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Feasibility Studies for Nucleon Structure Measurements with ¯ PANDA

Meson 2014 Ermias ATOMSSA, Binsong MA On behalf of the ¯ PANDA Collaboration

Institut de Physique Nucl´ eaire d’Orsay

June 2, 2014

Ermias ATOMSSA, Binsong MA (IPNO) Meson2014, ¯ PANDA Nucleon Structure June 2, 2014 1 / 16

Outline

¯ PANDA experimental setup ¯ PANDA physics program overview Nucleon structure: Form Factors and TDAs Feasibility studies of nucleon structure measurements

Ermias ATOMSSA, Binsong MA (IPNO) Meson2014, ¯ PANDA Nucleon Structure June 2, 2014 2 / 16

FAIR: Facility for Antiproton and Ion Research

Ermias ATOMSSA, Binsong MA (IPNO) Meson2014, ¯ PANDA Nucleon Structure June 2, 2014 3 / 16

The FAIR Accelerator Complex

Main component for PANDA: High Energy Storage Ring Antiprotons: p=1.5 - 15 GeV/c High Res. Mode: L=1031/cm2/s, δp/p=10-5 High Lumi. Mode: L=2x1032/cm2/s, δp/p=10-4

Ni/Be target 107 p/s 29 GeV protons Ermias ATOMSSA, Binsong MA (IPNO) Meson2014, ¯ PANDA Nucleon Structure June 2, 2014 4 / 16

Overview of ¯ PANDA physics program

¯ PANDA : Anti-Proton ANnihilation at DArmstadt

Meson Spectroscopy D mesons, charmonia Search for exotic QCD states Glueballs, tetraquarks, hybrids, molecules Single and double hypernuclei Hadrons in nuclear matter Nucleon structure using EM probes

Physics Performance Report - arXiv:0903.3905 Ermias ATOMSSA, Binsong MA (IPNO) Meson2014, ¯ PANDA Nucleon Structure June 2, 2014 5 / 16

¯ PANDA detector

Ermias ATOMSSA, Binsong MA (IPNO) Meson2014, ¯ PANDA Nucleon Structure June 2, 2014 6 / 16

Tracking and PID for Nucleon Structure Physics Program

Large coverage (2π, 5◦ < θ <145◦) Silicon MVD and Straw Tube and GEM tracker dE/dx for PiD from STTs PbWO crystal EMCal, APDs (barrel) VPT (forward) Operation at -25◦C for optimal photon production Wide dynamic range: 3 MeV Excellent resolution: σ(E)/E ≈ 1% ⊕ 2%/

• E(GeV )

Ermias ATOMSSA, Binsong MA (IPNO) Meson2014, ¯ PANDA Nucleon Structure June 2, 2014 7 / 16

Form Factors

Parametrizations of hadronic current in the matrix element for:

Elastic scattering of a lepton off a nucleon (l±N → l±N): Spacelike (SL) real analytic functions of q2 < 0 Well constrained to high values of −q2 ≈ 30 GeV 2 Annihilation reaction of l+l− or N ¯ N pairs (N ¯ N ↔ e+e−): Timelike (TL) complex analytic functions of q2 > 4m2

p

Scarce data for TL FF (especially at high q2)

Extraction in the TL region:

Cross section of ¯ pp → e+e− σtot = πα2 6M2

p

(2τ + 1) |Geff |2 τ

• τ (τ − 1)

G 2

eff = 2τ|GM|2 + |GE |2

2τ + 1 , and τ = q2 4M2

p

Angular distribution ¯ pp → e+e− dσ d cos θCM = πα2 8M2

pτ

• τ (τ − 1)

×

• τ|GM|2

1 + cos2 θCM

• + |GE |2 sin2 θCM
• Ermias ATOMSSA, Binsong MA (IPNO)

Meson2014, ¯ PANDA Nucleon Structure June 2, 2014 8 / 16

Form Factors

Parametrizations of hadronic current in the matrix element for:

Elastic scattering of a lepton off a nucleon (l±N → l±N): Spacelike (SL) real analytic functions of q2 < 0 Well constrained to high values of −q2 ≈ 30 GeV 2 Annihilation reaction of l+l− or N ¯ N pairs (N ¯ N ↔ e+e−): Timelike (TL) complex analytic functions of q2 > 4m2

p

Scarce data for TL FF (especially at high q2)

TL FFs existing data (Phys Rev D87 (2013) 092005)

|Geff | large uncertainties above q2 ≈ 16 GeV 2 Large uncertainties in |GM/GE | No data on relative phase

Ermias ATOMSSA, Binsong MA (IPNO) Meson2014, ¯ PANDA Nucleon Structure June 2, 2014 8 / 16

Feasibility of Timelike FF Measurements

Full MC of Main background sources: ¯ pp → π+π− σ ≈ 106 × ¯ pp → e+e−

• Param. by Ong and Van de Wiele (EPJA46 (2010) 291)

¯ pp → π0π0 followed by π0 Dalitz: Relatively easy to reject using kinematical constraints Requirement on background rejection: < 0.1% Full ¯ PANDA PiD with kinematical cuts: Rejection of 109 on background Efficiency for signal above 20% (average 40%)

• M. Sudol et al. EPJA44 (2010) 373

R=|GE|/|GM|

Significant improvement with 4 months @ 2x1032/cm2/s

Ermias ATOMSSA, Binsong MA (IPNO) Meson2014, ¯ PANDA Nucleon Structure June 2, 2014 9 / 16

