DIS-09, Madrid 1

Longitudinal polarization of and in DIS at COMPASS

M.G.Sapozhnikov

Joint Institute for Nuclear Research, Dubna

On behalf of the COMPASS Collaboration

DIS-09, Madrid 2

Physical motivation

Longitudinal polarization of and in DIS is sensitive to:

• s(x), s(x)• polarization of strange quarks s

spin structure

)]()()()([ xsxsxsxsdxs

M.Sapozhnikov, JINR

3

production in DIS, quark fragmentation

•

Spin transfer from polarized quark

Quark fragmentation

Spin transfer from polarized muon

spin structure

DIS-09, Madrid 4

spin structure• SU(6) quark model: s = 1, u = d = 0

100% polarization to u or d quarks is no influence on polarization of P() - 0 (for u –quarks dominance)

• Burkardt-Jaffe: u = d = -0.23 P() – negative

• B.Q.Ma et al.: u = d =s

P() – positive • Lattice calculations: u = d ~0, s=0.68 P() ~ 0

M.Sapozhnikov, JINR

5

• Production and is mainly due to fragmentation of target remnant and u,d-quarks

• Spin transfer to and is mainly due to interaction with strange quark and antiquark

DIS-09, Madrid M.Sapozhnikov, JINR

6DIS-09, Madrid

COMPASS Detector

160 GeV µ+ beam

2.8 . 108 µ/spill (4.8 s)

Polarizedtarget

SM1Drift. Ch. RICH

ECal1 & HCal1

Muon filter 1

SM2

MWPCs

Micromegas

ECal2 & HCal2

Muon filter 2

GEM & MWPCsSciFi

GEM & MWPCs

GEM & Straws

SiliconSciFi

Scintillatingfibers

Beam

LAS

SAS

Pb = -0.760.04 - 2003Pb = -0.800.04 - 2004

M.Sapozhnikov, JINR

Polarized 6LiD target (2002-2004)

7DIS-09, Madrid M.Sapozhnikov, JINR

8

Production of ()

p

Xd

No PID used

p

Xd

S

S

K

XKd

M.Sapozhnikov, JINR

9DIS-09, Madrid

Event selectionp

-

+

’+

•Primary vertex: in the target •Secondary vertex: 5 cm downstream the

target• pT > 23 MeV/c• < 0.01 rad•Q2 >1 (GeV/c)2

• 0.2<y<0.9

V1

V2

M.Sapozhnikov, JINR

DIS-09, Madrid 10

Comparison with other experiments

N() N()

E665 750 650

NOMAD 8 087 649

HERMES, 1996-2000

7 300 1 687

RHIC 30 000 24 000

COMPASS, 2003,2004

70 000 42 000

M.Sapozhnikov, JINR

11DIS-09, Madrid

<xBj> = 0.05

<xF> = 0.23

<y> = 0.46

<Q2>=3.31 GeV2

Good agreement between data and MCM.Sapozhnikov, JINR

12DIS-09, Madrid

<xBj> = 0.050

<xF> = 0.22

<y> = 0.48

<Q2>=3.27 GeV2

13DIS-09, Madrid

Longitudinal polarization PL

=+(-)0.642 ±0.013 - () decay parameter

P - polarization vector

k - unit vector along the decay proton momentum

L-axis - along the momentum of virtual

photon

)1(4

kPN

d

dN tot

)cos1(2

1

cos

1

L

obs

obstot

Pd

dN

NM.Sapozhnikov, JINR

14

Determination of the angular distribution:

• sidebands subtraction

DIS-09, Madrid M.Sapozhnikov, JINR

15

Angular distributions of and (run 2004)

Acceptance correction – using unpolarized MC

P(K0)=0.011±0.005

DIS-09, Madrid M.Sapozhnikov, JINR

DIS-09, Madrid 16

Longitudinal spin transfer DLL

PL = DLL Pb D(y)

Pb – beam polarization, D(y) – depolarization factor

2

2

)1(1

)1(1)(

y

yyD

DLL’ - polarization of the struck quark along the axis L is transferred to the along the secondary axis L’

In our case: L=L’

M.Sapozhnikov, JINR

17

Comparison of and : x

DLL() DLL()

