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Home , Lambda baryon

EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH

To be specified June 17, 2021

CERN internship report

Krystian Głuchowski

Warsaw University of Technology

Abstract √ √ This report shows results of lambda origin analysis for s = 13 TeV pp and sNN = 5.02 TeV Pb-Pb collisions using data-driven method for the DCA and CPA distributions. Report is the result of the realised student internship project for The European Organization for Nuclear Research (CERN). Contents

1 Introduction 1

2 CERN, LHC and ALICE 1 2.1 CERN ...... 1 2.2 LHC...... 1 2.2.1 and lead ions acceleration ...... 2 2.3 ALICE ...... 3 2.3.1 Inner Tracking System ...... 4 2.3.2 Time Projection Chamber ...... 4

3 Analysis software 4 3.1 Data sample ...... 5 3.1.1 ALICE collision data ...... 5 3.1.2 MC data ...... 5

4 Identification and track selection method 6 4.1 PID of daughter ...... 6 4.2 Kinematics cuts ...... 6

5 Data analysis 8 5.1 Lambda baryons origin prediction in MC data ...... 8 5.2 Template-fits method ...... 11

6 Summary 13 Warsaw University of Technology 1

1 Introduction Lambda baryons are neutrally charged particles which are made up of two of the first generation (up and down) and one strange from the second generation. As the particles with no electric , they can not be detected directly. They are only detected by applying cuts on some quantities measured between the reconstructed tracks of the daughters and mother particles. However, the same cuts used in the Monte-Carlo simulations and in the real collisions data can provide the lambda samples with a different purity. One of the tools to estimate the contamination factor in the sample of Λ baryons is the data-driven method, in which the theoretical distributions from the MC models for the primary, secondary, material and fake lambda baryons are fitted to the distribution obtained in the real collisions. In this report the DCA (Distance of the Closest Approach) and CPA (Cosine of the Pointing √ √ Angle) distributions were fitted to the distributions created for the s = 13 TeV pp and sNN = 5.02 TeV Pb-Pb collisions registered by the ALICE experiment.

2 CERN, LHC and ALICE 2.1 CERN CERN (Conseil Europeen´ pour la Recherche Nucleaire)´ [2] is a European scientific organisation, which mainly focus on the research in the field of subatomic particles and high energy physics. CERN was founded in 1954 and located on the French-Swiss border near Geneva. Until this day CERN has 23 member states including Poland, which joined this organisation in 1991. Scientists at CERN use the largest and most complex scientific instruments to study properties of fundamental components of in order to clarify the mechanism of its creation and fundamental interactions. These instruments are mainly particle accelerators and detectors. Accelerators are boosting beams of charged particles to the very high energy (with the velocity nearly equals the speed of light) and make them collide with each other or with the stationary target. Main purpose of the detectors is to identify and record information about products of these collisions. Most of the accelerators at CERN are connected into one of the world’s largest network of the linear and circular accelerators and for that reason beams of particles can be accelerated to higher and higher energies. Complex of accelerators at CERN is presented in Fig. 1.

2.2 LHC The Large Collider (LHC) [3] is the largest and the most powerful accelerator in the complex of accelerators at CERN. It was launched in 2008 as the latest addition to accelerator’s network. LHC is a synchrotron, which lies in a tunnel 27 km long in the circumference and around 100 m beneath the ground. The particles are accelerated in the opposite directions inside two ultra-vacuum pipes by 16 radiofrequency (RF) cavities. These instruments are increasing velocity of charged particles using changing electric field. In LHC every turn of RF cavities provides around 0.5 MeV energy for the beam and because of that fact accelerating protons from energy 450 GeV to 7 TeV lasts around 20 minutes. Particles are kept inside the circular accelerator by strong magnetic field inducted by thousands of superconductive electromagnets. In aim to afford the superconductive state of electromagnet’s coils, the whole device is cooled by liquid helium and kept in the temperature -271.3°C. Magnetic field is not only used to curve the beams of charged particles, but also to focus it and prepare to the collisions. For this purpose there are used 392, 5–7 m long quadrupole magnets in aim to focus the beam, and 1232 dipole magnets 15 metres in length which bend the beams. In addition there are 8 sets of inner quadropole triplet magnets which squeeze the particle beams and focus them to the size ≈16 µm in one of the four intersection points where are located the most important on the LHC experiments which are listed below.

