Measurement of þb þ X and þc þ X Production Cross Sections
in p
p Collisions at
ffiffiffi
s
p
¼ 1:96 TeV
V. M. Abazov,
36
B. Abbott,
75
M. Abolins,
65
B. S. Acharya,
29
M. Adams,
51
T. Adams,
49
E. Aguilo,
6
M. Ahsan,
59
G. D. Alexeev,
36
G. Alkhazov,
40
A. Alton,
64,
*
G. Alverson,
63
G. A. Alves,
2
M. Anastasoaie,
35
L. S. Ancu,
35
T. Andeen,
53
B. Andrieu,
17
M. S. Anzelc,
53
M. Aoki,
50
Y. Arnoud,
14
M. Arov,
60
M. Arthaud,
18
A. Askew,
49,†
B. A
˚
sman,
41
A. C. S. Assis Jesus,
3
O. Atramentov,
49
C. Avila,
8
J. BackusMayes,
82
F. Badaud,
13
L. Bagby,
50
B. Baldin,
50
D. V. Bandurin,
59
P. Banerjee,
29
S. Banerjee,
29
E. Barberis,
63
A.-F. Barfuss,
15
P. Bargassa,
80
P. Baringer,
58
J. Barreto,
2
J. F. Bartlett,
50
U. Bassler,
18
D. Bauer,
43
S. Beale,
6
A. Bean,
58
M. Begalli,
3
M. Begel,
73
C. Belanger-Champagne,
41
L. Bellantoni,
50
A. Bellavance,
50
J. A. Benitez,
65
S. B. Beri,
27
G. Bernardi,
17
R. Bernhard,
23
I. Bertram,
42
M. Besanc¸on,
18
R. Beuselinck,
43
V. A. Bezzubov,
39
P. C. Bhat,
50
V. Bhatnagar,
27
G. Blazey,
52
F. Blekman,
43
S. Blessing,
49
K. Bloom,
67
A. Boehnlein,
50
D. Boline,
62
T. A. Bolton,
59
E. E. Boos,
38
G. Borissov,
42
T. Bose,
77
A. Brandt,
78
R. Brock,
65
G. Brooijmans,
70
A. Bross,
50
D. Brown,
19
X. B. Bu,
7
N. J. Buchanan,
49
D. Buchholz,
53
M. Buehler,
81
V. Buescher,
22
V. Bunichev,
38
S. Burdin,
42,‡
T. H. Burnett,
82
C. P. Buszello,
43
P. Calfayan,
25
B. Calpas,
15
S. Calvet,
16
J. Cammin,
71
M. A. Carrasco-Lizarraga,
33
E. Carrera,
49
W. Carvalho,
3
B. C. K. Casey,
50
H. Castilla-Valdez,
33
S. Chakrabarti,
72
D. Chakraborty,
52
K. M. Chan,
55
A. Chandra,
48
E. Cheu,
45
D. K. Cho,
62
S. Choi,
32
B. Choudhary,
28
L. Christofek,
77
T. Christoudias,
43
S. Cihangir,
50
D. Claes,
67
J. Clutter,
58
M. Cooke,
50
W. E. Cooper,
50
M. Corcoran,
80
F. Couderc,
18
M.-C. Cousinou,
15
S. Cre
´
pe
´
-Renaudin,
14
V. Cuplov,
59
D. Cutts,
77
M. C
´
wiok,
30
H. da Motta,
2
A. Das,
45
G. Davies,
43
K. De,
78
S. J. de Jong,
35
E. De La Cruz-Burelo,
33
C. De Oliveira Martins,
3
K. DeVaughan,
67
F. De
´
liot,
18
M. Demarteau,
50
R. Demina,
71
D. Denisov,
50
S. P. Denisov,
39
S. Desai,
50
H. T. Diehl,
50
M. Diesburg,
50
A. Dominguez,
67
T. Dorland,
82
A. Dubey,
28
L. V. Dudko,
38
L. Duflot,
16
S. R. Dugad,
29
D. Duggan,
49
A. Duperrin,
15
S. Dutt,
27
J. Dyer,
65
A. Dyshkant,
52
M. Eads,
67
D. Edmunds,
65
J. Ellison,
48
V. D. Elvira,
50
Y. Enari,
77
S. Eno,
61
P. Ermolov,
38,xx
M. Escalier,
15
H. Evans,
54
A. Evdokimov,
73
V. N. Evdokimov,
39
A. V. Ferapontov,
59
T. Ferbel,
61,71
F. Fiedler,
24
F. Filthaut,
35
W. Fisher,
50
H. E. Fisk,
50
M. Fortner,
52
H. Fox,
42
S. Fu,
50
S. Fuess,
50
T. Gadfort,
70
C. F. Galea,
35
C. Garcia,
71
A. Garcia-Bellido,
71
V. Gavrilov,
37
P. Gay,
13
W. Geist,
19
W. Geng,
15,65
C. E. Gerber,
51
Y. Gershtein,
49,†
D. Gillberg,
6
G. Ginther,
71
B. Go
´
mez,
8
