session: “ tribute to john bahcall ” no-ve iii international workshop on: "neutrino...

Session: “Tribute to John Bahcall”

NO-VEIII International Workshop on: "Neutrino Oscillations in Venice"

Solar Neutrinos

Gianluigi Fogli

Gianluigi Fogli "Neutrino Oscillations in Venice" 2

Based on work with E. Lisi, A. Marrone, A. Palazzo, and A.M. Rotunno

Outline

John Bahcall: Memories of our

interactions

Solar physics: Established

facts

Solar physics: Are there little

“cracks” ?

Conclusions


John Bahcall: Memories of our interactions


John Bahcall’s countless seminars on the solar neutrino problem as a window to new physics are probably responsible for the interest in neutrino physics of many people in this audience - and they were definitely so for myself, in the early 90’s.

[Milla is also responsible in part: My first published contribution to neutrino physics was a talk on “Problems with Solar Neutrinos” at her Neutrino Telescope Workshop in 1993…]In collaboration with Eligio Lisi, I then gradually moved from electroweak precision physics to neutrinos. John’s book on “Neutrino Astrophysics” was the very first guidance in this new (for us) field of physics.

More direct interactions with John started in 1994, with correspondence on his famous “1,000 Standard Solar Models” (that we used to deal with SSM errors and correlations) and with his acceptance of Eligio as an INFN postdoc at his Institution (IAS, Princeton).


Interactions with John have been always both scientifically interesting and personally enjoyable.

I remember with great pleasure his participation to the Neutrino Oscillation Workshop in Otranto (NOW 2000), where he managed to come - and to present new results (the preliminary BP 2000 SSM) - despite many other obligations he had in that period.

With the same great pleasure I remember his “laurea honoris causa” at Milano in May 2004, with several of us in the Laurea Committee:a witness of the close bond of friendship with all of us in Italy.


These are just facets, from a personal perspective, of his life-long commitment to science, and to the scientific community. Any of us can add countless examples of such commitment. He was really a leading scientist in our field, and we all miss him greatly.

But, his greatest accomplishment remains with us: solar neutrinos as a window to new physics.


Solar Neutrinos: Some Established Facts


Fact #1: Solar astronomy is an established and recognized branch of science…

Sun direction from neutrinos (SK) Earth orbit from solar (SK)

Artist’s view of solar (Nobel 2002 - “annus mirabilis”)


The Pioneers

Fact #2: … It requires enduring efforts and difficult experiments…

John’s summary of 40 years of expt+theo work


Fact #3: … But it can be very rewarding in terms of new physics …

Each experiment (Cl, Ga, SK, SNO) requires nonzero mass/mixingData consistent with each other in terms of mass-mixing parametersAll current data converge towards a unique (LMA) solution


Fact #4: … Solar data are also consistent with SSM predictions …

Slanted ellipse = model-indep.combination of SNO-CC, SNO-NC and SK-ES data.

The data overconstrain the two variables ….

B vs. <Pee>

… and are consistent with B from SSM and <Pee> < 1

no new solar physics required

neutrino flavor change required


Fact #5: … and consistent with independent (KamLAND) reactor data …


Fact #6: … and consistent with the predicted MSW effects …

Study of the tolerance of the solar data for variations of standard MSW interaction energy

through a shift

V = 2 GF Ne

V V aMSW

Case of no matter effects in the Sun is ruled out at >5 sigma.

Clear indication in favor of standard matter effects (aMSW

= 1).


Fact #7: … and consistent with small 13 (<few x 10-2)…


… almost competitively with the CHOOZ+SKATM bound on

13!

[This and previous plots from GLF, Lisi, Marrone & Palazzo, hep-ph/0506083]


Fact #8: Overall agreement is so good that any conceivable

“perturbation” can be constrained

[GLF, Lisi, Palazzo & Rotunno, hep-ph/0505081]

An unorthodox example: Herndon’s natural reactor in the Earth’s core

Solar/KamLAND agreement ruined by neutrino flux from hypothetical georeactor:

PGEO < 13 TW at 95% C.L.


Solar physics: Are there little “cracks” ?


The previous beautiful and solid facts should not make us exceedingly confident in our current understanding of solar neutrino physics.

Words of caution came from John Bahcall himself:

“This is the first time in 40 years of giving talks in solar neutrinos that it seems to me that the people in the audience are more confident of the solar model predictions than I am”

(statement at Neutrino 2002)

“Half of all three-sigma results are wrong” (one of his favorite quotes)

So we should not be blind to small “cracks”, that might open up in the beautiful solar neutrino construction.


This is one of the possible “crack”, that has had a central role in the late interests of John Bahcall. It occurs when the newest metal abundance estimates are adopted.

Curiously, such revised metal estimates were motivated by better analyses of the solar atmosphere, rather than by new data.

In this sense: “Better is worse” (John Bahcall, astro-ph/0511337)

1. SSM predictions and helioseismological data

or, in Italian: “Il meglio è nemico del bene”


John Bahcall, Physics World, February 2005: “Chemical controversy at the solar surface”

Fractional difference between measured and predicted values of the speed of sound in the interior of the Sun vs. the solar Radius:

Previously, agreement was very good along the whole profile (red curve).

