kyoto univ. riken katsuro nakamura (kyoto university) 2012/ 2/ 13 kyoto university gcoe symposium...
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Kyoto Univ. RIKEN
Double Spin Asymmetryof Single Electron Productionon Proton-Proton CollisionsKatsuro Nakamura (Kyoto University)
2012/ 2/ 13Kyoto University GCOE Symposium
2012/2/131Kyoto University GCOE Symposium
Kyoto Univ. / JSPS / RIKEN
Internal Structure of a Nucleon Internal structure of a nucleon ~ parton
model ~– discovery of Bjorken scaling law
establishment of the parton model Bjorken : the momentum fraction of parton
– total momentum fractions for each parton
proton spin puzzle
– Deeply Inelastic Scattering (DIS) experiment
– ~ 25% !? Large contribution from gluon
polarization ?2012/2/13 Kyoto University GCOE Symposium 2
proton spin quark spin gluon spin orbital
proton (spin1/2)
𝑔1 (𝑥 )=12∑ 𝑒𝑞
2Δ𝑞(𝑥)
Acta.Phys.Polon.B33(2002)2813
Kyoto Univ. / JSPS / RIKEN
Gluon Polarization Measurement
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
effectively2012/2/13 Kyoto University GCOE Symposium 3
hep-ex/0612055
DIS experimentSIDIS experiment
not enough constraints
Kyoto Univ. / JSPS / RIKENCurrent Statusof Gluon Polarization Measurement
2012/2/13 Kyoto University GCOE Symposium 4
PRL 103(2009)012003
spin asymmetry of production
Nucl.Phys.B 813(2009)106
using only DIS data
using DIS + RHIC data
x
gluon polarization in a proton
Polarized p-p collision experiment– direct contribution from gluon– measurement provides the largest constraint
on Weak points of the measurement
– large uncertainty of fragmentation functions– dependence on function form of modeling
further multiple measurements with various channels are required
Diagram of pion production
Kyoto Univ. / JSPS / RIKENSpin Asymmetryof Heavy Quark Production
2012/2/13 Kyoto University GCOE Symposium 5
𝒄 ,𝒄
𝝅𝟎
PYTHIA simulation
spin asymmetry of heavy quark production– the main reaction is gluon-gluon
scattering– direct measurement for the gluon
polarization– hard process validity of
pQCD an ideal channel to measure
the gluon polarization
distribution of Bjorken of gluons contributed to each reaction
Kyoto Univ. / JSPS / RIKEN
Spin Asymmetryof Single Electron Production
measurement of the heavy quark at PHENIX– detect an electron from heavy meson decay
spin asymmetry of the single electron production– asymmetry of inclusive (Signal+BG) electron production ALL
S+BG
– BG reduction for large Signal Occupancy is important for the measurement of the spin asymmetry
2012/2/13 Kyoto University GCOE Symposium 6
eKD
eKD
e
e
0
0
D
0K e
e
cc
Occupancy Signal :
1
11
BGS
e single
BGSBGBGSe single
e
e
LLLLLLLL
N
ND
AD
AD
DA
DA
single electron
Kyoto Univ. / JSPS / RIKENBackgroundfor the Single Electron Measurement
7
photonic electron photon conversion
Dalitz decay
direct photon conversion small, but significant at high pT
non-photonic electron Heavy meson decay
Kaon decay
vector meson decay
material)(in )(0 ee
ee )(0
eKK ee : 03
eeJ ,,,,
XeD
dominant background
background
background~ a few% ofnon-photonic electronsat pT > 0.50GeV/c
photonic~95%
( signal )
PHENIX 05’ single e and BG cross section
rejected by HBD (shown in later)
single electrons can be estimated by subtractingphotonic electrons from total inclusive electrons
2011/10/9 PHENIX Collaboration Meeting
Kyoto Univ. / JSPS / RIKEN
AGSLINACBooster
Tandem
RHIC
Brookhaven National Lab. (U.S.)RHIC accelerator
2012/2/13 Kyoto University GCOE Symposium 8
PHENIX
AGS
LINAC BOOSTER
Pol. Proton Source
Spin RotatorsSiberian Snakes
RHIC CNI (pC) PolarimetersAbsolute Polarimeter (H jet)
RHIC
collisionspin directionspin direction
: a bunch of protons (protons) the world’s only accelerator for the polarized protons– bunch-by-bunch spin direction is
different
luminosity relative :
1
L
LR
RNN
RNN
PPA
YBLL
analyzed dataproton-proton collisions
at 200GeVintegrated luminosity ~ 6.1pb-
1 <beam polarization> ~ 57%
Kyoto Univ. / JSPS / RIKEN
RHIC PHENIX detector PHENIX : detector complex
– pseudrapidity: |η| < 0.35– azimuthal coverage: Δφ = 2× π/2
Drift Chamber + Pad Chamber (DC + PC)– tracking & momentum reconstruction
for charged tracks RICH Counter
– electron identification Electromagnetic Calorimeter (EMCal)
– energy measurement for electrons & photons
Hadron Blind Detector (HBD)– BG rejection for the electron
