richard hall-wilton university college london · 2017. 1. 30. · production is diffractive (7) ......
TRANSCRIPT
PPRP, 1 � � July 2002, RAL
�� �� �� �� � � � �� � � �� �� �� �
� � � � �
Richard Hall-Wilton
University College London
1�� July 2002
1
PPRP, RAL ZEUS UK Collaboration Status Report
Overview� Introduction to HERA and ZEUS
� Detector Status
� Central Tracking Detector
� Microvertex Detector
� Global Tracking Trigger
� Transverse Polarimeter Upgrade
� Physics Results on Heavy Flavour Production
1 � � July 2002 2 Richard Hall-Wilton, UCL
PPRP, RAL ZEUS UK Collaboration Status Report
Role of UK within ZEUS� Spokesman
� Vital UK role in data taking
� Runcoordinators, Shifts, Component coordination, Background studies
� Joint coordinators in 3 (of 5) physics groups
� Monte Carlo and Tracking Coordinators
� Leading a wide range of analyses
ZEUS UK plays an essential role within ZEUS
1 � � July 2002 3 Richard Hall-Wilton, UCL
PPRP, RAL ZEUS UK Collaboration Status Report
HERA — World’s only � � collider
HERA Physics program:
� Understanding p and � structure
� QCD studies
� Electroweak tests
� Searches
HERA luminosity upgrade (2000-1) — Increase in specific luminosity
Recommissioning: L� ��� � = 1.4 � � � � � � � � � �� � � � (design 1.8 � � � )
� Encouraging
1 � � July 2002 4 Richard Hall-Wilton, UCL
PPRP, RAL ZEUS UK Collaboration Status Report
HERA Recommissioning� Initially reproducability of beam orbits
was poor
� Machine now better understood
� Background conditions in experimentalareas too high
� New collimators installed in Marchreduced backgrounds significantly
� Backgrounds for ZEUS still too highto operate detector effectively
� CTD essential for solving problems0
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0 10 20 30 40 50
CTD SL1 currents, positrons only
Ie (mA)
SL1
curr
ent (
µA)
positrons only
lumi 2000 (Ip=99.3mA)
positrons only 2000
positrons only, 12 GeV
ZEUS and HERA working closely together to solve this problem
1 � � July 2002 5 Richard Hall-Wilton, UCL
PPRP, RAL ZEUS UK Collaboration Status Report
� � Collisions
ep collisions observed at HERA II
1 � � July 2002 6 Richard Hall-Wilton, UCL
PPRP, RAL ZEUS UK Collaboration Status Report
Upgrade of the ZEUS Detector during Shutdown� Significant upgrades to the ZEUS detctor
� Microvertex Detector � more later!
� Global Tracking Trigger � more later!
� Straw Tube Tracker � Tracking in forwarddirection
� Luminosity Monitor � 3 detectors installed
� Polarisation � more later!
1 � � July 2002 7 Richard Hall-Wilton, UCL
PPRP, RAL ZEUS UK Collaboration Status Report
1 � � July 2002 8 Richard Hall-Wilton, UCL
PPRP, RAL ZEUS UK Collaboration Status Report
Central Tracking Detector (CTD)� Primary ZEUS UK contribution � CTD essential for ZEUS running
� Very successful throughout HERA I
� Possibly observed “Malter” effect in 2000 � Fixed
� High Voltage Breakdown problems not observed since then
� dE/dx now understood for physics analysis
� dE/dx used in several results in past 2 years
� Essential for all 3 levels of the trigger at HERA I and II
� CTD used in virtually every ZEUS result published from HERA I
� Will be needed for every result from HERA II
1 � � July 2002 9 Richard Hall-Wilton, UCL
PPRP, RAL ZEUS UK Collaboration Status Report
Micro Vertex Detector (MVD) Installation
UK MVD Responsibilities:
� Clock + Control Electronics
� Laser Alignment System
� Patch box
� Installation
� MVD installed March - April 2001
MVD motivated by strong UK physicsprogram:
Understand charm and beautyproduction in QCD
1 � � July 2002 10 Richard Hall-Wilton, UCL
PPRP, RAL ZEUS UK Collaboration Status Report
Micro Vertex Detector (MVD) Commissioning� UK people heavily involved in pre-installation system test
� Provided shift people and visualisation software
� Involved in post-installationcommissioning
� MVD commissioned in ZEUS DAQchain for July 2001 cosmic test
� Offline alignment ongoing
MVD now installed + works in situ!
