Separated π - /π + Ratios from the Pion Form Factor Experiments → Separated π - /π + Ratios...

Separated Separated ππ--//ππ++ Ratios Ratios from the from the Pion Form Factor ExperimentsPion Form Factor Experiments

→ → Phys.Rev.Lett. 112, 182501 (2014)

JLab Users Group Meeting, June 4, 2014.JLab Users Group Meeting, June 4, 2014.

Garth Huber

Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 2

Jefferson Lab Jefferson Lab FFππ Collaboration Collaboration

R. Ent, R. Ent, D. GaskellD. Gaskell, M.K. Jones, , M.K. Jones, D. MackD. Mack, D. Meekins, J. Roche, G. Smith, W. Vulcan, , D. Meekins, J. Roche, G. Smith, W. Vulcan, G. Warren, S.A. WoodG. Warren, S.A. Wood

Jefferson Lab, Newport News, VA , USA

C. ButuceanuC. Butuceanu, E.J. Brash,, E.J. Brash, G.M. Huber G.M. Huber, V. Kovaltchouk, G.J. Lolos, S. Vidakovic, C. Xu , V. Kovaltchouk, G.J. Lolos, S. Vidakovic, C. Xu University of Regina, Regina, SK, CanadaUniversity of Regina, Regina, SK, Canada

H.P. BlokH.P. Blok, V. Tvaskis, V. TvaskisV.U. University, Amsterdam, NetherlandsV.U. University, Amsterdam, Netherlands

E. Beise, H. Breuer, C.C. Chang, E. Beise, H. Breuer, C.C. Chang, T. HornT. Horn, P. King, J. Liu, P.G. Roos, P. King, J. Liu, P.G. RoosUniversity of Maryland, College Park, MD, USAUniversity of Maryland, College Park, MD, USA

W. Boeglin, P. Markowitz, J. ReinholdW. Boeglin, P. Markowitz, J. ReinholdFlorida International University, FL, USAFlorida International University, FL, USA

J. Arrington, R. Holt, D. Potterveld, P. Reimer, X. ZhengJ. Arrington, R. Holt, D. Potterveld, P. Reimer, X. ZhengArgonne National Laboratory, Argonne, IL, USAArgonne National Laboratory, Argonne, IL, USA

H. Mkrtchyan, V. TadevosyanH. Mkrtchyan, V. TadevosyanYerevan Physics Institute, Yerevan, ArmeniaYerevan Physics Institute, Yerevan, Armenia

S. Jin, W. KimS. Jin, W. KimKyungook National University, Taegu, KoreaKyungook National University, Taegu, Korea

M.E. Christy, C. Keppel, L.G. TangM.E. Christy, C. Keppel, L.G. TangHampton University, Hampton, VA, USAHampton University, Hampton, VA, USA

J. VolmerJ. VolmerDESY, Hamburg, GermanyDESY, Hamburg, Germany

A. Matsumura, T. Miyoshi, Y. OkayasuA. Matsumura, T. Miyoshi, Y. OkayasuTohuku University, Sendai, JapanTohuku University, Sendai, Japan

B. Barrett, A. SartyB. Barrett, A. SartySt. Mary’s University, Halifax, NS, CanadaSt. Mary’s University, Halifax, NS, Canada

K. Aniol, D. MargaziotisK. Aniol, D. MargaziotisCalifornia State University, Los Angeles, CA, USACalifornia State University, Los Angeles, CA, USA

L. Pentchev, C. PerdrisatL. Pentchev, C. PerdrisatCollege of William and Mary, Williamsburg, VA, USACollege of William and Mary, Williamsburg, VA, USA


GPDs in Deep Exclusive Meson ProductionGPDs in Deep Exclusive Meson Production

Four GPDs at leading twist:Four GPDs at leading twist:

→→ Unpolarized: Unpolarized: H(x,ξ,t), E(x,ξ,t)H(x,ξ,t), E(x,ξ,t)

→→ Polarized: Polarized: H(x,ξ,t), E(x,ξ,t)H(x,ξ,t), E(x,ξ,t)~ ~

Second set of four GPDs at twist-3: Second set of four GPDs at twist-3: HHTT, H, HTT, E, ETT, E, ETT

In the forward limit, In the forward limit, HHTT reduces to the transversity distribution reduces to the transversity distribution hh11(x).(x).

→ → Dominant twist-3 contribution from Dominant twist-3 contribution from HHT T contributes to contributes to MM0-,++0-,++ amplitudeamplitude

→ → Manifested in the transverse cross section or interference terms:Manifested in the transverse cross section or interference terms:σσTT, σ, σTT, TT, σσLTLT,, and various single spin asymmetries. and various single spin asymmetries.

