Search For Higgs At Lhc

24 April. 2006, Khalsa College, Delhi S. Bhattacharya 1http://www.slideshare.net/worldTC

Last of the Last of the Particles?Particles?

SearchSearch for Higgs at LHCfor Higgs at LHC

24 April. 2006, Khalsa College, Delhi S. Bhattacharya 2

Prof. Higgs and his bosonProf. Higgs and his boson• Peter Ware Higgs (born May 29, 1929), FRSE, FRS, until recently held a

personal chair in theoretical physics at the University of Edinburgh and is now an emeritus professor.

• Higgs is best known for his 1960s proposal of broken symmetry in electroweak theory, explaining the origin of mass of elementary particles in general and of the W and Z bosons in particular. This so-called Higgs mechanism predicts the existence of a new particle, the Higgs boson. Although this particle has not turned up in accelerator experiments so far, the Higgs mechanism is generally accepted as an important ingredient in the Standard Model of particle physics. Higgs conceived of the mechanism in 1964 while walking the Cairngorms, and returned to his lab declaring he had had his "one big idea".

• Peter Higgs has been awarded a number of prizes in recognition of his work, including the Dirac Medal and Prize for outstanding contributions to theoretical physics from the Institute of Physics, the 1997 High Energy and Particle Physics Prize by the European Physical Society, and the 2004 Wolf Prize in Physics.

• Many others contributed to the concept – Englert, Brout, Anderson…

Ref: Wikipedia

Higgs boson is also referred as Higgs-Anderson boson(e.g. see Wikipedia)

http://en.wikipedia.org/wiki/May_29

http://en.wikipedia.org/wiki/1929

http://en.wikipedia.org/wiki/FRSE

http://en.wikipedia.org/wiki/Fellow_of_the_Royal_Society

http://en.wikipedia.org/w/index.php?title=Personal_chair&action=edit

http://en.wikipedia.org/wiki/Theoretical_physics

http://en.wikipedia.org/wiki/University_of_Edinburgh

http://en.wikipedia.org/wiki/Emeritus_professor

http://en.wikipedia.org/wiki/1960s

http://en.wikipedia.org/wiki/Broken_symmetry

http://en.wikipedia.org/wiki/Electroweak_theory

http://en.wikipedia.org/wiki/Mass

http://en.wikipedia.org/wiki/Elementary_particles

http://en.wikipedia.org/wiki/W_and_Z_bosons

http://en.wikipedia.org/wiki/Higgs_mechanism

http://en.wikipedia.org/wiki/Higgs_boson

http://en.wikipedia.org/wiki/Particle_accelerator

http://en.wikipedia.org/wiki/Standard_Model

http://en.wikipedia.org/wiki/Particle_physics


Mankind’s ancient questionMankind’s ancient question

न तत सू�यो� भातित न चनदतरकं� न�मा ति�दयो�त� भातिन कं� त�यो� योमागतिन�

त�मा�ब भानतमा� अन�भातित सू�� तसूयो भासू सू��मिमादमा ति�भातित

In the beginning there was no sun, neither did the moon shine, nor the stars,

man made light was no where.It is Your light that lit up everything else,

Every thing in this world shines from Your light

Where did everything come from? What is everything made up of?


Physicists’ latest answerPhysicists’ latest answer


Names of the actors: MatterNames of the actors: Matter

• All of matter is made up of spin ½ particles• Leptons:• electron (e), muon(), tau() (charge -1

and +1) and 3 neutrinos (charge 0)• Quarks:• Up, down, charm, strange, top, bottom• They have fractional charges (2/3 and -

1/3)!!


Names of the actors: ForcesNames of the actors: Forces

• Forces are carried by spin 1 particles called guage bosons:

• Electromagnetic:photon• Weak: W+-, Z0 • Strong: gluon• Gravitational: I don’t know – may be YOU will

find out one day…• quarks participate in all interactions (i.e. they

can exchange photon, W, Z, gluon)• Leptons can’t exchange gluons


Feynman DiagramsFeynman Diagrams

This is more than just a picture !