1 � � July 2002 11 Richard Hall-Wilton, UCL
PPRP, RAL ZEUS UK Collaboration Status Report
Global Tracking Trigger (GTT) Algorithm� Integrate tracking from CTD, MVD and STT at Second Level Trigger
� Harsh environment � high contribution from beam gas
� Operate within existing CTD SLT latency (Mean � 10 ms)
� CTD+MVD algorithm written and tested � compared to currentoffline
� Track Resolutions compara-ble or better than currentoffline
Event vertex
� � ��� � � �� � � �
� 1mm current offline
� 8cm present CTD-SLT
Combined CTD + MVD tracks areavailable at the SLT
1 � � July 2002 12 Richard Hall-Wilton, UCL
PPRP, RAL ZEUS UK Collaboration Status Report
Physics Motivation for Polarisation� Spin rotators installed around
HERA experiments duringshutdown
� Polarisation possible afterupgrade
AIM: 4 data sets from HERA II:
e� , e
�
; P > 0, P < 0
� Fully investigate structure functionsand electroweak physics
�
��� � � � required �
Transverse Polarimeter upgrade -A ZEUS UK Contribution
0
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-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
ZEUS CC Cross Sections
e-p Data (Prelim. 16 pb-1)
e-p SM √s=320 GeV
e-p SM (MC)
√s=320 GeV (50 pb-1)
e+p Data (48 pb-1)
e+p SM √s=300 GeV
e+p SM (MC)
√s=300 GeV (50 pb-1)
P
σCC
TO
T (
Q2 >
200
GeV
2 ) (p
b)
1 � � July 2002 13 Richard Hall-Wilton, UCL
PPRP, RAL ZEUS UK Collaboration Status Report
Transverse Polarimeter Upgrade� Built, calibrated and installed
� Testbeam in CERN and DESY� Results meets specification
� Silicon detector
� � �� � � 50 � m, S/N � 21
� TPOL Calorimeter
� � ��� � � � � � ��� � � �
� Installed November 2001
� Post-installation
� Operated successfully with unpolarised beams
� Measuring bunch-by-bunch polarisation
1 � � July 2002 14 Richard Hall-Wilton, UCL
PPRP, RAL ZEUS UK Collaboration Status Report
HERA I� Already a very successful physics
program from HERA I
� 113 Papers from ZEUS
� 131 pb
� � data taken
� Many more results to come ...
� Talk about results in heavy flavourphysics here
� Results on Structure Functions,Electro-Weak, Jets, Searches � � �
� See next talk � � �
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1992 1994 1996 1998 2000 2002
ZEUS
YearP
aper
s pu
blis
hed
per
Yea
r
1 � � July 2002 15 Richard Hall-Wilton, UCL
PPRP, RAL ZEUS UK Collaboration Status Report
Heavy Flavour Physics — Motivation� Boson-Gluon-Fusion dominant
contribution
� Sensitive to gluon content of proton
� m � and m � give a hard scale to process
� Good testing ground for QCD
� Q � and E����
can also provide a hard scale
� Multi-scale problem
� Beauty production in � � and e� e�
above expectations
� What about � � collisions?
Heavy Flavour Physics is a major unresolved topic in QCD
1 � � July 2002 16 Richard Hall-Wilton, UCL
PPRP, RAL ZEUS UK Collaboration Status Report
Heavy Flavour Physics
Topics Covered Here:
� Charm production in Deep Inelastic Scattering
� Diffractive Charm
� Charm + Jets
� Charm in the photon?
