the latest and greatest tricks in studying missing energy events n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
The latest and greatest tricks in studying missing energy events PowerPoint Presentation
Download Presentation
The latest and greatest tricks in studying missing energy events

Loading in 2 Seconds...

play fullscreen
1 / 42

The latest and greatest tricks in studying missing energy events - PowerPoint PPT Presentation


  • 108 Views
  • Uploaded on

The latest and greatest tricks in studying missing energy events. Konstantin Matchev. With: M. Burns, P. Konar, K. Kong, F. Moortgat, L. Pape, M. Park arXiv:0808.2472 [hep-ph], arXiv:0810.5576 [hep-ph], arXiv:0812.1042 [hep-ph], arXiv:0903.4371 [hep-ph],

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'The latest and greatest tricks in studying missing energy events' - ura


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
the latest and greatest tricks in studying missing energy events

The latest and greatest tricks in studying missing energy events

Konstantin Matchev

With: M. Burns, P. Konar, K. Kong, F. Moortgat, L. Pape, M. Park

arXiv:0808.2472 [hep-ph], arXiv:0810.5576 [hep-ph],

arXiv:0812.1042 [hep-ph], arXiv:0903.4371 [hep-ph],

arXiv:0906.2417 [hep-ph], arXiv:090?.???? [hep-ph]

Fermilab, LPC

August 10-14, 2009

these slides cover

67 pp

46 pp

32 pp

47 pp

37 pp

Total No of pages : 229 pp

These slides cover:
  • “A general method formodel-independentmeasurements of particle spins, couplings and mixing angles in cascade decays with missing energy at hadron colliders”, JHEP (2008)
    • Burns, Kong, KM, Park
  • “Using subsystem MT2 for complete mass determinations in decay chains with missing energy at hadron colliders”, JHEP (2009)
    • Burns, Kong, KM, Park
  • “s1/2min – a global inclusive variable for determining the mass scale of new physics in events with missing energy at hadron colliders”, JHEP (2009).
    • Konar, Kong, KM
  • “Using kinematic boundary lines for particle mass measurements and disambiguation in SUSY-like events with missing energy”, JHEP (2009)
    • Burns, KM, Park
  • “Precise reconstruction of sparticle masses without ambiguities”, JHEP (200?)
    • KM, Moortgat, Pape, Park
met events experimentalist s view
MET events: experimentalist’s view
  • What is going on here?

This is why I am

interested in MET!

why met signatures are important to study

e

e

b

n

W

t

W

n

W

n

W

n

t

e

b

e

Why MET signatures are important to study
  • WIMP dark matter? Perhaps, but see J. Feng’s talk for counterexamples.
  • Challenging – need to understand the detector very well.
  • Guaranteed physics in the early LHC (late Tevatron) data!
this talk is being given

The experimentalist asks:

The theorist answers:

Is it possible to have a theory

model which gives signature X?

Yes.

No.

Are there any well motivated

such models?

You bet. Let me tell you about those. Actually I have a paper…

No. But I’m the wrong person to ask anyway.

Is there any Monte Carlo which

can simulate those models?

MC4BSM workshops: http://theory.fnal.gov/mc4bsm/

This talk is being given
  • by a “theorist”
met events theorist s view
MET events: theorist’s view
  • Pair production of new particles (conserved R, KK, T parity)
  • Motivated by dark matter + SUSY, UED, LHT
    • How do you tell the difference? (Cheng, KM, Schmaltz 2002)
  • SM particles xi seen in the detector, originate from two chains
    • How well can I identify the two chains? Should I even try?
      • What about ISR jets versus jets from particle decays?
  • “WIMPs” X0 are invisible, momenta unknown, except pT sum
    • How well can I reconstruct the WIMP momenta? Should I even try?
      • What about SM neutrinos among the xi’s?
in place of a summary
In place of a summary

pessimism

optimism

pessimism

optimism

tuesday invariant mass studies

MET

Tuesday: invariant mass studies

Hinchliffe et al. 1997

  • Study the invariant mass distributions of the visible particles on one side of the event
  • Does not rely on the MET measurement
  • Can be applied to asymmetric events, e.g.
    • No visible SM products on the other side
    • Small leptonic BR on the other side
  • Well tested, will be done anyway.

ATLAS TDR 1999

Nojiri et al. 2000

Allanach et al. 2000

Gjelsten et al. 2004

KM,Moortgat,Pape,Park 2009

thursday spin measurements
Thursday: spin measurements

Burns, Kong, KM, Park 08

  • Separate the spin dependence from all the rest
    • Parameterize conveniently the effect from “all the rest”
  • Measure both the spin (S) as well as all the rest:
in place of a summary1
In place of a summary

pessimism

optimism

pessimism

optimism

wednesday m eff h t and s min
Wednesday: Meff (HT) and Smin

F. Paige hep-ph/9609373

Konar, Kong, KM 2008

in place of a summary2
In place of a summary

pessimism

optimism

pessimism

optimism

the cambridge m t2 variable
The “Cambridge” mT2 variable
  • A. Barr, C. Lester and P. Stephens, “mT2 : the truth behind the glamour”
    • hep-ph/0304226
  • C. Lester and D. Summers, “Measuring masses of semiinvisibly decaying particles pair produced at hadron colliders”
    • hep-ph/9906349
mass measurements
Mass measurements
  • Single semi-invisibly decaying particle

e

W

n

  • Use the transverse mass distribution
mass measurements1
Mass measurements
  • A pair of semi-invisibly decaying particles

e

Lester,Summers 99

Barr,Lester,Stephens 03

W

n

n

W

m

  • Use the “stransverse” mass (mT2)

