BESⅢ上χ_（cJ）→BB-bar（B∈∧，∑~0，∑~+）分支比的测量
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摘要
粲偶素(Charmonium)是由一对cc夸克通过强相互作用组成的束缚态。自从1974年实验上发现了粲偶素家族的第一个粒子J//ψ以来,许多粲偶素家族成员被相继发现,如ψ(2S),ψ(3S)和ψ(4S)等,其中ψ(2S)是DD质量阂以下的质量最重的粲偶素态,它可以辐射衰变到电荷共轭宇称为正的ηc(1S),ηc(2S),χc0,1,2等粲偶素态。
作为粲偶素家族成员之一的XcJ介子,对研究螺旋度(HSR)破坏和色八重态(COM)理论有着重要的意义。根据早期的量子色动力学(QCD)理论可知,螺旋度规则禁止Xc0介子衰变到重子对(pp,AA,Σ0Σ0,Σ-Σ-,(?)0(?)0,(?)-(?)+),但是目前的测量结果证明了它们的衰变分支比并没有消失。然而由于这些测量结果统计量的不足,导致了对X。0介子衰变到重子对分支比测量的精确度不是太高,甚至许多的衰变道还没被观测到。所以为了很好的理解螺旋度规则破缺理论和色八重态理论,本文利用工作在BEPCII上的BESIII收集的106M的ψ(2S)事例样本,大约是CLEO-c的4倍左右,详细地研究了XcJ(J=0,1,2)介子到BB(B=A,∑0,∑+)的衰变,测得它们的分支比分别为Br(Xe0→AA)=(33.3土2.0土2.6)×10-5, Br(Xe1→AA)=(12.2土1.1土1.1)×10-5, Br(Xe2→AA)=(20.8土1.6土2.2)×10-5, Br(Xe0→∑0Σ0)=(47.8土3.4土3.8)×10-5, Br(Xe1→∑0Σ0)=(3.8土1.0土0.5)×10-5, Br(Xe2→∑0Σ0)=(4.0土1.1土0.4)×10-5, Br(Xe0→∑十∑-)=(45.4土4.2土2.5)×10-5, Br(Xe1→∑+∑-)=(5.4土1.5土0.4)×10-5, Br(Xe2→∑+∑-)=(4.9土1.9土0.6)×10-5.
与以前的测量结果相比较,BESIII的测量精度有显著的提高,并且第一次提供了χc1,2到∑0Σ0,Σ+Σ-衰变的证据,它们的信号显著性分别为4.3σ,4.6σ,4.4σ和3.0σ,而且我们也利用Bayesian方法估计了它们在90%置信度下的上限,分别为Br(Xe1→∑0Σ0)<6.1×10-5, Br(Xe2→∑0Σ0)<6.4×10-5, Br(Xe1→∑-∑-)<8.5×10-5, Br(Xe2→∑-∑-)<8.6×10-5。
Charmonium is the Pairs of cc quark bound state formed by strong interaction.The first mem-ber of charmonium family,J/(?) particle,was discovered in1974.Subsequently,so many charmo-nium states were discovered,such as (?)(2S),(?)(3S),(?)(4S),etc,where,(?)(2S)state is the heaviest charmonium state under the DD mass threshold,and it can radiatively decay to positive charge-conjugation parity charmonium state,such as ηc(1s), ηc(2s),XcJ(J=0,1,2).
As one important member of charmonium states,XcJ(J=0,1,2)meson,it is essential and important to study the Violation of Helicity Selection Rule(HSR)and the Color Octet Mechanism (COM).According to the earlier theories of QCD,HSR prohibits XcO meson from decaying into the pairs of baryon-antibaryon(pp,AA,∑0∑0.,∑+∑-,Ξ0Ξ0,Ξ-Ξ+),but the observation of XcJ,decaying into baryon anti-baryon pairs indicates that those branching ratios did not vanish.However,the statistic of previous measurements are very low so that the precision of measured branching ratios for XcJ,decays in the previous measurements by other collaborations is not high and even so far many decay channels haven't been observed.Therefore,using the106×106(?)(2s)events collected by BESIII detector at BEPCII,which is about4times of the CLEO-c data sample,the XcJ(J0,1,2)meson decaying into BB(B=A,∑0,∑+)in this article have been studied in detail to further understand and test HSR and COM.And the corresponding branching ratios are measured to be Br(Xc0→AA)=(33.3土2.0土2.6)×105, Br(Xc1→AA)=(12.2土1.1土1.1)×105, Br(Xc2→AA)=(20.8土1.6土2.2)×10-5, Br(Xc0→∑0∑0)=(47.8土3.4土3.8)×105, Br(Xc1→∑0∑0)=(3.8土1.0土0.5)×10-5, Br(Xc2→∑0∑0)=(4.0土1.1土0.4)×105, Br(Xc0→∑-∑+)=(45.4土4.2土2.5)×10-5, Br(Xc1→∑-∑+)=(5.4土1.5土0.4)×10-5, Br(Xc3→∑∑1)=(4.9土1.9土0.6)×105.
