Download - Recent Results in Spin Physics at and
Recent Results in Spin Physics at and
Anselm VossenCenter for Exploration of
Energy and Matter
(Re)Stating the Obvious: Motivation for Studying QCD
QCD successful in describing high energy reactions BUT No consistent description of hadronic sector
Many phenomena that are not understood No consistent description of fundamental bound state of the theory
Compare to QED: Bound state: QED: atom Stringent tests of QED from study of spin structure of hydrogen
g-2 of the electron Lamb shift (Nobel prize 1955)
Vacuum effects: Polarization, Casimir Atomic physics
QCD: Phenomena fundamentally richer Fundamental bound state proton QCD binding energy : most of the visible energy in the universe Nucleon Sea, Theta vacua transitions related to EW Baryogenesis Use transverse spin to study QCD on amplitude level with
interference Tools: Light source p-p Collider
(Re)Stating the Obvious: Motivation for Studying QCD
QCD successful in describing high energy reactions BUT No consistent description of hadronic sector
Many phenomena that are not understood No consistent description of fundamental bound state of the theory
Compare to QED: Bound state: QED: atom Stringent tests of QED from study of spin structure of hydrogen
g-2 of the electron Lamb shift (Nobel prize 1955)
Vacuum effects: Polarization, Casimir Atomic physics
QCD: Phenomena fundamentally richer Fundamental bound state proton QCD binding energy : most of the visible energy in the universe Nucleon Sea, Theta vacua transitions related to EW Baryogenesis Use transverse spin to study QCD on amplitude level with
interference Tools: Light source p-p Collider
Millenium
Prize
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RHIC: The QCD Machine
Outline• RHIC and the STAR detector• Highlights of the longitudinal Spin Program at STAR
• Gluon Polarization• Sea Quark Polarization
• Transverse polarization of quarks in the proton• Measuring Spin Dependent Fragmentation Functions in
e+e- at Belle
RHIC: The QCD Machine
Versatility:• Polarized p+p Sqrt(s) collisions at 62.4 GeV, 200 GeV and 500 GeVRecent Spin Runs:• 2011 500 GeV, longitudinal at Phenix, transverse at STAR ~30 pb-1 sampled• 2012 200 GeV, Phenix and STAR, transverse ~20 pb-1 sampled (STAR: ~x10 statistics)
ANDY/ BRAHMS
STARPHENIX
AGS
LINACBOOSTERPol. H- Source
Spin Rotators(longitudinal polarization)
Siberian Snakes
200 MeV Polarimeter
RHIC pC PolarimetersAbsolute Polarimeter (H jet)
AGS pC PolarimeterStrong AGS Snake
Helical Partial Siberian Snake
Spin Rotators(longitudinal polarization)
Siberian Snakes
E-Lens and Spin Flipper
EBIS
STAR6
7Time Projection Chamber (TPC)Charged Particle Tracking |η|<1.3
Barrel Electromagnetic Calorimeter (BEMC):|η|<1
Endcap Electromagnetic Calorimeter:1<η<2
h = - ln(tan(q/2))
The STAR Detector in 2010
Forward EMC2<η<4
Full azimuth spanned with nearly contiguous electromagnetic calorimetry from -1<h<4
approaching full acceptance detectorPID (Barrel) with dE/dx, in the future: ToF pi/K separation up to 1.9 GeV 8
Central Region (-1<h<1)• Identified Pions, h• Jets
Endcap (1<eta<2)• Pi0, eta, (some) jets
FMS (2<eta<4)• Pi0, eta
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at ultra-relativistic energiesthe proton represents a beamof quark and gluon probes
Jet production provides direct probe of gluon content
Proton Spin Structure with Quark and Gluon Probes
Hard Scattering Process
2P
2 2x P
1P
1 1x P
jet
Dominates at RHIC:
10
20
30 pT(GeV)
10
~ probe gluon content in jet production
)...(
)()()()( 21
1
1
gggga
xAxGxGqgqga
NNNN
A
LL
LL
jetjet
jetjetLL
The related double spin asymmetry:
Gluon Polarization Measurement
experimental doublespin asymmetry
pQCD DIS?G2 Gq q2
Hard Scattering Process
2P
2 2x P
1P
1 1x P
Dominates at RHIC
LGS pz ΔΔΣ21
21
Polarized DIS: ~ 0.3 Poorly
constrained
Jets: Proven Capabilities in p+p, pQCD regime
Jets well understood in STAR, experimentally and theoretically
B.I. Abelev et al. (STAR Coll.), Phys.Rev.Lett. 97, 252001, 2006
SPIN-2010: Matt Walker/Tai Sakuma, for the collaboration
12
Improved precision from 2006 to 2009
Substantially larger figure of merit (P4 x L) than in all previous runs combined
STAR
13
New global analysis with 2009 RHIC data
DSSV++ is a new, preliminary global analysis from the DSSV group that includes 2009 ALL measurements from PHENIX and STAR
First experimental evidence of non-zero gluon polarization in the RHIC range (0.05 < x < 0.2)
2.0
05.0
06.007.0
22 10.0)GeV10,( dxQxg
Special thanks to the DSSV group!