– ATLAS (A Toroidal LHC ApparatuS) [4] is the largest general-purpose detector in the LHC. The researches on the ATLAS focus on the many fields of the like the discoveries 2 Internship report

Fig. 1: Complex of accelerators at CERN. From Ref. [9].

of the new particles which are predicted by the , asymmetry between matter and antimatter, or even prospecting for the particles beyond the predicted theory which could be a candidate for dark matter.

– CMS (Compact Solenoid) [5] is the second general purpose detector in the LHC. It has the same scientific goals as ATLAS, but it uses different technical instruments and magnet sys- tem in it’s design. Because of that fact these two detectors can examine and confirm each other discoveries.

– ALICE (A Large Ion Collider Experiment) [6] is the detector which mainly focus on the heavy- ion collisions where forms the quark- plasma. More information about the ALICE detector is presented in the section 2.3.

– LHCb ( beauty) [7] experiment investigate decays of the heavy which contain quarks of the second and third generation (like and beauty quarks). These researches are trying to explain the slight differences between the matter and the antimatter.

2.2.1 Protons and lead ions acceleration Every particle, which takes part in the -proton, p-Pb or Pb-Pb collisions in the one of four LHC’s intersection points, has it’s own starting point. In the case of protons it is the Duoplasmatron. It is the device which separate protons and in the hydrogen gas by strong electric field. Then pure sample of protons is speeded up to the energy 100 keV and sent to the linear accelerator LINAC 2 (which was replaced in the year 2020 by LINAC 4). Inside this accelerator particles are accelerated up to energy 50 MeV by multi-chamber RF cavities and transported into the first circular accelerator Proton Synchrotron Booster (PSB). PBS accelerates protons up to the energy 1.4 GeV in 530 ms inside four 157 m in circumference beam rings. When protons achieve adequate energy, they are injected into the Proton Synchrotron (PS). PS is the second circular accelerator in the way of protons to the LHC. It has a Warsaw University of Technology 3

Fig. 2: The ALICE detector [8]. length 628 m in circumference and is responsible for forming 81 particle bunches and accelerating them to energy 25 GeV to send them into the Super Proton Synchrotron (SPS). SPS is the second in large circular accelerator in CERN’s accelerators complex. It measures 7 km in circumference and speeds up protons to 450 GeV in 4.3 s. SPS provides the high energy beams for the LHC and also for other experiments like NA61/SHINE and NA62 experiments and the COMPASS experiment. 208 In the Pb-Pb collisions at the LHC the isotopes Pb96 are used, which are accumulated in a small piece of pure lead that weights 500 milligrams. This lead sample is heated to the temperature 500 °C to vaporize the group of the . Next step is removing all the electrons from the Pb atoms by electric current in aim to provide the sample of lead ions to the linear accelerator LINAC 3 inside which they are accelerated up to the energy 4.5 MeV per . The second accelerator for the lead ions is the Low Energy Ion Ring (LEIR). LEIR splits each pulse from LINAC 3 and form it into 4 bunches. It takes olny 2.5 s to boost up the heavy ions to the energy 72 MeV per nucleon. When the lead ions gains that energy, they are send to PS and then their next steps in the acceleration process are the same as in the proton-proton collisions. Heavy ions are accelerated up to energy 5.9 GeV per nucleon in the PS and next up to the energy 177 GeV per nucleon in the SPS. Finnally the bunches of lead ions are send from the SPS to the LHC in two separate pipes, each going in the opposite directions.

