BESIII上J/ψ总数的确定和J/ψ→μ~+μ~-分支比的测量
摘要
BESIII探测器是工作在北京正负电子对撞机BEPCII上的大型、通用、高精度谱仪,主要开展τ-粲物理能区的正负电子对撞物理实验、进行弱电相互作用和强相互作用研究以及新物理的寻找。BESIII自2008年夏天开始运行至今,各项性能不断提高,运行状态良好,并且先后从2008年5月到11月获取超过1000万的ψ(2S)数据;2009年3月获取了超过6000万的ψ(2S)数据。
J/ψ粒子是粲夸克偶素家族中极其重要的一员,对J/ψ粒子的各项基本参数的测定是进行其它各项研究的基础。由于在测量J/ψ衰变的各种反应道的绝对分支比中,都需要用到J/ψ总数这一基本的参量,所以对J/ψ事例的总数测量工作显得尤为重要,其测量精度直接影响到J/ψ衰变物理的各种物理分析的系统误差大小。在BESII上,J/ψ总数的测量精度为4.7%,而BESIII各项性能指标优于BESII,因此人们期望在BESIII上对J/ψ总数的确定有更小的误差。考虑到对J/ψ→μ+μ-的测量精度已经达到了1%以内,同时经过改造后的BESIII,μ子探测器有较大改进,对μ子的探测、分辨能力大幅提高,因而本文通过J/ψ衰变到μ+μ-来确定BESIII上J/ψ事例的总数。基于BESIII的离线软件系统BOSS634版本,详细地研究了事例的选择条件,并进行了最优化选取。蒙特卡罗分析表明,我们的做法能有效地排除本底事例,精确地确定J/ψ事例总数。本方法将会用来确定BESIII上J/ψ总数。
由于在实验上,J/ψ介子通常通过它的两个最大最干净的遍举衰变道J/ψ→e+e-和J/ψ→μ+μ-来作标记,二者的分支比也被用来确定强相互作用的耦合常数αs;并且它们的比例Be/Bμ也用来检验轻子的普适性;另外,J/ψ衰变到轻子对的分支比也是J/ψ粒子的基本参数之一。本文利用BESIII于2008年9月至10月试运行阶段获取的部分ψ(2S)数据,通过ψ(2S)→π+π-J/ψ(J/ψ→anything和J/ψ→μ+μ-)间接地测量J/ψ衰变到μ+μ-的分支比。先通过对事例末态特征的分析和计算,对所需要的挑选条件进行了仔细研究;然后基于BESIII的离线软件系统BOSS641版本,确定事例的挑选条件并进行事例挑选工作;对挑选出来的事例用Roofit作拟合,得到真正的好事例。利用Monte Carlo模拟,得到单举道和遍举道的效率,于是可以计算出J/ψ→μ+μ-的分支比。在拟合的过程中,我们采用双高斯拟合和用遍举道的π+π-反冲质量谱形状去拟合单举道的π+π-反冲质量谱形状的方法,并将二者得到的结果取平均,得到J/ψ→μ+μ-的分支比为5.70%,与PDG给出的值5.93%基本一致。
The BEijing Spectrometer III(BESIII) operating at Beijing Electron Positron Collider II (BEPCII) is a high quality magnetic detector built with modern techniques. It is used to do research on electron positron colliding physics at the energy range of tau-charm. Its main physics goal is to study the electro-weak interaction, strong interaction and search for new physics. BESIII began operating in last summer. It operates well, and gained more than 10 millionψ(2S) data from May to November last year. And it even acquired 60 millionψ(2S) data during March 2009.
J/ψparticle is an important member in charm quark family. It is a primary work to measure the parameters of J/ψparticle. J/ψtotal number is one of the most important parameters, for it is the inevitable parameter to measure the branching ratio of any J/ψdecay. So precise J/ψtotal number measurement is necessary to get a smaller systematic uncertainty. The uncertainty of J/ψtotal number measurement at BESII is 4.7%. Because the BESIII detector is better than BESII in many aspects, a precise J/ψtotal number is expected at BESIII. By 2008, the branching ratio precise of J/ψdecaying toμ+μ- is less than 1%, and BESIII has much better muon detector. In this article, we use J/ψdecaying toμ+μ- to measure the total number of J/ψ. The BESIII offline software system(BOSS) version used is BOSS634. The events selection conditions are studied and optimized in the article. Monte Carlo study shows that our method can exclude background events and can gain precise J/ψtotal number. And it will be used to determine the total number of J/ψfor the coming J/ψdata taking.