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Probing sea quark polarization through Ws
Weak interaction process Only left-handed quarks Only right-handed anti-quarks
Perfect spin separationParity violating single helicity asymmetry AL
lWdu
lWdu
ALW
u(x1)d (x2)d (x1)u(x2)
ALW d(x1)u (x2)u (x1)d(x2)
• Complementary to SIDIS measurements– High Q2 ~ MW
2
– No fragmentation function effects
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High precision W asymmetry era
First preliminary results from 2012 already provide substantial sensitivity Future results will provide a dramatic reduction in the uncertainties
Δu
Δd
PHENIX and STAR
through 2013 run
Discovery of Large Asymmetries in p+p
Test of QCD: Asymmetries for transverse spin are small at high energies (Kane, Pumplin, Repko, PRL 41, 1689–1692 (1978) )
Xpp π+
π-
π0
LRN
LR
PA
1 :Observable
GeV 20s
Experiment (E704, Fermi National Laboratory):
4q 10,20,3m example, N
qN AGeVsMeV
s
mA
Discovery of Large Asymmetries in p+p
Test of QCD: Asymmetries for transverse spin are small at high energies (Kane, Pumplin, Repko, PRL 41, 1689–1692 (1978) )
Xpp
LRN
LR
PA
1 :Observable
Experiment (STAR, Brookhaven National Laboratory):
4q 10,20,3m example, N
qN AGeVsMeV
s
mA
Effect persists at high energies (pQCD valid)
Possible AN Explanations: Transverse Momentum Dep. Distributions
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SP kT,p
p
p
SP
p
p
Sq kT,π
Sivers Effect:Introduce transverse momentum of parton relative to proton.
Collins Effect:Introduce transverse momentum of fragmenting hadron relative to parton.
Correlation between Proton spin (Sp) and quark spin (Sq) + spin dep. frag. function
Correlation between Proton spin (Sp) and parton transverse momentum kT,p
Number ofCitations:
Intrinsic transverse momentum challenges Current QCD framework
Possible AN Explanations: Transverse Momentum Dep. Distributions
19
SP kT,p
p
p
SP
p
p
Sq kT,π
Sivers Effect:Introduce transverse momentum of parton relative to proton.
Collins Effect:Introduce transverse momentum of fragmenting hadron relative to parton.
Correlation between Proton spin (Sp) and quark spin (Sq) + spin dep. frag. function
Correlation between Proton spin (Sp) and parton transverse momentum kT,p
Talk about this next time;-)
Number ofCitations:
Intrinsic transverse momentum challenges Current QCD framework
Next T
ime
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The three leading order, collinear PDFs
Parton Distribution Functions
q(x)f1
q (x)
q(x) g1
q(x)
Tq(x)h1
q(x)
chiral odd, poorly knownCannot be measured inclusively
unpolarized PDFquark with momentum x=pquark/pproton in a nucleon well known – unpolarized DIS
helicity PDFquark with spin parallel to the nucleon spin in a longitudinally polarized nucleon known – polarized DIS
transversity PDFquark with spin parallel to the nucleon spin in a transversely polarized nucleonHelicity – transversity: direct measurement of the nonzero angular momentum components in the protons wavefunction
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Probability to Find Polarized Quark
γ*
u,d,s
e-
Optical Theorem:
=-Im(Aforward scattering)
+
+ +
+
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Transversity is Chiral Odd
_
+1h
_
+↑
↑ ↑
↑ ↓
↑ ↑
↓ _
• Helicity base: chiral odd• Needs chiral odd partnerFragmentation Function• Does not couple to gluons adifferent QCD evolution than
g1(x)• Valence dominateda Tensor charge gT comparable to
Lattice calculations
Difference in densities for ↑, ↓ quarks in ↑ nucleon
• Transversity base:
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Chiral odd FFs
+_
+1h
_
* *
+
_1H
Collins effect
q
N
1H : Collins FF
24
Chiral odd FFs
+_
+ _
* *
+ q
N
_
Lz-1Lz
1H
Interference Fragmentation Function ( )
1h
25
J.C. Collins, Nucl. Phys. B396, 161(1993)
q
momentum hadron relative : 2
zmomentum hadron e transvers:
momentum hadron :
spinquark : momentumquark :
h
sE
EEpp
sk
h
qh
h
h
q
qs
k
hph ,
Collins Effect:Fragmentation with of a quark q with spin sq into a spinless hadron h carries anazimuthal dependence:
hp
( sin
qh spk
Collins effect in quark fragmentation
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Mid-Rapidity Collins Asymmetry Analysis at STAR
Aexp 2 N sin(C )dc
PBeam N
Φh
–pbeam
pbeamS⊥
pπ
PJET
jT
ΦS STAR provides the full mid-rapidity jet reconstruction and charged pion identification
Look for spin dependent azimuthal distributions of charged pions inside the jets! First proposed by F. Yuan in Phys.Rev.Lett.100:032003.
