# Presentation: 108869

## SSA in the target fragmentation region of SIDIS

- Cahn and Sivers effects
- Phenomenology & Data in the CFR
- Intrinsic transverse momentum of partons in LEPTO
- Results for TFR
- Discussion & Conclusions

**Aram Kotzinian**
- Torino University & INFN
*On leave in absence from YerPhI, Armenia* *and JINR, Russia*

- M.Anselmino, M.Boglione, U.D’Alesio, A.K., F.Murgia and A.Prokudin: **PRD 71, 074006 (2005)**
- A.K.: **arXiv:hep-ph/0504081**

## Unpolarized SIDIS & Cahn effect 

- x & z are light cone variables defined with respect  *z &     *axes

- No exact               factorization !

##                    approximation

-                    approximation

- Ji *et al: *QCD factorization holds for

- Quadratic in

- Linear in     and proportional to

## Comparison with data: 1

- EMC, 280 GeV muon SIDIS

## Comparison with data: 2 

## Comparison with data: 3

## Comparison with data: 4

- Non Gaussian tail; x, z and flavor dependence of
- intrinsic and fragmentation transverse momentum

- ?

## Sivers effect

- Collins, 2002; Belitski, Ji &Yuan, 2003: Wilson gauge link

- Boer, Mulders & Teryaev, 1997: twist three gluonic pole

## Parameterization for Sivers effect

## Asymmetry

## Data

## New HERMES data

## SIDIS in LO QCD: CFR

- Well classified correlations in TMD distr. and fragm. functions

- Sivers distribution

- Boer distribution

- Helicity distribution

- Collins effect in quark fragmentation

- Mulders distribution

## SIDIS in LO QCD: TFR

- 1994: Trentadue & Veneziano; Graudenz; ... Fracture functions:
- conditional probability of finding a parton ***q ***with momentum
- fraction ***x*** and a hadron*** h*** with the CMS energy fraction **z**

- More correlations for TMD dependent FracFuncs

## Ed. Berger criterion: separation of quark and target remnant fragmentations)

- The typical hadronic correlation length in rapidity is

- Illustrations from P. Mulders:

- EIC: good separation of two mechanisms

## LUND String Fragmentation

- LEPTO: Parton DF, hard X-section & Hadronization are factorized

- Double spin effect – polarized hadronization

## Asymmetry in longitudinally polarized  SIDIS

- The standard expression for SIDIS asymmetry is obtained when

- at HERMES energies in LEPTO ~10-15%

- A.K.: **arXiv:hep-ph/0410093; EPJC (2005)**

## Quark intrinsic transverse momentum in LEPTO

- - Generate virtual photon – quark scattering in collinear configuration:

- - Before

- - After hard scattering

- - Rotate in *l-l’* plane

- - Generate intrinsic transverse momentum of quark (Gaussian*** k******T***)

- - Generate uniform azimuthal distribution of quark (flat by default)

- - Rotate around virtual photon

## Implementing Cahn and Sivers effects in LEPTO

- The common feature of Cahn and Sivers effects
- Unpolarized initial and final quarks
- Fragmenting quark—target remnant system is similar to that in default LEPTO but the direction of      is now modulated

- Cahn:

- Sivers:

- Generate the final quark azimuth
- according to above distributions

## Results: Cahn

- Imbalance of measured
- in TFR and CFR: neutrals?

## Results: Sivers

- Predictions for JLab 12 GeV
- xF-dependence
- Red triangles with error bars – projected statistical accuracy for 1000h data taking
- (H.Avagyan).

- z and xBj-dependences

## Results: Sivers JLab 12 GeV

## SSA in PP-interactions

- E704. Curves:
- by Anselmino  *et al, *

- STAR
- hep-ex/0505024

- More complicated string (color) configurations in the final state.
- Both the active quark and the polarized proton remnant are flying
- in forward direction. Which picture gives dominant contribution?

- Which final hadrons provide
- transverse momentum balance?
- Look at forward baryons

## Discussion & Conclusions

- Both Cahn and Sivers effects are implemented in LEPTO. Possible effects of polarized hadronization were neglected.
- Existing data in CFR are well described by modified LEPTO
- The measured Cahn effect in the TFR is not well described
- Is there an universal mechanism describing SSA in SIDIS and PP interactions?
- It will be interesting to implement Cahn and Sivers effects in PHYTIA
- It is important to perform new measurements of both effects in the TFR (JLab,  HERMES, Electron Ion Colliders)
- This will help better understand hadronization mechanism
- Do the neutral hadrons compensate Cahn effect in CFR?
- Multihadron final states distributions can enhance effects
- Is there a similarity with PP-reaction?
- Fracture Function
- Classification of spin and TMD dependent correlations in Fracture Functions
- “Global” analysis

## Thanks to SSA05

- organizers
- for hospitality @ BNL