2011 QCD and High Energy Interactions - Rencontres de Moriond ...

e M(Dπ) distributions obtained
D + or D 0 candidate mass side-
mass spectra are presented in
eatures.
r D ∗ 2 (2460)0 and D ∗ 2 (2460)+ .
ucted mass to about 3 MeV/c 2 .
on due to fake D + and D0 can-
M(Dπ) distributions obtained
D + or D0 ectrum shows a peaking backat
about 2.3 GeV/c
candidate mass sidemass
spectra are presented in
atures.
2 due to de-
20) 0 and D∗ 2 (2460)0 to D∗+ π− .
ents decays to D + π0 and the π0 onstruction. The missing π0 has
because the D∗+ decay is very
Therefore, these decays have a
only 5.8 MeV/c 2 and a bias of
imilarly, D0π + shows peaking
the decays of the D1(2420) +
r D∗ 2 (2460)0 and D∗ 2 (2460)+ ∗0 + ∗0 π where the D decays. to
Events / (0.005 G
2
Events / (0.005 GeV/c 2
Events / (0.005 GeV/c )
2
Events / (0.005 GeV/c )
3
20
2
1
15
0
2.4 2.5 2.6 2.7 2.8
10
5
5
! 1000
! 1000
25
4
Fit AB
25
2 3
20
20
2
D
1
15
1
15
0
10
2.4 2.5 2.6 2.6 2.7 2.7 2.8
2.8
10
∗ D
(2760)
∗ didates by subtracting the M(Dπ) distributions obtained
by selecting events in the D
x1000
Peaking bkg
(2600)
+ or D0 candidate mass sidebands.
The D + π− and D0π + mass spectra are presented in
Fig. 2 and show similar features.
• Prominent peaks for D∗ 2 (2460)0 and D∗ 2 (2460)+ .
• The D + π− mass spectrum shows a peaking background
(feeddown) at about 2.3 GeV/c 2 due to decays
from the D1(2420) 0 and D∗ 2 (2460)0 to D∗+ π− .
The D∗+ in these events decays to D + π0 and the π0 is missing in the reconstruction. The missing π0 has
very low momentum because the D∗+ decay is very
close to threshold. Therefore, these decays have a
mass resolution of only 5.8 MeV/c 2 and a bias of
−143.2 MeV/c2 . Similarly, D0π + shows peaking
backgrounds due to the decays of the D1(2420) +
and D ∗ 2 (2460)+ to D ∗0 π + where the D ∗0 decays to
D 0 π 0 .
Events / (0.005 GeV
2
Events / (0.005 GeV/c )
25
20
15
10
5
x1000
25
Fit B
20
15
10
5
Peaking bkg
3
2
1
0
2.4 2.5 2.6 2.7 2.8
2
1
D ∗ (2600)
D ∗ (2760)
0
2.4 2.5 2.6 2.7 2.8
Events / ( 0.005 GeV/
)
2
Events / ( 0.005 GeV/c
16
14
12
10
8
6
4
4
3
2
1
0
2.4 2.5 2.6 2.7 2.8
2
2.2
45 Fit E
2.4
! 10
2.6
10
2.8 3 3.2
40
8
35
6
D
30
25
4
2
∗ (2600) 0
D(2550) 0
D(2750) 0
x1000
20
15
10
D ∗ 2(2460) 0
0
2.4 2.5 2.6 2.7 2.8
• Two additional enhanc
and ∼2.75 GeV/c 2 , whi
D ∗ (2600) 0 and D(2750) 0
Studies of the generic MC simu
the D ∗+ sidebands and the wr
show no peaking backgrounds
We fit M(D ∗+ π − ) by para
with the function in Eq. (1
D ∗ 2(2460) 0 resonances are mod
functions with appropriate Bla
The D ∗ (2600) 0 and D(2750) 0
tic BW functions. The broa
known to decay to this final st
sensitive to it due to its large w
because the background param
Due to the vector nature o
nal state contains additional in
parity (J P )quantumnumbers
rest frame of the D ∗+ ,wedefi
the angle between the primary
π + from the D ∗+ decay. The d
ectrum shows a peaking backat
about 2.3 GeV/c 2 due to de-
20) 0 and D∗ 2 (2460)0 to D∗+ π− .
