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Manabu Togawa for the PHENIX collaboration from Kyoto University
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Transcript of Manabu Togawa for the PHENIX collaboration from Kyoto University
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Measurement of the single transverse-spin asymmetry of forward neutrons in p-p
collisions at RHIC-PHENIX
Manabu Togawa
for the PHENIX collaboration
from Kyoto University
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Outline
• Motivation
• PHENIX neutron measurement– Setup– Neutron asymmetry at sqrt(s)=200GeV
• Simulation study• Estimation of asymmetry error at 2005 RUN
– First measurement of neutron asymmetry at sqrt(s)=410GeV
• Summary
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Motivation• In the forward neutron production, there are some inte
resting behaviors.– In ISR experiment, pp sqrt(s)=30~63GeV, cross section of forward
neutron production at low pT was measured to be larger than at high pT. [left pict.]
– In the RHIC IP12 experiment, pp sqrt(s)=200GeV. We found large single transverse-spin asymmetry AN (-10%) [right pict.]
– PHENIX data can shed new light to understand the production mechanism.
<AN>=-0.1090.0072
Kinematics ±2.8mrad
Forward region
xFNucl. Phys. B109 (1976) 347-356
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• Does Feynman scaling hold when going to RHIC energy?
• From the ISR result, C.S. are well scaling by xF at 30<sqrt(s)<63 GeV..
• Forward neutron C.S. has peak structure and it is well described by pion exchange model.
• What is the mechanism of neutron asymmetry ?– pion exchange model
• Asymmetry can be appeared by interference of spin flip amplitude with other’s one.
– Twist-3 model• It can explain asymmetries of forwar
d pion (E704).• Based on pQCD, does it work in suc
h forward kinematics?
Eur.Phys.J.A7:109-119,2000
xF
xF dependencesqrt(s) >= 200GeV - cross section - asymmetry
pT dependencesqrt(s) >= 200GeV - asymmetry
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Forward neutron measurement at PHENIX
~ 1800cm
10cm±2.8mrad
PHENIX Collision Point
Dx magnetblue beam yellow beam
LRRL
LRRLN
NNNN
NNNN
PA
1
AN ~1
P
1
N total
To calculate asymmetry, use square root formula.
Typical energy distribution
GeV
* Energy calibration was done by CuCu data. (1 neutron peak)
scintillator
100GeV
sqrt(s)=200GeV
At 2005 RUN, sqrt(s) = 200, 410GeV polarized proton beams.
Trigger set sqrt(s)=200 sqrt(s)=410
NORTH or SOUTH 12M 11M
(NORTH or SOUTH) & Minbias
90M 72M
NORTH & SOUTH 30M 20M
GeV
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ZDC (Zero Degree Calorimeter) and SMD (Shower Max Detector)
beam
beam
~ 1800cm
10cm±2.8mrad
PHENIX Collision Point
Dx magnetblue beam yellow beam
150
unit:mm
100
Hadronshower
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Hadron Calorimeter
(sampling by Tungsten and fiber plates.)
5.1λT 149X0 (3 ZDCs)Energy resolution ~20% @ 100GeV
Position resolution ~1cm @ 50GeV (sim).
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Neutron asymmetry at PHENIX from RUN5 data (200GeV)
LRRL
LRRLraw
NNNN
NNNNA
Using square root formula.
Detector
Forward
Raw
as
ymm
etry
Backward
Raw
as
ymm
etry
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Simulation study• ZDC and SMD have not been measured energy and
position resolution less than 100GeV.– In the test experiment, energy resolution was measured 100
and 160GeV by proton beam.
• It is necessary to study the response by simulation.– Asymmetry is smeared by position resolution
GeV GeV
~ 21% ~ 20%
Real data (1 neutron @ CuCu data)
Simulation out (neutron 100GeV input)
Simulation is based on geant3.
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Estimation of asymmetry error - energy dependence -
LRRL
LRRLraw
NNNN
NNNNA
)200(@100~
GeVs
energyxF
• A has energy dependence ?– Flat at IP12 experiment.– In this forward region,
rawN
total
raw AP
AN
A11
~
simulation studyError reach ~ 10-3 order
Asymmetry definition
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Estimation of asymmetry error - pT dependence -
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*ryx
yxEpT
simulation studyError reach ~ 10-3 order
pT distribution at sqrt(s) = 200GeV
pT(GeV)
r
(0,0)
(x,y)
n
detector
Max x and y : ~5 cm r ~ 1800 cm
0.1GeV
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Asymmetry at 410GeV
Forward
Raw
as
ymm
etry
Backward
Raw
as
ymm
etry
First measurement
• Asymmetry remains in higher energy region.– pT is larger compared with 200GeV.– Local polarimeter needs this asymmetry until 500GeV in RHI
C spin program. it is expected to remain at 500GeV !
pT(GeV)
Analysis cut effect is uncorrected.
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Summary• We took forward neutron data at sqrt(s)=200 an
d 410 GeV in 2005 RUN at RHIC-PHENIX.• The expected asymmetry error at 2005 RUN w
ere estimated.– Asymmetry will be obtained with 10-3 accuracy. – Energy and pT resolution were estimated by simulati
on.
