Four-fermion events have been selected in a data sample of 5.8 pb −1 collected with the aleph detector at centre-of-mass energies of 130 and 136 GeV. The final states ℓ + ℓ − q q , ℓ + ℓ − ℓ + ℓ − , ν ν q q , and ν ν ℓ + ℓ − have been examined. Five events are observed in the data, in agreement with the Standard Model predictions of 6.67±0.38 events from four-fermion processes and 0.14 −0.05 +0.19 from background processes.
The statistical and systematic uncertainties have been combined in quadrature in the background expectations.
The differential charged jet cross sections, jet fragmentation distributions, and jet shapes are measured in minimum bias proton-proton collisions at centre-of-mass energy $\sqrt{s}=7$ TeV using the ALICE detector at the LHC. Jets are reconstructed from charged particle momenta in the mid-rapidity region using the sequential recombination $k_{\rm T}$ and anti-$k_{\rm T}$ as well as the SISCone jet finding algorithms with several resolution parameters in the range $R=0.2$ to $0.6$. Differential jet production cross sections measured with the three jet finders are in agreement in the transverse momentum ($p_{\rm T}$) interval $20<p_{\rm T}^{\rm jet,ch}<100$ GeV/$c$. They are also consistent with prior measurements carried out at the LHC by the ATLAS collaboration. The jet charged particle multiplicity rises monotonically with increasing jet $p_{\rm T}$, in qualitative agreement with prior observations at lower energies. The transverse profiles of leading jets are investigated using radial momentum density distributions as well as distributions of the average radius containing 80% ($\langle R_{\rm 80} \rangle$) of the reconstructed jet $p_{\rm T}$. The fragmentation of leading jets with $R=0.4$ using scaled $p_{\rm T}$ spectra of the jet constituents is studied. The measurements are compared to model calculations from event generators (PYTHIA, PHOJET, HERWIG). The measured radial density distributions and $\langle R_{\rm 80} \rangle$ distributions are well described by the PYTHIA model (tune Perugia-2011). The fragmentation distributions are better described by HERWIG.
Measured charged jet differential cross sections for INEL proton-proton collisions at $\sqrt{s}$ = 7 TeV.
Measured charged jet differential cross sections for INEL proton-proton collisions at $\sqrt{s}$ = 7 TeV.
Measured charged jet differential cross sections for INEL proton-proton collisions at $\sqrt{s}$ = 7 TeV.
The yield of charged particles associated with high-$p_{\rm T}$ trigger particles ($8 < p_{\rm T} < 15$ GeV/$c$) is measured with the ALICE detector in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV relative to proton-proton collisions at the same energy. The conditional per-trigger yields are extracted from the narrow jet-like correlation peaks in azimuthal di-hadron correlations. In the 5% most central collisions, we observe that the yield of associated charged particles with transverse momenta $p_{\rm T}> 3$ GeV/$c$ on the away-side drops to about 60% of that observed in pp collisions, while on the near-side a moderate enhancement of 20-30% is found.
The ratio of near-side yields in Lead-Lead/Proton-Proton collisions in the central region.
The ratio of near-side yields in Lead-Lead/Proton-Proton collisions in the peripheral region.
The ratio of away-side yields in Lead-Lead/Proton-Proton collisions in the central region.
In this Letter, comprehensive results on ${\rm\pi}^\pm$, K$^\pm$, K$^0_S$, p, $\rm\bar{p}$, $\rm \Lambda$ and $\rm \bar{\Lambda}$ production at mid-rapidity ($0 < y_{\rm cms} < 0.5$) in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV, measured by the ALICE detector at the LHC, are reported. The transverse momentum distributions exhibit a hardening as a function of event multiplicity, which is stronger for heavier particles. This behavior is similar to what has been observed in pp and Pb-Pb collisions at the LHC. The measured $p_{\rm T}$ distributions are compared to results at lower energy and with predictions based on QCD-inspired and hydrodynamic models.
pT-differential invariant yield of charged pions in pPb collisions with centre-of-mass energy/nucleon=5.02 TeV.
pT-differential invariant yield of charged pions in pPb collisions with centre-of-mass energy/nucleon=5.02 TeV.
pT-differential invariant yield of charged pions in pPb collisions with centre-of-mass energy/nucleon=5.02 TeV.
