Spin Studies via Drell-Yan Process at PANDA

Marco Destefanis for the PANDA Collaboration Università degli Studi di Torino

MENU 2013 13th Conference on Meson-Nucleon Physics and the Structure of the Nucleon

Roma (Italy) September 30 – October 04, 2013

Overview

 pp -> µ + µ X • Drell-Yan process and background @ PANDA  A. Bianconi Drell-Yan generator • Investigation of Drell-Yan asymmetries  Summary

Motivation

Complete description of the nucleonic structure requires: ➠ Parton Distribution Functions (PDF) ➠ Fragmentation Functions (FF) Including k T dependence ➠ Transverse Momentum Dependent (TMD) PDF and FF ➠ Test of Universality

f

1

T



f

|

DY

 

f

1

T



f

|

SIDIS

J. C. Collins and D. E. Soper, Nucl. Phys. B 194, 445 (1982)

Helicity base

Twist-2 PDFs:

f

1

u

(

x

) 

u

(

x

),

g u

1 (

x

)  

u

(

x

),

h u

1 (

x

)  

u

(

x

)   

-

   δq(x) helicity flip   off diagonal in the helicity base

u

 

u

  1 

u R

2 1 2 

u R



u L

 

u L



Transversity

δq(x): a chirally-odd, helicity flip distribution function δg(x): no gluon transversity distribution; transversely polarised nucleon shows transverse gluon effects at twist-3 (g

2

) only SOFFER INEQUALITY • • An upper limit:

h x

1 ( )  1

f x

1 ( ) 

g x

1 ( ) 2 can be violated by factorisation at NNLO inequality preserved under evolution to larger scales only

TMD: K T -dependent Parton Distributions

Twist-2 PDFs f 1 ( x )   d 2 k T f 1 ( x , k T )

Transversity Sivers Boer-Mulders

Distribution functions Twist-2 U L T Chirality even odd f 1 f 1  T , g 1 g 1 T h 1 , h h 1  1  L h 1  T

➠

Energies

TMD PDF Investigation

@ FAIR unique energy range up to s~30 GeV 2 up to s~200 GeV 2 @ much higher energies → with PANDA with PAX big contribution from sea-quarks ➠

Process

SIDIS Drell-Yan → → convolution with FF PDF only pp annihilations: each valence quark can contribute to the diagram

Drell-Yan Process

• Drell-Yan: pp ->  +  X Kinematics x 1,2 = mom fraction of parton 1,2  = x 1 • x 2 = M 2 /s x F = x 1 - x 2 Collins-Soper frame Collins-Soper frame: Phys. Rev. D16 (1977) 2219 .

Drell-Yan Asymmetries

Di-Lepton Rest Frame NLO pQCD: λ  1,   0, υ  0 Lam-Tung sum rule: 1- λ = 2ν • reflects the spin-½ nature of the quarks • insensitive top QCD-corrections Experimental data [1] : υ  30 % [1] J.S.Conway et al., Phys. Rev. D39 (1989) 92 .

Drell-Yan Cross Section

UNPOLARISED SINGLE-POLARISED

.

U = N(cos2φ>0) D = N(cos2φ<0) Angular Asymmetry R.D. Tangerman and P.J. Mulders, Phys. Rev. D51, 3357-3372 (1995) A  U U   D D

Di-Lepton Production pp ->

l

+

l

-

X

CERN NA51 450 GeV/c Fermilab E866 800 GeV/c R.S. Towell et al., Phys. Rev. D 64, 052002 (2001) A. Baldit et al., Phys. Lett. 332-B, 244 (1994)

Phase space for Drell-Yan processes

x 1,2 x  F = mom fraction of parton 1,2 = x 1 • x 2 = x 1 - x 2  x F = const: hyperbolae = const: diagonal PANDA

1.5 GeV/c 2 ≤ M



≤ 2.5 GeV/c 2

PAX @ HESR symmetric HESR collider 1

The PANDA Spectrometer

STT Detectors

Physics Performance Report for PANDA arXiv:0903.3905

Drell-Yan Process and Background

• Drell-Yan: pp ->  +  X cross section   1 nb @ s = 30 GeV 2 • Background: pp -> N(  +  )X cross section   20-30  b m  = 105 MeV/c 2 ; m  = 140 MeV/c average primary pion pairs:  1.5

2 • Background studies: needed rejection factor of 10 7

A. Bianconi Drell-Yan Generator for pp

• Antiproton beam • Polarized/Unpolarized beam and target • Drell-Yan cross section from experimental data • Selects event depending on the variables: x 1 , x 2 , P T ,  ,  ,  S from a flat distribution • Cross section: d  dx 1 dx 2 dP T d   K  S



x 1 , x 2 S  S ' P T   ,  ,  S



A. Bianconi, Monte Carlo Event Generator DY_AB4 for Drell-Yan Events with Dimuon

Production in Antiproton and Negative Pion Collisions with Molecular Targets, internal note (PANDA collaboration)

A. Bianconi, M. Radici, Phys. Rev. D71, 074014 (2005) & D72, 074013 (2005) A. Bianconi, Nucl.Instrum.Meth. A593: 562-571, 2008

DY @ 15 GeV/c — pp->



+



X

Dilepton Mass Distribution s  5 .

5 GeV

A. Bianconi Drell-Yan Generator

[1] • layout studies for muon id with ABDYG (1.5 MEv)

M dilepton [GeV/c 2 ] x P x 2

σ 0 4≤M≤9

1.5 MEv in 1.5 < M



< 2.5 (GeV/c 2 )

σ 0 1.5≤M≤2.5

~ 0.8 nb [ 1] A. Bianconi and M. Radici, Phys. Rev. D71 (2005) 074014

x P x 1

DY Asymmetries @ Vertex UNPOLARISED SINGLE-POLARISED

1 < q T 2 < q T < 2 GeV/c < 3 GeV/c

x P x P 5·10 5 events included in asymmetries Acceptance corrections crucial!

Physics Performance Report for PANDA arXiv:0903.3905

x P x P x P x P

DY Asymmetries @ Vertex Statistical errors for 5·10 5 generated events

) )

x P x P R =

L

·σ· ɛ = 2·10 32 cm -2 s -1 × x 0.8·10 -33 cm 2 × 0.33

= 0.05 s -1 ~ 130 Kev/month

Physics Performance Report for PANDA arXiv:0903.3905

x P

Summary

 DY studies feasable at PANDA  New physics from unpolarized DY  Wide Single Spin Asymmetry program  Investigation of TMD PDFs and nucleon structure  Few months of data taking in High Luminosity mode are enough to:  evaluate unpolarised and single-spin asymmetries with good accuracy  investigate their dependence on q T, μμ