~ ~

ρ,π,η

p+Δ

γ*

Factorization


Deep Exclusive Deep Exclusive ππ±± Production Production

Single Single ππ++ produced from proton, produced from proton, or or ππ-- from neutron at high momentum from neutron at high momentum transfer.transfer.

Can form ratios of separated cross-Can form ratios of separated cross-sections for which non-perturbative sections for which non-perturbative corrections may partially cancel, corrections may partially cancel, yielding insight into soft-hard yielding insight into soft-hard factorization at modest factorization at modest QQ22..

q

A. Nachtmann, Nucl. Phys. B 115 (1976) 61.4

1

)3/2(

)3/1(

2

22

2

2

2

*

*

u

dthigh

T

TT Q

Q

np

pnR

Pseudoscalar meson production has been identified as especially Pseudoscalar meson production has been identified as especially sensitive to chiral-odd transverse GPDs. sensitive to chiral-odd transverse GPDs.

→ → RRTT is not complicated by the is not complicated by the ππ–pole term.–pole term.


±± t t-channel diagram is purely -channel diagram is purely isovectorisovector (G-parity conservation). (G-parity conservation).

A significant deviation of A significant deviation of RRLL from from

unity would indicate the presence unity would indicate the presence of isoscalar backgrounds (such as of isoscalar backgrounds (such as bb11(1235) contributions to (1235) contributions to

tt-channel).-channel).

2

2

[ ( , ' ) ]

[ ( , ' ) ]V SL

LL V S

A An e e pR

p e e n A A

*

N N’

At low At low –t–t, Meson-Nucleon Degrees of Freedom, Meson-Nucleon Degrees of Freedom

Relevant for extraction of pion form factor from Relevant for extraction of pion form factor from p(e,e’p(e,e’ππ++)n)n data, data, which uses model including some isoscalar backgroundwhich uses model including some isoscalar background..


Only Prior Only Prior 22H(e,e’H(e,e’ππ±±))NNNN Data Data

Only prior exclusive Only prior exclusive 22H(e,e’H(e,e’ππ±±)NN )NN data was obtained at DESY in data was obtained at DESY in the 1970’s.the 1970’s. Unseparated cross sections Unseparated cross sections

only, due to incomplete only, due to incomplete azimuthal azimuthal coverage.coverage.

QQ22=0.70, 1.35 =0.70, 1.35 GeVGeV22..

ππ--//ππ++ ratio intriguingly ratio intriguingly approaches Nachtmann’s approaches Nachtmann’s quark counting ratio quark counting ratio →1/4 →1/4 at high at high –t.–t.

Ratio approaches Ratio approaches ππ pole pole dominance dominance →1 →1 at low at low –t.–t.

Need separated Need separated 22H(e,e’H(e,e’ππ±±)NN )NN data over a wide kinematic range data over a wide kinematic range to better interpret ratios!to better interpret ratios!


2coscos122dt

d

dt

d

dt

d

dt

d

dtdd TTLTTL

1.1. At small At small ––tt, , L L has maximum contribution from the has maximum contribution from the pole. pole.2.2. Need to investigate Need to investigate t t dependence at relatively fixed dependence at relatively fixed QQ22,, W W, but only three , but only three

of of QQ22, W, t, , W, t, θθ are independent. are independent. Vary Vary θθ to measure to measure tt dependence. dependence. Since non-parallel data needed, LT and TT must also be determined.Since non-parallel data needed, LT and TT must also be determined.

12 22' '

2

Virtual-photon polarization:

( )1 2 tan

2e e eE E Q

Q


Jefferson Lab Hall C Experimental SetupJefferson Lab Hall C Experimental Setup

ExpExp QQ22

(GeV/(GeV/c)c)22

W W (GeV)(GeV)

|t|tminmin||

(Gev/c)(Gev/c)22

EEe e

(GeV)(GeV)

FFππ-1-1 0.6-1.60.6-1.6 1.951.95 0.03-0.1500.03-0.150 2.445-4.0452.445-4.045

FFππ-2-2 2.452.45 2.222.22 0.1890.189 4.210-5.2464.210-5.246

Hall C spectrometers: Coincidence measurement. SOS detects e-. HMS detects π+ and π-.

Targets: Liquid 4-cm H/D cells. Al target for empty cell measurement. 12C solid targets for optics calibration.

SOS:SOS: 1.7 GeV/c1.7 GeV/c

HMS:HMS: 7 GeV/c7 GeV/c


22HH(e,e’(e,e’ππ±±)NN)NN Event selection Event selectionElectron-pionElectron-pioncoincidencescoincidences

Random coincidences

Exclusivity assured via 0.875<MM<1.03 GeV

cut

Pions detected in HMS – Cerenkov &

Coincidence time for PID Electrons detected in

SOS –Cerenkov & Lead Glass CalorimeterCoincidence time Coincidence time

resolution ~200-230 ps.resolution ~200-230 ps.Cut value ±1 ns.Cut value ±1 ns.

