Study of B -> X gamma decays and determination of vertical bar V-td/V-ts vertical bar

TLDR: In this article, a sample of 471 million B{bar B} events collected with the BABAR detector was used to study the sum of seven exclusive final states B {yields} X{sub s(d){gamma}, where X is a strange (nonstrange) hadronic system with a mass of up to 2.0 GeV/c{sup 2}.

Abstract: Using a sample of 471 million B{bar B} events collected with the BABAR detector, we study the sum of seven exclusive final states B {yields} X{sub s(d){gamma}}, where X{sub s(d)} is a strange (non-strange) hadronic system with a mass of up to 2.0 GeV/c{sup 2}. After correcting for unobserved decay modes, we obtain a branching fraction for b {yields} d{gamma} of (9.2 {+-} 2.0(stat.) {+-} 2.3(syst.)) x 10{sup -6} in this mass range, and a branching fraction for b {yields} s{gamma} of (23.0 {+-} 0.8(stat.) {+-} 3.0(syst.)) x 10{sup -5} in the same mass range. We find {Beta}(b{yields}d{gamma})/{Beta}(b{yields}s{gamma}) = 0.040 {+-} 0.009(stat.) {+-} 0.010(syst.), from which we determine |V{sub td}/V{sub ts}| = 0.199 {+-} 0.022(stat.) {+-} 0.024(syst.) {+-} 0.002(th.).

Figures

TABLE II. Signal yields (NS), efficiencies ( ), partial branching fractions (PB), inclusive branching fractions (B) and the ratio of inclusive branching fractions for the measured decay modes. The first error is statistical and second is systematic (including an error from extrapolation to missing decay modes, for the inclusive B).

TABLE III. Systematic errors on the measured partial and inclusive branching fractions B. Systematic errors that do not cancel in the ratio of rates are marked with (*).

Full text

Study of B ! X decays and determination of jV
td
=V
ts
j
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(BABAR Collaboration)
1
Laboratoire d’Annecy-le-Vieux de Physique des Particules (LAPP), Universite
´
de Savoie, CNRS/IN2P3, F-74941 Annecy-Le-Vieux,
France
2
Universitat de Barcelona, Facultat de Fisica, Departament ECM, E-08028 Barcelona, Spain
3a
INFN Sezione di Bari, I-70126 Bari, Italy
3b
Dipartimento di Fisica, Universita
`
di Bari, I-70126 Bari, Italy
4
University of Bergen, Institute of Physics, N-5007 Bergen, Norway
5
Lawrence Berkeley National Laboratory and University of California, Berkeley, California 94720, USA
6
University of Birmingham, Birmingham, B15 2TT, United Kingdom
7
Ruhr Universita
¨
t Bochum, Institut fu
¨
r Experimentalphysik 1, D-44780 Bochum, Germany
8
University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
9
Brunel University, Uxbridge, Middlesex UB8 3PH, United Kingdom
10
Budker Institute of Nuclear Physics, Novosibirsk 630090, Russia
11
University of California at Irvine, Irvine, California 92697, USA
12
University of California at Riverside, Riverside, California 92521, USA
13
University of California at Santa Barbara, Santa Barbara, California 93106, USA
14
University of California at Santa Cruz, Institute for Particle Physics, Santa Cruz, California 95064, USA
15
California Institute of Technology, Pasadena, California 91125, USA
16
University of Cincinnati, Cincinnati, Ohio 45221, USA
17
University of Colorado, Boulder, Colorado 80309, USA
18
Colorado State University, Fort Collins, Colorado 80523, USA
19
Technische Universita
¨
t Dortmund, Fakulta
¨
t Physik, D-44221 Dortmund, Germany
20
Technische Universita
¨
t Dresden, Institut fu
¨
r Kern- und Teilchenphysik, D-01062 Dresden, Germany
21
Laboratoire Leprince-Ringuet, CNRS/IN2P3, Ecole Polytechnique, F-91128 Palaiseau, France
22
University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom
23a
INFN Sezione di Ferrara, I-44100 Ferrara, Italy
23b
Dipartimento di Fisica, Universita
`
di Ferrara, I-44100 Ferrara, Italy
24
INFN Laboratori Nazionali di Frascati, I-00044 Frascati, Italy
25a
INFN Sezione di Genova, I-16146 Genova, Italy
25b
Dipartimento di Fisica, Universita
`
di Genova, I-16146 Genova, Italy
26
Indian Institute of Technology Guwahati, Guwahati, Assam, 781 039, India
27
Harvard University, Cambridge, Massachusetts 02138, USA
28
Universita
¨
t Heidelberg, Physikalisches Institut, Philosophenweg 12, D-69120 Heidelberg, Germany
29
Humboldt-Universita
¨
t zu Berlin, Institut fu
¨
r Physik, Newtonstr. 15, D-12489 Berlin, Germany
30
Imperial College London, London, SW7 2AZ, United Kingdom
31
University of Iowa, Iowa City, Iowa 52242, USA
32
Iowa State University, Ames, Iowa 50011-3160, USA
33
Johns Hopkins University, Baltimore, Maryland 21218, USA
34
Laboratoire de l’Acce
´
le
´
rateur Line
´
aire, IN2P3/CNRS et Universite
´
Paris-Sud 11, Centre Scientifique d’Orsay, B. P. 34,
F-91898 Orsay Cedex, France
35
Lawrence Livermore National Laboratory, Livermore, California 94550, USA
36
University of Liverpool, Liverpool L69 7ZE, United Kingdom
37
Queen Mary, University of London, London, E1 4NS, United Kingdom
38
University of London, Royal Holloway and Bedford New College, Egham, Surrey TW20 0EX, United Kingdom
39
University of Louisville, Louisville, Kentucky 40292, USA
P. DEL AMO SANCHEZ et al. PHYSICAL REVIEW D 82, 051101(R) (2010)
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051101-2

