5.02 TeV pâPb碰撞中前向中心两粒子关联的高多态性现象

192 浏览量更新于2024-09-03 收藏 1.12MB PDF 举报

在本研究中，标题为"在sNN = 5.02 TeV的pâPb碰撞中的前向中心两粒子相关"的文章，发表在《物理 letters B》第753期，具体时间为2016年。这项工作由ALICE（A Large Ion Collider Experiment）合作组织完成，它是一个专注于高能核物理实验的国际团队。研究主要关注的是在质子-铅（pâPb）碰撞中，不同区域粒子之间的角关联。研究者利用了ALICE实验装置来测量在pâPb碰撞中，两个粒子的关联特性。特别关注的是，在前向伪快速度范围（2.5 < |α| < 4.0）的"触发"粒子（这里指的是通过muon spectrometer（缪子探测器）重建的粒子）与在中央区域（|η| < 1.0）的"关联"粒子（由central barrel tracking detectors处理的粒子）之间的二维角分布。这项研究的重点是在5.02 TeV的质子-核子对心能量下，这种关联特征的变化。文章发现，在高多粒子事件中，先前在中低rapidity（偏移角）区间观察到的双峰结构（double ridge structure）依然存在，并扩展到了更广泛的pseudorapidity（伪径向角）范围内。这是对高能重离子碰撞中多重粒子生成和动力学行为的重要洞察，因为双峰结构通常与局部热化、局部能量密度增高以及可能的集体效应有关。研究人员还提取了高多粒子事件中muons的二次谐波系数，这可能是对强子混合态或非弹性散射过程的定量度量，这些过程对于理解QCD（量子色动力学）在极端条件下的行为至关重要。这篇论文不仅提供了实验数据，也促进了理论模型的验证和修正，推动了对强相互作用在极端能量密度环境下的理解。这篇文章的核心知识点包括：前向-中心两粒子关联在高能pâPb碰撞中的观测，双峰结构的扩展，以及在高多粒子事件中二次谐波系数的测量，这些都是深入研究强相互作用在极简短距离尺度上的行为的重要窗口。

128 ALICE Collaboration / Physics Letters B 753 (2016) 126–139

Fig. 1 . Parent particle composition of reconstructed muon tracks (left panel) and reconstruction eﬃciency for muons from pion and kaon decays relative to that for heavy

ﬂavor (HF) decay muons (right panel) from a detector simulation of the ALICE muon spectrometer.

Table 1

V0S

multiplicity classes as fractions of the analyzed

event sample and the corresponding



/dη



|η|<0.5

The



/dη



values are not corrected for trigger and

vertex-reconstruction ineﬃciencies, which are about 4%

for non-single-diffractive events [61], mainly affecting

the 80–100% lowest mulitiplicity events [62]. Only sys-

tematic

uncertainties are listed, since the statistical un-

certainties

are negligible.

Event

class



/dη



|η|<0.5

> 0GeV/c

0–20% 35.8 ±0.8

20–40% 23

.2 ±0.5

40–60% 15

.8 ±0.4

60–100% 6

.8 ±0.2

unlike before, both beam orientations were investigated in this Let-

ter.

Therefore, the signals from only two out the four rings of V0-A

and

V0-C detectors were combined to guarantee a more symmet-

ric

acceptance. On the V0-A side, the two outermost rings with an

acceptance of 2.8 < η < 3.9, while on the V0-C side the two in-

nermost

rings with an acceptance of −3.7 < η < −2.7were used.

This combination is called V0S in the following. The deﬁnition of

the event classes as fractions of the analyzed event sample and

their corresponding average number of particles at midrapidity

(



/dη



|η|<0.5

), measured using tracklets as explained below,

is given in Table 1.

Muon

tracks are reconstructed in the geometrical acceptance of

the muon spectrometer (−4 < η < −2.5). The tracks are required

to exit the front absorber at a radial distance from the beam axis,

abs

, in the range 17.6 < R

abs

< 89.5cmin order to avoid regions

with large material density. The muon identiﬁcation is performed

by matching the tracks reconstructed in the tracking chambers

with the corresponding track segments in the trigger chambers.

