Probing New Physics with Jets at the LHC - PowerPoint PPT Presentation

Loading...

PPT – Probing New Physics with Jets at the LHC PowerPoint presentation | free to download - id: 4ffe33-OGUxY



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Probing New Physics with Jets at the LHC

Description:

with Jets at the LHC Robert M. Harris Fermilab Fermilab Colloquium August 29, 2007 1 Credits Study done at LHC Physics Center (LPC) A center of CMS physics at ... – PowerPoint PPT presentation

Number of Views:67
Avg rating:3.0/5.0
Slides: 39
Provided by: RobertMH150
Category:
Tags: lhc | jets | new | physics | probing

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Probing New Physics with Jets at the LHC


1
Probing New Physics with Jets at the LHC
  • Robert M. Harris
  • Fermilab
  • Fermilab Colloquium
  • August 29, 2007

1
2
Credits
  • Study done at LHC Physics Center (LPC)
  • A center of CMS physics at Fermilab
  • CMS approved, publicly available
  • CMS Physics TDR Volume II
  • J. Phys. G Nucl. Part. Phys. 34 995-1579
  • CMS Notes (2006 / 069, 070 and 071)
  • Ph.D thesis of two students
  • Selda Esen now a postdoc at Brown
  • Kazim Gumus from Texas Tech
  • Both mentored at the LPC
  • Demonstration of physics at LPC
  • Working within the CMS collaboration
  • Thanks to many CMS colleagues!

3
Outline
  • Motivation
  • Introduction
  • Jets
  • New Physics with Jets
  • CMS Jet Trigger and Jet Backgrounds from QCD
  • CMS Sensitivity to Signals of New Physics
  • New Particles Dijet Resonances
  • New Forces Contact Interactions
  • Jet Physics at the LPC
  • Conclusions

4
  • In 2008 science will start to explore a new
    energy scale
  • 14 TeV proton-proton collisions will allow us to
    see deeper into nature than ever before
  • Two large detectors will observe the collisions

ATLAS
CMS
Large Hadron Collider at CERN
Geneva Switzerland
5
  • ATLAS
  • 22 x 44 meters, 6000 tons
  • 2000 collaborators, 34 nations
  • CMS
  • 15 x 22 meters, 12500 tons
  • 3000 collaborators, 37 nations

6
What will the LHC detectors see?
  • We expect to see the standard model
  • The particles and forces already catalogued . . .
  • . . . perhaps a Higgs particle that remains to
    be discovered.
  • But we hope to see more than the standard model !

7
Questions in the Standard Model
  • The simple picture of the standard model raises
    many fundamental questions.
  • Why three nearly identical generations of quarks
    and leptons?
  • Like the periodic table of the elements, does
    this suggest an underlying physics?
  • Is it possible that quarks and leptons are made
    of other particles?
  • Can we unify the forces ?
  • g, Z and W are unified already.
  • Can we include gluons ?
  • Can we include gravity ?
  • Why is gravity so weak ?
  • These other questions suggest new physics
    beyond the standard model.
  • We can discover this new physics with simple
    measurements of jets at the LHC.

8
Introduction to Jets
9
Jets at LHC in Standard Model
Jet
The LHC collides protons containing colored
partons quarks, antiquarks gluons.
The dominant hard collision process is simple 2
g 2 scattering of partons off partons via the
strong color force (QCD).
Proton
Each final state parton becomes a jet of
observable particles.
Jet
The process is called dijet production.
10
Experimental Observation of Jets
CMS Barrel Endcap Calorimeters
h0
h-1
h1
Jet 1
Transverse
f
q
proton
proton
Jet 2
  • Dijets are easy to find
  • Two jets with highest PT
  • in the calorimeter.
  • A jet is the sum of calorimeter energy in a cone
    of radius

11
Dijet Rates and Cross Sections
Jet 1
  • QCD dijet cross section is large.
  • s from color force is large

PDF(xa)

Proton
Proton
107 events/ month at design L
PDF(xb)
Jet 2
  • Rate Cross Section x Luminosity
  • Luminosity (L) is rate of protons / area supplied
    by the LHC.
  • Design L1034 cm-2 s-1 10 fb-1/month
  • Cross section from two factors
  • Parton distributions functions (PDFs)
  • Probability of finding partons in proton with
    fractional momentum x
  • Valence quarks u and d have large PDFs at high x
    (high dijet mass).
  • Parton scattering cross section s

10 events/ month at design L
  • Many signals are also large
  • Either large PDFs or s or both.



