A measurement of the production cross section of top quark pairs (tt) in proton-proton collisions... more A measurement of the production cross section of top quark pairs (tt) in proton-proton collisions at a center-of-mass energy of 7 TeV recorded with the ATLAS detector at the Large Hadron Collider is reported. Candidate events are selected in the dilepton topology with large missing transverse energy and at least two jets. Using a data sample corresponding to an integrated luminosity of 35 pb −1 , a tt production cross section σ tt = 177 ± 20(stat.) ± 14(syst.) ± 7(lum.) pb is measured for an assumed top quark mass of m t = 172.5 GeV. A second measurement requiring at least one jet identified as coming from a b quark yields a comparable result, demonstrating that the dilepton final states are consistent with being accompanied by b-quark jets. These measurements are in good agreement with Standard Model predictions.
The ATLAS experiment has measured the production cross-section of events with two isolated photon... more The ATLAS experiment has measured the production cross-section of events with two isolated photons in the final state, in proton-proton collisions at √ s = 7 TeV. The full data set acquired in 2010 is used, corresponding to an integrated luminosity of 37 pb −1 . The background, consisting of hadronic jets and isolated electrons, is estimated with fully data-driven techniques and subtracted. The differential cross-sections, as functions of the di-photon mass (mγγ ), total transverse momentum (pT,γγ ) and azimuthal separation (∆φγγ ), are presented and compared to the predictions of nextto-leading-order QCD.
The deuteron elastic structure function A(Q 2 ) has been extracted in the range 0.7 ≤ Q 2 ≤ 6.0 (... more The deuteron elastic structure function A(Q 2 ) has been extracted in the range 0.7 ≤ Q 2 ≤ 6.0 (GeV/c) 2 from cross section measurements of elastic electron-deuteron scattering in coincidence using the Hall A Facility of Jefferson Laboratory. The data are compared to theoretical models based on the impulse approximation with the inclusion of meson-exchange currents, and to predictions of quark dimensional scaling and perturbative quantum chromodynamics.
Proton-proton collisions at √ s = 7 TeV and heavy ion collisions at √ s NN = 2.76 TeV were produc... more Proton-proton collisions at √ s = 7 TeV and heavy ion collisions at √ s NN = 2.76 TeV were produced by the LHC and recorded using the ATLAS experiment's trigger system in 2010. The LHC is designed with a maximum bunch crossing rate of 40 MHz and the ATLAS trigger system is designed to record approximately 200 of these per second. The trigger system selects events by rapidly identifying signatures of muon, electron, photon, tau lepton, jet, and B meson candidates, as well as using global event signatures, such as missing transverse energy. An overview of the ATLAS trigger system, the evolution of the system during 2010 and the performance of the trigger system components and selections based on the 2010 collision data are shown. A brief outline of plans for the trigger system in 2011 is presented.
We present data on the inclusive scattering of polarized electrons from a polarized 3 He target a... more We present data on the inclusive scattering of polarized electrons from a polarized 3 He target at energies from 0.862 to 5.06 GeV, obtained at a scattering angle of 15:5 . Our data include measurements from the quasielastic peak, through the nucleon resonance region, and beyond, and were used to determine the virtual photon cross-section difference 1=2 ÿ 3=2 . We extract the extended Gerasimov-Drell-Hearn integral for the neutron in the range of four-momentum transfer squared Q 2 of 0:1-0:9 GeV 2 .
