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LHC Physics - Experiments. M.Bosman IFAE-Barcelona. Baeza – February 4-8, 2008. Yesterday’s outline. Why a Large Hadron Collider? Accelerator challenge Detector concepts and performance Before the first data With the first data.

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lhc physics experiments

LHC Physics - Experiments

M.Bosman

IFAE-Barcelona

Baeza – February 4-8, 2008

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

yesterday s outline
Yesterday’s outline
  • Why a Large Hadron Collider?
  • Accelerator challenge
  • Detector concepts and performance
  • Before the first data
  • With the first data

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide3
With the very first collision data ( 100 pb-1) at 14 TeV
  • We will commission/calibrate the detector in situ in the LHC environment,

tune the software tools (simulation, reconstruction, etc.)

  • Perform first physics measurements of Standard Model processes:

e.g. cross-sections for W, Z, top, QCD jets with 10-30% precision;

PDF; etc. start to constrain theory and Monte Carlo generators

  • Maybe some early discovery?

More luminosity (at least 1 fb-1) will be needed to:

  • Precise SM physics
  • Put on firmer grounds any deviations and excesses
    • clear signatures of new physics
    • understand its nature and measure parameters

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide4
The path toward higher and higher luminosity

J.Wenninger

CERN-FNAL HC School

June 2007

Year ? (present schedule) 2008 2009 2009-2010 > 2010

 Ldt ? (my guess)up to 100 pb-1 1-few fb-1 O(10 fb-1) O(100 fb-1)

Note: at regime, ~ 6x106 s of pp physics running per year

 ~ 0.6 fb-1 /year if L= 1032

~ 6 fb-1 /year if L= 1033

~ 60 fb-1 /year if L= 1034

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

today s outline
Today’s outline
  • Searching for SUSY and measuring properties
  • Searching for the Higgs and measuring properties
  • Some examples of other Beyond the Standard Model physics

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

susy model framework
SUSY Model Framework

Minimal SuperSymmetric Extension of the Standard Model (MSSM) contains > 105 free parameters

Consider specific well-motivated model framework in which generic signatures can be studied:

Often assume SUSY broken by gravitational interactions mSUGRA/CMSSMframework

unified masses and couplings at the GUT scale

 5 free parameters (m0, m1/2, A0, tan(), sgn()).

R-Parity assumed to be conserved.

Inclusive studies : scan parameter space

Exclusive studies: use benchmark points in mSUGRA

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide7
“focus point”

Allowed 2 band a(exp)– a(e+e– SM)

“Higgs funnel”

Excluded by direct searches

dark matter

  • From direct accelerator searches

“low mass point”

“bulk region”

  • From indirect accelerator searches

“coannihilation point”

  • From cosmology

SUSY Model Framework

  • Choose a few “characteristic” points
    • At the limit of experimental exclusion (SU4)
    • “Typical” point (SU3, light LSP and sfermions)
    • Special-feature points (SU1, SU2, SU6)

0 large Higgsino fraction

J. Ellis et al, 2006

SU2

SU2

  • in the allowed regions
  • Since mSUGRA has only 5 parameters, it is already well constrained from data !

m(LSP) ~ ½m(A,H)

m0 (GeV)

SU6

SU6

m(LSP) ~ m(NLSP)

SU4

SU4

SU3

SU3

no neutral LSP

SU1

SU1

m½ (GeV)

t-channel for light sleptons

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide8
Can we discoverSupersymmetry ?

For

expect 10 evts/day at L=1032

  • If it is at the TeV scale, it should be found “quickly” ….
  • large (strong) cross-section for
  • spectacular signatures (many jets, leptons, missing ET)

Tevatron 95% C.L. reach:

up to ~400 GeV

LHC reach for gluino mass

Jets + ETmiss

Ldt Discovery

of well understood data (95% C.L. exclusion)

0.1-1 fb-1 (2009) ~1.1 TeV (1.5 TeV)

1 fb-1(2009-2010) ~1.7 TeV (2.2 TeV)

