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 Meson2014, ¯ Ermias ATOMSSA, Binsong MA (IPNO) 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 Meson2014, ¯ Ermias ATOMSSA, Binsong MA (IPNO) PANDA Nucleon Structure June 2, 2014 2 / 16
FAIR: Facility for Antiproton and Ion Research Meson2014, ¯ Ermias ATOMSSA, Binsong MA (IPNO) PANDA Nucleon Structure June 2, 2014 3 / 16
The FAIR Accelerator Complex 29 GeV protons Main component for PANDA: Ni/Be target 107 p/s High Energy Storage Ring Antiprotons: p=1.5 - 15 GeV/c High Res. Mode: L=10 31 /cm 2 /s, δ p/p=10 -5 High Lumi. Mode: L=2x10 32 /cm 2 /s, δ p/p=10 -4 Meson2014, ¯ Ermias ATOMSSA, Binsong MA (IPNO) 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 Meson2014, ¯ Ermias ATOMSSA, Binsong MA (IPNO) PANDA Nucleon Structure June 2, 2014 5 / 16
¯ PANDA detector Meson2014, ¯ Ermias ATOMSSA, Binsong MA (IPNO) PANDA Nucleon Structure June 2, 2014 6 / 16
Tracking and PID for Nucleon Structure Physics Program PbWO crystal EMCal, APDs (barrel) VPT (forward) Large coverage (2 π , 5 ◦ < θ < 145 ◦ ) Operation at -25 ◦ C for optimal photon production Silicon MVD and Straw Tube and GEM tracker Wide dynamic range: � 3 MeV dE/dx for PiD from STTs � Excellent resolution: σ ( E ) / E ≈ 1% ⊕ 2% / E ( GeV ) Meson2014, ¯ Ermias ATOMSSA, Binsong MA (IPNO) 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 q 2 < 0 Well constrained to high values of − q 2 ≈ 30 GeV 2 Annihilation reaction of l + l − or N ¯ N pairs ( N ¯ N ↔ e + e − ): Timelike (TL) complex analytic functions of q 2 > 4 m 2 p Scarce data for TL FF (especially at high q 2 ) Extraction in the TL region: pp → e + e − pp → e + e − Cross section of ¯ Angular distribution ¯ σ tot = πα 2 (2 τ + 1) | G eff | 2 πα 2 d σ = × 6 M 2 � � τ τ ( τ − 1) d cos θ CM 8 M 2 p τ τ ( τ − 1) p eff = 2 τ | G M | 2 + | G E | 2 1 + cos 2 θ CM + | G E | 2 sin 2 θ CM q 2 τ | G M | 2 � � � � G 2 , and τ = 4 M 2 2 τ + 1 p Meson2014, ¯ Ermias ATOMSSA, Binsong MA (IPNO) 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 q 2 < 0 Well constrained to high values of − q 2 ≈ 30 GeV 2 Annihilation reaction of l + l − or N ¯ N pairs ( N ¯ N ↔ e + e − ): Timelike (TL) complex analytic functions of q 2 > 4 m 2 p Scarce data for TL FF (especially at high q 2 ) TL FFs existing data (Phys Rev D87 (2013) 092005) | G eff | large uncertainties above q 2 ≈ 16 GeV 2 Large uncertainties in | G M / G E | No data on relative phase Meson2014, ¯ Ermias ATOMSSA, Binsong MA (IPNO) PANDA Nucleon Structure June 2, 2014 8 / 16
Feasibility of Timelike FF Measurements Full MC of Main background sources: pp → π + π − σ ≈ 10 6 × ¯ pp → e + e − ¯ Param. by Ong and Van de Wiele (EPJA46 (2010) 291) pp → π 0 π 0 followed by π 0 Dalitz: Relatively easy to ¯ reject using kinematical constraints Requirement on background rejection: < 0 . 1% Full ¯ PANDA PiD with kinematical cuts: Rejection of 10 9 on background Efficiency for signal above 20% (average 40%) M. Sudol et al. EPJA44 (2010) 373 R=|GE|/|GM| Significant improvement with 4 months @ 2 x 10 32 / cm 2 / s Meson2014, ¯ Ermias ATOMSSA, Binsong MA (IPNO) 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 pp → e + e − π 0 and γ ∗ N → π N ) pp → J /ψπ 0 , ¯ some exclusive processes (Eg: ¯ 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 N ) 2 ≈ 0 for π ¯ Near forward kinematics t = ( p π − p ¯ N TDA Near backward kinematics u = ( p π − p N ) 2 ≈ 0 for π N TDA Test universality of TDAs that occur also in γ ∗ N → π N and N ¯ N → l + l − π reactions Meson2014, ¯ Ermias ATOMSSA, Binsong MA (IPNO) PANDA Nucleon Structure June 2, 2014 10 / 16