ents decays to D + π0 and the π0 nstruction. The missing π0 has
because the D∗+ decay is very
Therefore, these decays have a
only 5.8 MeV/c 2 and a bias of
imilarly, D0π + shows peaking
the decays of the D1(2420) +
∗0 + ∗0 π where the D decays to
0 + π mass distributions show
nd 2.6 and 2.75 GeV/c 2 . We
ents D∗ (2600) and D∗ (2760).
se mass spectra with those ob-
− → ¯cc Monte Carlo (MC)
e generated using JETSET [9]
e resonances incorporated. The
cted using a detailed GEANT4
and the event selection procen
addition, we study Dπ mass
D0 candidate mass sidebands,
r wrong-sign D + π + and D0π− grounds or reflections that can
and 2.76 GeV/c 2 .Inthestudy
we find a peaking background
0 0 candidate is not a true D ,
the primary π + candidate are
+ decay. These combinations
M(D0 π + ) both in the D0 canand
sidebands. However, this
function of the D0 candidate
ideband subtraction.
d is modeled using the function:
+c2x 2
for x ≤ x0,
d1x+d2x 2
(1)
for x>x0,
mD + mπ) 2 ][x2 − (mD − mπ) 2 5
25
Fit B
2
20
1
15
0
10
2.4 2.5 2.6 2.7 2.8
5
0
2.2 2.4 2.6 2.8 3 3.2
2
M(D " ) (GeV/c )
FIG. 2: (color online) Mass distribution for D
]
e factor and x = M(Dπ). Only
in the piece-wise exponential:
rametersd0and d1 are fixed by
ontinuous and differentiable at
eaccountforthefeeddownof
convolving Breit-Wigner (BW)
ction describing the resolution
+ π − (top) and
D 0 π + (bottom) candidates. Points correspond to data, with
the total fit overlaid as a solid curve. The dotted curves are
the signal components. The lower solid curves correspond
to the smooth combinatoric background and to the peaking
backgrounds at 2.3 GeV/c 2 . The inset plots show the distributions
after subtraction of the combinatoric background.
and bias obtained from the simulation of these decays.
The mass and width of the D1(2420) feeddown are fixed
to the values obtained in the D∗+ π− analysis described
below, while the parameters of the D∗ 2 (2460) feeddown
are fixed to those of the true D∗ 2(2460) in the same
M(Dπ) distribution.
The D∗ 2 (2460) is modeled using a relativistic BW function
with the appropriate Blatt-Weisskopf centrifugal
barrier factor [2]. The D∗ (2600) and D∗ (2760) are modeled
with relativistic BW functions [2]. Finally, although
not visible in the M(D + π− ) mass distribution, we include
a BW function to account for the known resonance
D∗ 0(2400), which is expected to decay to this final state.
The χ2 per number of degrees of freedom (NDF) of the fit
decreases from 596/245 to 281/242 when this resonance
is included. This resonance is very broad and is present
together with the feeddown and D∗ 2(2460) 0 0 + π mass distributions show
und 2.6 and 2.75 GeV/c
;thereforewe
restrict its mass and width parameters to be within 2σ
of the known values [5]. The shapes of the signal components
are corrected for a small variation of the efficiency
as a function of M(Dπ) and are multiplied by the twobody
phase-space factor. They are also corrected for the
mass resolution by convolving them with the resolution
function determined from MC simulation of signal de-
2 . We
ents D∗ (2600) and D∗ (2760).
se mass spectra with those ob-
− → ¯cc Monte Carlo (MC)
e generated using JETSET [9]
le resonances incorporated. The
cted using a detailed GEANT4
and the event selection procen
addition, we study Dπ mass
D0 candidate mass sidebands,
r wrong-sign D + π + and D0π− grounds or reflections that can
6 and 2.76 GeV/c 2 .Inthestudy
we find a peaking background
D0 candidate is not a true D0 ,
d the primary π + candidate are
+ decay. These combinations
M(D0 π + ) both in the D0 canand
sidebands. However, this
function of the D0 candidate
sideband subtraction.