2.3 ALICE ALICE (A Large Ion Collider Experiment) is a general purpose detector, dedicated mainly for the heavy- ion collisions. The aim of ALICE is to study the physics of the strongly interacting matter at extremely high values of energies, temperatures and densities. In such conditions created by the heavy-ion colli- sions the quark-gluon plasma is formed. The data collected by the ALICE detector allow to study the process of hadrons and production process in the pp, p–Pb, Pb-Pb and Xe–Xe collisions. ALICE weights around 10 000 t, measures 26 m in length, 16 m in height, and 16 m in width, and is located 56 m below ground close to the village of St. Genis-Pouilly in France. The scheme of the ALICE detector is presented in Fig. 2. ALICE is built of many working together sub-detectors, which provides information about collisions parameters, particle tracking, particle identification, momentum and energy loss of passing through them particles. Devices in ALICE can be divided into two general groups – the central barrel part which col- 4 Internship report lects data of hadrons, electrons, and , and the foreward muon spectrometer. The central barrel detectors are located inside large solenoid magnet, and they can detect the particles in the whole azimuth angle range and the polar angle range from 45° to 135°. The closest device to the collision point is the In- ner Tracking System (ITS), which contains six planes of high-resolution silicon pixel (SPD), drift (SDD), and strip (SSD) detectors. Next detectors from the center are: Time-Projection Chamber (TPC), three particle identification arrays of Time-of-Flight (TOF), High Momentum Particle Identification Detector (HMPID), Transition Radiation Detector (TRD), and two electromagnetic calorimeters (PHOS and EM- Cal). Only HMPID, PHOS, and EMCal do not cover the full azimuth angle range. The ALICE Cosmic Ray Detector (ACORDE) is located on the top of the solenoid magnet. Several smaller detectors like Multiplicity Detector (PMD), Forward Multiplicity Detector (FMD), Cherenkov counters (T0) and Segmented scintillator counters (V0) are located just before the ITS. These detectors and two Zero Degree Calorimeters (ZDC), which are located around 116 m from the intersection point, collect data for the global event characterization. The forward muon spectrometer covers only short range of the polar angle (2°–9°) and consists a complex of absorbers, a large dipole magnet, and fourteen planes of tracking and triggering chambers. The most important detector for this analysis are ITS and TPC, which are responsible for track recon- struction and also for the particle identification. These detectors are described in the next subsections.

2.3.1 Inner Tracking System

ITS is a cylindrical detector measure 97.6 cm in length and has the total radius equal 43.6 cm. It is the closest detector to the intersection point. ITS is made of six layers of silicon detectors – two layers of pixel detectors SPD with radius 3.9 and 7.6 cm, two layers of the drift detectors SDD with radius 23.9 and 38.0 cm and two layers of the strip detectors SSD with radius equal 38.0 and 43.0 cm. They cover the pseudorapidity range |η| < 0.9. Main task of the ITS is to estimate the primary vertex and to estimate the secondary vertex for the hadrons decays. It is also responsible for tracking and identifying particles with the momentum less than 200 MeV/c. Data collected by ITS are also used to reconstruction of tracks these particles, which were passing through the dead zones of the TPC detector.

2.3.2 Time Projection Chamber

TPC in the ALICE experiment has the cylindrical shape and covers the full azimuth angle range (except of the dead zones between readout pads which cover around 10% of the azimuth range) and the pseudo- rapidity range |η| < 0.9 for the tracks with full radial track length. The length of the detector is equal 500 cm, it’s inner radius is around 85 cm and the outer radius is around 250 cm. The main part of the detector 3 is the field cage filled with the 90 cm mixture gas of Ne, CO2 and N2 in the proportion (90/10/5). The charged particles passing through the detector are ionizing the particles of the gas. Due to electric field (100 kV at the central catode) the electrons are transported to the readout pads. In this process there are collected data about momentum and energy loss of the charged particles. The TPC is also responsible for the secondary vertex reconstruction for the daughter particles, which tracks begins in this detector.

