13 TeV质子-质子碰撞中带电粒子的伪快速度与横向动量分析

66 浏览量更新于2024-09-04 收藏 1.08MB PDF 举报

"这篇论文是ALICE Collaboration在Physics Letters B期刊上发表的研究成果，主要探讨了在质子-质子碰撞中，当质心能量s等于13 TeV时，带电粒子的伪快速度（η）和横向动量（pT）的分布情况。实验数据用于分析非弹性事件以及至少有一个带电粒子在伪快速度绝对值小于1的事件。" 文章深入研究了带电粒子在不同条件下的分布特性。对于非弹性事件，他们在伪快速度范围|η| < 1.8内进行了测量，并且对于至少有一个带电粒子在|η| < 1的事件，报告了伪快速度分布。在|η| < 0.5的区域内，两类事件的带电粒子伪快速度密度分别为5.31±0.18和6.46±0.19。这表明随着伪快速度的不同，带电粒子的密度也会有所变化。此外，研究还涵盖了带电粒子的横向动量分布。在0.15 < pT < 20 GeV / c的范围内，以及伪快速度|η| < 0.8的条件下，至少有一个带电粒子在|η| < 1的事件中，对带电粒子的横向动量进行了详细分析。这项工作也探索了随着事件多重性变化，即参与碰撞的粒子数量增加时，带电粒子的横向动量谱如何演变。为了进一步理解这些观测结果，研究者将测量数据与两种流行的蒙特卡洛事件生成器，即PYTHIA和EPOS的模拟结果进行了比较。这种比较有助于检验和校准这些理论模型，以更好地理解和预测高能粒子碰撞中的物理过程。通过这样的实验和分析，物理学家可以更深入地了解基本粒子间的相互作用，以及在极端能量条件下物质的行为。这些数据对于理解强相互作用，特别是在强子碰撞中夸克和胶子的动态行为至关重要，同时也为未来高能物理实验提供了重要参考。

ALICE Collaboration / Physics Letters B 753 (2016) 319–329 321

kinematics of diffractive processes. For proton–proton collisions

√

s = 13 TeV there is not yet any experimental information

available about diffractive processes, therefore trigger and event-

selection

eﬃciency corrections are solely based on previous ex-

perimental

data at lower collision energies and simulations with

Monte Carlo event generators. The corresponding systematic un-

certainty

has been evaluated by varying the fractions of single-

diffractive

(SD) and double-diffractive (DD) events produced by

PYTHIA 6 (Perugia-2011) by ±50% of their nominal values at

√

s =

13 TeV. The resulting contribution to the systematic uncertainties

for INEL and INEL > 0events is estimated to be about 2% and 1.2%,

respectively. To estimate systematic uncertainties associated to the

model dependence of the normalisation correction we employed

PYTHIA 8 [23] (Monash-2013 [24]), which shows large differences

both in the multiplicity and transverse-momentum distributions of

charged particles with respect to PYTHIA 6, especially in diffractive

events [25]. Adifference of about 0.4% and 2% is observed for INEL

and INEL > 0events, respectively. Finally, an uncertainty of 2% has

been estimated by varying the oﬄine event-selection criteria ap-

plied

to the trigger detectors which only affects the normalisation

of the INEL sample.

