Dihadron production at JLab

Sergio Anefalos Pereira(INFN - Frascati)

Physics Motivation

Describe the complex nucleon structure in terms of partonic degrees of freedom of QCD

● measuring transverse momentum of final state hadrons in SIDIS gives access to the transverse momentum distributions (TMDs) of partons

● pT dependent spin asymmetries measurements give us access to different TMDs, providing information on how quarks are confined in hadrons

● azimuthal distributions of final-state particles in SIDIS, in particular, are sensitive to the orbital motion of quarks and play an important role in the study of TMD parton distribution functions of quarks in the nucleon.

● the goal of looking at dihadron SIDIS is have a full picture of the collinear structure of proton.

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What we measure at 6 GeV and 12 GeV @ Jlab with dihadrons

+ Higher Twist distribution functions6 GeV e(x) and hL(x)

Leading Twist

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+ Higher Twist distribution functions6 GeV e(x) and hL(x)

12 GeV h1(x), e(x) and hL(x) (since we will have higher Q2 coverage ~ 10 GeV2)

Leading Twist

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What we measure at 6 GeV and 12 GeV @ Jlab with dihadrons

+ Higher Twist distribution functions

In addition to pions, at 12 GeV we'll be able to detect also kaons with /k separation in the 3-8 GeV/c range.

Leading Twist

What we measure at 6 GeV and 12 GeV @ Jlab with dihadrons

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The dihadron channel have

some

disadvantages (more

complex kinematics, new

angles, unknown but measurable

DiFFs appear)

but it also brings a very useful advantage: in single

hadron production, the observables are convolution of

TMDs in double hadron production, observables are

product of TMDs

)()( zfragxpdf hhfff

hhSIDIS

Dihadron vs. single-hadron SIDIS

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The dihadron channel have

some

disadvantages (more

complex kinematics, new

angles, unknown but measurable

DiFFs appear)

but it also brings a very useful advantage: in single

hadron production, the observables are convolution of

TMDs in double hadron production, observables are

product of TMDs

)()( zfragxpdf hhfff

hhSIDIS

Dihadron vs. single-hadron SIDIS

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SIDIS kinematical plane and observables

longitudinal momentum fraction carried by the hadron

the fraction of the virtual-photon energy carried by the two hadrons

X

W

pxF

||2

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SIDIS kinematical plane and observables

longitudinal momentum fraction carried by the hadron

the fraction of the virtual-photon energy carried by the two hadrons

X

W

pxF

||2

it selects the current fragmentation region (CFR) and target fragmentation region (TFR). The first comprise hadrons produced in the forward hemisphere (along the virtual photon) and the latest, in the backward hemisphere

In these analysis we select events in the CFR

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Dihadron angles definition

the angle between the directionof P1 in the + - center-of-mass frame, and the direction of Ph in the photon-target rest frame.

qk'

k

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Structure functions in terms of PDF and DiFF in the limit M2 ≪ Q2

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Transversity extracted using the HERMES data for proton (red symbols) and COMPASS data for proton (blue ones)The dashed lines correspond to Torino’s transversity [arXiv:0812.4366]

Dihadron with transversely polarized target

Transversity using the COMPASS data for deuteron.

model-independent extractionin collinear approximation [arXiv:1206.1836v1]

JLab will provide much precise data and also extend x up to 0.6.

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Dihadron @ 6GeV

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CLAS

•Continuous Electron Beam•Energy 0.8-5.7 GeV•200A, polarization 85%•Simultaneous delivery to 3Halls

JLab Accelerator CEBAF

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Torus magnet6 superconducting coils Electromagnetic calorimeters

Lead/scintillator, 1296 photomultipliers

beam

Drift chambersargon/CO2 gas, 35,000 cells

Time-of-flight countersplastic scintillators, 684 photomultipliers

Gas Cherenkov counterse/ separation, 216 PMTs

Liquid D2 (H2)target + start counter; e minitorus • Broad angular coverage

(8° - 140° in LAB frame)• Charged particle momentum resolution ~0.5% forward dir

CLAS is designedto measure exclusive reactionswith multi-particle final states

Hall B: Cebaf Large Acceptance Spectrometer

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The e1f and eg1-dvcs experiments

Hydrogen target (NH3)Beam energy: 5.892 GeV

4.735 GeVLuminosity: 22.7 fb-1

Hydrogen target (NH3)Beam energy: 5.967 GeVLuminosity: 50.7 fb-1

Deuterium target (ND3)Beam energy: 5.764 GeVLuminosity: 25.3 fb-

1

Beam polarization ~ 85%

Proton polarization ~ 80%

Beam polarization ~ 75 %

Liquid Hydrogen target (unpolarized)

Beam energy: 5.5 GeV

Luminosity: 21 fb-1

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Channel identification

semi-inclusive channel

two topologies have been

analyzed:

e p e’ + - X

e p e’ + 0 X e’ + X

0 is identified as M( )

X

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Channel identification

semi-inclusive channel

two topologies have been

analyzed:

e p e’ + - X

e p e’ + 0 X e’ + X

0 is identified as M( )

X

+

-

dihadron sample defined by SIDIS cuts + CFR for both hadrons

0)( Fx

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+

-

Channel identification

semi-inclusive channel

two topologies have been

analyzed:

e p e’ + - X

e p e’ + 0 X e’ + X

0 is identified as M( )

X

dihadron sample defined by SIDIS cuts + CFR for both hadrons

0)( FxStruck quark fragmenting in a hadron pair

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MM > 1.5 GeV

Semi-inclusive selection

MM > 1.5 GeV

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Monte Carlo study

ClasDIS Monte Carlo (LUND) was used as event generator;

Polarized proton and unpolarized deuteron MC

were

used to “simulate” NH3 target;

the full MC chain; same cuts used on data were applied.

