We have measured the production of one and two large transverse momentum hadrons in p p and pp interactions in the range 2 < p T < 6 GeV/ c for the central rapidity region |y| < 0.9 at s = 63 and 31 GeV . No statistically significant difference between p p and pp collisions is observed. The results are in accordance with lowest order QCS perturbative calculations and rule out a large contribution of Constituent Interchange Model (CIM), di-quark of quark-fusion subprocesses in this kinematic range.
No description provided.
No description provided.
We present data obtained from a 1.7 sr hadron calorimeter, triggered on transverse energy, in pp collisions at s =63 GeV at the CERN-ISR. From the change in the distribution of energy in the calorimeter, we extract the cross section for two-constituent hard scattering for p T between 6 and 14 GeV at y = 0. The decrease of this jet cross section over this p T range is consistent with exp (− bp T ), with b = (1.02 ± 0.09) GeV −1 . The slope and normalization of the cross section agree well with a QCD motivated Monte Carlo model. The ratio between jet and single particle cross sections [ dσ JET / dp T )/( dσ π 0 / dp T )]| y = 0 changes from about 200 at 6 GeV to about 1500 at 14 GeV.
No description provided.
No description provided.
The production of charged hadrons with high p T in αα collisions at √ s =126 GeV and pp collisions at √ s =31 and 63 GeV is compared, and the structure of the events associated with the high- p T particles is studied. The probability of finding associated particles close to the trigger particle increases strongly between √ s =31 and 63 GeV for pp collisions. For p T >2.5GeV/ c the αα/pp cross section ratio at the same energy per nucleon is measured to be 18.7 ± 2.0, to be compared with A 2 = 16, and a higher associated multiplicity is observed for αα.
FIRST PP DATA IS AT SQRT(S)=31 AND THE SECOND PP DATA IS AT 63 GEV.
Measurements of charged particle multiplicity distributions in the central rapidity region in p-p and p-α, and α-α collisions are reported. They are better fitted to the “wounded nucleon” than to the “gluon string” model. The average transverse momenta, for all three reactions, are identical (and almost independent of multiplicity) up to very high multiplicities.
THE FIRST PP DATA IS AT 44 GEV, THE SECOND AT 63 GEV.
No description provided.
Measurements of transverse energy-energy correlations and their associated asymmetries in multi-jet events using the ATLAS detector at the LHC are presented. The data used correspond to $\sqrt{s} = 8$ TeV proton-proton collisions with an integrated luminosity of 20.2 fb$^{-1}$. The results are presented in bins of the scalar sum of the transverse momenta of the two leading jets, unfolded to the particle level and compared to the predictions from Monte Carlo simulations. A comparison with next-to-leading-order perturbative QCD is also performed, showing excellent agreement within the uncertainties. From this comparison, the value of the strong coupling constant is extracted for different energy regimes, thus testing the running of $\alpha_s(\mu)$ predicted in QCD up to scales over 1 TeV. A global fit to the transverse energy-energy correlation distributions yields $\alpha_s(m_Z) = 0.1162 \pm 0.0011 \mbox{ (exp.)}^{+0.0084}_{-0.0070} \mbox{ (theo.)}$, while a global fit to the asymmetry distributions yields a value of $\alpha_s(m_Z) = 0.1196 \pm 0.0013 \mbox{ (exp.)}^{+0.0075}_{-0.0045} \mbox{ (theo.)}$.
TEEC function for 800 GeV < HT2 < 850 GeV
ATEEC function for 800 GeV < HT2 < 850 GeV
TEEC function for 850 GeV < HT2 < 900 GeV
The analysis of the momentum difference between charged hadrons in high-energy proton-proton collisions is performed in order to study coherent particle production. The observed correlation pattern agrees with a model of a helical QCD string fragmenting into a chain of ground-state hadrons. A threshold momentum difference in the production of adjacent pairs of charged hadrons is observed, in agreement with model predictions. The presence of low-mass hadron chains also explains the emergence of charge-combination-dependent two-particle correlations commonly attributed to Bose-Einstein interference. The data sample consists of 190 inverse microbarns of minimum bias events collected with proton-proton collisions at a center-of-mass energy of 7 TeV in the early low-luminosity data taking with the ATLAS detector at the LHC.
The inclusive Delta as a function of $Q$, in the interval 0.02 GeV < Q < 2 GeV.
The Delta(3h), for 3-hadron chains with mass below 0.59 GeV, as a function of $Q$, in the interval 0.02 GeV < Q < 0.36 GeV.
The Dalitz plot, for 3-hadron chains with mass below 0.59 GeV. Coordinates X = sqrt(3)(T0-T2)/sum(T) , Y = 3T1/sum(T) - 1. T0/T1/T2 stand for kinetic energy of hadrons in the rest frame of the triplet ( hadrons 0 and 2 form like-sign pair).
