A
bstract
The exclusive photoproduction reactions
γp
→
J/ψ
(1
S
)
p
and
γp
→
ψ
(2
S
)
p
have been measured at an
ep
centre-of-mass energy of 318 GeV with the ZEUS detector at HERA using an integrated ...luminosity of 373 pb
−
1
. The measurement was made in the kinematic range 30
< W <
180 GeV,
Q
2
<
1 GeV
2
and |
t
|
<
1 GeV
2
, where
W
is the photon-proton centre-of-mass energy,
Q
2
is the photon virtuality and
t
is the squared four-momentum transfer at the proton vertex. The decay channels used were
J/ψ
(1
S
)
→ μ
+
μ
−
,
ψ
(2
S
)
→ μ
+
μ
−
and
ψ
(2
S
)
→ J/ψ
(1
S
)
π
+
π
−
with subsequent decay
J/ψ
(1
S
)
→ μ
+
μ
−
. The ratio of the production cross sections,
R
=
σ
ψ
(2
S
)
/σ
J/ψ
(1
S
)
, has been measured as a function of
W
and |
t
| and compared to previous data in photoproduction and deep inelastic scattering and with predictions of QCD-inspired models of exclusive vector-meson production, which are in reasonable agreement with the data.
The DIS diffractive cross section, , has been measured in the mass range GeV for c.m. energies GeV and photon virtualities to 140 GeV. For fixed and , the diffractive cross section rises rapidly with ..., with corresponding to a t-averaged pomeron trajectory of which is larger than observed in hadron-hadron scattering. The W dependence of the diffractive cross section is found to be the same as that of the total cross section for scattering of virtual photons on protons. The data are consistent with the assumption that the diffractive structure function factorizes according to . They are also consistent with QCD based models which incorporate factorization breaking. The rise of with decreasing and the weak dependence of on suggest a substantial contribution from partonic interactions.
Combined analyses of the Higgs boson production and decay rates as well as its coupling strengths to vector bosons and fermions are presented. The combinations include the results of the analyses of ...the Formula: see text and Formula: see text decay modes, and the constraints on the associated production with a pair of top quarks and on the off-shell coupling strengths of the Higgs boson. The results are based on the LHC proton-proton collision datasets, with integrated luminosities of up to 4.7 Formula: see text at Formula: see text TeV and 20.3 Formula: see text at Formula: see text TeV, recorded by the ATLAS detector in 2011 and 2012. Combining all production modes and decay channels, the measured signal yield, normalised to the Standard Model expectation, is Formula: see text. The observed Higgs boson production and decay rates are interpreted in a leading-order coupling framework, exploring a wide range of benchmark coupling models both with and without assumptions on the Higgs boson width and on the Standard Model particle content in loop processes. The data are found to be compatible with the Standard Model expectations for a Higgs boson at a mass of 125.36 GeV for all models considered.
The decays Formula: see text and Formula: see text are studied with the ATLAS detector at the LHC using a dataset corresponding to integrated luminosities of 4.9 and 20.6 fbFormula: see text of
...collisions collected at centre-of-mass energies Formula: see text TeV and 8 TeV, respectively. Signal candidates are identified through Formula: see text and Formula: see text decays. With a two-dimensional likelihood fit involving the Formula: see text reconstructed invariant mass and an angle between the Formula: see text and Formula: see text candidate momenta in the muon pair rest frame, the yields of Formula: see text and Formula: see text, and the transverse polarisation fraction in Formula: see text decay are measured. The transverse polarisation fraction is determined to be Formula: see text, and the derived ratio of the branching fractions of the two modes is Formula: see text, where the first error is statistical and the second is systematic. Finally, a sample of Formula: see text decays is used to derive the ratios of branching fractions Formula: see text and Formula: see text, where the third error corresponds to the uncertainty of the branching fraction of Formula: see text decay. The available theoretical predictions are generally consistent with the measurement.
The paper presents studies of Bose-Einstein Correlations (BEC) for pairs of like-sign charged particles measured in the kinematic range Formula: see text 100 MeV and Formula: see text 2.5 in proton ...collisions at centre-of-mass energies of 0.9 and 7 TeV with the ATLAS detector at the CERN Large Hadron Collider. The integrated luminosities are approximately 7 Formula: see textbFormula: see text, 190 Formula: see textbFormula: see text and 12.4 nbFormula: see text for 0.9 TeV, 7 TeV minimum-bias and 7 TeV high-multiplicity data samples, respectively. The multiplicity dependence of the BEC parameters characterizing the correlation strength and the correlation source size are investigated for charged-particle multiplicities of up to 240. A saturation effect in the multiplicity dependence of the correlation source size parameter is observed using the high-multiplicity 7 TeV data sample. The dependence of the BEC parameters on the average transverse momentum of the particle pair is also investigated.
Many extensions of the Standard Model predict the existence of charged heavy long-lived particles, such as
-hadrons or charginos. These particles, if produced at the Large Hadron Collider, should be ...moving non-relativistically and are therefore identifiable through the measurement of an anomalously large specific energy loss in the ATLAS pixel detector. Measuring heavy long-lived particles through their track parameters in the vicinity of the interaction vertex provides sensitivity to metastable particles with lifetimes from 0.6 ns to 30 ns. A search for such particles with the ATLAS detector at the Large Hadron Collider is presented, based on a data sample corresponding to an integrated luminosity of Formula: see text fbFormula: see text of
collisions at Formula: see text TeV. No significant deviation from the Standard Model background expectation is observed, and lifetime-dependent upper limits on
-hadrons and chargino production are set. Gluino
-hadrons with 10 ns lifetime and masses up to 1185 GeV are excluded at 95 Formula: see text confidence level, and so are charginos with 15 ns lifetime and masses up to 482 GeV.
A search for Higgs boson pair production Formula: see text is performed with 19.5 fbFormula: see text of proton-proton collision data at Formula: see text TeV, which were recorded by the ATLAS ...detector at the Large Hadron Collider in 2012. The decay products of each Higgs boson are reconstructed as a high-momentum Formula: see text system with either a pair of small-radius jets or a single large-radius jet, the latter exploiting jet substructure techniques and associated
-tagged track-jets. No evidence for resonant or non-resonant Higgs boson pair production is observed. The data are interpreted in the context of the Randall-Sundrum model with a warped extra dimension as well as the two-Higgs-doublet model. An upper limit on the cross-section for Formula: see text of 3.2 (2.3) fb is set for a Kaluza-Klein graviton Formula: see text mass of 1.0 (1.5) TeV, at the 95 % confidence level. The search for non-resonant Standard Model
production sets an observed 95 % confidence level upper limit on the production cross-section Formula: see text of 202 fb, compared to a Standard Model prediction of Formula: see text fb.
A search for heavy long-lived multi-charged particles is performed using the ATLAS detector at the LHC. Data collected in 2012 at Formula: see text TeV from
collisions corresponding to an integrated ...luminosity of 20.3 fbFormula: see textare examined. Particles producing anomalously high ionisation, consistent with long-lived massive particles with electric charges from Formula: see text to Formula: see text are searched for. No signal candidate events are observed, and 95 % confidence level cross-section upper limits are interpreted as lower mass limits for a Drell-Yan production model. The mass limits range between 660 and 785 GeV.
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
collisions in ...2012 with the ATLAS detector at the LHC center-of-mass energy Formula: see text Formula: see text. The performance of these algorithms is measured in most cases with Formula: see text decays to tau leptons using the full 2012 dataset, corresponding to an integrated luminosity of 20.3 fbFormula: see text. 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 Formula: see text. 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.
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