Determination of α S using OPAL hadronic event shapes at √ s = 91 − 209 GeV and resummed NNLO cal... more Determination of α S using OPAL hadronic event shapes at √ s = 91 − 209 GeV and resummed NNLO calculations
A selection of di-lepton events with significant missing transverse momentum has been performed u... more A selection of di-lepton events with significant missing transverse momentum has been performed using a total data sample of 237.4 pb −1 at e + e − centre-of-mass energies of 183 GeV and 189 GeV. The observed numbers of events -78 at 183 GeV and 301 at 189 GeV -are consistent with the numbers expected from Standard Model processes, which arise predominantly from W + W − production with each W decaying leptonically. This topology is also an experimental signature for the pair production of new particles that decay to a charged lepton accompanied by one or more invisible particles. Discrimination techniques are described that optimise the sensitivity to particular new physics channels. No evidence for new phenomena is apparent and model independent limits are presented on the production cross-section times branching ratio squared for sleptons and for leptonically decaying charginos and charged Higgs. Assuming a 100% branching ratio for the decaỹ ± R → ±χ0 1 , whereχ 0 1 is the lightest neutralino, we exclude at 95% CL: right-handed smuons with masses below 82.3 GeV for mμ − − mχ0 1 > 3 GeV and right-handed staus with masses below 81.0 GeV for mτ − − mχ0 1 > 8 GeV. Right-handed selectrons are excluded at 95% CL for masses below 87.1 GeV for mẽ − − mχ0 1 > 5 GeV, within the framework of the Minimal Supersymmetric Standard Model assuming µ < −100 GeV and tan β = 1.5. Charged Higgs bosons, H ± , are excluded at 95% CL for masses below 82.8 GeV, assuming a 100% branching ratio for the decay H ± → τ ± ν τ .
Searches for final states expected in models with light gravitinos have been performed, including... more Searches for final states expected in models with light gravitinos have been performed, including experimental topologies with multi-leptons with missing energy, leptons and photons with missing energy, and jets and photons with missing energy. No excess over the expectations from the Standard Model has been observed. Limits are placed on production cross-sections in the different experimental topologies. Additionally, combining with searches for the anomalous production of lepton and photon pairs with missing energy, results are interpreted in the context of minimal models of gauge mediated SUSY breaking. Exclusion limits at the 95% confidence level on the supersymmetric particle masses of ml > 83 GeV and mχ0 1 > 85 GeV for tan β = 2, and mτ > 69 GeV, mẽ ,μ > 88 GeV and mχ0 1 > 76 GeV for tan β = 20, are established.
Inclusive jet production (e + e − → e + e − +jet+X) is studied in collisions of quasi-real photon... more Inclusive jet production (e + e − → e + e − +jet+X) is studied in collisions of quasi-real photons radiated by the LEP beams at e + e − centre-of-mass energies √ s ee from 189 to 209 GeV. Jets are reconstructed using the k ⊥ jet algorithm. The inclusive differential cross-section is measured as a function of the jet transverse momentum, p jet T , in the range 5 < p jet T < 40 GeV for pseudo-rapidities, η jet , in the range -1.5 < η jet < 1.5. The results are compared to predictions of perturbative QCD in next-to-leading order in the strong coupling constant.
Physical Review D - Particles, Fields, Gravitation and Cosmology, 2012
A search is performed for heavy particle pairs produced in √ s = 7 TeV proton-proton collisions w... more A search is performed for heavy particle pairs produced in √ s = 7 TeV proton-proton collisions with 35 pb −1 of data collected by the CMS experiment at the LHC. The search is sensitive to squarks and gluinos of generic supersymmetry models, provided they are kinematically accessible, with minimal assumptions on properties of the lightest superpartner particle. The kinematic consistency of the selected events is tested against the hypothesis of heavy particle pair production using the dimensionless razor variable R, related to the missing transverse energy E miss T . The new physics signal is characterized by a broad peak in the distribution of M R , an event-by-event indicator of the heavy particle mass scale. This new approach is complementary to E miss T -based searches. After background modeling based on data, and background rejection based on R and M R , no significant excess of events is found beyond the standard model expectations. The results are interpreted in the context of the constrained minimal supersymmetric standard model as well as two simplified supersymmetry models.
