CON PIACERE PUBBLICHIAMO IL POST DELL'AMICO E COLLABORATORE DOTT. MIGUEL LUNETTA (FISICO), SULLA "CONTROVERSA" QUESTIONE DEL BOSONE DI HIGGS.
I FREQUENTATORI DEL BLOG SONO AL CORRENTE DEL MIO PENSIERO SULL'ARGOMENTO, QUINDI SENZA ULTERIORI COMMENTI, VI INVITO A LEGGERE CON ATTENZIONE LA DETTAGLIATA RELAZIONE DI MIGUEL SUL TORTUOSO PERCORSO CHE, INFINE, HA PORTATO IL NOBEL PER LA FISICA A PETER HIGGS.
BUONA LETTURA
MLR
On Higgs
boson detection
di: Dott.
M. Lunetta
Abstract:
Initially we talk on Higgs’ prediction, standard model, Higgs field properties
and describe particle accelerators. Successively we explain why the Higgs boson
gained the nickname of God particle, why the Standard Model is refuted, and we
described the Tevatron and LHC experiments. Then, after mentioning the Higgs
boson production, the collision of two proton beams and the evaluation of
standard model mass, we conclude reporting how the Tevatron found Higgs boson.
Résumé:
Nous parlons initialement sur la prévision de Higgs, le modèle standard, les
accélérations de particules. Ensuite, nous expliquons pourquoi le boson de
Higgs gagna le nom de particule de Dieu, pourqoui le modèle standard fut
réfuté, et nou décrions les expériences du Tevatron et du LHC. Ainsi, après
mentionner la production du boson de Higgs, le choc de deux rayons de protons
et le calcule de la mass du modèle standard, nous concluions expliquant comment
le Tevatron détecta le boson de Higgs.
Key words :
Higgs boson, standard model, particle accelerator, God particle, Tevatron,
Large Hadron Collider (LHC), Big Bang, Large Electron-Positron Collider (LEP),
Giant particle detectors ATLAS and CMS, Nuclear Physics Laboratory of High
Energies (LPNHE).
I. INTRODUCTION
A. Higgs prediction
The Higgs
particle is postulated as a part of the mechanism by which all other
fundamental particles acquire mass. The theory behind it was
a)ateness@oi.com.br
published
by six physicists - including Edimburg University physicist Peter Higgs -
within a few months of each other in 1964(1). Higgs idea was that the universe
contains an as yet undiscovered field. Interaction with what is now called the
Higgs field gives particles their mass and would explain why some particles
have high mass (that is are heavy) and some particles have almost no mass.
“Higgs bosons would not naturally exist in the universe today”, says David
Krofcheck, a physicist from the University of Auckland(2).
Physicists
therefore, have the challenge of searching for a theoretical particle that may
have briefly existed immediately after the Big Bang that created the universe.
The Higgs boson is a hypothetical elementary particle which belongs to a class
of subatomic particles known as bosons, characterized by an integer value of
their spin quantum number. The Higgs boson is an excitation of the Higgs field
above its ground state(3).
B. Standard model
The
existence of the Higgs boson is predicted by the Standard Model to explain how
spontaneous breaking of electroweak symmetry (the Higgs mechanism) takes place
in nature, which in turn explain why other elementary particles have mass. Only
1% of the mass of composite particles, such as the proton and neutron, is due
to the Higgs mechanism. The other 99% is due to the strong interaction (3). “If
you discover there is some particle at 120 GeV, to be absolutely sure it is the
Standard Model Higgs which we think it is, one would have to measure precisely
how it is produced and how it decays to determine its properties,” said
Söldner-Rembold. “That’s quite a way down the road because, for that, you need
much more data. There still remains quite a bit of work to be done to be
absolutely sure that it is actually the Higgs boson as the Standard Model predicts
it.”(1)
The Higgs
boson is the key piece of the Standard Model, an ambitious suite of equations
that has ruled the universe of high-energy physics for the last few decades,
explaining how three of the four fundamental forces of nature work. But the
boson itself has never been observed. The theory describes how it should work
and behave but does not predict one of its key attributes, namely its mass.(4)
C. Higgs field properties
The theory
hypothesizes that a sort of lattice, referred to as the Higgs field, fills the
universe. This is something like an electromagnetic field, in that it affects
the particles that move throughout, but it is also related to the physics of
solid materials. Scientists know that when an electron passes through a
positively charged crystal lattice of atoms (a solid), the electron’s mass can
increase as much as 40 times. The same might be true in the Higgs field: a
parting moving through it creates a little bit of distortion – like the croud
around the star at the party – and that lends mass to the particle.
