We review the present status of the Standard Model calculation of the anomalous magnetic moment of the muon. This is performed in a perturbative expansion in the fine-structure constant α and is ...broken down into pure QED, electroweak, and hadronic contributions. The pure QED contribution is by far the largest and has been evaluated up to and including O(α5) with negligible numerical uncertainty. The electroweak contribution is suppressed by (mμ∕MW)2 and only shows up at the level of the seventh significant digit. It has been evaluated up to two loops and is known to better than one percent. Hadronic contributions are the most difficult to calculate and are responsible for almost all of the theoretical uncertainty. The leading hadronic contribution appears at O(α2) and is due to hadronic vacuum polarization, whereas at O(α3) the hadronic light-by-light scattering contribution appears. Given the low characteristic scale of this observable, these contributions have to be calculated with nonperturbative methods, in particular, dispersion relations and the lattice approach to QCD. The largest part of this review is dedicated to a detailed account of recent efforts to improve the calculation of these two contributions with either a data-driven, dispersive approach, or a first-principle, lattice-QCD approach. The final result reads aμSM=116591810(43)×10−11 and is smaller than the Brookhaven measurement by 3.7σ. The experimental uncertainty will soon be reduced by up to a factor four by the new experiment currently running at Fermilab, and also by the future J-PARC experiment. This and the prospects to further reduce the theoretical uncertainty in the near future – which are also discussed here – make this quantity one of the most promising places to look for evidence of new physics.
The beam energy measurement system for the VEPP-2000 electron-positron collider is described. The method of Compton backscattering of CO laser photons on the electron beam is used. The relative ...systematic uncertainty of the beam energy determination is estimated as 610 super(-5). It was obtained through comparison of the results of the beam energy measurements using the Compton backscattering and resonance depolarization methods.
A
bstract
The cross section of the process
e
+
e
−
→
π
+
π
−
has been measured in the Spherical Neutral Detector (SND) experiment at the VEPP-2000
e
+
e
−
collider VEPP-2000 in the energy region 525
...<
s
<
883 MeV. The measurement is based on data with an integrated luminosity of about 4.6 pb
−
1
. The systematic uncertainty of the cross section determination is 0.8% at
s
>
0
.
600 GeV. The
ρ
meson parameters are obtained as
m
ρ
= 775
.
3 ± 0
.
5 ± 0
.
6 MeV, Γ
ρ
= 145
.
6 ± 0
.
6 ± 0
.
8 MeV,
B
ρ
→
e
+
e−
×
B
ρ
→
π
+
π−
= (4
.
89 ± 0
.
02 ± 0
.
04) × 10
−
5
, and the parameters of the
e
+
e
−
→
ω
→
π
+
π
−
process, suppressed by
G
-parity, as
B
ω
→
e
+
e−
×
B
ω
→
π
+
π−
= (1
.
32 ± 0
.
06 ± 0
.
02) × 10
−
6
and and
ϕ
ρω
= 110
.
7 ± 1
.
5 ± 1
.
0 degrees.
Future Physics Programme of BESIII Ahmed, S.; Amoroso, A.; Bennett, J. V. ...
Chinese physics C,
04/2020, Volume:
44, Issue:
4
Journal Article
Peer reviewed
Open access
Abstract
There has recently been a dramatic renewal of interest in hadron spectroscopy and charm physics. This renaissance has been driven in part by the discovery of a plethora of charmonium-like
...XYZ
states at BESIII and
B
factories, and the observation of an intriguing proton-antiproton threshold enhancement and the possibly related
X
(1835) meson state at BESIII, as well as the threshold measurements of charm mesons and charm baryons.
We present a detailed survey of the important topics in tau-charm physics and hadron physics that can be further explored at BESIII during the remaining operation period of BEPCII. This survey will help in the optimization of the data-taking plan over the coming years, and provides physics motivation for the possible upgrade of BEPCII to higher luminosity.