We present the measurement of R = B(t → W b)/B(t → W q) in pp collisions at √ s = 1.96 TeV, using... more We present the measurement of R = B(t → W b)/B(t → W q) in pp collisions at √ s = 1.96 TeV, using 230 pb −1 of data collected by the DØ experiment at the Fermilab Tevatron Collider. We fit simultaneously R and the number (N tt ) of selected top quark pairs (tt), to the number of identified b-quark jets in events with one electron or one muon, three or more jets, and high transverse energy imbalance. To improve sensitivity, kinematical properties of events with no identified b-quark jets are included in the fit. We measure R = 1.03 +0.19 −0.17 (stat + syst), in good agreement with the standard model. We set lower limits of R > 0.61 and |V tb | > 0.78 at 95% confidence level.
Dg ih qp sr tp vu xw y vg h tf Du i g g r t f Dg g w Dr u xw g g ir Uu xw w h g ed gf h ji lk nm ... more Dg ih qp sr tp vu xw y vg h tf Du i g g r t f Dg g w Dr u xw g g ir Uu xw w h g ed gf h ji lk nm eo p tq rk ni sm eo jt up ti v wp Dx ym h ji qp {z |i sq ¾ s¿ À ÁÀ s Pà "à $À ÅÄ µAE QÇ ÉÈ Â ËÊ ÍÌ ÏÎ ÑÐ ÓÒ µÀ VÔ ÉÇ ÖÕ ×Ð ØÕ ÑÌ 9Ê aÙ 9Ú QÐ «Ò "Ì ÏÎ ØÕ ÁÛ Ü sÝ À ÅÞ Ù Ïß Áß À ÁÕ «Õ ÑÙ àÐ 1á Qâ â ã Fä Óå å 9ae ae ae Ñç Øè Ïé 7ê 7ë Fç Øè Áá å 7ì 7í î í ï ï ð %
Abstract A measurement of the lepton charge asymmetry in inclusive pp→ WX production at√ s= 7 TeV... more Abstract A measurement of the lepton charge asymmetry in inclusive pp→ WX production at√ s= 7 TeV is presented based on data recorded by the CMS detector at the LHC and corresponding to an integrated luminosity of 36 pb− 1. This high precision measurement of the lepton charge asymmetry, performed in both the W→ eν and W→ µν channels, provides new insights into parton distribution functions.
In October and November 2008, the CMS collaboration conducted a programme of cosmic ray data taki... more In October and November 2008, the CMS collaboration conducted a programme of cosmic ray data taking, which has recorded about 270 million events. The Resistive Plate Chamber system, which is part of the CMS muon detection system, was successfully operated in the full barrel. More than 98 % of the channels were operational during the exercise with typical detection efficiency of 90 %. In this paper, the performance of the detector during these dedicated runs is reported. 2 2 RPC system layout RB2 out for the second one). The third and fourth DT layers are complemented with a single RPC layer, placed on their inner side (RB3 and RB4). A detailed description of the muon system geometry can be found in Ref.
Studies of the performance of the CMS drift tube barrel muon system are described, with results b... more Studies of the performance of the CMS drift tube barrel muon system are described, with results based on data collected during the CMS Cosmic Run at Four Tesla. For most of these data, the solenoidal magnet was operated with a central field of 3.8 T. The analysis of data from 246 out of a total of 250 chambers indicates a very good muon reconstruction capability, with a coordinate resolution for a single hit of about 260 µm, and a nearly 100% efficiency for the drift tube cells. The resolution of the track direction measured in the bending plane is about 1.8 mrad, and the efficiency to reconstruct a segment in a single chamber is higher than 99%. The CMS simulation of cosmic rays reproduces well the performance of the barrel muon detector.