300 fb-1 (ultimate) up to ~ 3 TeV

100 pb-1

m ~ 700 GeV

m ~ 1 TeV

Hints with only 100 pb-1 up to m~1 TeV, but

understanding backgrounds requires ~1 fb-1

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

crucial to understand e t miss
Crucial to understand ETmiss

SM ETmiss sources

Z  + n jets

W  l + n jets

W + (n-1) jets ( fakes jet)

Use Z  l+l- + n jets (e or ) as control sample

Tag leptonic Z and use to validate MC / estimate ETmiss from pT(Z) & pT(l)

Alternatively tag W  l + n jets and replace lepton with n (0l):

higher stats

biased by presence of SUSY

(Zll)

ATLAS

Preliminary

(Wln)

ATLAS

Preliminary

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

other susy useful signatures
Other SUSY useful signatures
  • Jets + 0 leptons + ETmiss
  • Jets + 2 leptons + ETmiss

ATLAS

„Bulk“ point

Meff (GeV)= ETmiss+ pT,1+ pT,2+ pT,3+ pT,4

4 Jets with PT>50 GeV,

PTjet1 >100 GeV

ETmiss > max(100 GeV, 0.2Meff )

Transverse sphericity ST>0.2

to reduce dijet background

(ETmiss, Jet1-3) > 0.4

Two isolated leptons (e/m) with PT>20 GeV

Transverse mass MT(l, ETmiss) > 100 GeV to reduce W+jet background

HP Beck - LHEP Bern

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

Standard Model and Beyond in the LHC Era

Valparaiso, January 7-12 2008, Chile 10

slide11
Once SUSY has been discovered, measure it !
  • Inclusive SUSY discovery will provide indications about underlying scenario:
    • SUSY mass scale and cross section
    • R-parity (ET,miss spectrum), Gauge-mediated SB (hard ’s, NLSP’s, long-lived gluinos), large tan(’s)
  • However, fundamental SUSY parameters (masses, couplings, spins, …) can only be inferred from direct measurements of sparticle properties
  • Exclusivereconstruction of SUSY final states is possible:
    • Select final state signatures that identify exclusive decay chains (e.g., 2 or 3 final state leptons)
    • Fit, e.g., masses of particles in decay chain
  • Remarks:
    • R-parity conservation: at least two LSP’s in event  no direct mass peaks, but kinematic “endpoints”
    • These endpoints depend on the masses of the involved particles
    • When cascade of at least 3 consecutive two-body decays occurred  full kinematics accessible

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide12
Di-lepton kinematic endpoint:

leptons have same flavour !

(use for background fighting)

Subtracting  ′ background

di-lepton mass (GeV)

di-lepton mass (GeV)

Exclusive Reconstruction: An Example

  • Let’s look again at the process:

3 two-body decays !

“edge” of kinematic endpoint

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide13
Theoretical kinematic endpoint of the q+–system:

Choose jet that minimisesmq to determine endpoint

Choose jet that maximisesmq to determine threshold

endpoint fit

threshold fit

… Also Reconstructing the Jet

  • We can also use jets from:

3 two-body decays !

  • One can also look into the corresponding q endpoints and thresholds
  • In total 6 distributions can be fit to determine the corresponding sparticle masses
    • An ATLAS study for 100 fb–1 finds mass precisions of 12% (1), 6% (2), 9% (R~), 3% (qR~)
  • Thorough experimental and theoretical work will be necessary to control the backgrounds from other jet-lepton(-lepton) combinations in the event and initial state radiation of jets

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide14
To reject combinatorial background, use only b jets

ATLAS estimate for 300 fb–1, with two peaks for the mass eigenstates b1 and b2

ATLAS estimate for 300 fb–1, with simulated mgluino = 588 GeV, giving (mgluino) of O(10 GeV)

… Reconstructing sbottom and gluino Masses

  • Let’s look again at the full decay chain:

Close to the +–endpoint, the 2 (~in rest) has residual momentum:

The neutralino masses are known from the preceding analysis  2 4-vector is known

  • The gluino and sbottom masses are then obtained from the bb2 and b2 invariant masses, respectively
  • The sbottom mass is then best obtained from mass difference (reduces errors)
  • One can do better by using all events
  • (not only those at +–endpoint) together
  • with a global fit to full decay kinematics