After PID & MM After PID & MM cuts, almost cuts, almost no random no random coincidences coincidences remain.remain.

Diamond cuts define common (W,Q2) coverage at both ε.


Corrections to Corrections to ππ--, , ππ++ DataData

Negative polarity of HMS fieldNegative polarity of HMS field for for 22H(e,e’H(e,e’ππ--)pp )pp means these means these runs have high electron rates runs have high electron rates not shared bynot shared by 22H(e,e’H(e,e’ππ++)nn )nn runs.runs.

Understanding rate dependent corrections very important with respect to separated π-/π+ ratios. Improved high rate HMS tracking Improved high rate HMS tracking

algorithm.algorithm. More accurate high rate tracking More accurate high rate tracking

efficiencies (91-98%).efficiencies (91-98%). HMS HMS ππ- - misidentification correction misidentification correction

due to edue to e-- pileup in Čerenkov pileup in Čerenkov (13%/MHz e(13%/MHz e--).).

High current High current 22H target boiling H target boiling correction (4.7%/100correction (4.7%/100μμA) for old A) for old `beer can’ target cell and square `beer can’ target cell and square beam raster.beam raster.

QQ22==0.600.60, , 0.750.75, , 1.01.0, 1.6 GeV, 1.6 GeV22


FFππ-1 ran in 1997. -1 ran in 1997. FFππ-2 ran in 2003. Many changes in between-2 ran in 2003. Many changes in between..

HMS Tracking Efficiencies for High Rate DataHMS Tracking Efficiencies for High Rate Data

1998 Engine overestimates tracking efficiencies, since 2-track events have lower efficiency than 1-track events.

For the Fπ-2 p(e,e’π+)n analysis (low rates), it was found that better results were found if the cut to exclude multiple good PMT ADC signals within the fiducial region of the hodoscope plane was removed.→ This removal fails at high rates.

2003 Engine tracking efficiencies are lower, but still overestimated.

2003 Engine tracking efficiencies with correction factor applied.

To bring FTo bring Fππ-1 data to same level of reconstruction quality as F-1 data to same level of reconstruction quality as Fππ-2 data, -2 data, a lot of effort went into modifying the Hall C Analysis Engine to accept a lot of effort went into modifying the Hall C Analysis Engine to accept the older format data.the older format data.

Makes use of redesigned tracking algorithm that does a significantly Makes use of redesigned tracking algorithm that does a significantly better job in selecting the best track for multi-track events.better job in selecting the best track for multi-track events.


Carbon Luminosity ScansCarbon Luminosity Scans To better understand HMS tracking efficiencies, the normalized To better understand HMS tracking efficiencies, the normalized

yields from carbon target were studied vs. rate and vs. current.yields from carbon target were studied vs. rate and vs. current. Carbon target should not “boil”, so normalized yields Carbon target should not “boil”, so normalized yields

should be flat vs. current if all efficiencies are should be flat vs. current if all efficiencies are calculated correctly.calculated correctly.

Unfortunately, no Unfortunately, no 1212C luminosity scans were taken at different C luminosity scans were taken at different beam currents in the Fbeam currents in the Fππ-1 experiment.-1 experiment. → → Conclusions from the FConclusions from the Fππ-2 study will have to be applied.-2 study will have to be applied.


22H Cryotarget Boiling CorrectionsH Cryotarget Boiling Corrections After the tracking efficiencies are finalized, the cryotarget boiling After the tracking efficiencies are finalized, the cryotarget boiling

corrections can be determined.corrections can be determined.

Fπ-2: “tuna can” target cell and uniform circular rastering.

• Consistent with no 1H cell correction in T. Horn Fπ-2 analysis.

Fπ-1: “beer can” target cell and non-uniform square rastering.

• Consistent with 6±1% 1H cell correction in J. Volmer Fπ-1 analysis.


HMS Čerenkov Blocking Correction (HMS Čerenkov Blocking Correction (ππ--))

In both FIn both Fππ-1,2, the HMS gas Čerenkov was -1,2, the HMS gas Čerenkov was used as a veto in the trigger for used as a veto in the trigger for 22H(e,e’H(e,e’ππ--) runs) runs→ → needed to avoid high DAQ deadtime due to large needed to avoid high DAQ deadtime due to large

ee-- rates in HMS. rates in HMS.

Čerenkov Blocking:Čerenkov Blocking:

ππ-- are lost when e are lost when e-- pass through the gas Čerenkov pass through the gas Čerenkov within ~100ns after within ~100ns after ππ-- has traversed the detector. has traversed the detector.