Beam-gas tracks, which do not point to the interaction vertex, are

removed by a selection on the product of the total momentum of a

given track and its distance to the interaction vertex in the trans-

verse

plane. In the analysis, muons in the transverse momentum

range 0.5 < p

< 4GeV/c were considered.

Reconstructed

muons mainly originate from weak decays of π ,

and mesons from heavy ﬂavor (HF) decays. Because of the dif-

ferent

distribution of the various sources and the absorber in

front of the spectrometer, which suppresses by design weak decays

Here, and in the following, pions and kaons refer to the sum of both charge

states. Neutral particles are also considered in the case of kaons.

from light hadrons, the parent particle composition for the recon-

structed

muon tracks changes as a function of p

. The composition

shown as a function of the reconstructed p

in the left panel of

Fig. 1 was evaluated using full detector simulations based on the

DPMJET Monte Carlo (MC) event generator [63]. The detector re-

sponse

was simulated using GEANT3 for particle transport [64].

The composition of parent particles in the simulation differs by

less than 10% for the two beam conﬁgurations. The reconstructed

muons are dominated by light-hadron decays below 1.5 GeV/c, and

by heavy ﬂavor decays above 2GeV/c. No signiﬁcant multiplic-

ity

dependence was found. Similar conclusions are obtained using

simulations with the AMPT generator [65].

Without

strong model assumptions, one cannot deduce the

composition of parent particles from the measured muon distribu-

tion,

and correct the data for muon decay and absorber effects. For

comparison of the v

data with calculations, however, only relative

contributions of the parent species matter. In order to ease future

model calculations, the reconstruction eﬃciencies for muons from

pion and kaon decays relative to those for muons from heavy ﬂa-

vor

decays are provided in the right panel of Fig. 1 as a function of

the generated decay muon p

in different pseudorapidity intervals.

Contributions from muon decays of other particles are signiﬁcantly

smaller than those for pions and can be ignored. The systematic

uncertainty on the relative eﬃciencies was estimated to be less

than 5%.

Tracks

reconstructed in the ITS and the TPC are selected in the

ﬁducial region |η| < 1 and 0.5 < p

< 4GeV/c. The track selection

used in this Letter is the same as in Ref. [24].

Tracklet

candidates are formed using information on the posi-

tion

of the primary vertex and the two hits on the SPD layers [66],

located at a distance of 3.9 and 7.6 cm from the detector centre.

The differences of the azimuthal (ϕ

, bending plane) and po-

lar

(θ

, non-bending direction) angles of the hits with respect

to the primary vertex are used to select particles, typically with

> 50 MeV/c. Particles below 50 MeV/c are mostly absorbed

by material. Compared to previous analyses [61,66] a tighter cut

in ϕ

is applied (ϕ

< 5mrad) to select particles with larger

and to minimize contributions of fake and secondary tracks to

below 2.5%. The corresponding mean p

of selected particles, esti-

mated

from the DPMJET MC, is about 0.75 GeV/c.

4. Analysis

The associated yield of tracks or tracklets per trigger particle in

the muon spectrometer is measured as a function of the difference

剩余13页未读，继续阅读

weixin_38637983

粉丝: 8
资源: 906

5.02 TeV pâPb碰撞中前向中心两粒子关联的高多态性现象

多奇异的重子产生在sNN = 5.02 TeV的p Pb碰撞中

在sNN = 5.02 TeV时Pb-Pb碰撞中带电粒子的伪快速密度分布的中心依赖性

在sNN = 5.02 TeV的pâPb碰撞中测量带电的喷射生产截面和核修饰

径向流对两个粒子相关性的影响，在sNN = 5.02 TeV的pâPb碰撞中，在中间p T具有已确定的触发条件

在sNN = 5.02 TeV的p–Pb碰撞中从重味强子衰变产生的介子

Ï•-前向速度的介子生产在sNN = 5.02 TeV处的p–Pb碰撞中和在s = 2.76 TeV处的pp碰撞中

5.02 TeV p-Pb碰撞中径向流对中间p_T两粒子相关性的影响

LHC能量下pPb和PbPb碰撞中奇异强子与带电粒子的远距离两粒子相关性

模具状态监测行业发展趋势：预计到2030年市场规模为5.06亿美元

Kubernetes DevOps实践工作坊-从理论到实战操作脚本集（含源码）.zip

最新资源