Kong, KM 04

  • This formula is valid for mn=0.
definition of mt2
Definition of MT2

e

Lester,Summers 99

Barr,Lester,Stephens 03

W

n

n

W

m

A pair of semi-invisibly decaying particles

If and were known:

But since unknown, the best one can do :

what is m t2 good for
What is mT2 good for?
  • So what? We still don’t know exactly the LSP mass
  • Provides a relation between the two unknown masses of the parent (slepton) and child (LSP)
    • Vary the child (LSP) mass, read the endpoint of mT2
lsp mass measurement from kinks
LSP mass measurement from kinks

Varying PT

ISR with some PT

  • A kink appears at the true masses of the parent and the child

Include pT recoil due to ISR

how big is this kink
How big is this kink?

FR

FL

It depends on the hardness of the ISR and the mass spectra

origin of the m t2 kink
Origin of the MT2 “kink”

FR

  • A kink may arise due to
    • “Composite” particle on each side
    • ISR recoils
    • Heavy particle decays

FL

Cho, Choi, Kim, Park 2007

Barr, Gripaios, Lester 2007

Burns, Kong, KM, Park 2008

subsystem m t2
Subsystem MT2

Burns, Kong, KM, Park 2008

  • Generalize the MT2 concept to MT2(n,p,c)
    • “Grandparents” (n): The total length of decay chain
    • “Parents” (p): Starting point of MT2 analysis
    • “Children” (c): End point of MT2 analysis
mass determination subsystem mt2
Mass determination: Subsystem MT2

Burns, Kong, KM, Park 2008

Sub MT2

NP : Number of unknownsNm : Number of measurements

NP= number of BSM particles = n+1

Nm=

How many undetermined

parameters (masses) are left?

n : Length of decay chain

in place of a summary3
In place of a summary

pessimism

optimism

pessimism

optimism

mass determination polynomial method
Mass determination – polynomial method

Cheng,Gunion,

Han,Marandella, McElrath, 2007

Sub MT2

n : Length of decay chain

subsystem m t2 applied to top pairs
Subsystem MT2 applied to top pairs

MT2(220)

e

b

t

W

n

n

W

t

b

e

Don’t assume prior knowledge of the W and neutrino masses

Traditional MT2 variable: MT2(2,2,0)

Combinatorial problem!

subsystem m t2 applied to top pairs1
Subsystem MT2 applied to top pairs

MT2(210)

e

b

t

W

n

n

W

t

b

e

No combinatorial problem!

Genuine subsystem variable: MT2(2,1,0)

subsystem m t2 applied to top pairs2
Subsystem MT2 applied to top pairs

MT2(221)

e

b

t

W

n

n

W

t

b

e

No combinatorial problem!

Another genuine subsystem variable: MT2(2,2,1)

mass measurements in the ttbar system
Mass measurements in the TTbar system
  • We have just measured three MT2 endpoints which are known functions of the hypothesized Top, W and neutrino masses.
    • MT2(2,2,0)
    • MT2(2,1,0)
    • MT2(2,2,1)
  • Problem: they are not independent, need an additional measurement
    • MT2(1,1,0)
    • Endpoint of the lepton+b-jet inv. mass distribution
m t2 applied to w pairs
MT2 applied to W pairs

e

W

n

W

n

e

MT2(110)

No combinatorial problem!

Yet another MT2 variable: MT2(1,1,0)

full t w nu mass determination
Full T, W, Nu mass determination

M(bl)max =

b

e

t

W

n

Correct bl pairs

W

n

t

b

e

Hybrid method: Inv. mass Subsystem MT2

on a positive note

e

e

b

b

LSP

t

W

n

stop

chargino

stop

chargino

LSP

W

n

t

b

e

b

e

On a positive note

Barr, Gwenlan 2009

  • MT2 can be used for background suppression
  • The dominant background to SUSY is TTbar
  • For illustration, let us choose a very challenging example with an identical signature
    • Stop pair production, with decays to chargino and LSP.
top stop separation
Top-Stop separation
  • What do we know about the stop sample?
    • Absolutely nothing.
  • What do we know about TTbar?
    • The endpoints of the subsystem MT2 variables that we just saw. All TTbar events fall below these endpoints, and there are none above!

KM, Park preliminary

combination m t2 cut
Combination MT2 cut
  • Accept the event if it is beyond at least one of the three subsystem MT2 endpoints.
  • This greatly enhances the signal acceptance, compared to a single MT2 cut, or an HT cut.
wedgebox technique
Wedgebox technique
  • Scatter plot of the invariant masses of the visible decay products on both sides

Bisset,Kersting,Li,Moortgat,Moretti,Xie 2005

m tgen
MTgen

Lester,Barr 2008

  • Inclusive application of MT2: minimize MT2 over all possible partitions of the visible decay products between two chains
    • Brute force way to deal with combinatorial issue
    • Preserves the endpoint, provides a measure of the scale
    • Endpoint smeared in the presence of ISR
    • Does not measure the LSP mass
    • Difficult to interpret when many processes contribute
polynomial method
Polynomial method

Cheng,Gunion,Han,Marandella,McElrath 2007

Cheng,Engelhardt,Gunion,Han,McElrath 2007

Cheng,Han 2008