Measure average weighted yield:
d dUU 1 AN sin(h s)
Run 12 Projections
Mid-rapidity Collins analysis
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Interference FF in Quark Fragmentation
q
qsR
Interference Fragmentation Function:Fragmentation of a transversely polarizedquark q into two spin-less hadron h1, h2 carries anazimuthal dependence:
R
( sin
T qk R s
1h
2h
𝑘𝑠𝑞𝑅𝑅𝑇𝑧𝑝𝑎𝑖𝑟
=2 𝐸𝑝𝑎𝑖𝑟 / √𝑠𝑚
: quark momentum:quark spin : momentum difference 𝑝h1−𝑝h2
transverse hadron momentum difference ¿𝐸𝑝𝑎𝑖𝑟 /𝐸𝑞
: relative hadron pair momentum: hadron pair invariant mass
Di-Hadron Correlations
291 2
1 2
1 2
p+p c.m.s. = lab frame
, : momenta of protons
, : momenta of hadrons
( ) / 2
: proton spin orientation
A B
h h
C h h
C h h
B
P P
P P
P P P
R P P
S
1hP
2hP
100 GeVAP
100 GeVBP
CP
BS
pp hhX
1 2hadron plane: ,
scattering plane: ,
h h
C B
P P
P P
: from scattering plane to hadron plane
R : from polarization vector to scattering plane
S
2 CR
Bacchetta and Radici, PRD70, 094032 (2004)
( ) sin( )S R UT S RA
1 1UTA h H
: Angle between polarisation vector and event plane
30
b
X1f p
a
X
1hSp,
Interference Fragmentation Function in p-p
c
0 / H
D0 /
( ) sin( )S R UT S RA
1 1UTA h H
S
R-S
: Angle between polarisation vector and event plane
NEW: STAR shows significant Signal!
Additional precision data from last years run+ increased kinematic reachExplore 0/channels
+/-+/-
Strong Rapidity DependenceSTAR upgrades will cover h<2 in the near future
<xBj>0.25 (current)0.45: Not probed in SIDIS yet!
Proposed Forward upgrade:h<4
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o Asymmetry is o Need fragmentation function
o Quark spin direction unknown: measurement of Interference Fragmentation function in one hemisphere is not possible
sin φ modulation will average out.
o Correlation between two hemispheres with sin φRi single spin asymmetries results in cos(φR1+φR2) modulation of the observed di-hadron yield.
Measurement of azimuthal correlations for di-pion pairs around the jet axis in two-jet events!
Spin Dependent FF in e+e- : NeedCorrelation between Hemispheres !
1 1UTA h H
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( )
q1
quark-1 spin
Spin dependence in e+e-
quark fragmentation will lead to (azimuthal)asymmetries incorrelation measurements!