project is to define the incidence and prevalence of cancer and high grade dysplasia (HGD) in pts... more project is to define the incidence and prevalence of cancer and high grade dysplasia (HGD) in pts with BE METHODS: Data (in different formats) from each of the participating centers were merged and generated into the main study database using Microsoft Access. Preliminary data from each center included pt age, gender, ethnicity, endoscopy dates with dysplasia grades & BE length. A standardized definition of BE (columnar lined distal esophagus of any length with intestinal metaplasia) was used as the inclusion criteria. Pts with at least 12 mos of follow up were included in the long-term follow up group. Cancers and HGD occurring within 12 rags of the index endoscopy were regarded as prevalent cases. RESULTS: 1376 pts met the study criteria with at least one endoscopy/biopsy revealing BE; 91 pts had cancer at the initial exam -prevalence 6.7%. Of these, 618 pts (95% Caucasians, 14% Females) have been followed for a total of 2546 pt years; mean lollow up 4.12 yrs (range: 1-22.5 yrs). 12 pts developed cancer during follow up, a cancer incidence of 1 in 212 pt yrs of follow up or 0.5% per yr. The mean time to development of cancer was 5.3 yrs (range: 2.4-11.2 yrs). 7 of 12 pts had HGD before cancer development, 2 had LGD only whereas 3 developed cancer from BE without dysplasia at any point. 22 pts developed HGD during follow up; HGD incidence of 1 in 116 pt yrs of follow up (0.9% per yr). The mean time to HGD development was 3.8 yrs (range: 1.2-7.9 yrs). 11 of 22 pts developed HGD from LGD, remaining 11 from BE without dysplasia. The combined incidence of HGD and/or cancer was 1 in 75 pt yrs of follow up or 1.3% per yr. CONCLUSIONS: Preliminary results from the BESTtrial define the incidence of HGD and cancer in a large cohort of pts with BE. These data can be an important resource for future research as well as for defining the risk factors for progression to HGD and cancer. (Funded by ADHF/ASGE)
Measurements of the electron and muon inclusive cross-sections in proton-proton collisions at √ s... more Measurements of the electron and muon inclusive cross-sections in proton-proton collisions at √ s = 7 TeV with the ATLAS detector
The generalized forward spin polarizabilities $\gamma_0$ and $\delta_{LT}$ of the neutron have be... more The generalized forward spin polarizabilities $\gamma_0$ and $\delta_{LT}$ of the neutron have been extracted for the first time in a $Q^2$ range from 0.1 to 0.9 GeV$^2$. Since $\gamma_0$ is sensitive to nucleon resonances and $\delta_{LT}$ is insensitive to the $\Delta$ resonance, it is expected that the pair of forward spin polarizabilities should provide benchmark tests of the current understanding of the chiral dynamics of QCD. The new results on $\delta_{LT}$ show significant disagreement with Chiral Perturbation Theory calculations, while the data for $\gamma_0$ at low $Q^2$ are in good agreement with a next-to-lead order Relativistic Baryon Chiral Perturbation theory calculation. The data show good agreement with the phenomenological MAID model.
Backward exclusive electroproduction of π 0 mesons on protons has been measured at Q 2 = 1.0 GeV ... more Backward exclusive electroproduction of π 0 mesons on protons has been measured at Q 2 = 1.0 GeV 2 by detecting protons in the forward direction in coincidence with scattered electrons from the 4 GeV electron beam in Jefferson Lab's Hall A. The data span the range of the total (γ * p) center-of-mass energy W from the pion production threshold to W = 2.0 GeV. The azimuthally separated differential cross sections σT + ǫ σL, σTL, and σTT from this experiment are presented together with the MAID2000 [10] and SAID parametrizations.
The deuteron elastic structure function A(Q^2) has been extracted in the Q^2 range 0.7 to 6.0 (Ge... more The deuteron elastic structure function A(Q^2) has been extracted in the Q^2 range 0.7 to 6.0 (GeV/c)^2 from cross section measurements of elastic electron-deuteron scattering in coincidence using the Hall A Facility of Jefferson Laboratory. The data are compared to theoretical models based on the impulse approximation with inclusion of meson-exchange currents, and to predictions of quark dimensional scaling and perturbative quantum chromodynamics
Abstract In this paper, a measurement of τ polarization in W → τ ν decays is presented. It is mea... more Abstract In this paper, a measurement of τ polarization in W → τ ν decays is presented. It is measured from the energies of the decay products in hadronic τ decays with a single final state charged particle. The data, corresponding to an integrated luminosity of 24 pb −1 , were collected by the AT-LAS experiment at the Large Hadron Collider in 2010. The measured value of the τ polarization is P τ = −1.06 ± 0.04 (stat) +0.05 −0.07 (syst), in agreement with the Standard Model prediction, and is consistent with a physically allowed 95% CL interval [−1, −0.91]. Measurements of τ polarization have not previously been made at hadron colliders.
