寻找电磁跃迁Ψ（2S）→γη_c（2S）
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摘要
粲偶素是由一对正反粲夸克通过强相互作用组成的束缚态。1974年,实验上观测到了第一个粲偶素家族的粒子J/Ψ,紧接着一系列的粲偶素成员相继被实验发现。Ψ(2S)是DD质量阀以下最重的粲偶素态,它可以辐射衰变到电荷宇称为正的粲偶素态,如ηc(2S),χcJ(J=1,2)以及ηc(1S)。但至今人们尚未在实验上观测到Ψ(2S)→γηc(2S)辐射跃迁。这方面最近的研究来自CLEO-c实验,他们没有观测到显著的信号,只确定了砂(2S)→γη。(2S)跃迁产额的上限。
BESⅢ探测器采集了106M的Ψ(2S)数据,它是目前为止世界上统计量最大的砂(2S)数据样本,大约是CLEO-c数据量的四倍。我们利用这个样本尝试寻找了Ψ(2S)到ηc(2S)的辐射跃迁,其中ηc(2S)共振态通过ΚSOΚ+π-+c.c.(ΚSOπ+π-)的强子末态重建。结果,我们观测到一个显著性为4.5a的信号,质量3636.0±2.0±0.7Me/c2,宽度7±7±3MeV,联合分支比为B(Ψ(2S)→γηc(2S))×B(ηc(2S)→ΚSOΚ+π-+c.c.)=(2.68±0.89±0.24)×10-6,测量结果中的第项误差均是统计误差,第二项都是系统误差。利用BaBar测量结果B(ηc(2S)ΚΚπ)=(1.9±0.4±1.1)%,我们抽取到分支比B(Ψ(2S)→γηc(2S))=(4.23±1.66±2.48)×10-4。
本文的观测结果是Ψ(2S)→γηc(2S)电磁偶极距跃迁的首个有力实验证据,我们测量到的ηc(2S)的质量和宽度与之前实验的测量结果符合,跃迁率的测量结果也与理论模型计算结果一致。
Charmonium is a bound state of a charm quark and an anti-charm quark by strong interaction.The first member of this family,J/Ψ,was first observed in 1974. Subsequently,a series of charmonium states were discovered.Ψ(2S)is the heaviest charmonium state below the DD mass threshold:it can decay radiatively into charge-parity even charmnonia,such asηc(2S),χcJ(J=0,1,2),andηc(1S). So far,the radiative transitionΨ(2s)→γηc(2s)is still not observed.The lastest study on this transition is form the CLEO-c experiment,with no significant signal observed,the bounds of the production rates are determined.
We search forΨ(2S)→γηc(2S)using the largestΨ(2S)data sample(106MΨ(2S)decays)collected with the BESⅢdetector.this sample is 4 times of the CLEO-c data sample.ηc(2S)is reconstrcuted withΚS0Κ+π-+c.c. final state,withΚS0 decays intoπ+π-. A 4.5σsignal is observed with the mass of 3636.0±2.0±0.7 McV/c2,width of 7±7±3 McV,and a product branching fraction ofΒ(Ψ(2S)→γηc(2S))×Β(ηc(2S)→ΚS0Κ+π-+c.c.)=(2.68±0.89±0.24)×10-6,with the first errors statistical and the second ones systematic.Taking the BaBar measurement ofΒ(ηc(2s)→ΚΚπ)=(1.9±0.4±1.1)%,we extractΒ(Ψ(2S)→γηc(2S)) (4.23±1.66±2.48)×10-4.
This is the first strong evidence for the M1 transitionΨ(2S)→γηc(2S),the measurements of mass and width agree with previous experiments,and the transition rate is in agreement with theoretical model calculations.
BESⅢ探测器采集了106M的Ψ(2S)数据,它是目前为止世界上统计量最大的砂(2S)数据样本,大约是CLEO-c数据量的四倍。我们利用这个样本尝试寻找了Ψ(2S)到ηc(2S)的辐射跃迁,其中ηc(2S)共振态通过ΚSOΚ+π-+c.c.(ΚSOπ+π-)的强子末态重建。结果,我们观测到一个显著性为4.5a的信号,质量3636.0±2.0±0.7Me/c2,宽度7±7±3MeV,联合分支比为B(Ψ(2S)→γηc(2S))×B(ηc(2S)→ΚSOΚ+π-+c.c.)=(2.68±0.89±0.24)×10-6,测量结果中的第项误差均是统计误差,第二项都是系统误差。利用BaBar测量结果B(ηc(2S)ΚΚπ)=(1.9±0.4±1.1)%,我们抽取到分支比B(Ψ(2S)→γηc(2S))=(4.23±1.66±2.48)×10-4。
本文的观测结果是Ψ(2S)→γηc(2S)电磁偶极距跃迁的首个有力实验证据,我们测量到的ηc(2S)的质量和宽度与之前实验的测量结果符合,跃迁率的测量结果也与理论模型计算结果一致。
Charmonium is a bound state of a charm quark and an anti-charm quark by strong interaction.The first member of this family,J/Ψ,was first observed in 1974. Subsequently,a series of charmonium states were discovered.Ψ(2S)is the heaviest charmonium state below the DD mass threshold:it can decay radiatively into charge-parity even charmnonia,such asηc(2S),χcJ(J=0,1,2),andηc(1S). So far,the radiative transitionΨ(2s)→γηc(2s)is still not observed.The lastest study on this transition is form the CLEO-c experiment,with no significant signal observed,the bounds of the production rates are determined.
