DIS 2011, Newport News, VA USA
Inderpal Singh
Panjab Univ./ MPI, Munich
On behalf of ZEUS collaboration
DIS cross-section can be described by :-Q²: Four momentum transfer ( probing power)x : Bjorken Scaling variable (momentumfraction of struck quark)y : inelasticity
Q2 = −q2 = −(k − k' )2,
y = q.k/p.k Q² = sxy
s = center of mass energy square
qp
Qx
.2
2
NC Deep inelastic scattering at HERA
2. Qxp
2DIS 2011
Motivation
The proton PDF’s are poorly determined at high-x.
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Relative difference of different valance u quark pdf’s
Is it possible to check this ?
Large x is relevant to understandPhysics at LHC
DGLAP evolution sensitive to values of x upto 1
Measurements from HERAupto x =1
HERA and LHC
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High x e±p
),(),(),(2)(
222
3
2
24
2
2
2
QxFyQxxFYQxFYxQdxdQ
pedNC
L
NCNCNC
Y 1 (1 y)2
At Born level (Lowest order in QED)
F2(x,Q2) x A f (Q
2)(q f (x,Q2) q f (x,Q
2))f
xF3(x,Q2) x B f (Q
2)(q f (x,Q2) q f (x,Q
2))f
contains parity violating part of cross-section which is negligible at low Q2
includes cross-section of both longitudinal and transversely polarized exchanged boson
Parton density function(PDF)probability density of finding parton q or q carrying the momentum fraction x at given Q2
Longitudinal structure function
NC cross sections and structure functions
5DIS 2011
)],(),(),([)(1
2)(~ 2
22
3
2
22
2
2
4
QxFY
yQxxF
Y
YQxF
dxdQ
ped
Y
xQpe
NC
L
NCNCNC
NC
Reduced cross section
HERA-I : 1992-2000HERA-II :2001-2007
In HERA-II the luminositycollected was at least 3 times of HERA-I
HERA luminosity
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ZEUS Prel. 2010
ZEUS Prel. 2011
Θjet<0.11, No jet foundGood Jet Electron
Jet defination: ET > 10. GeV , θjet>0.11
Event topology at high-x
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x : reconstructed from jet information, x<xedge
No jet information: x > xedge
FCALBCAL
RCAL
Q2 and x reconstruction
Electron + jets information used
Electron is well reconstructed for the Q2 range of this analysis
Define Q2 bins from Ee and e:
)cos1(2'2
eeeEEQ
In each Q2 bin, define x bins:If jets are not close to the beam pipe (θjet > 0.11) : • For one jet events Pt balance between jet and electron is used and
ET,jet is replaced by Ptel
If there is no well reconstructed jet count events as zero jet xedge < x < 1 integral of cross section
e
jetjetjetT
p
jetjetjetT
E
EE
Ex
2
)cos1(sin/12
)cos1(sin/
,
,
i
iTjetTEE
,, )(tan2 1 jetejet
jetT
iiiT
jet E
E
,
,
, ,
• For multijet events jet variables are calculated as:
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Calibration scheme
BCAL Electron
Calibration
BCAL + FCAL
jet energy scale
FCAL electron energy scale
Measured energy compared to expected energy to find the energy scale which is better than 1%
BCAL electron calibrationis key to whole detectorcalibration
Jet energy scale depends upon BCAL electronJet energy scale betterthan 2%
FCAL electron energy scale relies on jet energy scale
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Event propertiesElectron
Jet
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MC:ARIADNE with CTEQ5D
Event properties
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ET,jet > 10. GeV for Njet > 0
Double differential σ
σ integrated over x
Binning
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Results: NC(e±p) cross sections
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Comparison to theory: CTEQ6D
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Comparison to theory: HERAPDF1.5
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Comparison
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1. Latest HERA-II e+p data (142 pb-1)
2. New x-reconstruction method leading to better resolution
3. More x bins compared to HERA-l high x analysis.
4. Completes HERA-ll high-x analysis, cross sections for e-p were presented at DIS2010.
Expected outcome:
• F2 and xF3 can be calculated using e+p & e-p HERA-II data.
• PDF uncertainty at high x may reduce.
Thanks
Summary
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Back Up
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Q2 and x reconstruction
jetel TT pp
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)cos1(2'2
eeeEEQ
sy
Qx
2
y
p
Qjet
T
1
2
2
e
jetjet
p
jetjet
E
EE
Ex
2
)cos1(12
)cos1(
02
)(
E
PEy
jetz
)2
)cos1)(sin(1(2
)cos1)(sin(
e
jetjett
p
jetjett
E
pE
px
e
e
Reconstruction of x
Best resolution achieved
)1(
2
jbjb
t
ysy
px
jets
i
yi
xt
jetjetjets
ppp 222 )()(
e
ijetjet
jb E
E
yii
2
)]cos1([
)2
)cos1)(sin(1(2
)cos1)(sin(
e
jetjett
p
jetjett
E
pE
px
e
e
jet
jet
=
jet
Multi jet events
One jet events
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Projection of ZEUS detector onx and Q2 plane
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Jetelectron BCAL
BCAL
BCAL FCAL
FCAL
FCAL
RCAL
RCAL
RCAL
BCAL
FCAL
FCALFCAL
BCAL
BCAL
RCALRCAL
RCAL
At high x and high Q2 events the jets andthe electron can be found in BCAL and FCAL
Important to understand BCAL and FCAL electronand hadron energy scales