The BESIII's measurements further improve the Precision of the those decays by comparing with the previous works,and meanwhile we firstly provide the evidence for Xcl,2decays into∑0∑0,∑-∑-with the significance of4.3σ,4.6σ,4.4σand3.0σ.For the decays with more than3σ, we also present their upper limits at90%confidence level by using Bayesian method to be Br(Xc1→Σ0Σ0)<6.1×10-5, Br(Xc2→Σ0Σ0)<6.4×105, Br(Xc1→Σ-Σ+)<8.5×10-5, Br(Xc1→Σ-Σ+)<8.6×10-5.
作为粲偶素家族成员之一的XcJ介子,对研究螺旋度(HSR)破坏和色八重态(COM)理论有着重要的意义。根据早期的量子色动力学(QCD)理论可知,螺旋度规则禁止Xc0介子衰变到重子对(pp,AA,Σ0Σ0,Σ-Σ-,(?)0(?)0,(?)-(?)+),但是目前的测量结果证明了它们的衰变分支比并没有消失。然而由于这些测量结果统计量的不足,导致了对X。0介子衰变到重子对分支比测量的精确度不是太高,甚至许多的衰变道还没被观测到。所以为了很好的理解螺旋度规则破缺理论和色八重态理论,本文利用工作在BEPCII上的BESIII收集的106M的ψ(2S)事例样本,大约是CLEO-c的4倍左右,详细地研究了XcJ(J=0,1,2)介子到BB(B=A,∑0,∑+)的衰变,测得它们的分支比分别为Br(Xe0→AA)=(33.3土2.0土2.6)×10-5, Br(Xe1→AA)=(12.2土1.1土1.1)×10-5, Br(Xe2→AA)=(20.8土1.6土2.2)×10-5, Br(Xe0→∑0Σ0)=(47.8土3.4土3.8)×10-5, Br(Xe1→∑0Σ0)=(3.8土1.0土0.5)×10-5, Br(Xe2→∑0Σ0)=(4.0土1.1土0.4)×10-5, Br(Xe0→∑十∑-)=(45.4土4.2土2.5)×10-5, Br(Xe1→∑+∑-)=(5.4土1.5土0.4)×10-5, Br(Xe2→∑+∑-)=(4.9土1.9土0.6)×10-5.
与以前的测量结果相比较,BESIII的测量精度有显著的提高,并且第一次提供了χc1,2到∑0Σ0,Σ+Σ-衰变的证据,它们的信号显著性分别为4.3σ,4.6σ,4.4σ和3.0σ,而且我们也利用Bayesian方法估计了它们在90%置信度下的上限,分别为Br(Xe1→∑0Σ0)<6.1×10-5, Br(Xe2→∑0Σ0)<6.4×10-5, Br(Xe1→∑-∑-)<8.5×10-5, Br(Xe2→∑-∑-)<8.6×10-5。
Charmonium is the Pairs of cc quark bound state formed by strong interaction.The first mem-ber of charmonium family,J/(?) particle,was discovered in1974.Subsequently,so many charmo-nium states were discovered,such as (?)(2S),(?)(3S),(?)(4S),etc,where,(?)(2S)state is the heaviest charmonium state under the DD mass threshold,and it can radiatively decay to positive charge-conjugation parity charmonium state,such as ηc(1s), ηc(2s),XcJ(J=0,1,2).
As one important member of charmonium states,XcJ(J=0,1,2)meson,it is essential and important to study the Violation of Helicity Selection Rule(HSR)and the Color Octet Mechanism (COM).According to the earlier theories of QCD,HSR prohibits XcO meson from decaying into the pairs of baryon-antibaryon(pp,AA,∑0∑0.,∑+∑-,Ξ0Ξ0,Ξ-Ξ+),but the observation of XcJ,decaying into baryon anti-baryon pairs indicates that those branching ratios did not vanish.However,the statistic of previous measurements are very low so that the precision of measured branching ratios for XcJ,decays in the previous measurements by other collaborations is not high and even so far many decay channels haven't been observed.Therefore,using the106×106(?)(2s)events collected by BESIII detector at BEPCII,which is about4times of the CLEO-c data sample,the XcJ(J0,1,2)meson decaying into BB(B=A,∑0,∑+)in this article have been studied in detail to further understand and test HSR and COM.And the corresponding branching ratios are measured to be Br(Xc0→AA)=(33.3土2.0土2.6)×105, Br(Xc1→AA)=(12.2土1.1土1.1)×105, Br(Xc2→AA)=(20.8土1.6土2.2)×10-5, Br(Xc0→∑0∑0)=(47.8土3.4土3.8)×105, Br(Xc1→∑0∑0)=(3.8土1.0土0.5)×10-5, Br(Xc2→∑0∑0)=(4.0土1.1土0.4)×105, Br(Xc0→∑-∑+)=(45.4土4.2土2.5)×10-5, Br(Xc1→∑-∑+)=(5.4土1.5土0.4)×10-5, Br(Xc3→∑∑1)=(4.9土1.9土0.6)×105.
