观测Bs0衰变至χc2K+ K-在ϕ质量区域

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"这篇论文是LHCb合作组的研究成果，首次观察到了B\_s0粒子衰变为χc2 K+ K-的模式，并在ϕ（phi）粒子的质量附近的一个窗口内，测量了该衰变相对于χc1衰变模式的分支比。他们发现这个比例大约为17.1% ± 3.1% ± 0.4% ± 0.9%，其中误差分别来自统计、系统性和对辐射性χc衰变分支比的认识。同时，通过B\_s0 → χc1 K+ K-衰变模式，他们还测量了B\_s0粒子的质量，结果为5366.83 MeV/c²，误差分为统计误差和系统误差。" 这篇开放获取的文章详细报告了大型强子对撞机(LHC)的LHCb实验中的一项观测结果。研究者们专注于B\_s0介子的衰变过程，这是一种由一个下夸克和一个反奇异夸克组成的重味粒子。他们首次确认了B\_s0介子可以衰变为一个χc2态的charm夸克对以及两个Kaon（K+ K-）。χc2是charm夸克的一种激发态，属于J/ψ粒子（即ψ（2S））的同类。在研究中，他们在ϕ粒子（一种由Kaon对构成的共振态）的质量附近±15 MeV/c²的窗口内，分析了B\_s0介子衰变为χc2 K+ K-的分支比。通过比较这种衰变与χc1 K+ K-衰变，他们得到了一个相对分支比，这是理解B\_s0介子衰变动力学的关键数据。此外，LHCb合作组利用B\_s0 → χc1 K+ K-衰变模式，精确测量了B\_s0介子的质量，结果为5366.83 MeV/c²，精度达到亚MeV级别。这个测量结果与其他LHCb实验的数据相结合，可以进一步改进对B\_s0粒子质量的全球平均值。这项工作对于粒子物理中的味道物理和B介子物理学具有重要意义，因为它提供了对B\_s0介子衰变性质的新洞察，并且有助于检验标准模型的预测，同时可能揭示超出标准模型的新物理现象。文章的关键词包括味道物理、B介子物理以及实验中的hadron-hadron散射，表明了研究的核心领域。由于文章是开放获取的，意味着全球的研究人员都可以免费访问并利用这些数据进行进一步的研究。

JHEP08(2018)191

ﬁrst performs a partial event reconstruction and requires events to have two well-identiﬁed

oppositely charged muons with an invariant mass larger than 2.7 GeV/c

. The second stage

performs a full event reconstruction. Events are retained for further processing if they

contain a J/ψ → µ

−

candidate. The distance between the decay vertex of the J/ψ and

each PV, divided by its uncertainty, is required to be larger than three.

To study the properties of the signal and the most important backgrounds, simulated

pp collisions are generated using Pythia [15, 16] with a speciﬁc LHCb conﬁguration [17].

Decays of hadronic particles are described by EvtGen [18], in which ﬁnal-state radiation

is generated using Photos [19]. The interaction of the generated particles with the detec-

tor, and its response, are implemented using the Geant4 toolkit [20, 21] as described in

ref. [22

]. Other sources of background, such as those from b → ψ(2S) transitions, where the

ψ(2S) decays radiatively to a χ

meson, are studied using the RapidSim fast simulation

package [23].

3 Selection

A two-step procedure is used to optimize the selection of

→ χ

c1,c2

−

candidates.

These studies use simulation samples together with the high-mass sideband of the data,

5550 < m(χ

−

) < 6150 MeV/c

, which is not used for subsequent analysis. In a

ﬁrst step, loose selection criteria are applied to reduce the background signiﬁcantly whilst

retaining high signal eﬃciency. Subsequently, a multivariate selection is used to reduce

further the combinatorial background.

The selection starts from a pair of oppositely charged particles, identiﬁed as muons,

that form a common decay vertex. Combinatorial background is suppressed by requiring

that the χ

of the muon candidates, deﬁned as the diﬀerence between the χ

of the

PV reconstructed with and without the considered particle, be larger than four for all

reconstructed PVs. The invariant mass of the dimuon candidate must be within 50 MeV/c

of the known J/ψ mass [24].