→ → results in mis-identification of results in mis-identification of ππ-- as e as e--

Actual veto thresholds vary according to PMT gain Actual veto thresholds vary according to PMT gain variations at high rates.variations at high rates. slightly more restrictive software thresholds are applied slightly more restrictive software thresholds are applied

in the analysis:in the analysis: FFππ-1: accept < 1.5 hcer_npe-1: accept < 1.5 hcer_npe FFππ-2: accept < 2 hcer_npe-2: accept < 2 hcer_npe


HMS Čerenkov Blocking Correction (HMS Čerenkov Blocking Correction (ππ--))

Čerenkov Blocking Correction is Čerenkov Blocking Correction is obtained from Trigger TDC obtained from Trigger TDC information, since that is information, since that is independent of tracking independent of tracking efficiency and cryotarget efficiency and cryotarget corrections.corrections.

Result is consistent with Result is consistent with ττ from from other studies (not shown here) other studies (not shown here) within statistical errors.within statistical errors.

Fπ-2: 116±6 ns

Fπ-1: 138±6 ns

ELLOrateeCCblock

• Region due to early e- passing through Region due to early e- passing through detector before e- associated with detector before e- associated with trigger.trigger.

• Already addressed in coincidence time Already addressed in coincidence time blocking correction.blocking correction.

FFππ-2: -2: ττ = 115±6 ns= 115±6 ns

FFππ-1: -1: ττ = 138±6 ns= 138±6 ns


Extract Response Functions through Iterative ProcedureExtract Response Functions through Iterative Procedure

Improve Improve φφ coverage by taking data at coverage by taking data at multiple multiple ππ (HMS) angles, -4 (HMS) angles, -4oo<<θθππqq <4 <4oo..

θπq=0 θπq=+4

-t=0.1

-t=0.3

Extract via Extract via simultaneous fitsimultaneous fit of L,T,LT,TTof L,T,LT,TT

d2 σ/d

tdφ

(μb

/GeV

2 ) Q2=1.60 π+

φπq (deg)

2coscos122dt

d

dt

d

dt

d

dt

d

dtdd TTLTTL

For each π HMS setting, form ratio:

SIMC

EXP

Y

YR

Combine ratios for π settings together, propagating errors accordingly.

SIMCSIMC

EXP

EXP dtd

d

Y

Y

dtd

d

22


Over-constrained Over-constrained p(e,e’p)p(e,e’p) reaction and elastic reaction and elastic e+e+1212C C reactions used to calibrate reactions used to calibrate spectrometer acceptances, spectrometer acceptances, momenta, offsets, etc.momenta, offsets, etc.

Spectrometers well-understood Spectrometers well-understood after careful comparison with MC after careful comparison with MC simulations.simulations. Beam energy and Beam energy and

spectrometerspectrometer

momenta determined to momenta determined to <0.1%.<0.1%.

Spectrometer angles to <1 Spectrometer angles to <1 mrad.mrad.

Agreement with published Agreement with published p+ep+e

elastics cross sections <2%.elastics cross sections <2%.

Systematic Uncertainties (FSystematic Uncertainties (Fππ-1)-1)

SourceSource Pt-PtPt-Pt εε uncorr. uncorr.

t corr,t corr,

ScaleScale

Beam and Spectrometer Kinematic Beam and Spectrometer Kinematic OffsetsOffsets

0.2%0.2% 0.8-1.1%0.8-1.1%

HMS HMS ββ-cut corrections-cut corrections 0.4%0.4%

Particle IDParticle ID 0.2%

Pion Absorption CorrectionPion Absorption Correction 1.0%1.0%

Pion Decay CorrectionPion Decay Correction 0.03%0.03% 1.0%1.0%

HMS TrackingHMS Tracking 0.4% (0.4% (ππ+)+)

1.3%1.3% ( (ππ-)-)

1.0%1.0% ( (ππ+)+)

1.0%1.0% ( (ππ-)-)

SOS TrackingSOS Tracking 0.2%0.2% 0.5%0.5%

Integrated Beam ChargeIntegrated Beam Charge 0.3%0.3% 0.5%0.5%

Target ThicknessTarget Thickness 0.3%0.3% 1.0%1.0%

CPU and Trigger Dead timeCPU and Trigger Dead time 0.3%0.3%

HMS Cerenkov Veto Correction (HMS Cerenkov Veto Correction (ππ-)-) 0.7% 2.0%2.0%

Missing Mass CutMissing Mass Cut 0.8% 1.3%1.3%

Spectrometer AcceptanceSpectrometer Acceptance 1.0%1.0% 0.6%0.6% 1.0%1.0%

MC Model Dependence (L,T)MC Model Dependence (L,T) 0.4%0.4% 0.7-3.5%0.7-3.5% 0.3-2.0%0.3-2.0%