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Monte Carlo vs. Data+ data- Monte Carlo

pe p p

Xb y W2

Q2 xF() x

F()

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+ data- Monte Carlo

Z+ Z Zhh

Pt+ Pt-

Pthh

M() R

h

Monte Carlo vs. Data

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Beam-Spin Asymmetry (BSA)

p0 + p

1 sin

R + p

2 sin 2

R

A LU= 1Pbeam

N +- N -

N ++ N -

Monte Carlogenerated x reconstructed

asymmetries

we have generated events with the following input parameters:

p0 = 0.0, p1 = 0.03 and p2 = 0.0

According to this function

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Results

Fitting function:

integrated over all variables

p0 + p

1 sin

R + p

2 sin 2

R

A LU= 1Pbeam

N +- N -

N ++ N -

preliminary

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Beam-Spin Asymmetry (BSA)

ResultsBeam-Spin Asymmetry (BSA)

▲ Sin ▲ Sin

preliminary

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ResultsBeam-Spin Asymmetry (BSA)

▲ Sin (e1f)▲ Sin (eg1-dvcs)

preliminary

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Results

Fitting function:

integrated over all variables

Target-Spin Asymmetry (TSA)

p0 + p

1 sin

R + p

2 sin 2

R

AUL=1

DF1

Ptarg

N+

FC+ -N -

FC -

N +

FC+ +N -

FC -

preliminary

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ResultsTarget-Spin Asymmetry (TSA)

▲ Sin ▲ Sin

preliminary

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Dihadron @ 12GeV

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End physics program @ 6 GeV in 2012

6 GeV CEBAF

CHL-2

Upgrade magnets and power supplies

12 GeV CEBAF

add Hall D (and beam line)

Beam Power: 1MWBeam Current: 90 µAMax Pass energy: 2.2 GeVMax Enery Hall A-C: 10.9 GeVMax Energy Hall D: 12 GeV

May 2013 Accelerator Commissioning starts

October 2013 Hall Commissioning starts

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Q2

Kinematic coverage

extending to higher x means lower cross sectionsneed high luminosity: 1035 cm-2 s-1

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CLAS12 Configuration (Hall-B)

DC R3R2R1

DC R3R2R1

EC EC

TorusTorus

FTOFFTOF

PCALPCAL

HTCCHTCC

SolenoidSolenoid

RICH

Wide acceptance and high resolution important in particular for hadron pair production

Designed for luminosity 1035cm-

2sec-1

Highly polarized 11 GeV electron beam

Transverse an Longitudinal polarizedH and D targets

RICH detector allows kaon detection

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Layout of the RICH

Constraints:• the detector must fit in 1m • low material budget• large area for the photodetectors (several m2)

• increasing azimuthal angle decreasing momentum

beam

pipe

particle’s trajectory

target

DC1 DC

2

DC3

ONE CLAS12 SECTOR

Solutions:• mirrors to focalize the light in small area

• variable aerogel thickness from 2 to 6/8 cmDifferent pattern:• Cerenkov photons from small angle, high momentum particles directly detected

• photons from large angle and lower momentum particles are reflected toward the photodetectors and pass twice through the aerogel

Requirements:• /k/p separation in the 3-8 GeV/c range

• rejection >500

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SoLID Configuration (Hall-A)

Effective pol. neutron target

Wide acceptance and high resolution

High 1036 luminosity

8.8 and 11 GeV polarized beam

Transverse and Longitudinal Polarized 3HeTarget > 60% polarization

Large acceptance with full azimuthal-angle coverage

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Flavor separation at JLab

the asymmetry for a neutron target (for the specific case of the π+π− final state) can be written as:

the equivalent equation for the proton is

combining these two asymmetries (on neutron and proton targets) the uv and the dv flavors could be extracted separately.

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Flavor separation with JLab

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Dihadron production on neutron @ Jlab 11 GeV

Projected statistical error for data on a neutron target. The yellow band represent the spread in predictions using different models for h1(x)(top plots)

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Dihadron production on proton @ Jlab 11 GeV

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Summary6 Gev

●the first measurements of dihadron ALU and AUL asymmetries have been presented;

●preliminary results of a non-zero BSA and TSA for + - pair have been shown (will look at + 0 as well);

12 GeV

● Jlab @ 12 GeV will measure transverse target SSA in hadron pair production in SIDIS and study the transversity distribution function and interference effects in hadronization using transverse polarized protons (CLAS12) and neutrons (SoLID);

● Flavor separation will also be possible combining both data (proton and neutron) to to extract the uv and the dv flavors separately.

●Measurements with kaons in the final state will provide important information about strange quarks.

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Backup slides

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Generated and reconstructed asymmetries

p1 = 0p2 = 0

p1 = 0.03p2 = 0

p1 = 0.03p2 = 0.03

p1 = 0p2 = 0.03

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