We present the measurements of particle pair yields per trigger particle obtained from di-hadron azimuthal correlations in pp collisions at $\sqrt{s} = 0.9$, $2.76$, and $7$ TeV recorded with the ALICE detector. The yields are studied as a function of the charged particle multiplicity. Taken together with the single particle yields the pair yields provide information about parton fragmentation at low transverse momenta, as well as on the contribution of multiple parton interactions to particle production. Data are compared to calculations using the PYTHIA6, PYTHIA8, and PHOJET event generators.
Per-trigger near-side pair yield for pT(trig) > 0.7 GeV and pT(assoc) > 0.4 GeV measured at sqrt(s) = 7 TeV.
Per-trigger near-side pair yield for pT(trig) > 0.7 GeV and pT(assoc) > 0.7 GeV measured at sqrt(s) = 7 TeV.
Per-trigger away-side pair yield for pT(trig) > 0.7 GeV and pT(assoc) > 0.4 GeV measured at sqrt(s) = 7 TeV.
We present a search at Jefferson Laboratory for new forces mediated by sub-GeV vector bosons with weak coupling $\alpha'$ to electrons. Such a particle $A'$ can be produced in electron-nucleus fixed-target scattering and then decay to an $e^+e^-$ pair, producing a narrow resonance in the QED trident spectrum. Using APEX test run data, we searched in the mass range 175--250 MeV, found no evidence for an $A'\to e^+e^-$ reaction, and set an upper limit of $\alpha'/\alpha \simeq 10^{-6}$. Our findings demonstrate that fixed-target searches can explore a new, wide, and important range of masses and couplings for sub-GeV forces.
The binned invariant mass spectrum of e+e- pair events in the final event sample collected by APEX. The data correspond to Figure 3 of the paper, with the 0.05 MeV binning used for the profile likelihood analysis. The original plain-text file from <a href="https://doi.org/10.7484/inspirehep.data.lk95.m2gq">10.7484/inspirehep.data.lk95.m2gq</a> is accessible by clicking "Resources".
The unbinned invariant mass spectrum of e+e- pair events in the final event sample collected by APEX. The original data from <a href="https://doi.org/10.7484/inspirehep.data.ph21.l5rg">10.7484/inspirehep.data.ph21.l5rg</a> are accessible by clicking "Resources".
Many extensions of the Standard Model posit the existence of heavy particles with long lifetimes. In this Letter, results are presented of a search for such particles, which decay at a significant distance from their production point, using a final state containing charged hadrons and an associated muon. This analysis uses a data sample of proton-proton collisions at sqrt(s)= 7 TeV corresponding to an integrated luminosity of 4.4 fb-1 collected in 2011 by the ATLAS detector operating at the Large Hadron Collider. Results are interpreted in the context of R-parity violating supersymmetric scenarios. No events in the signal region are observed and limits are set on the production cross section for supersymmetric particles, multiplied by the square of the branching ratio for a neutralino to decay to charged hadrons and a muon, as a function of the neutralino lifetime. To allow these limits to be used in a variety of models, they are presented for a range of squark and neutralino masses.
Efficiency-vs-radial-vertex-position without re-tracking The efficiency for reconstructing a displaced vertex passing all cuts, as a function of radial distance from the z-axis to the vertex positon. The retrack and noretrack suffixes refer to whether or not the procedure known as re-tracking, where the tracking algorithm is re-run with looser cuts, on the leftover hits from standard tracking, was used to select the tracks that were input to the vertexing algorithm.
Efficiency-vs-radial-vertex-position with re-tracking The efficiency for reconstructing a displaced vertex passing all cuts, as a function of radial distance from the z-axis to the vertex positon. The retrack and noretrack suffixes refer to whether or not the procedure known as re-tracking, where the tracking algorithm is re-run with looser cuts, on the leftover hits from standard tracking, was used to select the tracks that were input to the vertexing algorithm.