40
Johannes Gutenberg-Universita
¨
t Mainz, Institut fu
¨
r Kernphysik, D-55099 Mainz, Germany
41
University of Manchester, Manchester M13 9PL, United Kingdom
42
University of Maryland, College Park, Maryland 20742, USA
43
University of Massachusetts, Amherst, Massachusetts 01003, USA
44
Massachusetts Institute of Technology, Laboratory for Nuclear Science, Cambridge, Massachusetts 02139, USA
45
McGill University, Montre
´
al, Que
´
bec, Canada H3A 2T8
46a
INFN Sezione di Milano, I-20133 Milano, Italy
46b
Dipartimento di Fisica, Universita
`
di Milano, I-20133 Milano, Italy
47
University of Mississippi, University, Mississippi 38677, USA
48
Universite
´
de Montre
´
al, Physique des Particules, Montre
´
al, Que
´
bec, Canada H3C 3J7
49a
INFN Sezione di Napoli, I-80126 Napoli, Italy
49b
Dipartimento di Scienze Fisiche, Universita
`
di Napoli Federico II, I-80126 Napoli, Italy
50
NIKHEF, National Institute for Nuclear Physics and High Energy Physics, NL-1009 DB Amsterdam, The Netherlands
51
University of Notre Dame, Notre Dame, Indiana 46556, USA
52
Ohio State University, Columbus, Ohio 43210, USA
53
University of Oregon, Eugene, Oregon 97403, USA
54a
INFN Sezione di Padova, I-35131 Padova, Italy
54b
Dipartimento di Fisica, Universita
`
di Padova, I-35131 Padova, Italy
55
Laboratoire de Physique Nucle
´
aire et de Hautes Energies, IN2P3/CNRS, Universite
´
Pierre et Marie Curie-Paris6,
Universite
´
Denis Diderot-Paris7, F-75252 Paris, France
56a
INFN Sezione di Perugia, I-06100 Perugia, Italy
56b
Dipartimento di Fisica, Universita
`
di Perugia, I-06100 Perugia, Italy
57a
INFN Sezione di Pisa, I-56127 Pisa, Italy
57b
Dipartimento di Fisica, Universita
`
di Pisa, I-56127 Pisa, Italy
57c
Scuola Normale Superiore di Pisa, I-56127 Pisa, Italy
58
Princeton University, Princeton, New Jersey 08544, USA
59a
INFN Sezione di Roma, I-00185 Roma, Italy
59b
Dipartimento di Fisica, Universita
`
di Roma La Sapienza, I-00185 Roma, Italy
60
Universita
¨
t Rostock, D-18051 Rostock, Germany
61
Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, United Kingdom
62
CEA, Irfu, SPP, Centre de Saclay, F-91191 Gif-sur-Yvette, France
63
SLAC National Accelerator Laboratory, Stanford, California 94309 USA
64
University of South Carolina, Columbia, South Carolina 29208, USA
65
Southern Methodist University, Dallas, Texas 75275, USA
66
Stanford University, Stanford, California 94305-4060, USA
67
State University of New York, Albany, New York 12222, USA
68
Tel Aviv University, School of Physics and Astronomy, Tel Aviv, 69978, Israel
69
University of Tennessee, Knoxville, Tennessee 37996, USA
70
University of Texas at Austin, Austin, Texas 78712, USA
71
University of Texas at Dallas, Richardson, Texas 75083, USA
72a
INFN Sezione di Torino, I-10125 Torino, Italy
72b
Dipartimento di Fisica Sperimentale, Universita
`
di Torino, I-10125 Torino, Italy
73a
INFN Sezione di Trieste, I-34127 Trieste, Italy
73b
Dipartimento di Fisica, Universita
`
di Trieste, I-34127 Trieste, Italy
74
IFIC, Universitat de Valencia-CSIC, E-46071 Valencia, Spain
75
University of Victoria, Victoria, British Columbia, Canada V8W 3P6
76
Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
77
University of Wisconsin, Madison, Wisconsin 53706, USA
(Received 21 May 2010; published 10 September 2010)
Using a sample of 471  10
6
B

