Measurements of the per-event charged-particle yield as a function of the charged-particle transverse momentum and rapidity are performed using $p+$Pb collision data collected by the ATLAS experiment at the LHC at a centre-of-mass energy of $\sqrt{s_{NN}}=5.02$ TeV. Charged particles are reconstructed over pseudorapidity $|\eta|<2.3$ and transverse momentum between $0.1$ GeV and $22$ GeV in a dataset corresponding to an integrated luminosity of $1$ $\mu b^{-1}$. The results are presented in the form of charged-particle nuclear modification factors, where the $p+$Pb charged-particle multiplicities are compared between central and peripheral $p+$Pb collisions as well as to charged-particle cross sections measured in pp collisions. The $p+$Pb collision centrality is characterized by the total transverse energy measured in $-4.9<\eta<-3.1$, which is in the direction of the outgoing lead beam. Three different estimations of the number of nucleons participating in the $p+$Pb collision are carried out using the Glauber model and two Glauber-Gribov colour-fluctuation extensions to the Glauber model. The values of the nuclear modification factors are found to vary significantly as a function of rapidity and transverse momentum. A broad peak is observed for all centralities and rapidities in the nuclear modification factors for charged-particle transverse momentum values around $3$ GeV. The magnitude of the peak increases for more central collisions as well as rapidity ranges closer to the direction of the outgoing lead nucleus.
Invariant differential $p_{T}$ spectra of charged particles which are produced in p+Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV shown in six $\eta$ intervals, for the 0--90% centrality interval. The individual spectra are scaled by constant factors (indicated in the legend) for visibility. The statistical uncertainties are indicated with vertical lines and the systematic uncertainties are indicated with boxes, but are generally much smaller than the size of the symbols.
Invariant differential $p_{T}$ spectra of charged particles which are produced in p+Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV shown in six y* intervals, for the 0--90% centrality interval. The individual spectra are scaled by constant factors (indicated in the legend) for visibility. The statistical uncertainties are indicated with vertical lines and the systematic uncertainties are indicated with boxes, but are generally much smaller than the size of the symbols.
The invariant differential y* spectra of charged particles produced in p+Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV are shown in five centrality intervals for $p_{T}>0.1$ GeV. The statistical uncertainties are indicated with vertical lines and the systematic uncertainties are indicated with boxes.
The ATLAS experiment has observed 1995 Z boson candidates in data corresponding to 0.15 inverse nb of integrated luminosity obtained in the 2011 LHC Pb+Pb run at sqrt(s_NN)=2.76 TeV. The Z bosons are reconstructed via di-electron and di-muon decay channels, with a background contamination of less than 3%. Results from the two channels are consistent and are combined. Within the statistical and systematic uncertainties, the per-event Z boson yield is proportional to the number of binary collisions estimated by the Glauber model. The elliptic anisotropy of the azimuthal distribution of the Z boson with respect to the event plane is found to be consistent with zero.
The corrected per-event rapidity distribution of Z bosons over the centrality region 0-80%.
The corrected per-event transverse momentum distribution of Z bosons in the centrality region 0-5%.
The corrected per-event transverse momentum distribution of Z bosons in the centrality region 5-10%.
The production of Kshort and Lambda hadrons is studied in inelastic pp collisions at sqrt(s) = 0.9 and 7 TeV collected with the ATLAS detector at the LHC using a minimum-bias trigger. The observed distributions of transverse momentum, rapidity, and multiplicity are corrected to hadron level in a model-independent way within well defined phase-space regions. The distribution of the production ratio of Lambdabar to Lambda baryons is also measured. The results are compared with various Monte Carlo simulation models. Although most of these models agree with data to within 15% in the Kshort distributions, substantial disagreements with data are found in the Lambda distributions of transverse momentum.
The corrected transverse momentum distribution of KS mesons at 7000 GeV.
The corrected rapidity distribution of KS mesons at 7000 GeV.
The corrected multiplicity distribution of KS mesons at 7000 GeV.
