Heavy Quark Measurementin High‐Energy Heavy‐Ion Collisions
高エネルギー原子核衝突における重いクォークの測定

Takashi HACHIYA
RIKEN
2013/12/20

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Outline• Introduction• Method– Heavy Quark Measurement• Result– p+p 200GeV– d+Au 200GeV– Cu+Cu 200GeV– Au+Au 200GeV• Charm / bottom separation in Au+Au200GeV– PHENIX Silicon Vertex Detector (VTX)• Summary
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Introduction• Quark Gluon Plasma (QGP)– deconfined quarks and gluons in the hot and dense environment– HI collision is only way to create QGP in the laboratory• QGP was formed at RHIC
– Parton energy loss in the medium– Strong v2 described by hydro picture
Parton Energy Lossin the medium

PRL98, 092301 (2007)

NPA757, 184 (2005)

Early thermalisation time

Our focus is moved from “observation of QGP”
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to the detailed investigation of QGP property

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Introduction‐ why heavy flavor?
• Charm and bottom (Heavy Flavors, HF or HQ) in HI collisions– HF is created at the early stage of the collisions• Mainly initial hard scattering due to large mass• the production can be calculated by pQCD
• Secondary and thermal production may happen

Calibrated probe– Pass through the hot and dense medium• Sensitive to the medium propertyg

Energy loss

AQAg

Q

Flowmedium

Heavy flavor is clean probe to study property of QGP
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Observables from QGP• Modification of pT spectrum at high pT

Energy loss

– Sensitive to parton energy loss in the medium
0

Nuclear Modification Factor
1 d 2 N AA ( pt ) / dpt dyRAA N coll d 2 N pp ( pt ) / dpt dy
RAA = 1 : Ncoll (binary) scaling
RAA < 1 : Suppression

Expected that HF suffers less energy loss than light quarks.
“Dead cone effect” : Energy loss: Eg >  ELQ >  EHQ

Similer with energy loss in the matter, Ee >  Eߤ
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Observables from QGP• Azimuthal anisotropy v2– Different pressure gradient in non‐central collision causes anisotropy
in particle emission
Non‐central collisions

Fourier Transformd 3N
1 d 2NE 3 (1   2 n cos[n(  r )])d p 2 pt dpt dyn 1zＹReaction
planex– Sensitive to the collective motion and thermalization at low pT• less (or no) flow for HQ was expected.

– Path length dependence of energy loss at high pT

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Cold Nuclear Matter EffectShadowing Effect• Shadowing effect– nPDF is different with PDF in pp– Heavy Quark yield might be small
antishadowing• Cronin effect– initial parton scattering causes
the kT modification• This effect must be in the HIC

shadowingSensitive regionarXiv:0802.0139• This effect can be studied usingp(d)+A collision where the QGP
doesn’t form

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Open Heavy Flavor Measurements
K+-Indirect method
D0cK
cD0Direct method• Direct method– Reconstruct parent HF hadron using decay products. B ‐> J/psi +X (BR: 1%)– Clear signal, but branting ratio is too small (large BG) D0  K (BR : 4% )D+  K (BR : 9.4% )but small acc.

• Indirect method– Measure electrons from semi‐leptonic decays of heavy‐flavors
Branching ratio– (relatively) Large branching ratio.
c  e + X (BR : 9.6%)– PHENIX relies on this methodb e + X (BR : 11%)2013/12/20

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8PHENIX Detector and electron ID• PHENIX Central Arm– 2 arm structure– ||<0.35– =/2 x 2,

• Charged particle tracking
and momentume+• Drift chamber• Pad chamber• Electron Identification• RICH is primary eIDdevice.
• EMCal measures energy :2013/12/20

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PHENIX detector

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Electron ID with RICH + EMCAL
Measured Ring Image in RICH
RICHSideview
E/p distribution•RICH

Charged particle– Ring Imaging Cherenkov Detector• C02 : ~4.8GeV/c + threshold• cosc =(n)‐1 : n– Hadron rejection ~ 50~100x– nHit and RING shape cut•

eID (RICH)– E/p ~ 1 for electrons,– E/p << 1 for hadrons– ~ 5~10x rejection•Net

E/p matching using EMCAL and momentum

In2013/12/20
total, ~300 rejection achieved

BG
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Electrons Source(HF decays and Backgrounds)• Non‐photonic Electrons

Relative yield of BG e (calculation)– Heavy Flavor Electrons (HFe)• Semi‐leptonic decays of heavy flavorc → e, b → e– Background Electrons ：• Ke3 (K → e） <6% @ pT>1GeV/c• ,, → ee <3%@pT>1GeV/c• J/ → ee, Drell‐Yan– Small contribution at low pT• Photonic Electrons– Dalitz decays : 0,→ee,  → 0ee
– Photon conversions : 0,→ ,  → ee
– Major background in experiment, needs
to subtract
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Photon Converter• Converter methodconvoutN

e+non N NNconvin  R N (1)Nnon– The converter increases photonic ewith fixed factor.