We search forΨ(2S)→γηc(2S)using the largestΨ(2S)data sample(106MΨ(2S)decays)collected with the BESⅢdetector.this sample is 4 times of the CLEO-c data sample.ηc(2S)is reconstrcuted withΚS0Κ+π-+c.c. final state,withΚS0 decays intoπ+π-. A 4.5σsignal is observed with the mass of 3636.0±2.0±0.7 McV/c2,width of 7±7±3 McV,and a product branching fraction ofΒ(Ψ(2S)→γηc(2S))×Β(ηc(2S)→ΚS0Κ+π-+c.c.)=(2.68±0.89±0.24)×10-6,with the first errors statistical and the second ones systematic.Taking the BaBar measurement ofΒ(ηc(2s)→ΚΚπ)=(1.9±0.4±1.1)%,we extractΒ(Ψ(2S)→γηc(2S)) (4.23±1.66±2.48)×10-4.
This is the first strong evidence for the M1 transitionΨ(2S)→γηc(2S),the measurements of mass and width agree with previous experiments,and the transition rate is in agreement with theoretical model calculations.
引文
[1]J. J. Aubert et al., Phys. Rev. Lett.33,1404 (1974).
[2]J. E. Augustin et al., Phys. Rev. Lett.33,1406 (1974).
[3]G. S. Abrams et al., Phys. Rev. Lett.33,1453 (1974).
[4]C. Amsler et al. (Particle Data Group), Phys. Lett. B667,1 (2008) and 2009 partial update for the 2010 edition
[5]G. LI and Z.Y. WANG, BESⅢ note (2010)
[6]章乃森,粒子物理学(第一版),科学出版社, (上册)1986年4月； (下册)1987年11月.
[7]高崇寿,秦旦华,粒子物理学概要,高等教育出版社出版,1988年.
[8]李政道,粒子物理和场论,山东科学技术出版社出版,1996年.
[9]D.H.Perkins, Introduction to High Energy Physics, Cambridge University Press(4th Edition)2000.
[10]A.Schafer and W.Greiner, Quantum Chromodynamics, Springer,1994
[11]J.F.Donoghue, E.Golowich, B.R. Holstein, Dynamics of Standard Model; M.E. Peskin and D.V. Schroeder, An introduction to Quantum Field Theory.
[12]H. Fritzsch, M. Gell-Mann and H. Leutwyler, Phys. Lett. B 47,365 (1973).
[13]D.J. Gross and F.Wilczek, Phys Lett.30,1343(1973); H.D.Politzer,Phys.Rev.Lett.30,1346(1973).
[14]M. Gell-Mann, Phys. Rev. Lett.8,214 (1964).
[15]Kaiyan Gao,Study of Radiative Decay of Psi(2S) Mesons,2008
[16]郑志鹏、朱永生主编,北京谱仪·正负电子物理
[17]M. S. Chanowitz, LBL-23437 and Proc. of the International Conference On Hadron Spectlreoscopy, April 16-18,1987, KEK, Tsukuba, Japan.
[18]张宗烨,多夸克态研究概况,原子核物理评论,第二十一卷第四期.
[19]Preliminary design report of BEPCⅡ (2003). Linac:IHEP-BEPCII-SB-03-2; Storage ring:IHEPBEPCⅡ-SB-03-3; BESⅢ detector:IHEPBEPCII-SB-03-4.
[20]郑志鹏,朱永生主编,北京谱仪正负电子物理(第一版),广西科学技术出版社,1998年11月
[21]Physics at BES-Ⅲ,IHEP-Physics-Report-BES-III-2008-001
[22]Design and Construction of the BES-Ⅲ Detector, p32,2009
[23]Design and Construction of the BES-Ⅲ Detector, p54,2009
[24]Design and Construction of the BES-Ⅲ Detector, p67,2009
[25]Design and Construction of the BES-Ⅲ Detector, p92,2009
[26]Design and Construction of the BES-Ⅲ Detector, p120,2009
[27]M.Suzuki, Phys.Rev. D63,054021, (2001).