3 Analysis software

The analysis was performed using AliFemto package, which is part of AliRoot framework. AliRoot version: 5.34/30 Task used: PWGCF/FEMTOSCOPY/EfficiencyTask/AliAnalysisTaskParticleEff.C and also from AliEn repository: /alice/cern.ch/user/k/kgluchow/AliAnalysisTaskParticleEff DCA5 to obtain the distributions with the DCA range < 5.0 All jobs were submitted via AliEn. Warsaw University of Technology 5

3.1 Data sample 3.1.1 ALICE collision data √ The data used in this analysis comes from pp collisions at the energy s = 13 TeV and Pb-Pb collisions √ at the energy sNN = 5.02 TeV registered by the ALICE experiment. In the analysis the Analysis Object Data (AOD) were used. Runs used in this analysis were suggested by Data Processing Group (DPG) for Central Barrel Tracking and hadron PID. In the analysis have been used following runs:

– pp collisions:

– Dataset LHC15i: 236557, 236459, 236453, 236444, 236443, 236395, 236393, 236389, 236360, 236357, 236354, 236348, 236281, 236248, 236246, 236244, 236242, 236238, 236234, 236227, 236222, 236203, 236163, 236159, 236138, 236062, 235898, 235897, 235896, 235895, 235893, 235892, 235891, 235890, 235889, 235888, 235886, 235841, 235839, 235813, 235759, 235721, 235710, 235694, 235687, 235685, 235684, 235573, 235547, 235454, 235443, 235436, 235435, 235432, 235423, 235383, 235380, 235364, 235362, 235347, 235346, 235345, 235344, 235245.

– Pb-Pb collisions:

– Dataset LHC15o: 245683, 245692, 245702, 245705, 245829, 245831, 245833, 245923, 245949, 245952, 245954, 246001, 246003, 246012, 246036, 246037, 246042, 246048, 246049, 246052, 246053, 246087, 246089, 246113, 246115, 246151, 246152, 246153, 246178, 246180, 246181, 246182, 246185, 246217, 246222, 246225, 246271, 246272, 246275, 246276, 246424, 246431, 246434, 246487, 246488, 246493, 246495, 246750, 246751, 246757, 246758, 246759, 246760, 246763, 246765, 246766, 246804, 246805, 246807, 246808, 246809, 246810, 246844, 246845, 246846, 246847, 246851, 246928, 246945, 246948, 246982, 246984, 246989, 246991, 246994.

3.1.2 MC data In this analysis it was used Pythia6 Perugia-2011 General Purpose Monte Carlo productions anchored to the data mentioned on the list in 3.1.1. The Dataset LHC17i4 2 is anchored to LHC15i and dataset LHC17i2 is anchored to LHC15o.

– pp collisions:

– LHC17i4 2: 236557, 236459, 236453, 236444, 236443, 236395, 236393, 236389, 236360, 236357, 236354, 236348, 236281, 236248, 236246, 236244, 236242, 236238, 236234, 236227, 236222, 236203, 236163, 236159, 236138, 236062, 235898, 235897, 235896, 235895, 235893, 235892, 235891, 235890, 235889, 235888, 235886, 235841, 235839, 235813, 235759, 235721, 235710, 235694, 235687, 235685, 235684, 235573, 235547, 235454, 235443, 235436, 235435, 235432, 235423, 235383, 235380, 235364, 235362, 235347, 235346, 235345, 235344, 235245. 6 Internship report

– Pb-Pb collisions:

– LHC17i2: 245683, 245692, 245702, 245705, 245829, 245831, 245833, 245923, 245949, 245952, 245954, 246001, 246003, 246012, 246036, 246037, 246042, 246048, 246049, 246052, 246053, 246087, 246089, 246113, 246115, 246151, 246152, 246153, 246178, 246180, 246181, 246182, 246185, 246217, 246222, 246225, 246271, 246272, 246275, 246276, 246424, 246431, 246434, 246487, 246488, 246493, 246495, 246750, 246751, 246757, 246758, 246759, 246760, 246763, 246765, 246766, 246804, 246805, 246807, 246808, 246809, 246810, 246844, 246845, 246846, 246847, 246851, 246928, 246945, 246948, 246982, 246984, 246989, 246991, 246994.