The
Standard Model describes three of nature’s
four forces: electromagnetic and the strong weak nuclear forces.
Electromagnetism has been fairly well understood for many decades. Recently,
physicists have learned much more about the strong force, which binds the
elements of atomic nuclei together, and the weak force, which governs
radioactivity and hydrogen fusion (which generates the sun’s energy).
Electromagnetism
describes how particles interact with photons, tiny packets of electromagnetic
radiation. In a similar way, the weak force describes how or three entities,
the W and Z particles, interact with electrons, quarks, neutrinos and others.
There is one very important difference between these two interactions: photons
have no mass, while the masses as W and Z are huge. In fact, they are some of
must massive particles known.
The first
inclination is to assume that W and Z simply exist and interact with other
elemental particles. But, for mathematical reasons, the giant masses of W and Z
raise inconsistencies in the Standard Model. To address this, physicists
postulate that there must be at least one other particle – the Higgs boson. The
simplest theories predict only one boson, but others say there might be
several. In fact, the search for the Higgs particle(s) is some of the most
exciting research happening, because it could lead to completely new
discoveries in particle physics. Some theorists say it could bring to light
entirely new types of strong interactions, and others believe research will
reveal a new fundamental physical symmetry called “supersymmetry.”
First,
Though, scientists want to determine whether the Higgs boson exists. The search
has been on for over ten years both at CERN’s Large Electron Positron Collider
(LEP) in Geneva and at Fermilab in Illinois. To look for the particle,
researchers must smash other particles together at very high speeds. If the
energy from that collision is high enough, it is converted into smaller bits of
matter - particles – one of which could be a Higgs boson. The Higgs will only
last for a small fraction of a second, and then decay into other particles. So
in order to tell whether the Higgs appeared in the collision, researchers look
for evidence of what it would have decayed into.(5)
D. Particle accelerators
The
particle accelerators performing experiments to find out whether the Higgs
boson exists are the following:
1. Large Hadron Collider (LHC) at CERN,
in Geneva, Switzerland.
2. Large Electron – Positron Collider
(LEP) at CERN, by detector ALEPH.
3. Tevatron particle collider in the
US.
4. Fermi
National Laboratory in Batavia, Illinois.
5. Giant particle detectors ATLAS and
CMS from the CERN collider.
6. Nuclear Physics Laboratory of the
High Energies (LPNHE) in Paris.
II. DISCUSSION
A. Why the God particle?
In the
popular media, the particle Higgs boson is sometimes referred to as the God
particle, a title generally disliked by the scientific community as media
hyperbole that misleads readers.(6)The Higgs boson is often referred to as ‘the
God particle’ by the media(7) after the title of Leon Lederman’s popular
science book on particle physics, The God Particle. If the Universe Is the
Answer, what is the Question?(8, 9) While the use of this term may have
contributed to increased medi9a interest, many scientists dislike it, since it
overstates the particle’s importance, not least since its discovery would still
leave unanswered questions about the unification of QCD, the electroweak
interaction and gravity, and the ultimate origin of the universe.
Lederman
said he gave it the nickname “The God Particle” because the particle is “so
central to the state of physics today, so crucial to our understanding of the
structure of matter, yet so elusive,(10) but jokingly added that a second reason
was because “the publisher wouldn’t let us call it the Goddamn Particle,
through that might be a more appropriate title, given its villainous nature and
the expense it is causing.”
