Combination of H1 and ZEUS DIS ep inclusive cross sections

1
Combination of H1 and ZEUS DIS ep inclusive
cross sections
E. Tassi - Zeus Monday mtg August,6 2007

H1-ZEUS working group A. Cooper-Sarkar,
C.Gwenlan, K. Nagano, J. Ferrando, Y. Ri, S. U.
Noor, A.F. Zarnecky, E.T,J. Feltesse, S. Glazov,
M. Klein, V. Shekelian, Z. Zhang, E. Rizvi, U.
Martyn

• Outline
• Introduction
• Combination method
• Results
• Checks

http//www-zeus.desy.de/tassi/ZEUS_ONLY/combineLP
07/main.html
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Electroweak Neutral currents at
HERAH1prelim-06-142/ZEUS-prel-06-022

• Interference structure function xF3(?Z)

- First combined H1-ZEUS SF result - Improved
xF3(?Z) determination - Simple weighted average
using the total uncertainties (w/o
correlations)
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Electroweak Neutral currents at
HERAH1prelim-06-142/ZEUS-prel-06-022

• Parity violating cross section
• asymmetries

- again simple data averaging method
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Aim of the analysis
Go a step forward combine the HERA I NC and CC
ep inclusive cross sections including full
correlations. - Simplicity ? provide a single
set of HERA inclusive cross sections
measurements blessed by the
experiments - Cross Calibration ? Reduction of
syst. unc. as a result of averaging
(S. Glazov - DIS05 and
HERA-LHC WS) - Cross Check ? also as a result
of the studies in this WG, the 96-97
H1 low-Q2 data had to be scaled
up by 3.4 (official) Analysis focus on the
combination method and the treatment of
the systematic uncert. in data combination (no
tables will be provided). Would like to present
these results to LP07 ? Preliminary Status

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Main technical issues addressed
- consistency of input data ? generally good
(but see previous slide) - Treatment of
systematic errors additive or multiplicative -
x-Q2 common grid ? H1 x and ZEUS Q2
(basically) - assumptions on correlations
between data sets and H1 and ZEUS (mostly
uncorrelated but theory links QED and ?p) -
treatment of 820 GeV and 920 GeV (see later) -
some of the average assumptions cause extra
uncertainties at the few level (with few
exceptions) added to the averaged data
points

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Cross section averaging procedure and
definition(s)
Averaging procedure based on the Least Squares
method
Data model (assume first only additive
systematics)
Likelihood
With
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Minimization
From the
minimization one gets for the averaged (true)
cross sections
Remember that ri Norm(0,1)
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Multiplicative vs additive syst. uncert.
Imagine that in addition to the additive syst. ß
we have a multiplicative systematic (e.g. lumi
norm. unc.) a1e
In order not to spoil the linearity of the
approach an iterative procedure is adopted where
initially the mult. syst. is treated as the other
ones but in each iteration the (ßa) and s are
rescaled by µi(n)/mi . Few iterations are
sufficient for the fit to converge. The
program remains extremely fast while avoiding
possible biases.
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Data sets and treatment
- All HERA I cross sections NC and CC ep -
1.5 lt Q2 lt30000 GeV2 ? 230 pb-1 - averages
cross sections determined in a simultaneous fit
of these data. - prior to combination the H1
and ZEUS measurements are transformed to a
common grid of x-Q2 points - treatment of
the 820 GeV and 920 GeV data sets In this
analysis and just for illustration have decide to
move all data points to 920 GeV In the future
may/will not correct points at high-y (ygt0.35)
in order to reduce model dependence (FL)

for CC, additive for NC (see draft)
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X-Q2 common grid

The grid points are chosen such that -
interpolation corrections are small - no two
separate measurements interpolate to common
grid point - 38x25 points ? Q2 ZEUS ? x
H1 (4 points per decade) Detailed list in
the analysis web page
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Results

