Virtual Bremsstrahlung B Kmpfer Research Center DresdenRossendorf Technical
Virtual Bremsstrahlung* B. Kämpfer Research Center Dresden-Rossendorf Technical University Dresden 1. goal 2004: tagging 2. goal 2008: shoulder in np at M ~ 450 Me. V Price for 1. : rough treatment of pp (not adjusted to DLS but „oriented“ at Shyam-Mosel, PRC 2003) Result for 2. : no significant shoulder in np if pp stays shoulder-free *) work by L. P. Kaptari
Motivation Workshop for Advanced Detectors 2001 Rossendorf HADES 2008 Zschocke 2002
DLS Puzzle Solved by Bremsstrahlung? (known since 111 years) Barz et al. C(1 AGe. V) + C Bratkovskaya, Cassing C(1 AGe. V) + C M [Ge. V] Aichelin et al. 2008: w/ bremsstrahlung Santini et al. 2008: w/o bremsstrahlung 1997: bremsstrahlung. . . contribution was found to be small 2007: DLS puzzle. . . may be solved when incorporating a stronger bremsstr. contribution no DLS puzzle at all?
N N e+ S N e. N 36 + ISI + FSI isovector (KK) or isoscalar (Shyam-Mosel `08) Aichelin et al. , Rossendorf BUU Kroll-Ruderman
Di-Electron Spectrum no information on y, p. T left M N q. J = 0 N Pure Bremsstrahlung require seagulls for M N N
Exchange of Neutral Mesons in pp off-shell N: q. J = 0 charge an. mag. mom. 8 FF‘s KK: to be done: check + or loop corrections VMD
Exchange of Charged Mesons in np p n n p + + q. J = 0 w/o FF‘s to fulfill WT id. - only for ps coupling sufficient - not unique derivative couplings: seagull N N M from minimal coupling
nucleons only parameters (similar to Shyam-Mosel 2003 [2]) differ slightly from KK 2006 p. 348: „our effective parameters have been fixed in such a way as to reproduce reasonably well the results of the study [2]. . . Our OBE parameters (listed in Table 1) and their energy dependence have been taken as in Ref. [2]. “ from exchange of charged mesons + seagulls real photons:
Gauge Invariance Restoration is Not Unique K + N Usov & Scholten: fixed parameters +. . .
Baryon Resonances N M Pascalutsa PRD 1998:
-1: common choice error bars range of our choice (compatible with helicity amplitiudes, e. m. decay width, pion-photoproduction)
with rho, pion exchange and seagull . . . pure bremsstrahlung --- Delta contribution coherent sum
results: see below
planar kinematics: M purely real or purely imaginary our choice
once more: on-mass vs. off-mass shell decays
all together -. . 1440 -. 1535. . . brems - total (w/ Delta) at kin. limit: FSI matters
solid: total broken: brems
interference matters HADES measured ratio solid: coherent sum dashed: incoherent sum disappointing/interesting: neither pp nor np HADES data are described to be done: pion production within same framework
OBE Approach is Fine for Mesons Why should it fail for bremsstrahlung?
check by HADES possible x = 0. 45 x = 0. 50 x = 0. 55
Spectator Distribution 1. 25 1. 90 3. 50 HADES: data for pp and pn for 1. 25 Ge. V are at our disposal
factorization works: VDM seems not to help sub-threshold production:
Transition Form Factors = hadronic matrix elements
Summary - bremsstrahlung: tree level diagrams + + FF‘s + gauge inv. + FSI - HADES puzzle: approach seems to fail in detail for pp, Dp(np) at 1. 25 Ge. V: „an understanding of the elementary channels remains challenging“ at least for KK - why we fail for pp? check pion production - check various gauge inv. restoration procedures - unitary approach is needed
- Slides: 28