Charged hadron production and two-particle correlation
3in He+Au collisions at 𝒔𝐍𝐍 = 200 GeV measured with PHENIX detector
Sakiko Kudo for the PHENIX collaboration
University of Tsukuba
Motivation

PHENIX detectors

Motivation & Goal

• For track reconstruction, Central arm
spectrometers (CNT, east and westarms) are used.

• Measurements in p+A and d+A collision systems– have been considered to study cold nuclear matter effects without QGP
formation 𝜂 < 0.35, Δ𝜙 = 90°
 Track reconstruction with drift chamberand first layer of the pad chamber (DCPC1) , and additional track confirmation
by requiring an associated hit in the thirdlayer of pad chamber (PC3)
 Momentum resolution ~1.5%(at pT = 1 GeV/c)

However,• hydrodynamic flow and long-range angular correlations in p+A
and d+A collisions– indicated that small but high-density systems could be produced

CNT• 3He+Au collisions– in order to perform a systematic study of small systems having spatial
anisotropy at initial stage

2 • For determination of event• The high pT hadron suppression in heavy ion collisions

information such as collisionvertex position or centrality,
Beam Beam Counter (BBC) is used.

– one of the evidences of Quark-Gluon-Plasma (QGP)

Goal• Charged hadron production and two-particle correlation
measurements in 3He+Au collisions at sNN = 200 GeV• Look for evidences of QGP formation via measurement of highpT hadron production

 3.0 < 𝜂 < 3.9, Δ𝜙 = 360°
 Z = +144.35 cm (north),-144.35 cm (south) BBC has 64 elements of 3 cm quarts
Cherenkov radiator with mesheddynode photo multiplier tubes(PMTs) .

*BBCCentrality determination• In 2014 data taking period, 3He+Au collisions,centrality is defined by BBC charge at south arm
based on Glauber Monte Carlo Simulation.

PHENIX
3He+Au 200GeV*VTX = SVX, ≠FVTX(Forward VTX)

𝒑𝐓 distribution & track cut process
Sample of charged tracks reconstructed with DC-PC1
only is strongly contaminated at pT > ~ 6 GeV/c by decay
products of long lived particles and conversion.
Contamination is an artifact of tracking algorithm whichassumes that all tracks originate from the collision vertex.
The background can be significantly reduced byrequiring track confirmation in the SVX.

Track cut process① SVX hit association cut② DCA cut to select primary track③ PC3 hit association cut
2 pixel layers!! pT spectra are not efficiency corrected !!

Silicon Vertex Detector (SVX) 𝜂 < 1.2, Δ𝜙 ~ 360°
 determine DCA (Distance ofclosest approach) of tracks
with resolution of ~ 100 𝜇m

BBC south(Au-going) charge sum

2 Stripixel layers(BBC narrow trigger ; z vertex <10)

2 types of triggers;
 Minimum Bias (M.B.) trigger
all of events with |z_vtx|<10 High Multiplicity (H.M.) triggerselect more central events
require [BBC PMT tubes > 48 or 49 hits]• Number of events for *Centrality 0-5% is 10
times larger in H.M. triggered sample comparedto M.B. one.

BG effect are reduced..

① SVX hit cut• number ofassociated hitswith CNT track• max 4 SVX layers• In this figure,require the mostinner 2 layers hits

②DCA cut
Background contributions can be
cut using DCA2DR (x,y), DCAZ
measured by SVX.
③ PC3 (most outer pad chamber)

SVX cuts effectively remove background at high pT. Estimationof sample purity and reconstruction efficiency are in progress.

*Centrality 0-5%
BBC(south) charge sum > about 80

Summary & Outlook
Summary Use of H.M. trigger allowed to enlarge data sample available for analysis by a factor of 10.
 We use CNT tracks to measure charged hadron spectra, but it has BG effects especially athigh pT because of decays and secondaries.
 Using 3 steps track cuts which are combination of Drift Chamber track with association tohits in SVX sublayers, DCA cut and PC3 track matching, high pT BG is reduced formeasured pT spectra.

Outlook Nuclear modification factor Rcp and RAA will be calculated with this BG reduction.
 To achieve this analysis goal, under relevant track cut conditions, it is necessary to verify
different BG reduction cuts using full Geant Monte-Carlo detector simulations.

Nuclear modification factor “Rcp”

1𝑐𝑒𝑛𝑡𝑑𝑁𝑐𝑒𝑛𝑡𝑐𝑒𝑛𝑡𝑁𝑐𝑜𝑙𝑙 𝑁𝑒𝑣𝑒
𝑑𝑝𝑇
𝑅𝑐𝑝 =
1𝑑𝑁 𝑝𝑒𝑟𝑖
𝑝𝑒𝑟𝑖
𝑝𝑒𝑟𝑖
𝑑𝑝𝑇𝑁
𝑁
𝑐𝑜𝑙𝑙𝑒𝑣𝑒“The ratio of spectra at Central event to Peripheral event”
 the yield in central 3He + Au (𝑁 𝑐𝑒𝑛𝑡 ) divided bythe yield in peripheral 3He + Au (𝑁 𝑝𝑒𝑟𝑖 ) normalized to the respective numbers of binary
nucleon + nucleon collisions (𝑁𝑐𝑜𝑙𝑙 ) normalized to the numbers of event (𝑁𝑒𝑣𝑒 )