J/ψparticle is usually tagged by its two largest and cleanest decaying channels: J/ψ→e+e-, J/ψ→μ+μ-. The branching ratios of the two decaying channels can be used to determine the coupling constant of strong interaction and to check the universal of leptons by Be/Bμ. The branching ratios of leptons are basic parameters. Theψ(2S) data, which acquired by BESIII from September to October, is used in our analysis. The method we used to measure the branching ratio of J/ψ→μ+μ- is to selectψ(2S)→π+π-J/ψ(J/ψ→anything and J/ψ→μ+μ-) events. This method is an indirect way to measure the branching ratio. First, after analysis and calculation of the character of the final particles, proper conditions can be determined to select the events we want. Then, we use our program to select good events and record them based on BOSS641. Finally , we fit the recorded good events with Roofit tool, to exclude background events and get the real events we want, and the selection efficiencies. Double guassian fitting method and fitting theπ+π- recoiling mass spectrum of inclusive process with exclusive process, and each fitting method gives a branching ratio value. We get the final result by averaging the two values. The result is Br(J/ψ→μ+μ-)=5.70%, which agrees the PDG value 5.93% on the whole.
J/ψ粒子是粲夸克偶素家族中极其重要的一员,对J/ψ粒子的各项基本参数的测定是进行其它各项研究的基础。由于在测量J/ψ衰变的各种反应道的绝对分支比中,都需要用到J/ψ总数这一基本的参量,所以对J/ψ事例的总数测量工作显得尤为重要,其测量精度直接影响到J/ψ衰变物理的各种物理分析的系统误差大小。在BESII上,J/ψ总数的测量精度为4.7%,而BESIII各项性能指标优于BESII,因此人们期望在BESIII上对J/ψ总数的确定有更小的误差。考虑到对J/ψ→μ+μ-的测量精度已经达到了1%以内,同时经过改造后的BESIII,μ子探测器有较大改进,对μ子的探测、分辨能力大幅提高,因而本文通过J/ψ衰变到μ+μ-来确定BESIII上J/ψ事例的总数。基于BESIII的离线软件系统BOSS634版本,详细地研究了事例的选择条件,并进行了最优化选取。蒙特卡罗分析表明,我们的做法能有效地排除本底事例,精确地确定J/ψ事例总数。本方法将会用来确定BESIII上J/ψ总数。
由于在实验上,J/ψ介子通常通过它的两个最大最干净的遍举衰变道J/ψ→e+e-和J/ψ→μ+μ-来作标记,二者的分支比也被用来确定强相互作用的耦合常数αs;并且它们的比例Be/Bμ也用来检验轻子的普适性;另外,J/ψ衰变到轻子对的分支比也是J/ψ粒子的基本参数之一。本文利用BESIII于2008年9月至10月试运行阶段获取的部分ψ(2S)数据,通过ψ(2S)→π+π-J/ψ(J/ψ→anything和J/ψ→μ+μ-)间接地测量J/ψ衰变到μ+μ-的分支比。先通过对事例末态特征的分析和计算,对所需要的挑选条件进行了仔细研究;然后基于BESIII的离线软件系统BOSS641版本,确定事例的挑选条件并进行事例挑选工作;对挑选出来的事例用Roofit作拟合,得到真正的好事例。利用Monte Carlo模拟,得到单举道和遍举道的效率,于是可以计算出J/ψ→μ+μ-的分支比。在拟合的过程中,我们采用双高斯拟合和用遍举道的π+π-反冲质量谱形状去拟合单举道的π+π-反冲质量谱形状的方法,并将二者得到的结果取平均,得到J/ψ→μ+μ-的分支比为5.70%,与PDG给出的值5.93%基本一致。
The BEijing Spectrometer III(BESIII) operating at Beijing Electron Positron Collider II (BEPCII) is a high quality magnetic detector built with modern techniques. It is used to do research on electron positron colliding physics at the energy range of tau-charm. Its main physics goal is to study the electro-weak interaction, strong interaction and search for new physics. BESIII began operating in last summer. It operates well, and gained more than 10 millionψ(2S) data from May to November last year. And it even acquired 60 millionψ(2S) data during March 2009.
J/ψparticle is an important member in charm quark family. It is a primary work to measure the parameters of J/ψparticle. J/ψtotal number is one of the most important parameters, for it is the inevitable parameter to measure the branching ratio of any J/ψdecay. So precise J/ψtotal number measurement is necessary to get a smaller systematic uncertainty. The uncertainty of J/ψtotal number measurement at BESII is 4.7%. Because the BESIII detector is better than BESII in many aspects, a precise J/ψtotal number is expected at BESIII. By 2008, the branching ratio precise of J/ψdecaying toμ+μ- is less than 1%, and BESIII has much better muon detector. In this article, we use J/ψdecaying toμ+μ- to measure the total number of J/ψ. The BESIII offline software system(BOSS) version used is BOSS634. The events selection conditions are studied and optimized in the article. Monte Carlo study shows that our method can exclude background events and can gain precise J/ψtotal number. And it will be used to determine the total number of J/ψfor the coming J/ψdata taking.