The cross-section for the production of two jets in association with a leptonically decaying Z boson ($Zjj$) is measured in proton-proton collisions at a centre-of-mass energy of 13 TeV, using data recorded with the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 3.2 fb$^{-1}$. The electroweak $Zjj$ cross-section is extracted in a fiducial region chosen to enhance the electroweak contribution relative to the dominant Drell-Yan $Zjj$ process, which is constrained using a data-driven approach. The measured fiducial electroweak cross-section is $\sigma^{Zjj}_{EW}= 119\pm 16 (\mathrm{stat.}) \pm 20 (\mathrm{syst.})\pm 2 (\mathrm{lumi.})$ for dijet invariant mass greater than 250 GeV, and $34.2\pm 5.8 (\mathrm{stat.})\pm 5.5 (\mathrm{syst.})\pm 0.7 (\mathrm{lumi.})$ for dijet invariant mass greater than 1 TeV. Standard Model predictions are in agreement with the measurements. The inclusive $Zjj$ cross-section is also measured in six different fiducial regions with varying contributions from electroweak and Drell-Yan $Zjj$ production.
Fiducial regions definitions
Measured and predicted inclusive Zjj production cross-sections in the six fiducial regions
Measured and predicted EW-Zjj production cross-sections in the EW-enriched fiducial regions with and without an additional kinematic requirement of $m_{jj} > $ 1 TeV
The results of a search for vector-like top quarks using events with exactly one lepton, at least four jets, and large missing transverse momentum are reported. The search is optimised for pair production of vector-like top quarks in the $Z(\rightarrow \! \! \nu \nu) \, t + X$ decay channel. LHC pp collision data at a centre-of-mass energy of $\sqrt{s}=13$ TeV recorded by the ATLAS detector in 2015 and 2016 are used, corresponding to an integrated luminosity of 36.1 $\mathrm{fb}^{-1}$. No significant excess over the Standard Model expectation is seen and upper limits on the production cross-section of a vector-like $T$ quark pair as a function of the $T$ quark mass are derived. The observed (expected) 95% CL lower limits on the $T$ mass are 870 GeV (890 GeV) for the weak-isospin singlet model, 1.05 TeV (1.06 TeV) for the weak-isospin doublet model and 1.16 TeV (1.17 TeV) for the pure $Zt$ decay mode. Limits are also set on the mass as a function of the decay branching ratios, excluding large parts of the parameter space for masses below 1 TeV.
Expected and observed 95% CL upper limit on the cross-section times branching ratio for VLQ $T$ pair production as a function of the $T$ mass for BR($T \rightarrow Zt$) = 100%.
Expected and observed 95% CL upper limit on the cross-section times branching ratio for VLQ $T$ pair production as a function of the $T$ mass for branching ratios according to the singlet model.
Expected and observed 95% CL upper limit on the cross-section times branching ratio for VLQ $T$ pair production as a function of the $T$ mass for branching ratios according to the doublet model. Contributions from the $X$ or $B$ quark in the $(X^{5/3}, T)$ or $(T, B)$ doublet models are neglected, leading to very conservative limits.
A search for the dimuon decay of the Higgs boson was performed using data corresponding to an integrated luminosity of 36.1 fb$^{-1}$ collected with the ATLAS detector in $pp$ collisions at $\sqrt{s}=13$ TeV at the Large Hadron Collider. No significant excess is observed above the expected background. The observed (expected) upper limit on the cross section times branching ratio is 3.0 (3.1) times the Standard Model prediction at the 95% confidence level for a Higgs boson mass of 125 GeV. When combined with the $pp$ collision data at $\sqrt{s}=7$ TeV and $\sqrt{s}=8$ TeV, the observed (expected) upper limit is 2.8 (2.9) times the Standard Model prediction.
Measurement of signal strength
The 95% CL upper limit on signal strength
A search is conducted for new resonant and non-resonant high-mass phenomena in dielectron and dimuon final states. The search uses 36.1 fb$^{-1}$ of proton-proton collision data, collected at $\sqrt{s}$ = 13 TeV by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the Standard Model prediction is observed. Upper limits at 95% credibility level are set on the cross-section times branching ratio for resonances decaying into dileptons, which are converted to lower limits on the resonance mass, up to 4.1 for the E$_{6}$-motivated Z'$_{\chi}$. Lower limits on the $qq \ell\ell$ contact interaction scale are set between 24 TeV and 40 TeV, depending on the model.
Product of acceptance and efficiency for the dielectron (upper curve) and dimuon (lower curve) selections as a function of the Z' (Chi) pole mass. Upper 95% CL limits on the Z' production cross-section times branching ratio to two electrons as a function of Z' pole mass.
Distribution of dielectron reconstructed invariant mass after selection, for data and the SM background estimates.
Distribution of dimuon reconstructed invariant mass after selection, for data and the SM background estimates.
Forum