A
bstract
A summary is presented of ATLAS searches for gluinos and first- and second-generation squarks in final states containing jets and missing transverse momentum, with or without leptons or
b
...-jets, in the
s
=
8
TeV data set collected at the Large Hadron Collider in 2012. This paper reports the results of new interpretations and statistical combinations of previously published analyses, as well as a new analysis. Since no significant excess of events over the Standard Model expectation is observed, the data are used to set limits in a variety of models. In all the considered simplified models that assume R-parity conservation, the limit on the gluino mass exceeds 1150 GeV at 95% confidence level, for an LSP mass smaller than 100 GeV. Furthermore, exclusion limits are set for left-handed squarks in a phenomenological MSSM model, a minimal Supergravity/Constrained MSSM model, R-parity-violation scenarios, a minimal gauge-mediated supersymmetry breaking model, a natural gauge mediation model, a non-universal Higgs mass model with gaugino mediation and a minimal model of universal extra dimensions.
A
bstract
The production of
W
boson pairs in proton-proton collisions at
s
=
8
TeV is studied using data corresponding to 20.3 fb
−1
of integrated luminosity collected by the ATLAS detector during ...2012 at the CERN Large Hadron Collider. The
W
bosons are reconstructed using their leptonic decays into electrons or muons and neutrinos. Events with reconstructed jets are not included in the candidate event sample. A total of 6636
WW
candidate events are observed. Measurements are performed in fiducial regions closely approximating the detector acceptance. The integrated measurement is corrected for all acceptance effects and for the
W
branching fractions to leptons in order to obtain the total
WW
production cross section, which is found to be 71
.
1 ± 1
.
1(stat)
− 5.0
+ 5.7
(syst) ± 1.4(lumi) pb. This agrees with the next-to-next-to-leading-order Standard Model prediction of 63. 2
− 1.4
+ 1.6
(scale) ± 1.2(PDF) pb. Fiducial differential cross sections are measured as a function of each of six kinematic variables. The distribution of the transverse momentum of the leading lepton is used to set limits on anomalous triple-gauge-boson couplings.
Differential mRNA display was used to comprehensively screen the murine thymic transcriptome for genes modulated in vivo by dietary zinc. A moderate feeding protocol rendered young adult, outbred ...mice zinc-deficient and zinc-supplemented without alterations in feeding behavior or growth. However, these levels of deficiency and supplementation altered specific mRNA abundances in a manner detectable by differential display. In total, 240 primer-pair combinations were used to generate >48,000 interpretable cDNA bands derived from thymic total RNA, of which only 265 or 0.55% were identified as zinc-modulated under these moderate dietary conditions. The most strongly zinc-modulated cDNAs identified by display were reamplified and sequenced. No cDNAs encoding zinc-metalloenzymes or zinc-finger transcription factors were identified as zinc-modulated in this global screening. Those zinc-regulated genes independently confirmed by quantitative PCR included: heat shock proteins 40 and 60; heat shock cognate 70; histocompatibility 2, class II antigen A, α; and the T cell cytokine receptor. In addition, a variety of transcription- and translation-related factors (such as ribosomal proteins L3, L5, and L28; nuclear matrix protein 84; matrin cyclophilin; the H3 histone family 3A protein; β3 microglobulin; and a cleavage and polyadenylation factor) were identified as zinc-modulated. These profiling data show that differential expression of genes in the thymus in response to the dietary zinc supply precedes many of the phenotypic effects on thymic function associated with severe zinc restriction or supplementation. Several genes involved in T cell development were identified as regulated by zinc and will be targets to evaluate the effects of zinc on immune function.