Radiative CorrectionsRadiative Corrections 0.4% 2.0%2.0%

TOTAL (TOTAL (ππ+)+) 1.4%1.4% 1.4-3.6%1.4-3.6% 3.1-3.5%3.1-3.5%

TOTAL (TOTAL (ππ-)-) 1.6%1.6% 2.3-4.4%2.3-4.4% 3.7-4.2%3.7-4.2%

Typical Statistical Typical Statistical UncertaintyUncertainty (per t-bin)(per t-bin)

5-10%5-10%


22H data Kinematic coverageH data Kinematic coverage

22H(e,e’H(e,e’ππ++)nn)nn 22H(e,e’H(e,e’ππ--)pp)pp

QQ22=0.6 GeV=0.6 GeV22, W=1.95 GeV, W=1.95 GeV (F (Fππ-1)-1)

εε=0.37=0.37, E, Eee=2.445 GeV=2.445 GeV 3 HMS settings: 3 HMS settings: θθππqq=+0.5,+2.0,+4.0=+0.5,+2.0,+4.0oo.. 2 HMS settings: 2 HMS settings: Missing +2.0Missing +2.0oo..

εε=0.74=0.74, E, Eee=3.548 GeV=3.548 GeV 4 HMS settings: 4 HMS settings: θθππqq=-2.7, +0.0,+2.0,+4.0=-2.7, +0.0,+2.0,+4.0oo.. 1 HMS setting: 1 HMS setting: Only +0.0Only +0.0oo..


εε=0.43=0.43, E, Eee=2.673 GeV=2.673 GeV 2 HMS settings: 2 HMS settings: θθππqq=+0.0,+4.0=+0.0,+4.0oo.. 2 HMS settings: 2 HMS settings: θθππqq=+0.0,+4.0=+0.0,+4.0oo..

εε=0.70=0.70, E, Eee=3.548 GeV=3.548 GeV 3 HMS settings: 3 HMS settings: θθππqq=-4.0, +0.0,+4.0=-4.0, +0.0,+4.0oo.. NO HMS settings.NO HMS settings.



εε=0.65=0.65, E, Eee=3.548 GeV=3.548 GeV 3 HMS settings: 3 HMS settings: θθππqq=-4.0, +0.0,+4.0=-4.0, +0.0,+4.0oo.. 1 HMS setting: 1 HMS setting: Only +0.0Only +0.0oo..



εε=0.63=0.63, E, Eee=4.045 GeV=4.045 GeV 3 HMS settings: 3 HMS settings: θθππqq=-4.0, +0.0,+4.0=-4.0, +0.0,+4.0oo.. 3 HMS settings: 3 HMS settings: θθππqq=-4.0, +0.0,+4.0=-4.0, +0.0,+4.0oo..



εε=0.55=0.55, E, Eee=5.248 GeV=5.248 GeV 3 HMS settings: 3 HMS settings: θθππqq=-3.0, +0.0,+3.0=-3.0, +0.0,+3.0oo.. 3 HMS settings: 3 HMS settings: θθππqq=-3.0, +0.0,+3.0=-3.0, +0.0,+3.0oo..


22HH(e,e’(e,e’ππ±±))NNNN Separated dSeparated dσσ/dt/dt

Longitudinal cross-Longitudinal cross-section shows steep rise section shows steep rise due to due to ππ pole at small pole at small –t–t..

Transverse cross-section Transverse cross-section much flattermuch flatter..

Both follow nearly Both follow nearly universal curves vs universal curves vs –t,–t, with weak with weak QQ22-dependence.-dependence.

• Data points have slightly different

• All data scaled to W=2.0 GeV assuming 1/(W2-M2) dependence, M=free nucleon mass.

• No scaling applied in Q2.

2 , QWL

T

L

T

Q2=0.6

Q2=1.0

Q2=1.6Q2=2.45

Error bars indicate statistical and pt-pt systematic uncertainties in quadrature.Error bars indicate statistical and pt-pt systematic uncertainties in quadrature.Bands indicate L,LT,TT MC model dependence systematic uncertainty.Bands indicate L,LT,TT MC model dependence systematic uncertainty.


Error bars indicate statistical and pt-pt Error bars indicate statistical and pt-pt systematic uncertainties in quadrature.systematic uncertainties in quadrature.Bands indicate L,LT,TT MC model Bands indicate L,LT,TT MC model dependence systematic uncertainty.dependence systematic uncertainty.

VGL Regge Model:VGL Regge Model:• Free parameters: Free parameters: ΛΛππ

22, , ΛΛρρ22

(from (from 11H data)H data)..