[28]M. Ablikim et al., Phys.Lett. B614,27, (2005).
[29]M. Ablikim et al.(BESⅢ Collaboration),arXiv:1001.5360v2(2010).
[30]M. Ablikim et al.(BESⅢ Collaboration),arXiv:1002.0501vl(2010).
[31]G.Li, Number of Ψ(2S) event,BESⅢ Software and Physics Workshop,2010.
[32]E. Barberio and Z. Was, Comput. Phys. Commun.79,291 (1994).
[33]M.Ablikim,M.N Achasov et al. Phys. Rev. D 81,052005 (2010).
[34]Tian MA,Performance of reconstruction efficiency of ΚSOmesson(2010) ppt.
[35]朱永生著,实验物理中的概率和统计(第二版),科学出版社,2006年4月
[36]B. Aubert,M. Bona et al.(Study of B-meson decays to ηcK(*),ηc(2S)(*) and ηcγΚ*),arXiv:0804.1208[hep-ex].
[2]J. E. Augustin et al., Phys. Rev. Lett.33,1406 (1974).
[3]G. S. Abrams et al., Phys. Rev. Lett.33,1453 (1974).
[4]C. Amsler et al. (Particle Data Group), Phys. Lett. B667,1 (2008) and 2009 partial update for the 2010 edition
[5]G. LI and Z.Y. WANG, BESⅢ note (2010)
[6]章乃森,粒子物理学(第一版),科学出版社, (上册)1986年4月； (下册)1987年11月.
[7]高崇寿,秦旦华,粒子物理学概要,高等教育出版社出版,1988年.
[8]李政道,粒子物理和场论,山东科学技术出版社出版,1996年.
[9]D.H.Perkins, Introduction to High Energy Physics, Cambridge University Press(4th Edition)2000.
[10]A.Schafer and W.Greiner, Quantum Chromodynamics, Springer,1994
[11]J.F.Donoghue, E.Golowich, B.R. Holstein, Dynamics of Standard Model; M.E. Peskin and D.V. Schroeder, An introduction to Quantum Field Theory.
[12]H. Fritzsch, M. Gell-Mann and H. Leutwyler, Phys. Lett. B 47,365 (1973).
[13]D.J. Gross and F.Wilczek, Phys Lett.30,1343(1973); H.D.Politzer,Phys.Rev.Lett.30,1346(1973).
[14]M. Gell-Mann, Phys. Rev. Lett.8,214 (1964).
[15]Kaiyan Gao,Study of Radiative Decay of Psi(2S) Mesons,2008
[16]郑志鹏、朱永生主编,北京谱仪·正负电子物理
[17]M. S. Chanowitz, LBL-23437 and Proc. of the International Conference On Hadron Spectlreoscopy, April 16-18,1987, KEK, Tsukuba, Japan.
[18]张宗烨,多夸克态研究概况,原子核物理评论,第二十一卷第四期.
[19]Preliminary design report of BEPCⅡ (2003). Linac:IHEP-BEPCII-SB-03-2; Storage ring:IHEPBEPCⅡ-SB-03-3; BESⅢ detector:IHEPBEPCII-SB-03-4.
[20]郑志鹏,朱永生主编,北京谱仪正负电子物理(第一版),广西科学技术出版社,1998年11月
[21]Physics at BES-Ⅲ,IHEP-Physics-Report-BES-III-2008-001
[22]Design and Construction of the BES-Ⅲ Detector, p32,2009
[23]Design and Construction of the BES-Ⅲ Detector, p54,2009
[24]Design and Construction of the BES-Ⅲ Detector, p67,2009
[25]Design and Construction of the BES-Ⅲ Detector, p92,2009
[26]Design and Construction of the BES-Ⅲ Detector, p120,2009
[27]M.Suzuki, Phys.Rev. D63,054021, (2001).
[28]M. Ablikim et al., Phys.Lett. B614,27, (2005).
[29]M. Ablikim et al.(BESⅢ Collaboration),arXiv:1001.5360v2(2010).
[30]M. Ablikim et al.(BESⅢ Collaboration),arXiv:1002.0501vl(2010).
[31]G.Li, Number of Ψ(2S) event,BESⅢ Software and Physics Workshop,2010.
[32]E. Barberio and Z. Was, Comput. Phys. Commun.79,291 (1994).
[33]M.Ablikim,M.N Achasov et al. Phys. Rev. D 81,052005 (2010).
[34]Tian MA,Performance of reconstruction efficiency of ΚSOmesson(2010) ppt.
[35]朱永生著,实验物理中的概率和统计(第二版),科学出版社,2006年4月
[36]B. Aubert,M. Bona et al.(Study of B-meson decays to ηcK(*),ηc(2S)(*) and ηcγΚ*),arXiv:0804.1208[hep-ex].