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide15
spin-0

spin- ½

mostly bino

phase space

If we Discovered Something… is it SUSY ? (*)

  • If observed, the signatures discussed so far provide strong hints for SUSY
  • To verify that the new fields are indeed the SM Superpartners  measure their spins
  • Not easy at LHC, but (hopefully) possible

“far” lepton

“near” lepton

Decay chain sensitive to fermionic character of 2

  • Invariant mass of quark-lepton system depends on the polarization of neutralino

quark

near lepton

Invariant mass of q system strongly charge-dependent

θ*

(at rest)

  • Problem: this effect is inverted for anti-squark decay !

(*) For example, UED KK signals with WIMP LKPs could fool us !

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide16
Residual charge asymmetry in invariant mass

Residual mass distributions after detector simulation

150 fb–1

squark decay

anti-squark decay

spin-½

spin-0

parton-level distributions

spin-½ (parton level)

Measuring the 2 Spin

  • Experimental Problems:
    • Cannot distinguish “near” from “far” lepton
    • Cannot distinguish quark from anti-quark jet
  • Plot mq for both leptons
  • Fortunately: LHC produces ~2x more squarks than anti-squarks
  • To 1) : Some residual asymmetry left from boost of slepton in the 2 rest frame
    •  see quark-lepton(far) invariant mass (parton-level):
  • Measure the asymmetry:

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide17
Constraining the MSSM Parameter Space
  • SUSY fits to observables usually work in particular scenario (mSUGRA, GMSB, …)
  • Mass differences (edges), sbottom & gluino masses can be measured, LSP less accurate
  • But: there are ambiguities on decay chain in the kinematic edge results
  • Cross sections versus mass scale can be used as additional information
  • Relative abundance of OSSF, OSOF, SSSF, SSOF lepton pairs model dependent
  • But: decay chains with leptons may simply not exist

In general:

Lester-Parker-White

hep-ph/0508143

  • Use statistical tricks to solve multi-parameter problem (Markov chains)
  • One can try to “inverse” the map of (1808) LHC signatures to (15 dim.) theory parameter space

Arkani-Hamed et al.

hep-ph/0512190

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide18
or

Gauge Mediated SUSY Breaking ?

  • Messenger scale MmMPl, SUSY breaking scale Fm (1010 GeV)2
  • Very light gravitino ( 1 GeV) is LSP
  • Signatures determined by NLSP: either neutralino or slepton …
  • and by Cgrav parameter determining lifetime of NLSP

Distinguish 4 cases:

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

some additional remarks about susy
Some additional remarks about SUSY
  • Yet, another possible scenario: SUSY could also break R-parity

(The signature could be  ’s in final state from 0 ~ decays)

etc...

 Proceed SUSY search as model-independently as possible

Check for anomalies:  ’s,  ’s, strange t ’s

  • We may about learn about SUSY from the Higgs sector, seelater
  • Signals due to other phenomena could look like SUSY

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

searching for the higgs
Searching for the Higgs

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide22
2006

2003

K factors included

Both LHC experiments have been designed to discover a SM Higgs on all the

expected mass range. Goal achievable after a few years of running at low L.

More than one channel available over most of the mass range.

Recently, most of the studies have been focused on the discovery of a light

Higgs (MH<200 GeV) during the initial lower luminosity period (L=1033 cm-2 s-1).

This is not the easiest region at LHC: for higher masses, the HZZ4l

represents the golden channel (at least up to 500-600 GeV)

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

best strategy to search for the higgs
Best strategy to search for the Higgs ?

A. Djouadi

“Compromise” between various factors: production mechanism, decay mode, trigger, background levels. In general final states with leptons or photons in the final state are easier to handle at the LHC.

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

inclusive analysis
Inclusive analysis

Do not use any feature of the production mechanism.

The gluon-gluon fusion channel

has the highest rate.

The gluon-gluon fusion process is dominated by top and bottom quark

loops. The large size of the top Yukawa coupling and of the gluon density

functions explains the high production rate for this process.

One makes less assumptions than in other search strategies. However to reduce the backgrounds need to have a clean final state with leptons or photons.

