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2
Contents
• Introduction
• Data and MC for Z0 decays
• Moments for restricted PS bins
• Moments for hadrons and jets
• Conclusions and outlook
3
Introduction
• Factorial and cumulant moments: Fq[n!/(n-q)!]P(n), Kq Fq-{(q-1)!/[(i-1)!(q-i)!]}Kq-iFi,
investigated usually for q<5 only.
• Pavia group (I.D.Dremin et al., PLB336): Hq Kq /Fq meaningful even for q>10; negative minimum at q=5, oscillations? Relation to NNLO pQCD?
4
Data and MC for Z0 decay
• LEP-1 data: sufficient statistics, accuracy. L3 analysis (PLB 577) confirms minimum at q=5 (Fig.1).
• JETSET OK.; oscillations seen only for truncated data (0.035% off).
• PYTHIA events: as above (Fig.2); stable results for statistics >2M events (no „natural” cut - Fig.3).
• Toy model with two NBD (2/3 ratio) OK.!
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Moments in restricted PS bins
• CERN collider data (UA5) suggested that MD for restricted PS change smoothly with bin size: good NBD fits, n/k scaling etc. What about high order moments? Test for PYTHIA events (Fig.4): dip at q=5 disappears even for very large bins, survives only for truncated distributions! Data?
10
Moments for hadrons and for jets
• pQCD predictions for gluons, not hadrons. Are the data similar for hadrons and „small” jets defined e.g. by PYCLUS? Test for PYTHIA events (Fig.5) negative: minimum shifts to q=4 even for very small jets. Counting neutrals or positive only destroys or shifts the minimum (Fig.6). Extending LPHD unjustified?
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Conclusions and outlook
• Analysis of PYTHIA events for Z0 decays in terms of Hq moments for high q:
• confirms agreement with data for full PS,
• shows stability of results for >2M events,
• suggests interesting features for PS bins,
• questions validity of extended LPHD,
• shows importance of charge conservation.