2011 QCD and High Energy Interactions - Rencontres de Moriond ...

1/N dN/dx
3.5
3
2.5
2
1.5
1
0.5
ALEPH
DELPHI
OPAL
SLD
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
weak xB
Figure 1: Comparison between the various measurements of the b-quark fragmentation distribution versus x weak
B .
• the perturbative contribution is taken from a parton shower Monte-Carlo generator;
• the perturbative contribution is taken to be a NLL QCD calculation. 5
For each case, the non-perturbative component fnon−pert.(x) is extracted using a method based
on the inverse Mellin transformation. The corresponding results, obtained from the world average
xweak B distribution, are shown in Fig 2. A non-perturbative component extracted in this way
does not depend on any hadronisation model, but on the other hand it depends on the choice of
the perturbative component and has to be used jointly with the adequate one. This dependence
is clearly seen from comparison of the two parts of Fig. 2. Notice that the non-perturbative
QCD component corresponding to the NLL QCD computation has to be extended in the region
x > 1. This “non-physical” behaviour is directly related to the break-down of the theory when
x weak
B
gets close to 1. The non-perturbative contribution extracted in this way may be used in
studies of b-hadron production in other experimental environments than e + e − collisions at the
Z pole. For a detailed explanation of the method see Refs. 1,6
(x)
non-pert.
f
7
6
5
4
3
2
1
0
perturbative QCD = JETSET
world average
uncertainty
ALEPH
DELPHI
OPAL
SLD
0 0.2 0.4 0.6 0.8 1 1.2
x
(x)
non-pert.
f
7
6
5
4
3
2
1
0
perturbative QCD = NLL computation
world average
uncertainty
ALEPH
DELPHI
OPAL
SLD
0 0.2 0.4 0.6 0.8 1 1.2
x
Figure 2: Comparison of the extracted non-perturbative QCD component of the b-quark fragmentation function
for the results from ALEPH, DELPHI, OPAL, SLD and the combined world average distribution. Left: The
perturbative QCD component has been taken from JETSET 7.3. Right: The perturbative QCD component has
been taken from NLL QCD. The shaded error bands represent the experimental uncertainty of the combined
distributions.