Please be patient while the object screen loads. Changez de vue : Choisir un site… UCL FUNDP FUSL... more Please be patient while the object screen loads. Changez de vue : Choisir un site… UCL FUNDP FUSL FUCaM. ...
The operation and general performance of the CMS electromagnetic calorimeter using cosmic-ray muo... more The operation and general performance of the CMS electromagnetic calorimeter using cosmic-ray muons are described. These muons were recorded after the closure of the CMS detector in late 2008. The calorimeter is made of lead tungstate crystals and the overall status of the 75 848 channels corresponding to the barrel and endcap detectors is reported. The stability of crucial operational parameters, such as high voltage, temperature and electronic noise, is summarised and the performance of the light monitoring system is presented.
The CMS Collaboration conducted a month-long data-taking exercise known as the Cosmic Run At Four... more The CMS Collaboration conducted a month-long data-taking exercise known as the Cosmic Run At Four Tesla in late 2008 in order to complete the commissioning of the experiment for extended operation. The operational lessons resulting from this exercise were addressed in the subsequent shutdown to better prepare CMS for LHC beams in 2009. The cosmic data collected have been invaluable to study the performance of the detectors, to commission the alignment and calibration techniques, and to make several cosmic ray measurements. The experimental setup, conditions, and principal achievements from this data-taking exercise are described along with a review of the preceding integration activities.
The pixel detector of the Compact Muon Solenoid experiment consists of three barrel layers and tw... more The pixel detector of the Compact Muon Solenoid experiment consists of three barrel layers and two disks for each endcap. The detector was installed in summer 2008, commissioned with charge injections, and operated in the 3.8 T magnetic field during cosmic ray data taking. This paper reports on the first running experience and presents results on the pixel tracker performance, which are found to be in line with the design specifications of this detector. The transverse impact parameter resolution measured in a sample of high momentum muons is 18 microns.
Di-jet producion is studied in collisions of quasi-real photons at e+e- centre- of-mass energies ... more Di-jet producion is studied in collisions of quasi-real photons at e+e- centre- of-mass energies sqrt(s)ee from 189 to 209 GeV at LEP. The data were collected with the OPAL detector. Jets are reconstructed using an inclusive k_t clustering algorithm for all cross-section measurements presented. A cone jet algorithm is used in addition to study the different structure of the jets
The effects of the final state interaction phenomenon known as colour reconnection are investigat... more The effects of the final state interaction phenomenon known as colour reconnection are investigated at centre-of-mass energies in the range $\sqrt{s}~ 189-209 GeV using the OPAL detector at LEP. Colour reconnection is expected to affect observables based on charged particles in hadronic decays of W+W-. Measurements of inclusive charged particle multiplicities, and of their angular distribution with respect to the
A measurement of the lepton charge asymmetry in inclusive pp → WX production at is presented base... more A measurement of the lepton charge asymmetry in inclusive pp → WX production at is presented based on data recorded by the CMS detector at the LHC and corresponding to an integrated luminosity of 36 pb−1. This high precision measurement of the lepton charge asymmetry, performed in both the W → eν and W → μν channels, provides new insights
A study of Z boson pair production in e+e- annihilation at center-of-mass energies near 183 GeV a... more A study of Z boson pair production in e+e- annihilation at center-of-mass energies near 183 GeV and 189 GeV is reported. Final states containing only leptons, (l+l-l+l- and l+l-nu nubar), quark and lepton pairs, (q qbar l+l-, q qbar nu nubar) and the all-hadronic final state (q qbar q qbar) are considered. In all states with at least one Z boson decaying hadronically, q qbar and b bbar final states are considered separately using lifetime and event-shape tags, thereby improving the cross-section measurement. At sqrt(s) = 189 GeV the Z-pair cross section was measured to be 0.80 (+0.14-0.13, stat.) (+0.06-0.05, syst.) pb, consistent with the Standard Model prediction. At sqrt(s) = 183 GeV the 95.L. upper limit is 0.55 pb. Limits on anomalous ZZgamma and ZZZ couplings are derived.