[PRC 57(1998)1454]

KM Regge+DIS Model:KM Regge+DIS Model:• σσLL from from 11H data, DIS H data, DIS

process dominates process dominates σσTT..

[PRC 81(2010)045202]

VR Regge+DIS Model:VR Regge+DIS Model:• Similar to KM but with Similar to KM but with

improved DIS parametersimproved DIS parameters [PRC 89(2014)025203]

Model dModel dσσxx/dt/dt


ππ--//ππ++ Separated Response Function RatiosSeparated Response Function Ratios

Transverse Ratios tend Transverse Ratios tend to ¼ as –t increases:to ¼ as –t increases:

→ → Is this an indication of Is this an indication of Nachtmann’s quark charge Nachtmann’s quark charge scaling? scaling?

-t=0.3 GeV-t=0.3 GeV22 seems too low seems too low for this to apply. Might for this to apply. Might indicate the partial indicate the partial cancellation of soft QCD cancellation of soft QCD corrections in the corrections in the formation of the ratio.formation of the ratio.

RRLL≈0.8 near ≈0.8 near –t–tminmin at at

each each QQ22..Predicted in large Predicted in large NNcc limit calculation. limit calculation. Frankfurt, et al. PRL 84(2000)2589.

Error bars indicate statistical and pt-pt systematic uncertainties in quadrature.Error bars indicate statistical and pt-pt systematic uncertainties in quadrature.Bands indicate MC model dependence systematic uncertainty.Bands indicate MC model dependence systematic uncertainty.


Relevance to Pion Form Factor ExtractionRelevance to Pion Form Factor ExtractionVrancx-Ryckebusch Vrancx-Ryckebusch Model:Model:

• VGL Regge Model VGL Regge Model underpredicts underpredicts σσTT by by

large factor.large factor.• VR extend VGL with VR extend VGL with

hard DIS process of hard DIS process of virtual photons off virtual photons off nucleons.nucleons.

[PRC 89(2014)025203]

Qualitatively in agreement with our FQualitatively in agreement with our Fππ-1 -1 analysis:analysis: We found evidence for small additional We found evidence for small additional

contribution to contribution to σσLL at W=1.95 GeV not taken into at W=1.95 GeV not taken into account by the VGL model.account by the VGL model.

We found little evidence for this contribution in We found little evidence for this contribution in F Fππ-2 -2 analysis at W=2.2 GeV.analysis at W=2.2 GeV.

RRLL=0.8 consistent =0.8 consistent

with with |A|ASS/A/AVV|<|<6%.6%.


Comparison with Goloskokov-Kroll GPD modelComparison with Goloskokov-Kroll GPD model

Model parameters optimized for small skewness (Model parameters optimized for small skewness (ξξ<0.1<0.1) and ) and WW>4 GeV.>4 GeV. Application to our kinematics requires substantial extrapolation in Application to our kinematics requires substantial extrapolation in W, W, ξξ..

→ → Please be cautious in the comparison.Please be cautious in the comparison. Although model does reasonable job at predicting ratios, agreement of model Although model does reasonable job at predicting ratios, agreement of model

with our with our σσTT is not good. is not good.

Model optimized for JLab kinematics should be sensitive to transverse GPD, Model optimized for JLab kinematics should be sensitive to transverse GPD, HHTT

• ππ±± electroproduction electroproduction in a handbag in a handbag framework.framework.

• Modified perturbative Modified perturbative approach with full approach with full FFππ(Q(Q22).).

• Substantial Substantial contributions from contributions from transverse photons transverse photons as twist-3 effect (as twist-3 effect (HHTT))

[Eur.Phys.J.A[Eur.Phys.J.A4747(2011)112](2011)112]


σσLL//σσT T and and σσTTTT//σσTT Ratios for Ratios for ππ++, , ππ--

L/T ratio becomes L/T ratio becomes more favorable for more favorable for ππ-- production as Qproduction as Q22 increases.increases.

Another prediction of Another prediction of quark-parton quark-parton mechanism is the mechanism is the suppression of suppression of σσTTTT//σσTT due to due to ss-channel -channel helicity conservation.helicity conservation.

Data qualitatively Data qualitatively consistent with this, consistent with this, since since σσTTTT decreases decreases more rapidly than more rapidly than σσTT with increasing Qwith increasing Q22..

Error bars indicate statistical and pt-pt Error bars indicate statistical and pt-pt systematic uncertainties in quadrature.systematic uncertainties in quadrature.Bands indicate MC model dependence Bands indicate MC model dependence systematic uncertainty.systematic uncertainty.