J/ψparticle is usually tagged by its two largest and cleanest decaying channels: J/ψ→e+e-, J/ψ→μ+μ-. The branching ratios of the two decaying channels can be used to determine the coupling constant of strong interaction and to check the universal of leptons by Be/Bμ. The branching ratios of leptons are basic parameters. Theψ(2S) data, which acquired by BESIII from September to October, is used in our analysis. The method we used to measure the branching ratio of J/ψ→μ+μ- is to selectψ(2S)→π+π-J/ψ(J/ψ→anything and J/ψ→μ+μ-) events. This method is an indirect way to measure the branching ratio. First, after analysis and calculation of the character of the final particles, proper conditions can be determined to select the events we want. Then, we use our program to select good events and record them based on BOSS641. Finally , we fit the recorded good events with Roofit tool, to exclude background events and get the real events we want, and the selection efficiencies. Double guassian fitting method and fitting theπ+π- recoiling mass spectrum of inclusive process with exclusive process, and each fitting method gives a branching ratio value. We get the final result by averaging the two values. The result is Br(J/ψ→μ+μ-)=5.70%, which agrees the PDG value 5.93% on the whole.
引文
[1]章乃森.粒子物理学上册[M].北京:科学出版社, 1986:5-78,328-343.
[2]章乃森.粒子物理学下册[M].北京:科学出版社, 1987:229-301.
[3]柳继锋.粒子物理[M].桂林:广西师范大学,2002:1-28,102-125.
[4]中国高能物理研究所.北京谱仪正负电子物理[M].南宁:广西科学技术出版社,1998:16-53,132-214.
[5]唐孝威等.正负电子物理[M].北京:科学出版社,1995:208-188.
[6]Particle Data Group.Review of Particle Physics[J].Physics Letters B,2008,667(1-5):1-1340.
[7]谢一冈等.粒子探测器与数据获取[M].北京:科学出版社,2003:5-362.
[8]唐孝威等.粒子物理实验方法[M].北京:人民教育出版社,1982:7-230.
[9]复旦大学、清华大学、北京大学合编.原子核物理实验方法[M].1997:69-189.
[10]赵天池.传感器和探测器的物理原理和应用[M] .北京:科学出版社,2008:520-587.
[11] L. K o&&pke and N.Wermes. J /ψDecay[R].Switzerland: CERN,1989.
[12] Zhu Kejun.Status of BESIII data taking[R].Beijing: BESIII Collaboration,2009.
[13] BEPC工程办. BEPCII/BESIII获取3000万ψ′事例[EB].:北京正负电子对撞机重大改造工程主页,2009-3-20.
[14]李晓玲. J /ψ→KS0K±πm过程的分波振幅分析[D].北京:中国科学院高能物理研究所,2007.
[1] BEPC工程办. BEPCII/BESIII工程介绍[EB].:北京正负电子对撞机重大改造工程主页.工程概况.
[2] BEPC工程办. BEPCII/BESIII工程方案[EB].:北京正负电子对撞机重大改造工程主页.工程方案.
[3] BEPC工程办. BEPCII/BESIII获取3000万 事例[EB].:北京正负电子对撞机重大改造工程主页.
[4]北京正负电子对撞机重大改造工程BEPCII初步设计报告?? BESIII探测器, 2003年11月, 62-65, 84-85, 127-133, 130-150, 178-187, 193-197.
[5]邓子艳.BESIII探测器模拟软件的设计和开发[D].北京:中国科学院高能物理研究所,2006.
[6] BEPC工程办.BEPCII再传捷报,对撞亮度迈上2×1032cm-2s-1台阶[EB].:北京正负电子对撞机重大改造工程主页.
[7] Zhu Kejun.Status of BESIII data taking[R].Beijing: BESIII Collaboration,2009.
[8] Dong Mingyi. Status of MDC[R].Beijing: BESIII Collaboration,2009.
[9] Heng Yuekun. TOF status[R].Beijing: BESIII Collaboration,2009.
[10] Fang Jian. Status of EMC[R].Beijing: BESIII Collaboration,2009.