A renaming
competition conducted by the science correspondent for the British Guardian
newspaper chose the name “the champagne bottle boson” as the best from among
their submissions: “The bottom of a champagne bottle is in the shape of the
Higgs potential and is often used as an illustration in physics lectures. So
it’s not are embarrassingly grandiose name, it is memorable, and [it] has some
physics connection too.”(11)
B. Refutation of Standard Model
Physicists
claim evidence of a new particle only if the probability that the data could be
due to a statistical fluctuation is less than 1 in 740, or three sigmas. A
discovery is claimed only if that probability is less than 1 in 3.5 million, or
five sigmas. This result sits well within the stringent constraints established
by earlier direct and indirect measurements made by CERN’s Large Hadron
Collider, the Tevatron, and other accelerators, which place the mass of the
Higgs boson within the range of 115 to 127 GeV. These findings are also
consistent with the December 2011 announcement of excesses seen in that range
by LHC experiments, which searched for the Higgs in different decay patterns.
None of the hints announced so far from the Tevatron or LHC experiments,
however, are strongly enough to claim evidence for the Higgs boson.(12)
Theories
that go beyond the “standard model” of particle physics (of which the Higgs is
the keystone – the one missing piece needed to explain how the universe we know
come to be) may be necessary. Steven Weinberg, who in this landmark 1967 paper
on the unification of the electromagnetic and weak interactions had made key
use of the Higgs for “breaking the symmetry” and separating the electromagnetic
from weak forces, has since gone beyond the standard model in his research.
Weinberg
has proposed a theory called Technicolor, within which the primeval symmetry
o0f our universe can be broken through a different mechanism than the action of
the elusive Higgs. But to prove the validity of the Technicolor theory may
require an energy level that would dwarf
that available to the LHC – at an equal astronomical cost.(13)
From recent
data of Fermilab in Batavia, Ill. It results that Higgs boson has not been
discovered yet, but its mass is 125 billion electron volts. If the Higgs does
not exist, they will have to come up with a new model of how the universe
works. If they do find the Higgs, studying it might give then clues to deeper
mysteries the Standard Model does not solve.
The
Standard Model does not predict the mass of the Higgs boson. If that mass is
between 115 and 180 GeV/c2, then the Standard Model can be valid at energy
scales all the way up to the Planck scale (1015TeV). Many theorists expect new
physics beyond the Standard Model to emerge at the TeV scale, based on
unsatisfactory properties of the Standard Model. The higher possible mass scale
allowed for the Higgs boson (or some other electroweak symmetry breaking
mechanism) is 1.4 TeV; beyond this point, the Standard Model becomes
inconsistent without such a mechanism, because unitarity is violated in certain
scattering processes.
On 7 March
2012, the DØ and CDF Collaborations announced that, after analyzing the full
data set from the Tevatron accelerator, they found excesses in their data might
be interpreted as coming from a Higgs boson with a mass in the region of 1/5 to
135 GeV/c2. It is expected that the LHC provide sufficient data to either
exclude or confirm the existence of the Standard Model Higgs boson by the end
of 2012.(14)
C. Description
of Tevatron and LHC experiments.
One reason
the Tevatron results are important is that there look for the Higgs in a
different way to the detectors at the LHC. In the LHC’s announcement in
December,, scientists had largely been looking for a signal in which the Higgs
boson decayed into a pair of photons, whereas the Tevatron located its signal
in the decay of the boson into a pair of heavy “bottom quarks”.
The Higgs
particle can decay into different particles and the Tevatron looks for
different decays of the Higgs than the LHC. The Large Hadron Collider (LHC), in
Geneva, smashes protons together at high energy, simulating in the laboratory
the conditions that occurred in the early universe, a trillionth of a second
after the Big Bang. This is the epoch when the Higgs boson is theorized to have
been abundant and to have seeded the structured universe within which we now
exist. More than four decades after the ideas were conceived, the experiments
began in earnest last year. On December 13 came the news that something
exciting was beginning to show – perhaps a Higgs Boson. However, no one seemed
prepared to go the full distance and claim that it has been discovered, at
least not yet.