B events collected with the BABAR detector, we study the sum of seven
exclusive final states B ! X
sðdÞ
, where X
sðdÞ
is a strange (nonstrange) hadronic system with a mass of up
to 2:0 GeV=c
2
. After correcting for unobserved decay modes, we obtain a branching fraction for b ! d
k
Also with Universita
`
di Sassari, Sassari, Italy.
x
Now at University of South Alabama, Mobile, Alabama 36688, USA.
‡
Also with Universita
`
di Roma La Sapienza, I-00185 Roma, Italy.
†
Also with Universita
`
di Perugia, Dipartimento di Fisica, Perugia, Italy.
*
Now at Temple University, Philadelphia, Pennsylvania 19122, USA.
STUDY OF B ! X DECAYS AND ... PHYSICAL REVIEW D 82, 051101(R) (2010)
RAPID COMMUNICATIONS
051101-3

of ð9: 2  2:0ðstatÞ2:3ðsystÞÞ  10
6
in this mass range, and a branching fraction for b ! s of ð23:0 
0:8ðstatÞ3:0ðsystÞÞ  10
5
in the same mass range. We find
Bðb!dÞ
Bðb!sÞ
¼ 0:040  0:009ðstatÞ
0:010ðsystÞ, from which we determine jV
td
=V
ts
j¼0:199  0:022ðstatÞ0:024ðsystÞ0:002ðthÞ.
DOI: 10.1103/PhysRevD.82.051101 PACS numbers: 14.40.Nd, 12.15.Hh
The decays b ! d and b ! s are flavor-changing
neutral current processes forbidden at tree level in the
standard model (SM). The leading-order processes are
one-loop electroweak penguin diagrams, for which the
top quark is the dominant virtual particle. In theories
beyond the SM, new virtual particles may appear in the
loop, which could lead to measurable effects on experi-
mental observables such as branching fractions and CP
asymmetries [1]. In the SM the inclusive rate for b ! d is
suppressed relative to b ! s by a factor jV
td
=V
ts
j
2
, where
V
td
and V
ts
are Cabibbo-Kobayashi-Maskawa matrix ele-
ments. Measurements of jV
td
=V
ts
j using the exclusive
modes B !ð; !Þ and B ! K

