John Womersley

The Physics of Run II

John WomersleyFermi National Accelerator Laboratory

DØ Software and Analysis MeetingPrague, 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

• Fermilab schedule slippage (always a sore point)– New schedule will be fixed in October– Data taking now seems unlikely before the end of 2000

CDF

DØMI

Tevatron

John Womersley

Run I Run II

Subprocess s

Numberof

Events

Run IIRun I

Increased reach for discovery physicsat highest masses

Huge statistics for precision physicsat low mass scales

Formerly rare processesbecome high statisticsprocesses

• The Tevatron is a broad-band parton-parton collider

Extend the third orthogonal axis:the breadth of our capabilities

John Womersley

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

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Jets

Missing ET

mW = 80.450 0.093 GeVDØ electrons

EM calorimetry

+ X

Inclusive jet cross section

John Womersley

New Tools: charged particle tracking

John Womersley

b W

W In Run I only one of these three muonswould have been found!

John Womersley

New tools: heavy flavor tagging

b

c

u,d,s~ 55% at large pT

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/

• Correlations– dilepton– muon + jet– forward - central

• Charmonium – color octet model

John Womersley

Exclusive B decays

B J / 6200

B J / 3300

Bs J / 570

b J / 300

Bc J / ~ 50

Expected yields in 500 pb-1

John Womersley

B Physics in the 21st Century

• Experiments will confront the Standard Model interpretation of CP violation

tbtstd

cbcscd

ubusud

VVV

VVV

VVV

1)1(

21

)(21

23

22

32

AλiηρAλ

Aλλλ

iηρAλλλ

– A and have been measured to a few percent

– unitarity condition:

0*** udubcdcbtdtb VVVVVV

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

Sin2 Expectations for 2fb-1

– (S/B ~ 0.75)

– e D2 ~ 6.7 %

mode J/ J/ e+e-

trigger eff. 32 25

reco’d events 8,500 6,500

0.13 0.15sin2 0.10

SB

DNx

x

d

d

111

)2(sin2

2

For a time independent analysis:

But, since most of the background is at small t’s, a time dependent analysis gives reduced error: (sin2 ) ~ 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

L (fb-1)Number ofBJ/KS

sin2

2 15 K 0.07

5 0.04

10 75 K 0.03

20 150 K 0.02

John Womersley

2002 - exciting times

• BaBar and BELLE will have results from their first physics runs (not at design luminosity)– 1 - 30 fb-1 (sin2~ 0.12 - 0.18

• We (and CDF) should have 1.0 - 2.0 fb-1 analyzed (sin2~ 0.10 - 0.07– Tevatron could beat the B-factories – everyone combined could signal new physics.

• 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/s

• But hey, look what we did in Run I without an inner tracker.

John Womersley

Top quark physicsSlides 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

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Where do we stand, circa 2000?

• The Standard Model works at the 10-3 level

• 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

• 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

• gg H dominates, but huge QCD background

• WH and ZH seem to offer the best potential

• SUSY enhances associated b production

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

• 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

2 fb-1

15 fb-1

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

signal

CDF observation in Run I DØ simulation for 2fb-1 Higgs simulation for 10fb-1

John Womersley

Minimal Supersymmetric Standard Model

i.e. SM particles plus two Higgs doublets and their SUSY partnersEven 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 sign()

• radiative EWSB occurs naturally from large top mass

• the is the LSP

• ,

, , sleptons and h are “light”

• ,

, , 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 backgrounds

John Womersley

estimatedbackground data

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

• Cascade decays to charginos can give leptons in final state: complementary analysis requiring

– 2 electrons, 2 jets + Missing ET

Run II limit:gluino mass ~ 400 GeV

Run I excluded

John Womersley

Chargino/neutralino production

• “golden” trilepton signature

• Run II reach on mass ~ 180 GeV (tan = 2, µ< 0) ~ 150 GeV (large tan )

– 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 sensitivity ~ 150-200 GeV in Run II

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

CDF Run I stop and sbottom limits

Sbottom sensitivity ~ 200 GeV in Run II

115 GeV 145 GeV

John Womersley

Gauge Mediated SUSY

• Is this selectron pair production?

• All we can say is that searches for related signatures have all been negative

– CDF and DØ + missing ET

– DØ + jets + missing ET

– LEP

DØ

2 events observed2.3 ± 0.9 expected

LEP

John Womersley

A taxonomy of GMSB signatures

• 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

NLSPneutralino

NLSPstau

SleptonCo-NLSP’s

Prompt + ETmiss taus multileptons

Delayed displaced kinks

Long-lived ETmiss “cannonball”

(massive, slow-moving)

John Womersley

Displaced photons

• Run II DØ direct reconstruction with z = 2.2 cm, r = 1.4 cm

• Non-pointing photon analysis used at LEP: excludes neutralino masses < 85 GeV for c < 1 m

Preshower

EM calorimeter

x

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)

~ 180 GeV

CDF Run II

TOF

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. ± 0 + soft)• extra dimension signatures ...

– Let’s look at the DØ straw-man trigger listhttp://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

• General MSSM scans find a few points that can evade limits• Invisible Higgs decays included in searches

Summer 1999:mh > 81 GeVmA > 81 GeV

Excludes0.9 < tan < 1.6 max mixing0.6 < tan < 2.6 no mixingbut no exclusion if mtop = 180 GeV

John Womersley

Assuming 1 TeV sparticle

masses, < 0

MSSM Higgs sector at the Tevatron

95% exclusion

95% exclusion 5 discovery

5 discovery

minimal stop mixing

maximal stop mixing (heaviest h)

But not always so straightforward:

Fixed A (= – = 1.5 TeV here) suppresses hbb, h couplings for certain (mA, tan)

Enhances h (branching ratio as high as 10%?)

John Womersley

Strong SUSY Higgs Production

• bb(h/H/A) enhanced at large tan :

~ 1 pb for tan = 30 and mh = 130 GeV

tan = 30

bb(h/A) 4b

CDF Run I3 b tags

150 GeV

John Womersley

Charged Higgs• Tevatron search in top decays• Standard tt analysis, rule out competing decay mode t Hb

• Assumes 2 fb-1, nobs = 600, background = 50 5

• LEP not really sensitive to MSSM region (expect mH > mW)

Run II

Run I

LEP summer 99

77 GeV

John Womersley

Non-Supersymmetric EWSB

• 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.

Technicolor T WT lbbTevatron, 1fb-1

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!