Dijet angular distributions from the first LHC pp collisions at center-of-mass energy sqrt(s) = 7 TeV have been measured with the ATLAS detector. The dataset used for this analysis represents an integrated luminosity of 3.1 pb-1. Dijet $\chi$ distributions and centrality ratios have been measured up to dijet masses of 2.8 TeV, and found to be in good agreement with Standard Model predictions. Analysis of the $\chi$ distributions excludes quark contact interactions with a compositeness scale $\Lambda$ below 3.4 TeV, at 95% confidence level, significantly exceeding previous limits.
CHI distribution for mass bin 340 to 520 GeV.
CHI distribution for mass bin 520 to 800 GeV.
CHI distribution for mass bin 800 to 1200 GeV.
Transverse mass spectra of protons emitted in Au+Au collisions at beam energies of 6, 8, and 10.8 GeV/nucleon have been measured as a function of collision centrality over a rapidity range 0.5
The inverse slope, mean transverse mass and rapidity density values for centrality 0 to 5 PCT for 6 GeV/nucleon collisions. Statistical errors only.
The inverse slope, mean transverse mass and rapidity density values for centrality 5 to 12 PCT for 6 GeV/nucleon collisions. Statistical errors only.
The inverse slope, mean transverse mass and rapidity density values for centrality 12 to 23 PCT for 6 GeV/nucleon collisions. Statistical errors only.
Mid-rapidity spectra and yields of K$^-$ and K$^+$ have been measured for Au+Au collisions at 4, 6, 8, and 10.7 AGeV. The K$^-$ yield increases faster with beam energy than for K$^+$ and hence the K$^-$/K$^+$ ratio increases with beam energy. This ratio is studied as a function of both $\sqrt{s}$ and $\sqrt{s}$-$\sqrt{s_{th}}$ which allows the direct comparison of the kaon yields with respect to the production threshold in p+p reactions. For equal $\sqrt{s}$ - $\sqrt{s_{th}}$ the measured ratio K$^-$/K$^+$=0.2 at energies above threshold in contrast to the K$^-$/K$^+$ ratio of near unity observed at energies below threshold. The use of the K$^-$/K$^+$ ratio to test the predicted changes of kaon properties in dense nuclear matter is discussed.
Only statistical errors are presented.
Only statistical errors are presented.
Only statistical errors are presented.
Positive pion and kaon production from Au+Au reactions have been measured as a function of beam energy over the range 2.0-10.7~AGeV. Both the kaon and the pion production cross-sections at mid-rapidity are observed to increase steadily with beam kinetic energy. The ratio of K$^+$ to $\pi^+$ mid-rapidity yields increases from 0.0271$\pm0.0015\pm0.0014$ at 2.0~AGeV to 0.202$\pm0.005\pm0.010$ at 10.7~AGeV and is larger than the K$^+$/$\pi^+$ ratio from p+p reactions over the same beam energy region. There is no indication of an onset of any new production mechanism in heavy-ion reactions in this energy range beyond rescattering of hadrons.
The centrality selection at each beam energy is the most central 5% of the total interaction cross-section (SIG(C=interaction) = 6.8b). A single exponential function in MT was fit simultaneously to the two kaonspectra at each beam energy D2(N)/D(MT)/D(YRAP)/2/PI/MT=D(N)/D(YRAP)/2/PI/T/(T+ M(KAON))/EXP((MT-M(KAON))/T). The fits reproduce the spectra well with two free parameters, the inverse slope parameter T and the rapidity density, D(N)/D(YRAP)in that rapidity slice. The mid-rapidity range for 2, 4, 6, 8 AGeV is ABS((YRAP-Ynn)/Ynn) < 0.25, for 10.7 AGeV the width is ABS((YRAP-Ynn)/Ynn) < 0.125, where Ynn is mid-rapidity in the laboratory frame. The errors are statistical only. The 1.96, 4. and 10.74 GeV are E866 data, another - E917 data.
