The Physics of Run II
John Womersley
Fermi National Accelerator Laboratory
DØ Software and Analysis Meeting
Prague, Czech Republic, September 1999
http://d0server1.fnal.gov/users/womersley/PragueSep99/Run2Physics.ppt
John Womersley
Run II redefined
•
The “Long Run II”
– 2 fb-1 by 2002
– 9 month shutdown
• install new silicon layers
– ~ 15 fb-1 (or more) by 2006
CDF
Tevatron
MI
•
Fermilab schedule slippage (always a sore point)
– New schedule will be fixed in October
– Data taking now seems unlikely before the end of 2000
John Womersley
DØ
Run I  Run II
•
The Tevatron is a broad-band parton-parton collider
Number
of
Events
Huge statistics
for precision physics
at low mass scales
Formerly rare processes
become high statistics
processes
Run I
Extend the third orthogonal axis:
the breadth of our capabilities
John Womersley
Run II
Increased reach
for discovery physics
at highest masses
Subprocess s
Three ways in which we gain
•
Statistics
– Huge statistics at “low” mass scales
• B-physics, QCD, W-mass
– Formerly rare processes enter the precision domain
• QCD with vector bosons, thousands of top events
– lay to rest some “undead” Run I anomalies
• the high-ET jet “excess”, the CDF ee event
•
Increased reach at the highest mass scales
– electroweak symmetry breaking
• SUSY, Higgs, etc.
•
New detector capabilities
– displaced vertex b-tagging
– much improved muon momentum resolution
– tracking triggers
John Womersley
Some of our strengths
EM calorimetry
Jets
Inclusive jet cross section
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Missing ET
 + X
mW = 80.450  0.093 GeV
DØ electrons
John Womersley
New Tools: charged particle tracking
John Womersley
In Run I only one of
these three muons
would have been found!
b
John Womersley
W
W
New tools: heavy flavor tagging
c
b
~ 55% at large pT
u,d,s
John Womersley
New tools: all new software
•
Full rewrite of online code,
level 3 trigger and offline
reconstruction in C++
John Womersley
Physics Goals of Run II
•
•
•
•
b-physics
 Targeted program including CP violation in B  KS
QCD
– Nucleon structure (parton distributions, diffraction)
– Jets, photons, Drell-Yan, vector bosons+jets, heavy flavour production
Standard-Model Physics
 High-statistics study of the top quark (mass, cross section, rare
decays, single top production)
– Precision measurement of the W mass (< 50 MeV)
Beyond the Standard Model
 Supersymmetry
 Higgs searches
 Technicolor, compositeness, new vector bosons, etc.
Take a closer look at the highlighted topics: low, medium and high
mass scales
John Womersley
B Physics
Slides from Rick Jesik, Indiana University
John Womersley
Run II B Physics Topics
•
Spectroscopy
•
Lifetimes
•
Branching ratios
•
Rare decays
•
CKM measurements
John Womersley
QCD measurements
•
•
•
•
Cross sections vs. pTmin
– single leptons (muons and electrons)
– dileptons
– muons with jets
– J/, (2s)
Differential cross sections
– B  J/ + K 
Correlations
– dilepton Df
– muon + jet
– forward - central
Charmonium
– color octet model
John Womersley
Exclusive B decays
Expected yields in 500 pb-1
B  J/ + K

B  J/ + K

3300
Bs  J/ + f
570
b  J/ + 
300
Bc
John Womersley
6200

 J/ + 

~ 50
B Physics in the 21st Century
•
Experiments will confront the Standard Model interpretation of CP
violation

1  λ2 2
λ
Aλ 3 ( ρ  iη) 
 Vud Vus Vub  



2
2


λ
1 λ 2
Aλ
 Vcd Vcs Vcb  


 
3
2

 Aλ
1
 Vtd Vts Vtb  
 Aλ (1  ρ  iη)

– A and l have been measured
to a few percent
– unitarity condition:
*
*
Vtb*Vtd + Vcb
Vcd + Vub
Vud  0
John Womersley
B  J/ KS Reconstruction
• J/   + - require two central tracks with pT > 1.5 GeV/c
• KS   + - use long lifetime to reject background: Lxy/ > 5
• Perform 4-track fit assuming B J/ KS
– constrain   and - to mass of KS and J/ respectively
– force KS to point to B vertex and B to point to primary
John Womersley
Sin2b Expectations for 2fb-1
For a time independent analysis:
1 + xd2
 (sin 2 b ) 
xd
1
ND 2
mode
– (S/B ~ 0.75)
–
e D2 ~ 6.7 %
trigger eff. 
1+
B
S
J/  + J/  e+e32
25
reco’d events
8,500
6,500
sin2b 
0.13
0.15
0.10
But, since most of the background is at small t’s, a time dependent
analysis gives reduced error:  (sin2b ) ~ 0.07
And this is just in the first two years - 2 fb-1. We won’t stop there…...
John Womersley
Expectations beyond 2fb-1
-1
L (fb )
John Womersley
Number of
 sin2b 
B J/ KS
2
15 K
0.07
5
 K
0.04
10
75 K
0.03
20
150 K
0.02
2002 - exciting times
•
BaBar and BELLE will have results from their first physics runs (not at design
luminosity)
– 1 - 30 fb-1  (sin2b ~ 0.12 - 0.18
•
We