Measurements of the center-of-mass energies at BESIII via the di-muon process 麦迪娜 M. N. Achasov X. C. Ai O. Albayrak M. Albrecht D. J. Ambrose A. Amoroso 安芬芬 安琪 白景芝 R. Baldini Ferroli 班勇 D. W. Bennett J. V. Bennett M. Bertani D. Bettoni 边渐鸣 F. Bianchi E. Boger I. Boyko R. A. Briere 蔡浩 蔡啸 O. Cakir A. Calcaterra 曹国富 S. A. Cetin 常劲帆 G. Chelkov 陈刚 陈和生 陈海云 陈江川 陈玛丽 陈申见 谌炫 陈旭荣 陈元柏 程和平 褚新坤 G. Cibinetto 代洪亮 代建平 A. D beyssi D. Dedovich 邓子艳 A. Denig I. Denysenko M Destefanis F. De Mori 丁勇 董超 董静 董燎原 董明义 杜书先 段鹏飞 范荆州 方建 房双世 方馨 方易 L. Fava F. Feldbauer G. Felici 封常青 E. Fioravanti M. Fritsch 傅成栋 高清 高鑫磊 高旭阳 高原宁 高榛 I. Garzia K. Goetzen 龚文煊 W. Gradl M. Greco 顾旻皓 顾运厅 管颖慧 郭爱强 郭立波 郭玥 郭玉萍 Z. Haddadi A. Hafner 韩爽 郝喜庆 F. A. Harris 何康林 T. Held 衡月昆 侯治龙 胡琛 胡海明 胡继峰 胡涛 胡誉 黄光明 黄光顺 黄金书 黄性涛 黄勇 T. Hussain 纪全 姬清平 季晓斌 季筱璐 姜鲁文 江晓山 蒋兴雨 焦健斌 焦铮 金大鹏 金山 T. Johansson A. Julin N. Kalantar-Nayestanaki 康晓琳 康晓珅 M. Kavatsyuk B. C. Ke P.Kiese R. Kliemt B. Kloss O. B. Kolcu B. Kopf M. Kornicer W. Kuhn A. Kupsc J. S. Lange M. Lara P. Larin C. Leng 李翠 李澄 李德民 李飞 李峰云 李刚 李海波 李家才 李瑾 李康 李科 李蕾 李培荣 李腾 李卫东 李卫国 李晓玲 李小梅 李小男 李学潜 李志兵 梁昊 梁勇飞 梁羽铁 廖广睿 D. X. Lin 刘北江 刘春秀 刘栋 刘福虎 刘芳 刘峰 刘宏邦 刘欢欢 刘汇慧 刘怀民 刘杰 刘建北 刘觉平 刘晶译 刘凯 刘魁勇 刘兰雕 刘佩莲 刘倩 刘树彬 刘翔 刘玉斌 刘振安 刘智清 H. Loehner 娄辛丑 吕海江 吕军光 卢宇 卢云鹏 罗成林 罗民兴 T. Luo 罗小兰 吕晓睿 马凤才 马海龙 马连良 马秋梅 马天 马旭宁 马骁妍 F. E. Maas M. Maggiora 冒亚军 毛泽普 S. Marcello J. G. Messchendorp 闵建 R. E. Mitchell 莫晓虎 莫玉俊 C. Morales Morales K. Moriya N. Yu. Muchnoi H. Muramatsu y. Nefedov F. Nerling I. B. Nikolaev 宁哲 S．Nisar 牛顺利 牛讯伊 马鹏 欧阳群 S. Pacetti 潘越 P．Patteri M. Pelizaeus 彭海平 K．Peters J. Pettersson 平加伦 平荣刚 R. Poling V. Prasad 祁鸣 钱森 乔从丰 秦丽清 覃拈 秦小帅 秦中华 邱进发 K. H. Rashid C. F. Redmer M. Ripka 荣刚 Ch. Rosner 阮向东 V. Santoro A. Sarantsev M. Savrie K. Schoennin S. Schumann 单葳 邵明 沈成平 沈培迅 沈肖雁 盛华义 宋维民 宋欣颖 S. Sosio S. Spataro 孙功星 孙俊峰 孙胜森 孙勇杰 孙永昭 孙志嘉 孙振田 唐昌建 唐晓 I. Tapan E. H. Thorndike M. Tiemens M. Ullrich I. Uman G. S. Varner 王斌 王东 王大勇 王科 王亮亮 王灵淑 王萌 王平 王佩良 王思广 王炜 王维平 王雄飞 王雅迪 王贻芳 王亚乾 王铮 王志刚 王志宏 王至勇 T. Weber 魏代会 韦江波 P. Weidenkaff 文硕频 U. Wiedner M. Wolke 伍灵慧 吴智 夏磊 夏力钢 夏宇18 肖栋 肖浩 肖振军 谢宇广 修青磊 许国发 徐雷 徐庆君 徐新平 严亮 鄢文标 闫文成 颜永红 杨海军 杨洪勋 杨柳 杨迎 杨永栩 叶梅 叶铭汉 殷俊昊 俞伯祥 喻纯旭 俞浩晟 苑长征 袁文龙 袁野 A. Yuncu A. A. Zafar A.Zallo 曾云 曾哲 张丙新 张炳云 张弛29 张长春 张达华 张宏浩 章红宇 张佳佳 张杰磊 张敬庆 张家文 张建勇 张景芝 张坤 张磊 张学尧 张瑶 张宇宁 张银鸿 张亚腾 张宇 张正好 张子平 张振宇 赵光 赵京伟 赵静宜 赵京周 赵雷 赵玲 赵明刚 赵强 赵庆旺 赵书俊 赵天玲 赵天池 赵豫斌 赵政国 A. Zhemchugov 郑波 郑建平 郑文静 郑阳恒 钟彬 周莉 周详 周晓康 周小蓉 周注玉 朱凯 朱科军 朱帅 朱世海 朱相雷 朱莹春 朱永生 朱自安 庄建 L．Zotti 邹冰松 邹佳恒