A. Goussiou,
82
P. D. Grannis,
72
H. Greenlee,
50
Z. D. Greenwood,
60
E. M. Gregores,
4
G. Grenier,
20
Ph. Gris,
13
J.-F. Grivaz,
16
A. Grohsjean,
25
S. Gru
¨
nendahl,
50
M. W. Gru
¨
newald,
30
F. Guo,
72
J. Guo,
72
G. Gutierrez,
50
P. Gutierrez,
75
A. Haas,
70
N. J. Hadley,
61
P. Haefner,
25
S. Hagopian,
49
J. Haley,
68
I. Hall,
65
R. E. Hall,
47
L. Han,
7
K. Harder,
44
A. Harel,
71
J. M. Hauptman,
57
J. Hays,
43
T. Hebbeker,
21
D. Hedin,
52
J. G. Hegeman,
34
A. P. Heinson,
48
U. Heintz,
62
C. Hensel,
22,x
K. Herner,
72
G. Hesketh,
63
M. D. Hildreth,
55
R. Hirosky,
81
T. Hoang,
49
J. D. Hobbs,
72
B. Hoeneisen,
12
M. Hohlfeld,
22
S. Hossain,
75
P. Houben,
34
Y. Hu,
72
Z. Hubacek,
10
N. Huske,
17
V. Hynek,
9
I. Iashvili,
69
R. Illingworth,
50
A. S. Ito,
50
S. Jabeen,
62
M. Jaffre
´
,
16
S. Jain,
75
K. Jakobs,
23
C. Jarvis,
61
R. Jesik,
43
K. Johns,
45
C. Johnson,
70
M. Johnson,
50
D. Johnston,
67
A. Jonckheere,
50
P. Jonsson,
43
A. Juste,
50
E. Kajfasz,
15
D. Karmanov,
38
P. A. Kasper,
50
I. Katsanos,
70
V. Kaushik,
78
R. Kehoe,
79
S. Kermiche,
15
N. Khalatyan,
50
A. Khanov,
76
A. Kharchilava,
69
Y. N. Kharzheev,
36
D. Khatidze,
70
T. J. Kim,
31
M. H. Kirby,
53
M. Kirsch,
21
B. Klima,
50
J. M. Kohli,
27
J.-P. Konrath,
23
A. V. Kozelov,
39
J. Kraus,
65
T. Kuhl,
24
A. Kumar,
69
A. Kupco,
11
T. Kurc
ˇ
a,
20
V. A. Kuzmin,
38
J. Kvita,
9
F. Lacroix,
13
D. Lam,
55
S. Lammers,
70
G. Landsberg,
77
P. Lebrun,
20
W. M. Lee,
50
A. Leflat,
38
J. Lellouch,
17
J. Li,
78,xx
L. Li,
48
Q. Z. Li,
50
S. M. Lietti,
5
J. K. Lim,
31
J. G. R. Lima,
52
D. Lincoln,
50
J. Linnemann,
65
V. V. Lipaev,
39
R. Lipton,
50
Y. Liu,
7
Z. Liu,
6
A. Lobodenko,
40
M. Lokajicek,
11
P. Love,
42
H. J. Lubatti,
82
R. Luna-Garcia,
33,k
A. L. Lyon,
50
A. K. A. Maciel,
2
D. Mackin,
80
R. J. Madaras,
46
P. Ma
¨
ttig,
26
A. Magerkurth,
64
P. K. Mal,
82
H. B. Malbouisson,
3
S. Malik,
67
V. L. Malyshev,
36
Y. Maravin,
59
B. Martin,
14
R. McCarthy,
72
M. M. Meijer,
35
A. Melnitchouk,
66
L. Mendoza,
8
P. G. Mercadante,
5
M. Merkin,
38
K. W. Merritt,
50
A. Meyer,
21
J. Meyer,
22,x
J. Mitrevski,
70
R. K. Mommsen,
44
N. K. Mondal,
29
R. W. Moore,
6
T. Moulik,
58
G. S. Muanza,
15
M. Mulhearn,
70
O. Mundal,
22
L. Mundim,
3
E. Nagy,
15
M. Naimuddin,
50
M. Narain,
77
H. A. Neal,
64
J. P. Negret,
8
P. Neustroev,
40
H. Nilsen,
23
H. Nogima,
3
S. F. Novaes,
5
T. Nunnemann,
25
D. C. O’Neil,
6
G. Obrant,
40
C. Ochando,
16
D. Onoprienko,
59
N. Oshima,
50
N. Osman,
43
J. Osta,
55
R. Otec,
10
G. J. Otero y Garzo
´
n,
1
M. Owen,
44
M. Padilla,
48
P. Padley,
80
M. Pangilinan,
77
N. Parashar,
56
S.-J. Park,
22,x
S. K. Park,
31
J. Parsons,
70
R. Partridge,
77
N. Parua,
54
A. Patwa,
73
G. Pawloski,
80
B. Penning,
23
M. Perfilov,
38
K. Peters,
44
Y. Peters,
26
P. Pe
´
troff,
16
M. Petteni,
43
R. Piegaia,
1
J. Piper,
65
M.-A. Pleier,
22
P. L. M. Podesta-Lerma,
33,{
V. M. Podstavkov,
