Transcript Strange Quarks Polarisation from Gluon Anomaly IWHSS

FINAL STATE SPIN
PHYSICS AT NICA
NICA-SPIN 2013
JINR, March 18, 2013
Oleg Teryaev
BLTP, JINR
Outline
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Initial and final state spin effects:
SPD/MPD/BM@N
T-odd and T-even effects - vector and tensor
polarization
Rotating QCD matter
Spin effects - search for signs of global
rotation
Chiral Vortical Effect & neutron asymmetries
@ NICA
Initial and final state effects
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Polarisations of final state particles -> angular
distributions
SSA (T-odd) and DSA (T-even)
May be studied in NN,NA,AA collsions
May be correlated to initial state polarisations
FS Spin effects - open possibility of spin
physics at all NICA detectors
(SPD,MPD,BM@N)
Single Spin Asymmetries
(vector polarisation)
Ʌ-polarisation
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Self-analyzing in weak decay
Directly related to s-quarks polarisation
Probe of QCD matter formation (Jacob,
Rafelsky, 80’s)
Randomization – smearing – no direction
normal to the scattering plane
Systematic study of in pp,pA,AA collisions at
the same detector (BM@N,MPD)
Perturbative PHASES IN QCD
Short+ large overlap–
twist 3
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Quarks – only from hadrons
Various options for factorization – shift of SH
separation (prototype of duality)
New option for SSA: Instead of 1-loop twist 2
– Born twist 3: Efremov, OT (85, Ferminonc
poles); Qiu, Sterman (91, GLUONIC poles)
Double spin asymmetries
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Tensor polarisation of vector mesons ->
angular distribution of decay products
(dileptons, pions,…)
Quadratic effects – no P(T)-violation
Correlation with initial state (vector)
polarization – Sivers function in DY
Modifications in QGP matter – randomizatio
Dileptons@(BM@N)/MPD?! (H)IC@SPD?!
BG/DYW type duality for DY
SSA in exclusive limit
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Proton-antiproton DY – valence annihilation - cross
section is described by Dirac FF squared
The same SSA due to interference of Dirac and Pauli
FF’s with a phase shift (Rekalo,Brodsky)
Exclusive large energy limit; x -> 1 :
T(x,x)/q(x) -> Im F2/F1
Both directions – estimate of Sivers at large x and
explanation of phases in FF’s
NN -> BG type duality with transition FF’s NN->NNπ
How fast is the rotation in
HIC?
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Magnetic field – highest possible ever =
CME
Rotation – another pseudovector –
angular velocity
Also highest possible! - velocities ~ c at
the distances ~ Compton length
Is it observable?!
Model calculations
(Baznat,Gudima,Sorin,OT)
arXiv:1301.7003v1 [nucl-th]
Structure of velocity and
vorticity fields (5 GeV/c)
Hydrodynamical Helicity
(=v rot v) separation
Energy dependence
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NICA range preferable
Anomaly in medium – new
external lines in VVA graph
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Gauge field -> velocity
CME -> CVE
Kharzeev,
Zhitnitsky (07) –
EM current
Straightforward
generalization:
any (e.g. baryonic)
current – neutron asymmeries@NICA Rogachevsky, Sorin, OT - PRC
Baryon charge with neutrons –
(Generalized) Chiral Vortical Effect
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Coupling:
Current:
- Uniform chemical potentials:
- Rapidly (and similarly) changing
chemical potentials:
Comparing CME and CVE
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Orbital Angular Momentum and
magnetic moment are proportional –
Larmor theorem
Vorticity for uniform rotation –
proportional to OAM
Same scale as magnetic field
Tests are required
Observation of GCVE
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Sign of topological field fluctuations
unknown – need quadratic (in induced
current) effects
CME – like-sign and opposite-sign
correlations – S. Voloshin
No antineutrons, but like-sign baryonic
charge correlations possible
Look for neutron pairs correlations!
MPD may be well suited for neutrons!
Estimates of statistical accuracy
at NICA MPD (months of running)
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UrQMD model :
2-particles -> 3-particles correlations
no necessity to fix
the event plane
2 neutrons from
mid-rapidity
+1 from ZDC
Other sources of quadratic
effects
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Quadratic effect of induced currents –
not necessary involve (C)P-violation
May emerge also as C&P even quantity
Complementary probes of two-current
correlators desirable
Natural probe – dilepton angular
distributions
Observational effects of
current correlators in medium
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McLerran Toimela’85
Dileptons production rate
Structures –similar to DIS F1, F2
(p ->v)
Tensor polarization of in-medium
vector mesons (Bratkovskaya,
Toneev, OT’95)
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Hadronic in-medium
tensor – analogs of
spin-averaged
structure functions:
p -> v
Only polar angle
dependence
Tests for production
mechanisms
General hadronic tensor and
dilepton angular distribution
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Angular distribution
Positivity of the matrix (= hadronic
tensor in dilepton rest frame)
+ cubic – det M> 0
1st line – Lam&Tung by SF method
Magnetic field conductivity
and asymmetries
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zz-component of conductivity
(~hadronic) tensor dominates
λ =-1
Longitudinal polarization with respect to
magnetic field axis
Effects of dilepton motion – work in
progress
Other signals of rotation
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Hyperons (in particular, Λ) polarization
(self-analyzing in weak decay)
Searched at RHIC (S. Voloshin et al.) –
oriented plane (slow neutrons) - no
signal observed
No tensor polarizations as well
Why rotation is not seen?
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Possible origin – distributed orbital angular
momentum and local spin-orbit coupling
Only small amount of collective OAM is
coupled to polarization
The same should affect lepton polarization
Global (pions) momenta correlations
(handedness) – OT,Usubov, work in progress
New sources of Λ polarization
coupling to rotation
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Bilinear effect of vorticity – generates
quark axial current (Son, Surowka)
Strange quarks - should lead to Λ
polarization
Proportional to (square of) chemical
potential – small at RHIC – may be
probed at
FAIR & NICA
Newly found T2 term –compensated by
(exponential) polarisation dilution
CONCLUSIONS
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FS spin effects – possibility for coherent
physical program of SPD, MPD, BM@N
Special role of hyperons (ʌ) and VM
polarisation
Possible probe of vorticity
Pion handedness under investigation
Another description of spin-rotation
coupling – gravitomagnetic effects
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Rotation +Equivalence Principle =
gravitomagnetic field
Coupled to Gravitational Formfactors
Analogous to EM ones – related to
Generalized Parton Distributions and
angular momenta of quarks and gluons
Dirac equation in (strong) gravitational
fields – Obukhov, Silenko, OT
HIC applications in progress
Induced current for (heavy - with
respect to magnetic field strength)
strange quarks
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Effective Lagrangian
~
~
4
4
L  c( FF )(GG) / m  d ( FF)(GG) / m
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Current and charge density from c (~7/45) –
~
~ 
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j

