中国高能物理学会第十届全国粒子物理学术会议, 南京 Observation of X(1835) in 房双世 “ 晨光杯 ” 论文报告

Outline  Introduction  Event Selection  Background Study  Results  Summary and Discussion

 A narrow enhancement is observed in. Assuming that the system is in an S-wave resulted in a resonance mass of MeV and a total width of MeV. M=1859 MeV/c 2  < 30 MeV/c 2 (90% CL)  10  25 M(pp)-2m p (GeV) Introduction

 It can be interpreted as a ppbar bound state. In such a case, it is desirable to observe such a state in other decay modes.  Many possible decay modes suggested in C. S. Cao and S.L. Zhu Commun. Theory. Phys. 42, 844(2004) C. J. Ding and M. L. Yan, Phys. Rev. C72(2005)  One possible decay modes, never studied before at BES easy to tag using

 Charged tracks 4 good charged tracks with |cos  |<0.8 in MDC; The total charge is required to be 0; PID: at least three of them are identified as pions with TOF and dE/Dx ;  Photon selection Energy deposited in BSC greater than 60 MeV Isolated from charged tracks by more than 5 o N  =3 for N  =2 for Event Selection

   used to improve the mass resolution  Event Selection for

Analysis of X(1835)

Event Selection for        

Analysis of X(1835)

 mass-sideband events  Main background,  60M decays by LUND model  Check efficiency curve  phase space Background Study

Bkg. study for LUND MC  sidebands data

Bkg. Study for Phase space events Efficiency curve MC

Bkg. Study for LUND MC  sidebands data

Bkg. Study for Efficiency curve Phase space events MC

Observation of X(1835) in The sum  +  -  mass spectrum for  decaying into  +  -  and  

Mass spectrum fitting 5.1  The  +  -  mass spectrum for

Mass spectrum fitting 6.0  The  +  -  mass spectrum for

Mass spectrum fitting 7.7  The sum  +  -  mass spectrum for  decaying into  +  -  and  

 Mass and width from m=  8.1MeV/c 2,  =54.2  34.5MeV/c 2  Mass and width from m=  7.9MeV/c 2,  =70.3  23.1MeV/c 2  The sum of mass spectrum for two decay modes m=  6.1  2.7MeV/c 2,  =67.7  20.3  7.7MeV/c 2   The sum of mass spectrum for two decay modes  The mass, width and branching fractions obtained from two different decay modes are consistent with each other. Results of mass spectrum fitting

Paper published in Phys. Rev. Lett. 95,262001(2005) (Received 11 August 2005; published 28 December 2005) SPIRES-HEP search ( ) 39 times cited

首次在以我国科学家为主 进行的北京谱仪实验中发 现新粒子。国际权威《粒 子数据手册》 PDG2006 首 次收录以中国科学家为主 发现的新粒子 X(1835) 等。 强烈反响和广泛的认同 (I)  《粒子数据手册》在 2006 年版的 “ 非常规介子 ” 综合 评述部分，因 BES 实验的 新发现而首次加入有关 “ 质 子－反质子束缚态 ” 的评述。

强烈反响和广泛的认同 (II) 在国内， “ 北京电子对撞机上发现 X1835 新粒子 ” 被评 为 –“2006 年度中国基础研究十大新闻 ” 第一名 –“2006 年度国内十大科技新闻 ” 第二名。

Summary and Discussion  A new resonance X(1835) observed in  The mass, width and branching fractions obtained from  two different decay modes are consistent with each other.  X(1835) could be the same structure as ppbar mass threshold enhancement.  It could be a ppbar bound state since it dominantly decays to ppbar when its mass is above ppbar mass threshold.  Its spin-parity should be 0 -+ : this would be an important test.  PDG2006 takes it as a possible ppbar bound state.

Fit to J/   pp including FSI Include FSI curve from A.Sirbirtsev et al.(hep-ph/ ) in the fit (I=0) M =  6.7 MeV  = 0  93 MeV In good agreement with X(1835)

Summary and Discussion  Other interpretations are not excluded.  Glueball? N. Kochelev, D. P. Min Phys. Lett. B633:283(2006); B.A. Li, Phys. Rev. D74:034019(2006); C. F. Qiao Phys. Lett. B642:53(2006)   radial excitation ? T. Huang S. L. Zhu Phys. Rev D73:014023(2006)

Determination of its I G J PC helps us to understand this resonance Confirmation of X(1835) in other decay modes needed With 100 times high quality data, may BESIII issue a new “birth certificate” for X(1835) soon ! Summary and Discussion

谢 谢谢 谢

Back up

BCK subtracted PS corrected

BCK subtracted PS corrected

Photon angular distributions in For Data – it is not inconsistent with statistics is too low. X(1835) region X(1835) sideband Sideband Subtracted & Eff. corrected