Determination of α S using OPAL hadronic event shapes at √ s = 91 − 209 GeV and resummed NNLO cal... more Determination of α S using OPAL hadronic event shapes at √ s = 91 − 209 GeV and resummed NNLO calculations
A selection of di-lepton events with significant missing transverse momentum has been performed u... more A selection of di-lepton events with significant missing transverse momentum has been performed using a total data sample of 237.4 pb −1 at e + e − centre-of-mass energies of 183 GeV and 189 GeV. The observed numbers of events -78 at 183 GeV and 301 at 189 GeV -are consistent with the numbers expected from Standard Model processes, which arise predominantly from W + W − production with each W decaying leptonically. This topology is also an experimental signature for the pair production of new particles that decay to a charged lepton accompanied by one or more invisible particles. Discrimination techniques are described that optimise the sensitivity to particular new physics channels. No evidence for new phenomena is apparent and model independent limits are presented on the production cross-section times branching ratio squared for sleptons and for leptonically decaying charginos and charged Higgs. Assuming a 100% branching ratio for the decaỹ ± R → ±χ0 1 , whereχ 0 1 is the lightest neutralino, we exclude at 95% CL: right-handed smuons with masses below 82.3 GeV for mμ − − mχ0 1 > 3 GeV and right-handed staus with masses below 81.0 GeV for mτ − − mχ0 1 > 8 GeV. Right-handed selectrons are excluded at 95% CL for masses below 87.1 GeV for mẽ − − mχ0 1 > 5 GeV, within the framework of the Minimal Supersymmetric Standard Model assuming µ < −100 GeV and tan β = 1.5. Charged Higgs bosons, H ± , are excluded at 95% CL for masses below 82.8 GeV, assuming a 100% branching ratio for the decay H ± → τ ± ν τ .
Searches for final states expected in models with light gravitinos have been performed, including... more Searches for final states expected in models with light gravitinos have been performed, including experimental topologies with multi-leptons with missing energy, leptons and photons with missing energy, and jets and photons with missing energy. No excess over the expectations from the Standard Model has been observed. Limits are placed on production cross-sections in the different experimental topologies. Additionally, combining with searches for the anomalous production of lepton and photon pairs with missing energy, results are interpreted in the context of minimal models of gauge mediated SUSY breaking. Exclusion limits at the 95% confidence level on the supersymmetric particle masses of ml > 83 GeV and mχ0 1 > 85 GeV for tan β = 2, and mτ > 69 GeV, mẽ ,μ > 88 GeV and mχ0 1 > 76 GeV for tan β = 20, are established.
Inclusive jet production (e + e − → e + e − +jet+X) is studied in collisions of quasi-real photon... more Inclusive jet production (e + e − → e + e − +jet+X) is studied in collisions of quasi-real photons radiated by the LEP beams at e + e − centre-of-mass energies √ s ee from 189 to 209 GeV. Jets are reconstructed using the k ⊥ jet algorithm. The inclusive differential cross-section is measured as a function of the jet transverse momentum, p jet T , in the range 5 < p jet T < 40 GeV for pseudo-rapidities, η jet , in the range -1.5 < η jet < 1.5. The results are compared to predictions of perturbative QCD in next-to-leading order in the strong coupling constant.
Physical Review D - Particles, Fields, Gravitation and Cosmology, 2012
A search is performed for heavy particle pairs produced in √ s = 7 TeV proton-proton collisions w... more A search is performed for heavy particle pairs produced in √ s = 7 TeV proton-proton collisions with 35 pb −1 of data collected by the CMS experiment at the LHC. The search is sensitive to squarks and gluinos of generic supersymmetry models, provided they are kinematically accessible, with minimal assumptions on properties of the lightest superpartner particle. The kinematic consistency of the selected events is tested against the hypothesis of heavy particle pair production using the dimensionless razor variable R, related to the missing transverse energy E miss T . The new physics signal is characterized by a broad peak in the distribution of M R , an event-by-event indicator of the heavy particle mass scale. This new approach is complementary to E miss T -based searches. After background modeling based on data, and background rejection based on R and M R , no significant excess of events is found beyond the standard model expectations. The results are interpreted in the context of the constrained minimal supersymmetric standard model as well as two simplified supersymmetry models.