50
Y. Pogorelov,
55
M.-E. Pol,
2
P. Polozov,
37
B. G. Pope,
65
A. V. Popov,
39
C. Potter,
6
W. L. Prado da Silva,
3
H. B. Prosper,
49
S. Protopopescu,
73
J. Qian,
64
A. Quadt,
22,x
B. Quinn,
66
A. Rakitine,
42
M. S. Rangel,
2
K. Ranjan,
28
P. N. Ratoff,
42
P. Renkel,
79
P. Rich,
44
PRL 102, 192002 (2009)
PHYSICAL REVIEW LETTERS
week ending
15 MAY 2009
0031-9007=09=102(19)=192002(7) 192002-1 Ó 2009 The American Physical Society
M. Rijssenbeek,
72
I. Ripp-Baudot,
19
F. Rizatdinova,
76
S. Robinson,
43
R. F. Rodrigues,
3
M. Rominsky,
75
C. Royon,
18
P. Rubinov,
50
R. Ruchti,
55
G. Safronov,
37
G. Sajot,
14
A. Sa
´
nchez-Herna
´
ndez,
33
M. P. Sanders,
17
B. Sanghi,
50
G. Savage,
50
L. Sawyer,
60
T. Scanlon,
43
D. Schaile,
25
R. D. Schamberger,
72
Y. Scheglov,
40
H. Schellman,
53
T. Schliephake,
26
S. Schlobohm,
82
C. Schwanenberger,
44
R. Schwienhorst,
65
J. Sekaric,
49
H. Severini,
75
E. Shabalina,
51
M. Shamim,
59
V. Shary,
18
A. A. Shchukin,
39
R. K. Shivpuri,
28
V. Siccardi,
19
V. Simak,
10
V. Sirotenko,
50
P. Skubic,
75
P. Slattery,
71
D. Smirnov,
55
G. R. Snow,
67
J. Snow,
74
S. Snyder,
73
S. So
¨
ldner-Rembold,
44
L. Sonnenschein,
17
A. Sopczak,
42
M. Sosebee,
78
K. Soustruznik,
9
B. Spurlock,
78
J. Stark,
14
V. Stolin,
37
D. A. Stoyanova,
39
J. Strandberg,
64
S. Strandberg,
41
M. A. Strang,
69
E. Strauss,
72
M. Strauss,
75
R. Stro
¨
hmer,
25
D. Strom,
53
L. Stutte,
50
S. Sumowidagdo,
49
P. Svoisky,
35
A. Sznajder,
3
A. Tanasijczuk,
1
W. Taylor,
6
B. Tiller,
25
F. Tissandier,
13
M. Titov,
18
V. V. Tokmenin,
36
I. Torchiani,
23
D. Tsybychev,
72
B. Tuchming,
18
C. Tully,
68
P. M. Tuts,
70
R. Unalan,
65
L. Uvarov,
40
S. Uvarov,
40
S. Uzunyan,
52
B. Vachon,
6
P. J. van den Berg,
34
R. Van Kooten,
54
W. M. van Leeuwen,
34
N. Varelas,
51
E. W. Varnes,
45
I. A. Vasilyev,
39
P. Verdier,
20
L. S. Vertogradov,
36
M. Verzocchi,
50
D. Vilanova,
18
F. Villeneuve-Seguier,
43
P. Vint,
43
P. Vokac,
10
M. Voutilainen,
67,
**
R. Wagner,
68
H. D. Wahl,
49
M. H. L. S. Wang,
50
J. Warchol,
55
G. Watts,
82
M. Wayne,
55
G. Weber,
24
M. Weber,
50,††
L. Welty-Rieger,
54
A. Wenger,
23,‡‡
N. Wermes,
22
M. Wetstein,
61
A. White,
78
D. Wicke,
26
M. R. J. Williams,
42
G. W. Wilson,
58
S. J. Wimpenny,
48
M. Wobisch,
60
D. R. Wood,
63
T. R. Wyatt,
44
Y. Xie,
77
C. Xu,
64
S. Yacoob,
53
R. Yamada,
50
W.-C. Yang,
44
T. Yasuda,
50
Y. A. Yatsunenko,
36
Z. Ye,
50
H. Yin,
7
K. Yip,
73
H. D. Yoo,
77
S. W. Youn,
53
J. Yu,
78
C. Zeitnitz,
26
S. Zelitch,
81
T. Zhao,
82
B. Zhou,
64
J. Zhu,
72
M. Zielinski,
71
D. Zieminska,
54
L. Zivkovic,
70
V. Zutshi,
52
and E. G. Zverev
38
(The DØ Collaboration)
1
Universidad de Buenos Aires, Buenos Aires, Argentina
2
LAFEX, Centro Brasileiro de Pesquisas Fı
´
sicas, Rio de Janeiro, Brazil
3
Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil
4
Universidade Federal do ABC, Santo Andre
´
, Brazil
5
Instituto de Fı