DIS-09, MadridThe results are averaged over target polarization

DLL() = -0.012 ± 0.047 ± 0.024

DLL() = 0.249 ± 0.056 ± 0.049

Preliminary

18

Comparison of and : xF

The results are averaged over target polarizationDIS-09, Madrid

PL: dependence on the target polarization

19

P= P--P+ =-0.010.04, = 0.010.05, DIS-09, Madrid

DIS-09, Madrid 20

Comparison with other experiments :

Preliminary

M.Sapozhnikov, JINR

DIS-09, Madrid 21

Comparison with other experiments :

Preliminary

M.Sapozhnikov, JINR

22

Theory predictions for and

J.Ellis et al., Eur.Phys.J. C52 (2007) 603

DIS-09, Madrid

Preliminary

M.Sapozhnikov, JINR

23

Theory predictions for and

DIS-09, Madrid

Preliminary

J.Ellis et al., Eur.Phys.J. C52 (2007) 603

M.Sapozhnikov, JINR

DIS-09, Madrid 24

Sensitivity to the strange distribution s(x)

CTEQ5L

GRV98

DLL(s)=0, BJ model

DLL(s)=0, SU(6) model

M.Sapozhnikov, JINR

DIS-09, Madrid 25

Sensitivity to the strange distribution s(x)

CTEQ5L

GRV98

DLL(s)=0, BJ model

DLL(s)=0, SU(6) model

DIS-09, Madrid 26

Conclusions• Preliminary results on and spin transfer in DIS are

obtained on statistics 70000 and 42000 • DLL() DLL()

• DLL() ~ 0

• DLL() may be as large as 0.4-0.5

• First measurement of the () polarization for different target polarization. No significant dependence is found.

• Comparison with theory:– Spin transfer to is sensitive to s(x)

• Present statistics is only 25% of already accumulated.

More interesting things are coming.

M.Sapozhnikov, JINR

DIS-09, Madrid 27

Backup slides

M.Sapozhnikov, JINR

DIS-09, Madrid 28

• Influence to different PDF’s

Q2 = 4 GeV2

CTEQ5L

GRV98LO

M.Sapozhnikov, JINR

29

Polarization of from quark fragmentation

)()]()()([

)()]()()([2

2

zDxqyDPPxqe

zDxqPxqyDPeP

qTbqq

qTbqq

Spin transfer from polarized muon

Spin transfer from polarized quark

qqq DDD qqq DDDDIS-09, Madrid M.Sapozhnikov, JINR

30

Polarization of : PT =0

)()(

)()()(2

2

zDxqe

zDxqyDPeP

qqq

qbqq

)()(

)()(

9

12 zDxqe

zDxsD

qqq

sLL

)()(

)()(

9

12 zDxqe

zDxsD

qqq

sLL

;0 du DD ;0

du DD

DIS-09, Madrid M.Sapozhnikov, JINR

31

DLL() > DLL()

)()(

)()(

9

12 zDxqe

zDxsD

qqq

sLL

)()(

)()(

9

12 zDxqe

zDxsD

qqq

sLL

Even if s(x)=s(x),DLL() > DLL() due to difference of the denominator:

Du,d() > Du,d()

Independent quark fragmentation: •DLL() > DLL()•Sensitivity to s(x)Are these conclusions still valid in a more advanced model?DIS-09, Madrid M.Sapozhnikov, JINR

Spin transfer from polarized quark to

32

ssZee 0

91.0sPPolarized quarks, indeed, transfer the polarization to .

DIS-09, Madrid M.Sapozhnikov, JINR

Impact of LEP data

33

D. de Florian, M.Stratmann, W.Vogelsang, PRD 57(1998)5811

1- SU(6)2 – BJ3 - u = d =s

DIS-09, Madrid M.Sapozhnikov, JINR

34

Theory predictions for /• Liang Zuo-tang et al. Phys.Rev.D72 (2005) 033006

-0.6 0 0.6 xFDIS-09, Madrid M.Sapozhnikov, JINR

35DIS-09, Madrid

Transverse polarization PY

M.Sapozhnikov, JINR

DIS-09, Madrid 36

- between virtual photon and p in c.m.s.

• Kaon background is important at large cos

• cut

-1 < cos <0.6

M.Sapozhnikov, JINR