1

ZEUS at HERA

Robin Devenish

� HERA and ZEUS

� Oxford ZEUS Group

� Topics

� Future & Resources

Projects Review 2011

2

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

3

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

5

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

6

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

13

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

2

Sensitivity to W mass and pdf flavour selectivity

(e p) [ (1 ) ( )]x u c y d sσ + = + + − +ɶ