Without Higgs…Without Higgs…

• Without Higgs we won’t be here because:

• All fundamental particles will be massless, travelling at the speed of light in vacuum

• Higgs boson – the charge less spin zero massive particle is the quantum of an all pervading Higgs field through which particles move – and interaction with this field gives them mass

According to standard model


How to discover new particles?How to discover new particles?• How do we discover

Higgs?• Good old principle:• Produce the particle by colliding

other particles• Look at decay products• Reconstructruct invariant mass• Look for a peak in the invariant

mass distribution

Measure E,p,

Get the mass of the original particle

E1E2(1-cos(theta12))

Beware of fake products!


ExampleExample


Plan for finding HiggsPlan for finding Higgs• What do we collide? 7 Tera electron Volt

Protons• At what rate? Once every 25 nano

seconds• How often do we expect to see Higgs? A

few every second.• What will they decay to? Could be a pair of

top-antitop or bottom antibottom or two photons or two Z0s…

OK! So we just have to catch these particles and measure E,p


The LHCThe LHC

Z


LHC in LHC in ACTIONACTION


ProtonProton

Proton is a rather complex bag of quarks and gluons


ProtonProtonProton Proton

7 TeV

7 TeV


partonpartonpartonparton

Z

500 GeV100 GeV

Two partons, usually with different momenta collide and often anihilate giving rise to other particlesin the final state

Beam axis

Note: parton = quark, antiquark or gluon


Of quark bondage: JetsOf quark bondage: Jets• There is no free quark in the

world• Quarks and gluons, as they fly

apart from each other – give birth to other quarks and gluons, eventually all these quarks and gluons combine with each other to make pions, nutrons, eta’s rho’s … known as hadrons

• They all more or less fly in the direction of the original quark/gluon and that is JET

• Jets are the only signatures of quarks and gluons that we can see experimentally

Two charm quarks moving apart from each other


Luminosity and cross sectionLuminosity and cross section• If I shoot 1011 protons every 25 ns through another 1011 protons most

of them will sail through.– how many will collide/ sec?– Out of every hundred collition how many will produce Higgs?

• Ans: no. of collisions / sec = (1011X 1011)/25ns/500sq-micron (provided the beam cross section is 500 sq-micron).

• Sigma() is called reaction cross section and contains the entire physics of all possible interactions between the colliding quarks and gluons (calculated by phenomenologists)

• The remaining terms in the formula together are called luminosity(L)

• In general: Number of collisions/sec = L(the actual formula for luminosity is somewhat more complicated, which

takes into account the crossing angle of the beams, lorentz contraction of the bunches etc.)


Higgs production at LHCHiggs production at LHC


Higgs Decays Higgs Decays se

arch

chan

nels


* numbers are for barrel

data taking starts 2007 ?

Startup Luminosity 2X1033 cm-2/s

that is: 10 fb-1 per year

Silicon Tracker15 ( )%T

TT

p p TeVp

2.7% 0.150.5% E

E EE

PbWO4 ECAL

sampling brass HCAL 120

5%E

E E

solenoid4Tesla field

1.0 1.5%@100T

T

pglobal GeV

p

MUON Chambers


The TrackerThe Tracker


The ECALThe ECAL



The HCALThe HCAL


The Muon ChamberThe Muon Chamber



CMS in CMS in ACTIONACTION


Transverse slice through CMS detectorClick on a particle type to visualise that particle in CMS

Press “escape” to exit


CMS Detector: schematic X-sectional view

HCAL

ECAL

TRACKER

h h Two clean electromagnetic clusters(For unconverted photons)

Backgrounds: gg,qq,qgq @low luminosityjet-jet 105 events/sjet+photon 102 events/s2 photon 1 event/12.5sHiggs 1 event/25sh2photon 1 event/10,000s

@low luminosityjet-jet 105 events/sjet+photon 102 events/s2 photon 1 event/12.5sHiggs 1 event/25sh2photon 1 event/10,000s

two photon background

gamma+jet background


hh mass peakmass peak

=646MeVe

ven

ts/5

0M

eV

mfor 130 GeV Higgs

CMS full detector simulation. Ref: CMS Note 2003/033


H H ZZ ZZ 4 4Clean, resolution better than 1GeV

Discovery Luminosity:


Significance (or what we hope…)Significance (or what we hope…)


You can do it too…You can do it too…


Technology

Search For Higgs At Lhc