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I. Abt

Publications and source records attributed to I. Abt.

62 records · Page 4Linked to original sources
arXiv2006

Bottom production cross section from double muonic decays of b-hadrons in 920 GeV proton-nucleus collision

The b-bbar production cross section in 920 GeV proton-nucleus fixed target collisions is measured by observing double muonic decays of b-flavored hadrons in the kinematic region $-0.3<\xF(μ)<0.15$. A total number of $76\pm12$ b-bbar events is obtained with a likelihood fit of the signal and background simulated events to the data. The resulting cross section is $\sigbb = 16.2 \pm 2.5_{stat} \pm 2.8_{sys} \nbpn$, or, when combined with a previous Hera-B measurement of similar precision, $\sigbb = 15.4 \pm 1.7_{stat} \pm 1.2_{sys}^{uncorr.} \pm 1.9_{sys}^{corr.} \nbpn$, which is consistent with recent NLO calculations.

hep-ex↗
arXiv2006

Measurement of the Upsilon Production Cross Section in 920 GeV Fixed-Target Proton-Nucleus Collisions

The proton-nucleon cross section ratio $R=Br(Υ\to l^+l^-) dσ(Υ)/dy|_{y=0} / {σ(J/ψ)}$ has been measured with the HERA-B spectrometer in fixed-target proton-nucleus collisions at 920 GeV proton beam energy corresponding to a proton-nucleon cms energy of sqrt{s}=41.6 GeV. The combined results for the Upsilon decay channels Upsilon $\to e^+e^-$ and Upsilon $\toμ^+μ^-$ yield a ratio $R=(9.0 \pm 2.1) 10^{-6}$. The corresponding Upsilon production cross section per nucleon at mid-rapidity (y=0) has been determined to be $Br(Υ\to{}l^+l^-) {dσ(Υ)/dy}|_{y=0}= 4.5 \pm 1.1 $ pb/nucleon.

hep-ex↗
arXiv2005

Improved Measurement of the b-bbar Production Cross Section in 920 GeV Fixed-Target Proton-Nucleus Collisions

A new measurement of the b-bbar production cross section in 920 GeV proton-nucleus collisions is presented by the HERA-B collaboration. The b-bbar production is tagged via inclusive bottom quark decays into J/psi mesons, by exploiting the longitudinal separation of J/psi->ll decay vertices from the primary proton-nucleus interaction point. Both e+e- and mu+mu- channels are reconstructed, for a total of 83 +- 12 inclusive b->J/psi X events found. The combined analysis yields a b-bbar to prompt J/psi cross section ratio of ${\frac{Δσ(bbbar)}{Δσ_{\jpsi}}} = 0.032\pm 0.005 \stat \pm 0.004 \sys$ measured in the x_f acceptance (-0.35 <x_f <0.15), extrapolated to $σ(bbbar) = 14.9 \pm 2.2 \stat \pm 2.4 \sys $ nb/nucleon in the total phase space.

hep-ex↗
arXiv2004

Limits for the central production of Theta^+ and Xi^{--} pentaquarks in 920 GeV pA collisions

We have searched for Theta^+(1540) and Xi^{--}(1862) pentaquark candidates in proton-induced reactions on C, Ti and W targets at mid-rapidity and \sqrt{s} = 41.6 GeV. In 2x10^8 inelastic events we find no evidence for narrow (sigma~5 MeV) signals in the Theta^+ -> pK_s and Xi^{--} -> Xi^-pi^- channels; our 95% CL upper limits (UL) for the inclusive production cross section times branching fraction Bx(dsigma/dy)|_{y~0} are 3.7 and 2.5 microb/N. The UL of the yield ratio of [Theta^+ / Lambda(1520)] < 2.7% is significantly lower than model predictions. Our UL of [BxXi^{--} / Xi(1530)^0] < 4% is at variance with the results that have provided first evidence for the Xi^{--} signal.

hep-ex↗
arXiv2004

A Detector for Forward Physics at eRHIC: Feasibility Study

The eRHIC facility planned for the Brookhaven National Laboratory will allow detailed studies of the strong hadronic interactions. Among the exciting research topics discussed are the pursuit of the Color Glass Condensate, the three dimensional scan of nucleons and nuclei, and the solution to the mystery of how the proton spin is built up from its constituents. This document describes a detector optimized for forward physics at such an accelerator. The experience gained at HERA allows for the design of a detector which will give optimal performance in the kinematic regions of highest priority, the small and large $x$ regimes. Detailed simulations of the detector were carried out, and performance results for structure function measurements are presented.

hep-ex↗
arXiv2004

A New 76Ge Double Beta Decay Experiment at LNGS

This Letter of Intent has been submitted to the Scientific Committee of the INFN Laboratori Nazionali del Gran Sasso (LNGS) in March 2004. It describes a novel facility at the LNGS to study the double beta decay of 76Ge using an (optionally active) cryogenic fluid shield. The setup will allow to scrutinize with high significance on a short time scale the current evidence for neutrinoless double beta decay of 76Ge using the existing 76Ge diodes from the previous Heidelberg-Moscow and IGEX experiments. An increase in the lifetime limit can be achieved by adding more enriched detectors, remaining thereby background-free up to a few 100 kg-years of exposure.

hep-ex↗
arXiv1996

First Measurement of the Left-Right Charge Asymmetry in Hadronic Z Boson Decays and a New Determination of sin^2(theta_eff)

We present the first measurement of the left-right charge asymmetry A_Q^{obs} in hadronic Z boson decays. This was performed at E_cm = 91.27 GeV with the SLD at the SLAC Linear Collider with a polarized electron beam. Using 89838 events, we obtain A_Q^{obs}=0.225+-0.056+-0.019 which leads to a measurement of the electron left-right asymmetry parameter, A_e=0.162+-0.041+-0.014, and sin^2(theta_eff)=0.2297+-0.0052 +-0.0018. Also, the A_Q^{obs} measurement combined with the left-right cross section asymmetry determines A_e independently of the value of the electron-beam polarization.

hep-ex↗