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