Measurement of upsilon production in 7 TeV pp collisions at ATLAS

Using
1
:
8fb
1
of
pp
collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at
the Large Hadron Collider, we present measurements of the production cross sections of
ð
1S
;
2S
;
3S
Þ
mesons.
mesons are reconstructed using the dimuon decay mode. Total production cross sections for
p
T
<
70 GeV
and in the rapidity interval
j
y
j
<
2
:
25
are measured to be,
8
:
01
0
:
02
0
:
36
0
:
31 nb
,
2
:
05
0
:
01
0
:
12
0
:
08 nb
,and
0
:
92
0
:
01
0
:
07
0
:
04 nb
, respectively, with uncertainties sepa-
rated into statistical, systematic, and luminosity measurement effects. In addition, differential cross section
times dimuon branching fractions for
ð
1S
Þ
,
ð
2S
Þ
, and
ð
3S
Þ
as a function of
transverse momentum
p
T
and rapidity are presented. These cross sections are obtained assuming unpolarized production. If the
production polarization is fully transverse or longitudinal with no azimuthal dependence in the helicity
frame, the cross section may vary by approximately
20%
. If a nontrivial azimuthal dependence is
considered, integrated cross sections may be significantly enhanced by a factor of 2 or more. We compare
our results to several theoretical models of
meson production, finding that none provide an accurate
description of our data over the full range of
transverse momenta accessible with this data set