Research Center Dresden-Rossendorf Technical University Dresden Virtual Bremsstrahlung* B. Kämpfer Research Center Dresden-Rossendorf Technical University Dresden 1. goal 2004: tagging 2. goal 2008: shoulder in np at M ~ 450 MeV 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 HADES Workshop for Advanced Detectors Rossendorf 2001 2008 Zschocke 2002

DLS Puzzle Solved by Bremsstrahlung? (known since 111 years) Barz et al. Bratkovskaya, Cassing C(1 AGeV) + C C(1 AGeV) + C C(1 AGeV) + C M [GeV] 1997: bremsstrahlung ... contribution was found to be small 2007: DLS puzzle... may be solved when incorporating a stronger bremsstr. contribution Aichelin et al. 2008: w/ bremsstrahlung Santini et al. 2008: w/o bremsstrahlung no DLS puzzle at all?

S N e+ e- 36 + ISI + FSI Kroll-Ruderman isovector (KK) or isoscalar (Shyam-Mosel `08) Aichelin et al., Rossendorf BUU

Di-Electron Spectrum Pure Bremsstrahlung require seagulls for q.J = 0 no information on y, pT left N M Pure Bremsstrahlung require seagulls for N M

Exchange of Neutral Mesons in pp + q.J = 0 to be done: check charge an. mag. mom. off-shell N: 8 FF‘s or loop corrections  VMD KK:

Exchange of Charged Mesons in np + + q.J = 0 w/o FF‘s n p to fulfill WT id. only for ps coupling sufficient not unique N M derivative couplings: seagull from minimal coupling

parameters (similar to Shyam-Mosel 2003 [2]) 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:

our choice -1: common choice error bars  range of (compatible with helicity amplitiudes, e.m.decay width, pion-photoproduction)

with rho, pion exchange and seagull ... pure bremsstrahlung --- Delta contribution coherent sum

(i) (ii) (i)

results: see below

planar kinematics: M purely real or purely imaginary our choice

once more: on-mass vs. off-mass shell decays

all together at kin. limit: FSI matters -.. 1440 -. 1535 ... brems - total (w/ Delta) at kin. limit: FSI matters

solid: total broken: brems

dashed: incoherent sum 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

Why should it fail for bremsstrahlung? 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 GeV 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 GeV: „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