12
Introduction to New Physics with Jets
13
Quark Compositeness and Scattering
  • Three nearly identical generations suggests quark
    compositeness.
  • Compositeness is also historically motivated.
  • Molecules g Atoms g Nucleus g Protons Neutrons
    g Quarks g Preons ?
  • Scattering probes compositeness.
  • In 1909 Rutherford discovered the nucleus inside
    the atom via scattering.
  • Scattered a particles off gold foil.
  • Too many scattered at wide angles to the incoming
    a beam
  • Hit the nucleus inside the atom!
  • A century later, we can discover quark
    compositeness in a similar way !
  • Searching for more dijets in center of the CMS
    Barrel than at the edge.
  • More about this when we discuss sensitivity to
    contact interactions!

Discovery of Nucleus
Detector
a
a
Gold
Quark Compositeness Signal
q
q
q
q
q
q
q
q
More of this
Than of this
14
Dijet Resonances
They are observed as dijet resonances mass
bumps.
New particles, X, produced in parton-parton annihi
lation will decay to 2 partons (dijets).
Rate
space
time
Mass
M
Tevatron has searched but not found any dijet
resonances so far
D0 Run 1
15
Why Search for Dijet Resonances?
  • Experimental Motivation
  • LHC is a parton-parton resonance factory in a
    previously unexplored mass region
  • With the higher energy we have a good chance of
    finding new physics.
  • Nature may surprise us with previously
    unanticipated new particles.
  • We will search for generic dijet resonances, not
    just specific models.
  • One search can encompass ALL narrow dijet
    resonances.
  • Resonances narrower than jet resolution produce
    similar mass bumps in our data.
  • We can discover dijet resonances if they have a
    large enough cross section.
  • Theoretical Motivation
  • Dijet Resonances found in many models that
    address fundamental questions.
  • Why Generations ? g Compositeness
    g Excited Quarks
  • Why So Many Forces ? g Grand Unified Theory g
    W Z
  • Can we include Gravity ? g Superstrings GUT
    g E6 Diquarks
  • Why is Gravity Weak ? g Extra Dimensions
    g RS Gravitons
  • Why Symmetry Broken ? g Technicolor
    g Color Octet Technirho
  • More Symmetries ? g Extra Color
    g Colorons Axigluons

Next Slide
After Talk?
16
Example Resonance Model Excited Quarks
  • Excited states are common in nature.

Light from Excited States of Hydrogen
Hydrogen Atom
Excited State
ground state
  • If quarks are composite particles then excited
    states, q, are expected
  • Excited quarks are produced when a ground state
    quark absorbs a gluon.
  • q decay to the ground state q by re-emitting a
    gluon (qg g q g qg).

q
g
q
q
g
Initial State
Final State
Resonance
  • Cross section is large because the interaction is
    from the color force (QCD).
  • Similar number of events produced as the QCD
    background !

17
CMS Jet Trigger Dijets from QCD
18
Trigger and Luminosity
  • Collision rate at LHC is expected to be 40 MHz
  • 40 million events every second !
  • CMS cannot read out and save that many.
  • Trigger chooses which events to save
  • Two levels of trigger are used to reduce rate in
    steps
  • Level 1 (L1) reduces rate by a factor of 400.
  • High Level Trigger (HLT) reduces rate by a factor
    of 700.
  • Trigger tables are intended for specific
    luminosities
  • Weve specificied a jet trigger table for three
    luminosities
  • L 1032 cm-2 s-1. Integrated luminosity 100
    pb-1.
  • LHC schedule projects this after 1 months
    running.
  • L 1033 cm-2 s-1. Integrated luminosity 1
    fb-1.
  • LHC schedule projects these amounts by end of
    2008.
  • L 1034 cm-2 s-1. Integrated luminosity 10
    fb-1.
  • One months running at design luminosity.

19
Jet Trigger Table and Dijet Mass Analysis
  • CMS jet trigger saves all high ET jets
    pre-scales the lower ET jets.
  • Prescale means to save 1 event out of every N
    events.

