “Dalitz plot analysis of Ds
+ +,” arXiv:0808.0971
Conclusions (Preliminary)Conclusions (Preliminary) We present an updated result for the first measurement of
Assuming a simple pole model for the form-factor, |f+(q2)|, we estimate the pole mass as
In the final state the only hadron present is the f0. This provides a particular clean environment that allows us to measure the mass and width as
We update our measurement of
We measure the ratio of decay rates at q2 = 0 of
This ratio has been predicted by Stone and Zhang [1] to equal Our measurement indicates that the Bs J/ f0 may indeed be a useful place to measure CP violation in the Bs system since the rate can be ~ 40% that of the J/ mode, especially since an angular analysis is not necessary as the J/ f0 mode is a CP-eigenstate.
)%.01.003.020.0(),)980(( 00 fefDsB
.GeV 2.07.1 5.47.0
.lyrespectiveMeV,)391(andMeV)1977( 3022
119
)%.13.023.036.2()( eDsB
)%.1142()0,,(
)0,,)980((2
200
qKKeD
qfefD
s
s
.),/(
)),980(/( 00
KKJB
ffJB
s
s
Yf0(q2=0) = 39 9 2
f0e+
Use pole model
222
/1
)0()(
Amq
fqf
e+
Y(q2=0) = 93 9
+30- 22
+11- 9
+28-21
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