Status of LHC. Proton-on-proton collision at LHC. ( sx 1 x 2 ) = ( sx ). [ “Hard scattering partons” ]. x 1 p. x 2 p. proton. proton. proton beams. Kajari Mazumdar Department of Experimental High Energy Physics Tata Institute of Fundamental Research Mumbai.
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Status of LHC
Proton-on-proton collision at LHC
(sx1x2) = (sx)
[ “Hard scattering partons” ]
Department of Experimental High Energy Physics
Tata Institute of Fundamental Research
IACS Kolkata, September 27, 2010
Today’s, emphasis is on analyses done already with real data.
Results shown are mostly prepared for ICHEP Conference, July, 2010, with data
collected till almost mid-July.
What lies within…?
The probe wavelength should
be smaller than the distance
scale to be probed:
(1 TeV = 1012electronVolt
= 1.6 * 10 -7 Joule)
Tool at hand: Large Hadron Collider (LHC @ CERN)
LHC is the biggest and the most expensive scientific endeavour
Price tag ~ USD 9.1 billion
No. of scientists involved ~ 10K
1232 dipole magnets
+ 400 quadrupole magnets
+ Various other types of magnets
SC coils: 12000 tonnes/7600 km
27 km at 1.9 K (superfluid He)
Vaccuum ~ 10-13 Atm.
100 – 150 m under the surface
Technological progress pushes frontiers of basic science research and there are important spin offs.
Eg. World Wide Web was born to meet the needs of avaiilability of scientific info for HEP experiments of 1990s. today it is a household item which had changed our lifestyle.
Cosmic Recipe: How we understand the universe
Length scale = hc/E
Present wisdom: Behaviour of matter particles can be explained in terms of very few fundamental interactions, which might have evolved over time as the universe cooled down from a single unified one.
GRAND UNIFIED THEORY!
Standard Model (SM) of Particle Physics as of today
10 -40: 10 -5: 10-2: 1
We got to unravel the mystery of mass!
Most plausible: all fundamental particles acquire mass by interacting with an all pervading field, as a consequence, this idea also evokes another fundamental particle, the Higgs boson!
Higgs particle not yetseen most uncomfortable situation.E
==>may be it is too heavy to be produced in the experiments?
Strategy: Heavy particles (by nature unstable) of interesting properties should show up if enough energy is gathered to produce them in the experiment,
provided they existed when the universe was hotter.
LHC is an exploratory, high energy, high intensity machine which can produce heavy particles of mass upto few TeV.
The primary goal of the LHC is to find the Higgs boson…
… if it isn’t found, to find out why it isn’t there!
Mass spectrum in Standard Model
Quantum corrections to Higgs boson mass require some New Physics at TeV energy scale.
The nature of this Beyond Standard Model physics is not known, though several contenders are more favourable, eg., SuperSymmetry.
New Physics also invokes new set of additional particles!
Further problem with SM
even with a single Higgs
Nature has various symmetries (translational, rotational, ..) and related
conservation laws: guiding principles in theoretical formulations.
Some of the symmetries are also broken, sometimes spontaneously.
Eg. behaviour of ferromagnet wrt temperature: above Curie point, the spin
alignments are all random. Below critical temperature, the alignment direction is degenerate.
Below C point
Above C point
In particle physics, symmetry considerations required, carriers of weak interaction (W, Z bosons) also to be massless as photon, carrier of EM interaction.
Spontaneously broken electroweak symmetry endows masses to W,Z bosons and various fundamental particles, via Higgs mechanism this is still a postulate.
Experiments at LHC
ATLAS, CMS: general
purpose p-p experiment.
ALICE: study of quark-gluon plasma in heavy ion collisions.
What happens in LHC experiment
Mammoth detectors register signals for
Energetic, mostly (hard) inelastic collisions
involving large momentum transfer.
Basic features in hadron collisions
Most sophisticated and complex detectors for general-purpose
physics, planned, constructed by thousands since last 20/15 years
107 electronic readout channels, to be ready every 25 ns
Higgs event in CMS
one “good” event (e.g Higgs in 4 muons )
+ ~20 minimum bias events)
All charged tracks with pt > 2 GeV
Reconstructed tracks with pt > 25 GeV
Event size: ~1 MByte Processing Power: ~X TFlop
The GRID:the new information Super highway.
LHC employs a novel computing technology, a distributed computing and data storage infrastructure: to meet the unprecedent challenge of data processing.
250 Million events simulated at TIFR during April ‘09 to March.’10. ~ 300 TB storage
GRID computing centres for regional scientists at : TIFR for CMS experiment and VECC for ALICE experiment.
First 5 minutes!
Prologue for physics from collision
to understand and optimize the
detector performance : 10 billion events analysed.
need high instantaneous luminosity to have enough number of even rarer events produced within a relatively short time period higher the integrated luminosity, quicker we can probe with greater significance.
Even at low luminosity, collision
data has been extremely important
for studying various features of
hadron interactions led to paper
publications by various collaborations, sometimes within
few days of data collection!
Strategy of LHC experiements
Charged Hadron Multiplicity
Important to study particle production model,
mostly non-perturbative regime
Steep rise in average number
Charged particle multiplicity grows faster
than predicted in most of the models.
Rapidity distribution, expected to be flat
at h = 0.Rapidity and pseudo-rapidity
values are numerically different for pions,
kaons with momentum of few hundred MeV
Charged Hadron Momentum distribution
Different pieces in the cartoon are indeed connected.
2-particle correlations can be studied in terms of independent clusters, whose
size and density have energy dependence.
Correlations between 2 particles are stronger than described in Monte Carlo.
Correlations between identical bosons (pions) due to constructive interference of
multi-particle wave function.
Effect observable in regions of phase space populated by bosons of similar momenta.