We present studies of W and Z bosons with associated high energy photons produced in pp collision... more We present studies of W and Z bosons with associated high energy photons produced in pp collisions at √ s = 7 TeV. The analysis uses 35 pb −1 of data collected by the ATLAS experiment in 2010. The event selection requires W and Z bosons decaying into high p T leptons (electrons or muons) and a photon with E T > 15 GeV separated from the lepton(s) by a distance ∆R(l, γ) > 0.7 in η-φ space. A total of 95 (97) pp → e ± νγ + X (pp → µ ± νγ + X) and 25 (23) pp → e + e − γ + X (pp → µ + µ − γ + X) event candidates are selected. The kinematic distributions of the leptons and photons and the production cross sections are measured. The data are found to agree with Standard Model predictions that include next-to-leading-order O(αα s ) contributions.
Clouds exert an important influence on tropospheric photochemistry through modification of solar ... more Clouds exert an important influence on tropospheric photochemistry through modification of solar radiation that determines photolysis frequencies (J-values). We assess the radiative effect of clouds on photolysis frequencies and key oxidants in the troposphere with a global three-dimensional (3-D) chemical transport model (GEOS-CHEM) driven by assimilated meteorological observations from the Goddard Earth Observing System data assimilation system (GEOS DAS) at the NASA Global Modeling and Assimilation Office (GMAO). We focus on the year of 2001 with the GEOS-3 meteorological observations. Photolysis frequencies are calculated using the Fast-J radiative transfer algorithm. The GEOS-3 global cloud optical depth and cloud fraction are evaluated and generally consistent with the satellite retrieval products from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the International Satellite Cloud Climatology Project (ISCCP). Results using the linear assumption, which assumes linear scaling of cloud optical depth with cloud fraction in a grid box, show global mean OH concentrations generally increase by less than 6% because of the radiative effect of clouds. The OH distribution shows much larger changes (with maximum decrease of ˜20% near the surface), reflecting the opposite effects of enhanced (weakened) photochemistry above (below) clouds. The global mean photolysis frequencies for J[O1D] and J[NO2] in the troposphere change by less than 5% because of clouds; global mean O3 concentrations in the troposphere increase by less than 5%. This study shows tropical upper tropospheric O3 to be less sensitive to the radiative effect of clouds than previously reported (˜5% versus ˜20-30%). These results emphasize that the dominant effect of clouds is to influence the vertical redistribution of the intensity of photochemical activity while global average effects remain modest, again contrasting with previous studies. Differing vertical distributions of clouds may explain part, but not the majority, of these discrepancies between models. Using an approximate random overlap or a maximum-random overlap scheme to take account of the effect of cloud overlap in the vertical reduces the impact of clouds on photochemistry but does not significantly change our results with respect to the modest global average effect.
A search for production of supersymmetric particles in final states containing jets, missing tran... more A search for production of supersymmetric particles in final states containing jets, missing transverse momentum, and at least one hadronically decaying τ lepton is presented. The data were recorded by the ATLAS experiment in √ s = 7 TeV proton-proton collisions at the Large Hadron Collider. No excess above the Standard Model background expectation was observed in 2.05 fb −1 of data. The results are interpreted in the context of gauge mediated supersymmetry breaking models with M mess = 250 TeV, N 5 = 3, µ > 0, and C grav = 1. The production of supersymmetric particles is excluded at 95% C.L. up to a supersymmetry breaking scale Λ = 30 TeV, independent of tan β, and up to Λ = 43 TeV for large tan β.
