A. A. Abdelalim

Measurement of hard double-parton interactions in W(to lv) positive 2-jet events at square root of s equals to TeV with the ATLAS detector

The production of W bosons in association with two jets in proton-proton collisions at a centre-of-mass energy of root s = 7 TeV has been analysed for the presence of double-parton interactions using data corresponding to an integrated luminosity of 36 pb(-1), collected with the ATLAS detector at the Large Hadron Collider. The fraction of events arising from double-parton interactions, f(DP)((D)), has been measured through the p(T) balance between the two jets and amounts to f(DP)((D)) = 0.08 +/- 0.01 (stat.) +/- 0.02 (sys.) for jets with transverse momentum p(T) > 20 GeV and rapidity vertical bar y vertical bar < 2.8. This corresponds to a measurement of the effective area parameter for hard double-parton interactions of sigma(eff) = 15 +/- 3 (stat.)(-3)(+5) (sys.) mb.The production of W bosons in association with two jets in proton-proton collisions at a centre-of-mass energy of sqrt(s)=7 TeV has been analysed for the presence of double-parton interactions using data corresponding to an integrated luminosity of 36/pb, collected with the ATLAS detector at the LHC. The fraction of events arising from double-parton interactions, fDP(D) has been measured through the momentum balance between the two jets and amounts to fDP(D) = 0.08 +- 0.01 (stat.) +- 0.02 (sys) for jets with transverse momentum PT>20 GeV and rapidity |y|<2.8. This corresponds to a measurement of the effective area parameter for hard double-parton interactions of \sigma_eff = 15 +- 3 (stat.) +5 -3 (sys.) mb.

Measurements of the electron and muon inclusive cross-sections in proton-proton collisions at root s=7 TeV with the ATLAS detector

This Letter presents measurements of the differential cross-sections for inclusive electron and muon production in proton-proton collisions at a centre-of-mass energy of root s = 7 TeV, using data collected by the ATLAS detector at the LHC. The muon cross-section is measured as a function of p(T) in the range 4 < p(T) < 100 GeV and within pseudorapidity vertical bar eta vertical bar < 2.5. In addition the electron and muon cross-sections are measured in the range 7 < p(T) < 26 GeV and within vertical bar eta vertical bar < 2.0, excluding 1.37 < vertical bar eta vertical bar < 1.52. Integrated luminosities of 1.3 pb(-1) and 1.4 pb(-1) are used for the electron and muon measurements, respectively. After subtraction of the W/Z/gamma* contribution, the differential cross-sections are found to be in good agreement with theoretical predictions for heavy-flavour production obtained from Fixed Order NLO calculations with NLL high-p(T) resummation, and to be sensitive to the effects of NLL resummation

Measurement of the cross section for the production of a W boson in association with b-jets in pp collisions at root s=7 TeV with the ATLAS detector

A measurement is presented of the cross section for the produ cti n of aW boson with one or two jets, of which at least one must be a b-jet, in pp collisions at √ s = 7 TeV. Production via top decay is not included in the signal definition. The measurement is based on 35 pb −1of data collected with the ATLAS detector at the LHC. The W+b-jet cross section is defined for jets reconstructed with the anti -kt clustering algorithm with transverse momentum above 25 GeV and rapidity within±2.1. Theb-jets are identified by reconstructing secondary vertices. The fiducial cross section is measured both for the electron and muon decay chan nel of theW boson and is found to be 10.2 ± 1.9 (stat) ± 2.6 (syst) pb for one lepton flavour. The results are compared with next-to-leading order QCD calculations, which predict a cross section smaller than, though consistent wit h, the measured value.

Search for extra dimensions in diphoton events from proton-proton collisions at (square root)s (equivalent to) 7 TeV in the ATLAS detector at the LHC