´
sica Teo
´
rica, Universidade Estadual Paulista, Sa
˜
o Paulo, Brazil
6
University of Alberta, Edmonton, Alberta, Canada,
Simon Fraser University, Burnaby, British Columbia, Canada,
York University, Toronto, Ontario, Canada,
and McGill University, Montreal, Quebec, Canada
7
University of Science and Technology of China, Hefei, People’s Republic of China
8
Universidad de los Andes, Bogota
´
, Colombia
9
Center for Particle Physics, Charles University, Prague, Czech Republic
10
Czech Technical University, Prague, Czech Republic
11
Center for Particle Physics, Institute of Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic
12
Universidad San Francisco de Quito, Quito, Ecuador
13
LPC, Universite
´
Blaise Pascal, CNRS/IN2P3, Clermont, France
14
LPSC, Universite
´
Joseph Fourier Grenoble 1, CNRS/IN2P3, Institut National Polytechnique de Grenoble, Grenoble, France
15
CPPM, Aix-Marseille Universite
´
, CNRS/IN2P3, Marseille, France
16
LAL, Universite
´
Paris-Sud, IN2P3/CNRS, Orsay, France
17
LPNHE, IN2P3/CNRS, Universite
´
s Paris VI and VII, Paris, France
18
CEA, Irfu, SPP, Saclay, France
19
IPHC, Universite
´
Louis Pasteur, CNRS/IN2P3, Strasbourg, France
20
IPNL, Universite
´
Lyon 1, CNRS/IN2P3, Villeurbanne, France and Universite
´
de Lyon, Lyon, France
21
III. Physikalisches Institut A, RWTH Aachen University, Aachen, Germany
22
Physikalisches Institut, Universita
¨
t Bonn, Bonn, Germany
23
Physikalisches Institut, Universita
¨
t Freiburg, Freiburg, Germany
24
Institut fu
¨
r Physik, Universita
¨
t Mainz, Mainz, Germany
25
Ludwig-Maximilians-Universita
¨
tMu
¨
nchen, Mu
¨
nchen, Germany
26
Fachbereich Physik, University of Wuppertal, Wuppertal, Germany
27
Panjab University, Chandigarh, India
28
Delhi University, Delhi, India
29
Tata Institute of Fundamental Research, Mumbai, India
30
University College Dublin, Dublin, Ireland
31
Korea Detector Laboratory, Korea University, Seoul, Korea
32
SungKyunKwan University, Suwon, Korea
33
CINVESTAV, Mexico City, Mexico
PRL 102, 192002 (2009)
PHYSICAL REVIEW LETTERS
week ending
15 MAY 2009
192002-2
34
FOM-Institute NIKHEF and University of Amsterdam/NIKHEF, Amsterdam, The Netherlands
35
Radboud University Nijmegen/NIKHEF, Nijmegen, The Netherlands
36
Joint Institute for Nuclear Research, Dubna, Russia
37
Institute for Theoretical and Experimental Physics, Moscow, Russia
38
Moscow State University, Moscow, Russia
39
Institute for High Energy Physics, Protvino, Russia
40
Petersburg Nuclear Physics Institute, Saint Petersburg, Russia
41
Lund University, Lund, Sweden,
Royal Institute of Technology and Stockholm University, Stockholm, Sweden,
and Uppsala University, Uppsala, Sweden
42
Lancaster University, Lancaster, United Kingdom
43
Imperial College, London, United Kingdom
44
University of Manchester, Manchester, United Kingdom
45
University of Arizona, Tucson, Arizona 85721, USA
