Central exclusive production in proton-proton collisions

Bc. Tomáš Truhlář

Faculty of Nuclear Sciences and Physical EngineeringCzech Technical University in Prague

Supervisor: W lodzimierz Guryn, Ph.DConsultant: doc. Mgr. Jaroslav Bielčík, Ph.D.

September 18, 2019

Bc. Tomáš Truhlář (FNSPE, CTU) Research project defense September 18, 2019 1 / 17

Introduction Experimental setup Event selection Results Summary and the next steps

Overview

1 Introduction

2 Experimental setup

3 Event selection

4 Results

5 Summary and the next steps

Bc. Tomáš Truhlář (FNSPE, CTU) Research project defense September 18, 2019 2 / 17

Introduction Experimental setup Event selection Results Summary and the next steps

1 Introduction

2 Experimental setup

3 Event selection

4 Results

5 Summary and the next steps

Bc. Tomáš Truhlář (FNSPE, CTU) Research project defense September 18, 2019 3 / 17

Introduction Experimental setup Event selection Results Summary and the next steps

Introduction

Central exclusive production (CEP):

Diffractive processes

Potential source of the gluon bound states,glueballs

Glueballs are predicted by the QCD theory

Their existence has not been unambiguouslyconfirmed yet

Goals of this work:

Develop software for picoDST production and validate it

Validate data from proton-proton collisions at√s = 510 GeV collected by the

STAR experiment in 2017 (Run17)

Produce picoDSTs for all Run17

Data:

Run17 RHICf period pp√s = 510 GeV

Data were taken: Jun 25 - 27, 2017

Priorly produced for testing reasons

Bc. Tomáš Truhlář (FNSPE, CTU) Research project defense September 18, 2019 4 / 17

Introduction Experimental setup Event selection Results Summary and the next steps

Central Exclusive Production

Looking for Double IPomeron Exchange(dominant CEP mechanism)

Colliding protons emerge intact

Each proton ”emits” a IPomeron

Two IPomerons produce neutral state X

p + p → p∆η1⊕ X

∆η2⊕ p

pp

pp

p

XIP

IP

State X is separated by rapidity gap fromoutgoing protons p

Central state X is fully measured in the TPCand TOF

From the conservation of momentum we have: pmissT = 0 = (~p1 + ~p2 + ~q+ + ~q−)T

⇒ events with small pmissT are Exclusive

I focus on p + p → p π+π−p

Bc. Tomáš Truhlář (FNSPE, CTU) Research project defense September 18, 2019 5 / 17

Introduction Experimental setup Event selection Results Summary and the next steps

1 Introduction

2 Experimental setup

3 Event selection

4 Results

5 Summary and the next steps

Bc. Tomáš Truhlář (FNSPE, CTU) Research project defense September 18, 2019 6 / 17

Introduction Experimental setup Event selection Results Summary and the next steps

Experiment STAR

STAR:

Solenoidal Tracker at RHICMassive, large-acceptance multi-purposeparticle detectorDesigned to study the stronglyinteracting matter at high temperatureand high energy densityOnly one active experiment at present

RHIC:

Relativistic Heavy Ion Collider withcircumference of 3, 834 mLocated at Brookhaven NationalLaboratory in one of the biggestscientific facilities in the U.S.Only major accelerator capable ofcolliding polarized protons

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Introduction Experimental setup Event selection Results Summary and the next steps

Experimental setup

STAR’s unique capabilities:

High-resolution tracking of charged particles in TPC covering |η| < 1 and full φ

Precise PID through the measurement of dE/dx and Time-of-Flight

BBC detectors covering forward rapidity 2.1 < |η| < 5.0 to ensure rapidity gap

Silicon Strip Detectors in Roman Pots for measurement of forward protons

Roman Pot Phase II*:

8 Silicon Strip Detectorpackages installed in RomanPot vessels

Detectors are mounted in 4stations: 2 stations on eachsite of STAR

Each stations containing 2Roman Pots (above andbelow the beamline)

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Introduction Experimental setup Event selection Results Summary and the next steps

1 Introduction

2 Experimental setup

3 Event selection

4 Results

5 Summary and the next steps

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Introduction Experimental setup Event selection Results Summary and the next steps

Event selection

At least one of central productionstriggers

Only Elastic or Inelastic combinationin Roman Pots

Exactly 2 good quality tracks inRoman Pots (one per side)