The large difference between the Planck scale and the electroweak scale, known as the hierarchy problem, is addressed in certain models through the postulate of extra spatial dimensions. A search for evidence of extra spatial dimensions in the diphoton channel has been performed using the full set of proton-proton collisions at √ s = 7 TeV recorded in 2011 with the ATLAS detector at the CERN Large Hadron Collider. This dataset corresponds to an integrated luminosity of 4.9 fb−1. The diphoton invariant mass spectrum is observed to be in good agreement with the Standard Model expectation. In the context of the model proposed by Arkani-Hamed, Dimopoulos and Dvali, 95% confidence level lower limits of between 2.52 TeV and 3.92 TeV are set on the ultraviolet cutoff scale MS depending on the number of extra dimensions and the theoretical formalism used. In the context of the Randall– Sundrum model, a lower limit of 2.06 (1.00) TeV at 95 % confidence level is set on the mass of the lightest graviton for couplings of k/MP l = 0.1 (0.01). Combining with the ATLAS dilepton searches based on the 2011 data, the 95 % confidence level lower limit on the Randall–Sundrum graviton mass is further tightened to 2.23 (1.03) TeV for k/MP l = 0.1 (0.01). Search for Extra Dimensions in diphoton events from proton-proton collisions at √The large difference between the Planck scale and the electroweak scale, known as the hierarchy problem, is addressed in certain models through the postulate of extra spatial dimensions. A search for evidence of extra spatial dimensions in the diphoton channel has been performed using the full set of proton-proton collisions at root s = 7 TeV recorded in 2011 with the ATLAS detector at the CERN Large Hadron Collider. This dataset corresponds to an integrated luminosity of 4.9 fb(-1). The diphoton invariant mass spectrum is observed to be in good agreement with the Standard Model expectation. In the context of the model proposed by Arkani-Hamed, Dimopoulos and Dvali, 95% confidence level lower limits of between 2.52 and 3.92 TeV are set on the ultraviolet cutoff scale MS depending on the number of extra dimensions and the theoretical formalism used. In the context of the Randall-Sundrum model, a lower limit of 2.06 (1.00) TeV at 95% confidence level is set on the mass of the lightest graviton for couplings of k/(M) over bar (Pl) = 0.1(0.01). Combining with the ATLAS dilepton searches based on the 2011 data, the 95% confidence level lower limit on the Randall-Sundrum graviton mass is further tightened to 2.23 (1.03) TeV for k/(M) over bar (Pl) = 0.1(0.01).

Search for contact interactions and large extra dimensions in dilepton events from pp collisions at square root of s equals to 7 TeV with the ATLAS detector

A search for nonresonant new phenomena, originating from either contact interactions or large extra spatial dimensions, has been carried out using events with two isolated electrons or muons. These events, produced at the LHC in proton-proton collisions at √ s = 7 TeV, were recorded by the ATLAS detector. The data sample, collected throughout 2011, corresponds to an integrated luminosity of 4.9 and 5.0 fb−1 in the e+e− and μ+μ− channels, respectively. No significant deviations from the Standard Model expectation are observed. Using a Bayesian approach, 95% confidence level lower limits ranging from 9.0 to 13.9 TeV are placed on the energy scale of llqq contact interactions in the left-left isoscalar model. Lower limits ranging from 2.4 to 3.9 TeV are also set on the string scale in large extra dimension models. After combining these limits with results from a similar search in the diphoton channel, slightly more stringent limits are obtained. Search for contact interactions and large extra dimensions in dilepton events from pp

Search for dark matter in events with a Z boson and missing transverse momentum in pp collisions at root s=8 TeV with ATLAS detector

A search is presented for production of dark-matter particles recoiling against a leptonically decaying Z boson in 20.3 fb(-1) of pp collisions at root s = 8 TeV with the ATLAS detector at the Large Hadron Collider. Events with large missing transverse momentum and two oppositely charged electrons or muons consistent with the decay of a Z boson are analyzed. No excess above the Standard Model prediction is observed. Limits are set on the mass scale of the contact interaction as a function of the dark-matter particle mass using an effective field theory description of the interaction of dark matter with quarks or with Z bosons. Limits are also set on the coupling and mediator mass of a model in which the interaction is mediated by a scalar particle.A search is presented for production of dark matter particles recoiling against a leptonically decaying Z boson in 20.3 fb−1 of pp collisions at √ s = 8 TeV with the ATLAS detector at the Large Hadron Collider. Events with large missing transverse momentum and two oppositely-charged electrons or muons consistent with the decay of a Z boson are analyzed. No excess above the Standard Model prediction is observed. Limits are set on the mass scale of the contact interaction as a function of the dark matter particle mass using an effective field theory description of the interaction of dark matter with quarks or with Z bosons. Limits are also set on the coupling and mediator mass of a model in which the interaction is mediated by a scalar particle. c