46
Lawrence Berkeley National Laboratory and University of California, Berkeley, California 94720, USA
47
California State University, Fresno, California 93740, USA
48
University of California, Riverside, California 92521, USA
49
Florida State University, Tallahassee, Florida 32306, USA
50
Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA
51
University of Illinois at Chicago, Chicago, Illinois 60607, USA
52
Northern Illinois University, DeKalb, Illinois 60115, USA
53
Northwestern University, Evanston, Illinois 60208, USA
54
Indiana University, Bloomington, Indiana 47405, USA
55
University of Notre Dame, Notre Dame, Indiana 46556, USA
56
Purdue University Calumet, Hammond, Indiana 46323, USA
57
Iowa State University, Ames, Iowa 50011, USA
58
University of Kansas, Lawrence, Kansas 66045, USA
59
Kansas State University, Manhattan, Kansas 66506, USA
60
Louisiana Tech University, Ruston, Louisiana 71272, USA
61
University of Maryland, College Park, Maryland 20742, USA
62
Boston University, Boston, Massachusetts 02215, USA
63
Northeastern University, Boston, Massachusetts 02115, USA
64
University of Michigan, Ann Arbor, Michigan 48109, USA
65
Michigan State University, East Lansing, Michigan 48824, USA
66
University of Mississippi, University, Mississippi 38677, USA
67
University of Nebraska, Lincoln, Nebraska 68588, USA
68
Princeton University, Princeton, New Jersey 08544, USA
69
State University of New York, Buffalo, New York 14260, USA
70
Columbia University, New York, New York 10027, USA
71
University of Rochester, Rochester, New York 14627, USA
72
State University of New York, Stony Brook, New York 11794, USA
73
Brookhaven National Laboratory, Upton, New York 11973, USA
74
Langston University, Langston, Oklahoma 73050, USA
75
University of Oklahoma, Norman, Oklahoma 73019, USA
76
Oklahoma State University, Stillwater, Oklahoma 74078, USA
77
Brown University, Providence, Rhode Island 02912, USA
78
University of Texas, Arlington, Texas 76019, USA
79
Southern Methodist University, Dallas, Texas 75275, USA
80
Rice University, Houston, Texas 77005, USA
81
University of Virginia, Charlottesville, Virginia 22901, USA
82
University of Washington, Seattle, Washington 98195, USA
(Received 8 January 2009; published 12 May 2009)
First measurements of the differential cross sections d
3
=ðdp
T
dy
dy
jet
Þ for the inclusive production of
a photon in association with a heavy quark (b, c) jet are presented, covering photon transverse momenta
30 <p
T
< 150 GeV, photon rapidities jy
j < 1:0, jet rapidities jy
jet
j < 0:8, and jet transverse momenta
p
jet
T
> 15 GeV. The results are based on an integrated luminosity of 1fb
1
in p
p collisions at
ffiffiffi
s
p
¼
1:96 TeV recorded with the D0 detector at the Fermilab Tevatron Collider. The results are compared with
next-to-leading order perturbative QCD predictions.