Decay channels accessibles:

H, HZZ(*), HWW(*)

24

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide25
H→γγ

Need good photon ID to reduce g+jet and jet+jet backgrounds well below

the irreducible one: R~103for eg≈80%.

The background of isolated high PTp0 is particularly dangerous. Make use of:

Photon isolation (with tracker and calorimeter)

Study of shower shapes in calorimeter

Photon conversion recovery:

about 50% g convert before the calorimeter in the tracker material

(on average 1 X0). Need to be reconstructed using tracking information

ATLAS

Signal:

Simplest analysis: count events in mass windows. This gives a S6 for 30 fb-1 at MH=130 GeV

Level of background will be known from data. A 10-15% sys error from the fit to the background has been estimated.

25

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide26
H→γγ

The significance can be increased (~30-40%) including additional handles:

Builds a likelihood including also

gg PT (background has softer spectrum and less pronounced rise at low PT)

cosq*, the photon decay angle in the H rest frame with respect to the H flight direction in the lab rest frame (the background distribution is somewhat enhanced for collinear photons)

ATLAS:

Uses 6 variables: isolation of each photon, ETi/Mgg, |h1-h2|, PLgg

(ETi and hi are the transverse energy and pseudorapidity of i-th g)

CMS:

CMS

26

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide27
H→ZZ*→4l

Features:

Clean channel: can see peak over background; low statistic for MH<130 GeV and MH~170 GeV. Can use 4e, 4m, 2e2m.

Trigger:

High PT single and dilepton triggers

Irreducible: qq,gg→ZZ*/g*4l

Reducible: Zbb→4l, tt→4l

Backgrounds:

Analysis:

Need reconstruction of relatively low PTelectrons and muons

Need good electron and muon energy resolution (1-2%); recover

brems effects for electrons

Reducible background is handled via lepton isolation (tracking and

calorimeter) and impact parameter cuts

Background level can be estimated from sidebands

27

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide28
CMS study
  • Uncertainty includes:
    • Stat error on the estimation of the background from side bands (from 2 % to 13% for MH<200 GeV/c)
    • Theory uncertainty on the bkg shape (0.5% to 4.5%)

MH=200 GeV

MH=140 GeV

28

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide29
H→WW*→2l2ν

Particularly interesting for 2MW

However no mass peak and high background that needs to be well

understood.

Features:

Trigger:

High PT dilepton and single lepton triggers

Continuum WW, WZ, ZZ (including gg→WW)

tt production and single top production tWb

also: Z, bb, W+jets

Backgrounds:

Select events with exactly two isolated (tracking and calorimeter) opposite sign primary leptons and ETmiss.

Apply a jet veto in the event.

Cut also on small dilepton mass and opening angle.

Analysis:

29

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide30
CMS study
  • Estimated background uncertainties:
  • tt±16%
  • WW ±17%
  • Wt ± 22%
  • gg→ WW ± 30%

(from control samples)

(from theory)

30

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide31
Vector Boson Fusion

Features:

Originally studied for the medium-high mass range (MH>300 GeV), this process has been found useful also in the low mass range.

Lower rate than gluon-gluon fusion but clear signature.

Signature:

Two distinct signatures:

Two forward “tag” jets (large h separation with high-pT) with large Mjj

No jet activity in the central region (between the two tag jets): jet veto

31

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide32
Vector Boson Fusion

Experimental issues:

Good efficiency for the reconstruction of forward jet is required.

There are also uncertainties on the robustness of the jet veto with respect to radiation in the underlying event and to the presence of pile-up.

So far VBF channels have been studied at low luminosity only.

ATLAS

Channels:

qqH  qq

qqH  qqWW(*)with WW(*)  ln ln and ln jj

qqH  qq withtt lnnlnn, lnnhadand had had

32

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide33
qqH→qq→qq l had 

Experimental issues:

Need good ETmiss resolution

Need identification of hadronic t’s

In the end H mass resolution ≈9%.