Projected Data from FProjected Data from Fππ-12 Experiment-12 Experiment E12-06-101 approved for 52 E12-06-101 approved for 52

days of beam with SHMS+HMS, days of beam with SHMS+HMS, A rating, selected by PAC41 as A rating, selected by PAC41 as “High Impact”.“High Impact”.

22H H data to determinedata to determine RRLL ππ--//ππ+ + ratio ratio to constrain modeling of non-pole to constrain modeling of non-pole backgrounds in backgrounds in σσLL, relevant for , relevant for extraction of pion form factorextraction of pion form factor 44 hrs (44 hrs (ππ++), 174 hrs (), 174 hrs (ππ--).).

If If RRTT is ~1/4 at higher Q is ~1/4 at higher Q22 and and similar xsimilar xBB, the hypothesis of a , the hypothesis of a quark knockout mechanism will quark knockout mechanism will be strengthened.be strengthened.

Projected Data

Predictions ofPredictions of

Vrancx-Ryckebusch Vrancx-Ryckebusch Regge+DIS ModelRegge+DIS Model[PRC 89(2014)025203]


SummarySummary

Separated σL, σT, σLT, σTT cross sections for the 2H(e,e’π±)NN reactions were extracted using the Rosenbluth L/T separation technique. FFππ-1: W=1.95 GeV: Q-1: W=1.95 GeV: Q22=0.6, 1.0, 1.6 GeV=0.6, 1.0, 1.6 GeV22.. FFππ-2: W=2.2 GeV: Q-2: W=2.2 GeV: Q22=2.45 GeV=2.45 GeV22..

π-/π+ ratios for σL, σT extracted as a function of -t. RRLL≈0.8, trending towards unity at low –t.≈0.8, trending towards unity at low –t.

Indicates the dominance of isovector processes at low –t in the Indicates the dominance of isovector processes at low –t in the longitudinal response function.longitudinal response function.

The evolution of The evolution of RRTT with –t shows rapid fall off consistent with with –t shows rapid fall off consistent with

earlier theoretical predictions, expected to approach ¼, the earlier theoretical predictions, expected to approach ¼, the square of the ratio of the quark charges involved.square of the ratio of the quark charges involved.

Further theoretical work needed re. alternate explanations.Further theoretical work needed re. alternate explanations.


Cerenkov trigger about 90% efficient at vetoing electrons.

FFππ-2 HMS Čerenkov Trigger TDC study-2 HMS Čerenkov Trigger TDC study

Multi-hit TDC of the Čerenkov signal into the HMS trigger was Multi-hit TDC of the Čerenkov signal into the HMS trigger was investigated for HMS singles rate up to ~600 kHz.investigated for HMS singles rate up to ~600 kHz.

Compare runs without and with HMS Čerenkov veto.Compare runs without and with HMS Čerenkov veto.

Main peak:Signal (primarily e-) that starts TDC.

2nd peak:Second e- arriving within timing window, but after 1st 40ns long discriminator pulse.

Pedestal:Earlier or later e-.

Tail to 410ns:Noise crossing discriminator threshold.

Chan 4096:Very late TDC stops.

Chan 0:• Mostly π-, not giving

TDC stop.• Ratio of 0 to 1st

peak much greater with veto trigger.

Without Veto

With Veto

Normalized Difference


FFππ-2 HMS Singles Yield Study-2 HMS Singles Yield Study

Plot normalized HMS singles Plot normalized HMS singles yields for each kinematic setting yields for each kinematic setting vs. rate. vs. rate.

For each setting, fit with For each setting, fit with AeAe-b-bττ and and divide by divide by AA..

ττ values sensitive to applied values sensitive to applied tracking eff. and cryotarget boiling tracking eff. and cryotarget boiling corrections.corrections.

These These ττ values determined with values determined with singles events, and need to be singles events, and need to be adjusted for effective gate width for adjusted for effective gate width for coincidence evts.coincidence evts.

22H(H(e,e’e,e’ππ--)) runs were taken without HMS Cerenkov trigger veto at runs were taken without HMS Cerenkov trigger veto at different currents for several kinematic settings.different currents for several kinematic settings.

Apply “veto” via hcer_npe<2.0 cut.Apply “veto” via hcer_npe<2.0 cut. Expect a loss of yield at higher rate due to Cerenkov blocking.Expect a loss of yield at higher rate due to Cerenkov blocking.

nsstudyyield 1999_

ττ value found in 2009 analysis value found in 2009 analysis significantly larger, 160ns.significantly larger, 160ns.


Final HMS Tracking Efficiency CorrectionFinal HMS Tracking Efficiency Correction

)1076236.6*)(11(__ 5 kHzXrateSoldhtrcorrectedhtr

• Correction is applied to both FCorrection is applied to both Fππ-1 and F-1 and Fππ-2 tracking efficiencies.-2 tracking efficiencies.