4 Particle Identification and track selection method

Lambda and anti-lambda baryons are the neutrally charged particles and because of that reason they can not be identified directly by the detector. Only the secondary tracks, which means tracks of the charged daughter particles, are detected. The most probable decay of the lambda baryon is Λ → p + π− (and Λ → p + π+ for anti-lambda) with the probability 63.9%. The second very probable decay (35.8%) into and neutral was not considered in this analysis because these daughters with the neutral electric charge can not be detected directly. The other decays with the probability much less than 1% was also not considered in this analysis. For this analysis the filterbit 16 was used, what means the standard cuts for the tracks coming from the TPC and ITS were used with the very loose cut on DCA. In the analysis there was also used the trigger AliVEvent::kINT7. Selection of the lambda baryons to the analysis has two steps. First of them is the identification of the daughter particles for which was reconstructed secondary vertex, and the second step are kinematics cuts into the most of important parameters of the lambda baryon decay.

4.1 PID of daughter particles Particle Identification (PID) method for the lambda baryons daughters is based on the Nσ where N stands for number of standard deviations of the Gaussian distribution around the theoretical values. The information for the daughters identification comes from the TPC detector. Measured energy loss dE/dx of detected particles was compared to the theoretical values of Bethe–Bloch parametrization of ionization energy loss. Only particles with the Nσ < 5.0 were added to the analysis.

4.2 Kinematics cuts In this subsection are listed the kinematics cuts for the lambda baryons and their daughters taken to the the analysis. Some of these cuts are based on the distance of the closest approach (DCA) between reconstructed tracks or vertexes. Scheme of the lambda decay are presented in Fig. 3. In this analysis were applied following kinematic cuts into the lambda baryons candidates: Transverse momentum and pseudorapidity

The cuts on the pT and the η values were applied both to the mother particles and to the daughter particles. Only particles which fulfill the following cuts were selected to the analysis:

– Transverse momentum range:

– Lambda baryons: 0.5 < pT < 4 GeV/c Warsaw University of Technology 7

Fig. 3: Scheme of the lambda baryon decay.

– Daughter protons: 0.3 < pT < 4 GeV/c

– Daughter : 0.16 < pT < 4 GeV/c – Pseudorapidity range:

– |η| < 0.8 (both for the mother and the daughters particles)

DCA between daughter tracks The closest distance between the pion–proton pair tracks is one of the most important kinematic cuts, because if the pair passes the applied condition, it is selected to the analysis and considered as the daughters of the ”candidate” for the lambda baryon. Due to inaccuracy of the detector, it is impossible to define directly if these tracks begin in the same point of the weak decay. However, if the measurable quantity like the DCA between daughter tracks is close to zero value, it is very probable for them to originate from the same point. In this analysis only lambda baryons candidates with the DCA between the daughter tracks < 1 cm were selected. Cosine of the Pointing Angle The pointing angle is the angle between the reconstructed momentum of the lambda baryon and the line joining the primary and the secondary vertex. If a value of cos(θ) = 1, it would indicate that the lambda baryon comes directly from the primary vertex and could be defined as the primary particle. Candidates for the lambda baryon with the values of cosine of the pointing angle (CPA) less than 1 are possibly the secondary particles, which come from the decays of the heavier particles, or the particles coming as a result collision any primary particle with the detector’s material. In this analysis the minimum CPA>0.99 cut was used. DCA to the primary vertex DCA to the primary vertex is defined as the distance between the tracks reconstructions and the primary vertex. The minimum cuts on the DCA to the primary vertex for the daughters in aim to avoid joining the primary particles to the pair of lambda baryon candidates daughters. Only these particles, which daughters with the DCA to the primary vertex > 0.06 cm were applied to the analysis. 8 Internship report

Decay length The distance between the primary and the secondary vertex is called the decay length. It is the estimated distance that the lambda baryon passes from the moment of its creation to the decay. If the decay length is too short, what means the decay point was estimated very close to the primary vertex, the sample of daughter particles may be contaminated by the primary particles. Lambda baryons with the decay length range (0.5,100) cm were added to the analysis. Number of TPC clusters Sample of the daughter tracks might be contaminated by the fake tracks reconstructed by the TPC. In aim to reduce this contamination there was applied the cut on the minimal number of the TPC clusters responsible for the track reconstruction. The daughter tracks were applied to the analysis if at least 70 clusters were used in the process of the track reconstruction.