We present the measurement of R = B(t → W b)/B(t → W q) in pp collisions at √ s = 1.96 TeV, using... more We present the measurement of R = B(t → W b)/B(t → W q) in pp collisions at √ s = 1.96 TeV, using 230 pb −1 of data collected by the DØ experiment at the Fermilab Tevatron Collider. We fit simultaneously R and the number (N tt ) of selected top quark pairs (tt), to the number of identified b-quark jets in events with one electron or one muon, three or more jets, and high transverse energy imbalance. To improve sensitivity, kinematical properties of events with no identified b-quark jets are included in the fit. We measure R = 1.03 +0.19 −0.17 (stat + syst), in good agreement with the standard model. We set lower limits of R > 0.61 and |V tb | > 0.78 at 95% confidence level.
Dg ih qp sr tp vu xw y vg h tf Du i g g r t f Dg g w Dr u xw g g ir Uu xw w h g ed gf h ji lk nm ... more Dg ih qp sr tp vu xw y vg h tf Du i g g r t f Dg g w Dr u xw g g ir Uu xw w h g ed gf h ji lk nm eo p tq rk ni sm eo jt up ti v wp Dx ym h ji qp {z |i sq ¾ s¿ À ÁÀ s Pà "à $À ÅÄ µAE QÇ ÉÈ Â ËÊ ÍÌ ÏÎ ÑÐ ÓÒ µÀ VÔ ÉÇ ÖÕ ×Ð ØÕ ÑÌ 9Ê aÙ 9Ú QÐ «Ò "Ì ÏÎ ØÕ ÁÛ Ü sÝ À ÅÞ Ù Ïß Áß À ÁÕ «Õ ÑÙ àÐ 1á Qâ â ã Fä Óå å 9ae ae ae Ñç Øè Ïé 7ê 7ë Fç Øè Áá å 7ì 7í î í ï ï ð %
Abstract A measurement of the lepton charge asymmetry in inclusive pp→ WX production at√ s= 7 TeV... more Abstract A measurement of the lepton charge asymmetry in inclusive pp→ WX production at√ s= 7 TeV is presented based on data recorded by the CMS detector at the LHC and corresponding to an integrated luminosity of 36 pb− 1. This high precision measurement of the lepton charge asymmetry, performed in both the W→ eν and W→ µν channels, provides new insights into parton distribution functions.
In October and November 2008, the CMS collaboration conducted a programme of cosmic ray data taki... more In October and November 2008, the CMS collaboration conducted a programme of cosmic ray data taking, which has recorded about 270 million events. The Resistive Plate Chamber system, which is part of the CMS muon detection system, was successfully operated in the full barrel. More than 98 % of the channels were operational during the exercise with typical detection efficiency of 90 %. In this paper, the performance of the detector during these dedicated runs is reported. 2 2 RPC system layout RB2 out for the second one). The third and fourth DT layers are complemented with a single RPC layer, placed on their inner side (RB3 and RB4). A detailed description of the muon system geometry can be found in Ref.
Studies of the performance of the CMS drift tube barrel muon system are described, with results b... more Studies of the performance of the CMS drift tube barrel muon system are described, with results based on data collected during the CMS Cosmic Run at Four Tesla. For most of these data, the solenoidal magnet was operated with a central field of 3.8 T. The analysis of data from 246 out of a total of 250 chambers indicates a very good muon reconstruction capability, with a coordinate resolution for a single hit of about 260 µm, and a nearly 100% efficiency for the drift tube cells. The resolution of the track direction measured in the bending plane is about 1.8 mrad, and the efficiency to reconstruct a segment in a single chamber is higher than 99%. The CMS simulation of cosmic rays reproduces well the performance of the barrel muon detector.