Experimental requirements: Small asymmetries very large data sample! Good particle ID to high momenta. Hermetic detector
Measuring spin dependent FFsin e+e- Annihilation into Quarks
electron
positron
q2
quark-2 spin
z1,2 relative pion pair momenta
z2 z1
( )
( ( ( 21221111 m,zHm,zHA cos
Here for di-hadron correlations:
Anselm Vossen 3535
Belle detectorKEKB
Measurement of Fragmentation Functions @
●KEKB: L>2.11 x 1034cm-2s-1
●Asymmetric collider:●8GeV e- + 3.5 GeV e+
●√s=10.58 GeV ((4S))●e+e-(4S)BB●Integrated Luminosity: > 1000 fb-1
●Continuum production: 10.52 GeV●e+e-(u, d, s, c)●>70 fb-1 => continuum
36Collins Asymmetries in Belle 36Large acceptance, good tracking and particle identification!
He/C2H6
Measuring Light Quark Fragmentation Functions on the ϒ(4S) Resonance37
ii
ii
p
npTThrust
ˆ :
• small B contribution (<1%) in high thrust sample• >75% of X-section continuum under ϒ(4S) resonance• ~100 fb-1 ~1000 fb-1
9.44 9.46
e+e- Center-of-Mass Energy (GeV)
0
5
10
15
20
25
(e+ e
- ha
dron
s)(n
b)
(1S)10.0010.02
0
5
10
15
20
25
(2S)10.34 10.37
0
5
10
15
20
25
(3S)10.54 10.58 10.62
0
5
10
15
20
25
(4S)9.44 9.46
e+e- Center-of-Mass Energy (GeV)
0
5
10
15
20
25
(e+ e
- ha
dron
s)(n
b)
(1S)10.0010.02
0
5
10
15
20
25
(2S)10.34 10.37
0
5
10
15
20
25
5
10
15
20
25
(2S)10.34 10.37
0
5
10
15
20
25
(3S)10.54 10.58 10.62
0
5
10
15
20
(3S)10.54 10.58 10.62
0
5
10
15
20
25
(4S)
BB00 BB
e+e-qq, q uds∈
e+e-cc
0.5 0.8 1.0
4s“off”
Interference Fragmentation – thrust method
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e+e- (+-)jet1()jet2X Find pion pairs in opposite
hemispheresObserve angles 1+2
between the event-plane (beam, jet-axis) and the two two-pion planes.
Theoretical guidance by papers of Boer,Jakob,Radici[PRD 67,(2003)] and Artru,Collins[ZPhysC69(1996)]
Early work by Collins, Heppelmann, Ladinsky [NPB420(1994)]
( ( ( 21221111 m,zHm,zHA cos
2
1
1hP
2hP
2h1h PP
Model predictions by:•Jaffe et al. [PRL 80,(1998)]•Radici et al. [PRD 65,(2002)]
39
Transverse Spin Dependent FFs: Cuts and Binning
Full off-resonance and on-resonance data(7-55): ~73 fb-1 + 588 fb-1
Visible energy >7GeV PID: Purities in for pion pairs > 90% Opposite hemisphere between pairs pionsAll hadrons in barrel region: -0.6 < cos (q) <0.9Thrust axis in central area: cosine of thrust axis
around beam <0.75Thrust > 0.8 to remove B-events < 1% B events in
sampleZhad1 >0.2
Asymmetry extractionBuild normalized
yields:
Fit with:
or
,)( 21
NN
)sin()(2cos)cos(
21122112
122112
dcba
122112 )cos( ba
Amplitude a12 directly measures ( IFF ) x ( -IFF ) (no double ratios)
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(z1x m1) Binning
arXiv:1104.2425AV et. al, PRL 107, 072004(2011)
(m1x z1) Binning
arXiv:1104.2425AV et. al, PRL 107, 072004(2011)
42
43
Comparison to theory predictions
• Mass dependence : Magnitude at low masses comparable, high masses significantly larger (some contribution possibly from charm )• Z dependence : Rising behavior steeper
Red line: theory prediction + uncertaintiesBlue points: data
Subprocess contributions (MC)448x8 m1 m2 binning
tau contribution (only significant at high z)charged B(<5%, mostly at higher mass)Neutral B (<2%)charm( 20-60%, mostly at lower z)uds (main contribution)
M. Radici at FF workshop, RIKEN, 11/2012See also: Courtoy: Phys. Rev. Lett. 107:012001,2011
Measurement at Belle leads to first point by point extraction of Transversity