measurement– this measurement is the first operation
of the HBD– important detector for the
measurement2012/2/13 Kyoto University GCOE Symposium 9
PHENIX detectors
polarized-p 100GeV
polarized-p100GeV
drift chamberpad chamber
RICH
EM. Calorimeter
HBD
e
Kyoto Univ. / JSPS / RIKEN
Hadron Blind Detector (HBD)
2012/2/13 Kyoto University GCOE Symposium 10
D
e
single electron
ee
photonic electron( electron pair )
0 ~ field
0 ~ masspair
BHBD cluster charge distributions
each histograms arenormalized asintegral=1(or0.1)
HBD
CF4 gas
e
50cmp beam
p beam
Hadron Blind Detector– gas Cerenkov detector read out with
CsI evaporated GEM– electron identification
this analysis is the first time of physics measurement with HBD
Kyoto Univ. / JSPS / RIKENNew Analysis Methodfor the Single Electron
11
HBD cluster charge distribution
electronsingleN
electronmergeNelectron
scintiN
reference charge distributionsfitting result 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
accept
~70%
~20%
electron events0.75<pT<1.00GeV/c
Yield of single electrons is estimated with this method
2011/10/9 PHENIX Collaboration Meeting
Yield of single electrons
reconstructedelectrons
estimatedsingle electrons
established a new analysis method for single electron analysis
Kyoto Univ. / JSPS / RIKEN
Check of Cross Section Spectrum
2012/2/13 Kyoto University GCOE Symposium 12
cross section of single electron production– good consistency with
previous measurements different analysis method
from previous measurements– converter & cocktail
method for 2005 and 2006 results
confirmation of the reliabilityof the analysis method with HBD
w/ HBD(this analysis)
w/o HBD(previous measurements)
cross section of single electron production
Kyoto Univ. / JSPS / RIKENmeasurement of spin asymmetryof single electron production
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
w/ HBD(this measurement)
w/o HBD(previous measurements)
signal occupancy
Kyoto Univ. / JSPS / RIKENSpin Asymmetry forSingle Electron Production
142011/10/9 PHENIX Collaboration Meeting
success of an approach to by using the very clean channel
– estimation of the constraint for from the result is on going now
spin asymmetry of single electron production
Kyoto Univ. / JSPS / RIKEN
SummarySummary 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 with the very clean channel is succeeded.
Future Prospect estimation of constraint on from the result is on going now
2012/2/13 Kyoto University GCOE Symposium 15
Kyoto Univ. RIKEN
backup slides
2012/2/1316Kyoto University GCOE Symposium
Kyoto Univ. / JSPS / RIKEN
Table of systematic errors
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
Kyoto Univ. / JSPS / RIKEN
charge distribution of merged clusters(pi0 combined events)
18
Blue: definition in offline codeRed: ideal definition
Sect2 South Sect2 North
Sect3 North
Sect4 South
Sect8 South Sect8 North
Sect9 South Sect9 North
Sect10 South Sect10 North
slightly different
21% 28%
17%
38%
14%
(fraction-fraction)/fraction
16%
19% 31%
31% 40%
2012/2/13 Kyoto University GCOE Symposium
Spin Puzzle ~EMC measurement~• polarized DIS measurement
– 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 19
)(2
1)(
)1(2
21
12
1
xqexg
ARx
Fg
Kyoto University GCOE Symposium
Kyoto Univ. / JSPS / RIKEN
パートンの軌道角運動量
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
2012/2/13 21)'(
)1,0,0,1(
)'(
2
)(2
)'(),,(~
)()'(),,(~
)2()2('2
)(2
)'(),,()()'(),,()2()2('2
22
2
52525
22
PPn
n
PPt
qP
Qx
PUM
PUxEPUPUxHPnnPed
PUM
iPUxEPUPUxHPnnPe
d
xi
xi
definition:
Bjorken x
Mandelstam-tlight-cone vector
difference of longitudinal momentum Kyoto University GCOE Symposium
Deeply Virtual Compton Scattering(DVCS)
• DVCS amplitude measurement of GPD
2012/2/13 22
GPD
e
e
qq’ = q - Δ
P’ = P + ΔP
)(2
)'(),,(~
)()'(),,(~
2/
1
2/
1
2
)(2
)'(),,()()'(),,(
2/
1
2/
1)(
2
1),,(
5252
1
1
22
1
1
PUM
PUxEPUnPUxH
ixixdxnp
i
PUM
niPUxEPUnPUxH
ixixdxgnpnpqPT
Δ = P’-P
x + ξ x - ξ
Kyoto University GCOE Symposium
Model-dependent constraintson Ju and Jd
• large model dependence
• cannot refer about quark angular momentum contribution for the proton spin yet
2012/2/13 23
another model
Sd
Su
Kyoto University GCOE Symposium
Kyoto Univ. / JSPS / RIKEN
charm quark fragmentation function
2012/2/13 Kyoto University GCOE Symposium 24
PRD 73(2006)032002