Direct Measurement of A{sub c} using Inclusive Charm Tagging at the SLD Detector Page: 4 of 12
This report is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
The mass of the secondary vertex is calculated using the tracks that are associated with
the vertex. Each track is assigned the mass of a charged pion and the invariant mass of the
vertex is calculated. The reconstructed mass is corrected to account for neutral particles as
follows. Using kinematic information from the vertex flight path and the momentum sum
of the tracks associated with the secondary vertex, we add a minimum amount of missing
momentum to the invariant mass. This is done by assuming the true quark momentum is
aligned with the flight direction of the vertex. The so-called Pt-corrected mass is given by:
MVx= M2tkPt2 __p
where Mtk is the mass for the tracks associated with the secondary vertex. We restrict the
contribution to the invariant mass that the additional transverse momentum adds to be less
than the initial mass of the secondary vertex. This cut ensures that poorly measured vertices
in uds events do not leak into the sample by adding large Pt.
3.3 Flavor Tag
A bottom tag is defined as a hemisphere with an invariant mass above 2 GeV/c2. The
intermediate mass region, between 0.5 and 2 GeV/c2 contains a mixture of b and c, with a
small uds background. We define some additional cuts to reject b and uds. A charm tag is
defined as follows:
* 0.55 < MVTx < 2 GeV/c2
* Vertex momentum (PvTx) greater than 5 GeV/c.
* Fragmentation cut: 15MvTx - PVTx < 10. This uses the fact that D hadrons from
direct charm have a higher momentum than those from B hadron decays.
These tags are calibrated against the data as described in [11]. The efficiencies 7c (for
the charm tag) and Eb (for the bottom tag), and partial widths R, and Rb are found by
comparing the single- vs. double-tagged event rates for the two tags. In addition, the b mis-
tag efficiency 'lb can be found from the fraction of events with a charm tag in one hemisphere
and a bottom tag in the other (mixed tag). The light-flavor efficiencies and c, are taken from
Monte Carlo.
A charm event is defined to be one with at least one charm-tagged hemisphere and no
bottom-tagged hemispheres. This is found to be ~ 28% efficient for charm events. With the
calibrated efficiencies and partial widths the charm purity of these events is calculated to
be f, = 82.1 + 0.5%. This is in good agreement with the Monte Carlo value 82.6%. The b
background fraction is 15.5% with uds making up the remainder.3
Upcoming Pages
Here’s what’s next.
Search Inside
This report can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Report.
Abe, K. Direct Measurement of A{sub c} using Inclusive Charm Tagging at the SLD Detector, report, July 14, 1999; Menlo Park, California. (https://digital.library.unt.edu/ark:/67531/metadc620984/m1/4/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.