Ratios of Separated Response Functions Cornel Butuceanu in Forward Pion Electroproduction Hall C...

Ratios of Separated Response Functions

Cornel Butuceanu

ππin Forward Pion Electroproduction

Hall C Users Meeting, JLab, January 19, 2008

Motivation Data Analysis Prelim. Results Outlook

Fπ CollaborationR. Ent, D. GaskellD. Gaskell, M.K. Jones, D. MackD. Mack, D. Meekins, J. Roche, G. Smith, W. Vulcan,

G. Warren, S.A. WoodJefferson Lab, Newport News, VA , USA

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

H. BlokH. Blok, V. TvaskisVrije Universiteit, Amsterdam, Netherlands

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

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

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

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

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

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

J. VolmerDESY, Hamburg, Germany

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

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

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

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


Motivation

2

2

SAVASAVA

n)πpvσ(γp)πnvσ(γ

R

Pion electroproduction can proceed via isovector and isoscalar photons.

Testing the t-pole (isovector) dominance – key factor in the extraction of the pion ff ( ).

The experimental ratio evolution with

-t gives a good indication of the presence of isoscalar processes. Separated ratio tests the t-pole contribution to . Good existent 2H data sets E93-021 : Q2=0.6, 1.0 & 1.6 GeV2. E01-004 : Q2=2.45 GeV2.

Both data sets needed to be brought to the same level of analysis.

π

LR Lσ


πF

t-pole

q)s(ps)ne'π2H(e, reactio

ns

Previous Studies

LLL / σσRR


Earlier studies at DESY suggested:

At low –t we have purely isovectorprocesses:

Deviations of from 1 gives indication of the amount of isoscalar backgrounds in the .At large –t the ratio is dominated by isoscalar processes:

LRLσ

TTT / σσRRUnseparated cross section

ratios

Experimental Setup

Exp Q2(GeV/c)2

W (GeV

)

|tmin| (Gev/c)2

Ee

(GeV)

Fπ-1 0.6-1.61.6 1.95 0.03-0.1500.150 2.445-4.045Fπ-2 1.61.6,2.5 2.22 0.0930.093,0.18

93.779-5.246


Hall C spectrometers: Coincidence measurement. SOS detects e-. HMS detects π+ and π-. Targets: Liquid 4-cm H/D cells. Al (dummy) target for

background measurement. 12C solid targets for optics

calibration.

Event selection


Coincidence measurement Coincidence measurement between charged pions in between charged pions in HMS and electrons in SOS.HMS and electrons in SOS.

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

Missing mass cut 0.875<MM<1.05 assures exclusivity of the event.

ππ+ and + and ππ- are detected in HMS- are detected in HMS using Cerenkov and Cerenkov and coincidencecoincidence time for PID.time for PID. -random coincidences subtracted Electrons in SOS – identified Electrons in SOS – identified by by Cerenkov /Lead Glass Cerenkov /Lead Glass Calorimeter Calorimeter ..

0.6E/P0.5Nphe

Corrections to Fpi1 data set By using the new tracking algorithm (2003 CVS engine) on

1998 data (E93021) we extended multitrack event capabilities and implicit a more accurate event reconstruction.

We corrected the HMS Delta/xpfp correlations with a linear dependent function of form .

• New wire chambers tracking efficiencies as a function of event rate were extracted.

HMS Cerenkov blocking correction as a function of event rate was used to recover pions lost due to a severe threshold cut in the Fpi1 initial trigger.

New target boiling corrections were extracted for H and D using elastic data with updated tracking efficiencies.


'fpδ xCδδ'

SOS Optics Calibration

For low momentum (<1.6 GeV/c) we used the Fpi1 (1999) optics matrix & delta/xpfp correction.For high momentum (>1.6 GeV/c) we used the Fpi2 (2003) new optics matrix & delta/xpfp correction.


HMS Cerenkov Blocking

CCτeR1CC

ε

Used data taken with open trigger (el. & pions) to fit the effective time window. The TDC time window in Fpi1 is 23% larger than in Fpi2. Used the Fpi2 data to fit the effective TDC gate (for the same CC cut). For a CC cut of npe<1.5 the effective TDC gate for Fpi1 set is ~184 ns. Implies a larger correction for Fpi1 data (18-20 % at 1MHz). Significant impact in pi- (high rate) data.


HMS CC TDC spectrum for e as identified by the HMS CC ADC

ns 5184ττR-1ε

CC

CCeCC

Uncertainties associated with this correction are of the order of 1.6% at 1MHz.

Tracking efficiency

Two issues:1. The Fpi1 version of the Trk. Eff.

algorithm used a ‘’cleaner’’ data sample by removing the multiple hits events resulting in overevaluated trk. eff.

2. The Fpi2 version used a ‘’dirty’’ data sample by including the multiple hits events resulting in subevaluated trk. eff.