Sound speed profile no longer in good agreement with new metallicity (blue curve)


No clear solution is emerging for the metallicity problem, as also recognized in John’s last paper (astro-ph/0511337). There is no “recommended” SSM metal input at present.

From Bahcall, Serenelli, Basu astro-ph/0511337: SNO data vs. 10,000 SSM with new metal abundances + optimistic errors (“worst case” for helioseismology)

Luckily, the effect on current solar neutrino mass-mixing parameters is marginal, because:

Therefore, all previous mass/mixing bounds are largely insensitive to SSM “metallicity perturbations”.

All SSM metal input uncertainties (included and properly propagated in our analysis) are conservatively large;

SNO (which dominates solar neutrino fits) measures the 8B flux with an error a factor of ~2 smaller than typical SSM predictions (see figure below).


This is another small “discrepancy”, which might have some implications on solar neutrino parameter estimation. The recent claim (Dec. 2005) comes from the combined radioactive source experiments at SAGE & GALLEX/GNO [see the SAGE Collaboration paper, nucl-ex/0512041]

Combination (nucl-ex/0512041):

= 0.88±0.05 (1 total error)predictedmeasured

where “predicted” refers to the Ga cross section calculation by John Bahcall, hep-ph/9710491

2. A smaller neutrino-Gallium cross section at low-energy ?


The radioactive “calibration” data seem to suggest a downward revision of the low-energy (< 2 MeV) solar neutrino cross-section on Gallium, relevant for the pp, pep, Be, N, and O contributions, by more than 2 sigma (not a negligible shift)

The high-energy cross section (> 2 MeV), relevant for the B and hep contributions, is instead basically decoupled from the low-energy one (see John’s Gallium cross-section paper, hep-ph/9710491).

Therefore, it is tempting to see what happens if the predicted LE contributions in Ga experiments are renormalized by 0.88±0.05 (with HE contributions from 8B and hep unchanged).


Our preliminary results for this exercise seem to show that, at face value, such a “Ga cross section renormalization”:

Worsen the current agreement between Ga and SNO data;Worsen the reliability of the current bounds on 13 from solar data only.

In order to understand such results, let us recall that the relation between 2 survival probability (13=0) and 3 survival probability (13>0):

and that Pee changes with energy in the LMA solution:


Low energy:(small matter effects)

As a consequence:

High energy:(dominant matter effects)


The different behavior of LE and HE rates is at the root of the upper bound on 13 from solar neutrino data only (see S. Goswami and A.Yu. Smirnov, hep-ph/0411359)

In general, to keep the predicted Gallium rate constant (LE):

if 13 increases, then 12 must decrease.

Viceversa, to keep the predicted SNO CC/NC ratio constant (HE):

if 13 increases, then 12 must increase.


1) Ga and SNO data (bands) are in very good agreement with predictions (curves) for 13=0 and sin

212=0.31.

The current situation, without Ga cross-section renormalization, is that:

2) The agreement is ruined for increasing 13, since the Ga and

SNO allowed regions drift in different directions of sin212; this fact (together with the other data) places an upper bound on 13 from solar neutrino data only.

agreement at 13=0

agreement at 13=0,increasingmismatch at 13>0


The situation with Ga cross-section renormalization (0.88±0.05 at LE), is that:

1) Ga and SNO data are no longer in good agreement with predictions for 13=0 (Ga prefers lower sin

2 12)

3) Thus, there is never a very good agreement between Ga and SNO constraints, in particular for nonzero 13.

2) The disagreement becomes rapidly worse for increasing 13, since the Ga and SNO allowed regions become even more separated in sin2 12.

mismatch at 13=0

mismatch at 13=0,increasingmismatch at 13>0


As a consequence, with “renormalized” Ga cross-section, the bound on 13 from “solar data only” becomes stronger, but also less reliable (LE-HE agreement not particularly good even at 13=0):

Standard Ga cross section “Renormalized” Ga cross section

(Recommended bounds)


In conclusion, a smaller Ga cross section (as suggested by the SAGE paper) seems to create a small “disturbance” in the current solar neutrino construction. Of course, it’s too early to tell if it is an innocent fluctuation or a hint at something deeper.

Certainly, it provides a reason to revisit the theoretical neutrino absorption cross section on Ga and, in general, it provides one more motivation to perform new solar neutrino experiments and solar neutrino spectroscopy in the low-energy range: two topics (among many others) where John’s contribution and support will be greatly missed.


Solar neutrinos provide us with solid evidence for mass & mixing, and with a beautiful synthesis of physics and astrophysics.

But … as for any synthesis, we are eager to go beyond it! More accurate (astro)physical measurements, or further explorations of the low-energy domain, might reveal something unexpected.

A good place to discuss further these and other issues will be

Time will tell us if current “disturbances” (metallicity problem, Ga cross section) will grow or die.

NOW 2006 Conca Specchiulla (Otranto), September 9-16

www.ba.infn.it/˜now2006

Conclusions

session: “ tribute to john bahcall ” no-ve iii international workshop on: "neutrino...

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