1] Clouds exert an important influence on tropospheric photochemistry through modification of sol... more 1] Clouds exert an important influence on tropospheric photochemistry through modification of solar radiation that determines photolysis frequencies (J-values). We assess the radiative effect of clouds on photolysis frequencies and key oxidants in the troposphere with a global three-dimensional (3-D) chemical transport model (GEOS-CHEM) driven by assimilated meteorological observations from the Goddard Earth Observing System data assimilation system (GEOS DAS) at the NASA Global Modeling and Assimilation Office (GMAO). We focus on the year of 2001 with the GEOS-3 meteorological observations. Photolysis frequencies are calculated using the Fast-J radiative transfer algorithm. The GEOS-3 global cloud optical depth and cloud fraction are evaluated and generally consistent with the satellite retrieval products from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the International Satellite Cloud Climatology Project (ISCCP). Results using the linear assumption, which assumes linear scaling of cloud optical depth with cloud fraction in a grid box, show global mean OH concentrations generally increase by less than 6% because of the radiative effect of clouds. The OH distribution shows much larger changes (with maximum decrease of $20% near the surface), reflecting the opposite effects of enhanced (weakened) photochemistry above (below) clouds. The global mean photolysis frequencies for J[O 1 D] and J[NO 2 ] in the troposphere change by less than 5% because of clouds; global mean O 3 concentrations in the troposphere increase by less than 5%. This study shows tropical upper tropospheric O 3 to be less sensitive to the radiative effect of clouds than previously reported ($5% versus $20-30%). These results emphasize that the dominant effect of clouds is to influence the vertical redistribution of the intensity of photochemical activity while global average effects remain modest, again contrasting with previous studies. Differing vertical distributions of clouds may explain part, but not the majority, of these discrepancies between models. Using an approximate random overlap or a maximum-random overlap scheme to take account of the effect of cloud overlap in the vertical reduces the impact of clouds on photochemistry but does not significantly change our results with respect to the modest global average effect. Citation: Liu, H., et al. (2006), Radiative effect of clouds on tropospheric chemistry in a global three-dimensional chemical transport model,
A measurement of the production cross section of top quark pairs (tt) in proton-proton collisions... more A measurement of the production cross section of top quark pairs (tt) in proton-proton collisions at a center-of-mass energy of 7 TeV recorded with the ATLAS detector at the Large Hadron Collider is reported. Candidate events are selected in the dilepton topology with large missing transverse energy and at least two jets. Using a data sample corresponding to an integrated luminosity of 35 pb −1 , a tt production cross section σ tt = 177 ± 20(stat.) ± 14(syst.) ± 7(lum.) pb is measured for an assumed top quark mass of m t = 172.5 GeV. A second measurement requiring at least one jet identified as coming from a b quark yields a comparable result, demonstrating that the dilepton final states are consistent with being accompanied by b-quark jets. These measurements are in good agreement with Standard Model predictions.
The ATLAS experiment has measured the production cross-section of events with two isolated photon... more The ATLAS experiment has measured the production cross-section of events with two isolated photons in the final state, in proton-proton collisions at √ s = 7 TeV. The full data set acquired in 2010 is used, corresponding to an integrated luminosity of 37 pb −1 . The background, consisting of hadronic jets and isolated electrons, is estimated with fully data-driven techniques and subtracted. The differential cross-sections, as functions of the di-photon mass (mγγ ), total transverse momentum (pT,γγ ) and azimuthal separation (∆φγγ ), are presented and compared to the predictions of nextto-leading-order QCD.
The deuteron elastic structure function A(Q 2 ) has been extracted in the range 0.7 ≤ Q 2 ≤ 6.0 (... more The deuteron elastic structure function A(Q 2 ) has been extracted in the range 0.7 ≤ Q 2 ≤ 6.0 (GeV/c) 2 from cross section measurements of elastic electron-deuteron scattering in coincidence using the Hall A Facility of Jefferson Laboratory. The data are compared to theoretical models based on the impulse approximation with the inclusion of meson-exchange currents, and to predictions of quark dimensional scaling and perturbative quantum chromodynamics.
