# Difference: AVFedotovLogA009 (6 vs. 7)

#### Revision 72010-09-10 - AlexanderFedotov

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 META TOPICPARENT name="AVFedotovLogA"
-- AlexanderFedotov - 09-Sep-2010
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## correlation between end partons of a string

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 >4 226752 976802
Changed:
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Shown below for each bin are
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Shown below for each bin (a subsection per bin) are

1. a 2-d pair distribution in
2. one or two zoomed versions of 1,
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1. and a 1-d distribution in for 3.75 < < 4
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1. and a 1-d distribution in for 3.75 < < 4

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• There is a "ridge" at = 0 clearly extending to = 4 -- the effect we looked for. * the relative height of the bump at 3.75 < < 4 (0 degree / 110 degree - 1) is 5.8 %
• There is another ridge/bump at = 180 which is completely unexpected in a string fragmentation picture if there is no back-to-back correlation between end partons , and we did not see such a correlation in the corresponding plot

### Two particles : 0 < pt < 0.5 GeV

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• The enhancement towards = 0 is available, though its size is smaller than that in the all-pt case:
((0 deg / 170 deg) - 1) = 3.0 % at =3.75 - 4
• no back-to-back enhancement

### Two particles : 0.5 < pt < 1 GeV

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• the "parallel" enhancement gets larger:
9.0% at = 3.75-4
• the back-to-back one appears

### Two particles : 1 < pt < 2 GeV

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• the "parallel" enhancement grows further:
23% at = 3.75-4
• the back-to-back one does too

### Two particles : 2 < pt < 3 GeV

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• for the "parallel" enhancement, a decreased statistics does not allow to tell the trend; the size is
10-30% at = 3.75-4
• the back-to-back enhancement continues to grow (up to 50% ?)

### Two particles : 3 < pt < 4 GeV

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• the "parallel" enhancement: statistics is low,
the size in the interval 0-30% ( = 3.75-4)
• the back-to-back one: gets very high to about 200% ( = 3.75-4)

### Two particles : pt > 4 GeV

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Changed:
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• the "parallel" enhancement: disappears completely (in the tail of the back-to-back one?)
• the back-to-back enhancement: reached maximum size of ~700%

### A summary for two particles correlations

• a "parallel" enhancement is observed at = 3.75-4 in the interval of pt 0 to 4 GeV. Its size grows from 3% at pt < .5 GeV to 23% at 1 < pt < 2 GeV, the further trend is unclear with the current statistics.
• the "parallel" enhancement is what was expected to be observed in a string fragmentation picture. However, its nature is not revealed in the current observation. E.g. the reason may be correlations between decay products of resonances and other unstable particles (even the photons from -decays may play a role; by the way, these photons may constitute up to 50% of the studied stable particle sample)
• a huge back-to-back enhancement is observed, which was not expected at all in the naive string fragmentation picture.

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• "parallel" and "back-to-back" enhancements are present

### particle-parton : 0 < pt < 0.5 GeV

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• "parallel" and "back-to-back" enhancements are present

### particle-parton : 0.5 < pt < 1 GeV

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• "parallel" and "back-to-back" enhancements are present

### particle-parton : 1 < pt < 2 GeV

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• "parallel" and "back-to-back" enhancements are present

### particle-parton : 2 < pt < 3 GeV

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• the "back-to-back" enhancement remains only

### particle-parton : 3 < pt < 4 GeV

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• the "back-to-back" enhancement is available only

### particle-parton : pt > 4 GeV

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• the "back-to-back" enhancement available only

### A summary for particle-parton correlations

• a "parallel" enhancement is observed at = 3.75-4 in the interval of pt 0 to 2 GeV.
• a "parallel" enhancement is what was expected to be observed in a string fragmentation picture. Unlike to a similar enhancement in two-particle distribution, this one supports the naive string fragmentation picture, because this case ia a direct study of correlation between the particle and string variables.
• a back-to-back enhancement is also observed. Why does pythia produce it? A correlated appearence of gluons within a parton shower? The fragmentation of a string proceeding not independently of the fragmentation of other strings in an event?

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