DOI: 10.1103/PhysRevLett.102.192002 PACS numbers: 13.85.Qk, 12.38.Qk
PRL 102, 192002 (2009)
PHYSICAL REVIEW LETTERS
week ending
15 MAY 2009
192002-3
Photons () produced in association with heavy quarks
Q (c or b) in the final state of hadron-hadron interactions
provide valuable information about the parton distributions
of the initial state hadrons [1,2]. Such events are produced
primarily through the QCD Compton-like scattering pro-
cess gQ ! Q, which dominates up to photon transverse
momenta (p
T
)of90 GeV for þ c þX and up to
120 GeV for þ b þ X production, but also through
quark-antiquark annihilation q
q ! g ! Q
Q. Conse-
quently, þ Q þ X production is sensitive to the b, c,
and gluon (g) densities within the colliding hadrons, and
can provide constraints on parton distribution functions
(PDFs) that have substantial uncertainties [3,4]. The heavy
quark and gluon content is an important aspect of QCD
dynamics and of the fundamental structure of the proton. In
particular, many searches for new physics, e.g., for certain
Higgs boson production modes [5–8], will benefit from a
more precise knowledge of the heavy quark and gluon
content of the proton.
This Letter presents the first measurements of the in-
clusive differential cross sections d
3
=ðdp
T
dy
dy
jet
Þ for
þb þ X and þ c þ X production in p
p collisions,
where y
and y
jet
are the photon and jet rapidities [9].
The results are based on an integrated luminosity of 1:02
0:06 fb
1
[10] collected with the D0 detector [11] at the
Fermilab Tevatron Collider at
ffiffiffi
s
p
¼ 1:96 TeV. The highest
p
T
(leading) photon and jet are required to have jy
j < 1:0
and jy
jet
j < 0:8, and transverse momentum 30 <p
T
<
150 GeV and p
jet
T
> 15 GeV. This selection allows one
to probe PDFs in the range of parton-momentum fractions
0:01 & x & 0:3, and hard scatter scales of 9 10
2
&
Q
2
ðp
T
Þ
2
& 2 10
4
GeV
2
. Differential cross sections
are presented for two regions of kinematics, defined by
y
y
jet
> 0 and y
y
jet
< 0. These two regions provide
greater sensitivity to the parton x because they probe differ-
ent sets of x
1
and x
2
intervals, as discussed in Ref. [12].
The triggers for this analysis identify clusters of large
electromagnetic (EM) energy, and are based on p
T
and on
the spatial distribution of energy in the photon shower. The
trigger efficiency is 96% for photon candidates with
p
T
¼ 30 GeV and rises to nearly 100% for p
T
> 40 GeV.
To reconstruct photon candidates, towers [11] with large
depositions of energy are used as seeds to create clusters of
energy in the EM calorimeter in a cone of radius R ¼ 0:4,
where R
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
ðÞ
2
þðÞ
2
p
[13]. Once an EM energy
cluster is formed, the final energy E
EM
is defined by a
smaller cone of R ¼ 0:2. Photon candidates are required
to be isolated within the calorimeter, and must also have
>96% of their energy in its EM section. We require the
sum of the total energy inside a cone of R ¼ 0:4, after the
subtraction of E
EM
,tobe<7% of E
EM
. We also require the
width of the energy-weighted shower in the most finely
segmented part of the EM calorimeter to be consistent with
that expected for an electromagnetic shower, and the
probability for any track spatially matched to the photon
EM cluster to be <0:1%. Background from dijet events
containing
0
and mesons that can mimic photon sig-
natures is also rejected using an artificial neural network
for identifying photons (-ANN), described in Ref. [12].