The LHC is
currently operating at only half its planned power. So if this is indeed the
long sought Higgs, this offers the prospect that a wealth of discoveries may be
within the LHC’s reach when operating at full capacity. The hints are also
consistent with the theories that predict the Higgs to be but one number of new
families of particles, including the seeds of the mysterious “dark matter”
throughout the cosmos.(15)
Colliding
protons remain intact but still generate new particles, according to results
from Fermilab. A similarly clean process could produce the elusive Higgs
particle at CERN’s Large Hadron Collider (LHC). Particle physicists at LHC hope
to discover the Higgs boson amid the froth of particles born from proton –
proton collisions. Results in the 19 June Physical Review Letters show that
there may be a way to cut through some of that froth. An experiment at
Fermilab’s proton – antiproton collider in Illinois has identified a rare
process that produces matter from the intense field of the strong nuclear force
but leaves the proton and antiproton intact. There’s a chance the same basic
interaction could give LHC physicists a clean look at the Higgs.
In the new
experiment, researchers were looking for signs that the interaction of virtual
gluons had generated short – lived particles including the Xc(Chi-c) and J/ψ mesons, which are charm – anticharm
quark pairs that decay into muons and antimuons. Now the team has sifted through
nearly 500 muons – antimuons pairs, identifying 65 that must have come from the
decay of the Xc – very close to the rate predicted in 2005 by a team at Durham
University in England.(16)
Because the
Xc has similar particle properties to the much heavier Higgs boson, the same
basic reaction should produce the Higgs at the higher collision energies
provided by the LHC, says Albrow. “It’s the strongest evidence that the Higgs
boson must be produced this way, if it does exist.” Based on the rate of Xc
production, Albrow estimates LHC collisions could produce 100 to 1000 Higgs
bosons per year in each of the accelerator’s two largest particle detectors,
ATLAS and CMS.
“It looks
hard, but one should never say never,” says Joseph Incandela of the University
of California, Santa Barbara, deputy physics coordinator for CMS. Incandela
points out that once the LHC is operating at full capacity, every crossing of
its twin proton beams is expected to yeld about 20 collisions, throwing up
other particles that may obscure exclusive reactions. If a Higgs boson is
created in a high – energy particle collision, it immediately decays into
lighter more stable particles before even the world’s best detectors and
fastest computers can snap a picture of it. To find the Higgs boson, physicists
retraced the path of these secondary particles and ruled out processes that
mimic its signal.
III. METHODOLOGY
A. Production of Higgs boson
Unknown
Lamer on Wednesday March 07, 10:36 AM, 2012 writes with exciting news from the
world of the particle physics: “A hint of the Higgs boson, the missing piece in
the standard model pf particle physics, has been found in data collected by the
Tevatron, the now – shuttered U.S. particle collider at Fermilab in Batavia,
Illinois. While not statistically significant enough in themselves to count as
a ‘discovery’, the indications announced on 7 March at the Moriond conference
in La Thuile, Italy, are consistent with 2011 reports of a possible standard
model Higgs particle with a mass of around 125 GeV from experiments at the
Large Hadron Collider at CERN near Geneva, Switzerland. The data is more direct
evidence of the Higgs than the constraints in its mass offered by the precise W
boson mass measurement reported on Monday. On a sad note, the find vindicates Tevatron
scientists who campaigned unsuccessfully to extend the collider’s run. The
request was turned down by the Department of Energy but this last hurrah
suggests that Tevatron might indeed have found the Higgs ahead of CERN’s Large
Hadron Collider if they’d recued the funding required. The Tevatron is
currently being raided for parts.”
New
measurements announced today’(March 7, 2012) by scientists from CDF and DZero
collaborations at the U.S. Department of Energy’s Fermi National Accelerator
Laboratory indicate that the elusive Higgs boson may nearly be cornered. After
analyzing the full data set from the Tevatron accelerator, which completed its
last run in September 2011, the two independent experiments see hints of a
Higgs boson.(17)
“The end
game is approaching in the hunt for Higgs boson,” said Jim Siegrist, DOE
Associate Director of Science for High Energy Physics. “This is an important
milestone fo9r the Tevatron experiments, and demonstrates the continuing
importance of independent measurements in the quest to understand the building
blocks of nature.” Fermilab scientist Don Lincoln describes the concept of how
the search for the Higgs boson is accomplished.
B. Collision
of proton beams
The Large
Hadron Collider (LHD), with a circumference of 27 Km, boosts protons to high
speeds, smashes them together, and uses sophisticated detectors to see what
results from the high – speed, High – temperature collisions that mimic
collisions one – thousand of a billionth of a second after the Big Bang.