[11] Zhang Jiawen. Status of Muon chamber[R].Beijing: BESIII Collaboration,2009.
[1]房双世,陈海璇等.用四叉事例样本确定J/ψ事例总数[J].高能物理与核物理,2003, 27(4):277-281.
[2]房双世.J/ψ衰变中赝标量介子混合的研究[D].北京:中国科学院高能物理研究所,2003年.
[3]衡月昆.博士后出站报告[R].北京:中国科学院高能物理研究所,2001.
[4] Particle Data Group.Review of Particle Physics[J].Physics Letters B,2008,667(1-5):1-1340.
[5] MO Xiao-Hu et al. Determination ofψ(2S) Total number by Inclusive Hadron Decay[J]. High Energy Physics and Nuclear Physics, 2004, 28(5):455-462.
[6] CHI Shao-Peng et al. Measurement of the Integrated Luminosity at s =3.650, 3.686 GeV for the BES Detector[J].High Energy Physics and Nuclear Physics, 2004,28(11):1135-1140.
[7]黄光顺等.北京谱仪积分亮度的测量方法[J].高能物理与核物理,2000, 24(5):373-378.
[8] YU Zhong-Qiang et al. Determination of Total Number of the Fourth set J/ψ.[R]. Beijing: IHEP, BES internal report, 1993.
[9] BES Collaboration, arXiv:0709. 3371v1 [hep-ex] 21 Sep 2007.
[10] Kuang-Ta Chao and Yifang Wang, Physics at BES-III[M].Beijing, IHEP, 2008.9-20.
[11] Wang Zhi-yong, Determination of BESIII Offline Integral Luminosity[R].Beijing, BESIII Collaboration meeting July, 2008.
[1]Particle Data Group.Review of Particle Physics[J].Physics Letters B,2008,667(1-5):1-1340.
[2]CLEO Collaboration. Measurement of the branching fraction for J/ψ→l+l-[J]. Physics Review D,2005,71:111103-1-111103-5.
[3]BES Collaboration. Determination of J/ψleptonic branching fraction viaψ→π+π-J/ψ[J].Physics Review D (1998)58:092006-1-092006-5.
[4]MarkIII Collaboration. Direct Measurement of the J/ψLeptonic Branching Fraction[J].Physics Review Letters,1992,68:282-285.
[5]中国高能物理研究所.北京谱仪正负电子物理[M].南宁:广西科学技术出版社,1998:16-53,132-214.
[6]Zhu Kejun.Status of BESIII data taking[R].Beijing: BESIII Collaboration,2009.
[7]Dong Mingyi. Status of MDC[R].Beijing: BESIII Collaboration,2009.
[8]Heng Yuekun. TOF status[R].Beijing: BESIII Collaboration,2009.
[9]Fang Jian. Status of EMC[R].Beijing: BESIII Collaboration,2009.
[10] Zhang Jiawen. Status of Muon chamber[R].Beijing: BESIII Collaboration,2009.
[1]Particle Data Group.Review of Particle Physics[J].Physics Letters B,2008,667(1-5):1-1340.
[2]CLEO Collaboration. Measurement of the branching fraction for J/ψ→l+l-[J]. Physics Review D,2005,71:111103-1-111103-5.
[2]章乃森.粒子物理学下册[M].北京:科学出版社, 1987:229-301.
[3]柳继锋.粒子物理[M].桂林:广西师范大学,2002:1-28,102-125.
[4]中国高能物理研究所.北京谱仪正负电子物理[M].南宁:广西科学技术出版社,1998:16-53,132-214.
[5]唐孝威等.正负电子物理[M].北京:科学出版社,1995:208-188.
[6]Particle Data Group.Review of Particle Physics[J].Physics Letters B,2008,667(1-5):1-1340.
[7]谢一冈等.粒子探测器与数据获取[M].北京:科学出版社,2003:5-362.
[8]唐孝威等.粒子物理实验方法[M].北京:人民教育出版社,1982:7-230.
[9]复旦大学、清华大学、北京大学合编.原子核物理实验方法[M].1997:69-189.
[10]赵天池.传感器和探测器的物理原理和应用[M] .北京:科学出版社,2008:520-587.
[11] L. K o&&pke and N.Wermes. J /ψDecay[R].Switzerland: CERN,1989.
[12] Zhu Kejun.Status of BESIII data taking[R].Beijing: BESIII Collaboration,2009.
[13] BEPC工程办. BEPCII/BESIII获取3000万ψ′事例[EB].:北京正负电子对撞机重大改造工程主页,2009-3-20.
[14]李晓玲. J /ψ→KS0K±πm过程的分波振幅分析[D].北京:中国科学院高能物理研究所,2007.