d is modeled using the function:
+c2x 2
for x ≤ x0,
d1x+d2x 2
(1)
for x>x0,
(mD + mπ) 2 ][x2 − (mD − mπ) 2 5
0
2.2 2.4 2.6 2.8 3 3.2
2
M(D " ) (GeV/c )
FIG. 2: (color online) Mass distribution for D
]
e factor and x = M(Dπ). Only
in the piece-wise exponential:
rametersd0and d1 are fixed by
ontinuous and differentiable at
eaccountforthefeeddownof
convolving Breit-Wigner (BW)
ction describing the resolution
+ π − (top) and
D 0 π + (bottom) candidates. Points correspond to data, with
the total fit overlaid as a solid curve. The dotted curves are
the signal components. The lower solid curves correspond
to the smooth combinatoric background and to the peaking
backgrounds at 2.3 GeV/c 2 . The inset plots show the distributions
after subtraction of the combinatoric background.
and bias obtained from the simulation of these decays.
The mass and width of the D1(2420) feeddown are fixed
to the values obtained in the D∗+ π− analysis described
below, while the parameters of the D∗ 2 (2460) feeddown
are fixed to those of the true D∗ 2(2460) in the same
M(Dπ) distribution.
The D∗ 2 (2460) is modeled using a relativistic BW function
with the appropriate Blatt-Weisskopf centrifugal
barrier factor [2]. The D∗ (2600) and D∗ (2760) are modeled
with relativistic BW functions [2]. Finally, although
not visible in the M(D + π− ) mass distribution, we include
a BW function to account for the known resonance
D∗ 0(2400), which is expected to decay to this final state.
The χ2 per number of degrees of freedom (NDF) of the fit
decreases from 596/245 to 281/242 when this resonance
is included. This resonance is very broad and is present
together with the feeddown and D∗ 2(2460) 0 M(D
;thereforewe
restrict its mass and width parameters to be within 2σ
of the known values [5]. The shapes of the signal components
are corrected for a small variation of the efficiency
as a function of M(Dπ) and are multiplied by the twobody
phase-space factor. They are also corrected for the
mass resolution by convolving them with the resolution
function determined from MC simulation of signal de-
+ π − )=m(K − π + π + π − ) − m(K − π + π + 0
)+mD +
Resonance Mass (MeV) Signif.
D∗ (2600) 0 2608.7 ± 2.4 ± 2.5 3.9σ
D∗ (2760) 0 2763.3 ± 2.3 ± 2.3 8.9σ
(a) D + π − • Both D
system
+ π− and D0π + mass distributions show
new structures around 2.6 and 2.75 GeV/c 2 . We
call these enhancements D∗ (2600) and D∗ (2760).
We have compared these mass spectra with those obtained
from generic e + e− → ¯cc Monte Carlo (MC)
events. These events were generated using JETSET [9]
with all the known particle resonances incorporated. The
events are then reconstructed using a detailed GEANT4
[10] detector simulation and the event selection procedure
used for the data. In addition, we study Dπ mass
spectra from the D + and D0 candidate mass sidebands,
as well as mass spectra for wrong-sign D + π + and D0π− samples. We find no backgrounds or reflections that can
cause the structures at 2.6 and 2.76 GeV/c 2 .Inthestudy
of the D0π + final state we find a peaking background
due to events where the D0 candidate is not a true D0 ,
but the K− candidate and the primary π + candidate are
from a true D0 → K−π + decay. These combinations
produce enhancements in M(D0 π + ) both in the D0 candidate
mass signal region and sidebands. However, this
background is linear as a function of the D0 candidate
mass, is removed by the sideband subtraction.
