1. Contalbrigo Marco INFN Ferrara CLAS Transverse Target Meeting 4th March, 2010 Frascati

2. M. Contalbrigo2Frascati: CLAS Transverse Target Meeting Resolution:  p/p ~ 1-2%  <~0.6 mrad Electron-hadron separation efficiency ~ 98-99% kinematic range ~ 7 GeV: 1 < Q 2 < 10 GeV 2 0.02 < x < 0.4 self-polarised electrons: e 27 GeV

3. Hyperfine energy levels as a function of the holding field M. Contalbrigo3Frascati: CLAS Transverse Target Meeting The 75  m Al coated cell N 27.5 GeV lepton beam High polarization ~ 80+/-3% No dilution factor ms polarization switching No radiation damage L ~ O(10 31 ) cm -2 s -1

5. Synchrotron radiation cone M. Contalbrigo5Frascati: CLAS Transverse Target Meeting Beam trajectory 2mm shift at cell center 5 kW emitted power at 50 mA beam

6. The holding magnetic field is required to inhibit depolarization mechanism by effectively decoupling the electrons and nucleons magnetic moments while providing the target spin direction. Due to the RF fields induced by the bunched HERA beam, depolarization resonances could happen between different hyperfine states at certain B values. The magnetic flux density has to be stabilized within 0.18 mT M. Contalbrigo6Frascati: CLAS Transverse Target Meeting

7. M. Contalbrigo7Frascati: CLAS Transverse Target Meeting Automatic compensating system added: pair of correcting coils to the main coils The magnetic flux density decreased with time due to the increasing temperature of the main yoke, pole and pole tips, affecting the magnetic permeability of the material (magnet is off during beam injection) Additional correction coils mounted into the cell to increase spatial uniformity of the field Before After

9. M. Contalbrigo9Frascati: CLAS Transverse Target Meeting Two Transverse Magnet Correction algorithms:  TMC1: look up table  TMC2: inverted transfer matrix In order to reconstruct the correct kinematics, it is necessary to measure lepton momentum and angle at the scattering vertex. A correction must be applied to account for how much the trajectory has been deflected by the transverse target magnet between the interaction point and the first drift-chamber plane. Both corrections need accurate field maps

10. M. Contalbrigo10Frascati: CLAS Transverse Target Meeting Field in un-measured regions extrapolated from:  high order polynomials fitting measured points  MAFIA simulations tuned in the measured region

11. M. Contalbrigo11Frascati: CLAS Transverse Target Meeting Gives a trajectory that reaches the (0,0,z) line Look-up table: correction based on a reference track from a database. Reference track selected to match position (closest distance cryterium) momentum and charge measured at the entrance of the HERMES spectrometer. The database maps initial and final coordinates of a simulated sample of tracks. The correction is defined from the reference track as the difference between the initial values extrapolated backward by assuming the trajectory is a straight line and the true values.

12. M. Contalbrigo12Frascati: CLAS Transverse Target Meeting Transfer function T: Transfer function as commonly used in ion-optical system design. Initial coordinates: Reference particle has Final coordinates: Momentum deviation (in percent) Real particle has Parameters evaluated by numerically integrating the equations of motion by a Runge-Kutta algorithm over a testing set of particles at different starting position Z and momentum P.

13. M. Contalbrigo13Frascati: CLAS Transverse Target Meeting Approximated initial coordinate from a linearized transfer function L (all non-linear T terms are dropped) : Iterative procedure starts from final coordinates (as defined by HERMES spectrometer): New estimate of initial coordinate: Corresponding final coordinate and its deviation from the true one: Approximated error on initial coordinate: Vertex is found as the point of minimum approach to the beam axis. Does not require particle and beam trajectory coincide at a given point

14. M. Contalbrigo14 Depends on beam charge! Frascati: CLAS Transverse Target Meeting Main shift due to the beam deviation in the upstream correction-coils