Mass values are efficient for each trigger,
measured with prior trigger
Path L1 L1 L1 HLT HLT ANA
Path ET (GeV) Pre- scale Rate (Hz) ET (GeV) Rate (Hz) Dijet Mass (GeV)
Low 25 2000 146 60 2.8
Med 60 40 97 120 2.4 330
High 140 1 44 250 2.8 670
L 1032 100 pb-1
As luminosity increases new trigger paths are
added Each with new unprescaled threshold.
Ultra 270 1 19 400 2.6 1130
Super 450 1 14 600 2.8 1800
20
Trigger Rates Dijet Cross Section (QCD CMS
Simulation)
  • Include data from each trigger where it is
    efficient in dijet mass.
  • Stop analyzing data from trigger where next
    trigger is efficient
  • Prescaled triggers give low mass spectrum at a
    convenient rate.
  • Measure mass down to 300 GeV
  • Overlap with Tevatron measurements.
  • Trigger without any prescaling saves all the high
    mass dijets
  • Expect the highest mass dijet event to be
  • 7.5 TeV for 10 fb-1
  • 5 TeV for 100 pb-1
  • LHC will open a new mass reach early!
  • Put the triggers together to form a cross
    section.

Prescaled Trigger Samples
21
Uncertainties on Dijet Cross Section
  • Statistical Uncertainties
  • Simplest measure of our sensitivity to new
    physics as a fraction of QCD background
  • lt 3 in prescaled region.
  • As luminosity increases our statistical error
    shrinks at high mass.
  • Systematic Uncertainties are large
  • Dominated by uncertainty in jet energy
    measurement.
  • Correlated with dijet mass.
  • Smooth changes, not bumps.

22
CMS Sensitivity to Dijet Resonances
23
Resonances and Background (CMS Simulation)
  • QCD cross section falls smoothly as a function of
    dijet mass.
  • Resonances produce mass bumps we can see if xsec
    is big enough.

24
Resonances and QCD Statistical Errors
  • Many resonances give obvious signals above the
    QCD error bars
  • Resonances produced via color force
  • q (shown)
  • Axigluon
  • Coloron
  • Color Octet rT
  • Resonances produced from valence quarks of each
    proton
  • E6 Diquark (shown)
  • u d g D g u d
  • Others may be at the edge of our sensitivity.

25
Statistical Sensitivity to Dijet Resonances
  • Sensitivity estimates
  • Statistical likelihoods done for both discovery
    and exclusion
  • 5s Discovery
  • We see a resonance with 5s significance
  • 1 chance in 2 million of effect being due to QCD.
  • 95 CL Exclusion
  • We dont see anything but QCD
  • Exclude resonances at 95 confidence level.
  • Plots show resonances at 5s and 95 CL
  • Compared to statistical error bars from QCD.

5 TeV
2 TeV
0.7 TeV
2 TeV
0.7 TeV
26
Sensitivity to Resonance Cross Section
  • Cross Section for Discovery or Exclusion
  • Including systematics.
  • Shown here for 1 fb-1
  • Also done for 100 pb-1, 10 fb-1
  • Compared to cross section for 8 models
  • CMS expects to have sufficient sensitivity to
  • Discover with gt 5s significance any model above
    solid black curve
  • Exclude with gt 95 CL any model above the dashed
    black curve.

27
Sensitivity to Dijet Resonance Models
  • Discover models up to 5 TeV in 10 fb-1
  • 1 month at design luminosity 10 fb-1
  • Discovery up to 2.5 TeV with 100 pb-1
  • Wide exclusion sensitivity
  • Extending Tevatron exclusions (lt1 TeV)

28
CMS Sensitivity to Quark Contact Interactions
29
Contact Interactions Compositeness
  • New physics at a large scale L
  • For example composite quarks.
  • Intermediate state looks like a point for dijet
    mass ltlt L.
  • Giving a contact interaction.
  • Increases rate at high dijet mass.
  • But the signal in rate alone is hard to find due
    to uncertainties in jet energy parton
    distributions.

Composite Quarks
New Interactions
q
q
M L
M L
q
q
Dijet Mass ltlt L
  • We will use a ratio of two rates.
  • Look at angles like Rutherford did !

