Моделирование
электромагнитного форм-фактора
протона во времени-подобной
области в среде PandaRoot
Д. Морозов
ИФВЭ (Протвино)
Outline
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Introduction
Experimental setup
FSC PandaRoot Development
Generators
What is also needed
Near term plans
Conclusions
June 22 2011
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Introduction
• The electromagnetic probe is an excellent tool
to investigate the structure of the nucleon
• GE and GM of the proton parametrize the
hadronic current in the ME for e-p → e-p and
in its crossed process p+p- → e+e-
June 22 2011
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Introduction
• Matrix element for elastic electron proton
scattering in the frame of one-photon exchange:
• k1(p1), k2(p2) - four-momenta of the initial and
final electron (nucleon)
• u(k) ,u(p) – spinors
• q = k 1 - k2 , q 2 < 0
• Annihilation - k2(p2) change sign and q2 = s
June 22 2011
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Introduction
• Annihilation process - access positive q2 (time-like) from q2 = 4m2p
• Unitarity of ME:
– space-like FFs are real functions of q2
– time-like - complex functions
• In the Breit frame, space-like FFs have concrete interpretations, they
are the Fourier transforms of the spatial charge (GE) and the
magnetization distribution (GM) of the proton
– slope at q2 = 0 gives the charge and magnetization radius of the
proton
• In time-like region, FFs reflect the frequency spectrum of the
electromagnetic response of the nucleon
• two complementary aspects of nucleon structure can be studied
• complete description of the electromagnetic FF over full q2 range.
June 22 2011
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Introduction
• Estimation: PANDA will be able to get |GE| and |GM| in time-like
domain from ~5 (GeV/c)2 up to ~14 (GeV/c)2 by measuring angular
distribution of p+p- → e+e-. GM up to 22 (GeV/c)2 by measuring total
cross section
• Unpolorized diff. cross section:
where τ = q2/4m2p
• independent measurements of |GE| and |GM|
• Only BABAR and LEAR had enough statistics to extract |GE| and
|GM| independently, but accuracy on R= |GE|/|GM| is ~ 50%.
• PANDA aim is few % in 107 sec
June 22 2011
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FF in space-like region (JLab)
JLAB arXiv:1102.2463 [nucl-ex]
June 22 2011
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Introduction
• The challenge is to suppress the huge background from hadronic
channels. It’s ~106 times higher in cross section then signal e+e– π+π-, K+K• EMC is ~20X0 ~ λ0: 30% of hadronic interactions, charge exchange is the most
harmful
• can produce deposition as e with same momentum
– π0π0
• one(two) Dalitz decay e+e-γ with 1% branching still big enough
• direct decay then conversion in material
• e+e-X, where X – mesons, lepton pairs, photons
– direct e+e-X
– produced γ materializes in detector material
• a good e/pion separation is mandatory up to ~15 GeV/c
• PID from each detector and kinematical constrained have to be
exploited
June 22 2011
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Experimental setup
• Pipe
• Central spectrometer
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Solenoid Magnet
TPC (STT) → PID, tracking
MVD → vertex, tracking
EMC: Barrel, Endcaps → PID
TOF → c PID (0.3 – 1 GeV)
MDT → PID muon
GEM → tracking
DIRC → charged PID
June 22 2011
• Forward spectrometer
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Dipole Magnet
EMC: FSC → PID
Forward DIRC(DSK)→ c PID
DCH → tracking
FTOF → charged PID
FTS: straw tubes→tracking
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FSC PandaRoot Development
• Geometry
– emc_module5_fsc.root in 16 and 17 GeometryVersions
– 1496 modules (54x28 with 4x4 spacing)
– cell 5.5 x 5.5 x 67.5 cm3 consists of 380 lead (0.275 mm ) scintillator
(1.5 mm ) layers
– wrapped by tyvek and black paper
– 6x6 optical fibers 1.4 mm thick docked to PMT photocathode by a
single bunch
• Macro to create geometry
• PndEmc class modified to load geometry
• PndEmcStructure class modified to transform the cells coordinates
to the global system of geometrical indexes (for fast searching and
cluster formation)
• PndEmcHit and PndEmcHitProducer updated to collect the hits
from transport code at VMC level
June 22 2011
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FSC PandaRoot Development
• Digitization model
– Hit → electronics signal shape (Waveform):
PndEmcHitsToWaveform
• Signal shape: analytic function of RC-CR circuit with
– Tint = 5 nsec — integration time,
– Tdiff = 20 nsec — differential time and
– Tsig = 15 nsec — time of raising the signal in shashlyk module
• For each hit discrete signal shape simulating SADC was built up
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Nsamples = 20 — the number of SADC counts
SampleRate = 180 Mhz — ADC rate
NPhotonsPerMev = 21 — N of photons per 1 MeV of deposited energy
ENF = 1.3 – excess noise factor for PMT
• Gaussian incoherent electronics noise with 3 MeV width added to each
ADC bin
• the signal was converted to the integer value in each bin
– Waveform → ADC digitized signal in energy units:
PndEmcWaveformToDigi
• maximum was searched inside each digitized signal shape: magnitude →
value, position→ time of signal arrival
• Absolute value normalization by 1 GeV delta function signal as input
• Cells with Edigi > EdigiThreshold = 8 MeV are stored for the following analysis
June 22 2011
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FSC PandaRoot Development
• Energy resolution for Digi hits
– σE/E = (3.0 ± 0.1)%/√E + (0.6 ± 0.1)%
• Compare to test beam
– σE/E = (2.8 ± 0.2)%/√E + (1.3 ± 0.1)%
• Utilize the algorithms for cluster finding and bumps splitting already
implemented in EMC code
• Absent:
– e PID → shower shape analysis (it’s different compare to PWO)
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E1/E9 (E1/E25)
lateral moment of the cluster
a set of zernike moments (radial and angular dependent polynomials)
parameters are partially correlated
– Multilayer Perceptron (MLP) may be applied (for PWO as well). The
training of the MLP requires big set of single tracks for e, μ, π, K and p
– Leakage correction for FSC
June 22 2011
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MLP output example
PWO in BABAR framework
June 22 2011
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Generators
• Signal channel – exist in PandaRoot
• Background – absent but in preparation
– Extrapolation of experimental data
June 22 2011
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What is also needed
• Forward tracking?
• CPU/Storage
– About 5∙108 events need to be simulated
– Requires at least 30 TB of disk space
– Now: local cluster (400 CPU, no space) is not
sufficient. PANDA Grid can be used?
– In a ~1 year: the hope is to have ~50 TB and cluster
will be helpful for PANDA
• IHEP cluster can be incorporated to PANDA Grid
June 22 2011
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Near term plans
• Finish FSC reco code
– Shower shape parameters for shashlyk modules
– MLP training?
– Leakage
• Generator issues
• Production of MC data
• Background suppression
– PID cuts
– Kinematical constrains
• Efficiencies
June 22 2011
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Conclusions
• FSC in PandaRoot is implemented
– Some tuning and e PID required
• Time like form-factor could be interesting but
challenging
– High hadronic background
– Huge amount of events → storage
• IHEP might be a part of Panda Grid
June 22 2011
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