–
–
•
The new detector puts us in a great position to do significant B physics
measurements in Run II, but we have a lot of hard work ahead of us
– getting the detector and triggers ready and working
– reconstruction programs for B  J/ + Ks 
•
But hey, look what we did in Run I without an inner tracker.
(and CDF) should have 1.0 - 2.0 fb-1 analyzed
(sin2b ~ 0.10 - 0.07
Tevatron could beat the B-factories
everyone combined could signal new physics.
John Womersley
Top quark physics
Slides from Ann Heinson, UC Riverside
DØ Workshop, Seattle, June 1999
http://www-d0.fnal.gov/~heinson/top500/
John Womersley
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Beyond the Standard
Model
John Womersley
Where do we stand, circa 2000?
•
•
The Standard Model works at the 10-3 level
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All observations are consistent with a single light SM Higgs, though no
such beast has yet been observed
– mH > 95.2 GeV (LEP) and mH < 245 GeV (SM fit, Eidelman & Jegerlehner)
John Womersley
Beyond the Standard Model
•
•
•
General arguments for new physics at the EW scale (250 GeV)
Standard Model fits suggest the new physics is weakly coupled
Indirect pointers to supersymmetry
Direct searches all negative so far
•
LEP2
– squarks (stop, sbottom) > 80-90 GeV
– sleptons (selectron, smuon, stau) > 70-90 GeV
– charginos > 70-90 GeV
– lightest neutralino > 36 GeV
•
Tevatron Run I
– squarks and gluinos
– stop, sbottom
– charginos and neutralinos
John Womersley
Your mission
(should you choose to accept it)
At your earliest convenience, please carry
out one or more of the following
challenges:
•
•
•
•
•
Discover the SM Higgs
Discover or exclude lightest SUSY Higgs
with masses up to ~ 130 GeV
Discover one or more superpartners
Exclude supersymmetry at the TeV scale
by discovering some other new physics
Can any of this be done in the next five
years?
John Womersley
SM Higgs: LEP2 prospects
•
Eilam Gross at EPS99
•
mH excluded
<
108.5 GeV
with 150 pb-1 per expt
at s = 200 GeV
John Womersley
Higgs Production at the Tevatron
•
•
•
gg  H dominates, but huge QCD
background
WH and ZH seem to offer the best
potential
SUSY enhances associated b
production
•
Run II SUSY/Higgs workshop
– http://fnth37.fnal.gov/higgs.html
•
•
repeated and extended previous studies, combining all possible channels
simulated “average” of CDF and DØ (SHW parameterized simulation)
program
John Womersley
SM Higgs Channels
mH < 130-140 GeV
•
•
•
•
WH  l bb
backgrounds Wbb, WZ, tt, single top
– factor ~ 1.3 improvement in S/B with neural network
– possibility to exploit angular distributions (WH vs. Wbb) Parke and Veseli,
hep-ph/9903231
WH  qq bb overwhelmed by QCD background
ZH  l l bb
backgrounds Zbb, ZZ, tt
ZH   bb
backgrounds QCD, Zbb, ZZ, tt
– requires relatively soft missing ET trigger (35 GeV?)
mH > 130-140 GeV
•
gg  H  WW*
backgrounds Drell-Yan, WW, WZ, ZZ, tt, tW, 
signal:background ratio ~ 7  10-3 !
– Angular cuts to separate signal from “irreducible” WW background
John Womersley
Combined reach
15 fb-1
2 fb-1
•
•
•
•
Bayesian combination of two experiments
30% improvement in bb mass resolution over Run I
SHW acceptance but no neural network improvement assumed
10% systematic error on backgrounds
John Womersley
SM Higgs: Issues
•
LEP2 analysis is clear-cut, and the reach is predictable
•
The Tevatron analysis is an exciting prospect. Is it credible?
– In my view, yes: it is an exercise similar in scale to the top discovery, with
a similar number of backgrounds and requiring similar level of detector
understanding.
– but it will be harder: the irreducible signal:background is worse
– it has caught the imagination of experimenters
– the single biggest problem with the studies so far (in my opinion) is the
assumptions about the bb dijet mass resolution
• can the assumed resolution really be achieved
(and in a high luminosity environment)?
• can it be improved (through the use of “smarter” algorithms)? e.g. kT?
John Womersley