The requirement that the -ANN output be >0:7, com-
bined with all other photon selection criteria, reduces the
dijet event efficiency to 0.1%–0.5%. We calculate photon
detection efficiencies using a Monte Carlo (MC) simula-
tion. Signal events are generated using
PYTHIA [14] and
processed through a
GEANT-based [15] simulation of the
detector geometry and response, and reconstructed using
the same software as for the data. The MC efficiencies are
calibrated to those in data using small correction factors
measured in Z ! e
þ
e
samples. The total efficiency of the
above photon selection criteria is 63%–80%, depending on
p
T
. The systematic uncertainties on these values are 5%,
and are mainly due to uncertainties in the isolation, the
track-match veto, and the -ANN requirements.
At least one jet must be present in each event. Jets are
reconstructed using the D0 Run II algorithm [16] with a
radius of 0.5. The efficiency for a jet to be reconstructed
and to satisfy the jet identification criteria is 93%, 96.5%,
and 94.5% for light (u, d, s quark or g), c, and b jets at
p
T
¼ 30 GeV and increases to 98% at p
T
¼ 150 GeV,
independent of the jet flavor. The impact from uncertainties
on jet energy scale, jet energy resolution, and difference in
energy response between light and bðcÞ jets is found to be
between 8%(6%) and 2%(2%) for p
jet
T
between 15 GeVand
150 GeV. The leading jet is also required to have at least
two associated tracks with p
T
> 0:5 GeV and the track
leading in p
T
must have p
T
> 1:0 GeV, and each track
must have at least one hit in the silicon microstrip tracker.
The criteria ensure that the jet has sufficient information to
be classified as a heavy-flavor (HF) candidate. Light jets
are suppressed using a dedicated artificial neural network
(b-ANN) [17] that exploits the longer lifetimes of heavy-
flavor hadrons relative to their lighter counterparts. The
leading jet is required to have a b-ANN output >0:85.
Depending on p
T
, this selection is 55%–62% efficient for
þ b jet, and 11%–12% efficient for þ c jet events,
with 3%–5% relative uncertainties on these values. Only
0.2%–1% of light jets are misidentified as heavy-flavor
jets.
A primary collision vertex with 3 tracks is required
within 35 cm of the center of the detector along the beam
axis. The missing transverse momentum in the event is
required to be <0:7p
T
so as to suppress background from
cosmic-ray muons and W ! ‘ decays. Such a require-
ment is highly efficient for signal, achieving an efficiency
96% even for events with semileptonic heavy-flavor
quark decays.
About 13 000 events remain in the data sample after
applying all selection criteria. Background for photons,
stemming mainly from dijet events in which one jet is
misidentified as a photon, is still present in this sample.
PRL 102, 192002 (2009)
PHYSICAL REVIEW LETTERS
week ending
15 MAY 2009
192002-4
To estimate the photon purity, a template fitting technique
is employed [18]. The -ANN distribution in data is
fitted to a linear combination of templates for photons
and jets obtained from simulated þ jet and dijet samples,
respectively. An independent fit is performed in each p
T
bin, yielding photon purities between 51% and 93% for
30 <p
T
< 150 GeV. The fractional contributions of b and
c jets are determined by fitting templates of P
HFjet
¼
ln
Q
i
P
i
track
to the data, where P
i
track
is the probability
that a track originates from the primary vertex, based on
the significance of the track’s distance of closest approach
to the primary vertex. All tracks within the jet cone are
used in the fit, except the one with lowest value of P
track
.
Jets from b quarks usually have large values of P
HFjet
,
whereas light jets mostly have small values, as their tracks
originate from the primary vertex. Templates are used for
the shape information of the P
HFjet
distributions. For b
and c jets these are extracted from MC events whereas the
light jet template is taken from a data sample enriched in
light jets, which is corrected for contributions from b and c
quarks. The result of a maximum likelihood fit, normalized
to the number of events in data, is shown in Fig. 1 for 50 <
p
T
< 70 GeV. The estimated fractions of b and c jets in all
p
T
bins vary between 25%–34% and 40%–48%, respec-
tively. The corresponding uncertainties range between
7%–24%, dominated at higher p
T
by the limited data
statistics.
