Bs0→J/ψπ+π-衰变中CP违反相位的测量研究

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B′s0→J/ψπ+π-衰变中违反CP的相位ϕs的测量在 particle physics 中，CP violation（违反CP）是指在粒子物理学中，charge conjugation（电荷共轭）和parity（宇称）同时变化时，物理规律不保持不变的一种现象。CP violation 是一种重要的物理现象，它可以帮助我们更好地理解粒子物理学中的基本相互作用。 Bs0→J/ψπ+π-衰变是 B meson 的一種衰变方式，它可以用来研究 CP violation。在这个衰变过程中，Bs0粒子衰变成 J/ψ介子和π+π-介子。通过测量 Bs0→J/ψπ+π-衰变的相位 ϕs，可以研究 CP violation。在这篇论文中，作者使用 LHCb 检测器在 7 和 8 TeV 中心质量 pp 碰撞中收集的数据，测量 Bs0 和 B’s0 衰变中的混合诱导的违反 CP 的相位 ϕs。他们使用了时间变化的带有风味标签的幅度分析，允许直接违反 CP。结果表明，相位 ϕs 的值为 70±68±8 mrad，这与标准模型预期和先前的测量结果一致。这个结果对于理解 CP violation 的机理非常重要。CP violation 是一种基本的物理现象，它在粒子物理学中扮演着关键角色。研究 CP violation 可以帮助我们更好地理解粒子物理学中的基本相互作用，并且可以帮助我们发现新的物理规律。在这篇论文中，作者还使用了 time-dependent flavour-tagged amplitude analysis，这是一种常用的方法来测量 CP violation。在这个方法中，作者使用了 flavour tagging 将 Bs0 和 B’s0 粒子区分开来，然后使用 amplitude analysis 来测量相位 ϕs。此外，这篇论文还讨论了 CP violation 在 B Physics 中的应用。CP violation 是一种重要的物理现象，它可以帮助我们更好地理解粒子物理学中的基本相互作用。研究 CP violation 可以帮助我们发现新的物理规律，并且可以帮助我们更好地理解粒子物理学中的基本相互作用。这篇论文对 Bs0→J/ψπ+π-衰变中违反 CP 的相位 ϕs 的测量进行了研究，并讨论了 CP violation 在 B Physics 中的应用。这篇论文对于理解 CP violation 的机理非常重要，并且可以帮助我们更好地理解粒子物理学中的基本相互作用。

Physics Letters B 736 (2014) 186–195

Contents lists available at ScienceDirect

Physics Letters B

www.elsevier.com/locate/physletb

Measurement of the CP-violating phase φ

in B

→ J/ψπ

−

decays

.LHCb Collaboration

a r t i c l e i n f o a b s t r a c t

Article history:

Received

16 May 2014

Received

in revised form 25 June 2014

Accepted

30 June 2014

Available

online 3 July 2014

Editor:

W.-D. Schlatter

The mixing-induced CP-violating phase φ

in B

and B

decays is measured using the J /ψπ

−

ﬁnal

state in data, taken from 3fb

−1

of integrated luminosity, collected with the LHCb detector in 7 and 8TeV

centre-of-mass pp collisions at the LHC. A time-dependent ﬂavour-tagged amplitude analysis, allowing for

direct CP violation, yields a value for the phase φ

= 70 ± 68 ± 8mrad. This result is consistent with the

Standard Model expectation and previous measurements.

(http://creativecommons.org/licenses/by/3.0/). Funded by SCOAP

1. Introduction

One of the most sensitive ways of detecting the presence of

heretofore unseen particles or forces is through the observation

of effects they may have on CP-violating decays of neutral B

mesons

[1]. Measurements of CP violation through the interfer-

ence

of B

mixing and decay amplitudes are particularly sensitive

because the Standard Model (SM) prediction of the CP-violating

phase is very small and accurate in quark level b → ccs transitions,

with φ

≡−2 arg(−

∗

) =−36.3

+1.6

−1.5

mrad, ignoring sublead-

ing

corrections from Penguin amplitudes [2]. Initial measurements

of φ

at the Tevatron indicated possible large values inconsistent

with the SM expectation [3], while LHCb measurements using both

(−)

→ J/ψφ and

(−)

→ J/ψπ

−

decays from 1fb

−1

of inte-

grated

luminosity were consistent with the SM value [4,5], as were

more recent results from CDF [6], and ATLAS [7].

In this Letter, we present a new measurement of φ

(−)

→

J/ψ π

−

decays using data taken from an integrated luminos-

ity

of 3fb

−1

, obtained from pp collisions at the LHC. One-third of

the data was collected at a centre-of-mass energy of 7TeV, and

the remainder at 8TeV. In the previous study we used the re-

sult

of our amplitude analysis [8], which showed that the CP-odd

component of the decay was larger than 97.7% at 95% conﬁdence

level (CL). Here we perform a more sophisticated amplitude anal-

ysis

[9], which uses an additional angular variable, and thereby

directly determines the CP-odd and CP-even components. Previ-

ously

it was found that ﬁve interfering π

−

states required to

describe the decay are: f

(980), f

(1500), f

(1790), f

(1270), and



(1525) [10]. In the same analysis, an alternative model includ-

ing

these states and a nonresonant J /ψπ

−

component was

also found to provide a good description of the data; the limit

on the CP-even component is unchanged. The J/ψ f

(980) ﬁnal

state was suggested as being a useful ﬁnal state for measuring

as it is a CP-eigenstate [11] and inspired these studies. Sub-

sequently, it was suggested that the f

(980) resonance might be

formed of tetraquarks [12], and could then provide an additional

SM contribution to φ

beyond that originally expected. Studies of

→ J/ψ π

−

decays [13] indicate that the light scalar mesons

are familiar qq states [14], so this concern has been ameliorated.

The method used here allows the measurement of the CP-vio-

lating

phase φ

, without any assumption on the CP content, by

measuring simultaneously the CP-even and CP-odd decay ampli-

tudes

and φ

2. Decay rates for B

→ J /ψh

−

The time dependent formalism for decays of neutral B mesons

to a J /ψ meson, that subsequently decays into a μ

−

pair, and

two pseudo-scalar particles h

−

is derived in Ref. [9]. The differ-

ential

decay rates for

(−)

→ J/ψh

−

, allowing for possible direct

CP violation, can be written in terms of the decay time t, and the

decay amplitudes A and A as [15]

Γ(t) = N e

−Γ



+|A|

cosh

Γ

−|A|

cos

(m

t) − Re



∗



sinh

Γ

− Im



∗



sin(m



, (1)

Γ(t) =



N e

−Γ



+|A|

cosh

Γ

−

−|A|

cos

(m

t) − Re



∗



sinh

Γ

+ Im



∗



sin(m



, (2)

http://dx.doi.org/10.1016/j.physletb.2014.06.079

0370-2693/

SCOAP

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