Mass resolution
•
•
•
Directly influences signal significance
Requires corrections for missing ET and muon
Z  bb will be a calibration signal
CDF observation in Run I
DØ simulation for 2fb-1
Higgs simulation for 10fb-1
signal
John Womersley
Minimal Supersymmetric Standard Model
i.e. SM particles plus two Higgs doublets and their SUSY partners
Even this minimal spectrum can have many faces:
•
•
Is R-parity conserved?
– Is the LSP (lightest supersymmetric particle) stable?
How is supersymmetry broken?
– Supergravity-inspired (mSUGRA): the typical benchmark
• parameters m1/2, m0, A0, tan b, sign()
• radiative EWSB occurs naturally from large top mass
• the c1 is the LSP
• c1 , c2 , c1 , sleptons and h are “light”
• c , c4 , c2 , squarks and gluinos are “heavy”
– Gauge-mediated (GMSB): LSP can be Gravitino
• signatures with photons and/or slow-moving particles which may decay within
or outside detector
– Anomaly mediated
• lightest chargino and neutralino almost degenerate
John Womersley
Hadron collider SUSY signatures
•
•
The highest production cross section at a hadron collider is for the pair
production of squarks and gluinos
As long as R-parity is conserved, jets + missing transverse energy:
Missing ET
SUSY
John Womersley
backgrounds
DØ search for squarks and gluinos
•
•
Demand
– 3 jets, ET > 25 GeV, one jet ET > 115 GeV
– HT > 100 GeV
– veto electrons, muons
Main Backgrounds: top, QCD jets, W/Z+jets
estimated
background
•
data
Cascade decays to charginos can give leptons
in final state: complementary analysis
requiring
– 2 electrons, 2 jets + Missing ET
John Womersley
Run II limit:
gluino mass ~ 400 GeV
Run I excluded
Chargino/neutralino production
•
“golden” trilepton signature
•
Run II reach on c mass ~ 180 GeV (tan b = 2, µ< 0)
~ 150 GeV (large tan b)
– this channel becomes increasingly important as squark/gluino production
reaches its kinematic limits (masses 400-500 GeV)
Low pT triggering?
Can we include tau modes?
•
•
John Womersley
Stop and Sbottom
•
•
Stop
– stop  b + chargino or W
(top like signatures)
– stop  c + neutralino
– top  stop and gluino  stop
Sbottom
– 2 acollinear b-jets + ETmiss
Stop sensitivity
~ 150-200 GeV in Run II
CDF Run I stop and sbottom limits
115 GeV
John Womersley
145 GeV
Sbottom sensitivity
~ 200 GeV in Run II
Gauge Mediated SUSY
•
Is this selectron pair production?
DØ 
2 events observed
2.3 ± 0.9 expected
•
All we can say is that searches for
related signatures have all been negative
– CDF and DØ  + missing ET
– DØ  + jets + missing ET
– LEP
John Womersley
LEP
A taxonomy of GMSB signatures
•
•
•
•
NLSP
neutralino
NLSP
stau
Slepton
Co-NLSP’s
Prompt
 + ETmiss
taus
multileptons
Delayed
displaced 
kinks
Long-lived
ETmiss
“cannonball”
(massive, slow-moving)
Are event generators available for non-prompt scenarios?
– Interface to detector simulation maybe non-trivial
Standard searches pick up taus, multileptons and missing ET.
Prompt photons are “easy”
Challenges: Displaced photons, kinked tracks and cannonballs
John Womersley
Displaced photons
•
Run II DØ direct reconstruction with z = 2.2 cm, r = 1.4 cm
EM calorimeter
x
Preshower
•
Non-pointing photon analysis used at LEP: excludes neutralino masses
< 85 GeV for c < 1 m
John Womersley
Massive charged particles
•
•
Kinked tracks:
– c < 1 cm  OK: impact parameter
– 1 cm < c < 1 m  difficult: hard to trigger
Cannonballs
– LEP limits: stau > 76 GeV, sleptons > 85 GeV
– Tools:
dE/dx and timing (TOF counter in CDF; muon system in DØ)
CDF Run II
TOF
~ 180 GeV
John Womersley
Anomaly mediated SUSY
•
•
delayed decay of chargino: cannonball type signatures
decays may be in detector, soft pion plus missing ET
•
Do event generators exist?
John Womersley
Large extra dimensions
•
•
•
Gravitons propagate into higher dimensional space?
Direct searches for
– e+e-   + nothing
– pp   + nothing, jet+nothing
Indirect effects in e+e-  , , 
•
Do event generators exist?
John Womersley
R parity violation
•
Usual assumption: decay chain as in mSUGRA but LSP decays via B or
