# Prompt/non-prompt J/psi separation in pp at sqrt(s) = 13.6 TeV with ALICE

Emilie Martine Barreau

► To cite this version:

Emilie Martine Barreau. Prompt/non-prompt J/psi separation in pp at sqrt(s) = 13.6 TeV with ALICE. The 21st International Conference on Strangeness in Quark Matter, Jun 2024, Strasbourg, France. . hal-04682012

HAL Id: hal-04682012

https://hal.science/hal-04682012v1

Submitted on 30 Aug 2024

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<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
## Quarkonia as probe of the QGP

The quark-gluon plasma (QGP) is a state of matter in which quarks and gluons are no more confined inside hadrons and can be produced in ultrarelativistic heavy-ion collisions. Heavy quarkonia, bound states of quark/antiquark pairs, are a valuable tool to investigate the properties of the QGP.

Quarkonia production in nuclear collisions is affected by different mechanisms:

* **suppression** through color screening and dynamical dissociation

* **(re)generation**: recombination of uncorrelated $c\bar{c}$ pairs, produced with high multiplicity at the LHC energies, expected to be almost negligible for beauty quarks

**This study**: focus on J/Ψ production in small and large collision systems

The nuclear modification factor $R_{AA}$ is the key observable to study quarkonium modification in presence of the QGP:

* $R_{AA} = 1$: no modification with respect to pp collisions

* $R_{AA} < 1$: suppression

$$R_{AA} = \frac{N_{J/\psi}^{AA}}{\langle T_{AA} \rangle \cdot \sigma_{pp}^{J/\psi}} \quad (1)$$

J/Ψ inclusive production can be separated into two contributions :

**prompt J/Ψ**:

* produced at the primary vertex (PV)

* interacts with the QGP

* probe for charm sector

**non-prompt J/Ψ**:

* from B hadron decays

* vertex topology

* probe for beauty sector

**Motivation for prompt/non-prompt J/Ψ separation** :

* access another channel for b-hadron studies

* precise study of the regeneration mechanism

<figure><img src="image_2.png" /></figure>

## The ALICE experiment

The ALICE experiment is designed for the study of heavy-ion collisions. It consists of a central barrel ($|y| < 0.9$) and Muon Spectrometer ($2.5 < y < 4$).

**Central barrel** :

* Inner Tracking System (ITS) : Si-pixel sensors used for vertex reconstruction

* Fast Interaction Trigger (FIT) : provides timing indications

* Time Projection Chamber (TPC) : used for vertexing, tracking and PID

**Muon Spectrometer** :

* Muon Forward Tracker (MFT) (9) :

* installed in Run 3

* five disks made of Si-pixel sensors (CMOS based)

* measures charged tracks with high spatial resolution

* provides vertex capability, allowing to measure non-prompt decay

* Absorber :

* suppresses hadronic contributions

<figure><img src="image_3.png" /></figure>

MCH-MID tracks matched to MFT tracks : global tracks

<figure><img src="image_4.png" /></figure>

## Prompt/non-prompt J/Ψ separation : analysis strategy

J/Ψ from b-hadron decays are characterized by displaced topology :

<figure><img src="image_5.png" /></figure>

**Forward rapidity** : longitudinal boost increases time of flight of b hadrons up to mm scale, providing better discrimination power for prompt/non-prompt separation

**Run 2** : no information between vertex and tracking chambers, all muon track reconstructed as coming from PV

**Run 3** : now possible to do prompt/non-prompt separation at forward rapidity

Prompt/non-prompt separation is done using pseudo-proper decay length $l_{J/\psi}$ :

* J/Ψ vertex ($Z_{J/\psi}$) along z axis

* primary vertex ($Z_{vtx}$) along z axis

* J/Ψ invariant mass ($M_{J/\psi}$)

* longitudinal momentum ($p_z$)

* pseudo-proper decay time ($\tau_z$)

$$l_{J/\psi} = c \cdot \tau_z = c \cdot \frac{(z_{J/\psi} - z_{vtx}) \cdot M_{J/\psi}}{p_z} \quad (2)$$

Analysis procedure: template fit to the pseudo-proper decay time:

* Data : Monte Carlo simulation

* background : mainly composed of combinatorial muon pairs and decay from $\pi$ and K

* prompt distribution : centered around $\tau_z = 0$, symmetric shape

* non-prompt distribution : right tail for $\tau_z > 0$, asymmetric shape

<figure><img src="image_6.png" /></figure>

## Extraction of prompt/non-prompt fraction

**Event selection** :

* -10 cm < $Z_{vertex}$ < 10 cm

* event quality cuts

**Dimuon pairs selections** :

* opposite sign muon pairs

* $2.5 < y < 3.6$

* $M_{\mu\mu} > 1.8$ GeV/c²

Dataset : pp 13.6 TeV, 2022 sample (60%)

**Tracks selections** :

* -3.6 < $\eta$ < -2.5, muon spectrometer + MFT acceptance

* $2^\circ < \theta_{abs} < 10^\circ$ : absorber exit angle, limits multiple scattering in the thickest parts of the absorber

* 0 GeV.cm/c < $p$.DCA < 594 GeV.cm/c : product of momentum and distance of closest approach, removes beam/gas interaction

* ambiguous tracks from pile-up collisions removed

* Global tracks (MFT+MCH+MID matching)

The extraction of the non-prompt fraction is performed using the sPlot package and it is based on the following steps:

1. Fit to the invariant mass distribution to separate J/Ψ signal from the background

2. Fit to the $l_{J/\psi}$ distribution using the signal and background weights from invariant mass fit (step 1)

* $l_{J/\psi}$ resolution is extracted fitting the distribution for $l_{J/\psi} < 0$ (non-prompt contribution excluded)

3. 2D fit of mass and $l_{J/\psi}$ distribution :

* non-prompt $l_{J/\psi}$ distribution initialized using Monte Carlo input

* signal and background shapes for the invariant mass and $l_{J/\psi}$ resolution are fixed in the previous steps

* non-prompt fraction, number of J/Ψ and number of background events are kept free

**Results** :

* prompt and non-prompt components are well identified : promising results for prompt/non-prompt separation

**Next step** : acceptance-efficiency evaluation via Monte Carlo simulation and correction of the measured non-prompt J/Ψ fraction

<figure><img src="image_7.png" /></figure>

ALI-PERF-571263

ALI-PERF-571258

ALI-PERF-571268

**Outlook** :

The datasets collected for pp collisions at $\sqrt{s} = 13.6$ TeV will allow a precise differential measurement in $p_T$ and $y$ of the prompt/non-prompt J/Ψ fraction

First step toward prompt/non-prompt J/Ψ $R_{AA}$ study in Pb-Pb