5 Data analysis 5.1 Lambda baryons origin prediction in MC data The AOD files obtained from the MC models contain the all necessary data about track reconstruction, type and origin of the analysed particles. Because of that fact the origin analysis for the accepted by PID and kinematics cuts particles can be made. The origin analysis for the lambda baryons in the MC models were determined as follows:

1. If the pair pπ− coming from the same collision passes PID and kinematics cuts, and the DCA of mother particle to Primary Vertex < 0.6 cm then the particle, from which decay this pair may come, is classified as candidate to the lambda baryon and is added to the ”Lambda All” distribution.

2. Checking if particles in the pair pπ− do not come directly from the collision.

3. Checking if particles in the pair pπ− have the same mother particle.

4. Checking if the mother particle exists in MC tracks.

5. Checking if the PGD code of the mother particle is equal 3122.

6. Checking if the Λ baryon is not the product of the weak decay.

7. Checking if the Λ baryon do not come from the material of the detector.

8. Checking if the Λ baryon comes directly from the collision.

If candidate for the lambda baryon do not pass one of the following conditions, it is added to adequate bin in the Origin Percentage histogram and it is no longer considered in next conditions. For the Λ¯ baryons the adequate analysis was made, where as the Λ¯ baryons candidates the pairsp ¯π− were used. The origin percentage for the primary and weak decay baryons are estimated as the ratio of number√ of these kinds of particles to the total number of candidates. Obtained results for the pp collisions at s = 13 TeV and √ Pb-Pb collisions at sNN = 5.02 TeV for different pT ranges are presented in Fig. 4 (pp collisions) and Fig. 5 (Pb-Pb collisions). The template-fit method requires Primary, Weak Decay, Material and Fake distributions as well for the DCA and the CPA values. Creating process of these distributions was based on the above origin analysis conditions but in this case the inforamtion about the transverse momentum and the DCA or the CPA values of classified particles were saved to the adequate distributions. The DCA distributions were created with DCA mother particle to the primary vertex < 5.0 cm cut in the first condition. All lambda Warsaw University of Technology 9

√ Fig. 4: Lambda and anti-lambda origin percentage estimated by MC model for pp collisions at s = 13 TeV for different pT ranges.

Fig. 5: Lambda and anti-lambda origin percentage estimated by MC model for Pb-Pb collisions at √ sNN = 5.02 TeV for different pT ranges. 10 Internship report

(or antilambda) baryons which did not pass the cut number 8, they were added to√ the Fake distributions. All DCA and CPA distributions for the whole p ranges for the pp collisions at s = 13 TeV and Pb-Pb √ T collisions at sNN = 5.02 TeV are presented in Fig. 6 and Fig. 7.

Fig. 6: DCA and the CPA distributions for the primary (black), from weak decays (red), from material ¯ p (green)√ and fake (blue) Λ and Λ baryons in whole T range obtained in the MC model for pp collisions at s = 13 TeV.

Fig. 7: DCA and the CPA distributions for the primary (black), from weak decays (red), from material (green) and fake (blue) Λ and Λ¯ baryons in whole p range obtained in the MC model for Pb-Pb collisions √ T at sNN = 5.02 TeV. Warsaw University of Technology 11

5.2 Template-fits method In the data from the real collisions there is no information about if the Λ baryons are primary, from material or from weak decays. There is only information about candidates to Λ baryons and because of that fact only Lambda All distributions can be created. In aim to estimate the origin percentage of detected particles the template-fits method was used in which MC distributions for DCA and CPA mentioned in the previous subsection were fitted to the real collisions data distributions. The template- fits method was made according to the following steps:

1. The Primary, Weak Decay, Material and Fake distributions are normalized to the total number of entrances to All distributions from the real data collisions.

2. All MC distributions are added with the wages equal 1.0 into one MC All distribution.

3. The MC All distribution is fitted to the real collisions data distribution by the method fit() from TFractionFitter which is implemented into the ROOT environment. As the result of this method the wages of the MC distributions are changed in order to fit their sum to the real data distributions.