Dominant background:

Z+jets with Z→tt

(dangerous for low Higgs masses)

Control samples for the background:

Z+jets with Z→ee, Z→mm

For 30 fb-1, at MH=135 GeV, expect about 8 signal events with a significance of about 4 (CMS)

CMS

33

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide34
Other search channels

Associated productions

pp → WH, ZH, ttH with W → ln, Z → ll or Z → nn

Low rates.

Leptons from W, Z and t→Wb→lnb can provide trigger and discrimination from background. Provide useful channels with higher integrated luminosity (~100 fb-1).

34

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

summary
Summary

2003

2006

K factors included

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

combining atlas cms
Combining ATLAS + CMS

For mH>140 GeV an accumulated statistics of order ~1 fb−1 might be sufficient

For low mass higgs (< 140 GeV) the situation is more complex: around 5 fb-1 are needed and several channels need to be combined

In both cases it is assumed that the detectors and the data are well understood.

36

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide37
Measurement of Higgs properties

Mass measurement

Best channels for this measurement are

H→gg and at higher masses H→4l.

CMS estimates a precision <0.3 % up to 350 GeV (stat error only) with 30 fb-1

ATLAS estimated about 0.1 % up to 400 GeV with 300 fb-1 including sys errors.

The precision will be limited by the uncertainty on the lepton and photon energy scale, which is expected to be at

the level of 0.1%

37

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

higgs properties
Higgs properties

To define Higgs properties (mass, coupling, spin) more luminosity

than ~30 fb-1 is needed (a few examples given below)

  • Higgs spin (CP):In the SM, H has JPC=0++
    • If we observe the process ggH or H then spin 1 is excluded
    • For MH>200 GeV, study spin/CP from HZZ4l
    • Exclusion can be deduced from  and  distributions

Atlas-sn-2003-025

Θ polar angle of the decay

leptons relative to the Z

Φ angle between the

decay plane of the two Zs

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

higgs properties39
Atlas note phys-2003-030Higgs properties

Higgs couplings:Concentrate on low mH scenario and define 3 steps:

1st step: assume spin 0 and measure  x BR

in different channels

2nd step: assume only one H and

measure the ratio of BRs

Relative error for the

measurement of rates  x BR

Relative error for the

measurement of relative BR

3rd step: assume no new particles on the loop,

no strong coupling to light fermions and

express rates and BR as a function

of 5 couplings gw,gZ,gtop,gb,g

like for example:

(VBF): aWF.gW2+aZF.gZ2

BR(): (b1.gW2 – b2.gtop2)/H

Relative error for the measurement

of relative couplings

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

mssm higgs searches overall discovery potential 300 fb 1
MSSM Higgs searches/ overall discovery potential (300 fb-1)

Some remarks

from this plot

  • In the whole parameter space
  • at least 1 Higgs boson is observable
    • in some parts >1 Higgs
    • bosons observable
  • But large area in which only one
  • Higgs boson observable

Basic question: Could we distinguish between

SM and MSSM Higgs sector

- e.g via rate measurements?

Result assuming no HSUSY

- On going studies to include Susy decays

of Higgs bosons e.g H±χ ±1,2χ01,2,3,43l+ETmiss

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

mssm higgs searches distinguish between sm and mssm higgs sector
MSSM Higgs searches/ distinguish between SM and MSSM Higgs sector

Basic question: Could we distinguish between SM and MSSM Higgs sector

(e.g via rate measurements?)

Method: - Looking at VBF channels (30 fb-1) and estimate the sensitivity from rate (R) measurements

- Compare expected rate R in MSSM with prediction from SM

exp = expected error on the

ratio in the particular

MSSM parameter space

Assuming knowing Mh mass precisely

No systematic errors included

No systematic errors included

(study ongoing)

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

conclusion on higgs search
Conclusion on Higgs search
  • The LHC experiments are well set up to explore the existence of a Standard Model or MSSM Higgs bosons
  • The full Standard Model mass range and the full MSSM parameter space can be covered (CP-conserving models)
  • in addition: important parameter measurements (mass, spin, ratio of couplings) can be performed, vector boson fusion channels are important
  • In general, experiments are well prepared for unexpected scenarios
  • more difficult:
    • invisible Higgs boson decays or NMSSM models
    • measurement of Higgs boson self coupling