Photons are selected from well-identiﬁed neutral clusters, reconstructed in the electro-

magnetic calorimeter [8

], that have a transverse energy in excess of 700 MeV/c. Selected

J/ψ and photon candidates are combined to form χ

c1,c2

candidates. The invariant mass

of the combination, obtained from a kinematic ﬁt [25

] with a J/ψ mass constraint [24], is

required to be within the range 3400–3700 MeV/c

Pairs of oppositely charged kaons with p

> 200 MeV/c and displaced from all PVs

(χ

> 4) are selected. Good kaon identiﬁcation is achieved by using information from

the RICH detectors. This is combined with kinematic and track quality information using

neural networks which provide a response that varies between 0 and 1 for each of the

diﬀerent mass hypotheses: kaon (P

), pion (P

), and proton (P

). The closer to one

this value is, the higher the likelihood that the particular mass hypothesis is correct. The

chosen requirements on these variables have an eﬃciency of (86.8±0.2)% and (86.4±0.2)%

for the

→ χ

−

and B

→ χ

−

modes, respectively, where the uncertainty

is due the size of the available simulation samples. The invariant mass of the selected kaon

pair is required to be within 15 MeV/c

of the known value of the φ mass [24]. These criteria

– 3 –

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观测Bs0衰变至χc2K+ K-在ϕ质量区域

B粒子的四体重子衰变研究：B→pp¯π+π-，Λp¯π+π-和Λp¯K+K-

探究新物理对Λb 0→Λc +μ− vμ衰变的影响

NNLO精度计算：H→b b¯j衰变研究

衰落的证据BS0→K ∗0μ+ μ− $$ {B} _S ^ 0 \至{\ overline {K}} ^ {\ ast 0} {\ mu} ^ {+} {\ mu} ^ { -} $$

在Λb 0→Λc +μ− v¯μ$$ {\ varLambda} _b ^ 0 \至{\ varLambda} _c ^ {+} {\ mu} ^ {-} {\ overline { v}} _ {\ mu} $$衰减

$$ \ bar {K} ^ {0} \ Lambda _ {c} ^ {+} $$K¯0Λc+中结构的证据与带电荷的$$ \ Xi _c（2930）^ {+} $$Ξc一致 （2930）+，并更新了$$ \ bar {B} ^ {0} \ rightarrow \ bar {K} ^ {0} \ Lambda _ {c} ^ {+} \ bar {\ Lambda} _ {c } ^ {-} $$B¯0→K¯0Λc+Λ¯c-在Belle

B \→D ∗τν$$ $$ \ overline {B} \ to {D} ^ {\ left（\ ast \ right）} \ tau \ overline {\ nu} $$受B限制的ALRSM中过剩，D衰减 和D 0 − D¯0 $$ {D} ^ 0-{\ overline {D}} ^ 0 $$混合

B s 0→K ∗ 0 K ∗ 0 $$ {B} _ {{s}} ^ 0 \至{K} ^ {\ ast 0} {\ overline {K}} ^ {\ ast的幅度分析 0} $$衰变并测量B的分支分数0→K ∗ 0 K ∗ 0 $$ {B} ^ 0 \至{K} ^ {\ ast 0} {\ overline {K}} ^ { \ ast 0} $$衰减

K +→μ+νμννν$$ {\ mathrm {K}} ^ {+} \ to {\ mu} ^ {+} {\ nu} _ {\ mu} \ nu \ overline {\ nu} $$和K +→e +νeνν¯$$ {\ mathrm {K}} ^ {+} \ to {\ mathrm {e}} ^ {+} {\ nu} _ {\ mathrm {e} } \ nu \ overline {\ nu} $$在手征扰动理论中衰减

如何将B d 0→J /ψπη，K K $$ {\ overline {B}} _ d ^ 0 \应用于J / \ psi \ left（\ uppi \ eta，\ overline {K} K \ 右）$$衰减以提取有关πη散射的信息

最新资源

$$ \ bar {K} ^ {0} \ Lambda _ {c} ^ {+} $$K¯0Λc+中结构的证据与带电荷的$$ \ Xi _c（2930）^ {+} $$Ξc一致（2930）+，并更新了$$ \ bar {B} ^ {0} \ rightarrow \ bar {K} ^ {0} \ Lambda _ {c} ^ {+} \ bar {\ Lambda} _ {c } ^ {-} $$B¯0→K¯0Λc+Λ¯c-在Belle

B \→D ∗τν$$ $$ \ overline {B} \ to {D} ^ {\ left（\ ast \ right）} \ tau \ overline {\ nu} $$受B限制的ALRSM中过剩，D衰减和D 0 − D¯0 $$ {D} ^ 0-{\ overline {D}} ^ 0 $$混合