 [2,3] are now well
established, with theoretical uncertainties of 7% from
weak annihilation and hadronic form factors [4]. This ratio
can also be obtained from the B
d
and B
s
mixing frequen-
cies and is found to be 0: 206  0:0007ðexpÞþ0:0081 
0:0060ðthÞ [5]. It is important to confirm the consistency of
the two methods of determining jV
td
=V
ts
j, since new phys-
ics effects would enter in different ways in mixing and
radiative decays. A measurement of the branching frac-
tions of inclusive b ! d relative to b ! s would deter-
mine jV
td
=V
ts
j with reduced theoretical uncertainties
compared to that from exclusive modes [6].
This paper supersedes [7], and presents the first signifi-
cant observation of the b ! d transition in the hadronic
mass range MðX
d
Þ > 1:0 GeV=c
2
, resulting in a significant
improvement in the determination of jV
td
=V
ts
j via the ratio
of inclusive widths. Inclusive b ! s and b ! d rates
are extrapolated from the measurements of the partial
decay rates to seven exclusive final states (see Table I)in
the hadronic mass ranges 0:5 <MðX
d
Þ < 1:0 GeV=c
2
(low mass, containing the previously measured K

,  and
! resonances) and 1:0 <MðX
d
Þ < 2:0 GeV=c
2
(high
mass). We combine these measurements and make a
model-dependent extrapolation to higher hadronic mass
to obtain an inclusive branching fraction (B) for b !
ðs; dÞ. These measurements use the full data set of 471 
10
6
B

B pairs collected at the ð4SÞ resonance at the PEP-II
B factory with the BABAR detector [8].
High-energy photons are reconstructed from an isolated
energy cluster in the barrel of the calorimeter, with shape
consistent with a single photon, and energy 1:15 <E


<
3:50 GeV, where * denotes the center-of-mass (CM) frame
of the B

B system. We remove photons that can form a 
0
() candidate in association with another photon of
energy greater than 30 (250) MeV if the two-photon in-
variant mass is in the range 110 <m

< 160 ð520 <
m

< 560Þ MeV=c
2
for the low mass region and 95 <
m

< 155 ð530 <m

< 565Þ MeV=c
2
for the high mass
region.
Charged pion and kaon candidates are selected from
well-reconstructed tracks. We use a pion selection algo-
rithm to differentiate pions from kaons, with a typical
selection efficiency of 95% and kaon misidentification
rate of 4%. Kaons are identified as tracks failing the pion
selection criteria. We reconstruct 
0
ðÞ candidates
from pairs of photons of minimum energy 20 MeV with
an invariant mass 115 <m

< 150 ð470 <m

<
620Þ MeV=c
2
. We require all pion, eta, and kaon candi-
dates to have a momentum in the laboratory frame greater
than 600 ð425Þ MeV=c in the low (high) mass region.
The selected pion, eta, kaon, and high-energy photon
candidates are combined to form B meson candidates
consistent with one of the seven decay modes. The charged
particles are combined to form a common vertex, whose 
2
probability is required to be greater than 1%. We use the
kinematic variables E ¼ E

B
 E

beam
, where E

B
is the
energy of the B meson candidate and E

beam
is the beam
energy, and m
ES
¼
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
E
2
beam

~
p
2
B
q
, where
~
p

B
is the momen-
tum of the B candidate. We consider candidates in the
range 0:3 < E<0:2 GeV and m
ES
> 5:22 GeV=c
2
.
Contributions from continuum processes (e
þ
e

! q

q,
with q ¼ u, d, s, c) are reduced by considering only events
for which the ratio R
2
of second-to-zeroth order Fox-
Wolfram moments [9] is less than 0.98. To further discrimi-
nate between the jetlike continuum background and the
more spherically symmetric signal events, we compute the
angle 

T
between the photon momentum and the thrust
axis of the rest of the event (ROE) and require j cosð

T
Þj <
0:8. The ROE is defined as all charged tracks and neutral
energy deposits that are not used to reconstruct the B
candidate.
Ten other event shape variables that distinguish between
signal and continuum events are combined in a neural
TABLE I. The reconstructed decay modes. Charge conjugate
states are implied throughout this paper.
B ! X
d
B! X
s

B
0
! 
þ


B
0
! K
þ



B
þ
! 
þ

0
B
þ
! K
þ

0

B
þ
! 
þ



þ
B
þ
! K
þ

þ



B
0
! 
þ



0
B
0
! K
þ



0

B
0
! 
þ



þ


B
0
! K
þ



þ



B
þ
! 
þ



þ

0
B
þ
! K
þ



þ

0

B
þ
! 
þ
 B
þ
! K
þ

P. DEL AMO SANCHEZ et al. PHYSICAL REVIEW D 82, 051101(R) (2010)
RAPID COMMUNICATIONS
051101-4

network (NN). These include the ratio R
0
2
, which is R
2
calculated in the frame recoiling against the photon mo-
mentum; the B meson production angle with respect to the
beam axis in the CM frame; 