• Particularly important for FParticularly important for Fππ-1 -1 22H(e,e’H(e,e’ππ--) data, with HMS rate up to 1.4 MHz.) data, with HMS rate up to 1.4 MHz.

After application of correction, carbon normalized yields show NO residual current dependence.


22H(e,e’H(e,e’ππ±±)NN )NN MC Model and ReconstructionMC Model and Reconstruction L/T/LT/TT separation needs a model to take into account L/T/LT/TT separation needs a model to take into account

kinematic correlations between Qkinematic correlations between Q22, W, t and , W, t and θθππ in a given (t,in a given (t,φφ) bin.) bin. Various choices can be made for treating off-shell effects, and Various choices can be made for treating off-shell effects, and

these could affect the interpretation of our results.these could affect the interpretation of our results.

In SIMC Monte Carlo simulation:In SIMC Monte Carlo simulation: Generate vertex quantities, taking Fermi motion into account with spectator on-Generate vertex quantities, taking Fermi motion into account with spectator on-

shell and the struck nucleon carrying all off-shellness.shell and the struck nucleon carrying all off-shellness. E_struck depends on the assumed Fermi momentum (taken from Bonn E_struck depends on the assumed Fermi momentum (taken from Bonn 22H H

wave function)wave function) Follow outgoing particles (including radiation) through target, spectrometer, Follow outgoing particles (including radiation) through target, spectrometer,

detectors and determine 'experimental' values of kdetectors and determine 'experimental' values of ke'e' and k and kππ..

Data reconstruction (both exp data and simulation):Data reconstruction (both exp data and simulation): Since the Fermi momentum of the struck nucleon is not known, the values of Since the Fermi momentum of the struck nucleon is not known, the values of

QQ22, W, t, M, W, t, MXX, , φφ, , θθ are computed in the quasi-free are computed in the quasi-free approximation where the struck nucleon is at rest.approximation where the struck nucleon is at rest. CM frame is γ* and stationary CM frame is γ* and stationary NN, φ, φCMCM=φ=φLABLAB, as in , as in 11H analysis.H analysis. t=(pt=(ptargettarget-p-precoilrecoil))2 2 used.used. N Not necessarily equivalent to ot necessarily equivalent to t=(pt=(pγγ-p-pππ))22 due to Fermi momentum due to Fermi momentum

and radiation.and radiation.

Reconstructed Reconstructed QQ22, W, t, W, t are also used to compute the weighting for are also used to compute the weighting for simulated events according to the model cross section.simulated events according to the model cross section.

'* NN


Good Agreement for Optics and Kinematic VariablesGood Agreement for Optics and Kinematic Variables

DataDataSIMCSIMC


Comparison of Comparison of ππ++ from from 11H and H and 22HH

Intriguing differences Intriguing differences between between ππ++ production from production from hydrogen and hydrogen and deuterium.deuterium.

Keep in mind that Keep in mind that 22H H cross sections are cross sections are effective ones, not effective ones, not trivially comparable trivially comparable to to 11H.H.

Role of off-shell effects Role of off-shell effects in in 22H?H?

Role of Fermi Role of Fermi momentum in momentum in 22H?H?

L

T

11H(e,e’H(e,e’ππ++)n)n22H(e,e’H(e,e’ππ++)nn)nn

Error bars indicate statistical and pt-pt systematic uncertainties in Error bars indicate statistical and pt-pt systematic uncertainties in quadrature.quadrature.Bands indicate MC model dependence systematic uncertainty.Bands indicate MC model dependence systematic uncertainty.


Error bars indicate statistical and pt-pt Error bars indicate statistical and pt-pt systematic uncertainties in quadrature.systematic uncertainties in quadrature.Bands indicate L,LT,TT MC model Bands indicate L,LT,TT MC model dependence systematic uncertainty.dependence systematic uncertainty.

MAID07 Isobar Model:MAID07 Isobar Model:• Parameters optimized for

W<2 GeV. • Q2=2.45 GeV2 results are an

extrapolation.

[EPJA 34(1999)145]

GK GPD-Based Model:GK GPD-Based Model:• σσLL based on full F based on full Fππ(Q(Q22) ) from from

11H data, H data, σσTT substantial substantial

contribs from twist-3 contribs from twist-3 HHTT..

• Params optimized for Params optimized for small skewness (ξ<0.1) small skewness (ξ<0.1) and W>4 GeV.and W>4 GeV.

[EPJA 47(2011)112]

Model dModel dσσxx/dt/dt

Separated π - /π + Ratios from the Pion Form Factor Experiments → Separated π - /π + Ratios...

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Transcript of Separated π - /π + Ratios from the Pion Form Factor Experiments → Separated π - /π + Ratios...