The smooth background is modeled using the function:
e
B(x) =P (x) ×
c1x+c2x2 for x ≤ x0,
ed0+d1x+d2x2 (1)
for x>x0,
where P (x) ≡ 1
0
2.2 2.4 2.6 2.8 3 3.2
2
M(D " ) (GeV/c )
FIG. 2: (color online) Mass distribution for D
2x [x2 − (mD + mπ) 2 ][x2 − (mD − mπ) 2 ]
is a two-body phase-space factor and x = M(Dπ). Only
four parameters are free in the piece-wise exponential:
c1, c2, d2, and x0. Theparametersd0and d1 are fixed by
requiring that B(x) be continuous and differentiable at
the transition point x0. Weaccountforthefeeddownof
peaking backgrounds by convolving Breit-Wigner (BW)
functions [11] with a function describing the resolution
+ π − (top) and
D 0 π + (bottom) candidates. Points correspond to data, with
the total fit overlaid as a solid curve. The dotted curves are
the signal components. The lower solid curves correspond
to the smooth combinatoric background and to the peaking
backgrounds at 2.3 GeV/c 2 . The inset plots show the distributions
after subtraction of the combinatoric background.
and bias obtained from the simulation of these decays.
The mass and width of the D1(2420) feeddown are fixed
to the values obtained in the D∗+ π− analysis described
below, while the parameters of the D∗ 2 (2460) feeddown
are fixed to those of the true D∗ 2(2460) in the same
M(Dπ) distribution.
The D∗ 2 (2460) is modeled using a relativistic BW function
with the appropriate Blatt-Weisskopf centrifugal
barrier factor [2]. The D∗ (2600) and D∗ (2760) are modeled
with relativistic BW functions [2]. Finally, although
not visible in the M(D + π− ) mass distribution, we include
a BW function to account for the known resonance
D∗ 0(2400), which is expected to decay to this final state.
The χ2 per number of degrees of freedom (NDF) of the fit
decreases from 596/245 to 281/242 when this resonance
is included. This resonance is very broad and is present
together with the feeddown and D∗ 2(2460) 0 M(D
;thereforewe
restrict its mass and width parameters to be within 2σ
of the known values [5]. The shapes of the signal components
are corrected for a small variation of the efficiency
as a function of M(Dπ) and are multiplied by the twobody
phase-space factor. They are also corrected for the
mass resolution by convolving them with the resolution
function determined from MC simulation of signal de-
0π + )=m(K−π + π + ) − m(K−π + )+mD0 Resonance Mass (MeV) Signif.
D∗ (2600) + 2621.3 ± 3.7 ± 4.2 2.8σ
D∗ (2760) + 2769.7 ± 3.8 ± 1.5 3.5σ
(b) D 0 π + 5
2.2 2.4 2.6 2.8 3 3.2
*+ -
2
M(D " ) (GeV/c )
FIG. 3: (color online) Mass distributions for D
system
∗+ π − candidates.
Top: candidates with | cos θH| > 0.75. Middle: candidates
with | cos θH| < 0.5. Bottom: all candidates. Points
correspond to data, with the total fit overlaid as a solid curve.
The lower solid curve is the combinatoric background, and
the dotted curves are the signal components. The inset plots
show the distributions after subtraction of the combinatoric
background.
cays. The fit to the M(D + π− ) distribution (Fit A) is
shown in Fig. 2 (top). The results of this fit, as well as
fits to the other final states described below, are shown
in Table I. In this table, the significance for each new
signal is defined as the signal yield divided by its total
uncertainty.
The fit to the D0π + mass spectrum is similar to that
described for the D + π− system. Because the feeddown
is larger and the statistical precision of the resonances is
not as good as for D + π− , we fix the width parameters
of all resonances to the values determined from D + π− the predicted resonances, assu
are given in Table II. Initially
the M(D∗+ π− ) distribution in
signals at ∼2.6 GeV/c 2 and at
when we extract the yields as a
that the mean value of the pea
by ∼70 MeV/c2 between cosθ and decreases again as cos θH
suggests two resonances with d
tributions are present in this m
incorporate a new component
into our model at ∼2.55 GeV/
eters of this component by re
order to suppress the other re
C), shown in Fig. 3 (top), we
D∗ 2(2460) 0 and D∗ (2600) 0 to
We obtain a χ2 /NDF of 214/2
determines the parameters of
perform a complementary fit
(middle), in which we require
nate in favor of the D∗ (2600) 0
210/209 for this fit. To determ
the D(2750) 0 D1(2420)
signal we fit the
0
M(D ∗+ π − )=m(K − π + (π + π − )π + s π − ) − m(K − π + (π + π − )π + s )+mD∗+ Resonance Mass (MeV) Signif.
