Kyoto Univ.
RIKEN
Katsuro Nakamura (Kyoto University)
2012/ 2/ 13
Kyoto University GCOE Symposium
Kyoto University GCOE Symposium
1
2012/2/13
Kyoto Univ. / JSPS / RIKEN

Internal structure of a nucleon ～parton
model ～
𝑔1 𝑥 =
1
2
𝑒𝑞 2 Δ𝑞(𝑥)
– discovery of Bjorken scaling law


establishment of the parton model
Bjorken 𝑥 : the momentum fraction of parton
– total momentum fractions for each parton


𝑈: 𝐷: 𝑔 ～ 36%: 18%: 46%
proton spin puzzle
1
1 ΔΣ + Δ𝐺 + 𝐿
=
2
2
gluon spin orbital
quark spin
proton spin
– Deeply Inelastic Scattering (DIS)
experiment
– ΔΣ～25% !?
proton (spin1/2)

Acta.Phys.Polon.B33(2002)2813
2012/2/13
Kyoto University GCOE Symposium
2
Kyoto Univ. / JSPS / RIKEN

SIDIS
experiment
DIS
experiment
DIS experiment
– lepton-nucleon scattering
– cannot access to gluon in
leading order

semi-inclusive DIS
experiment
– next leading order



high pT hadron pair
measurement
open charm measurement
difficult to constraint on
𝚫𝑮 effectively
hep-ex/0612055
2012/2/13
not enough constraints
Kyoto University GCOE Symposium
3
Kyoto Univ. / JSPS / RIKEN

Polarized p-p collision experiment
– direct contribution from gluon
– 𝜋 0 measurement provides the largest
constraint on Δ𝐺

Weak points of the 𝝅𝟎 measurement
– large uncertainty of fragmentation functions
– dependence on function form of Δ𝑔
modeling

Diagram of pion production
spin asymmetry of 𝝅𝟎 production
gluon polarization in a proton
using only DIS data
PRL 103(2009)012003
using DIS + RHIC data
Nucl.Phys.B 813(2009)106
2012/2/13
Kyoto University GCOE Symposium
x
4
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𝑨𝑳𝑳
𝑯𝒆𝒂𝒗𝒚 𝑸𝒖𝒂𝒓𝒌
~

𝝈++ 𝑯𝑸 − 𝝈+− 𝑯𝑸
≡
𝝈++ 𝑯𝑸 + 𝝈+− 𝑯𝑸
𝒅𝒙𝟏 𝒅𝒙𝟐 𝒂𝑳𝑳 𝒈𝒈
𝚫𝒈 𝚫𝒈
𝒈 𝒈
spin asymmetry of heavy quark
production
– the main reaction is gluon-gluon
scattering
– direct measurement for the gluon
polarization
distribution of Bjorken 𝒙 of gluons
contributed to each reaction
𝒄, 𝒄
0.5 < 𝑝𝑇 𝑒 < 1.5
PYTHIA simulation
– hard process  validity of pQCD

an ideal channel to measure the
gluon polarization
2012/2/13
𝝅𝟎
Kyoto University GCOE Symposium
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
measurement of the heavy quark at PHENIX
– detect an electron from heavy meson decay
 D   K 0  e e 
 0
 D  K   e e 

single electron
D
K0

e
e
c
c
spin asymmetry of the single electron production
– asymmetry of inclusive (Signal+BG) electron production ALLS+BG
1 S BG 1  D BG
1 S BG
ALL 
ALL 
ALL
D
D
D
N esinglee
D  S BG : Signal Occupancy
Ne
singlee
ALL

– BG reduction for large Signal Occupancy is important
for the measurement of the spin asymmetry
2012/2/13
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photonic
electron
dominant
background

PHENIX 05’ single e and BG cross section
photon conversion
background
Dalitz decay
rejected by HBD (shown in later)
 ( )     e e (in material)
0


 
 0 ( )   e  e 
photonic
~95%
direct photon conversion
small, but significant at high pT
single electrons can be estimated by subtracting
non-photonic
electron from total inclusive electrons
photonic electrons
D  e  X