Proton-proton collisions at √ s = 7 TeV and heavy ion collisions at √ s NN = 2.76 TeV were produc... more Proton-proton collisions at √ s = 7 TeV and heavy ion collisions at √ s NN = 2.76 TeV were produced by the LHC and recorded using the ATLAS experiment's trigger system in 2010. The LHC is designed with a maximum bunch crossing rate of 40 MHz and the ATLAS trigger system is designed to record approximately 200 of these per second. The trigger system selects events by rapidly identifying signatures of muon, electron, photon, tau lepton, jet, and B meson candidates, as well as using global event signatures, such as missing transverse energy. An overview of the ATLAS trigger system, the evolution of the system during 2010 and the performance of the trigger system components and selections based on the 2010 collision data are shown. A brief outline of plans for the trigger system in 2011 is presented.
We present data on the inclusive scattering of polarized electrons from a polarized 3 He target a... more We present data on the inclusive scattering of polarized electrons from a polarized 3 He target at energies from 0.862 to 5.06 GeV, obtained at a scattering angle of 15:5 . Our data include measurements from the quasielastic peak, through the nucleon resonance region, and beyond, and were used to determine the virtual photon cross-section difference 1=2 ÿ 3=2 . We extract the extended Gerasimov-Drell-Hearn integral for the neutron in the range of four-momentum transfer squared Q 2 of 0:1-0:9 GeV 2 .
project is to define the incidence and prevalence of cancer and high grade dysplasia (HGD) in pts... more project is to define the incidence and prevalence of cancer and high grade dysplasia (HGD) in pts with BE METHODS: Data (in different formats) from each of the participating centers were merged and generated into the main study database using Microsoft Access. Preliminary data from each center included pt age, gender, ethnicity, endoscopy dates with dysplasia grades & BE length. A standardized definition of BE (columnar lined distal esophagus of any length with intestinal metaplasia) was used as the inclusion criteria. Pts with at least 12 mos of follow up were included in the long-term follow up group. Cancers and HGD occurring within 12 rags of the index endoscopy were regarded as prevalent cases. RESULTS: 1376 pts met the study criteria with at least one endoscopy/biopsy revealing BE; 91 pts had cancer at the initial exam -prevalence 6.7%. Of these, 618 pts (95% Caucasians, 14% Females) have been followed for a total of 2546 pt years; mean lollow up 4.12 yrs (range: 1-22.5 yrs). 12 pts developed cancer during follow up, a cancer incidence of 1 in 212 pt yrs of follow up or 0.5% per yr. The mean time to development of cancer was 5.3 yrs (range: 2.4-11.2 yrs). 7 of 12 pts had HGD before cancer development, 2 had LGD only whereas 3 developed cancer from BE without dysplasia at any point. 22 pts developed HGD during follow up; HGD incidence of 1 in 116 pt yrs of follow up (0.9% per yr). The mean time to HGD development was 3.8 yrs (range: 1.2-7.9 yrs). 11 of 22 pts developed HGD from LGD, remaining 11 from BE without dysplasia. The combined incidence of HGD and/or cancer was 1 in 75 pt yrs of follow up or 1.3% per yr. CONCLUSIONS: Preliminary results from the BESTtrial define the incidence of HGD and cancer in a large cohort of pts with BE. These data can be an important resource for future research as well as for defining the risk factors for progression to HGD and cancer. (Funded by ADHF/ASGE)
Measurements of the electron and muon inclusive cross-sections in proton-proton collisions at √ s... more Measurements of the electron and muon inclusive cross-sections in proton-proton collisions at √ s = 7 TeV with the ATLAS detector
The generalized forward spin polarizabilities $\gamma_0$ and $\delta_{LT}$ of the neutron have be... more The generalized forward spin polarizabilities $\gamma_0$ and $\delta_{LT}$ of the neutron have been extracted for the first time in a $Q^2$ range from 0.1 to 0.9 GeV$^2$. Since $\gamma_0$ is sensitive to nucleon resonances and $\delta_{LT}$ is insensitive to the $\Delta$ resonance, it is expected that the pair of forward spin polarizabilities should provide benchmark tests of the current understanding of the chiral dynamics of QCD. The new results on $\delta_{LT}$ show significant disagreement with Chiral Perturbation Theory calculations, while the data for $\gamma_0$ at low $Q^2$ are in good agreement with a next-to-lead order Relativistic Baryon Chiral Perturbation theory calculation. The data show good agreement with the phenomenological MAID model.
