M. Ahsan

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.

Measurement of the B(c) meson mass in the exclusive decay B(c) ---> J / psi pi

A fully reconstructed Bc-->J/psipi signal is observed with the D0 detector at the Fermilab Tevatron pp[over] collider using 1.3 fb(-1) of integrated luminosity. The signal consists of 54+/-12 candidates with a significance that exceeds 5 standard deviations, and confirms earlier observations of this decay. The measured mass of the Bc meson is 6300+/-14(stat)+/-5(syst) MeV/c2.

Observation and Properties of

This Letter presents the first strong evidence for the resolution of the excited B mesons B(1) and B(2)* as two separate states in fully reconstructed decays to B(+)(*)pi(-). The mass of B(1) is measured to be 5720.6+/-2.4+/-1.4 MeV/c(2) and the mass difference DeltaM between B(2)* and B(1) is 26.2+/-3.1+/-0.9 MeV/c;{2}, giving the mass of the B(2)* as 5746.8+/-2.4+/-1.7 MeV/c(2). The production rate for B(1) and B(2)* mesons is determined to be a fraction (13.9+/-1.9+/-3.2)% of the production rate of the B+ meson.

L 1 B_ 1

We report results from a search for the decay B{sup 0}{sub S} {yields} {mu}{sup +}{mu}{sup -} using 1.3 fb{sup -1} of p{bar p} collisions at {radical}s = 1.96 TeV collected by the D0 experiment at the Fermilab Tevatron Collider. We find two candidate events, consistent with the expected background of 1.24 {+-} 0.99, and set an upper limit on the branching fraction of B(B{sub S}{sup 0} {yields} {mu}{sup +}{mu}{sup -}) < 1.2 x 10{sup -7} at the 95% C.L.

and

We report on a first search for resonant pair production of neutral long-lived particles (NLLP) which each decay to a bb pair, using 3.6 fb(-1) of data recorded with the D0 detector at the Fermilab Tevatron collider. We search for pairs of displaced vertices in the tracking detector at radii in the range 1.6-20 cm from the beam axis. No significant excess is observed above background, and upper limits are set on the production rate in a hidden-valley benchmark model for a range of Higgs boson masses and NLLP masses and lifetimes.

B^*_2

We have measured the b lifetime using the exclusive decay bJ/, based on 1.2 fb-1 of data collected with the D0 detector during 2002–2006. From 171 reconstructed b decays, where the J/ and are identified via the decays J/µ+µ- and p, we measured the b lifetime to be (b)=1.218(stat)±0.042(syst) ps. We also measured the B0 lifetime in the decay B0J/(µ+µ-)K(+-) to be (B0)=1.501(stat)±0.050(syst) ps, yielding a lifetime ratio of (b)/(B0)=0.811(stat)±0.034(syst).We have measured the Lambda b lifetime using the exclusive decay Lambda b --> J/psi Lambda, based on 1.2 fb(-1) of data collected with the D0 detector during 2002-2006. From 171 reconstructed Lambda b decays, where the J/psi and Lambda are identified via the decays J/psi --> mu+ mu- and Lambda --> ppi, we measured the Lambda b lifetime to be tau(Lambda b)=1.218 (+0.130)/(-0.115) (stat) +/- 0.042(syst) ps. We also measured the B0 lifetime in the decay B0 --> J/psi(mu+ mu-)K(0)/(S)(pi+ pi-) to be tau(B0)=1.501 (+0.078)/(-0.074) (stat) +/- 0.050(syst) ps, yielding a lifetime ratio of tau(Lambda b)/tau(B0)=0.811 (+0.096)/(-0.087) (stat) +/- 0.034(syst).

Mesons

ATLAS is one of the two general purpose detectors at the worlds largest particle accelerator, the Large Hadron Collider (LHC). The LHC will be colliding proton beams at a center of mass energy {\surd}s= 14 TeV and is currently operating at {\surd}s = 7 TeV. During the commissioning phase since September 2008, the ATLAS recorded cosmic-rays data and proton-proton collisions at {\surd}s = 0.9 TeV. This data has extensively been used for the alignment and calibration of various sub-detectors. The ATLAS detector has a precision tracking system installed around the beam pipe for the measurements of the position and momentum of charged particles emerging from the collisions. The precise knowledge of misalignments of the tracking devices is crucial for the important physics measurements. At the time of writing the alignment corrections were obtained from the cosmic-rays and 0.9 TeV proton-proton collisions data, while the large statistics of proton-proton collisions at 7 TeV was used to check the performance of the alignment. This article gives an overview of the alignment strategy and the alignment performance using the data collected from proton-proton collisions at 7 TeV.

Search for Bs --> mu+ mu- at D0

We report on a first search for production of the lightest neutral CP-even Higgs boson (h) in the next-to-minimal supersymmetric standard model, where h decays to a pair of neutral pseudoscalar Higgs bosons (a), using 4.2 fb{sup -1} of data recorded with the D0 detector at Fermilab. The a bosons are required to either both decay to {mu}{sup +}{mu}{sup -} or one to {mu}{sup +}{mu}{sup -} and the other to {tau}{sup +}{tau}{sup -}. No significant signal is observed, and we set limits on its production as functions of M{sub a} and M{sub h}.

Search for Resonant Pair Production of long-lived particles decaying to b anti-b in p anti-p collisions at s**(1/2) = 1.96-TeV

A search for the production of neutral Higgs bosons Phi decaying into tau^+tau^- final states in p-pbar collisions at a center-of-mass energy of 1.96 TeV is presented. The data, corresponding to an integrated luminosity of up to 348 pb^-1, were collected by the D0 experiment at the Fermilab Tevatron Collider. Since no excess compared to the expectation from standard model processes is found, limits on the production cross section times branching ratio are set. The results are combined with those obtained from the D0 search for Phi b(b) to b-bbar-b(bbar) and are interpreted in the minimal supersymmetric standard model.