Search for new phenomena in the WW???l??l???????? final state in pp collisions at s=7TeV with the ATLAS detector

This Letter reports a search for a heavy particle that decays to WW using events produced in pp collisions at √ s = 7 TeV. The data were recorded in 2011 by the ATLAS detector and correspond to an integrated luminosity of 4.7 fb−1. WW → lνlν ′ (l, l = e or μ) final states are considered and the distribution of the transverse mass of the WW candidates is found to be consistent with Standard Model expectations. Upper limits on the production cross section times branching ratio into W boson pairs are set for Randall-Sundrum and bulk Randall-Sundrum gravitons, which result in observed 95% CL lower limits on the masses of the two particles of 1.23 TeV and 0.84 TeV, respectively. Search for new phenomena in the WW → lνlν final state in pp collisions at √ s = 7 TeV with the ATLAS detector The ATLAS Collaboration (Dated: May 2, 2014) This Letter reports a search for a heavy particle that decays to WW using events produced in pp collisions at √ s = 7 TeV. The data were recorded in 2011 by the ATLAS detector and correspond to an integrated luminosity of 4.7 fb. WW → lνl′ν′ (l, l′ = e or μ) final states are considered and the distribution of the transverse mass of the WW candidates is found to be consistent with Standard Model expectations. Upper limits on the production cross section times branching ratio into W boson pairs are set for Randall-Sundrum and bulk Randall-Sundrum gravitons, which result in observed 95% CL lower limits on the masses of the two particles of 1.23 TeV and 0.84 TeV, respectively. PACS numbers: 14.70.Kv, 04.60.Kz, 12.60.Cn The existence of new phenomena can be probed by studying heavy gauge boson pair production. Heavy particles that can decay to gauge boson pairs are predicted in many scenarios of physics beyond the Standard Model (SM), including the Extended Gauge Model (EGM) [1], Extra Dimensions [2–6], and Technicolor models [7–9]. This paper describes a search for resonant WW production in the WW → lνlν (l, l = e or μ) decay channel using a data sample corresponding to an integrated luminosity of 4.7 fb, collected by the ATLAS detector during 2011 at a center-of-mass energy of 7 TeV. A spin2 Randall-Sundrum (RS) graviton model [2] and one of its extensions, the bulk RS graviton model [10], are used as benchmarks to interpret the analysis result. The original RS model (RS1) was proposed to solve the hierarchy problem. It postulates a warped 5-dimensional universe, where the SM particles are localized on the TeV brane and the graviton is located on the Planck brane. In this model gravitons can propagate in the extra dimension, leading to a Kaluza-Klein tower of states which can be detected as massive spin-2 resonances that couple to all SM particles. The resonance with the lowest mass is known as the RS graviton G. The model has two parameters: the graviton mass mG∗ , and the dimensionless coupling κ/M̃pl, where κ is the curvature of the warped fifth dimension and M̃pl = Mpl/ √ 8π is the reduced Planck mass. The RS1 model introduces higher-dimensional operators that give excessively large contributions to flavour changing neutral current (FCNC) processes and to observables related to SM electroweak precision tests. An extension of the RS1 model, the bulk RS model, has been proposed to address this issue. In this model, the SM fields are also allowed to propagate in the extra dimension: the first and second generation fermions are chosen to be localized near the Planck brane, while the top-quark and the Higgs boson are localized near the TeV brane to account for the large top-quark Yukawa coupling. In this scenario, FCNCs and contributions to electroweak observables from higher-dimensional operators are suppressed, the graviton (here denoted by G∗bulk) production and decay via light fermion channels is highly suppressed, the probability for the graviton to decay into photons is negligible, and the coupling to heavy particles, such as top-quark, W , Z and Higgs bosons is strongly enhanced. In this model the branching ratio of G∗bulk →WW is about 15%. Direct searches for a heavy WW resonance have been performed by the CDF and D0 collaborations at the Tevatron. The D0 collaboration explored diboson resonant production using the lνlν and lνjj final states [11]; these searches excluded an RS graviton with a mass between 300 GeV and 754 GeV, assuming κ/M̃pl = 0.1. The CDF collaboration also searched for resonant WW production in the eνjj final state, resulting in a lower limit of 607 GeV on the mass of an RS graviton [12], assuming the same coupling strength κ/M̃pl = 0.1. No previous work on searches for G ∗ bulk has been published. The ATLAS detector [13] is a multi-purpose particle physics detector with forward-backward symmetric cylindrical geometry [14]. The inner tracking detector (ID) covers the region |η| < 2.5, and consists of a silicon pixel detector, a silicon microstrip detector, and a straw tube tracker with transition radiation detection capability. The ID is surrounded by a thin superconducting solenoid providing a 2 T axial magnetic field. A highgranularity lead/liquid-argon (LAr) sampling calorimeter measures the energy and the position of electromagnetic showers with |η| < 3.2. LAr sampling calorimeters are also used to measure hadronic showers in the endcap (1.5 < |η| < 3.2) and forward (3.1 < |η| < 4.9) regions, while an iron/scintillator tile calorimeter measures hadronic showers in the central region (|η| < 1.7). The muon spectrometer (MS) surrounds the calorimeters and consists of three large superconducting air-core toroids, each with eight coils, a system of precision tracking chambers (|η| < 2.7), and fast tracking chambers for triggering. A three-level trigger system selects events to be recorded for offline analysis.