Please be patient while the object screen loads. Changez de vue : Choisir un site… UCL FUNDP FUSL... more Please be patient while the object screen loads. Changez de vue : Choisir un site… UCL FUNDP FUSL FUCaM. ...
The operation and general performance of the CMS electromagnetic calorimeter using cosmic-ray muo... more The operation and general performance of the CMS electromagnetic calorimeter using cosmic-ray muons are described. These muons were recorded after the closure of the CMS detector in late 2008. The calorimeter is made of lead tungstate crystals and the overall status of the 75 848 channels corresponding to the barrel and endcap detectors is reported. The stability of crucial operational parameters, such as high voltage, temperature and electronic noise, is summarised and the performance of the light monitoring system is presented.
The CMS Collaboration conducted a month-long data-taking exercise known as the Cosmic Run At Four... more The CMS Collaboration conducted a month-long data-taking exercise known as the Cosmic Run At Four Tesla in late 2008 in order to complete the commissioning of the experiment for extended operation. The operational lessons resulting from this exercise were addressed in the subsequent shutdown to better prepare CMS for LHC beams in 2009. The cosmic data collected have been invaluable to study the performance of the detectors, to commission the alignment and calibration techniques, and to make several cosmic ray measurements. The experimental setup, conditions, and principal achievements from this data-taking exercise are described along with a review of the preceding integration activities.
The pixel detector of the Compact Muon Solenoid experiment consists of three barrel layers and tw... more The pixel detector of the Compact Muon Solenoid experiment consists of three barrel layers and two disks for each endcap. The detector was installed in summer 2008, commissioned with charge injections, and operated in the 3.8 T magnetic field during cosmic ray data taking. This paper reports on the first running experience and presents results on the pixel tracker performance, which are found to be in line with the design specifications of this detector. The transverse impact parameter resolution measured in a sample of high momentum muons is 18 microns.
Di-jet producion is studied in collisions of quasi-real photons at e+e- centre- of-mass energies ... more Di-jet producion is studied in collisions of quasi-real photons at e+e- centre- of-mass energies sqrt(s)ee from 189 to 209 GeV at LEP. The data were collected with the OPAL detector. Jets are reconstructed using an inclusive k_t clustering algorithm for all cross-section measurements presented. A cone jet algorithm is used in addition to study the different structure of the jets
The effects of the final state interaction phenomenon known as colour reconnection are investigat... more The effects of the final state interaction phenomenon known as colour reconnection are investigated at centre-of-mass energies in the range $\sqrt{s}~ 189-209 GeV using the OPAL detector at LEP. Colour reconnection is expected to affect observables based on charged particles in hadronic decays of W+W-. Measurements of inclusive charged particle multiplicities, and of their angular distribution with respect to the
A measurement of the lepton charge asymmetry in inclusive pp → WX production at is presented base... more A measurement of the lepton charge asymmetry in inclusive pp → WX production at is presented based on data recorded by the CMS detector at the LHC and corresponding to an integrated luminosity of 36 pb−1. This high precision measurement of the lepton charge asymmetry, performed in both the W → eν and W → μν channels, provides new insights
A study of Z boson pair production in e+e- annihilation at center-of-mass energies near 183 GeV a... more A study of Z boson pair production in e+e- annihilation at center-of-mass energies near 183 GeV and 189 GeV is reported. Final states containing only leptons, (l+l-l+l- and l+l-nu nubar), quark and lepton pairs, (q qbar l+l-, q qbar nu nubar) and the all-hadronic final state (q qbar q qbar) are considered. In all states with at least one Z boson decaying hadronically, q qbar and b bbar final states are considered separately using lifetime and event-shape tags, thereby improving the cross-section measurement. At sqrt(s) = 189 GeV the Z-pair cross section was measured to be 0.80 (+0.14-0.13, stat.) (+0.06-0.05, syst.) pb, consistent with the Standard Model prediction. At sqrt(s) = 183 GeV the 95.L. upper limit is 0.55 pb. Limits on anomalous ZZgamma and ZZZ couplings are derived.
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Papers by O. Boeriu