Quark Contact Interaction
30
Dijet Ratio and New Physics
h -1 - 0.5 0.5 1
  • Dijet Ratio
  • N(hlt0.5) / N(0.5lthlt1)
  • Number of events in which each leading jet has
    hlt0.5, divided by the number in which each
    leading jet has 0.5lthlt1.0
  • Simplest measurement of angle dist.
  • Most sensitive part for new physics
  • It was first introduced by D0

Jet 1
Numerator Sensitive to New Physics Signal
z
Jet 2
Jet 1
Denominator Dominated by QCD Background
z
or
Jet 2
Jet 2
(rare)
31
Dijet Ratio and Uncertainties (Smoothed CMS
Simulation)
  • QCD Background Simulation is flat
  • Signal rises with mass
  • Clear statistical sensitivity to contact signal
  • Small systematic uncertainties.
  • Cancel in the ratio
  • We find 5s discovery and 95 CL exclusion
    sensitivities for L.
  • Including both the statistical and systematic
    uncertainties.

32
CMS Sensitivity to Contact Interactions
Left-Handed Quark Contact Interaction (Eichten, Lane Peskin) L for 100 pb-1 (TeV) L for 1 fb-1 (TeV) L for 10 fb-1 (TeV)
95 CL Exclusion 6.2 10.4 14.8
5s Discovery 4.7 7.8 12.0
  • Published Limit (D0) L gt 2.7 TeV at 95 CL
  • CMS could quadruple this limit in 2008.
  • L can be translated roughly into the radius of a
    composite quark.
  • h Dx Dp (2r) (L / c)
  • r 10-17 cm-TeV / L
  • For L 10 TeV, r 10-18 cm

Preon
r
Composite Quark
33
LPC and Jets
34
Jet Physics Efforts at LPC
  • The simulation analysis I have just shown was
    finished in April 2006.
  • Done by people working at the LPC.
  • LPC efforts in jet physics have grown over the
    last year.
  • We are well integrated into the physics groups of
    CMS.
  • U.S. institutions with Tevatron experience are
    actively involved in jet physics at LPC.
  • Brown, Fermilab, Maryland, Rochester,
    Rockefeller, Rutgers, UIC, Virginia,
  • Other CMS institutions also collaborate with the
    LPC on jet physics.
  • Antwerpen, Cukurova, CERN, Delhi, ETH Zurich,
    Karlsruhe,
  • The LPC is also hosting a series of workshops on
    First Physics at CMS
  • Next workshop is October 11 13 at Fermilab.
  • Includes all the physics activities at the LPC,
    not just jets.

35
Jet Developments at LPC
  • Jet developments at the LPC over the last year
    include
  • Jet Physics Analysis
  • Optimized the h cuts for dijet resonance and
    contact interactions at CMS.
  • Began to use the dijet ratio to search for dijet
    resonances.
  • Began to study the inclusive jet PT from QCD and
    contact interactions.
  • Jet Fundamentals
  • Jet trigger has been refined and extended to
    lower ET.
  • Jet energy calibrations (corrections) are a major
    effort and a focus of the LPC.
  • Corrections based on jet simulations are
    routinely produced.
  • Techniques for finding jet corrections from
    collision data are being developed.
  • Modern jet algorithms implemented KT, midpoint
    seedless cone, etc.
  • Jet performance is actively being studied
    response, resolution, efficiency, etc.

36
Conclusions
  • The LHC will probe exciting new physics with
    simple measurements of jets.
  • We have presented a jet trigger table and dijet
    analysis developed at LPC.
  • CMS can discover a strongly produced dijet
    resonance up to several TeV.
  • An excited quark, an E6 diquark, or even an
    unanticipated new particle!
  • CMS can discover a quark contact interaction up
    to L12 TeV with 10 fb-1.
  • Corresponds to a quark radius of order 10-18 cm
    if quarks are composite.
  • The LHC Physics Center at Fermilab is active in
    jet physics analysis.
  • Mentoring the postdocs and graduate students who
    will analyze first CMS data.
  • Well integrated in the CMS physics organization.
  • We are looking forward to exciting discoveries at
    the TeV energy scale!

37
Advanced Resonance Model E6 Diquarks
  • In superstring theory space has 10 dimensions.
  • 6 unseen dimensions must be compactified.
  • In one compatification proposal each generation
    has 27 particles in E6.

Standard Model
  • D Dc new particles
  • Spin 0, charge 1/3, color triplet.
  • D Dc can give dijet resonances with large cross
    section
  • u d g Dc g u d
  • u and d are valence quarks of the proton with
    large PDFs.

Diquarks
27
SU(3)C X SU(2)L X U(1)
Standard Model
Diquarks
38
Dijet Resonance Cross Sections
  • Resonances produced via color force, or from
    valence quarks in each proton, have the highest
    cross sections.
About PowerShow.com