# Presentation: 813829

## Ratios of Separated Response Functions

**Cornel Butuceanu**

**from Pion Electroproduction **

**     ****1                                                          Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

** ****Motivation**
** ****Analysis**
** ****Results **
** ****Summary**

**at**

**and**

## Jefferson Lab Fπ Collaboration

**R. Ent, ****D. Gaskell****, M.K. Jones, ****D. Mack****, D. Meekins, J. Roche, G. Smith, W. Vulcan, **
**G. Warren, S.A. Wood**
- Jefferson Lab, Newport News, VA , USA
** ****C. Butuceanu,**** E.J. Brash,**** G.M. Huber****, V. Kovaltchouk, G.J. Lolos, S. Vidakovic, ****C. Xu**** **
- University of Regina, Regina, SK, Canada
**H. Blok****, V. Tvaskis**
- Vrije Universiteit, Amsterdam, Netherlands
**E. Beise****, H. Breuer, C.C. Chang, ****T. Horn****, P. King, J. Liu, P.G. Roos**
- University of Maryland, College Park, MD, USA
**W. Boeglin, P. Markowitz, J. Reinhold**
- Florida International University, FL, USA
**J. Arrington, R. Holt, D. Potterveld, P. Reimer, X. Zheng**
- Argonne National Laboratory, Argonne, IL, USA
**H. Mkrtchyan, ****V. Tadevosyan**
- Yerevan Physics Institute, Yerevan, Armenia
**S. Jin, W. Kim**
- Kyungook National University, Taegu, Korea
**M.E. Christy, C. Keppel, L.G. Tang**
- Hampton University, Hampton, VA, USA
**J. Volmer**
- DESY, Hamburg, Germany
**A. Matsumura, T. Miyoshi, Y. Okayasu**
- Tohuku University, Sendai, Japan
**B. Barrett, A. Sarty**
- St. Mary’s University, Halifax, NS, Canada
**K. Aniol, D. Margaziotis**
- California State University, Los Angeles, CA, USA
**L. Pentchev, C. Perdrisat**
- College of William and Mary, Williamsburg, VA, USA

**   ****2                                                            Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

## Motivation

** ****Testing the t-pole dominance – key factor in**
**  ****the extraction of the  pion form factor     .**
** ****Pion     electroproduction can proceed **
**  ****via isovector and isoscalar photons.**
** ****The experimental ratio                                evolution with**
**  ****-t gives a good indication of the presence of isoscalar processes.**
**  ****Separated ratios     and      tests the t-pole contribution to     .**

**t-pole**

**q**

**reactions**

**   ****3                                                            Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

## Previous Studies

**Unseparated cross section ratios**

**At low -t**

**At high -t**

**[A. Nachmann, Nucl. Phys. B 115 (1976) 61]**

**   ****4                                                            Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

##  Kinematics Coverage & L/T Separation Technique

**Take data at three angles:**
** ****θ****π****q****=0****o****, +4****o****, -4****o.**

**Diamond cuts define common**
** *****(W,Q******2******)***** coverage at both ****ε****.**

**Extract ****σ****L**** by simultaneous fit **** **of L,T,LT,TT using  measured azimuthal angle (φπ) and knowledge of photon polarization (ε).

**   ****5                                                            Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

## Event selection

**Electron-pion**
**coincidences**

**Exclusivity assured via  0.875<MM<1.05 GeV cut**

**Random **
**coincidences**

**Pions detected in HMS – Cerenkov &**
**Coincidence time for PID **

**Electrons detected in SOS –Cerenkov & Lead Glass Calorimeter**

**   ****6                                                            Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

## Collimator Pion Punch Through in SIMC 

**Simulated Missing Mass spectrum was improved by implementing pions that were penetrating the HMS collimator.**** **

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

**   ****7                                                            Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

##  Magnetic Spectrometer Calibrations 

**   ****  ****- ****Over-constrained ****p(e,e’p) ****and elastic ****e + ****12****C ****reactions were**
**    ****used to calibrate spectrometer acceptances, momenta and**
**    ****angular offsets.**
**     ****- ****SOS & HMS Delta/xpfp correlations were corrected with a **
**    ****linear dependent function of form                        .****                        **

** ****Corrections to the high rate    data set**

**        ****data were taken at high rates while      data were taken at**
**   ****low rates. Understanding the rate dependent corrections was very**
**   ****important with respect to the final           ratios. **
**     ****-New high rate tracking algorithm****.**
**     ****-Improved high rate tracking efficiencies (2-9%).**
**        ****-          ****HMS Cerenkov blocking  correction (2-18%). **
**     ****-High current (    data set) target boiling correction (2-13%).  **

**Data Analysis**

**   ****8                                                            Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

## Tracking Efficiency For High Rate Data

** ****Tracking Efficiency as defined for Fpi2 data fails for Fpi1 high**
**   ****rate data (pi-).**

**   ****9                                                           Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

## Tracking Efficiencies For High Rate Data

** ****A ~8% correction to the tracking efficiencies at 1.4MHz was**
** ****applied to the Fpi1 high rate data (pi-). **

**   ****10                                                          Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

## Target Boiling Corrections

** ****Hydrogen had a boiling effect  of ~ ****11%**** at 100 microA.**

** ****Deuterium had a boiling effect of ~ ****13.5% ****at 100 microA.**

**   ****11                                                          Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

- Hydrogen

- Deuterium

## Fpi2  Pion Absorption and Beta efficiency

**P****i- data**

**Pi+ data**

**   ****12                                                          Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

**Fpi2  Pion Absorption and Beta efficiency**

** ****The thick HMS exit window and the addition of the aerogel Cherenkov resulted in an improved overall pion transmission.**