4. The origin percentages are estimated as the ratio of integral in the certain range of the adequate waged distributions to the integral in the same range of the MCAll distribution. The range of these integrations for DCA distributions was equal 0.0−0.6 cm and for the CPA distributions it was the whole range (0.99,1.00)

Results obtained in this analysis for the DCA distributions are presented in Fig. 8 (Λ baryons obtained in pp collisions), Fig. 9 (Λ¯ baryons obtained in pp collisions), Fig. 10 (Λ baryons obtained in Pb- Pb collisions), Fig. 11 (Λ¯ baryons obtained in Pb-Pb collisions). Fractions for primary, weak decay, material and fake particles obtained in the analysis in transverse momentum bins are presented in Fig. 12 (pp collisions) and Fig. 13 (Pb-Pb collisions). It can be seen that there is visible difference between the origin percentage in the MC predictions and in the template-fits method especially for the lower transverse momentum ranges. All fractions obtained in this analysis are written in tables (1,2) (MC predictions for pp collisions), tables (3,4) (results from DCA template-fit method for pp collisions), tables (5,6) (MC predictions for Pb-Pb collisions) and tables (7,8) (results from DCA template-fit method for Pb-Pb collisions).

pT range Primaries Weak Decay Material Fake 1-2 GeV/c 87.0% 11.2% 0.1% 0.5% 2-3 GeV/c 87.8% 10.8% 0.1% 0.3% 3-4 GeV/c 88.3% 10.7% 0.1% 0.2%

Table√ 1: Fractions for primary, weak decay, material and fake Λ predicted by MC data for pp collisions at s = 13 TeV

pT range Primaries Weak Decay Material Fake 1-2 GeV/c 87.0% 11.3% 0.0% 0.5% 2-3 GeV/c 87.6% 11.0% 0.0% 0.3% 3-4 GeV/c 88.1% 10.4% 0.0% 0.2%

Table√ 2: Fractions for primary, weak decay, material and fake Λ predicted by MC data for pp collisions at s = 13 TeV

The same template-fits analysis for the CPA distributions was not possible due to small statistic for the CPA values < 0.9975, especially for the higher pT ranges. In these cases the template-fits method 12 Internship report

pT range Primaries Weak Decay Material Fake 0.5-1.0 GeV/c 75.3% 20.4% 1.8% 2.4% 1.0-1.5 GeV/c 71.6% 25.1% 1.2% 2.1% 1.5-2.0 GeV/c 83.1% 16.8% 0.0% 0.1% 2.0-2.5 GeV/c 75.5% 22.5% 0.0% 0.0% 2.5-3.0 GeV/c 76.2% 23.8% 0.0% 0.0% 3.0-3.5 GeV/c 78.5% 21.4% 0.0% 0.1% 3.5-4.0 GeV/c 80.7% 19.1% 0.0% 0.1%

Table 3: Fractions for√ primary, weak decay, material and fake Λ obtained in DCA template-fit method for pp collisions at s = 13 TeV

pT range Primaries Weak Decay Material Fake 0.5-1.0 GeV/c 70.8% 28.2% 0.2% 0.9% 1.0-1.5 GeV/c 68.0% 30.4% 0.2% 1.5% 1.5-2.0 GeV/c 75.9% 24.0% 0.0% 0.1% 2.0-2.5 GeV/c 73.2% 26.7% 0.0% 0.0% 2.5-3.0 GeV/c 76.8% 23.1% 0.0% 0.1% 3.0-3.5 GeV/c 74.7% 25.2% 0.0% 0.0% 3.5-4.0 GeV/c 79.1% 20.9% 0.0% 0.0%

Table 4: Fractions for√ primary, weak decay, material and fake Λ obtained in DCA template-fit method for pp collisions at s = 13 TeV

pT range Primaries Weak Decay Material Fake 1-2 GeV/c 75.0% 9.4% 0.1% 10.6% 2-3 GeV/c 81.4% 8.7% 0.0% 7.1% 3-4 GeV/c 84.6% 7.5% 0.0% 6.1% Table 5: Fractions for primary, weak decay, material and fake Λ predicted by MC data for Pb-Pb colli- √ sions at sNN = 5.02 TeV