15. M. Contalbrigo15 Correction of the beam shift due to the transverse target holding field 2004: electron beam 2005: positron beam Frascati: CLAS Transverse Target Meeting

16. M. Contalbrigo16 Slightly different efficiency depending on track multiplicity No effect in the observed azimuthal moments Frascati: CLAS Transverse Target Meeting

17. M. Contalbrigo17Frascati: CLAS Transverse Target Meeting Resolution similar to longitudinal target spin set-up xx zVzV

18. 18M. Contalbrigo ┴┴ ┴ ┴ ┴ g 1L h1h1 Distribution Functions (DF) Azimuthal moments require careful study of instrumental effects Frascati: CLAS Transverse Target Meeting

19. M. Contalbrigo19Frascati: CLAS Transverse Target Meeting To avoid inefficiency related to track spatial position (azimuthal angles) Likelihood based on full event topology Dual radiator Ring Imaging Cerenkov No ring for p 2 rings for e, 

20. M. Contalbrigo20Frascati: CLAS Transverse Target Meeting The event distribution and probability density distribution for target polarization P In a binned analysis residual acceptance dependence for integrated quantities

21. M. Contalbrigo21Frascati: CLAS Transverse Target Meeting Accounts for acceptance, radiative and smearing effects: depends only on instrumental and radiative effects Probability that an event generated with kinematics  is measured with kinematics  ’ Includes the events smeared within kinematical cuts Remove systematics but introduce statistical correlations The correction is averaged over the bin

22. One-dimensional analysis Multi-dimensional analysis M. Contalbrigo22Frascati: CLAS Transverse Target Meeting x Best output for phenomenological models of TMDs Q2Q2

23. M. Contalbrigo23Frascati: CLAS Transverse Target Meeting Sophisticated generator of the unpolarized cross-section  tuned to the HERMES multiplicities  polarization dependence is introduced a-posteriori randomly sort the spin state with probability defined by a given asymmetry model Pythia:  Generator implementing models for TMDs and azimuthal moments  tuned to reproduce i.e. the observed dP hT /dz distribution  no radiative effects up to now GMC_trans:

24. M. Contalbrigo24Frascati: CLAS Transverse Target Meeting Different tracking algorithms  alternative correction methods for bending inside the transverse magnet  standard tracking and improved version with refined Kalmann filter implementation, accounting for all B fields, misalignments and providing goodness of fit estimator. Tracking: Monte Carlo study comparing  reconstructed azimuthal moments with physical model in input to the simulation (evaluated at the average kinematics or integrated in 4  ); Acceptance/Resolution: Monte Carlo study comparing  different beam position and slopes within ranges estimates  by special alignment runs (dipole off);  detector aligned and misaligned geometry, the latter from survey measurements of the sub-detector positions;  indicator: top versus bottom detector halve response comparison. Misalignment:

25. set of SIDIS events based on a Taylor expansion on : The full kinematic dependence of the Collins and Sivers moments on is evaluated from the real data through a fit of the full e.g.: acceptance effects vanish model assumptions minimized M. Contalbrigo25Frascati: CLAS Transverse Target Meeting The extracted azimuthal moments and are folded with the spin-independent cross section (known!) in 4  and within the HERMES acceptance : Testing the method: Extraction:

26. Standard extraction method New extraction method Blue: within acceptance Black: in 4  The method works nicely at MC level! Small effect on DATA systematic error M. Contalbrigo26Frascati: CLAS Transverse Target Meeting Arbitrary input model

27. M. Contalbrigo27Frascati: CLAS Transverse Target Meeting Transverse data required special care during Account for beam and scattered particles bending in target holding field Account for full event topology in particle ID Special algorithms to minimize/correct instrumental effects (ML fits, unfolding, multi-D) evaluate systematic effects (full differential model of the signal) Preserve beam orbit Minimize depolarizing effects Data-taking: Offline analysis: