final state spin physics at nica spin-praha-2013 and nica-spin-2013 praha, july 8, 2013 oleg teryaev...
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FINAL STATE SPIN PHYSICS AT NICA SPIN-Praha-2013 and NICA-SPIN-2013Praha, July 8, 2013
Oleg TeryaevBLTP, JINR
MOTIVATION: SEARCH for COMMON/RELATED SPIN PHYSICS PROBLEMS for MPD/SPD/BM@N
Talks of D. Peshechonov, A. Nagaytsev,A.V.Efremov, A. Guskov, O.Shevchenko…:
Developing program for SPD
HIC@MPD
Suggestion: explore polarisation of Lambda hyperons and tensor polrisation of vector mesons at MPD&BM@N
Outline
Initial and final state spin effects: SPD/MPD/BM@N
T-odd and T-even effects - vector and tensor polarization
Spin effects - search for signs of global rotation of QCD matter
Chiral Vortical Effect & neutron asymmetries @ NICA
Hyperon polarizations Dilepton angular distributions
Initial and final state effects 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)
(Lambda) hyperon polarisation 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 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 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 –
randomization Dileptons@(BM@N)/MPD?! (H)IC@SPD?!
Positivity for dilepton angular distribution
Angular distribution
Positivity of the matrix (= hadronic tensor in dilepton rest frame)
+ cubic – det M0> 0 1st line – Lam&Tung by SF method
Positivity bound for Sivers asymmetry Not allowed for pure thansverse photons!
Consistency tests for Sivers vs unpolarized asymmetries
For partially polarized nucleons : |µ| -> |µ|/|s|
Stronger bound for λ deviation from 1!
Positivity bounds vs unpolarized data: Peng, Roloff,OT’11 (plot by diploma student S. Khlebtsov)
BG/DYW type duality for DY SSA in exclusive limit 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?
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
NICA range preferable
Anomaly in medium – new external lines in VVA graph
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
Coupling:
Current: - Uniform chemical potentials: - Rapidly (and similarly) changing
chemical potentials:
Comparing CME and CVE
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 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)
UrQMD model : 2-particles -> 3-particles correlations
no necessity to fix the event plane
2 neutrons from mid-rapidity
+1 from ZDC PP?!
Other sources of quadratic effects
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
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)
Hadronic in-medium tensor – analogs of spin-averaged structure functions: p -> v
Only polar angle dependence
Tests for production mechanisms
Positivity tests!
Magnetic field conductivity and asymmetries
zz-component of conductivity (~hadronic) tensor dominates
λ =-1 Longitudinal polarization with
respect to magnetic field axis Excludes “Collins-type” angular
distributions
Other signals of rotation
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? 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 Bilinear effect of vorticity – generates quark
axial current Strange quarks - should lead to Λ polarization Scale – of % order (due to relatively small
volume occupied by vorticity) 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
FS spin effects – possibility for coherent physical program of SPD, MPD, BM@N
Special role of hyperons (Λ) and VM polarisation
Possible probe of vorticity Pion handedness under
investigation
Another description of spin-rotation coupling – gravitomagnetic effects
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
Effective Lagrangian
Current and charge density from c (~7/45) –term
(multiscale medium!)
Light quarks -> matching with D. Kharzeev et al’ -> correlation of density of electric charge with a gradient of topological one (Lattice ?)
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Properties of perturbative charge separation 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 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
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
C-violation by chemical potential -> (Weldon ’92)
(OT’96; Radzhabov, Volkov, Yudichev ’05,06 - NJL)
New (?) option: in magnetic field
Polarization (angular distribution in c.m. frame ) of dilepton (with respect to field direction!)
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Approximation: EM part – vacuum value Two-stage forbidden decays - I
Two-stage forbidden decays -II
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Relating forbidden and allowed decays
In the case of complete mass degeneracy (OT’05, unpublished):
Tests and corrections – in progress
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Conclusions
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