The systematic uncertainties for the transverse-momentum dis-

tribution

analysis are evaluated in a similar way as in previous

analyses of pp [9,10], p–Pb [11,12], and Pb–Pb [14] data. The dom-

inant

sources of uncertainty are the track selections, the eﬃciency

corrections and, for low p

, the contamination from weak decays

of strange hadrons. The systematic uncertainties for the pseudo-

rapidity

distribution analysis are discussed in the following. The

uncertainty in detector acceptance and eﬃciency is estimated to

be about 1.5%, determined from the change of the multiplicity at

a given η by varying the range of the z position of the vertex

and performing the measurement in different runs. The material

budget in the ALICE central barrel

1is known with a preci-

sion

of about 5% [16]. The corresponding systematic uncertainty,

obtained by varying the material budget in the simulation, is es-

timated

to be about 0.1% and is negligibly small compared to the

other sources. The sensitivity to tracklet selection criteria was es-

timated

varying the selection requirements and is negligible. The

uncertainty due to the particle composition is estimated to be

about 0.2% and was determined by changing the relative fractions

of charged kaons and protons with respect to charged pions pro-

duced

by the Monte Carlo generator by ±30%. The uncertainty

resulting from the subtraction of the contamination from weak de-

cays

of strange hadrons is estimated to amount to about 0.5% by

varying the strangeness correction by ±30%. The uncertainty due

to the correction down to zero p

is estimated to be about 1% by

varying the amount of particles below the 50 MeV/c low-p

cutoff

+100

−50

5. Results

Fig. 1 shows the average charged-particle density distribution

dN

/dη measured in INEL and INEL > 0events in the pseudora-

pidity

range

1.8. The data points have been symmetrised av-

eraging

the results obtained in ±η, which were consistent within

statistical uncertainties. The corresponding pseudorapidity densi-

ties

0.5are 5.31 ± 0.18 and 6.46 ± 0.19, respectively. The

pseudorapidity density for the INEL > 0events is also measured

1for direct comparison with INEL > 0results reported

by ALICE at lower energies [5] and is 6.61 ± 0.20. Also shown in

Fig. 1 are the results recently published by the CMS Collaboration

for inelastic collisions [15], which agree, within the uncertainties,

with the measurement presented here. We compared our mea-

surement

to Monte Carlo calculations performed with PYTHIA 6

[18] (Perugia-2011 [19]), PYTHIA 8 [26] (Monash-2013 [24]) and

Fig. 1 . Average pseudorapidity density of charged particles as a function of η pro-

duced

in pp collisions at

√

s = 13 TeV. The ALICE results are shown in the normali-

sation

classes INEL and INEL > 0and compared to Monte Carlo calculations [18,19,

24,26–28] and

to the results from the CMS Collaboration [15]. The uncertainties are

the quadratic sum of statistical and systematic contributions.

Fig. 2. Charged-particle pseudorapidity density measured in the central pseudora-

pidity

region

0.5for INEL and INEL > 0events[4–6,15,29–33]. The uncertain-

ties

are the quadratic sum of statistical and systematic contributions. The lines are

power-law ﬁts of the energy dependence of the data and the grey bands represent

the standard deviation of the ﬁts.

EPOS LHC

[27,28] in both the INEL and INEL > 0event classes.

PYTHIA 6 calculations are in better agreement with the data than

PYTHIA 8 in both classes, with PYTHIA 8 being higher than the

data by about 12% (7%) in INEL events and about 7% (3%) in

INEL > 0events at η ∼ 0(η ∼ 1.5). EPOS LHC calculations are

about 7% (4%) and about 7% (5%) higher than the data in INEL and

INEL > 0events, respectively, at η ∼ 0(η ∼ 1.5). In Fig. 2 we show

Calculations performed with CRMC package version 1.5.3.

剩余10页未读，继续阅读

weixin_38623080

粉丝: 5
资源: 1002

13 TeV质子-质子碰撞中带电粒子的伪快速度与横向动量分析

CMS实验：5.02和8.16 TeV质子-铅碰撞中带电强子伪快速分布研究

CMS实验：13TeV质子-质子碰撞中寻找带电夏奇诺和顶级夸克对产生的研究

13 TeV质子-质子碰撞中单顶夸克与光子关联生产的证据

使用s = 13 TeV质子-质子碰撞，利用ATLAS搜索具有大射流多重性且缺少横向动量的最终状态中的新现象

在s = 13 TeV质子-质子碰撞中单顶夸克和光子的联合产生的证据

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s = 13 TeV的质子-质子碰撞中寻找长寿命粒子衰变成置换射流

s = 33TeV和s = 100TeV质子-质子超级对撞机的受约束超对称前景

在s = 13 TeV的质子-质子碰撞中使用延迟光子搜索长寿命粒子

在s = 8TeV的质子-质子碰撞中具有高射流多样性和低横向动量缺失的事件中寻找新现象

最新资源