Marcel Merk

Probing New Physics via the

We have recently seen new upper bounds for B(s)(0)→μ(+)μ(-), a key decay to search for physics beyond the standard model. Furthermore a nonvanishing decay width difference ΔΓ(s) of the B(s) system has been measured. We show that ΔΓ(s) affects the extraction of the B(s)(0)→μ(+)μ(-) branching ratio and the resulting constraints on the new physics parameter space and give formulas for including this effect. Moreover, we point out that ΔΓ(s) provides a new observable, the effective B(s)(0)→μ(+)μ(-) lifetime τ(μ(+)μ(-)), which offers a theoretically clean probe for new physics searches that is complementary to the branching ratio. Should the B(s)(0)→μ(+)μ(-) branching ratio agree with the standard model, the measurement of τ(μ(+)μ(-)), which appears feasible at upgrades of the Large Hadron Collider experiments, may still reveal large new physics effects.

B^0_s\to \mu^+\mu^-

latter feature leads to a subtle complication for the extraction of branching ratios of Bs decays from untagged data samples, leading to systematic biases as large as Oð10%Þ that depend on the dynamics of the considered decay. We point out that this effect can only be corrected for using information from a time-dependent analysis and suggest the use of the effective Bs decay lifetime, which can already be extracted from the untagged data sample, for this purpose. We also address several experimental issues that can play a role in the extraction of effective lifetimes at a hadron collider, and advocate the use of the Bs branching ratios, as presented in this note, for consistent comparisons of theoretical calculations and experimental measurements in particle listings.

Effective Lifetime

AbstractThe charged particle multiplicity distribution has been studied for non-single-diffractive π+p andpp collisions at

B_s

\sqrt s = 22

Phase space dependence of the multiplicity distribution in π+ andpp collisions at 250 GeV/c

GeV, for full phase space as well as for intervals in rapidity, azimuthal angle and transverse momentum. In general, the multiplicity distribution is well described by a negative binomial. From comparison of the distribution for negative or positive particles to that of all charged particles, cascading is favoured as an interpretation over stimulated emission. Interesting consequences follow from a comparison of our results to those at collider energies and toe+e− data at comparable energy. Furthermore, evidence is given that the multiplicity distribution is not exactly of negative binomial type in every (connected or disconnected) phase space region.

Application of vertex and mass constraints in track-based alignment

The software alignment of planar tracking detectors using samples of charged particle trajectories may lead to global detector distortions that affect vertex and momentum resolution. We present an alignment procedure that constrains such distortions by making use of samples of decay vertices reconstructed from two or more trajectories and putting constraints on their invariant mass. We illustrate the method by using a sample of invariant-mass constrained vertices from D-0 -> K-pi(+) decays to remove a curvature bias in the LHCb spectrometer. (c) 2013 Elsevier B.V. All rights reserved.

Measurement of the (B)over-bar(0)-B-0 and (B)over-bars(0)-B-s(0) production asymmetries in pp collisions at root s=7 TeV

Abstract The B ¯ 0 – B 0 and B ¯ s 0 – B s 0 production asymmetries, A P ( B 0 ) and A P ( B s 0 ) , are measured by means of a time-dependent analysis of B 0 → J / ψ K ⁎ 0 , B 0 → D − π + and B s 0 → D s − π + decays, using a data sample corresponding to an integrated luminosity of 1.0 fb − 1 , collected by LHCb in pp collisions at a centre-of-mass energy of 7 TeV . The measurements are performed as a function of transverse momentum and pseudorapidity of the B 0 and B s 0 mesons within the LHCb acceptance. The production asymmetries, integrated over p T and η in the range 4 p T 30 GeV / c and 2.5 η 4.5 , are determined to be A P ( B 0 ) = ( − 0.35 ± 0.76 ± 0.28 ) % and A P ( B s 0 ) = ( 1.09 ± 2.61 ± 0.66 ) % , where the first uncertainties are statistical and the second systematic.

Multiplicity distributions in separated phase space intervals of π+p collisions at 250 GeV/c

Abstract The charged particle multiplicity distribution is studied for non-single-diffractive π + p collisions at √ s =22 GeV, in central rapidity intervals separated from the outer regions by empty gaps. A priori unexpectedly, also these distributions yield good negative binomial fits. The variation of the parameter 1/ k as a function of the gap size can be understood in terms of cascading clans of limited rapidity range if events with a large number of clans preferably contribute to the central region. The Fritiof-3 model agrees quantitatively with the data.