Chinese physics C,
06/2016, Volume:
40, Issue:
6
Journal Article
Peer reviewed
Open access
From 2011 to 2014, the BESIII experiment collected about 5 fb^-1 data at center-of-mass energies around 4 GeV for the studies of the charmonium-like and higher excited charmonium states. By analyzing ...the di-muon process e＋e- →yma/Fsμ^＋μ^-, the center-of-mass energies of the data samples are measured with a precision of 0.8 MeV. The center-of-mass energy is found to be stable for most of the time during data taking.
The process
e
+
e
-
→
η
η
γ
is studied in the center-of-mass energy range 1.17–2.00 GeV using data with an integrated luminosity of 201 pb
-
1
collected by the SND detector at the VEPP-2000
e
+
e
-
...collider. The
e
+
e
-
→
η
η
γ
cross section is measured for the first time. It is shown that the dominant mechanism of this reaction is the transition through the
ϕ
η
intermediate state. Our result on the
e
+
e
-
→
η
η
γ
cross section is consistent with the
e
+
e
-
→
ϕ
η
measurement in the
ϕ
→
K
+
K
-
mode. The search for radiative processes contributing to the
e
+
e
-
→
η
η
γ
cross section is performed, and no significant signal is observed.
The process
e
+
e
-
→
n
n
¯
is studied in the experiment at the VEPP-2000
e
+
e
-
collider with the SND detector. The technique of the time measurements in the multichannel NaI(Tl) electromagnetic ...calorimeter is used to select
n
n
¯
events. The value of the measured cross section in the center-of-mass energy range from 1.894 to 2 GeV varies from 0.5 to 0.35 nb. The effective neutron timelike form factor is derived from the measured cross section and compared with the proton form factor. The ratio of the neutron electric and magnetic form factors is obtained from the analysis of the antineutron polar angle distribution and found to be consistent with unity.
The SND is a non-magnetic detector deployed at the VEPP-2000
e
+
e
−
collider (BINP, Novosibirsk) for hadronic cross-section measurements in the center of mass energy range below 2 GeV. The important ...part of the detector is a hodoscopic electromagnetic calorimeter (EMC) with three layers of NaI(Tl) counters. EMC signal shaping and digitizing electronics based on FADC allow us to obtain both the energy deposition and the signal arrival time. We demonstrate how EMC time is applied to detect background pileup and cosmic events.
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