Is Soffer Bound violated?h(x)<|f(x)+g(x)|/2
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Handedness Correlations
Thrust direction
Handedness :¿¿
L R
L/RJet handedness:
𝑁 𝑅 − 𝑁 𝐿
𝑁 𝑅+𝑁 𝐿
C:𝑁 𝑅𝐿+𝑁 𝐿𝑅− 𝑁 𝑅𝑅− 𝑁 𝐿𝐿
𝑁𝑅𝐿+𝑁 𝐿𝑅+𝑁 𝑅𝑅+𝑁 𝐿𝐿
QCD Vacuum Transitions carry Chirality QN
The QCD Vacuum
Difference in winding number:Net chirality carried byInstanton/Sphaleron
– Vacuum states are characterized by “winding number”
– Transition amplitudes: Gluon configurations, carry net chirality
– e.g. quarks: net spin momentum alignment
– Similar mechanism to EW baryogenesis
QCD Vacuum Transitions carry Chirality QN
Kharzeev, McLerran and Warringa, arXiv:0711.0950,Fukushima, Kharzeev and Warringa, arXiv:0808.3382
arXiv:0909.1717v2 [
49
Handedness Correlations
Expect negative correlation for local p-odd effect
Thrust direction
Handedness :¿¿
L R
L/RJet handedness:
𝑁 𝑅 − 𝑁 𝐿
𝑁 𝑅+𝑁 𝐿
C:𝑁 𝑅𝐿+𝑁 𝐿𝑅− 𝑁 𝑅𝑅− 𝑁 𝐿𝐿
𝑁𝑅𝐿+𝑁 𝐿𝑅+𝑁 𝑅𝑅+𝑁 𝐿𝐿
Q=1
Unpolarized Fragmentation Functions
Precise knowledge of upol. FFs necessary for virtually all SIDIS measurements
First FF extraction including uncertainties (e+e-): Hirai, Kumano, Nagai, Sudoh (KEK)Phys. Rev. D 75, 094009 (2007)
q
qγ*e-
e+
hhqD
51
KEKB/BelleSuperKEKB, Upgrade
Aim: super-high luminosity ~1036 cm-2s-1 (~40x KEK/Belle) Upgrades of Accelerator (Microbeams + Higher Currents) and Detector
(Vtx,PID, higher rates, modern DAQ) Significant US contribution
http://belle2.kek.jpFirst data in 2016
52
Highlights for FF Measurements
Kaon efficiency > 95% over relevant kinematics, fake rate < 5%
Vertex resolution improved by order of magnitude
Obviously more statistics
Belle II Status
Summary and Outlook
RHIC is ideal machine to study gluonic properties of the nucleon First result indicating non-zero Gluon polarization in the proton Sea-quark polarization Investigation in surprising transverse spin effects Transversity in di-hadron Correlations and from Collins effect
Investigate high x, high Q2 region Contribution to AN Evolution of kT dependent Collins FF Soffer bound, tensor charge
Belle is the ideal machine to study quark fragmentation Unpolarized Fragmentation functions
Charged pions and kaons Vector mesons and di-hadrons
Polarized fragmentation functions in correlation between hemispheres IFF in charged pion pairs IFF with neutral pions Collins in charged pion pairs Collins in charged kaons, 0, h, vector mesons
Theory of transverse single spin asymmetries is developing rapidly Tests will come from upgrades at STAR/PHENIX and Belle II STAR and Belle are in the middle of major upgrades Far Future: eSTAR at eRHIC
Backup
57
Jet ReconstructionD
etec
tor
GE
AN
TPY
TH
IAetcp
e,,
,
gq,
Part
icle
Data Jets MC Jets Midpoint Cone Algorithm:• Adapted from Tevatron II (hep-exp/0005012• Cone radius = √(Δη2+Δφ2) = 0.7• Split / Merge fraction = 0.5
Anti-KT Algorithm:• Radius = 0.6• Less sensitive to underlying event affectsSTAR Detector has:• Full azimuthal coverage • Charged particle tracking from TPC for |η| < 1.3• E/BEMC provide electromagnetic energy reconstruction for -1 < η < 2.0STAR well suited for jet measurements
58
Spin Decomposition of the Proton
( v v s1 1 Δu Δd Δq2 2
Σ 1 ???
Naïve quark model – 3 valence quark
CERN, SLAC, DESY, JLAB:S ~ 0.30
…and orbital angular momentum…
12 q gJ J
1 Σ2
G
q
g
L
L
QCD:..additional contributions from gluons and gluon splitting, sea quarks…
GΣ21
21
ΔG, Δ/Σ= ?