Kaon decay
background

0

K e3 : K    e e ~ a few% of
vector meson decay non-photonic electrons
 ,  ,  , J  ,   e  e at pT > 0.50GeV/c
2011/10/9
PHENIX Collaboration Meeting
7
Kyoto Univ. / JSPS / RIKEN
Absolute Polarimeter
(H jet)
RHIC CNI (pC) Polarimeters
PHENIX
  
  
    

Siberian Snakes
Spin Rotators
LINAC BOOSTER
Pol. Proton Source

the world’s only accelerator for
the polarized protons
– bunch-by-bunch spin direction is
different
ALL 
R
2012/2/13
collision
AGS
    
1 N    RN  

       PB PY N    RN  
: a bunch of protons (~2 × 1011 protons)
analyzed data
proton-proton collisions
at 𝒔 =200GeV
integrated luminosity ～6.1pb-1
<beam polarization> ～ 57%

L 
: relative luminosity
Kyoto University GCOE Symposium
L 
8
Kyoto Univ. / JSPS / RIKEN
polarized-p
100GeV

polarized-p
PHENIX : detector complex
– pseudrapidity: |η| < 0.35
– azimuthal coverage: Δφ = 2× π/2
100GeV
(DC + PC)
– tracking & momentum
reconstruction for charged tracks
PHENIX detectors
EM. Calorimeter
drift chamber
pad chamber
e
HBD
RICH
2012/2/13
– electron identification
(EMCal)
– energy measurement for electrons
& photons
(HBD)
– BG rejection for the electron
measurement
– this measurement is the first
operation of the HBD
– important detector for the
measurement
Kyoto University GCOE Symposium
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Kyoto Univ. / JSPS / RIKEN
photonic electron
( electron pair )
single electron
p beam
e
CF4
gas
HBD

e
D
p beam
50cm
e

e
pair mass ~ 0
B field ~ 0
HBD cluster charge distributions
Hadron Blind Detector
– gas Cerenkov detector read out
with CsI evaporated GEM
each histograms are
normalized as
integral=1(or0.1)
– electron identification

this analysis is the first time of
physics measurement with HBD
2012/2/13
Kyoto University GCOE Symposium
10
Kyoto Univ. / JSPS / RIKEN
reference
charge
distributions
HBD
cluster
fitting
charge
result
distribution

N
 N ~70%
electron
scinti
~20%
electron
single
electron
events
electron
 N merge
0.75<pT<1.00GeV/c
electron analysis with HBD
– estimate the fractions of single e
clusters and merged clusters by
fitting HBD charge distribution
– reject merged clusters with HBD
charge cut effectively
Yield of single electrons
accept

Yield of single electrons is
estimated with this method
reconstructed
electrons
estimated
single electrons
2011/10/9
PHENIX Collaboration Meeting
11
Kyoto Univ. / JSPS / RIKEN
cross section of single electron production


cross section of single
w/ HBD
electron production
(this analysis)
– good consistency with
previous measurements
different analysis method
w/o HBD
from previous
(previous measurements)
measurements
– converter & cocktail
method for 2005 and
2006 results
2012/2/13
Kyoto University GCOE Symposium
12
Kyoto Univ. / JSPS / RIKEN
signal occupancy
w/ HBD
(this measurement)
w/o HBD
(previous measurements)

Signal Occupancy: D
– the important value for the asymmetry measurement
– increase by about factor of 1.5 from previous
measurements due to the HBD performance
2012/2/13
Kyoto University GCOE Symposium
13
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spin asymmetry of single electron production

– estimation of the constraint for ∆𝒈/𝒈(𝒙) from the result is on going now
2011/10/9
PHENIX Collaboration Meeting
14
Kyoto Univ. / JSPS / RIKEN
Summary