pp → J /ψπ 0 in ¯ Feasibility of ¯ 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 π 0 = 0 ◦ for ¯ π 0 = 180 ◦ for p π TDA Cross section peaked around θ ∗ p π TDA and at θ ∗ Compared to e + e − : Pros: mass cut for background rejection, Cons: fixed Q 2 Expected counting rates for PANDA Forward π emission ϴ π * =0° * =90° ϴ π 4 months @ 2x10 32 /cm 2 /s N tot = 13000 Meson2014, ¯ Ermias ATOMSSA, Binsong MA (IPNO) PANDA Nucleon Structure June 2, 2014 11 / 16
pp → J /ψπ 0 in ¯ Feasibility of ¯ PANDA (Background) Main background: π + π − π 0 σ ≈ 400 µ b Two string fragmentation models DPM and FTF give similar π 0 CM polar angle π 0 = 0 ◦ and θ ∗ π 0 = 180 ◦ like signal (simulations by A. Galoyan) distribution peaked near θ ∗ π + π − invariant mass distribution, with substantial difference between models High precision measurement by ¯ PANDA will help discriminate between models 2 σ mass cut for J /ψ rejects ≈ 90% of π + π − π 0 background (before PID) Better momentum resolution = ⇒ better rejection → π π π + - 0 2 + - 0 2 p p @ mom( p )=5.513 GeV, s=12.25 GeV p p → π π π @ mom( p )=5.513 GeV, s=12.25 GeV 0 inv π π + - * π θ M in DPM * dN/dM dN/d 350 250 inv θ in DPM 0 π + π - π M in FTF inv 300 σ ψ * 2 M cut (J/ ) 200 θ in FTF 0 π 250 150 200 150 100 100 50 50 0 0 20 40 60 80 100 120 140 160 180 0 0.5 1 1.5 2 2.5 3 3.5 4 * π π - + M [GeV/c^2] θ 0 inv π Meson2014, ¯ Ermias ATOMSSA, Binsong MA (IPNO) 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/X 0 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) Meson2014, ¯ Ermias ATOMSSA, Binsong MA (IPNO) PANDA Nucleon Structure June 2, 2014 13 / 16
Event by event correction of Bremsstrahlung Exploit spatial correlation between γ Brem 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 γ Brem Approach works: clear improvement in electron momentum resolution Counts Counts with correction 3000 4000 with correction electron P =2 GeV/c electron P =1 GeV/c no correction t t no correction 3000 2000 2000 Barrel 1000 Barrel 1000 0 0 Counts -0.2 -0.1 0 0.1 0.2 Counts -0.2 -0.1 0 0.1 0.2 3000 2000 Forward Endcap 1500 2000 Forward Endcap 1000 1000 500 0 0 -0.2 -0.1 0 0.1 0.2 -0.2 -0.1 0 0.1 0.2 (P -P)/P (P -P)/P MC MC MC MC Meson2014, ¯ Ermias ATOMSSA, Binsong MA (IPNO) PANDA Nucleon Structure June 2, 2014 14 / 16
Improvement on nucleon structure observables pp → J /ψπ 0 60% gain in efficiency with 2 σ cut for ¯ 70% gain in efficiency with minimum mass cut of √ s − m π 0 for ¯ pp → e + e − Meson2014, ¯ Ermias ATOMSSA, Binsong MA (IPNO) 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 q 2 Excellent test bed for the universality TDAs Correcting momentum reconstruction for Bremsstrahlung yields quantitaive improvements Meson2014, ¯ Ermias ATOMSSA, Binsong MA (IPNO) PANDA Nucleon Structure June 2, 2014 16 / 16
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