Search for new phenomena in the WW -> vertical bar v vertical bar ' v ' final state in pp collisions at root s=7 TeV with the ATLAS detector

This Letter reports a search for a heavy particle that decays to WW using events produced in pp collisions at √ s = 7 TeV. The data were recorded in 2011 by the ATLAS detector and correspond to an integrated luminosity of 4.7 fb−1. WW → lνlν ′ (l, l = e or μ) final states are considered and the distribution of the transverse mass of the WW candidates is found to be consistent with Standard Model expectations. Upper limits on the production cross section times branching ratio into W boson pairs are set for Randall-Sundrum and bulk Randall-Sundrum gravitons, which result in observed 95% CL lower limits on the masses of the two particles of 1.23 TeV and 0.84 TeV, respectively. Search for new phenomena in the WW → lνlν final state in pp collisions at √ s = 7 TeV with the ATLAS detector The ATLAS Collaboration (Dated: May 2, 2014) This Letter reports a search for a heavy particle that decays to WW using events produced in pp collisions at √ s = 7 TeV. The data were recorded in 2011 by the ATLAS detector and correspond to an integrated luminosity of 4.7 fb. WW → lνl′ν′ (l, l′ = e or μ) final states are considered and the distribution of the transverse mass of the WW candidates is found to be consistent with Standard Model expectations. Upper limits on the production cross section times branching ratio into W boson pairs are set for Randall-Sundrum and bulk Randall-Sundrum gravitons, which result in observed 95% CL lower limits on the masses of the two particles of 1.23 TeV and 0.84 TeV, respectively. PACS numbers: 14.70.Kv, 04.60.Kz, 12.60.Cn The existence of new phenomena can be probed by studying heavy gauge boson pair production. Heavy particles that can decay to gauge boson pairs are predicted in many scenarios of physics beyond the Standard Model (SM), including the Extended Gauge Model (EGM) [1], Extra Dimensions [2–6], and Technicolor models [7–9]. This paper describes a search for resonant WW production in the WW → lνlν (l, l = e or μ) decay channel using a data sample corresponding to an integrated luminosity of 4.7 fb, collected by the ATLAS detector during 2011 at a center-of-mass energy of 7 TeV. A spin2 Randall-Sundrum (RS) graviton model [2] and one of its extensions, the bulk RS graviton model [10], are used as benchmarks to interpret the analysis result. The original RS model (RS1) was proposed to solve the hierarchy problem. It postulates a warped 5-dimensional universe, where the SM particles are localized on the TeV brane and the graviton is located on the Planck brane. In this model gravitons can propagate in the extra dimension, leading to a Kaluza-Klein tower of states which can be detected as massive spin-2 resonances that couple to all SM particles. The resonance with the lowest mass is known as the RS graviton G. The model has two parameters: the graviton mass mG∗ , and the dimensionless coupling κ/M̃pl, where κ is the curvature of the warped fifth dimension and M̃pl = Mpl/ √ 8π is the reduced Planck mass. The RS1 model introduces higher-dimensional operators that give excessively large contributions to flavour changing neutral current (FCNC) processes and to observables related to SM electroweak precision tests. An extension of the RS1 model, the bulk RS model, has been proposed to address this issue. In this model, the SM fields are also allowed to propagate in the extra dimension: the first and second generation fermions are chosen to be localized near the Planck brane, while the top-quark and the Higgs boson are localized near the TeV brane to account for the large top-quark Yukawa coupling. In this scenario, FCNCs and contributions to electroweak observables from higher-dimensional operators are suppressed, the graviton (here denoted by G∗bulk) production and decay via light fermion channels is highly suppressed, the probability for the graviton to decay into photons is negligible, and the coupling to heavy particles, such as top-quark, W , Z and Higgs bosons is strongly enhanced. In this model the branching ratio of G∗bulk →WW is about 15%. Direct searches for a heavy WW resonance have been performed by the CDF and D0 collaborations at the Tevatron. The D0 collaboration explored diboson resonant production using the lνlν and lνjj final states [11]; these searches excluded an RS graviton with a mass between 300 GeV and 754 GeV, assuming κ/M̃pl = 0.1. The CDF collaboration also searched for resonant WW production in the eνjj final state, resulting in a lower limit of 607 GeV on the mass of an RS graviton [12], assuming the same coupling strength κ/M̃pl = 0.1. No previous work on searches for G ∗ bulk has been published. The ATLAS detector [13] is a multi-purpose particle physics detector with forward-backward symmetric cylindrical geometry [14]. The inner tracking detector (ID) covers the region |η| < 2.5, and consists of a silicon pixel detector, a silicon microstrip detector, and a straw tube tracker with transition radiation detection capability. The ID is surrounded by a thin superconducting solenoid providing a 2 T axial magnetic field. A highgranularity lead/liquid-argon (LAr) sampling calorimeter measures the energy and the position of electromagnetic showers with |η| < 3.2. LAr sampling calorimeters are also used to measure hadronic showers in the endcap (1.5 < |η| < 3.2) and forward (3.1 < |η| < 4.9) regions, while an iron/scintillator tile calorimeter measures hadronic showers in the central region (|η| < 1.7). The muon spectrometer (MS) surrounds the calorimeters and consists of three large superconducting air-core toroids, each with eight coils, a system of precision tracking chambers (|η| < 2.7), and fast tracking chambers for triggering. A three-level trigger system selects events to be recorded for offline analysis.