L violating operator (hence no missing ET)
– LEP sensitivity comparable to mSUGRA with R conserved
– CDF and DØ searches for ee + jets; again, comparable sensitivity
•
R violation in production process:
– HERA “leptoquark” searches ep  squark
– LEP e+e-  sneutrino  tau pairs
John Womersley
Supersymmetry: Issues
•
The basic menu of Run II searches is well-defined and we should have
no trouble in exploring:
– minimal SUGRA
– GMSB with prompt photon signatures
– some subset of R violation
•
Concerns: what have we forgotten?
– This is especially true at the Tevatron where triggering is a crucial issue
– For example, can we cover:
• slow moving massive particles
• GMSB with detached photons or taus
• anomaly-mediated (e.g. c±  c0 + soft)
• extra dimension signatures ...
– Let’s look at the DØ straw-man trigger list
http://www-d0.fnal.gov/~lucotte/TRG/trigger_list.html
John Womersley
MSSM Higgs at LEP2
•
Complementary processes: e+e-  (h/H)Z and (h/H)A
Summer 1999:
mh > 81 GeV
mA > 81 GeV
Excludes
0.9 < tan b < 1.6 max mixing
0.6 < tan b < 2.6 no mixing
but no exclusion if mtop = 180 GeV
•
•
General MSSM scans find a few points that can evade limits
Invisible Higgs decays included in searches
John Womersley
MSSM Higgs sector at the Tevatron
Assuming 1 TeV sparticle
masses,  < 0
minimal stop mixing
95% exclusion
But not always so straightforward:
Fixed A (= – = 1.5 TeV here) suppresses
hbb, h couplings for certain (mA, tanb)
5 discovery
maximal stop mixing (heaviest h)
95% exclusion
John Womersley
5 discovery
Enhances h  
(branching ratio as high as 10%?)
Strong SUSY Higgs Production
•
bb(h/H/A) enhanced at large tan b:
•
 ~ 1 pb for tanb = 30
and mh = 130 GeV
bb(h/A)  4b
CDF Run I
3 b tags
tan b = 30
150 GeV
John Womersley
Charged Higgs
•
•
•
Tevatron search in top decays
Standard tt analysis, rule out competing decay mode t  Hb
Assumes 2 fb-1, nobs = 600, background = 50  5
Run II
Run I
LEP summer 99
77 GeV
•
LEP not really sensitive to MSSM region (expect mH > mW)
John Womersley
Non-Supersymmetric EWSB
Technicolor T  WT  lbb
Tevatron, 1fb-1
•
Dynamical schemes like
technicolor and topcolor predict
– new particles in the mass range
100 GeV - 1 TeV
– with strong couplings and large
cross sections
– decaying to vector bosons and
(third generation?) fermions
•
Plus we should always be looking for
– Leptoquarks
– Fourth generation fermions or isosinglet fermions
– W’ and Z’
– contact interactions, etc etc.
John Womersley
Some final remarks
John Womersley
Common Features
•
To fully explore the broad range of physics in Run II we will need to seek out
the common features in this menu — so as to make the most of our
bandwidth and our personnel
– for example:
• isolated, moderate pT leptons (W/Z, SUSY, top . . .)
• b-jets
– other examples:
• W+jets is QCD, top, single top, SUSY, technicolor, Higgs . . .
• Photons are QCD, SUSY, technicolor . . .
•
This is why I would like to see a strong, continuing role for the physics object
ID groups
John Womersley
Run II Strategy
•
•
•
play to our strengths
– EM calorimetry
– Jets
– Missing ET
put in the effort to exploit our new tools
– charged particle tracking
– muon acceptance and resolution
– heavy flavor tagging
remain grounded
– don’t all start searching for the Higgs with 500 pb-1
John Womersley
A message to our European colleagues
DØ wants you!
•
Run II offers a broad and compelling physics program, but it’s going
to take a lot of work on the detector, trigger, infrastructure software,
calibration . . .
•
We need to make sure that all our collaborators are full participants in
this enterprise — we can’t do it without your help
John Womersley
Conclusions
•
The Tevatron is an immensely productive facility
– s from 10 GeV to 1 TeV
•
Run II offers three ways to gain over Run I:
– increased statistics for standard model processes
– increased reach for new particle searches
– increased detector capabilities
There’s nowhere more
exciting to do physics!
John Womersley