The search
for Higgs boson has been on for over ten years, both at CERN’s Large Electron
Position Collider (LEP) in Geneva and at Fermilab in Illinois. To look for the
particle, researchers must smash other particles together at very high speeds.
If the energy from that collision is high enough, it is converted into smaller
bits of matter – particle – one of which could be a Higgs boson. The Higgs will
only last for a small fraction of a second, and then decay into other
particles. In 2011, the LHC collided two proton beams at 7 tera-electronvolts
(TeV). On average more than 100 million collisions per second took place, but
most of those collisions were “conventional”, in that they involved only the
most common elementary particles. If the standard model is correct, then on
rare occasions, a Higgs boson should have been produced.
Assuming
the Higgs mass lies in the expected mass range, about 75,000 Higgs bosons were
produced in the ATLAS and CMS collider detections in 2011.
C.Evaluation
of standard model mass
There may
be a 95% chance that the Higgs does not exist between 146 – 446 GeV, but that
it exists between 140 – 145 GeV.
Three
papers now appearing in Physical Review Letters, two from ATLAS
Collaboration(18) and one from CMS Collaboration(19) report searches for the
Higgs boson in the debris of high – energy
proton – proton collisions at LHC. The results of these searches, and
several others being published elsewhere(20), were announced in December, 2011.
Collectively, they have shown that the Higgs boson of the standard model, if it
exists, must be lie in a narrow range of masses around 126 giga – electron –
volts (GeV). Moreover, an excess of events around this mass value provides a
tantalizing hit that experimentalist could be only the verge of discovering the
long – sought particle.
From
experiments at the CERN LEP
colliders(21) which shut down in 2000, it is known that the standard model
Higgs boson mass cannot be below 114GeV, while subsequent data from the
Fermilab Tevatron(22), which shut down
in 2011, excludes a Higgs boson mass between 156 and 177 GeV.
Based on a
statistical analysis of LEP and Tevatron colliders, the Higgs mass cannot be
larger than 169 GeV((23). Combining the direct Higgs research limits quoted
above with the indirect constraints implies that the standard model is viable
if, and only if, the standard model Higgs boson mass lies between 114 and 156
GeV(24).
The results
of two recent experiments at the Large Hadron Collider (LHC) near Geneva
suggest physicists are close to discovering the Higgs boson, the so – called
God particle. Combined, the two experiments have narrowed the possible band of
possible Higgs boson masses to between 115 and 130 GeV (gigaelectron volt).
Rather than look directly for this fleeting would – be particle itself, physicists
look for the various combination of particles
into which Higgs bosons are though to decay. Independent analyses have
verified excesses of these particles from the low mass region 124 to 126
GeV.(25)
IV.CONCLUSIONS
A.Tevatron
might found Higgs boson
Last
December, two groups, which run giant particle detectors named ATLAS and C.M.S. from the CERN collider, reported
that they have found promising bumps in their data at masses of 124 billion
electron volts and 126 billion electron volts, respectively, those being the
units of mass or energy preferred by particle physicists.
The
Fermilab physicists have found a broad hump in their data in the same region,
between 115 billion and 135 billion electron volts. Those results came from
combining the data from two detectors operated on the Tevatron: the Collider
Detector at Fermilab, and DZero. The chances of this signal being the result of
a random fluctuation in the data where only about 1 in 100, the group said.
This is the
first time in the long search for the particle that different groups, indeed different colliders,
are in vague agreement. It has led to a joke in physics circles now: the Higgs
boson has not been discovered yet, but its mass is 125 billion electron volts.
Physicists
base in the US have presented evidence of the Higgs boson particle that
correlates closely with European researchers’ work at the Large Hadron Collider.(26)
The data,
from the Tevatron particle collider, was presented at a physics conference in
Italy, and indicate that the particle
could exist at a mass of between 115 gigaelectronvolts and 135
gigaelectronvolts. This result is consistent
with last December’s finding from CERN’s Large Hadron Collider in
Switzerland, wich narrowed down the Higgs Boson’s mass to about 125 gigaelectronvolts.