The centrality selection at each beam energy is the most central 5% of the total interaction cross-section (SIG(C=interaction) = 6.8b). A single exponential function in MT was fit simultaneously to the two kaonspectra at each beam energy D2(N)/D(MT)/D(YRAP)/2/PI/MT=D(N)/D(YRAP)/2/PI/T/(T+ M(KAON))/EXP((MT-M(KAON))/T). The fits reproduce the spectra well with two free parameters, the inverse slope parameter T and the rapidity density, D(N)/D(YRAP)in that rapidity slice. The mid-rapidity range for 2, 4, 6, 8 AGeV is ABS((YRAP-Ynn)/Ynn) < 0.25, for 10.7 AGeV the width is ABS((YRAP-Ynn)/Ynn) < 0.125, where Ynn is mid-rapidity in the laboratory frame. The errors are statistical only. The 1.96, 4. and 10.74 GeV are E866 data, another - E917 data.
The centrality selection at each beam energy is the most central 5% of the total interaction cross-section (SIG(C=interaction) = 6.8b). The spectra were fit with a scaled exponential, D2(N)/D(YRAP)/D(MT)/2/PI/MT=D(N)/D(YRAP)/2/PI/(T**(2-L))/GAMMA(2-L,M(PION)/T)/MT**L/EXP(MT/T), where GAMMA(2-L,M(PION)/T), the complementary incomplete gamma function, is introduced in the normalization so that D(N)/D(YRAP) is a fitted parameter (and other free parameters are L and T). The mid-rapidity range for 2, 4 (E866 data), 6, 8 AGeV (E917 data) beam energy is ABS((YRAP-Ynn)/Ynn) < 0.25, for 10.7 AGeV (E917 data) the width is ABS((YRAP-Ynn)/Ynn) <0.125, where Ynn is mid-rapidity in the laboratory frame. The errors are statistical only.
Gluon jets are identified in hadronic Z0 decays as all the particles in a hemisphere opposite to a hemisphere containing two tagged quark jets. Gluon jets defined in this manner are equivalent to gluon jets produced from a color singlet point source and thus correspond to the definition employed for most theoretical calculations. In a separate stage of the analysis, we select quark jets in a manner to correspond to calculations, as the particles in hemispheres of flavor tagged light quark (uds) events. We present the distributions of rapidity, scaled energy, the logarithm of the momentum, and transverse momentum with respect to the jet axes, for charged particles in these gluon and quark jets. We also examine the charged particle multiplicity distributions of the jets in restricted intervals of rapidity. For soft particles at large transverse momentum, we observe the charged particle multiplicity ratio of gluon to quark jets to be 2.29 +- 0.09 +- 0.15 in agreement with the prediction that this ratio should approximately equal the ratio of QCD color factors, CA/CF = 2.25. The intervals used to define soft particles and large transverse momentum for this result, p<4 GeV/c and 0.8
(C=GLUON) and (C=QUARK) stand for jets originated from gluon and any light quark (Q=u, d, s), correspondingly. The ratio of gluon to quark jets are evaluated for 40.1 GeV jet energy.
(C=GLUON) and (C=QUARK) stand for jets originated from gluon and any light quark (Q=u, d, s), correspondingly. The ratio of gluon to quark jets are evaluated for 40.1 GeV jet energy.
(C=GLUON) and (C=QUARK) stand for jets originated from gluon and any light quark (Q=u, d, s), correspondingly. The ratio of gluon to quark jets are evaluated for 40.1 GeV jet energy.
D ∗± production via e + e − → D ∗± X was studied at CM energies near 34 GeV. The charged particles produced in the hemisphere opposite to that of the D ∗ were used to investigate the fragmentation of charm jets. All spectra studied show a close similarity between the charm jet and the average jet obtained by summing over all quark flavours. The spectra of particles produced in the D ∗ hemisphere were used to study separately first rank and higher rank fragmentation.
THE C-JET IS THE JET IN THE HEMISPHERE OPPOSITE TO THAT CONTAINING THE D* MESON. DIVISION IS MADE BY A PLANE PERPENDICULAR TO THE THRUST AXIS.
No description provided.