e-• Photonic e calibration– Advantage: small sys. error– Dis: Small statistics, low pT• Cocktail method– Based on measured pion yield(and others)• mT scaling– Calculated by the decay generator– Advantage: reach to high pT– Dis : sys error limited by pionmeasurement

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HF electrons in p+p and Au+Au 200GeVp+p 200GeV••Au+Au 200GeV

Heavy Flavor electrons was measured with wide pT range in both pp and Au+Au
Heavy Flavor electrons in p+p200GeV– FONNL is consistent w/ data .
– FONNL : Charm < bottom around 4GeV/c in pT•

Heavy Flavor electrons in Au+Au 200GeV– Binary scaling at low pT
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Heavy Flavor Electrons in Au+Au 200GeV• RAA: large suppression

PRC 84 (2011) 044905

ଵே௘ሺ஺௨ା஺௨ሻ– RAA =ே೎೚೗೗ே௘ሺ௣ା௣ሻ– RAA (HFe) shows• Large suppression similar
with pion at high pT– Indicating similar energy
loss with pion

• Consistent with Ncoll
scaling at low pT• v2 : non‐zero flow
– HF is also affected byflow

One of the most surprising results
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Model comparison & /s evaluation• Collisional energy loss
models with common D
failed to reproduce RAAand v2.
• RAA and v2 is comparedwith langevin basedmodel– DHQ = 4~6/(2T)reproduces the data• D ~ 6 × /Ts at mu_B =0– /s ~ (4/3‐2)/4

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pQCD based modelMore comparisonsRadiative
Radiative + Collisional• Some models reproduces our data
– Which one ?

• Separated B and D measurement
gives more constraint to themodels.
– Is it possible to separate radiativeand collisional energy loss?
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Heavy Flavor Electrons in d+Au and Cu+Cu• d+Au– study the CNM effect since no QGP is created inp(d)+Au• Cu+Cu– study the energy loss effect in smaller system

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Heavy Flavor Electronsin d+Au and Cu+Cu 200GeV
d+Au (2008) PRL 109, 242301 (2012)

Cu+Cu arXiv:1310.8286v1• Heavy flavor electrons were measured in bothd+Au and Cu+Cu 200GeV with wide pT range

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Heavy Flavor Electron RAA in d+Au 200GeVPRL 109, 242301 (2012)

In peripheral,• RAA =1 for all pT range:– Consistent with p+p within
uncertainty.

In central,• RAA > 1 at mid pT:
 Cronin‐like initial scattering?
similar trend is seen in pion
• No suppression from CNM– Large suppression in Au+Au canbe attributed to the hot anddense matter effect• Enhancement may also beapparent in Au+Au
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Heavy Flavor Electrons in Cu+Cu 200GeVRAA

arXiv:1310.8286v1 [nucl‐ex]• In peripheral,– Significant enhancement– Similar with d+Au.

pT[GeV/c]
RAA• In central,– Slight suppression at highpT

pT[GeV/c]
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System Size Dependence
HFe in 200GeV

arXiv:1310.8286v1

Central RCuCu ~ Peripheral RAuAu• RdAu > RCuCu > RAuAuNpart(5.4±1.0)(98.2±2.4)

Central RdAu ~ Peripheral RCuCu(352.2±3.3)– Npart ~ system size

• Similar enhancement inRdAu@cent ~ RCuCu@peri• Similar suppression inRCuCu@cent ~ RAuAu@peri
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System size : <RAA> vs <Npart>1<pT<3 GeV/c3<pT<5 GeV/c• Smoothly changing in dAu ‐> CuCu ‐> AuAu
– Enhancement at small size (small Npart)– Suppression at large size (large Npart)– Consistent behavior in 2 different pT bins

• This trend is dependent on the system size (Npart)• OverallunderstandHF energy loss seen in Au+Au
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Bottom / Charm Separation• Direct Measurement– D meson reconstruction at RHIC
– D meson reconstruction at ALICE– Non‐prompt J/psi at CMS (B from Jpsi)• Bottom and Charm separation using HFe

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DK+

Direct Measurement of D/B

LHC measurement

STAR measurement @ QM12

arXiv:1310.7366v1 [hep‐ex]

NPA 904–905 (2013) 170c–177c•

At RHIC (STAR)– Suppression is comparable with pi (consistent with HFe)
– The maximum at 2GeV/c is consistent with transverse flow models•

At LHC (ALICE and CMS)
– First measurement of non‐prompt Jpsi
– Clear mass ordering of HF suppression ( RAA(D)< RAA(np Jpsi))

2013/12/20•

What happen in RHIC?