D(2550) 0 2539.4 ± 4.5 ± 6.8 3.0σ
D(2750) 0 2752.4 ± 1.7 ± 2.7 4.2σ
(c) D ∗+ π − system
Figure 1: Mass distribution of the reconstructed candidates. Points correspond to data, with the total fit overlaid
as a solid blue curve. The red dashed curves are the signal components. The black solid curve correspond to
the smooth combinatoric background and to the peaking backgrounds at 2.3 GeV/c 2 . The inset plots show the
distributions after subtraction of the combinatoric background. In the table, the first error for the mass is statistic,
while the second is the systematic one.
backgrounds are larger in the M(D0π + ) distribution, when fitting that distribution additional
parameters need to be fixed to the values fitted to M(D + π− ) distribution, assuming isospin
symmetry. The parameters and the significances for the new structures are shown in the tables
in Fig. 1. The new resonances found in the D0π + system are consistent with being the isospin
partners of the D + π− system resonances.
To search for new states in the D∗+ π− system we define the variable M(D∗+ π− ) =
m(K−π + (π + π− )π + s π− )−m(K −π + (π + π− )π + s )+m ∗+
D , where m∗+
D is the value of the D∗+ mass 5 .
The M(D∗+ π− ) distribution is shown in Fig. 1(c) and shows the following features: prominent
D1(2410) 0 and D∗ 2 (2460)0 peaks, and two structures at ∼ 2.60 GeV/c2 and ∼ 2.75 GeV/c2 . The
fit to this distribution is really similar to the previous ones, but here the final state contains
additional information about the spin-parity quantum number of the resonances. In the rest
frame of the D∗+ , we define the helicity angle θH as the angle between the pion π− and the slow
pion π + from the D∗+ decay. Fitting the M(D∗+ π− ) distribution in a limited range of θH, we
find that another resonance around 2.55 GeV/c2 need to be introduced, in addition to the two
mentioned above. Again some parameters need to be fixed to the values obtained from the fit to
M(D + π− ) distribution. The parameters and the significances for the new structures are shown
in Fig. 1(c). The final model is then used to extract the signal yields as a function of cos θH for
10 sub-samples. The cos θH distribution parameter for the D1(2420) are consistent with previous
measurements 6 . The D(2550) 0 and D∗ (2600) 0 have mass values and cos θH distributions
consistent with the predicted radial excitations, respectively, D1 0 (2S) and D3 1 (2S).
3 D1(2420) 0 → D 0 γ radiative transistion using BELLE dataset
In this analysis we search for the radiative transition D1(2420) 0 → D 0 γ using a dataset of 656
fb −1 collected at CM energies near 10.58 GeV by the BELLE detector 7 . The standard ∆E
and m bc variables are used to select the B mesons in the B − → π − D1(2420) 0 mode. The
corresponding pionic decays B − → π − D 0 (0,2) → π0 D 0 → K − π + form an important background
to the radiative transition analysis, with the D2 peaking close to the signal region, and have
never previously been measured. This background is included in the final fit performed on the
m(D 0 γ) distribution. In the rest frame of the D 0 , we define the decay angle θJ as the angle
between the γ and the pion π + from the D 0 decay. The final fit is performed simultaneously
over 4 separate ranges of cos θJ, as shown in Fig. 2.
The preliminary result we obtain for the branching fraction is: B(B − → π − D1(2420) 0 ) ×
B(D1(2420) 0 → D 0 γ) = 5.0 ± 0.5(stat) ± 1.5(syst). Candidates in the cos θJ range [−1.0, 0.7]