The BESIII's measurements further improve the Precision of the those decays by comparing with the previous works,and meanwhile we firstly provide the evidence for Xcl,2decays into∑0∑0,∑-∑-with the significance of4.3σ,4.6σ,4.4σand3.0σ.For the decays with more than3σ, we also present their upper limits at90%confidence level by using Bayesian method to be Br(Xc1→Σ0Σ0)<6.1×10-5, Br(Xc2→Σ0Σ0)<6.4×105, Br(Xc1→Σ-Σ+)<8.5×10-5, Br(Xc1→Σ-Σ+)<8.6×10-5.
引文
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[16]J. Z. Bai et al.(BES Collaboration), Study of the hadronic decays of XcJ states [J]. Phys. Rev. D,1999,60(7):072001;
[17]J. Z. Bai et al.(BES Collaboration), Study of the P-wave charmonium state XcJ to (?)(2S) decays [J]. Phys. Rev. Lett.,1998,81(23):3091-3095.
[18]D. M. Asner et al.(CLEO Collaboration), Measurement of exclusive baryon-antibaryon decays of XcJ mesons [J]. Phys. Rev. D,2008,78(3):031101(R).
[19]S. J. Brodsky G. P. Lepage. Helicity selection rules and tests of gluon spin in exclusive QCD processes [J]. Phys. Rev. D,1981,24(11):2848-2855.
[20]Preliminary design report of BEPCII(2003).Linac:IHEP-BEPCII-SB-03-2; Storage ring:IHEPBEPCII-SB-03-3; BESIII detector:IHEPBEPCII-SB-03-4.(in Chinese)(北京正负电子对撞机重大改造工程BEPCII初步设计(2003).直线加速器IHEP-BEPCII-SB-03-2;储存环IHEP-BEPCII-SB-03-3; BESIII探测器IHEP-BEPCII-SB-03-4.
[21]G. Barrand, P. Binko, M. Donszelmann, A. Johnson, A. Pfeiffer. Abstract interfaces for data analysis:Component architecture for data analysis tools [J]. Conf. Proc. C0109031,2001:215-218.
[22]W. D. Li. The offline software for the BESIII experiment, Proceeding of CHEP06[R], Mumbai, India2006.
[23]M. XU et al. Decay vertex reconstruction and3-dimensional lifetime determination at BESIII [J]. Chin Phys. C,2009,33(6):428-435.
[24]王至勇Determination of total number of (?)1events at BESIII [EB/OL]: http://hnbes3.ihep.ac.cn/HyperNews/get/AUX/2011/12/19/08.06-798-npsp. pdf,2012-03-07/2012-3-24.
[25]M. Ablikim et al.(BESIII collabofraction), Measurements of hc(1P1) in (?)1Decays [J]. Phys. Rev. Lett.,2010,104(13):132002.
[26]王雄飞Measurement of XcJ→AA, Σ0Σ0, Σ+Σ-[EB/OL]:http://hnbes3.ihep.ac.cn/HyperNews/get/AUX/2011/12/13/14.09-79220-first_version_reply11.pdf; http://hnbes3.ihep.ac.cn/HyperNews/get/AUX/2012/02/06/20.05-57163-ion_last_questions1.pdf,2012-01-06/2012-3-24.
[27]M. Ablikim et al.(BESIII collabofraction), Branching fraction measurements of Xc0and Xc2to π0π0and ηη [J]. Phys. Rev. D,2010,81(5):052005.
[28]9. Tracking and PID Efficiency [R]. Liaoning University: IHEP&Liaoning University,2010;G R. Summary of data quality check [R]. Liaoning University: IHEP&Liaoning University,2010.
[29] Xiao-Hai Liu, Qiang Zhao. Further study of the helicity selection rule evading mechanism inηc, χcJand hcdecaying to baryon anti-baryon pairs [J]. J. Phys. G G,2011,38(3):035007.