Search for pair production of heavy top-like quarks decaying to a high-pT W boson and a b quark in the lepton plus jets final state at (square root)s (equivalent to) 7TeV with the ATLAS detector

A search is presented for production of a heavy up-type quark (t′) together with its antiparticle, assuming a significant branching ratio for subsequent decay into a W boson and a b quark. The search is based on 4.7 fb−1 of pp collisions at √ s = 7 TeV recorded in 2011 with the ATLAS detector at the CERN Large Hadron Collider. Data are analyzed in the lepton+jets final state, characterized by a high-transverse-momentum isolated electron or muon, large missing transverse momentum and at least three jets. The analysis strategy relies on the substantial boost of the W bosons in the t′t̄′ signal when mt′ & 400 GeV. No significant excess of events above the Standard Model expectation is observed and the result of the search is interpreted in the context of fourth-generation and vector-like quark models. Under the assumption of a branching ratio BR(t′ → Wb) = 1, a fourth-generation t′ quark with mass lower than 656 GeV is excluded at 95% confidence level. In addition, in light of the recent discovery of a new boson of mass ∼ 126 GeV at the LHC, upper limits are derived in the two-dimensional plane of BR(t′ → Wb) versus BR(t′ → Ht), where H is the Standard Model Higgs boson, for vector-like quarks of various masses. Search for pair production of heavy top-like quarks decaying to a high-pT W boson and a b quark in the lepton plus jets final state at √ s = 7 TeV with the ATLAS detector

Measurement of Z boson production in Pb-Pb collisions at Square root of s NN equals to 2.76 TeV with the ATLAS detector

The ATLAS experiment has observed 1995 Z boson candidates in data corresponding to 0.15 nb−1 of integrated luminosity obtained in the 2011 LHC Pb+Pb run at √ sNN=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. ar X iv :1 21 0. 64 86 v1 [ he pex ] 2 4 O ct 2 01 2 Measurement of Z boson Production in Pb+Pb Collisions at √ sNN = 2.76 TeV with the ATLAS Detector