Construct a double
Monte carlo events do not have
Inclusive diffraction in minimum bias events at LHC
Diffractive events observed by looking at the
absence of forward hadronic activity due to
presence of large rapidity gap look at
opposite directions, require low activity on one side.
Important tuning needed for generators.
Low mass resonances
Invariant mass distribution
for different combinations
(Ω±ΛK± or ±Λ± ) fit to a common vertex.
1672.43 ± 0.29
1321.71 ± 0.07
Jets and Missing ET
The highest mass dijet event in the first 120nb-1 of data
Dijet mass: 2.130 TeV
Highest ever produced in
any hadron collision
Missing energy measurement in various methods is highly reliable missing
Energy characteristics can be utilised to search for interesting events, eg. SUSY
Inclusive jet cross section
All results are in good agreement with NLO theory: success of QCD!
Various jet reconstruction algorithms produce matching results.
Particle Flow approach the distributions can be extended to a low pT value of 18 GeV.
Inclusive b-jet cross section
Important test of our capability to master the b-tagging tools (eg.High Purity version of the Secondary Vertex Tagger).
Reasonable agreement with NLO but discrepancies in h and pT shapes.
Physics with Dijet final state
At 95% CL, non-resonant New Physics excluded : L < 930 GeV
Resonant New Physics (excited quark) excluded: 400<m q⃰<1290 GeV
Search for narrow resonances in di-jet final states
Dijet mass differential cross section distribution is sensitive to the coupling of any new massive object from New Physics to quarks and gluons.
If no bump in mjj, set limit on excited quark production
Latest published limit:
CDF: 260 < M (q*) < 870 GeV
0.4 < M (q*) < 1.29 TeV
excluded at 95% C.L.
Stopped gluinos and Heavy, Stable Charged Particles
Search for long living particles decaying in the detector after the end of each LHC fills (special trigger to record important release of energy in “no beam condition”) and for heavy particles releasing anomalous signals in CMS while traversing the tracking system (high momentum, highly ionizing “muons”).
Gluino masses are excluded <229GeV (t=200ns) and <225GeV (t=2.6ms).
Limits on gluinos from HSCP analysis at 271 and 284 GeV (with muon id).
Prompt photon production at hadron colliders:
High pT photon identification: important signal for many search physics:
test SM Gauge Boson couplings at
high energy: V1 V2g
Higgs boson: H gg
gauge-mediated SUSY breaking model
exotics: graviton decay G gg, excited
fermion decay f⃰ f g
But huge background from hadron decays, dominated by p0 and h decays to photons demand isolated photons
Here is the Compact Muon Solenoid!
Heavy Stable Charged particles
Prospect of discovery of Higgs boson at LHC at CM energy 7 TeV
Current Tevatron exclusion limit: for Higgs mass: 158 to 175 GeV
For Mx> 140 GeV, S/N ratio better LHC competitive to Tevatron.
Comparable to the sensitivity of Tevatron with lumi ~300-500 pb-1 by 2011
Prospects at 7 TeV with 1 fb –1
Higgs discovery sensitivity:
Higgs mass which can be excluded: 145 to 190 GeV
Several “first studies” have been made in the context of the experiment.
The status of LHC at this moment is similar to asking what a new continent is going to be like when we can just glimpse the shore….
LHC will also have heavy ion collisions during 2010 and 2011.
All the experiments are successfully collecting and analysing the collision data.
This is only the beginning of an exciting physics phase and a major
achievement of the worldwide LHC Collaboration after > 20 years of efforts
to build a machine and detectors of unprecedented technology, complexity
a la` Newton: To me there has never been a higher source of earthly honour or distinction than that connected with advancement in science.
TeV resonance Z’ e+e-
Prospect for SuperSymmetry
SUSY Higgs tt @1 /fb
Large region of m A – tan b plane, much beyond current limits can be excluded
J/y→μ+μ- differential and total cross section
Signal events: 17156 ± 569
Sigma: 43.3 ±0.5 (stat.) MeV
M0 : 3.0927 ± 0.0005 (stat.) GeV
S/B= 6.4 ; c2/ndof = 1.7
Signal events: 710 ± 29
Sigma: 20.3 ±0.7 (stat.) MeV
M0 : 3.0945 ± 0.0008 (stat.) GeV
S/B= 64 ; c2/ndof = 1.1
Differential cross section as a function of pT for the two different rapidity intervals and in the null polarization scenario. The total cross section for inclusive J/ψ production in the di-muon decay channel is
BR(J/ψ→µ+µ−)·σ(pp→J/ψ + X) = (289.1 ± 16.7(stat) ± 60.1(syst)) nb
(4 ≤pT≤30GeV/c and |y| <2.4; the systematic uncertainty is dominated by the statistical precision of the muon efﬁciency determination from data).
Event with 4 pp interactions in the same bunch-crossing
~ 10-45 tracks with pT >150 MeV per vertex
Vertex z-positions : −3.2, −2.3, 0.5, 1.9 cm (vertex resolution better than ~200 μm)
Multiplicity distribution 7 TeV
reasonably described by negative-binomial distributions
comparison with different models – not satisfactory
05/05/2010, ALICE status and first physics, Karel Safarik, CERN LHC open presentation
LHC is a giant!
27 km at 1.9 K (superfluid He)
700K litres of liq. He + 12M litres of liq. nitrogen
Vaccuum ~ 10-13 Atm. 100 times more tenuous than the space of communication satellite
SC coils: 12000 tonnes/7600 km
Measurement of top quark production rate
Light quark content of top: Br(tWb)/ Br.(tWq)
Search for high mass ttbar resonance
Single top measurement
Multiple primary vertices multiple pp collisions (“pile-up”)
Jets & muons originate from same primary vertex
Very clean candidate sitting in a region where we expect very little background!