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

b eyond s tandard m odel shopping corner
Beyond Standard Model Shopping Corner
  • not complete - your favorite may not be mentioned here...
  • SuperSymmetry
    • sparticles, charginos, neutralinos, gravitino
  • Little Higgs SU(5)
    • extra gauge bosons ZH, WH, AH, heavyTop quark (T), 5 Higgs 0,  
    • cure hierarchy problem without SUSY
  • Left-Right Symmetric models SU(3)LSU(2)RSU(2)L U(1)B-L
    • extra gauge bosons W´ , Z´
  • Dynamical Electro-Weak Symmetry Breaking (Higgs-less models)
    • Technicolor techni-pion pT, techni-rho rT, techni-omega wT,...
    • Top Condensate (Topcolour Z´, Topgluon gt)
  • Extra Dimensions
    • Kaluza Klein states of particles and gravitons
    • micro black holes
  • GUT´s e.g. exceptional group E6 or SO(10) or, ... to embed SM group
    • extra gauge bosons W´ , Z´
    • Diquarks, ....
    • Heavy quarks Q, heavy leptons L, heavy RH Neutrinos N
  • Many of these new states predicted to be produced with LHC
  •  Looking for new heavy state resonances with ATLAS
slide44
Large Extra Dimensions (ADD)
  • The most direct manifestation of EDs would be the presence of KK gravitons: GKK
  • Tiny graviton coupling:
    • MPl replaced by new fundamental scale MD in 4+d dimensions
    • (partonic) cross section:  ~ (√s / MD2)d can be macroscopic
  • The produced gravitons do not interact in detector
  • Signature: mono-jet or high-ET + ET,miss, no lepton ( veto)

100 fb-1

  • ET,miss distribution for signal for varying MD and d, and for the dominant background
    • Can probe ED up to MD ≈ 9 TeV with 100 fb-1
    • No sensitivity to larger scales or EDs at LHC
    • In case of a discovery, it will be difficult to extract both MD and d

ETmiss (GeV)

ATL-SN-2001-005

HP Beck - LHEP Bern

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

Standard Model and Beyond in the LHC Era

Valparaiso, January 7-12 2008, Chile 44

large extra dimensions add
Large Extra Dimensions (ADD)
  • Virtual gravitons can change the Drell-Yan cross section: pp X + +–,  leading to large +–,  invariant mass tails

Allanach et al JHEP12(2002)039

mG up to 2080 GeV for k/MPl=0.01

at 5 σ after 100 fb-1

HP Beck - LHEP Bern

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

Standard Model and Beyond in the LHC Era

Valparaiso, January 7-12 2008, Chile 45

slide46
Entering Trans-Planck Scales: Black Holes

Strong gravity in extra dimensions allows black hole production at colliders

Cross section BH ~ r2, where r is Schwarzschild radius in 4+d dimensions

With MD ~ 2–3 TeV  BH ~ O(pb)  fast discovery for MBH < 4 TeV, d = 2-6

Fast ( ~10–27 s) thermal decay via Hawking radiation, TH ~ MD·(MD/MBH)1/(d+1)

It may be possible to determine from the observed final state energy spectrum and the BH cross section the characteristic Hawking temperature TH of the BH

TH can then be related to the mass of the BH (through r) and the number of EDs

Black hole universally and spherically evaporating into leptons, photons and jets in ATLAS. Final state multiplicity increases with MBH

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

black hole event in atlas
Black Hole Event in ATLAS

HP Beck - LHEP Bern

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

Standard Model and Beyond in the LHC Era

Valparaiso, January 7-12 2008, Chile 47

slide48
LHC vs time: a (wild) guess ?

?