[30] S. M. H. Wong. Color octet contribution in exclusive P-wave charmonium decay into octet anddecuplet baryons [J]. Eur. Phys. J. C,2000,14(4):643-671.
-, Σ
-and ω-production by negative hyperons on nuclei [J] Phys. Rev. D,1974,10(7),2051-2055.[11]G. T. Bodwin, E. Braaten, G. P. Lepage. Rigorous QCD analysis of inclusive annihilation and production of heavy quarkonium [J]. Phys. Rev. D,1995,51(3):1125-1171.[12]M. Ablikim et al.(BES Collaboration), First observations of o(2S) and XcJ(1P) decays to four-body final states h+h-KS0KS0[J]. Phys. Lett. B,2005,630(1-2):21-30.[13]M. Ablikim et al.(BES Collaboration), Partial wave analysis of XcJ→π+π-K-K-)[J]. Phys. Rev. D,2005,72(9):092002.[14]J. Z. Bai et al.(BES Collaboration), Search for neutrino-induced cascades with the AMANDA detector [J]. Phys. Rev. D,2003,67(1):032004;[15]J. Z. Bai et al.(BES Collaboration), First evidence of AA in XcJ decays [J]. Phys. Rev. D,2003,67(11):112001;
[16]J. Z. Bai et al.(BES Collaboration), Study of the hadronic decays of XcJ states [J]. Phys. Rev. D,1999,60(7):072001;
[17]J. Z. Bai et al.(BES Collaboration), Study of the P-wave charmonium state XcJ to (?)(2S) decays [J]. Phys. Rev. Lett.,1998,81(23):3091-3095.
[18]D. M. Asner et al.(CLEO Collaboration), Measurement of exclusive baryon-antibaryon decays of XcJ mesons [J]. Phys. Rev. D,2008,78(3):031101(R).
[19]S. J. Brodsky G. P. Lepage. Helicity selection rules and tests of gluon spin in exclusive QCD processes [J]. Phys. Rev. D,1981,24(11):2848-2855.
[20]Preliminary design report of BEPCII(2003).Linac:IHEP-BEPCII-SB-03-2; Storage ring:IHEPBEPCII-SB-03-3; BESIII detector:IHEPBEPCII-SB-03-4.(in Chinese)(北京正负电子对撞机重大改造工程BEPCII初步设计(2003).直线加速器IHEP-BEPCII-SB-03-2;储存环IHEP-BEPCII-SB-03-3; BESIII探测器IHEP-BEPCII-SB-03-4.
[21]G. Barrand, P. Binko, M. Donszelmann, A. Johnson, A. Pfeiffer. Abstract interfaces for data analysis:Component architecture for data analysis tools [J]. Conf. Proc. C0109031,2001:215-218.
[22]W. D. Li. The offline software for the BESIII experiment, Proceeding of CHEP06[R], Mumbai, India2006.
[23]M. XU et al. Decay vertex reconstruction and3-dimensional lifetime determination at BESIII [J]. Chin Phys. C,2009,33(6):428-435.
[24]王至勇Determination of total number of (?)1events at BESIII [EB/OL]: http://hnbes3.ihep.ac.cn/HyperNews/get/AUX/2011/12/19/08.06-798-npsp. pdf,2012-03-07/2012-3-24.
[25]M. Ablikim et al.(BESIII collabofraction), Measurements of hc(1P1) in (?)1Decays [J]. Phys. Rev. Lett.,2010,104(13):132002.
[26]王雄飞Measurement of XcJ→AA, Σ0Σ0, Σ+Σ-[EB/OL]:http://hnbes3.ihep.ac.cn/HyperNews/get/AUX/2011/12/13/14.09-79220-first_version_reply11.pdf; http://hnbes3.ihep.ac.cn/HyperNews/get/AUX/2012/02/06/20.05-57163-ion_last_questions1.pdf,2012-01-06/2012-3-24.
[27]M. Ablikim et al.(BESIII collabofraction), Branching fraction measurements of Xc0and Xc2to π0π0and ηη [J]. Phys. Rev. D,2010,81(5):052005.
[28]9. Tracking and PID Efficiency [R]. Liaoning University: IHEP&Liaoning University,2010;G R. Summary of data quality check [R]. Liaoning University: IHEP&Liaoning University,2010.
[29] Xiao-Hai Liu, Qiang Zhao. Further study of the helicity selection rule evading mechanism inηc, χcJand hcdecaying to baryon anti-baryon pairs [J]. J. Phys. G G,2011,38(3):035007.
[30] S. M. H. Wong. Color octet contribution in exclusive P-wave charmonium decay into octet anddecuplet baryons [J]. Eur. Phys. J. C,2000,14(4):643-671.