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
Bc. Tomáš Truhlář (FNSPE, CTU) Research project defense September 18, 2019 7 / 17
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)
Bc. Tomáš Truhlář (FNSPE, CTU) Research project defense September 18, 2019 8 / 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 9 / 17
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
Bc. Tomáš Truhlář (FNSPE, CTU) Research project defense September 18, 2019 10 / 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
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
Bc. Tomáš Truhlář (FNSPE, CTU) Research project defense September 18, 2019 13 / 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 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!
Bc. Tomáš Truhlář (FNSPE, CTU) Research project defense September 18, 2019 17 / 17