Update on DVCS what can we do if 1 fb -1 ? S. Fazio EIC Task Force meeting BNL – May 2nd, 2013

2 May 2013S.Fazio - EIC Task force meeting, BNL2 From the EIC white paper ~ 1 year of data taking Simulation: y>0.01 (detector acceptance) Detector smearing The |t|-binning is (3*reso) Exponential |t|-dependence exp(B*|t|) B-slope=5.6 compatible with H1 data, to facilitate Dieter’s global fitting 5% systematic uncertainties

Submitted paper on DVCS at EIC 2 May 20133S.Fazio - EIC Task force meeting, BNL arXiv: v1

2 May 2013S.Fazio - EIC Task force meeting, BNL4 Let us consider an eRHIC with 5x100 GeV 2 and 1fb -1 and lets see what changes for the error bands shown in the white paper Statistical errors rescaled them from 10 fb -1 to 1 fb -1. 5% systematic uncertainty and added in quadrature to the rescaled statistical uncertainty ROOT used to do an exponential fit: A*exp(B*t) and calculate the values and errors of the normalization A and the slope B plus the correlation coefficient c. The fitted values (A, dA, B, dB, c) are used as an input to the Markus’ GNU-plot code which computes errors using method of eigenvector distributions. The output of the GNU-plot code is used as input to a Markus' FORTRAN code which computes the error bands for the cross section and the partonic distribution using the Fourier Bessel function integral and gives tables in text format. This code, in calculating the error bars, considers the |t| range achievable experimentally and extrapolates beyond. the text output from the Bessel code can be plotted using ROOT (my thanks to Tom for the useful PYTON example-script which easily does it).

2 May 2013S.Fazio - EIC Task force meeting, BNL5 First exercise: reproducing the white paper 20x250 figures using input cards from Markus White paper Beam energy: 20x250 GeV 2 10 < Q 2 < GeV x10 -3 < x < 6.31x10 -3 the white paper is reproduced! went trough the whole exercise as in the previous slide...

2 May 2013S.Fazio - EIC Task force meeting, BNL6 5x100 GeV 2 We want to study the impact of having only a low energy – low luminosity eRHIC at hand Beam energy: 5x100 GeV 2 10 < Q 2 < GeV < x < fb -1 1 fb -1 if eRHIC collects 10 times less lumi: with 1 fb -1 (10 years of data taking at ?) only the |t|<0.85 GeV 2 can be measured

2 May 2013S.Fazio - EIC Task force meeting, BNL7 Error bands TO BE COMPARED WITH 5x100 1 fb -1 5x100 1 fb -1 ~ 10 y of data taking ~ 1 y of data taking

2 May 2013S.Fazio - EIC Task force meeting, BNL8 Exponential vs dipole What if d  /dt follows a dipole dependence rather than en exponential? Can we discriminate with 1 fb -1 ? Lets try to fit a dipole parameterization and superimpose it to the data generated according to an exponential A*exp(B*|t|) We can hardly discriminate a dipole dependence with 1 fb -1. We must keep in mind that only error bars are rescaled -> play the same game simulating a small sample with 1 fb -1 to reproduce fluctuations actual fluctuations no rescaling

2 May 2013S.Fazio - EIC Task force meeting, BNL9  Can we measure the asymmetries and still preserve some discriminatory power among different theoretical assumptions with 1 fb -1 ? OUTLOOK I will ask Dieter for the code (or the parameterization of the theory curves) for A UT at 5x100 and rescale the errors for the expected uncertainty with 1 fb fb -1 20x250 UPDATE by next week...