Backward exclusive electroproduction of π 0 mesons on protons has been measured at Q 2 = 1.0 GeV ... more Backward exclusive electroproduction of π 0 mesons on protons has been measured at Q 2 = 1.0 GeV 2 by detecting protons in the forward direction in coincidence with scattered electrons from the 4 GeV electron beam in Jefferson Lab's Hall A. The data span the range of the total (γ * p) center-of-mass energy W from the pion production threshold to W = 2.0 GeV. The azimuthally separated differential cross sections σT + ǫ σL, σTL, and σTT from this experiment are presented together with the MAID2000 [10] and SAID parametrizations.
The deuteron elastic structure function A(Q^2) has been extracted in the Q^2 range 0.7 to 6.0 (Ge... more The deuteron elastic structure function A(Q^2) has been extracted in the Q^2 range 0.7 to 6.0 (GeV/c)^2 from cross section measurements of elastic electron-deuteron scattering in coincidence using the Hall A Facility of Jefferson Laboratory. The data are compared to theoretical models based on the impulse approximation with inclusion of meson-exchange currents, and to predictions of quark dimensional scaling and perturbative quantum chromodynamics
Abstract In this paper, a measurement of τ polarization in W → τ ν decays is presented. It is mea... more Abstract In this paper, a measurement of τ polarization in W → τ ν decays is presented. It is measured from the energies of the decay products in hadronic τ decays with a single final state charged particle. The data, corresponding to an integrated luminosity of 24 pb −1 , were collected by the AT-LAS experiment at the Large Hadron Collider in 2010. The measured value of the τ polarization is P τ = −1.06 ± 0.04 (stat) +0.05 −0.07 (syst), in agreement with the Standard Model prediction, and is consistent with a physically allowed 95% CL interval [−1, −0.91]. Measurements of τ polarization have not previously been made at hadron colliders.
We present studies of W and Z bosons with associated high energy photons produced in pp collision... more We present studies of W and Z bosons with associated high energy photons produced in pp collisions at √ s = 7 TeV. The analysis uses 35 pb −1 of data collected by the ATLAS experiment in 2010. The event selection requires W and Z bosons decaying into high p T leptons (electrons or muons) and a photon with E T > 15 GeV separated from the lepton(s) by a distance ∆R(l, γ) > 0.7 in η-φ space. A total of 95 (97) pp → e ± νγ + X (pp → µ ± νγ + X) and 25 (23) pp → e + e − γ + X (pp → µ + µ − γ + X) event candidates are selected. The kinematic distributions of the leptons and photons and the production cross sections are measured. The data are found to agree with Standard Model predictions that include next-to-leading-order O(αα s ) contributions.