B
; and the L-moments [10]of
the ROE with respect to either the thrust axis of the ROE or
the direction of the high-energy photon. Differences in
lepton, pion, and kaon production between background
and B decays are exploited by including several flavor-
tagging variables applied to the ROE [11]. Using the NN
output, we reject 99% of continuum background while
preserving 25% of signal decays.
After all selections are applied, there remain events with
more than one B candidate. In these events the candidate
with the reconstructed 
0
or  mass closest to nominal is
retained. Where there is no 
0
or  we retain the candidate
with the highest vertex 
2
probability.
The signal yields in the data for the sum of the seven
decay modes are determined from two-dimensional ex-
tended maximum likelihood fits to the E and m
ES
dis-
tributions. We consider the following contributions: signal,
combinatorial backgrounds from continuum processes,
backgrounds from other B decays, and cross-feed from
misreconstructed B ! X decays. The fits to B ! X
d

events contain components from misidentified b ! s
decays, with an expected contribution of 345 events. We
neglect the small b ! d background in the fits to B !
X
s
 events.
Each contribution is modeled by a probability density
function (PDF) that is determined from Monte Carlo (MC)
simulated events unless otherwise specified. For the mis-
identified signal cross-feed components, we use a binned
two-dimensional PDF to account for correlations. All the
other PDFs are products of one-dimensional functions of
E and m
ES
. For signal, the m
ES
spectrum is described by a
Crystal Ball function [12], and E by a Cruijff function
[13]. The parameters of these functions are determined
from the fit to the high-statistics B ! X
s
 data sample.
We use these fitted values to fix the signal shape in the fits
to B ! X
d
 events.
The remaining B backgrounds contain a small compo-
nent that peaks in m
ES
but not E, which is modeled by a
Gaussian distribution in m
ES
. Continuum and other non-
peaking backgrounds are described by an ARGUS shape
[14]inm
ES
and a second-order polynomial in E.
We perform separate fits for B ! X
d
 and B ! X
s
 in
each of the hadronic mass ranges 0:5–1:0 GeV=c
2
and
1:0–2:0 GeV=c
2
. For each of the four fits, we combine
the component PDFs and fit for the signal, generic B and
continuum yields, the ARGUS and two polynomial shape
parameters. We scale the cross-feed contributions propor-
tionally to the fitted signal yield, refit and iterate until the
procedure converges. Projections of m
ES
and E from fits
to data for B ! X
s
 and B ! X
d
 are shown in the low
mass region in Fig. 1 and in the high mass region in Fig. 2.
Table II gives the signal yields, efficiencies (after correc-
FIG. 1 (color online). Projections of E with 5:275 <m
ES
<
5:286 GeV=c
2
for (a) B ! X
s
 and (c) B ! X
d
, and of m
ES
with 0:1 < E<0:05 GeV for (b) B ! X
s
 and
(d) B ! X
d
 in the mass range 0:5–1:0 GeV=c
2
. Data points
are compared with the sum of all the fit contributions (solid line).
The jagged line is an artifact of the fit projection over the sum of
several binned histograms. The dashed line shows the signal
component.
FIG. 2 (color online). Projections of E with 5:275 <m
ES
<
5:286 GeV=c
2
for (a) B ! X
s
 and (c) B ! X
d
, and of m
ES
with 0:1 < E<0:05 GeV for (b) B ! X
s
 and
(d) B ! X
d
 in the mass range 1:0–2:0 GeV=c
2
. Data points
are compared with the sum of all the fit contributions (solid line).
The jagged line is an artifact of the fit projection over the sum of
several binned histograms. The dashed line shows the signal
component.
STUDY OF B ! X DECAYS AND ... PHYSICAL REVIEW D 82, 051101(R) (2010)
RAPID COMMUNICATIONS
051101-5

Frequently asked questions

Q1. What are the contributions in this paper?

In this paper, the authors present a survey of the state-of-the-art work in this area.