Phenylalanine dehydrogenase catalyzes the reversible, pyridine nucleotide-dependent oxidative deamination of l-phenylalanine to form phenylpyruvate and ammonia. We have characterized the steady-state ...kinetic behavior of the enzyme from Rhodococcus sp. M4 and determined the X-ray crystal structures of the recombinant enzyme in the complexes, E·NADH·l-phenylalanine and E·NAD+ · l-3-phenyllactate, to 1.25 and 1.4 Å resolution, respectively. Initial velocity, product inhibition, and dead-end inhibition studies indicate the kinetic mechanism is ordered, with NAD+ binding prior to phenylalanine and the products' being released in the order of ammonia, phenylpyruvate, and NADH. The enzyme shows no activity with NADPH or other 2‘-phosphorylated pyridine nucleotides but has broad activity with NADH analogues. Our initial structural analyses of the E·NAD+·phenylpyruvate and E·NAD+·3-phenylpropionate complexes established that Lys78 and Asp118 function as the catalytic residues in the active site Vanhooke et al. (1999) Biochemistry 38, 2326−2339. We have studied the ionization behavior of these residues in steady-state turnover and use these findings in conjunction with the structural data described both here and in our first report to modify our previously proposed mechanism for the enzymatic reaction. The structural characterizations also illuminate the mechanism of the redox specificity that precludes α-amino acid dehydrogenases from functioning as α-hydroxy acid dehydrogenases.
A
bstract
Differential cross sections are presented for the prompt and non-prompt production of the hidden-charm states
X
(3872) and
ψ
(2
S
), in the decay mode
J/ψπ
+
π
−
, measured using 11.4 fb
−1
...of
pp
collisions at
s
=
8
TeV by the ATLAS detector at the LHC. The ratio of cross-sections
X
(3872)
/ψ
(2
S
) is also given, separately for prompt and non-prompt components, as well as the non-prompt fractions of
X
(3872) and
ψ
(2
S
). Assuming independent single effective lifetimes for non-prompt
X
(3872) and
ψ
(2
S
) production gives
R
B
=
ℬ
B
→
X
3872
+
any
ℬ
X
3872
→
J
/
ψ
π
+
π
−
ℬ
B
→
ψ
2
S
+
any
ℬ
ψ
2
S
→
J
/
ψ
π
+
π
−
=
3.95
±
0.32
stat
±
0.08
s
y
s
×
10
−
2
separating short- and long-lived contributions, assuming that the short-lived component is due to
B
c
decays, gives
R
B
= (3
.
57 ± 0
.
33(stat) ± 0
.
11(sys)) × 10
−2
, with the fraction of non-prompt
X
(3872) produced via
B
c
decays for
p
T
(
X
(3872))
>
10 GeV being (25 ± 13(stat) ± 2(sys) ± 5(spin))%. The distributions of the dipion invariant mass in the
X
(3872) and
ψ
(2
S
) decays are also measured and compared to theoretical predictions.
This paper describes the trigger and offline reconstruction, identification and energy calibration algorithms for hadronic decays of tau leptons employed for the data collected from
pp
collisions in ...2012 with the ATLAS detector at the LHC center-of-mass energy
s
=
8
TeV
. The performance of these algorithms is measured in most cases with
Z
decays to tau leptons using the full 2012 dataset, corresponding to an integrated luminosity of 20.3 fb
-
1
. An uncertainty on the offline reconstructed tau energy scale of 2–4 %, depending on transverse energy and pseudorapidity, is achieved using two independent methods. The offline tau identification efficiency is measured with a precision of 2.5 % for hadronically decaying tau leptons with one associated track, and of 4 % for the case of three associated tracks, inclusive in pseudorapidity and for a visible transverse energy greater than 20
GeV
. For hadronic tau lepton decays selected by offline algorithms, the tau trigger identification efficiency is measured with a precision of 2–8 %, depending on the transverse energy. The performance of the tau algorithms, both offline and at the trigger level, is found to be stable with respect to the number of concurrent proton–proton interactions and has supported a variety of physics results using hadronically decaying tau leptons at ATLAS.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The centrality dependence of the mean charged-particle multiplicity as a function of pseudorapidity is measured in approximately 1
μ
b
-
1
of proton–lead collisions at a nucleon–nucleon ...centre-of-mass energy of
s
NN
=
5.02
TeV
using the ATLAS detector at the Large Hadron Collider. Charged particles with absolute pseudorapidity less than 2.7 are reconstructed using the ATLAS pixel detector. The
collision centrality is characterised by the total transverse energy measured in the Pb-going direction of the forward calorimeter. The charged-particle pseudorapidity distributions are found to vary strongly with centrality, with an increasing asymmetry between the proton-going and Pb-going directions as the collisions become more central. Three different estimations of the number of nucleons participating in the