Transition Distribution Amplitudes

Universal non perturbative objects that appear in the factorized calculation of cross sections of some exclusive processes (Eg: ¯ pp → J/ψπ0, ¯ pp → e+e−π0 and γ∗N → πN) Short distance dominated part computed within pQCD Validity requires large scale (usually taken as virtuality of lepton pair emission) Universal non-perturbative components: TDA and DA TDA: Probe the mesonic content of nucleon wave functions Factorization description valid in two kinematical regimes Near forward kinematics t = (pπ − p ¯

N)2 ≈ 0 for π ¯

N TDA Near backward kinematics u = (pπ − pN)2 ≈ 0 for πN TDA Test universality of TDAs that occur also in γ∗N → πN and N ¯ N → l+l−π reactions

Ermias ATOMSSA, Binsong MA (IPNO) Meson2014, ¯ PANDA Nucleon Structure June 2, 2014 10 / 16

Feasibility of ¯ pp → J/ψπ0 in ¯ PANDA (Signal)

Background in charmonium spectroscopy studies (c¯ c resonances that decay into J/ψπ) Cross section calculation from Pire et.al (Phys. Lett. B. 724 99-107): σ ≈ 2x100 pb Cross section peaked around θ∗

π0 = 0◦ for ¯

pπ TDA and at θ∗

π0 = 180◦ for pπ TDA

Compared to e+e−: Pros: mass cut for background rejection, Cons: fixed Q2

Forward π emission Expected counting rates for PANDA

ϴπ

*=90°

ϴπ

*=0°

4 months @ 2x1032/cm2/s Ntot = 13000 Ermias ATOMSSA, Binsong MA (IPNO) Meson2014, ¯ PANDA Nucleon Structure June 2, 2014 11 / 16

Feasibility of ¯ pp → J/ψπ0 in ¯ PANDA (Background)

Main background: π+π−π0 σ ≈ 400 µb Two string fragmentation models DPM and FTF give similar π0 CM polar angle distribution peaked near θ∗

π0 = 0◦ and θ∗ π0 = 180◦ like signal (simulations by A. Galoyan)

π+π− invariant mass distribution, with substantial difference between models High precision measurement by ¯ PANDA will help discriminate between models 2σ mass cut for J/ψ rejects ≈90% of π+π−π0 background (before PID) Better momentum resolution = ⇒ better rejection

π *

θ 20 40 60 80 100 120 140 160 180

π *

θ dN/d 50 100 150 200 250 300 350

in DPM

π *

θ in FTF

π *

θ

2

)=5.513 GeV, s=12.25 GeV p @ mom( π

• π

+

π → p p

[GeV/c^2]

• π

+

π inv

M 0.5 1 1.5 2 2.5 3 3.5 4

inv

dN/dM 50 100 150 200 250

in DPM

• π

+

π inv

M in FTF

• π

+

π inv

M ) ψ M cut (J/ σ 2

2

)=5.513 GeV, s=12.25 GeV p @ mom( π

• π

+

π → p p

Ermias ATOMSSA, Binsong MA (IPNO) Meson2014, ¯ PANDA Nucleon Structure June 2, 2014 12 / 16

Electron momentum reconstruction in ¯ PANDA

Resolution loss due to Bremsstrahlung

Tracking points: MVD (4 to 6) and STT (up to 24) 80% of X/X0 inside tracking system from MVD Significant Bremsstrahlung photon emission (Almost collinear with photon direction) Helix prefit used as input for Kalman filter Kalman filter assumes Gaussian errors = ⇒ External radiation not taken into account

E loss through Bremsstrahlung emission e-, pT=1 GeV (barrel region) Ermias ATOMSSA, Binsong MA (IPNO) Meson2014, ¯ PANDA Nucleon Structure June 2, 2014 13 / 16

Event by event correction of Bremsstrahlung

Exploit spatial correlation between γBrem and e+/e− clusters Combined with low threshold EMCal, possible to Find Bremsstrahlung photon candidates track by track Correct each track’s momentum by adding back total energy from all γBrem Approach works: clear improvement in electron momentum resolution

• 0.2
• 0.1

0.1 0.2

Counts

1000 2000 3000 4000

Barrel

=1 GeV/c

t

electron P

MC

• P)/P

MC

(P

• 0.2
• 0.1

0.1 0.2

Counts

1000 2000 3000

Forward Endcap

with correction no correction

• 0.2
• 0.1

0.1 0.2

Counts

1000 2000 3000

Barrel

=2 GeV/c

t

electron P

MC

• P)/P

MC

(P

• 0.2
• 0.1

0.1 0.2

Counts

500 1000 1500 2000

Forward Endcap

with correction no correction

Ermias ATOMSSA, Binsong MA (IPNO) Meson2014, ¯ PANDA Nucleon Structure June 2, 2014 14 / 16

Improvement on nucleon structure observables

60% gain in efficiency with 2σ cut for ¯ pp → J/ψπ0 70% gain in efficiency with minimum mass cut of √s − mπ0 for ¯ pp → e+e−

Ermias ATOMSSA, Binsong MA (IPNO) Meson2014, ¯ PANDA Nucleon Structure June 2, 2014 15 / 16

Summary

¯ PANDA will open exciting opportunities for hadronic physics Form factor measurements in the TL region over an extended range of q2 Excellent test bed for the universality TDAs Correcting momentum reconstruction for Bremsstrahlung yields quantitaive improvements

Ermias ATOMSSA, Binsong MA (IPNO) Meson2014, ¯ PANDA Nucleon Structure June 2, 2014 16 / 16