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ZEUS at HERA
Robin Devenish
� HERA and ZEUS
� Oxford ZEUS Group
� Topics
� Future & Resources
Projects Review 2011
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HERA (1992 – 2007)
0
HERA-I (1992-2000); HERA-II (2003-7 after upgrade)
27.5 GeV polarised e on 920 GeV protons, E 31
Charg
8
ed
GeV
N
Cur
eutral C
rent
urrent , V= or Z
Two general purp
, V= W
o
cm
ep e
X
X
ep
γυ ±
± =
→→
ZEUS se detectors: H1 and
ZEUS
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Oxford ZEUS Group
� Faculty – A Cooper-Sarkar, R Walczak, C Gwenlan
– R Devenish (retired but still active)
– B Foster (Humboldt Professor, DESY and Hamburg University)
� Graduate students– Aileen Robertson (about to submit)
– (Katie Oliver - successful viva, Aug 2011)
� Consultant Support Staff – Mike Dawson, Ewan MacMahon
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Oxford Projects
� Strangeness correlations – Aileen Roberston & Roman Walczak
� Combining H1 and ZEUS data – Mandy Cooper-Sarkar & Robin Devenish
� HERA parton densities– Mandy Cooper-Sarkar
� ZEUS data preservation – Robin Devenish
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Strangeness correlations
( )2 2
Function of Q = 4
LH plot shows (data - black; MC - red)
Strange b
aryon pair prod
- large excess of at small Q
uction (
,
R
H
)
M M
N N
ΛΛ Λ
ΛΛ ΛΛ
ΛΛ Λ
•
Λ•
Λ
−
•
Λ
( ) ( )
1/2
= 1 pairs all pairs
- spin states selected using angle between protons from decays
- expect = 3/4 for two spin- states coupling statistically
Sε
ε
= ΛΛ ΛΛΛ
( )2 2 4Q M MΛΛ Λ= −
> 4 GeV
ratio flattens,
long range
correlations?
Q
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Combined H1 and ZEUS analyses
� To gain the ultimate precision in HERA physics
� Some examples
– inclusive structure functions
– charm structure function
* 0 neutral current, NC, ( and exchange)
, charged current, CC, (W exchange)
e p e X Z
e p X
γ
ν ν
± ±
± ±
+ → +
+ → +
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Longitudinal structure function FL
2 22 2 2 2
2 32 4
2 2
( ) 2( , ) ( , ) ( , )
where 1 (1 ) and 1- sin2
: proton structure functions - given by quark and gluon parton densities
F
L
e
e
i
d e pY F x Q y F x Q Y xF x Q
dxdQ Q x
EY y y
E
F
σ πα
θ
±
+ −
±
= −
′= ± − =
∓
2 2
is the longitudinal SF - most difficult to measure;
require a range of CM energies ( ) for fixed ( , )
L
Q sxy s x Q= ⇒
FL: small but not zero,depends directly on gluondensity
Simple QPM gives zero
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NC and CC cross-sections vs Q2
Complete HERA data from H1 & ZEUS
: e + p e + X
CC: e + p , +X
NC
ν ν
± ±
±
→→
2
2
2 sinF W
W
G Mπα
θ=
2 2Classic plot - showing electroweak unification for ~ and larg r eWQ M
2 2
, given by proton parton densities
e.g ( ) (1 ) ( ) ; ( ) (1 ) ( )
NC CC
CC CCx u c y d s x u c y d s
Φ Φ
Φ + = + + − + Φ − = + + − +
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F2(charm)
*, 0
*
LH plot: data from H1, ZEUS separately; RH plot: combined data
Charm identified using ( ) - ( ), from D
Extrapolate to full phase-space, and use ( ) fragmentation pr
m M K M K D K
c D
ππ π π π π+ + − + +
•
• ∆ = → →• → obability
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HERA parton densities
� Accurate knowledge of proton structure is essential for LHC physics
� Crucial measurements still to be completed – e.g.– ZEUS inclusive NC e+p cross-sections
– Various H1 and ZEUS inclusive jet measurements
� Proposal to form a HERAPDF group from H1 and ZEUS collabs with strong support from the DESY ATLAS and CMS groups
� Some examples from recent HERA pdf fitting
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F2(charm)
Comparison of combined HERA F2(charm) data with recent pdfs
MSTW NLO and NNLO pdfs (blue lines)
HERAPDF1.0 (line + light blue
uncertainty band)
Good description for Q2 > 4 GeV2
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charm mass scan
Using F2(charm) explicitly in the HERA pdf determination fixes thecharm mass parameter quite precisely
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Impact of new high Q2 data sets
HERA II(high Q2) data
reduces the uncertaintiesfor all partondensities
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HERA pdf with everything
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Data preservation
� HERA stopped running in 2007
� Unique data set – how best to preserve for posterity?
� Common Ntuple in ROOT and PAW formats – only ROOT is guaranteed to survive
� Started with HERA-II data plus Monte-Carlo samples (most time consuming)
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A future for HERA physics?
Achim Geiser – valedictory – ZEUS physco
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Next steps for Oxford ZEUS
� Complete strangeness analysis
� Ensure ZEUS data is preserved for posterity
� Join HERA pdf project (proposal for joint HERA-LHC partondensities) - AMCS
� Access to local and DESY computing facilities� Occasional advice and help from local IT staff
Resources
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BACKUP
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αS from HERA data
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Deep Inelastic Scattering at HERA
2
0
2
2 2
Neutral Current , V= or Z
Kinematics
.
Charged Cu
.
( )
(
rrent ,
) 2 .
V= W
ep eX
p qy q k k
p k
ep X
QQ k k x
p q
s k p
γυ ±
′= − −
→
′= = −
=
=
+
→
2 2 1 (1 ) Q sxy Y y±= = ± −
2 2†2 2
2 2
422†2 2
2
3
22
4
2 32
( ) 2( , ) ( , )
( )( , ) ( , )
4 ( )
CCWF
W
NC NC
CC CC
NC
MGd e pY x Q Y x x Q
d
d e pY x Q Y x x Q
dxdQ xQF F
FQ x Q M
Fxd
σπ
σ πα±
+
±
+ −
− =
= +
∓
∓
L
2
2
2 2 3
† F has been ignored
( ) ( only);
( , ) - momentum density of quark flavour
( );
in proton
(
)i i ii
i
i i i iC C
i
C
i
N C Ce x q q
q x Q i
F F x q q x x q qFγ+ = + = −∑∑ ∑≃
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2 4 2 Neutral Current, 2.5 10 GeV , 0.34e p e X Q x+ → + = × =
2
0
Sensitivity to ( ) ( ); proton pdfs and
Z axial and vector couplings
i i ii
A Q xq xq∗ +∑
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2 4 2 Charged Current, 1.7 10 GeV , 0.32e p X Q xυ+ → + = × =
Missing transverse energy
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Sensitivity to W mass and pdf flavour selectivity
(e p) [ (1 ) ( )]x u c y d sσ + = + + − +ɶ