The high rate data (pi-) is the most sensitive to the tracking efficiency correction (~10% at 1.4 MHz). A linear correction dependent of event rate was applied to the tracking efficiencies of pi- data.Hall C Users Meeting, JLab, January 19, 2008

Corrections due to the Target Boiling

18

• Hydrogen has a boiling

effect of 8 1% at 100 microA.

• Deuterium has a boiling effect of 12 2% at 100

microA.

Hall C Users Meeting, Jlab, January 19, 2008

To account for target boiling effects the pion yields were normalized with a linear function of the beam current.

KinematicKinematic CoverageCoverage

• Need full coverage in Need full coverage in φφ toto

measure σTT and σLT.

• Take data at three angles: θπq=0o, +4o, -4o.

• (W,Q(W,Q22)) phase space phase space covered at low and high covered at low and high εε is different.is different.

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


2coscos122dtd

dtd

dtd

dtd

dtdd TTLTTL

= [1+2(1+)tan2(/2)]-1

Simulations vs Experimental data

Simulated Missing Mass spectrum was improved by implementing pions that were penetrating the collimator. Hall C Users Meeting, JLab January 19, 2008

Pion Punchthrough Implementation resulted in an overall improved simulated kinematic variables (W,Q2,-t).

Extraction of separated cross sectionsExtraction of separated cross sections

2coscos122dtd

dtd

dtd

dtd

dtdd TTLTTL

MCMC dttQWd

Y

Y

dttQWd

),,,(),,,( 2exp

exp

2


MC is based on the quasielastic pion electroproduction data. Radiative effects, pion decay, energy loss, multiple scattering. COSY model for spectrometer optics.

were extracted bywere extracted by a simultaneous fita simultaneous fit using measured azimuthal angle and calculated photon polarization ε.

LTTTTL σ,σ,σ,σ

= [1+2(1+)tan2(/2)]-1

πφ The unseparated pi- & pi+ cross sections were obtained from the model cs weighted by the ratio of experimental to simulated yields.

Preliminary Results vs VGL ModelPreliminary Results vs VGL Model

Pi- : Pi- : ΛΛππ22=0.450 GeV=0.450 GeV22, , ΛΛρρ

22=1.5 GeV=1.5 GeV22..

Pion electroproduction in terms of exchange of π and ρ Regge trajectories.

[VGL, PRC 57(1998)1454]

Model parameters fixed

from pion photoproduction.

Free parameters: ΛΛπ22 and

ΛΛρ2 2 .

ρ exchange does not significantly influence σL

at small –t. Hall C Users Meeting, JLab, January 19, 2008Pi+ : Pi+ : ΛΛππ

22=0.500 GeV=0.500 GeV22, , ΛΛρρ22=1.5 GeV=1.5 GeV22..

Separated Response Functions Ratio ππ


LR


22=1.5 GeV=1.5 GeV22.. Pi+ : Pi+ : ΛΛππ22=0.500 GeV=0.500 GeV22, , ΛΛρρ

22=1.5 GeV=1.5 GeV22..

Separated Response Functions Ratio ππ


TR


22=1.5 GeV=1.5 GeV22.. Pi+ : Pi+ : ΛΛππ22=0.500 GeV=0.500 GeV22, , ΛΛρρ

22=1.5 GeV=1.5 GeV22..

OUTLOOK• Completed all the corrections to Fpi1 (E93-021) data set (CC blocking, Rate Dependent, Tracking Efficiencies and Target Boiling) and optical calibrations.

• Preliminary separated cross sections were extracted using L/T separation Rosenbluth technique.

• Preliminary ratios were extracted as a function of -t.

• To do list: - include the Fpi2 Q2=2.45 in these results. - estimate the correlated and uncorrelated sys. err. - fine tuning of MC deuterium model. - prepare a draft paper by the end of the summer.

TTLTTL σ,σ,σ,σ

n)πpvσ(γp)πnvσ(γ

R


Kinematic Variables

DNP Meeting, NN, Virginia, 13 October 2007

HMS Q3 corrections

• The W vs X’ distribution was the fitted with 1 degree polynomial for each.


• Using central HMS kinematics and detected proton momentum we reconstruct the invariant mass W (electron mass).

'fpδ xCδδ'

Corrected Tracking Efficiencies

Hall C Collaboration Meeting, JLab, January 19, 2008

A ~8% correction to the tracking efficiencies at 1.4MHz was applied to the high rate data (pi-).

Simulations vs Experimental data (optics)

HMS & SOS exp vs sim comparison of the optics for pi+

data.Hall C Users Meeting, JLab, January 19, 2008

SIM/EXP comparison for other kinematic

variables.

Ratios of Separated Response Functions Cornel Butuceanu in Forward Pion Electroproduction Hall C...

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