The differential cross sections are extracted in five bins
of p
T
and in the two regions of y
y
jet
, and are all listed in
Table I. The measured cross sections are corrected for the
effect of finite calorimeter energy resolution affecting p
T
using the unfolding procedure described in Ref. [20]. Such
corrections are 1%–3%. The measured differential cross
sections are shown in Fig. 2 for þ b þ X and þ c þ X
production as a function of p
T
for the jet and photon
rapidity intervals in question. The cross sections fall by
more than 3 orders of magnitude in the range 30 <p
T
<
150 GeV. The statistical uncertainty on the results ranges
from 2% in the first p
T
bin to 9% in the last bin, while
the total systematic uncertainty varies between 15% and
28%. The main uncertainty at low p
T
is due to the photon
purity (10.5%) and the heavy-flavor fraction fit (9%). At
higher p
T
, the uncertainty is dominated by the heavy-flavor
fraction. Other significant uncertainties result from the jet-
selection efficiency (between 8% and 2%), the photon
selection efficiency (5%), and the luminosity (6.1%) [10].
Systematic uncertainties have a 60%–68% correlation be-
tween adjacent p
T
bins for 30 <p
T
< 50 GeV and 20%–
30% for p
T
> 70 GeV.
HF-jet
P
24681012
Events
0
50
100
150
200
250
300
350
data
b jets
c jets
light jets
b + c + light jets
-1
= 1.0 fb
int
DØ, L
< 70 GeV
γ
T
50 < p
FIG. 1 (color online). Distribution of observed events for
P
HFjet
after all selection criteria for the bin 50 <p
T
<
70 GeV. The distributions for the b, c, and light jet templates
are shown normalized to their fitted fraction. Error bars on the
templates represent combined uncertainties from statistics of the
MC and the fitted jet flavor fractions, while the data contain just
statistical uncertainties. Fits in the other p
T
bins are of similar
quality.
TABLE I. The þ b þ X and þ c þ X cross sections in bins of p
T
in the two regions y
y
jet
> 0 and y
y
jet
< 0 together with
statistical,
stat
, and systematic,
syst
, uncertainties. The theory cross sections
theory
are taken from Ref. [19].
y
y
jet
> 0 y
y
jet
< 0
p
T
bin
(GeV)
hp
T
i
(GeV)
Cross section
(pb/GeV)
stat
(%)
syst
(%)
theory
(pb/GeV)
hp
T
i
(GeV)
Cross section
(pb/GeV)
stat
(%)
syst
(%)
theory
(pb/GeV)
þ b þ X 30–40 34.1 2:73 10
1
1.5 18.5 2:96 10
1
34.1 2:23 10
1
1.6 19.1 2:45 10
1
40–50 44.3 1:09 10
1
2.5 15.5 9:31 10
2
44.2 9:53 10
2
2.6 16.0 8:18 10
2
50–70 57.6 2:72 10
2
3.3 15.2 2:66 10
2
57.4 2:67 10
2
3.3 15.3 2:22 10
2
70–90 78.7 6:21 10
3
6.6 20.8 6:39 10
3
78.3 6:10 10
3
6.7 20.8 5:49 10
3
90–150 108.3 1:23 10
3
8.2 26.2 1:11 10
3
110.0 1:09 10
3
8.9 25.7 1:05 10
3
þ c þ X 30–40 34.1 1.90 1.5 18.1 2.02 34.1 1.56 1.6 18.7 1.59
40–50 44.3 5:14 10
1
2.5 17.7 5:82 10
1
44.2 4:51 10
1
2.6 18.1 4:56 10
1
50–70 57.6 1:53 10
1
3.3 17.9 1:41 10
1
57.4 1:50 10
1
3.3 18.0 1:10 10
1
70–90 78.7 4:45 10
2
6.6 21.3 2:85 10
2
78.3 4:39 10
2
6.7 21.3 2:22 10
2
90–150 108.3 9:63 10
3
8.2 27.5 3:69 10
3
110.0 8:57 10
3
8.9 27.0 3:28 10
3
PRL 102, 192002 (2009)
PHYSICAL REVIEW LETTERS
week ending
15 MAY 2009
192002-5
![TABLE I. The þ bþ X and þ cþ X cross sections in bins of p T in the two regions y yjet > 0 and y yjet < 0 together with statistical, stat, and systematic, syst, uncertainties. The theory cross sections theory are taken from Ref. [19].](/figures/table-i-the-th-bth-x-and-th-cth-x-cross-sections-in-bins-of-28jg116b.webp)