Exactly 2 TPC tracks matched with 2TOF hits coming from the samevertex (looking for π+π−)

Total charge of those tracks equals 0

No cuts on TPC/TOF track quality

pmissT < 100 MeV (next slide)

PID cut (next slide)

There are 1477 exclusive eventsremaining

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Introduction Experimental setup Event selection Results Summary and the next steps

Missing pT distributions

Missing pT defined as:

pmissT = (~p1+ ~p2+~π++~π−)T

From the conservation ofmomentum: pmiss

T ≡ 0

Since there is a trackresolution of detector

pmissT < 100 MeV

Less than the mass ofpion, the lightest meson

Peak from exclusiveevent is clearly visible.

Bc. Tomáš Truhlář (FNSPE, CTU) Research project defense September 18, 2019 11 / 17

Introduction Experimental setup Event selection Results Summary and the next steps

Missing pT distributions

Missing pT defined as:

pmissT = (~p1+ ~p2+~π++~π−)T

From the conservation ofmomentum: pmiss

T ≡ 0

Since there is a trackresolution of detector

pmissT < 100 MeV

Less than the mass ofpion, the lightest meson

Peak from exclusiveevent is clearly visible.

Bc. Tomáš Truhlář (FNSPE, CTU) Research project defense September 18, 2019 11 / 17

Introduction Experimental setup Event selection Results Summary and the next steps

Particle identification

At RHIC energies DIPE with π+π− is expected to be dominant

Based on dE/dx most of the particles are pions, especially after the pmissT cut

For particle pair identification was used only nσpairπ < 3 cut

nσpairπ =

√(nσtrk

π+

)2+(nσtrk

π−

)2

Bc. Tomáš Truhlář (FNSPE, CTU) Research project defense September 18, 2019 12 / 17

Introduction Experimental setup Event selection Results Summary and the next steps

1 Introduction

2 Experimental setup

3 Event selection

4 Results

5 Summary and the next steps

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Introduction Experimental setup Event selection Results Summary and the next steps

Invariant mass of π+π−

The first measurement of invariant mass ofπ+π− from RHICf period

The latest measurement by the STARexperiment

arXiv:1811.03315

The expected features in the invariant mass distribution are seen: drop at about 1GeV and peak at about 1270 MeVThe distribution is not corrected for acceptance, efficiencies etc.

Bc. Tomáš Truhlář (FNSPE, CTU) Research project defense September 18, 2019 14 / 17

Introduction Experimental setup Event selection Results Summary and the next steps

Invariant mass of π+π−

The first measurement of invariant mass ofπ+π− from RHICf period

The latest measurement by the STARexperiment

arXiv:1811.03315

The expected features in the invariant mass distribution are seen: drop at about 1GeV and peak at about 1270 MeVThe distribution is not corrected for acceptance, efficiencies etc.

Bc. Tomáš Truhlář (FNSPE, CTU) Research project defense September 18, 2019 14 / 17

Introduction Experimental setup Event selection Results Summary and the next steps

Invariant mass of π+π−

The first measurement of invariant mass ofπ+π− from the first 5 % of Run17

The latest measurement by the STARexperiment

arXiv:1811.03315

The expected features in the invariant mass distribution are seen: drop at about 1GeV and peak at about 1270 MeVThe distribution is not corrected for acceptance, efficiencies etc.

Bc. Tomáš Truhlář (FNSPE, CTU) Research project defense September 18, 2019 15 / 17

Introduction Experimental setup Event selection Results Summary and the next steps

1 Introduction

2 Experimental setup

3 Event selection

4 Results

5 Summary and the next steps

Bc. Tomáš Truhlář (FNSPE, CTU) Research project defense September 18, 2019 16 / 17

Introduction Experimental setup Event selection Results Summary and the next steps

Summary and the next steps

Summary:

The software for picoDST production was developed

The picoDST production was validated

There is a peak from exclusive events in missing pT

The expected features in the invariant mass distribution are seen: drop at about 1GeV and peak at about 1270 MeV

The first 5% of Run17 were analyzed and it looks promising

The next steps:

Produce picoDSTs for whole Run17

Apply TPC/TOF track quality cuts

Apply more complex PID methods

Study processes with K+K−, pp̄ and π+π−π+π−

Thank you!

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