collision have been carried out using the Glauber model as well as two Glauber–Gribov inspired extensions to the Glauber model. Charged-particle multiplicities per participant pair are found to vary differently for these three models, highlighting the importance of including colour fluctuations in nucleon–nucleon collisions in the modelling of the initial state of
collisions.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The detrimental sequelae of severe zinc deficiency on the thymus and T-lymphocyte compartment of the mammalian immune system have been established, but underlying mechanisms remain unknown. ...Hypothesizing that the alterations in T-lymphocyte number and function observed during zinc deficiency may result from changes in gene expression, we sought to compare thymic mRNA expression profiles of zinc-deficient and zinc-normal mice utilizing cDNA arrays. For our murine model described herein, 3 wk of dietary zinc deficiency did not perturb food intake or growth rate in young adult, outbred mice, but significantly depressed multiple parameters of zinc status. Furthermore, fluorescence-activated cell sorting (FACS) analysis demonstrated no changes in thymocyte populations expressing the cell surface markers CD3, CD4 or CD8, establishing that observed changes in mRNA abundances were not attributable to different thymocyte populations. Yet notably, at this moderate level of zinc deficiency, cDNA array analysis identified four potentially zinc-regulated mRNAs whose modulation was confirmed independently, twice, using both semiquantitative and real-time quantitative reverse transcription-polymerase chain reaction. Expression of one of these genes (myeloid cell leukemia sequence-1) was depressed, whereas the others DNA damage repair and recombination protein 23B, the mouse laminin receptor and the lymphocyte-specific protein tyrosine kinase (LCK) were elevated in the zinc-deficient mice. Further Western analysis demonstrated that the zinc binding protein LCK was elevated in these zinc-deficient mice. Results demonstrate that 3 wk of dietary zinc insufficiency can alter specific thymic mRNA and protein abundances before alterations occur in thymocyte development as detectable by FACS analysis.
A search for singly produced vector-like
Q
quarks, where
Q
can be either a
T
quark with charge
+
2
/
3
or a
Y
quark with charge
-
4
/
3
, is performed in proton–proton collisions recorded with the ...ATLAS detector at the LHC. The dataset corresponds to an integrated luminosity of 20.3 fb
-
1
and was produced with a centre-of-mass energy of
s
=
8
TeV. This analysis targets
Q
→
W
b
decays where the
W
boson decays leptonically. A veto on massive large-radius jets is used to reject the dominant
t
t
¯
background. The reconstructed
Q
-candidate mass, ranging from 0.4 to 1.2 TeV, is used in the search to discriminate signal from background processes. No significant deviation from the Standard Model expectation is observed, and limits are set on the
Q
→
W
b
cross-section times branching ratio. The results are also interpreted as limits on the
QWb
coupling and the mixing with the Standard Model sector for a singlet
T
quark or a
Y
quark from a doublet.
T
quarks with masses below 0.95 TeV are excluded at 95 % confidence level, assuming a unit coupling and a BR
(
T
→
W
b
)
=
0.5
, whereas the expected limit is 1.10 TeV.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A
bstract
Various differential cross-sections are measured in top-quark pair
t
t
¯
events produced in proton-proton collisions at a centre-of-mass energy of
s
=
7
TeV at the LHC with the ATLAS ...detector. These differential cross-sections are presented in a data set corresponding to an integrated luminosity of 4
.
6 fb
−1
. The differential cross-sections are presented in terms of kinematic variables, such as momentum, rapidity and invariant mass, of a top-quark proxy referred to as the pseudo-top-quark as well as the pseudo-top-quark pair system. The dependence of the measurement on theoretical models is minimal.
The measurements are performed on
t
t
¯
events in the lepton+jets channel, requiring exactly one charged lepton and at least four jets with at least two of them tagged as originating from a
b
-quark. The hadronic and leptonic pseudo-top-quarks are defined via the leptonic or hadronic decay mode of the
W
boson produced by the top-quark decay in events with a single charged lepton. Differential cross-section measurements of the pseudo-top-quark variables are compared with several Monte Carlo models that implement next-to-leading order or leading-order multi-leg matrix-element calculations.
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