� Fragmentation
� Beauty production
All results shown here led by UK people
Topics not covered here:D� meson branching ratiosAlternative D� meson decay channels
1 � � July 2002 17 Richard Hall-Wilton, UCL
PPRP, RAL ZEUS UK Collaboration Status Report
Charm in Deep Inelastic Scattering� Important for understanding
charm in the proton
� Tag charm by D� mesons
� Vast improvement in errorsfrom previous results
� First time � � ��
� measured atHERA
� � � �� � and � � ��
� in agreementwith pQCD
1 � � July 2002 18 Richard Hall-Wilton, UCL
PPRP, RAL ZEUS UK Collaboration Status Report
Diffractive Charm� Diffraction at HERA is important topic
� Characterised by a large rapidity gap in the final state� Exchange of colour singlet � Often termed pomeron
� What is the diffractive exchange?
� Charm is sensitive to gluons
� Gluonic content of pomeron
� Models with 2 gluon exchangeseem to be able to describeresults better
� Significant fraction of DIS charmproduction is diffractive (7 � )
ZEUS(d)ZEUS 95-97
prot. diss. BJLW qq–BJLW
ACTW fit BSATRAP-CDM
β
dσ/
dβ
(pb
)
10
10 2
10 3
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
1 � � July 2002 19 Richard Hall-Wilton, UCL
PPRP, RAL ZEUS UK Collaboration Status Report
Charm and Jets
Now high enough statistics to look at charm + dijet production
Direct
High ��� � ��
Resolved
Low ��� � ��
� In resolved events, photon acts as a source of partons
� Resolved charm production � sensitive to � structure
� Charm with dijets give access to the production dynamics
� Charm Fragmentation can be studied
1 � � July 2002 20 Richard Hall-Wilton, UCL
PPRP, RAL ZEUS UK Collaboration Status Report
Charm and Jets� Idea: Probe production
mechanism
� Direct: Approx. Sym-metric
� Boson Gluon Fusion
� Resolved: Strongassymetry in photondirection
ZEUS
ZEUS (prel.) 1996-2000
PYTHIAHERWIGCASCADE
xγ obs < 0.75
1/σ
(all
x γ
obs
)dσ/
dcos
Θ*
PYTHIA: Direct
e p → D*±+ dijets + XMjj > 18 GeV ; |η
–| < 0.7
xγ obs > 0.75
cosΘ*
PYTHIA: Resolved
0
0.5
1
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8
0
0.5
1
0
0.5
1
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.80
0.5
1
� Strong evidence for charm in the photon1 � � July 2002 21 Richard Hall-Wilton, UCL
PPRP, RAL ZEUS UK Collaboration Status Report
Charm Fragmentation� Is charm fragmentation
universal?
� Measure fragmentation:charm � D� meson
� Energy fraction, z,carried by D�
� Strong sensitivity to �
� Data similar to that from
�� � �ZEUS
ZEUS (prel.) 1996-2000
Fit: ε = 0.064 ± 0.006 +0.011Fit: ε = 0.064 ± 0.006 -0.008
PYTHIA (Peterson)
ε = 0.02ε = 0.064ε = 0.1
z
1/σd
σ/dz
0
0.5
1
1.5
2
2.5
0.2 0.4 0.6 0.8 1
Precision competitive with LEP - very different production processfor charm1 � � July 2002 22 Richard Hall-Wilton, UCL
PPRP, RAL ZEUS UK Collaboration Status Report
Beauty Production� Electrons from semi-leptonic heavy quark decays
� Tag using dE/dx in CTD
� Technically difficult
� Sensitive to b quark production
� 15 � contribution from beauty
� HERA results on beauty aboveNLO pQCD predictions
� In both Deep Inelastic Scatteringand photoproduction
� Statistical uncertainty still large
HERA II data will be very interesting
1 � � July 2002 23 Richard Hall-Wilton, UCL