• Neutron asymmetry at sqrt(s)=410GeV was measured for the first time.– It remains in such high energy.– It is expected that asymmetry will remain when go t
o sqrt(s) = 500GeV.
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Back up
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How to measure how longitudinal?
AL 1
P
AN 1
P L R
L R
Parity violation : allow by weak decay unconvincing
Basic idea is from FNAL704 (AN of forward pion)
The E704 experiment at Fermilab
pp XSqrt(s)=19.4GeVpT=0.2~2.0GeV/c
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Electro Magnetic Cal-based System
-performance-
Calibrated with the beam experiment at SLAC.
E/E ~ 10/sqrt(E) %Noise ~ 1.4GeVx = y ~ 0.15cm for x = y ~ 0.5cm for N
Particle ID logic
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EMCal based results
Succeed in 0 reconstructionM/M ~ 9.3%
Average beam pol. ~ 11%Calculate asymmetry using sqrt root formula.
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Hadron Cal-basedsystem (1 ZDC)
-performance-Energy is calibrated by using cosmic-ray data and simulation. Flat response E>20GeV
E/E ~ 40 to 50 % at E>20GeVx ~ 3 to 4cm(post shower)
Particle ID logic
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Shower MAX Detector
For x-pos : 7For y-pos : 8
150
Unit : mm
• For measuring neutron position, SMD (Shower Max Detector) was installed btw ZDC1 and ZDC2. – Arrays of plastic scintillators – Obtain the position by calculating the center of gravity of
shower generating in first ZDC.– Position resolution ~1cm @ 50GeV neutron (simulation
study).
1 ZDC
SMD
100
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Hadronshower
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Looking neutron peak
After subtract pedestals and apply calibration constant. To match 1 neutron peak is 100. (should be 100 GeV)
SOUTH NORTH
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ZDC shape
GeV
BLUE : SOUTHRED : NORTH
Very agree both shape after calibration.
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Gluon polarization• To understand the spin structure in the nucleon• -> 1/2(proton) = 1/2DS(quark) + DG + L
ALL ( ) ( )
( ) ( )
ALL ~g(x1)
g(x1)
ei2
i
qi(x2)
ei2
i
qi(x2)ˆ a LL (qg q)
γ
For ex. gq -> qγ
Measured in DIS Calculated by pQCD
The experiment of longitudinal polarized proton collide had been started from this year by introducing the spin rotator.
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Square root furmula
LRRL
LRRLN
NNNN
NNNN
PA
1
AN ~1
P
1
N total
where : N total N R N R N L N L
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• Calculate for each bunch.• As a fit function,
Fit for all bunch as D,AB,AY
variables. (55 bunch mode at RUN3)
ALR (i) NL (i) NR (i)
NL (i) NR (i)
ALR D AB PB AY PY
1 DAB PB DAY PY
NL(R) : Number of Left(Right) D : detector asymmetryAB : BLUE asymmetryAY : YELLOW asymmetryPB : BLUE polarizationPY : YELLOWpolarization
Measured by CNI polarimeter
Our measurement
Bunch Fittinig
Pol derection
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Neutron energy (sim)neutron put to center
Input energy
Input energy
Ou
tput
ene
rgy
En
ergy
reso
lution
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Xpos
Ypos
Neutron energy
Neutron energy* Position resolution is defined as RMS.
Input line
Position resolution (sim)neutron put to center
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Neutron energy (sim)neutron put to edge
* Resolution is defined as RMS/Energy
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Asymmetry as function of ZDC2 cut
beam
Gamma stop at ZDC1.Neutron hadron shower goes to ZDC2.
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Reducing asymmetry valueby energy and position smearing
Input : neutron with flat energy distribution, 10 ~ 100GeV input positions are flat for x and y.
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EMCal based results
Calibrated for the photon only.
<AN>=-0.1090.0072
<AN>=-0.1080.0087Detector
Hadron Cal based results
<AN>=-0.1090.0072
AN 1
P L R
L R
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As a local polarimeter system
PHOBOS BRAHMS
STARPHENIX
Spin Rotators
Siberian Snakes
RHIC ( Relativistic Heavy Ion Collider )CNI polarimeter
• One of the main program of RHIC experiment is that the determination of the polarized parton distribution function.– It needs longitudinally polarized proton-proton collision.
• Polarimeter at the collision point is necessary to confirm “beam is longitudinal”. (Local polarimeter)
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RUN5(2005) result.
AAT
AL
2
1cos
A
A
A
A TL
<(RawAsymmetry)/(pol.)/A>
BLUE 9.5 ± 2.2 (%)
YELLOW 15.5 ± 2.4 (%)
Through the RUN5, longitudinal component : <pL/p> BLUE = 99.54 ± 0.12 ± 0.03 (%)<pL/p> YELL = 98.78 ± 0.24 ± 0.06 (%)
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Fill by fill analysisby sqrt formula
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Bunch shuffling : sqrt formula (sim with 1% asymmetry)
Forward LR Forward UD
Backward LR Backward UD
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Bunch shuffling : sqrt formula (forward region)
BLUE LR BLUE UD
YELLOW LR YELLOW UD
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Bunch shuffling : sqrt formula (backward region)
BLUE LR BLUE UD
YELLOW LR YELLOW UD
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