2
c
F

(
G
G
) / m4
term
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
 ~ H 
(multiscale medium!)
~
~
 ~ (GG ) / m 4   d 4 xGG
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Light quarks -> matching with D. Kharzeev et al’ ->
correlation of density of electric charge with a
gradient of topological one (Lattice ?)
Properties of perturbative
charge separation
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Current carriers are obvious - strange quarks -> matching ->
light quarks?
NO obvious relation to chirality – contribution to axial current
starts from pentagon (!) diagram
No relation to topollogy (also pure QED effect exists)
Effect for strange quarks is of the same order as for the light
ones if topological charge is localized on the distances ~ 1/ms ,
strongly (4th power!) depends on the numerical factor : Ratio of
strange/light – sensitive probe of correlation length
Universality of strange and charm quarks separation - charm
separation suppressed as (ms /mc)4 ~ 0.0001
Charm production is also suppressed – relative effects may be
comparable at moderate energies (NICA?) – but low statistics
Comparing CME to
strangeness polarization
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Strangeness polarization – correlation of
(singlet) quark current
(chromo)magnetic field
(nucleon) helicity
Chiral Magnetic Effect - correlation of
(electromagnetic) quark current
(electro)magnetic field
(Chirality flipping) Topological charge
gradient
Local symmetry violation
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CME – assumed to be the sign of local
P(C) violation
BUT Matrix elements of topological
charge, its density and gradient are
zero
Signs of real C(P) violation – forbidden
processes
Forbidden decays in vacuum –
allowed in medium
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C-violation by chemical potential ->
 
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e
e
(Weldon ’92)
  
(OT’96; Radzhabov, Volkov,
Yudichev ’05,06 - NJL)
 
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e
e
New (?) option:
in magnetic
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H
~
field 
m
Polarization (angular distribution in c.m.
2
~
1

cos
 (with
frame ) of dilepton
respect to field direction!)
 e e
 
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2
4
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Approximation: EM part – vacuum
value Two-stage forbidden decays - I
 
  
Two-stage forbidden decays II
 
  e e
Relating forbidden and
allowed decays
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In the case of complete mass
degeneracy (OT’05, unpublished):
 e e
 
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9  e e

4  
Tests and corrections – in progress
Conclusions
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Chiral Vortical Effect – to be probed in the neutron
asymmetries (at NICA?)
Bilinear current correlator may be probed in dilepton
asymmetries
Various medium-induced decays may be related to
each other