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{\center A 12 GeV Research Proposal to Jefferson Lab (PAC 38)}
\vspace*{1cm}
{\center \large\bf Studies of pion and kaon Electroproduction in semi-inclusive DIS}
{\center \large\bf with Transversely Polarized Hydrogen and Deuterium Targets}

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{\center \large A CLAS collaboration proposal\\}

\vspace*{10 pt}
\begin{center}
M. Aghasyan (Frascati), H. Avakian (JLab), M. Contalbrigo$^*$ (Ferrara),

K. Joo (UConn), F.J. Klein (CUA)
%{\small $^{\dagger}$ Co-spokespersons: M. Aghasyan (Frascati), H. Avakian (JLab), K. Joo (UConn), F.J. Klein (CUA), L.L. Pappalardo (Ferrara)}

\vspace*{5 pt}
{\small $^*$ Contact: M. Contalbrigo, INFN-Ferrara, Email: contalbrigo@fe.infn.it}
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\begin{abstract}

We propose to study the azimuthal spin asymmetries in semi-inclusive DIS 
(SIDIS) with the CLAS12 spectrometer completed with a RICH detector, 
using the upgraded JLab 11 GeV polarized electron beam with 
transversely polarized proton and deuteron targets.
The Fourier decomposition of the transverse-polarization-dependent cross-section 
term of the reaction \EPX (with h=$\pi$, K)
provides access to a variety of fundamental quark correlation
functions probing the parton dynamics within the nucleon and in the fragmentation 
process. Among them is the poorly known transversity function, whose precise
measurement represents the missing piece for the full comprehension
of the collinear structure of the nucleon at leading-twist. It differs
from the helicity distribution due to the relativistic effects of the
quark motion within the nucleon. Other prominent examples are the
Sivers and Pretzelosity transverse-momentum-dependent (TMD) quark distributions.
The Sivers function is related to the quark orbital motion in a transversely 
polarized nucleon and, being naive-T-odd, undergoes peculiar universality 
properties whose experimental verification is considered a key validation of 
the TMDs formalism. The Pretzelosity distribution function is sensitive
to the D-wave component and probes any non-spherical shape of the nucleon.
The measurable azimuthal asymmetries, interpreted as 
transverse-momentum-convolutions of parton distribution and fragmentation 
functions in the TMDs formalism, are expected to be in the range 2-10\%
from leading order calculations, depending on the kinematics and on
the model used for the predictions. Chirally-odd distribution functions can be studied
in conjunction with the Collins fragmentation function, which 
describes spin-orbit effects in the fragmentation of transversely 
polarized quarks. Alternatively, 
the transversity distribution can be studied in a collinear approach 
in conjunction with a di-hadron interference fragmentation function.

Flavor sensitivity is achieved by the identification of the final-state
hadron, in particular kaon mesons, and the use of hydrogen and deuteron 
nucleon targets. This will help to clarify the "kaon puzzle" for, e.g., asymmetries 
related to transversity in conjunction with the Collins fragmentation function. 
HERMES results indicate that the single-spin asymmetries for pions and
kaons may be very different. The asymmetries for $K^+$ 
are found of the same sign of those of $\pi^+$, which is expected 
if the valence quarks provide the dominant contribution, but significantly
larger in magnitude. The naive interpretation based on valence quark dominance 
is challenged also by the peculiar signal of $K^-$, compatible with 
zero with a hint of opposite sign with respect the large signal of $\pi^-$. 

Thanks to the large detector acceptance, 
the $x,z,P_T$ and  $Q^2$ dependences of the asymmetries will  
be studied in a wide kinematic range to probe the underlying
distribution and fragmentation functions. 
The investigation of the transition from current to target
fragmentation region will be possible.
A multi-dimensional
analysis is planned in order to best decouple the nucleon intrinsic
properties from the fragmentation features. In particular a scan 
over $Q^2$, to isolate sub-leading contributions, and over $P_T$,
to explore the perturbative to non-perturbative regime transition and
the match between the TMD (at $P_T<<Q$) and collinear (at $P_T>>M$) 
factorization formalisms, will be performed. 
By exploiting novel event-weighing techniques, it will be
possible to solve the transverse-momentum-convolution and access 
parton distributions in a model independent way. 

Thanks to the polarized beam, double spin asymmetries for \EPp, 
giving access to distribution of longitudinally polarized quarks 
in the transversely polarized nucleon, will be measured
simultaneously.
In addition, important information on the 
sub-leading order parton distributions will be accessible, i.e.
a significantly extended $(x,Q^2)$ range of 
precision measurements of $g_2$ will be achieved.

A total of 100 days of running of the upgraded CLAS12 detector with 11 GeV highly polarized
electron beam on transversely polarized HD-Ice (or possibly NH$_3$ and ND$_3$ or $^6$LiD) 
target is requested for this experiment including about 20\% overhead for target replacements, 
polarization reversal, and auxiliary measurements.

\end{abstract}
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