L=1035

3/10/2014

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

48

final remark
Final remark
  • Experimentalists cannot afford to have theoretical prejudice.
  • Because most new-physics signatures are ambiguous
  • Only the combination of observations and precision measurements can guide us to the fundamental theory

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

back up slides
BACK-UP SLIDES

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide51
x-sections and event rates @ =1033cm-2s-1

High-pT QCD jets

q

g

g

q

W, Z

g

Higgs mH=150 GeV

H

t

q

g

W, Z

q

g

g

108 Hz

2-3 / beam crossing

soft inelastic interactions

~2 kHz

few 100 Hz

~ 1 Hz

top

~2 /minute

~5 /hour

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide52
Constraining the MSSM Parameter Space
  • SUSY fits to observables usually work in particular scenario (mSUGRA, GMSB, …)
  • Mass differences (edges), sbottom & gluino masses can be measured, LSP less accurate
  • But: there are ambiguities on decay chain in the kinematic edge results
  • Cross sections versus mass scale can be used as additional information
  • Relative abundance of OSSF, OSOF, SSSF, SSOF lepton pairs model dependent
  • But: decay chains with leptons may simply not exist

In general:

Lester-Parker-White

hep-ph/0508143

  • Use statistical tricks to solve multi-parameter problem (Markov chains)
  • One can try to “inverse” the map of (1808) LHC signatures to (15 dim.) theory parameter space

Arkani-Hamed et al.

hep-ph/0512190

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide53
A light SM Higgs boson (mH < 180 GeV): who will find it first ?

LHC

pb

Tevatron

pb

  • Main search channels Tevatron Main search channels LHC
  • mH~115 GeV WH  lbb H  
  • ZH  bb qqH  qq
  • ttH  lbbX (t.b.c.)
  • mH~160 GeV H  WW  ll H  WW  ll
  • qqH  qqWW  qqll
          •   ZZ*  4l

Cross-section

too small

at Tevatron

Huge backgrounds at LHC

(LHC)/(Tevatron):

~70 gg  H

~ 60 qqH  qqH

~10 qq WH/ZH

for mH<200 GeV

 channels being

explored also at

Tevatron

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide54
Needed Ldt (fb-1)

of well-understood data

per experiment

ATLAS

(2003)

30 fb-1

 1 fb-1 for 95% C.L. exclusion

 5 fb-1 for 5 discovery

over full allowed mass range

Final word about Higgs

mechanism by 2010?

10

1

H  ZZ* 4l, 10 fb-1

ATLAS preliminary,

selections not

optimized

Events / 0.5 GeV

ATLAS + CMS

(March 2006)

10-1

mH (GeV)

Most difficult region:

need to combine several

channels (e.g. H  ,

qqHqq) with small S/B

For mH > 140 GeV discovery easier with H  ZZ(*) 4l

(narrow mass peak, small B). H  WW  ll (dominant

at ~160 GeV) is counting experiment (no mass peak)

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide55
J.Konigsberg, R.Roser and D.Glenzinski, P5 meeting, 24 September 2007

2010

CDF x 2

2009

LEP exclusion

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

D0 projection: 1 error band gives 3 sensitivity over most mass range except ~ 130 GeV

slide56
SUSY Higgs Discovery Potential
  • The neutral and charged bosons from the two SUSY Higgs doublets are produced via:
    • h, H, A: gluon-gluon- or vector-boson fusion, qq scattering with associated vector boson or heavy quark
    • H±: top decay, gluon-bottom fusion, light qq′ annihilation
  • Search strategies for lightest SUSY and SM Higgs are similar
  • Since the Higgs couples to masses, interactions with heavy particles (t, ) are preferred

5 contours

30 fb–1

300 fb–1

The h can be excluded in all parameter scenarios

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

slide57
SUSY Higgs
  • Because of the large parameter space, searches are performed for specific choice of parameters: benchmark scenarios.
  • In the MSSM (but there are also NMSSM preliminary studies):
  • Mhmax: maximum allowed mass for h. Replaces the “maximal mixing” scenario used in the past.
  • No-mixing: as above but no mixing in stop sector. Smaller Mh
  • Gluophobic H: large mixing suppresses gluon fusion production gg→h and h→gg, h→4l
  • Small aeff: small mixing angle of the neutral CP-even Higgs boson can suppress h →bb, tt
  • CPX: CP eigenstates h, A, H mix to mass eigenstates H1, H2, H3. Maximal mixing.

57

M.Bosman LHC Experiments Winter Meeting 08 - Baeza

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