**Beta > .925**

## Fpi1 Beta Cut 

**   ****13                                                         Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

**Random coincidences**

**Real coincidences**

**protons**

**beta cut**

** ****A tight beta cut was applied to remove protons from the ********data sample.**
** ****No Aerogel used in Fpi1 experiment.**

****** ****> .95**

**********data**

**********data**

## Error Analysis

**Spectrometers well-understood after careful comparison with MC simulations.**
**Beam energy and spectrometer**
**	****momenta determined to <0.1%.**
**Spectrometer angles to ~0.5 mr.**
**Agreement with published p+e **
**	****elastics cross sections <2%.**
**Per data t-bin:**
**Typical statistical error per bin: 1-2%.**
**Uncorrelated syst. unc. in ********UNS **
**	****        ****common to all t-bins:****	****      1.8(1.9)%.**
**Additional uncorrelated unc. also **
**   ****uncorrelated in t: ****	****      1.1(0.9)%.**
**Total correlated uncertainty: 3.5%.**
**Uncorrelated uncertainties in ********UNS**** are amplified by**** 1/Δε ****in L-T separation.**
**Scale uncertainty propagates directly into separated cross section.**

| Systematic
Uncertainty
Source                                                                                                                         | ε-uncorrelated
common to all t-bins | Pt-Pt
ε-random
t-random | Scale
ε-global
t-global |
| --- | --- | --- | --- |
| Spectrometer Acceptance | 0.6% | 1.0(0.6)% | 1.0% |
| Radiative Corrections | 0.4% | 0.1% | 2.0% |
| Pion Absorption Correction | 0.1% | - | 2.0% |
| Pion Decay Correction | - | 0.03% | 1.0% |
| MC Model Dependence | 1.1(1.3)% | 0.2% | - |
| Kinematic Offsets | 1.0% | 0.2% | - |
| HMS Tracking | 0.4% | 0.1% | 1.0% |
| Integrated Beam Charge | 0.3% | - | 0.5% |
| Target Thickness | 0.2% | - | 0.8% |
| Detection Efficiency | 0.3% | - | 0.5% |

**   ****14                                                         Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

**Error Analysis**

## VGL Regge Model

**Pion electroproduction in terms of exchange of ****π**** and ****ρ**** Regge trajectories.**
**   ****- exchanged of a series of particles**
**      ****compared to a single particle.**
**       **
**Model parameters fixed from pion photoproduction.**
**Free parameters: **Λ**π**2** and **Λ**ρ**2  (**trajectory cutoffs**)**.**
**ρ**** exchange does not **
**   ****significantly influence ****σ****L**** at small *****–t*****.**

**   ****15                                                         Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

**[Vanderhaeghen, Guidal, Laget, PRC 57(1998)1454]**

##    Separated Response Functions 

**   ****16                                                         Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

##    Separated Response Functions Ratios 

**   ****17                                                         Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

## Summary

**Separated                            cross sections were extracted using**
**    ****Rosenbluth  L/T separation technique.**
**Ratios                 were extracted as a function of -t.**
**Preliminary results show that     is consistent with ****1**** over the whole **
**    ****range in –t indicating a dominance of isovector processes at low –t in the longitudinal response function      .**
**These findings confirm the expectation that      is indeed dominated by**
**    ****the t-pole term.**
**In the kinematic region studied here both ratios     and     present a **
**    ****very slight dependence of      . **
**The evolution of      with –t shows a rapid fall off which is consistent**
**    ****with earlier theoretical predictions, expected to approach ****1⁄4****, the square**
**    ****of the ratio of the quark charges involved.**

**   ****18                                                        Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

## HMS Cerenkov Blocking

**Using data taken with open trigger (el. & pions).**
**The TDC time window in Fpi1 is 23% larger than in Fpi2.**
**Use the Fpi2 data to fit the effective gate (same CC cut).**
**For npe<2.0 gate width – 190 ns.**
**Implies a larger correction in Fpi1 (18-20 % at 1MHz).**
**Significant impact in pi- (high rate) data.**

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

**Backup slide 1                                      Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

## Beta Cut Corrections

**Backup Slide 2                                       Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

**Random coincidences**

**Real **
**Coincidences**

**Slow pions**

**Included in the pion absorption correction**

## SOS Q3 Corrections

**Low momentum (<1.6 GeV/c) – old settings & corrections  works fine.**
**High momentum (>1.6 GeV/c) – use of new SOS optic matrix & new delta/xpfp correction.**

**Backup Slide 3                                      Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

## HMS Cerenkov Blocking

** ****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 used in Fpi1).**
** ****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**

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

**Backup Slide 4                                      Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

## HMS Q3 corrections

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

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

**Backup Slide 5                                      Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

## Deuterium Corrections & Uncertainties

| 
Source                                                                                                                      | Size of the correction
(%) | ε-uncorrelated
common to all t-bins (%) | Pt-to-Pt
ε-random
t-random (%) | Scale
ε-global
t-global (%) |
| --- | --- | --- | --- | --- |
| Beta  Cut |     3 – 3.5 |        0.5 |        - |     0.5 |
| Missing Mass  |       1 - 2 |        0.2 |       - |     1.5 |
| Cherenkov Block. |     2 - 15 |          0.5 |        - |     1.5 |
| Target Boiling |       2 - 13.5 |         0.2 |       - |     1.6 |
| Tracking    Eff. |       1 – 13.5 |        0.4 |        - |     1.0   |

**Backup Slide 6                                     Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

**Deuterium Corrections & Uncertainties**

## Uncertainties Associated with Applied Corrections

**Backup Slide 6                                     Hall C  Collaboration Meeting,  JLab,  January 31,  2009           ****                ccbutu@jlab.org     **

**Uncertainties Associated with Applied Corrections**