pT range Primaries Weak Decay Material Fake 1-2 GeV/c 72.2% 14.4% 0.0% 10.6% 2-3 GeV/c 80.0% 12.2% 0.0% 7.1% 3-4 GeV/c 82.8% 10.8% 0.0% 6.1% Table 6: Fractions for primary, weak decay, material and fake Λ predicted by MC data for Pb-Pb colli- √ sions at sNN = 5.02 TeV Warsaw University of Technology 13

pT range Primaries Weak Decay Material Fake 0.5-1.0 GeV/c 51.0% 32.1% 6.0% 10.9% 1.0-1.5 GeV/c 55.2% 39.4% 1.6% 3.8% 1.5-2.0 GeV/c 62.4% 37.6% 0.0% 0.0% 2.0-2.5 GeV/c 66.0% 34.0% 0.0% 0.0% 2.5-3.0 GeV/c 68.2% 31.8% 0.0% 0.0% 3.0-3.5 GeV/c 70.6% 29.4% 0.0% 0.0% 3.5-4.0 GeV/c 80.6% 19.4% 0.1% 0.0% Table 7: Fractions for primary, weak decay, material and fake Λ obtained in DCA template-fit method √ for Pb-Pb collisions at sNN = 5.02 TeV

pT range Primaries Weak Decay Material Fake 0.5-1.0 GeV/c 45.9% 51.5% 0.1% 2.5% 1.0-1.5 GeV/c 57.6% 42.1% 0.0% 0.2% 1.5-2.0 GeV/c 62.6% 37.4% 0.0% 0.1% 2.0-2.5 GeV/c 65.4% 34.6% 0.0% 0.0% 2.5-3.0 GeV/c 67.3% 32.7% 0.0% 0.0% 3.0-3.5 GeV/c 69.7% 30.3% 0.0% 0.0% 3.5-4.0 GeV/c 71.8% 28.2% 0.0% 0.0% Table 8: Fractions for primary, weak decay, material and fake Λ obtained in DCA template-fit method √ for Pb-Pb collisions at sNN = 5.02 TeV returned equal values for primary and weak decay distributions, or the not a number values. The attempt of making the template-fits analysis for the CPA distributions are presented in Fig. 14 (pp collisions) and Fig. 15 (Pb-Pb collisions).

6 Summary √ In this report the results of the MC origin and the data-driven method analysis for the s = 13 TeV pp √ and sNN = 5.02 TeV Pb-Pb collisions are shown. Results from the template-fits method show that for the lower pT ranges there is visible difference between the secondary contamination estimated by the MC models and the template-fits in DCA distributions. Results obtained in the same method for the CPA distributions are not reliable, because of the lack of the statistics in the CPA range < 0.9975. 14 Internship report

p Fig. 8: Data-driven√ method used on the DCA distributions for Λ baryons for different T ranges obtained for pp collisions at s = 13 TeV

¯ p Fig. 9: Data-driven√ method used on the DCA distributions for Λ baryons for different T ranges obtained for pp collisions at s = 13 TeV Warsaw University of Technology 15

Fig. 10: Data-driven method used on the DCA distributions for Λ baryons for different p ranges ob- √ T tained for for Pb-Pb collisions at sNN = 5.02 TeV

Fig. 11: Data-driven method used on the DCA distributions for Λ¯ baryons for different p ranges ob- √ T tained for for Pb-Pb collisions at sNN = 5.02 TeV 16 Internship report

p Fig. 12: Primary, weak decay, material and fake fractions√ in T bins obtained in the DCA template-fit method for Λ (left) and Λ (right) for pp collisions at s = 13 TeV.

Fig. 13: Primary, weak decay, material and fake fractions in p bins obtained in the DCA template-fit √ T method for Λ (left) and Λ (right) for Pb-Pb collisions at sNN = 5.02 TeV.

p Fig. 14: Data-driven√ method used on the CPA distributions for Λ baryons for different T ranges obtained for pp collisions at s = 13 TeV Warsaw University of Technology 17

Fig. 15: Data-driven method used on the CPA distributions for Λ baryons for different p ranges obtained √ T for for Pb-Pb collisions at sNN = 5.02 TeV 18 Internship report

References

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