UE7@CMS
June 22, 2010
Ratio : 7 TeV divided by 900 GeV
I suggest we include only D6T,
DW, and CW in this plot.
We can include all the
tunes in this plot.
"Transverse" Charged Particle Density: dN/ddf
"Transverse" Charged Particle Density Ratio
3.0
1.5
D6T
Tune D6T
data uncorrected
theory + SIM
data uncorrected
theory + SIM
2.0
Theory/Data
Ratio: 7 TeV/900 GeV
CMS Preliminary
CMS Preliminary
DW
1.0
CW
Fake Figure!
Tune P0
1.0
Charged Particles (||<2.0, PT>0.5 GeV/c)
Charged Particles (||<2.0, PT>0.5 GeV/c)
0.0
0.5
0
2
4
6
8
10
12
PT(chgjet#1) (GeV/c)
14
16
18
0
2
4
6
8
10
12
14
16
18
PT(chgjet#1) (GeV/c)
Fig. X. (left) CMS data on the ratio of the charged particle density in the “transverse”
region for charged particles (pT > 0.5 GeV/c, || < 2) at 900 GeV and 7 TeV (7 TeV
divided by 900 GeV) as defined by the leading charged particle jet, chgjet#1, compared
with PYTHIA Tune D6T, DW, and CW and at the detector level (i.e. Theory + SIM).
(right) Theory divided by data for energy dependence of the charged particle density in
the “transverse” region.
Remarks: In the left plot I suggest we include only Tune D6T (PARP(90)=0.16), Tune
DW (PARP(90)=0.25), Tune CW (PARP(90)=0.30). Perugia 0 has PARP(90)=0.26
which is very similar to Tune DW. In the right plot we can include all the tunes. We
should also do the same two plots for the transverse PTsum density.
Words: Fig. X shows the data on the ratio of the charged particle density in the
“transverse” region for charged particles at 900 GeV and 7 TeV versus the transverse
momentum of the leading charged particle jet. The uncorrected data are compared with
PYTHIA Tune D6T (PARP(90)=0.16), Tune DW (PARP(90)=0.25), Tune CW
(PARP(90)=0.30). This ratio is very sensitive to the PYTHIA MPI energy scaling
parameter, PARP(90). None of the tunes describe the energy dependence of the low
transverse momentum region, PT(chgjet1) < 8 GeV/c. At high transverse momentum
where the activity in the transverse region forms a plateau, the data favor the energy
dependence of Tune DW. The RHIC underlying event analysis at 200 GeV also favors
PYTHIA tunes with PARP(90) ≈ 0.25 [ref].
Rick Field
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