Measurement of the Z-boson mass using $e^+e- \to Z\gamma$ event at centre-of-mass energies above the Z pole
Events from the e+e- -> Zgamma process with hard initial state radiation collected with the L3... more Events from the e+e- -> Zgamma process with hard initial state radiation collected with the L3 detector at centre-of-mass energies between 183 GeV and 209 GeV are used to measure the mass of the Z boson. Decays of the Z boson into hadrons or muon pairs are considered and the Z mass is determined to be 91.272 +- 0.032 (stat.) +- 0.033 (syst.) GeV, in agreement with the value measured at the Z resonance. Alternatively, assuming this measured value of the Z mass, the method determines the LEP beam energy, found to be 87 +- 34 (stat.) \pm 34 (syst.) MeV lower than the nominal value.
Measurement of $B\overline{B}$ Angular Correlations based on Secondary Vertex Reconstruction at $\sqrt{s}$ = 7 TeV in CMS
Journal of High Energy Physics
A measurement of the angular correlations between beauty and anti-beauty hadrons (B B-bar) produc... more A measurement of the angular correlations between beauty and anti-beauty hadrons (B B-bar) produced in pp collisions at a centre-of-mass energy of 7 TeV at the CERN LHC is presented, probing for the first time the region of small angular separation. The B hadrons are identified by the presence of displaced secondary vertices from their decays. The B hadron angular separation is reconstructed from the decay vertices and the primary-interaction vertex. The differential B B-bar production cross section, measured from a data sample collected by CMS and corresponding to an integrated luminosity of 3.1 inverse picobarns, shows that a sizable fraction of the B B-bar pairs are produced with small opening angles. These studies provide a test of QCD and further insight into the dynamics of b b-bar production.
Search for the standard model Higgs boson in the H textrightarrow ZZ textrightarrow l +l -? +? - decay channel in pp collisions at ?s = 7 TeV
Journal of High Energy Physics
ABSTRACT n/a
Search for a Higgs boson in the decay channel H textrightarrow ZZ* textrightarrow qql-l-+ in pp collisions at p?s = 7TeV
A search for exclusive decays of B 0 d and B 0 s mesons has been performed in the channels B 0 d ... more A search for exclusive decays of B 0 d and B 0 s mesons has been performed in the channels B 0 d ! J; B 0 s !J; B 0 d !J 0 and B 0 s ! J 0 . The data sample consisted of more than three and half million hadronic Z decays collected by the L3 experiment at LEP from 1991 through 1995. No candidate events have been observed for any of the modes thus determining upper limits at 90% condence level: 3:2 10 4 on Br(B 0 d ! J 0 ) and the rst experimental limits: Br(B 0 d ! J) < 1:2 10 3 ; Br(B 0 s ! J) < 3:8 10 3 ; Br(B 0 s ! J 0 ) < 1:2 10 3 :
New measurements at a centre-of-mass energy √ s 183 GeV of the hadronic photon structure function... more New measurements at a centre-of-mass energy √ s 183 GeV of the hadronic photon structure function F γ 2 (x) in the Q 2 interval, 9 GeV 2 ≤ Q 2 ≤ 30 GeV 2 , are presented. The data, collected in 1997 with the L3 detector, correspond to an integrated luminosity of 51.9 pb -1 . Combining with the data taken at a centreof-mass energy of 91 GeV, the evolution of F γ 2 with Q 2 is measured in the Q 2 range from 1.2 GeV 2 to 30 GeV 2 . F γ 2 shows a linear growth with ln Q 2 ; the value of the slope α -1 dF γ 2 (Q 2 )/d ln Q 2 is measured in two x bins from 0.01 to 0.2 and is somewhat higher than predicted.
The e + e -→ e + e -K 0 S K ± π ∓ and e + e -→ e + e -η π + π -final states are studied with the ... more The e + e -→ e + e -K 0 S K ± π ∓ and e + e -→ e + e -η π + π -final states are studied with the L3 detector at LEP using data collected at centre-of-mass energies from 183 GeV up to 202 GeV. The mass spectrum of the K 0 S K ± π ∓ final state shows an enhancement around 1470 MeV, which is identified with the pseudoscalar meson η (1440). This state is observed in γγ collisions for the first time and its two-photon width is measured to be Γ γγ η (1440) × BR η (1440) → K Kπ = 212 ± 50 (stat.) ± 23 (sys.) eV. Clear evidence is also obtained for the formation of the axial vector mesons f 1 (1420) and f 1 (1285). In the η π + π -channel the f 1 (1285) is observed, and upper limits for the formation of η (1440) and η (1295) are obtained.
Events from the e+e- -> Zgamma process with hard initial state radiation collected with the L3... more Events from the e+e- -> Zgamma process with hard initial state radiation collected with the L3 detector at centre-of-mass energies between 183 GeV and 209 GeV are used to measure the mass of the Z boson. Decays of the Z boson into hadrons or muon pairs are considered and the Z mass is determined to be 91.272 +- 0.032 (stat.)
The L3 detector at LEP has been used to determine the number of light neutrino families by measur... more The L3 detector at LEP has been used to determine the number of light neutrino families by measuring the cross section of single photon even in e+e -collisions at energies near the Z ° resonance. We have observed 61 single photon candidates with more than 1.5 GeV of deposited energy in the barrel electromagnetic calorimeter, for a total integrated luminosity of 3.0 pb-1. From a likelihood fit to the single photon cross sections, we determine Nv = 3.24 ± 0.46 (statistical) _+ 0.22 (systematic).