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Fit results and pulls

NC e-p
NC ep
µ0.01 s0.7
µ-0.09 s1.4
CC ep
CC e-p
µ0.1 s0.8
µ-0.05 s1.7
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Fit Results Syst. shifts
20 zd1_e_eff 0.4572 0.7486 21
zd2_e_theta_a 0.1576 0.6797 22
zd3_e_theta_b -0.3849 0.7746 23
zd4_e_escale 0.8342 0.5079 24
zd5_had1 0.3157 0.5906 25
zd6_had2 0.0581 0.6496 26
zd7_had3 -0.7649 0.7413 27
zd8_had_flow 0.6947 0.6619 28 zd9_bg
-0.2358 0.4175 29
zd10_had_flow_b 0.0730 0.2375 30 zd11
-0.4055 0.6174 31
z1nce-_e_scale 0.1777 0.9383 32
z2nce-_bg -0.4073 0.9178 33
z3nce-_eff1 -0.1819 0.9120 34
z4nce-_eff2 0.5536 0.5544 35
z5nce-_vtx -0.5180 0.9262 36
z6nce- 0.1218 0.4138 37
z1cce- 0.0296 0.8350 38
z2cce- -0.0152 0.8680 39
zlumi2_zccem 0.0708 0.7778 40 zd5nc00
0.1386 0.9843 41 zd7nc00
0.1566 0.2093 42 zd8nc00
0.5163 0.9280 43 zluminc00
-0.4854 0.3837
Name Syst
Unc. 1 zlumi1_zncepl 0.0554
0.5887 2 h2_Ee_Spacal 0.6568
0.3314 3 h3_Ee_Lar_00 -0.3645
0.4448 4 h4_ThetaE_spacal -0.7437
0.6556 5 h5_ThetaE_94-97 -0.0655
0.7799 6 h6_ThetaE_00 -0.4051
0.5290 7 h7_H_Scale_Spacal 0.4592
0.4755 8 h8_H_Scale_Lar -0.9265
0.5351 9 h9_Noise_Hcal -0.5037
0.3645 10 h10_GP_BG_Spacal -0.5141
0.8179 11 h11_GP_BG_LAr 0.9073
0.8510 12 h12_BG_CC_94-97 0.3389
0.7871 13 h13_BG_CC_98-00 -0.7856
0.8846 14 h14_ChargeAsym 0.0262
0.9993 15 hllumi1_SPACAL_bulk 1.5543
0.5588 16 hllumi2_SPACAL_MB 0.8375
0.5984 17 h1lumi3_LAr_94-97_ep -1.0706
0.6211 18 h1lumi4_LAr_e-p -0.0708
0.7778 19 h1lumi5_LAr_2000 -0.7462
0.5982

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CC e-p

Preliminary request
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CC e-p

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CC ep

Preliminary request
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CC ep

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NC e-p

Preliminary request
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NC ep

Preliminary request
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NC ep

Preliminary request
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NC ep two low-Q2 bins

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NC ep two high-Q2 bins

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NC ep

Preliminary request
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NC ep

Preliminary request
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Systematic Checks

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CME corrections FL 0
(Default/NoFL -1)x1000
To test model (FL) dependence at high-y we have
repeated the combination (with FL0) Almost
negligible (but up to 4-5 at high-y)
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Correlation between Experiments
(Uncorrelated/Largest change -1)x1000
To quantify them is a highly non trivial
problem Tried to evaluate them by
identifying a list of possible common sources
(?p back, lumi,CAL E scales, ?e, etc), assume
100 correlation, and compare the new averages
with uncorrelated ones Mostly negligible (but
up to 2-3 in particular regions of the phase
space)
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Multiplicative vs Additive
(Uncorrelated/Largest change -1)x1000
Comparison of the averaged cross sections
obtained assuming all syst unc. as multiplicative
in nature w.r.t. to a combination were only
normalizations were treated ad
multiplicative Mostly negligible (but
strangely large in a few high-x high-Q2
points)
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Summary

• Thinking the results are interesting we would
• like, if approved by collaborations, to
  present the results to LP07 ? feedback wider
  circle
• Draft being completed
• E. Rizvi will present these results to H1 tomorrow

For additional information visit analysis web
page http//www-zeus.desy.de/tassi/ZEUS_ONLY/com
bineLP07/main.html
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Backup Slides

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Minimization
From the
minimization one gets the following system
That can be re-written in matrix form
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Minimization
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Fitted cross sects and r parameters
Basic Idea
We can now determine the parameters
Once the are known we can easily determine
the
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X 0.02
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(No Transcript)
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Lumi unc.
Norms Mult.
All Add.
Use of the correct underlying model for each
error contribution is important ? Improper
treatment may lead to strong biases (G.
Dagostini (CELLO 87) Peelles Pertinent Puzzle
(R. Peelle 87))
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15 hllumi1_SPACAL_bulk 1.5377
0.5628 16 hllumi2_SPACAL_MB
0.8464 0.6001 17 h1lumi3_LAr_94-97_ep
-1.0869 0.6227 18 h1lumi4_LAr_e-p
-0.0808 0.7780 19
h1lumi5_LAr_2000 -0.7334
0.6002 1 zlumi1_zncepl
0.0277 0.5919 39 zlumi2_zccem
0.0809 0.7779 43
zluminc00
-0.5196 0.3859 30 zd11
-0.3856 0.6204
15 hllumi1_SPACAL_bulk 0.4054
0.5700 16 hllumi2_SPACAL_MB -0.0838
0.6035 17 h1lumi3_LAr_94-97_ep -2.3520
0.6139 18 h1lumi4_LAr_e-p
-0.6815 0.7738 19 h1lumi5_LAr_2000
-2.1614 0.5915 1 zlumi1_zncepl
-0.9276 0.5901 39
zlumi2_zccem -0.7298
0.7740 43 zluminc00
-1.5020 0.3798 30 zd11
-0.1974 0.6159