Study of the Hardness Property of Quark and Gluon Jets

CHEN Gang; LIU Lian-Shou

Chinese Physics C> 2004, Vol. 28> Issue(5) : 469-474

Study of the Hardness Property of Quark and Gluon Jets

CHEN Gang ,
LIU Lian-Shou ^,

Department of Physics,China University of Geosciences,Wuhan 430074,China2 Institute of Particle Physics,Huazhong Normal University,Wuhan 430079,China

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Abstract：
The 3-jet events from hadronic Z⁰ decay is studied using Monte-Carlo simulation. Quark and Gluon jets are identified through the b-tag method. A new physical quantity——hardness is defined, and the hardness distributions of quark and gluon jets are calculated. The dependence of the average multiplicity and average transverse momentum on hardness as well as the multiplicity and transverse momentum distributions in a certain hardness range in the quark and gluon jets are calculated respectively, and compared. It is found that the properties of quark and gluon jets are considerably different in these respects. The properties of quark jets are almost independent on hardness, while those of gluon jets have strong correlation with hardness. When H_d>10GeV the average multiplicity and average tranverse momentum of gluon jets are higher than those of quark jets; but when H-d<6GeV the results are reversed. This indicates that the conclusion on gluon jets being “fatter” than quark jets is valid only for hard gluons.

References

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. Brandel ik R et al (TASSO Collab. ) . Phys. Lett. , 1979, B86: 2432. Abreu P et al ( DELPHI Collab. ) . Eur. Phys. J. , 1998, C4: 1 .. 173. Buskulic D et ak ( ALEPH Collab. ) . Phys. Lett . , 1996, B383: 3534. Acton P D et al ( OPAL Collab. ) . Z. Phys. , 1993, C58: 387; 1995,C68: 1795. ZHANG Kun Shi, CHEN Gang, YU Mei Ling et al. HEP NP, 2002,26: 1110 (in Chinese)(张昆实,陈刚,喻梅凌等.高能物理与核物理,2002,26:111)6. CHEN Gang, ZHANG Kun Shi, LIU Lian Shou. SCIENCE IN CHINA,2002, A32: 1088(in Chinese)(陈刚,张昆实,刘连寿.中国科学,2002, A32:1088)7. YU Mei Ling, LIU Lian Shou. A Mont e Carlo Study on the Iden tification of Quark andGluon Jets. In: Proc. of the XXXI International Symposium on Mult ipart icle Dynamics. Datong China. Sept. 2001, eds.BAI Yu Ting, YU Mei Ling, WU Yuan Fang, Singapore: World Scientific; hep- ph/01114248. Derrick M et al (HRS Collab. ) . Phys. Let t. , 1985, B165: 4499. Derrick M et al (HRS Collab. ) . Phys. Rev. Lett. , 1989, 63: 1710. YU Mei Ling, LIU Lian Shou. Chin. Phys. Lett. , 2002, 19: 647 ..65111. Abreu P et al (DELPHI Collab. ) . Phys. Lett. , 1999, B449: 383

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CHEN Gang and LIU Lian-Shou. Study of the Hardness Property of Quark and Gluon Jets[J]. Chinese Physics C, 2004, 28(5): 469-474.

CHEN Gang and LIU Lian-Shou. Study of the Hardness Property of Quark and Gluon Jets[J]. Chinese Physics C, 2004, 28(5): 469-474. shu

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Received: 2003-06-27
Revised: 1900-01-01

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沈阳化工大学材料科学与工程学院沈阳 110142

Study of the Hardness Property of Quark and Gluon Jets

CHEN Gang
LIU Lian-Shou ^,

Corresponding author: LIU Lian-Shou,

Department of Physics,China University of Geosciences,Wuhan 430074,China2 Institute of Particle Physics,Huazhong Normal University,Wuhan 430079,China

Received Date: 2003-06-27
Accepted Date: 1900-01-01
Available Online: 2004-05-05

Abstract: The 3-jet events from hadronic Z⁰ decay is studied using Monte-Carlo simulation. Quark and Gluon jets are identified through the b-tag method. A new physical quantity——hardness is defined, and the hardness distributions of quark and gluon jets are calculated. The dependence of the average multiplicity and average transverse momentum on hardness as well as the multiplicity and transverse momentum distributions in a certain hardness range in the quark and gluon jets are calculated respectively, and compared. It is found that the properties of quark and gluon jets are considerably different in these respects. The properties of quark jets are almost independent on hardness, while those of gluon jets have strong correlation with hardness. When H_d>10GeV the average multiplicity and average tranverse momentum of gluon jets are higher than those of quark jets; but when H-d<6GeV the results are reversed. This indicates that the conclusion on gluon jets being “fatter” than quark jets is valid only for hard gluons.