Annual SFB School 2014, Boppard, Peter-Bernd Otte Transversal Target Asymmetries in Threshold 0 Photoproduction Peter-Bernd Otte, Annual SFB School Boppard,

Annual SFB School 2014, Boppard, Peter-Bernd Otte

Transversal Target Asymmetries in Threshold

p0 Photoproduction

Peter-Bernd Otte, Annual SFB SchoolBoppard, October 2014


Introduction

Photoinduced Reactions on Protons

Xp

np

pp 0

pp

pp 'Ethr = 145MeV (Eg)

MAMI energy range


Introduction

• S- und P-wave multipole amplitudes

• Models: large differences, although they all describe the existing (published) data• Determination of multipole amplitudes model independent

Pion Photoproductionpp 0


1) Experimental Setup

• cw electron accelerator– 100% duty factor

• sources:– unpol.: Imax = 100µA

– pol.: Imax = 20µA with Pe≈80%

• MAMI-B/C:– 180-883MeV

DE = 13keV– 900-1604MeV

DE = 110keV

Mainz Microtron



• Photon tagging spectrometer („Glasgow-Mainz-Tagger“):1. e- Bremsstrahlung2. momentum determination of scattered e-3. Eg = E0-Ee

• coverage: 7..93% E0

• DE ≈ 1MeV (@E0=450MeV)• flux: 4*105 g/s/MeV

• Polarised photons– e- long. pol. circ. pol.– Crystal lin. pol.

Photon beam

electrons E0

Helicity transfere- -> g

g beam



Target Cell

electrons E0

Target cell• Butanol C4H9OH• 2 cm long and 2 cm diameter• or Carbon foam / LH2

g beam



• 4π photon spectrometer(n and charged particles as well)

Detector System

Target cell• Butanol C4H9OH• 2 cm long and 2 cm diameter• or Carbon foam / LH2

g beam




Detector System

Particle ID (DE/E)with thin plastic scintilators

20°<q<160° : barrel of 24x2°<q<20° : 384x

g beam




Detector System

MWPC• 2 cylindrical chambers• charged particles only

g beam

optional:Threshold C Detector



• 4π photon spectrometer (n and charged particles as well)

Detector System

TAPS• 366 BaF2 crystals (PMTs)• 12 radiation lengths• 1°<q<20° (3%)• self triggering

Crystal Ball• 672 NaI(Tl) crystals (PMTs)• 16 radiation lengths• 20°<q<160° (94%)• s ≈ 2-3°• self triggering

g beam



Detector System

photons

TAPSCB



• Target:– See talk J. Linturi tomorrow!

– „Dynamic Nucleon Polarisation“• polarise free electrons (radical)• transfer pol. to protons

– P0 ≈ 90% (only H), P=P0e-t/t

– 3He/4He dilution cryostat• T = 26mK & B = 0.44T

for t≈2*10³h– H spin:

• transversal or• longitudinal

Target: Mainz-Dubna Pol. Frozen Spin Target

super conducting saddle coil


Polarisable Material

• Butanol

(advantages: DNP, high P, large t, radiation hard, large d, high f)


Unpolarised

• unpol. liquid Hydrogen (lH2)

@ low T: parahydrogen (spins: ) not polarisable

Target Material

HHHH

HOCCCCH

HHHH

unpol. BGI(12C) = I(16O) = 0

only H polarised



• not trivial!

• Best mess. method: melting f=60(3)% for butanol

Butanol Target: important properties

tot

material

V

Vf

butanol balls

Filling FactorDilution Factor

6410

10

)Nucl.(

)H(stat

N

Nd

• Effective d(q,E) necessary

• Mandatory: decent statistics Does not work in threshold region

HHHH

HOCCCCH

HHHH


2) Photo p Production

Photoinduced Reactions on Protons

Xp

np

pp 0

pp

pp 'Ethr = 145MeV (Eg)

MAMI energy range

threshold D region 2nd and 3rd resonant region



• Spin observables Oi (q, W)

• Legendre expansion up to Lmax

• Legendre coefficients Aik bilinear combinations of multipoles, e.g.:

• Omelaenko (1981): 5 observables necessary for complete experiment

Amplitudes in Pion Photo Production

Talk from Y. Wunderlich tomorrow



• In threshold region (Eg=144-180MeV):– PWA (L=1): only S- and P-wave amplitudes E0+ & M1+, M1-, E1+

– near threshold assumption: E0+ complex, all other real

– but Im(E0+) is fixed by Fermi Watson theorem (unitarity):

– necessary: determine 4 real numbers from experiment– independent. meas. of Im(E0+) requires add. observable “complete data base”

Threshold p0 production

)()(Re)(Im 0

.exp00

0 pnanpEqppE

Beam / Target Polarisation:



• 2001: First measurements with TAPS (A. Schmidt et al., PRL2001, 87.232501)– lin. pol. photons– unpol. H target – s0, but only one S point

p0 threshold production pp 0

))2cos(1(,

lin

unpolpol

pd

dE

d

d



• 2001: First measurements with TAPS (A. Schmidt et al., PRL2001, 87.232501)– lin. pol. photons– unpol. H target – s0, but only one S point

• 2008: high precision measurement s0, S with CB/TAPS (D. Hornidge et al., PRL2013, 111.062004)

p0 threshold production

2coscos CBAd

d

D 2sin

Re(E0+, M1+, M1-, E1+)

pp 0

example:

))2cos(1(,

lin

unpolpol

pd

dE

d

d



P-Waves Amplitudes

deviationsfor large E D res.



• Fermi Watson theorem or measurement

S wave amplitude

...)Im( 0

Ed

dT

direct measurement via:

(p+n thr.)

unitarity cusp



• add measurement with unpol. photons & trans. pol. target: (2010, 2011)

• Measurement ofwith T b and known E0+

Threshold p production

sin)),,(Im( 1110

EMMfEd

dT Direct measurement of Im(E0+)

Check consistency with S measurements (2008)

pp 0

)()(Re 0.exp0 pnanpE

)()( 0.exp

0.exp npapna

TpTy

1d

d

d

d

unpol.pol.

Test strong isospin breaking

)( 0.exp pna

?



• Relevant:

• Determination of Obs.: asymmetry

• Event by event selection into 2 bins: „+“ and „-“

– for T: for F:

Analysis: Definitions

p0

g

p

A

pp 0

1 , 1d

d

d

dcirc

unpol.pol.

FppTp Tx

Ty

p spin (incoming)

effpPEPPA

PT )( ,

1

0

0sin

cos

cos

Physical results <>0 expected =0 expected

for T’:


Objective: get T of pure pol. hydrogen

Diluted asymmetry on butanol target:

Methods:1. determine (works only >220MeV)2. denominator normalise with simulation & f3. denominator normalise with unpol. Measurement & f


Analysis: 3 Methods

pp

pp

NN

NN

PA

1

HHHH

HOCCCCH

HHHH

Same results expected…

Cpp

pp

NNN

NN

PA

2

1

),( Edeff“Ingredients:”butanol + carbon meas.butanol + simulationbutanol + hydrogen


3) Results

• 2 g p0 reconstruction (no problem)

• proton detection (problematic, does not emerge the target)

Technique: Missing Mass

Analysis details

pp 0

(half of the total data set, all energies and q)

Butanol

Signal FF

FF ,

missing mass /MeV


3) Results

Photoinduced Reactions on Protons: Measured

Xp

np

pp 0

pp

pp '

MAMI energy range

Threshold & D region 2nd and 3rd resonant region

V. KashevarovS. Schumann P. BarrientosP. Otte

Analysis by:


3) Results

• All analyses completed

• possible overview via Legendre Polynoms

Status & Results for T and F

T @ 330MeV

F @ 330MeV

𝐴⋅𝜎=𝜌⋅ sin (𝜃)(𝑝0+𝑝1 cos𝜃+𝑝2 (3 cos2𝜃−1 )

2+…)

Black = But/Simred = But/Hgreen = But/CBlue = MAID


3) Results

• Sources, O(~%)– different analysis techniques (e.g. carbon subtraction)– Helicity dep. photon flux (A=0,005)– Detector asymmetries– Goodness of detectors maintenance

• butanol target, contribution of I=1/2 atoms – C13 (1,1%) and O17 isotopes.

– F4 in container

– (He3 for cooling)

Systematic uncertainties

limits resolution

future investigations


3) Results

Systematic Errors

ssys(T) = global Difference between analyses T’

ssys(F) = global Difference between analyses DA(beam flux)

%

Error in g flux (tagger poblems) 3,0

Unstable detectors and electronics 3,0

f 2,0 (?)

P(target) 2,0

P(beam) 2,7

total global sys. Error(indep. of q, E)

5,1 (T)5,8 (F)

depends on q, E


4) Outlook

• Goal: model independent PWA– from threshold up to W=2GeV– Using techniques from Stahov? talk tomorrow

• Measured & analysed– Pion photoproduction: S, T, F

• Actual work in group– measurements with “n”– longitudinal pol.: G, E (in analysis)– ditto: – other channels

• Ideal: remeasure T – with all improvements we learned

Summary / Outlook

pp 0

pp Thank you


Documents

Annual SFB School 2014, Boppard, Peter-Bernd Otte Transversal Target Asymmetries in Threshold 0 Photoproduction Peter-Bernd Otte, Annual SFB School Boppard,