Spin asymmetry of single electron production is an ideal
probe to measure the gluon polarization in a proton.
A new analysis method for the single electron with HBD is
established and confirmed its reliability.
The new method increases the “Signal Occupancy” by a
factor of about 1.5 compared with previous measurements
The approach to the ∆𝒈/𝒈(𝒙) with the very clean channel
is succeeded.
Future Prospect

estimation of constraint on ∆𝒈/𝒈(𝒙) from the result is on
going now
2012/2/13
Kyoto University GCOE Symposium
15
Kyoto Univ.
RIKEN
Kyoto University GCOE Symposium
16
2012/2/13
Kyoto Univ. / JSPS / RIKEN

Single Electron Yield
– HBD cluster charge fitting

25% of merged clusters
– HBD ring charge fitting
– analysis cut


~ 6%
Cross Section
– MB cross section

9.7%
– MB trigger bias

2.5%
– acceptance x reco eff

8%
– trigger efficiency
2012/2/13
Kyoto University GCOE Symposium
17
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Sect2 South
21%
(fraction-fraction)/fraction
Sect2 North
28%
Sect3 North
17%
Sect4 South
38%
Sect8 South
Sect8 North
16%
14%
Sect9 South
Sect9 North
19%
31%
Sect10 South
Sect10 North
31%
40%
Blue: definition in offline code

slightly
Kyoto
University
GCOE
Symposium
2012/2/13
Red: ideal definition
different
18
Spin Puzzle ~EMC measurement~
• polarized DIS measurement
F2
A1
2 x(1  R )
1
2
g1 ( x)   eq q ( x)
2 q
g1 
– SLAC (1976, 1983)
– EMC (1988)
• quarks polarization is only
0.012±0.116±0.234 of the proton
spin
• (assuming Ellis-Jaffe sum rule)
• current quark polarization
– ~ 25% of the proton spin (SIDIS)
2012/2/13
Kyoto University GCOE
Symposium
19
Kyoto Univ. / JSPS / RIKEN
2012/2/13
Kyoto University GCOE Symposium
20
Generalized Parton Distribution (GPD)
• GPD is all-inclusive distribution function of parton
– PDF: momentum distribution of parton
– FF: spatial distribution of parton
• spatial x momentum  orbital angular momentum
definition:
i  
d ix

2

2
 2 e P'  ( n 2)  (n 2) P  H ( x,  ,  )U ( P' ) U ( P)  E ( x,  ,  )U ( P' ) 2M U ( P)  
d ix
 5 
~
~
 5
2
 5
2
 2 e P'  ( n 2)   (n 2) P  H ( x,  ,  )U ( P' )  U ( P)  E ( x,  ,  )U ( P' ) 2M U ( P)  
Q2
x
Bjorken x
2P  q
2012/2/13
2  t  ( P ' P ) 2 Mandelstam-t
light-cone vector
n  (1,0,0,1)
  nKyoto
 ( P 'University
P)
GCOE
difference
of longitudinal
Symposium
21
momentum
Deeply Virtual Compton Scattering
(DVCS)
e
e
q’ = q - Δ
q
x+ξ
P
x-ξ
GPD
Δ = P’-P
P’ = P + Δ
• DVCS amplitude  measurement of GPD
T  ( P, q,  )  
1

1
1
1
( p  n  p n   g  )  dx

2
x   / 2  i
 x   / 2  i
1

 



i  n  
2
2
U ( P)
 U ( P )  E ( x,  ,  )U ( P ' )
 H ( x,  ,  )U ( P ' )n
2M


1

i 
1
1
 
p n  dx

2
x   / 2  i
 x   / 2  i
1
2012/2/13

 

~

 5 
~
2
5
2
H
(
x
,

,

)
U
(
P
'
)
n

U
(
P
)

E
(
x
,

,

)
U
(
P
'
)
U ( P)


Kyoto University GCOE
2M


Symposium
22
Model-dependent constraints
on Ju and Jd
• large model
dependence
• cannot refer about
quark angular
momentum
contribution for
the proton spin yet
2012/2/13
Su
another model
Kyoto University GCOE
Symposium
Sd
23
Kyoto Univ. / JSPS / RIKEN
PRD 73(2006)032002
2012/2/13
Kyoto University GCOE Symposium
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