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Bottom / Charm Separation• Direct Measurement– D meson reconstruction at RHIC
– D meson reconstruction at ALICE– Non‐prompt J/psi at CMS• Bottom and Charm separation using HFe

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Charm/bottom separation using DCA
SecondaryVertex

Ke

•DDCA

YieldbeamPrimary Vertex

Distance of Closest Approach• DCA of electron track fromprimary vertex• DCA corresponds to the lifetime(c)beamUnique lifetime of c and b

Data
Charm
BottomBackground

D0
D+
B0
B+

122.9 μm
311.8 μm457.2 μm
491.1 μm

Charm
BottomPrecise DCA measurement allows
clear separation of charms and bottoms
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DCA

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PHENIX Silicon Vertex Detector(VTX)• VTX was installed from Run2011– Large coverage

Layer 3• ||<1.2,  ~ 2

Layer 2Layer 1Layer 0– 4 layer silicon detectors• 2 inner pixel detector• 2 outer stripixel detector

AuAu– Placed near collision (R~2.5cm)– DCA & Primary vertex• DCA resolution of 77um isarchived
AuAu at 200 GeV
y (cm)

RUN2011: Au+Au at 200 GeV

Beam size (beam) ~ 90 um

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x (cm)
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Pixel Detector in detail cross‐section view
Solder bump

• Developed by RIKEN with ALICE• Channels: : 3900k channels– PHENIX EMCAL :buswire25 m25k channels

Sensor module(Sensor+4ROchip)• Spec:– Pixel Size: 50 um () x 425 um (z)– sensor module + 4 RO chips.
– Bump bonding

sensorSupport &Cooling

Wires with encap.

Readout chip

BusSensor

Stave
Cooling Tube20cm

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DCA decomposition

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DCA Decomposition
DCA data are fit by expected DCA shapes of••

Signal components : ce and be (right column)
Background components (left column)
 expected DCA shape Charm/Bottom
assumes PYTHIAspectra Background : detector
simulation withmeasured data input

Fit range :0.2<|DCA|<1.5(mm)2013/12/20

b/(b+c)=0.22+‐0.06
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Bottom to HF(b+c) ratio in p+pbe
From Fit of the DCA distributionc eb eFirst direct measurements of bottom production at RHIC in p+p
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32Comparison
From Fit of the DCA distribution
PHENIX
Published dataagree with new data

FONLL agreewith data

VTX direct measurement of b/b+c using DCA confirms
published results using e‐h correlation
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From Fit of the DCA distribution
PHENIX
Published dataagree with new data

FONLL agreewith data

STAR indirect
measurement isconsistent with ourdata

VTX direct measurement of b/b+c using DCA confirms
published results using e‐h correlation
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DCA decompositionin Au+Au

PHENIX Preliminary

DCA distribution shows:• N(e) at large DCA is smaller than inpp
• This implies b suppression
 B has longer decay length• Difficulty in Au+Au– The expected DCA shape depends on the its parent pT shape• It is a convolution of parent pT spectrum and decay kinematics• Especially for pT<MB/2 e

At a centain low pT,
p+p: expected DCA wideAuAu：expected DCAnarrow

B
DCA

Currently, we are developing new method.
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DCA35

Snapshot of c/b separation
This is simulation• Some methods are being tested if charm and bottom contribution can beseparated properly using HFe DCA distribution.
– Unfolding technique.

• This method work well to reproduce the input pT distribution of D and Bmeson• We keep testing the method what is the best way to remove the bias inthe method.
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Summary• Heavy Flavor electrons (from heavy flavor decay) were measured
in p+p, d+Au, Au+Au, Cu+Cu 200GeV at RHIC
– Strong suppression and v2 in Au+Au 200GeV• Small eta/s, consistent with other measurement– Enhancement in central d+Au
– Smooth changing from enhancement to suppression in Cu+Cu– Some models succeeded reproduce the data.
• It is necessary to describe overall behavior of Raa and v2 for small‐large system• Separated measurement of bottom and charm provides further constraint• Direct measurement– D is consistent with HFe suppression at RHIC and LHC– Non‐prompt J/psi from Bdecay shows RAA(np‐Jpsi) > RAA(D) at LHC• Bottom / charm separation is in progress– New method shows better separation in simulation.
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Outlook• Cu+Au and U+U data in run12 is in hand
– Data analysis is on‐going– Systematic study of RAA and v2 extends to other systems.

• Au+Au 200 GeV in run14 will start soon
– We plan to take more data with run11 Au+Au• VTX is fully functional– Large statistics allows us to measure non‐prompt Jpsi inPHENIX

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