Event selection efficiency vs mean proper decay length The MH, HH, ML suffix used for overlaying the graphs refers to the combinations of squark and neutralino masses in the signal MC sample: MH is 700GeV squarks and 494GeV neutralinos, HH is 1.5TeV squarks and 494GeV neutralinos, and ML is 700GeV squarks and 108GeV neutralinos. The tables show the efficiency for reconstructing a signal event, where at least one vertex candidate passes all selection requirements, as a function of the proper decay length c*tau of the neutralino.
Measurements of inclusive jet suppression in heavy ion collisions at the LHC provide direct sensitivity to the physics of jet quenching. In a sample of lead-lead collisions at $\sqrt{s_{NN}}$ = 2.76 TeV corresponding to an integrated luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with a calorimeter over the pseudorapidity interval |$\eta$| < 2.1 and over the transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the anti-$k_t$ algorithm with values for the distance parameter that determines the nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of the jet yield is characterized by the jet "central-to-peripheral ratio," $R_{cp}$. Jet production is found to be suppressed by approximately a factor of two in the 10% most central collisions relative to peripheral collisions. $R_{cp}$ varies smoothly with centrality as characterized by the number of participating nucleons. The observed suppression is only weakly dependent on jet radius and transverse momentum. These results provide the first direct measurement of inclusive jet suppression in heavy ion collisions and complement previous measurements of dijet transverse energy imbalance at the LHC.
Glauber model calculation of the mean numbers of Npart and its associated errors, the mean Ncoll ratios, and Rcoll with fractional errors as a function of the centrality bins.
The Rcp values as a function of jet PT for the four R values, 0.2, 0.3, 0.4 and 0.5 for the collision centrality in the range 0 - 10 %.
The Rcp values as a function of jet PT for the four R values, 0.2, 0.3, 0.4 and 0.5 for the collision centrality in the range 10 - 20 %.
This paper presents a search for the t-channel exchange of an R-parity violating scalar top quark (\={t}) in the emu continuum using 2.1/fb of data collected by the ATLAS detector in sqrt(s) = 7 TeV pp collisions at the Large Hadron Collider. Data are found to be consistent with the expectation from the Standard Model backgrounds. Limits on R-parity-violating couplings at 95% C.L. are calculated as a function of the scalar top mass (m_{\={t}}). The upper limits on the production cross section for pp->emuX, through the t-channel exchange of a scalar top quark, ranges from 170 fb for m_{\={t}}=95 GeV to 30 fb for m_{\={t}}=1000 GeV.
The observed E-MU invariant mass distribution plus SM background and signal predicitons for a n stop mass of 95 GeV.
Information about the signal samples used.
The ratios of the observed and expected upper cross section limits to the theoretical cross sections as a function of the scalar top mass.
Results are presented of a search for new particles decaying to large numbers of jets in association with missing transverse momentum, using 4.7 fb^-1 of pp collision data at sqrt(s) = 7 TeV collected by the ATLAS experiment at the Large Hadron Collider in 2011. The event selection requires missing transverse momentum, no isolated electrons or muons, and from >=6 to >=9 jets. No evidence is found for physics beyond the Standard Model. The results are interpreted in the context of a MSUGRA/CMSSM supersymmetric model, where, for large universal scalar mass m_0, gluino masses smaller than 840 GeV are excluded at the 95% confidence level, extending previously published limits. Within a simplified model containing only a gluino octet and a neutralino, gluino masses smaller than 870 GeV are similarly excluded for neutralino masses below 100 GeV.
Distribution of the variable ETmiss/sqrt(HT) for events with >= 7 jets each having transverse momentum > 55 GeV. The table gives the number of observed data events, the expected standard model backgroud prediction and the signal expected from the SUSY signal process.
Distribution of the variable ETmiss/sqrt(HT) for events with >= 6 jets each having transverse momentum > 80 GeV. The table gives the number of observed data events, the expected standard model backgroud prediction and the signal expected from the SUSY signal process.
Distribution of the variable ETmiss/sqrt(HT) for events with >= 8 jets each having transverse momentum > 55 GeV. The table gives the number of observed data events, the expected standard model backgroud prediction and the signal expected from the SUSY signal process.
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