We present a study of the inclusive ! and 0 production based on 3.1 million hadronic Z decays rec... more We present a study of the inclusive ! and 0 production based on 3.1 million hadronic Z decays recorded with the L3 detector at LEP during 1991{1994. The production rates per hadronic Z decay have been measured to be 1:17 0:17 ! mesons and 0:25 0:04 0 mesons. The production rates and the dierential cross sections have been compared with predictions of the JETSET and the HERWIG Monte Carlo models. We have observed that the dierential cross sections can be described by an analytical quantum chromodynamics calculation.
Recent theories propose that quantum gravity effects may be observable at LEP energies via gravit... more Recent theories propose that quantum gravity effects may be observable at LEP energies via gravitons that couple to Standard Model particles and propagate into extra spatial dimensions. The associated production of a graviton and a photon is searched for as well as the effects of virtual graviton exchange in the processes: e + e -→ γγ, ZZ, W + W -, µ + µ -, τ + τ -, qq and e + e -. No evidence for this new interaction is found in the data sample collected by the L3 detector at LEP at centre-of-mass energies up to 183 GeV. Limits close to 1 TeV on the scale of this new scenario of quantum gravity are set.
We describe the sample of energetic single-photon events (Ey > 15 GeV) collected by L3 in the 199... more We describe the sample of energetic single-photon events (Ey > 15 GeV) collected by L3 in the 1991-1993 LEP runs. The event distributions agree with expectations from the Standard Model. The data are used to constrain the 77.y coupling and to set an upper limit of 4.1 x 10(90% C.L.) on the the magnetic moment of the r neutrino.
The hadronic photon structure function F 2 is studied in the reaction e + e ! e + e hadrons at LE... more The hadronic photon structure function F 2 is studied in the reaction e + e ! e + e hadrons at LEP with the L3 detector. The data, collected from 1991 to 1995 at a centre-of-mass energy p s ' 91 GeV, correspond to an integrated luminosity of 140 pb 1 . The photon structure function F 2 is measured in the Q 2 interval 1:2 G e V 2 Q 2 9 : 0 G e V 2 and the x interval 0:002 < x < 0 : 2. F 2 shows a linear growth with ln Q 2 . The value of the slope 1 dF 2 (Q 2
The reactions e + e -→ e + e -π 0 X and e + e -→ e + e -K 0 S X are studied using data collected ... more The reactions e + e -→ e + e -π 0 X and e + e -→ e + e -K 0 S X are studied using data collected at LEP with the L3 detector at centre-of-mass energies between 189 and 202 GeV. Inclusive differential cross sections are measured as a function of the particle transverse momentum p t and the pseudo-rapidity. For p t 1.5 GeV, the π 0 and K 0 S differential cross sections are described by an exponential, typical of soft hadronic processes. For p t 1.5 GeV, the cross sections show the presence of perturbative QCD processes, described by a power-law. The data are compared to Monte Carlo predictions and to NLO QCD calculations.
A first measurement of the cross section of the process e + e -→ Zγγ is reported using a total in... more A first measurement of the cross section of the process e + e -→ Zγγ is reported using a total integrated luminosity of 231 pb -1 collected with the L3 detector at centre-of-mass energies of 182.7 GeV and 188.7 GeV. By selecting hadronic events with two isolated photons the e + e -→ Zγγ cross section is measured to be 0.49 +0.20 -0.17 ± 0.04 pb at 182.7 GeV and 0.47 ± 0.10 ± 0.04 pb at 188.7 GeV. The measurements are consistent with Standard Model expectations. Limits on Quartic Gauge Boson Couplings a 0 /Λ 2 and a c /Λ 2 of -0.009 GeV -2 < a 0 /Λ 2 < 0.008 GeV -2 and -0.007 GeV -2 < a c /Λ 2 < 0.013 GeV -2 are derived at 95% confidence level.
Using the data recorded with the L3 detector at LEP, w e study the process e + e ! + () for event... more Using the data recorded with the L3 detector at LEP, w e study the process e + e ! + () for events with hard initial-state photon radiation. The eective centre-of-mass energies of the muons range from 50 GeV t o 8 6 G e V. The data sample corresponds to an integrated luminosity of 103.5 pb 1 and yields 293 muonpair events with a hard photon along the beam direction. The events are used to determine the cross sections and the forward-backward charge asymmetries at centre-of-mass energies below the Z resonance.
In clu siv e L a m b d a P r o d u c tio n in T w o -P h o to n C ollisions a t L E P The L3 Coll... more In clu siv e L a m b d a P r o d u c tio n in T w o -P h o to n C ollisions a t L E P The L3 Collaboration The reactions e+e_ -► e+e" AX and e+e_ -► e+e" AX are studied using data collected at LEP with the L3 detector at centre-of-mass energies between 189 and 209 GeV. Inclusive differential cross sections are measured as a function of the lambda transverse momentum, pt , and pseudo-rapidity, n, in the ranges 0.4 GeV < pt < 2.5 GeV and |n| < 1.2. The data are compared to Monte Carlo predictions. The differential cross section as a function of pt is well described by an exponential of the form A e x p (-p t/(p t)).
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Papers by Atul Gurtu