[1] BEPC工程办. BEPCII/BESIII工程介绍[EB].:北京正负电子对撞机重大改造工程主页.工程概况.
[2] BEPC工程办. BEPCII/BESIII工程方案[EB].:北京正负电子对撞机重大改造工程主页.工程方案.
[3] BEPC工程办. BEPCII/BESIII获取3000万 事例[EB].:北京正负电子对撞机重大改造工程主页.
[4]北京正负电子对撞机重大改造工程BEPCII初步设计报告?? BESIII探测器, 2003年11月, 62-65, 84-85, 127-133, 130-150, 178-187, 193-197.
[5]邓子艳.BESIII探测器模拟软件的设计和开发[D].北京:中国科学院高能物理研究所,2006.
[6] BEPC工程办.BEPCII再传捷报,对撞亮度迈上2×1032cm-2s-1台阶[EB].:北京正负电子对撞机重大改造工程主页.
[7] Zhu Kejun.Status of BESIII data taking[R].Beijing: BESIII Collaboration,2009.
[8] Dong Mingyi. Status of MDC[R].Beijing: BESIII Collaboration,2009.
[9] Heng Yuekun. TOF status[R].Beijing: BESIII Collaboration,2009.
[10] Fang Jian. Status of EMC[R].Beijing: BESIII Collaboration,2009.
[11] Zhang Jiawen. Status of Muon chamber[R].Beijing: BESIII Collaboration,2009.
[1]房双世,陈海璇等.用四叉事例样本确定J/ψ事例总数[J].高能物理与核物理,2003, 27(4):277-281.
[2]房双世.J/ψ衰变中赝标量介子混合的研究[D].北京:中国科学院高能物理研究所,2003年.
[3]衡月昆.博士后出站报告[R].北京:中国科学院高能物理研究所,2001.
[4] Particle Data Group.Review of Particle Physics[J].Physics Letters B,2008,667(1-5):1-1340.
[5] MO Xiao-Hu et al. Determination ofψ(2S) Total number by Inclusive Hadron Decay[J]. High Energy Physics and Nuclear Physics, 2004, 28(5):455-462.
[6] CHI Shao-Peng et al. Measurement of the Integrated Luminosity at s =3.650, 3.686 GeV for the BES Detector[J].High Energy Physics and Nuclear Physics, 2004,28(11):1135-1140.
[7]黄光顺等.北京谱仪积分亮度的测量方法[J].高能物理与核物理,2000, 24(5):373-378.
[8] YU Zhong-Qiang et al. Determination of Total Number of the Fourth set J/ψ.[R]. Beijing: IHEP, BES internal report, 1993.
[9] BES Collaboration, arXiv:0709. 3371v1 [hep-ex] 21 Sep 2007.
[10] Kuang-Ta Chao and Yifang Wang, Physics at BES-III[M].Beijing, IHEP, 2008.9-20.
[11] Wang Zhi-yong, Determination of BESIII Offline Integral Luminosity[R].Beijing, BESIII Collaboration meeting July, 2008.
[1]Particle Data Group.Review of Particle Physics[J].Physics Letters B,2008,667(1-5):1-1340.
[2]CLEO Collaboration. Measurement of the branching fraction for J/ψ→l+l-[J]. Physics Review D,2005,71:111103-1-111103-5.
[3]BES Collaboration. Determination of J/ψleptonic branching fraction viaψ→π+π-J/ψ[J].Physics Review D (1998)58:092006-1-092006-5.
[4]MarkIII Collaboration. Direct Measurement of the J/ψLeptonic Branching Fraction[J].Physics Review Letters,1992,68:282-285.
[5]中国高能物理研究所.北京谱仪正负电子物理[M].南宁:广西科学技术出版社,1998:16-53,132-214.
[6]Zhu Kejun.Status of BESIII data taking[R].Beijing: BESIII Collaboration,2009.
[7]Dong Mingyi. Status of MDC[R].Beijing: BESIII Collaboration,2009.
[8]Heng Yuekun. TOF status[R].Beijing: BESIII Collaboration,2009.
[9]Fang Jian. Status of EMC[R].Beijing: BESIII Collaboration,2009.
[10] Zhang Jiawen. Status of Muon chamber[R].Beijing: BESIII Collaboration,2009.
[1]Particle Data Group.Review of Particle Physics[J].Physics Letters B,2008,667(1-5):1-1340.
[2]CLEO Collaboration. Measurement of the branching fraction for J/ψ→l+l-[J]. Physics Review D,2005,71:111103-1-111103-5.