While not
statistically significant enough in themselves to count as a ‘discovery’, the
indication announced on 7 March at the Moriond conference in La Thuile, Italy,
are consistent with 2011 reports of a possible standard model Higgs particle
with a mass of around 125 GeV from experiments at the Large Hadron Collider at
CERN near Geneva, Switzerland.(27)
References:
1The
Guardian, Edition UK.
2Rebecca
Prriestley, Higgs boson solution, New Zealand Listener, Saturday, 17 March
2012.
3Wikipedia,
the free encyclopedia, Gold particle (1964).
4Dennis
Overbye, Data Hint at hypothetical Particle, Key to Mass in the Universe, March
7, 2012.
5CERN, The
heart of the Matter, Ideas The Higgs boson.
6National
Post, The Higgs boson: Why scientists hate that you call it the “God
particle”,14 December 2011.
7Ian Sample
(29 May 2009), “Anithing but the God particle”, London. The Guardian. Retrieved
24 June 2009.
8Leon M.
Lederman and Dick Teresi (1993). The God Particle. If the Universe is the
Answer, What is the Question, Houghton Miffin Company.
9Ian Sample
(3 March 2009). Father of the God particle. Portrait of Peter Higgs unveiled.
London: The Guardian. Retrieved 24 June 2009.
10Alisses
McGrath, Higgs boson: the particle of faith, The Daily Telegraph, published 15
December2011. Retrieved 15 December 2011.
11Ian
Sample (12 June 2009). “Higgs competition: Crack open the bubbly, the God
particle is dead”. The Guardian (London). Retrieved 4 May 2010.
12Science
News, Elusive Higgs Boson May Nearly Be Cornered, March 7, 2012.
13Amir
Aczel (August 23, 2011). A Higgs Setback: Did Stephen Hawking Just Win the Most
Outrageous Bet in Physics History? Scientific American.
14CERN
press release # 25.11.13 December 2011, “The statistical significance is not
large enough to say anything conclusive. As of today what we see is consistent
either with a background fluctuation or with the presence of the boson. Refined
analyses and additional data delivered in 2012 by this magnificent machine will
definitely give an answer”.
15SCIENCE,
Finding Higgs Boson, or God Particle, Will Resolve Scientific Mysteries, Dec.
16, 2011 11:00 PM EST.
16V. A.
Khoze, A. D. Martin, M. G. Ryskin, and W. J. Stirling, Diffraction γγ Production at Hadron Collider,”
Eur. Phys. J. C. 38, 475 (2005).
17Science
News, Elusive Higgs Boson May Nearly Be Cornered, ScienceDaily, Mar. 7, 2012.
18G. Aad et
al.(ATLAS Collabiration), Phys. Rev. Lett. 108, 111802/111803 (2012).
19S.
Chatrchyan et al.(CMSCollaboration), Phys. Rev. Lett. 108. 111804 (2012).
20G. Aad et
al.(ATLAS Collaboration), Phys. Lett. B (2012, DOI :
10.1016/J.Physletb.2012.02.044/to be published); S.Chatuchyan et al./CMS
Collaboration), Phys. Lett.B(2012), DOI:10.1916/j. physletb.2012.02064 (to be
published).
21ALEPH
Collaboration, DELPHI Collaboration, L3 Collaboration, OPAL Collaboration, and
The LEP Working Group for Higgs Boson Searches, Phys.Lett. B 565, 61 (2003).
22TEVNPH
(Tevatron New Phenomena and Higgs Working Group) and CDF and DO Collaborations,
arXiv: 1107.5518(hep-ex).
23M. Baak,
M. Goebel, J. Haller, A. Hoecker, D. Ludwig, K. Moenig, M. Schott, and J.
Stelzer, arXiv: 1107.0975 (hep-ph).
24(http://teonphwg.fnal.gov/results/SM_Higgs_Winter_12/).
25James
Holloway, LHC physicists sniff Higgs boson discovery, 04: 59 December 14, 2011.
26Martin
LaMonica, CNET News, US Higgs boson data backs CERN’S finding so far, Daily
Newletters, 7 March, 2012 15:45.
27Unknown
Lamer, Final Analysis Suggests Tevatron Saw Hint of the Higgs Boson, Slashdot,
Wednesday March 07, 10: 36 AM, 2012, from the America-hates-science dept.
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