Clouds exert an important influence on tropospheric photochemistry through modification of solar ... more Clouds exert an important influence on tropospheric photochemistry through modification of solar radiation that determines photolysis frequencies (J-values). We assess the radiative effect of clouds on photolysis frequencies and key oxidants in the troposphere with a global three-dimensional (3-D) chemical transport model (GEOS-CHEM) driven by assimilated meteorological observations from the Goddard Earth Observing System data assimilation system (GEOS DAS) at the NASA Global Modeling and Assimilation Office (GMAO). We focus on the year of 2001 with the GEOS-3 meteorological observations. Photolysis frequencies are calculated using the Fast-J radiative transfer algorithm. The GEOS-3 global cloud optical depth and cloud fraction are evaluated and generally consistent with the satellite retrieval products from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the International Satellite Cloud Climatology Project (ISCCP). Results using the linear assumption, which assumes linear scaling of cloud optical depth with cloud fraction in a grid box, show global mean OH concentrations generally increase by less than 6% because of the radiative effect of clouds. The OH distribution shows much larger changes (with maximum decrease of ˜20% near the surface), reflecting the opposite effects of enhanced (weakened) photochemistry above (below) clouds. The global mean photolysis frequencies for J[O1D] and J[NO2] in the troposphere change by less than 5% because of clouds; global mean O3 concentrations in the troposphere increase by less than 5%. This study shows tropical upper tropospheric O3 to be less sensitive to the radiative effect of clouds than previously reported (˜5% versus ˜20-30%). These results emphasize that the dominant effect of clouds is to influence the vertical redistribution of the intensity of photochemical activity while global average effects remain modest, again contrasting with previous studies. Differing vertical distributions of clouds may explain part, but not the majority, of these discrepancies between models. Using an approximate random overlap or a maximum-random overlap scheme to take account of the effect of cloud overlap in the vertical reduces the impact of clouds on photochemistry but does not significantly change our results with respect to the modest global average effect.
A search for production of supersymmetric particles in final states containing jets, missing tran... more A search for production of supersymmetric particles in final states containing jets, missing transverse momentum, and at least one hadronically decaying τ lepton is presented. The data were recorded by the ATLAS experiment in √ s = 7 TeV proton-proton collisions at the Large Hadron Collider. No excess above the Standard Model background expectation was observed in 2.05 fb −1 of data. The results are interpreted in the context of gauge mediated supersymmetry breaking models with M mess = 250 TeV, N 5 = 3, µ > 0, and C grav = 1. The production of supersymmetric particles is excluded at 95% C.L. up to a supersymmetry breaking scale Λ = 30 TeV, independent of tan β, and up to Λ = 43 TeV for large tan β.
1] Clouds exert an important influence on tropospheric photochemistry through modification of sol... more 1] Clouds exert an important influence on tropospheric photochemistry through modification of solar radiation that determines photolysis frequencies (J-values). We assess the radiative effect of clouds on photolysis frequencies and key oxidants in the troposphere with a global three-dimensional (3-D) chemical transport model (GEOS-CHEM) driven by assimilated meteorological observations from the Goddard Earth Observing System data assimilation system (GEOS DAS) at the NASA Global Modeling and Assimilation Office (GMAO). We focus on the year of 2001 with the GEOS-3 meteorological observations. Photolysis frequencies are calculated using the Fast-J radiative transfer algorithm. The GEOS-3 global cloud optical depth and cloud fraction are evaluated and generally consistent with the satellite retrieval products from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the International Satellite Cloud Climatology Project (ISCCP). Results using the linear assumption, which assumes linear scaling of cloud optical depth with cloud fraction in a grid box, show global mean OH concentrations generally increase by less than 6% because of the radiative effect of clouds. The OH distribution shows much larger changes (with maximum decrease of $20% near the surface), reflecting the opposite effects of enhanced (weakened) photochemistry above (below) clouds. The global mean photolysis frequencies for J[O 1 D] and J[NO 2 ] in the troposphere change by less than 5% because of clouds; global mean O 3 concentrations in the troposphere increase by less than 5%. This study shows tropical upper tropospheric O 3 to be less sensitive to the radiative effect of clouds than previously reported ($5% versus $20-30%). These results emphasize that the dominant effect of clouds is to influence the vertical redistribution of the intensity of photochemical activity while global average effects remain modest, again contrasting with previous studies. Differing vertical distributions of clouds may explain part, but not the majority, of these discrepancies between models. Using an approximate random overlap or a maximum-random overlap scheme to take account of the effect of cloud overlap in the vertical reduces the impact of clouds on photochemistry but does not significantly change our results with respect to the modest global average effect. Citation: Liu, H., et al. (2006), Radiative effect of clouds on tropospheric chemistry in a global three-dimensional chemical transport model,
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Papers by Edward Gao Gao